Fluent Essays

Assist with Discussion Information is attached Discussion part 1 Read these two articles, Failure to detect changes to people during a real-world interaction and Failure to detect changes to attended objects in motion pictures and then discuss the following: What are the methods used? What are the primary results? What is the significance of the study? Discussion part 2 Read UNDERSTANDING THE COGNITIVE REVOLUTION IN PSYCHOLOGY and discuss how the field of cognitive psychology had changed since the 1950s when radical behaviorism was the dominant paradigm in psychology. Psychonomic Bulletin & Review 1998. 5 (4). 644-649 BRIEF REPORTS Failure to detect changes to people during a real-world interaction DANIELJ. SIMONS Harvard University, Cambridge, Massachusetts and DANIELT. LEVIN Kent State University, Kent, Ohio Recent research on change detection has documented surprising failures to detect visual changes oc- curring between views of a scene, suggesting the possibility that visual representations contain few de- tails. Although these studies convincingly demonstrate change blindness for objects in still images and motion pictures, they may not adequately assess the capacity to represent objects in the real world. Here we examine and reject the possibility that change blindness in previous studies resulted from pas- sive viewing of 2-D displays. In one experiment, an experimenter initiated a conversation with a pedes- trian, and during the interaction, he was surreptitiously replaced by a different experimenter. Only half of the pedestrians detected the change. Furthermore, successful detection depended on social group membership; pedestrians from the same social group as the experimenters detected the change but those from a different social group did not. A second experiment further examined the importance of this effect of social group. Provided that the meaning of the scene is unchanged, changes to attended objects can escape detection even when they occur during a natural, real-world interaction. The dis- cussion provides a set of guidelines and suggestions for future research on change blindness. Despite our impression that we retain the visual details of our surroundings from one view to the next, we are surprisingly unable to detect changes to such details. Re- cently, experiments from a number of laboratories have shown that people fail to detect substantial changes to pho- tographs of objects and real-world scenes when the abil- ity to detect retinal differences is eliminated (Blackmore, Brelstaff, Nelson, & Troscianko, 1995; Grimes, 1996; Henderson, 1997; McConkie & Currie, 1996; ORegan, Deubel, Clark, & Rensink, 1997; Pashler, 1988; Phillips, 1974; Rensink, ORegan, & Clark, 1997; Simons, 1996; for a review see Simons & Levin, 1997). That is, when retinally localizable information signaling a change is masked by an eye movement or a flashed blank screen, observers have difficulty detecting changes to the visual The authors contributed equally to this report, and authorship order was determined arbitrarily. Thanks to Leon Rozenblit, Carter Smith, Julia Noland, and Joy Beck for helping to carry out the experiments and to Linda Hermer for reading an earlier draft of the manuscript. DJ.S. was supported by NSF and Jacob K. Javits fellowships, and parts of this research appeared in his doctoral thesis. Correspondence should be ad- dressed to D. J. Simons, Department of Psychology, Harvard University, 820 William James Hall, 33 Kirkland St., Cambridge, MA 02138 (e- mail: [email protected]) or D. T. Levin, Department of Psy- chology, Kent State University, P.O. Box 5190, Kent, OH 44242-000 I (e-mail: [email protected]). details of a scene. These findings of change blindness suggest that observers lack a precise visual representa- tion of their world from one view to the next. Although we have known for some time that memory for scenes is often distorted, sometimes quite sparse, subject to sugges- tions, and influenced by expectations and goals (Bartlett, 1932/1977; Brewer & Treyens, 1981; Loftus, 1979; Nick- erson & Adams, 1979), studies of change blindness sug- gest that such details may not be retained even from one instant to the next, a claim that is consistent with earlier studies of the integration of information from successive fixations (Bridgeman & Mayer, 1983; Dennett, 1991; Hochberg, 1986; Irwin, 1991; McConkie & Currie, 1996; Pashler, 1988; Rayner & Pollatsek, 1992). Given the richness of our visual world, it is perhaps unsurprising that we cannot represent all the visual de- tails of every object and instead must focus on a few im- portant objects. Recent models of attention have argued that observers can fully represent the details of only a few centrally attended objects in a scene. For example, models based on object files (e.g., Treisman, 1993) suggest that we can simultaneously represent several distinct objects in our environment, updating our representations for changes in their properties and features. Such models sug- gest the possibility that representations of centrally at- tended objects are relatively detailed even if those for pe- ripheral objects are not. Copyright 1998 Psychonomic Society, Inc. 644 A recent series of studies directly examined the role of attention in the detection of changes to natural images (Rensink et al., 1997). In their flicker paradigm, an orig- inal version and a modified version of an image were pre- sented in rapid alternation (240 msec each), with a blank screen (80-msec duration) interposed between them, pro- ducing a flickering appearance. On each trial, subjects were asked to identify the changing part of the image as soon as they saw it. Consistent with earlier studies of in- tegration across views (for a review, see Irwin, 1991), ob- servers rarely noticed changes during the first cycle of alternation and often required many cycles to detect the change. The change detection process requires observers to shift their attention among the objects in the scene, ac- tively searching for a change. As predicted by models of object files, changes to objects that independent raters consider to be the center of interest of a scene are de- tected in significantly fewer alternations than changes to peripheral objects. That is, changes to the details of at- tended objects are detected more readily. Clearly, focused attention to an object is helpful and possibly necessary for change detection, as evidenced by such center of interest effects (ORegan, Rensink, & Clark, 1996; Rensink et aI., 1997; Tarr & Aginsky, 1996, July) and by findings of more successful change detection when explicit cues specify the location or the type of change (Aginsky, Tarr, & Rensink, 1997). However, atten- tion may not be sufficient for change detection. In fact, observers often fail to detect changes even when atten- tion is focused directly on the changing object (Levin & Simons, 1997; ORegan et al., 1997; Simons, 1996). In a recent series of studies, we used motion pictures to directly examine the ability to detect changes to attended objects (Levin & Simons, 1997). These brief motion pictures de- picted a simple action performed by a single actor. Dur- ing the film, the actor was replaced by a different person. For example, in one film an actor walked through an empty classroom and began to sit in a chair. The camera then changed, or cut, to a closer view and a different actor completed the action. Even though the actors were easily discriminable and were the focus of attention, only 33\% of the 40 participants reported noticing the change from one actor to another (Levin & Simons, 1997). Although the motion picture experiments demonstrate that attention alone is not sufficient for a complete rep- resentation of the visual details of an object, they do not fully assess our ability to represent objects in the real world. Motion picture perception is similar in many ways to perception in the real world, but motion pictures are still a subset of a complete visual experience (Arnheim, 1933/1966). Most importantly, they are viewed passively and may not completely engage the processes necessary for a complete representation of attended objects. Fur- thermore, cuts from one view to another in motion pictures may artificially hamper our ability to detect changes. Al- though cuts are similar in some ways to eye movements, CHANGE DETECTION 645 they also instantaneously change the simulated observa- tion point. This artificial jump in viewing position may somehow disrupt the ability to detect changes even if it has little effect on our understanding of a scene. Similar objections might be raised about most studies document- ing change blindness (for a discussion, see Simons & Levin, 1997). In all previous studies of change blindness, exposure to scenes has been mediated via photographs, computer displays, or television monitors. Perhaps peo- ple can more fully represent the details of a scene when they are direct participants, interacting with the objects in the real world. Here we assess this possibility by taking the study of change blindness into the real world. Rather than changing the sole actor in a video, we changed the subjects con- versation partner during a typical daily interaction. EXPERIMENT 1 In Experiment 1, we created a situation that allowed us to surreptitiously substitute one individual for another in the middle of a natural, real-world interaction. The situ- ation we chose was asking directions of a pedestrian on a college campus. We temporarily interrupted this inter- action by carrying a door between the experimenter and the pedestrian. While the experimenter was occluded by the door, another experimenter took his place and con- tinued the interaction after the door had passed. If change- detection failures are based on the passive nature of me- diated stimuli, these substitutions should be clearly detectable. Method Subjects. A total of 15 pedestrians were approached on the campus of Cornell University. They ranged in approximate age from 20 to 65. Only pedestrians walking alone or together with one other person (two cases) were approached. Procedure. An experimenter carrying a campus map asked unsus- pecting pedestrians for directions to a nearby building (see Figure la). Pedestrians had a clear view of the experimenter starting from a dis- tance of approximately 20 m as they walked down a sidewalk. After the experimenter and pedestrian had been talking for 10-15 sec, two other experimenters carrying a door rudely passed between them. As the door passed, the first experimenter grabbed the back of the door. and the ex- perimenter who had been carrying that part of the door stayed behind and continued to ask for directions (Figure Ic). The first experimenter kept his map during the interruption, and the second experimenter pro- duced an identical copy of the map after the door passed. The door blocked the pedestrians view for approximately I sec (Figure I b). From the subjects perspective, the door briefly occluded his/her conversation partner. and when it was gone, a different person was revealed. As the door passed, subjects typically made eye contact with the second ex- perimenter before continuing to give directions.? The entire interaction took 2-5 min. The two experimenters wore different clothing and dif- fered in height by approximately 5 cm (Figure Id). Their voices were also clearly distinguishable. After a pedestrian finished giving directions. the experimenter told him/her, Were doing a study as part of the psychology department [ex- perimenter points to the psychology building next door] of the sorts of things people pay attention to in the real world. Did you notice anything unusual at all when that door passed by a minute ago? Responses were 646 SIMONS AND LEVIN Figure 1. Frames from a video of a subject from Experiment 1. Frames a~ show the sequence ofthe switch. Frame d shows the two experimenters side by side. noted by the experimenter. and if subjects failed to report the change, they were directly asked. Did you notice that Im not the same person who approached you to ask for directions? After answering this ques- tion. all subjects were informed about the purpose of the experiment. Results and Discussion If change blindness results from the passive nature of mediated stimuli, then these real-world substitutions should be detected, When asked if they had noticed any- thing unusual, most pedestrians reported that the people carrying the door were rude. Yet, despite clear differences in clothing, appearance, and voice, only 7 of the 15 pedes- trians reported noticing the change of experimenters. Those who did not notice the change continued the con- versation as if nothing had happened (in fact, some pedestrians who did notice the change also continued the conversation!). Pedestrians who did not notice the change were quite surprised to learn that the person standing in front of them was different from the one who initiated the conversation. One pedestrian who reported noticing nothing unusual nonetheless claimed to have noticed the change when asked directly. Interestingly, those who noticed the change were all students of roughly the same age as the experimenters (approximately 20~30 years old). Those who failed to detect the change were slightly older than the experi- menters (approximately 35-65 years old). One possible explanation for this difference is that younger pedestri- ans were more likely to expend effort encoding those features that would differentiate the experimenters be- cause the experimenters were roughly of their own gen- eration. In contrast, older pedestrians would likely en- code the experimenters without focusing on features that could differentiate the two of them, instead viewing them as members of a social group other than their own. This hypothesis draws on findings from social psychology that members of ones own social group (in-group) are treated differently from members of social groups dis- tinctly apart from ones own (out-group). Upon encoun- tering a member of an in-group, people tend to focus at- CHANGE DETECTION 647 -~-- Figure 2. The experimenters dressed as construction workers for Experiment 2. tention on individuating features and to pay little attention to the persons social-group membership. In contrast, for members of out-groups, people direct more attention to attributes associated with the out-group as a whole and generally do not focus on features that distinguish one in- dividual from others in the group (see, e.g., Rothbart & John, 1985). These differences in processing of members of in-groups and out-groups extend to many aspects of cognition. For example, people are likely to assume that members of out-groups are collectively less variable on a variety of traits and variables (Judd & Park, 1988; Linville, Fischer, & Salovey, 1989). This tendency to code group- specifying information for members of out-groups can even determine what represents a visual feature for a par- ticular category (Levin, 1996). Applying these differences in the coding of in-groups and out-groups to the findings of Experiment I, we hy- pothesize that the younger subjects considered them- selves members of the same social group as the experi- menters and older subjects considered the experimenters to be members of an out-group. To test this hypothesis, we changed the appearance of the experimenters so that they could be classified as members of an out-group by the younger subjects. EXPERIMENT 2 To examine the role of social group membership in the detection of changes, a second experiment was conducted using the same procedure as the first, but with one criti- cal change: The same two experimenters dressed as con- struction workers (see Figure 2). The experimenters again wore different clothing: One wore a construction hat with writing on the front, a large tool belt, and a light blue shirt, and the other wore a newer hat without writing, no tool belt, and a black shirt. The experiment was conducted in the same location as Experiment 1, which happened to be approximately 50 m from a construction site. As in Ex- periment I, an experimenter approached a pedestrian to ask for directions to a building on campus. During the conversation, the experimenters were switched. Unlike in the first experiment, all 12 pedestrians who partici- pated in Experiment 2 were from the younger age group (Cornell graduate or undergraduate students), the group that had always detected the change in Experiment 1. The questions asked of the subjects were identical to those of Experiment 1 except that subjects were informed im- mediately after providing directions that the experimenters were not actually construction workers but were doing a study as part of the psychology department. Results and Discussion In contrast to the younger pedestrians in Experiment I, all of whom noticed the change, only 4 of the 12 pedes- trians in Experiment 2 reported noticing the switch when asked if they had seen anything unusual. Five subjects failed to report the change and were surprised to learn of the switch. An additional 3 subjects reported noticing nothing unusual but then claimed to have noticed the switch of experimenters. Unlike pedestrians who clearly noticed the change, these 3 pedestrians could not accu- rately describe any of the differences between the exper- imenters, suggesting that the demands of the task led them to report noticing the change even though they prob- 648 SIMONS AND LEVIN ably had not. Thus, subjects from the same age group that had successfully detected the change in Experi- ment I detected it only 33\% of the time in Experiment 2. When the experimenters appeared to be members of an out-group, thereby decreasing the likelihood that stu- dents would code individuating features, the ability to detect a change to the centrally attended object in a scene was dramatically reduced. One subject who failed to de- tect the change essentially stated our predicted hypothe- sis: She said that she had just seen a construction worker and had not coded the properties of the individual. That is, she quickly categorized the experimenter as a con- struction worker and did not retain those features that would allow individuation. Even though the experimenter was the center of attention, she did not code the visual details and compare them across views. Instead, she formed a representation of the category, trading the visual details of the scene for a more abstract understanding of its gist or meaning. GENERAL DISCUSSION These simple experiments build on classic findings offailures of eye- witness identification (e.g., Loftus, 1979) and distortions in memory (Bartlett, 1932/1977) as well as recent demonstrations of change blind- ness for objects (Pashler, 1988; Phillips, 1974; Simons, 1996), pho- tographs (Aginsky et al., 1997; Grimes. 1996; ORegan et aI., 1996; Rensink et aI., 1997), and motion pictures (Levin & Simons, 1997; Si- mons, 1996; Simons & Levin, 1997). Yet,unlike earlier demonstrations, this experiment shows that people may not notice changes to the central object in a scene even when the change is almost instantaneous and hap- pens in the middle of an ongoing, natural event. Attention alone does not suffice for change detection, even in the real world. Instead, suc- cessful change detection probably requires effortful encoding of pre- cisely those features or properties that will distinguish the original from the changed object. One potential objection to our results derives from the pragmatics of the interaction. Specifically, subjects may have detected the change but the social demands of the situation precluded them from reporting it. This possibility is substantially diminished by the subjects in each ex- periment who reported noticing nothing unusual but then reported noticing the switch. Although these subjects probably did not notice the change, the social demands of the situation encouraged them to report having noticed the switch when asked directly. Thus, the demands of the situation seem biased to increase reports of the switch rather than to decrease them. Another possible objection is that the task of giving directions dis- tracted subjects from focusing their attention on the experimenters. That is, subjects were focused on the map rather than their conversational partner. Anecdotally at least, subjects appeared focused on the inter- action and the conversation, often making eye contact with the experi- menters, hearing their voices, and taking turns in a conversation. Al- though we believe the results are not specific to this situation, ongoing experiments using a different type of interaction are directly examining the possible distraction caused by the map and possible disruptions to the representation of the first experimenter caused by the unusual na- ture of the interruption. A more fundamental question involves assessing the similarity of the experimenters. Clearly, no one would be surprised if pedestrians failed to notice a substitution of identically dressed identical twins. The in- ability to notice small changes is unsurprising because such changes naturally occur between views. For example, people rarely notice vari- ation in the position and orientation of moveable objects such as body parts (Levin & Simons, 1997). If we constantly noticed such changes, they would likely detract from our ability to focus on other, more im- portant aspects of our visual world. Change detection as a method re- lies on the tendency of our visual system to assume an unchanging world. The fact that we do not expect one person to be replaced by an- other during an interaction may contribute to our inability to detect such changes. A critical question for future research is why some changes are more likely to be detected than others. Clearly we would be quite surprised ifsubjects missed a switch between enormously different peo- ple (e.g., a switch from a 4 ft 9 in. female of one race to a 6 ft 5 in. male of another). The change in this case would alter not only the visual de- tails of the person, but also their category membership. If, as suggested by other recent findings of change blindness, we retain only abstracted information and not visual details from one view to the next, changes to category membership may well be detectable. Abstraction of cate- gory information is clearly central to coding other people (e.g., the ef- fects of in-group and out-group discussed earlier) and may underlie the representation of other objects across views as well. What, then, separates inconsequential changes to details from changes that are worth noting? Although there is no easy answer to this question, we would like to propose several guidelines or heuristics for identifying consequential changes for future studies of change blind- ness. These guidelines, used individually or together, can help constrain the generation of significant changes to scenes. First, significant changes to a scene should be easily verbalizable, and often verbalized (see Simons, 1996). Changes that are easily ver- balized likely cross a category boundary, making them more likely to be detected. The best example of this principle is the change in the color of the experimenters shirt in Experiment 2. Both shirt colors (blue and black) have basic color names. Second, the original and changed objects should be easily discrim- inable in simultaneous viewing. Everyone is familiar with the comics- page game of finding differences between two extremely similar im- ages. In such cases, the change is camouflaged, making it difficult to detect even when both the original and changed version are present. In our experiment, as in most studies of change blindness (see Simons & Levin, 1997), changes generally meet this criterion (e.g., the difference in shirt colors is plainly visible in Figure 2). Third, changes should affect the immediate functional needs of the perceiver. For example, changes to the spatial configuration of objects or their parts can be significant, even if they are not easy to verbalize. Spatial layout information is crucial to navigation and other immediate needs of the organism. For our experiments, variation in the configura- tion of facial features is precisely the information used in identifying other people; hence the person change should be readily detectable. Fourth, naive subjects should predict successful change detection. If change blindness is counterintuitive, we can be certain that the change is not trivial. For our experiments, individuals unfamiliar with our research consistently predicted that the change of experimenters would be plainly detectable. To examine this possibility for our experiments, we informally polled a class of 50 introductory psychology students by reading them the following description of our event: You are walking on the Cornell campus and a man with a puzzled look asks you to help him find Olin li- brary. Youstop and give him directions. While you are giving directions, two people carrying a door rudely walk between you and the lost pedes- trian. After the door has passed, the person you were giving directions to is now a different person wearing different clothes. By a show of hands, they claimed without exception that they would detect the change. By applying these four heuristics, researchers can be fairly certain that a change is detectable and that change blindness would be an im- portant finding. In our experiments, the change from one experimenter to another met all of these criteria. Yet, a substantial number of pedes- trians failed to detect the switch. Taken together, these experiments show that even substantial changes to the objects with which we are di- rectly interacting will often go unnoticed. Our visual system does not automatically compare the features of a visual scene from one instant to the next in order to form a continuous representation; we do not form a detailed visual representation of our world. Instead, our abstract ex- pectations about a situation allow us to focus on a small subset of the available information that we can use to check for consistency from one instant to the next. REFERENCES AGINSKY, v.. TARR, M. J., & RENSINK, R. A. (1997). The stability of color, location, and object presence in mental representations of nat- ural scenes. Investigative Ophthalmology & Visual Science, 38, S1009. ARNHEIM, R. (1966). Film as art. Berkeley: University of California Press. (Original work published 1933) BARTLETT, E C. (1977). Remembering: A study in experimental and so- cial psychology. Cambridge: Cambridge University Press. (Original work published 1932) BLACKMORE, S. J., BRELSTAFF, G., NELSON, K., & TROSCIANKO, T. (1995). Is the richness of our visual world an illusion? Transsaccadic memory for complex scenes. Perception, 24, 1075-1081. BREWER, W E, & TREYENS, J. C. (1981). Role of schemata in memory for places. Cognitive Psychology, 13,207-230. BRIDGEMAN, B., & MAYER, M. (1983). Failure to integrate visual infor- mation from successive fixations. Bulletin ofthe Psychonomic Soci- ety, 21, 285-286. DENNETT, D. C. (1991). Consciousness explained. Boston: Little, Brown. GRIMES, J. (1996). On the failure to detect changes in scenes across sac- cades. In K. Akins (Ed.), Perception: Vol. 2. Vancouv;r studies in cognitive science (pp. 89-1 10). New York: Oxford University Press. HENDERSON, J. M. (1997). Transsaccadic memory and integration dur- ing real-world object perception. Psychological Science, 8, 51-55. HOCHBERG, J. (1986). Representation of motion and space in video and cinematic displays. In K. R. Boff, L. Kaufman, & 1. P.Thomas (Eds.), Handbook ofperception and human performance: Vol. 1. Sensory processes and perception (pp. 22.21-22.64). New York: Wiley. IRWIN, D. E. (1991 ). Information integration across saccadic eye move- ments. Cognitive Psychology, 23, 420-456. JUDD, C. M., & PARK, B. (1988). Out-group homogeneity: Judgments of variability at the individual and group levels. Journal ofPersonality & Social Psychology, 54, 778-788. LEVIN, D. T (1996). Classifying faces by race: The structure of face categories. Journal of Experimental Psychology: Leaning, Memory, & Cognition, 22, 1364-1382. LEVIN, D. T, & SIMONS, D. J. (1997). Failure to detect changes to at- tended objects in motion pictures. Psychonomic Bulletin & Review, 4,501-506. LINVILLE, P. W, FISCHER, G. W, & SALOVEY, P. (1989). Perceived dis- tributions of the characteristics of in-group and out-group members: Empirical evidence and a computer simulation. Journal ofPersonality & Social Psychology, 57, 165-188. LOFTUS, E. E (1979). Eyewitness testimony. Cambridge, MA: Harvard University Press. MCCONKIE, G. W., & CURRIE, C. B. (1996). Visual stability across sac- CHANGE DETECTION 649 cades while viewing complex pictures. Journal ofExperimental Psy- chology: Human Perception & Performance, 22, 563-581. NICKERSON, R. S., & ADAMS, M. J. (1979). Long-term memory for a common object. Cognitive Psychology, 11,287-307. OREGAN, J. K., DEUBEL, H., CLARK, J. J., & RENSINK, R. A. (1997). Picture changes during blinks: Not seeing where you look and seeing where you dont look. Investigative Ophthalmology & Visual Science, 38, S707. OREGAN, J. K., RENSINK, R. A, & CLARK, J. J. (1996). Mud splashes render picture changes invisible. Investigative Ophthalmology & Vi- sual Science, 37, S213. PASHLER, H. (1988). Familiarity and visual change detection. Percep- tion & Psychophysics, 44, 369-378. PHILLIPS, W. A (1974). On the distinction between sensory storage and short-term visual memory. Perception & Psychophysics, 16, 283-290. RAYNER, K., & POLLATSEK, A. (1992). Eye movements and scene per- ception. Canadian Journal ofPsychology, 46, 342-376. RENSINK, R. A, OREGAN, J. K., & CLARK, J. J. (1997). To see or not to see: The need for attention to perceive changes in scenes. Psychologi- cal Science, 8, … Psychonomic Bulletin & Review 1997,4 (4), 501-506 BRIEF REPORTS Failure to detect changes to attended objects in motion pictures DANIEL T. LEVIN and DANIEL J. SIMONS Cornell University, Ithaca, New York Our intuition that we richly represent the visual details of our environment is illusory. When view- ing a scene, we seem to use detailed representations of object properties and interobject relations to achieve a sense of continuity across views. Yet, several recent studies show that human observers fail to detect changes to objects and object properties when localized retinal information signaling a change is masked or eliminated (e.g., by eye movements). However, these studies changed arbi- trarily chosen objects which may have been outside the focus of attention. We draw on previous re- search showing the importance of spatiotemporal information for tracking objects by creating short motion pictures in which objects in both arbitrary locations and the very center of attention were changed. Adult observers failed to notice changes in both cases, even when the sole actor in a scene transformed into another person across an instantaneous change in camera angle (or cut). Our immediate experiences of the world seem to include rich and detailed visual information about the locations and properties of objects. If this is true, then we should readily detect changes to objects in our environment. Yet, a num- ber of recent findings show that observers are surprisingly slow and often fail to detect changes to successive views of both natural and artificial scenes (Blackmore, Brelstaff, Nelson, & Troscianko, 1995; Grimes, 1996; McConkie & Currie, 1996; McConkie & Zola, 1979; ORegan, Rensink, & Clark, 1996; Pashler, 1988; Rensink, ORegan, & Clark, 1996; Simons, 1996; Tarr & Aginsky, 1996). Recent ex- periments have used a paradigm in which observers view two rapidly alternating versions of a photographed natural scene that differ by a change to an object or an object part (e.g., Blackmore et aI., 1995; Rensink et aI., 1996). Ob- servers simply try to detect the changing element. Assum- ing apparent motion is eliminated or masked by a blank in- terval (e.g., Rensink et aI., 1996) or by the simultaneous appearance of additional objects (ORegan et aI., 1996), The authors contributed equally to this report. and authorship order was determined arbitrarily. The contents of this paper were included as part of DJ.S.s doctoral dissertation. Thanks are extended to Ulric Neisser, Romi Nijhawan, Julie Noland, Kathy Richards, Carter Smith, Michael Spivey-Knowlton, and Arthur Woll, for reading earlier drafts of this report, and to Mark Andrews, Justin Barrell, James Beale, Laura Free, Grant Gutheil, Sabina Lamsfuss, Carole Lunney, Julie Noland, Kathy Richards, and Andrea Rosati, for appearing as actors in the films. DJ.S. was supported by NSF and Jacob K. Javits fellowships. Correspondence may be directed to either author at the following ad- dresses: D. T. Levin, Department of Psychology, Kent State University, Kent, 011 44242 (e-mail: [email protected]) and D. 1. Simons, Depart- ment of Psychology, Harvard University, Cambridge, MA 02138 (e- mail: [email protected]). observers require a large number of alternations before fi- nally identifying the change. Here we extend this finding by showing that change-detection failures occur not only for objects at some arbitrarily chosen location in a scene, but also for the very object that is the center of attention. One way of understanding previous change-detection failures is to assume that long detection latencies are generally consistent with a serial search among the ob- jects in the scene which terminates when the search process reaches the changing object. Noticing a change requires successively attending to and encoding each ob- ject in the scene. Accordingly, changes to unattended ob- jects will go unnoticed, but property changes will be de- tected immediately if the changed object becomes the center of attention. This hypothesis is supported by find- ings that changes to objects rated as more important or central in a scene are detected more quickly (Rensink et aI., 1996); they are given higher priority in a limited-ca- pacity visual search. Together with evidence that people cannot visually integrate information across eye move- ments (Bridgeman & Mayer, 1983; Irwin, Brown, & Sun, 1988; Irwin, Yantis, & Jonides, 1983; Jonides, Irwin, & Yantis, 1983) and that briefly presented pictures are quickly forgotten (Intraub, 1981; Potter, 1976), these findings suggest that only the objects that receive fo- cused attention are retained across views. If the properties of centrally attended objects are rep- resented more fully and are maintained across fixations, these might be the basis of a perceptually rich between- view representation. Serial-search accounts often assume that attention is not only necessary, but also sufficient for change detection; changes to an object that is the center of attention will be detected. Although the notion that at- 501 Copyright 1997 Psychonomic Society, Inc. 502 LEVIN AND SIMONS tended objects will be more fully represented has some empirical and intuitive appeal, even objects that are the center of interest may require extensive, effortful pro- cessing to be represented precisely. Here we examine the role of attention in change detection and consider the possibility that even if attending to an object is neces- sary for change detection, it may not be sufficient. The notion that effortful encoding is necessary to repre- sent even centrally attended objects gains support from re- cent work showing that 10-month-old preverbal infants seem unable to detect changes to a moving object that occur during an occlusion event (Xu & Carey, 1996). In these studies, an object (e.g., a toy duck) passes behind an occluding screen and another object (e.g., a toy truck) ap- pears on the other side. Patterns of dishabituation and pref- erentiallooking show that 1O-month-old infants do not use object properties to determine how many objects are in the display. Interestingly, 12-month-old infants who under- stand the objects labels successfully detect the change, suggesting that verbal or effortful processing is necessary for change detection even when the object is the center of interest (Simons, 1996; Xu & Carey, 1996). The need for effortful, attentional processing to detect object changes suggests that we do not rely on representations of objects or their properties to perceive the continuity of dynamic events. However, both infants and adults can use spatial in- formation to track objects over time, across discrete views, and across occlusion events (Simons, 1996; Spelke, Kestenbaum, Simons, & Wein, 1995; Xu & Carey, 1996). On the basis of these findings, we reasoned that if track- ing the properties of attended objects requires explicit cod- ing, then it should be possible to induce change-detection errors in attended objects if observers did not feel the need to explicitly label their features. Change-detection failures would therefore reflect between-view representations which contain little property information, both for scenes as a whole and for attended objects. To test for change-detec- tion failures, we created a series of short videos in which objects changed either at unpredictable locations or in the center ofattention. Experiment 1 was designed to assess the degree to which change-detection failures would occur in edited motion pictures when the objects changed were not necessarily in the center ofattention. InExperiments 2A and 2B, change detection for attended objects was examined. In these experiments, observers viewed videos depicting sim- ple events in which a single actor changed into a different person across an edit. In both cases, if object properties were not automatically retained across views, then a signif- icant proportion of changes should go unnoticed. EXPERIMENT 1 Although researchers have only recently begun to ex- amine between-view representation of natural scenes, film makers have long known that viewers do not store all of the visual details of each view of a scene (Kuleshov, 1920/ I987). Fiction films typically consist of events that are presented piecemeal through a series of partial views. These views are often filmed individually, and usually in a different order than depicted in the finished movie. This reordering process can lead to substantial mis- matches in object properties, body positions, and cloth- ing across views, yet these inconsistencies (referred to as continuity errors) are rarely noticed by audiences (Hochberg, 1986; Kuleshov, 1920/1987). To demonstrate empirically the undetectability of such continuity errors, we created a short edited video ofa con- versation between two actors. Each cut from one shot to the next resulted in at least one intentional continuity error (see Figure 1). For example, in one case, the red plates on the table changed to white across a cut (Figure lC-ID). We tested subjects ability to detect such errors, both when they were unaware that they might occur and when they had been explicitly instructed to look for them. Method Ten Cornell University undergraduates viewed the test video in ex- change for candy. These subjects viewed a short color VHS video de- picting a conversation between two actors. The video included sound and was shown on a 19-in. television with a viewing distance of ap- proximately 100 em. It initially showed a side view of both actors (Figure I A) and then cut to close up shots of each in turn as they spoke (I B-1 D). Across each cut, we made at least one continuity error, for a total of nine intentional errors in the film. For example, in one shot an actor is wearing a large colorful scarf and in the next it has instan- taneously disappeared (1 A-I B; see also the Appendix). Other changes shown in the figure include a switch from red to white plates (lC-I D) and a change in hand position (I C-I D). No blanks were in- serted between cuts, so the changes occurred within the 60-Hz refresh rate of a conventional TV (30 two-field frames per second). The sub- jects who viewed the film were instructed to pay close attention but were not forewarned of the changes. After they had viewed the film, they were handed a form that asked, Did you notice any unusual dif- ferences from one shot to the next where objects, body positions, or clothing suddenly changed. They responded by circling yes or no on the response sheet. The subjects who circled yes were then asked to describe any changes you noticed. After writing their responses, the subjects were told, In the film you just viewed, changes occurred every time the camera angle changed. Now (II show you the film again. This time, try to spot the changes. The question on the first part of the response form cued them to the sorts of changes that might occur (i.e., objects, body po- sitions, or clothing). After viewing the film a second time, the sub- jects were again asked to describe any changes they had noticed. Results and Discussion Of the 10 subjects who viewed this film, only 1 claimed to notice any of the 9 changes during the first viewing. Thus, 89 of90 total changes went unnoticed. The single detected change was vaguely described as a difference in the way the people were sitting. Even during the second viewing, when subjects were explicitly told to look for changes, they noticed an average of only 2 of the 9 changes. The most frequently noticed change was the appearance and disap- pearance of the scarf, which was detected by 7 of the 10 subjects. These results parallel recent findings offailures to detect changes to scenes across views (Blackmore et aI., 1995; Grimes, 1996; ORegan et aI., 1996; Rensink et al., 1996; Tarr & Aginsky, 1996), and suggest that edited mo- tion pictures provide a compelling medium for studying naturalistic scene perception and representation. Although this experiment suggests that we generally do not integrate sensory information across views, we appar- CHANGES TO OBJECTS IN MOTION PICTURES 503 A c o Figure 1. Four sample views from the stimulus film in Experiment 1. The figure is also available at http://www.wjh.harvard. eduz-dstmons on the World-Wide Web. ently can form longer lasting representations through ef- fortful encoding-subjects were able to notice a subset of changes when they intentionally searched for continuity errors. Those attended objects are processed more thor- oughly, leading to richer representations. These findings are entirely consistent with the limited-capacity serial- search model discussed earlier; we cannot fully process all objects and properties in a scene (Neisser, 1967), and we are more likely to detect changes to central objects that garner more attentional resources. This finding again confirms the notion that attention is necessary for change detection. However, it does not di- rectly assess the possibility that attention may not be suf- ficient for change detection. The next experiment tested the hypothesis that simply focusing attention on an object might not automatically lead to accurate change detection. EXPERIMENT 2A If continuous perception is based on representations of an objects spatial position and motion but not its static properties, then even changes to attended objects may go undetected when spatiotemporal information does not signal a change. We tested this hypothesis by creating new motion pictures which focused attention on the very ob- ject that changed while maintaining a consistent direction of object motion across cuts. These films portrayed a simple action performed by a single actor. But rather than changing small objects which might or might not be attended, we changed the actors themselves. For exam- ple, in one film, an actor sitting at a desk hears a tele- phone ring, gets up, and moves toward the door. The cam- era then cuts to a view of the hallway where a different actor walks to the telephone and answers it (Figure 2). In Experiment 2A, each observer viewed one of these films with no prior instructions and then wrote a brief descrip- tion of the film. Experiment 2B was a test of the dis- criminability of the two actors in which subjects were forewarned that changes would be occurring. This was necessary to ensure that the differences between the actors in the videos were large enough to be plainly visible. Method A total of 40 Cornell University undergraduates participated as sub- jects in Experiment 2A in exchange for candy or course credit. For this experiment, we created a series of eight color VHS videos fol- lowing the conventional editing practice of maintaining direction of 504 LEVIN AND SIMONS Figure 2. Sample frames from an actor-change film used in Experiment 2. The figure is also available at http://www.wjh.harvard. edu/-dslmons on the World-Wide Web. body motion from one shot to the next. The videos were silent and were shown on 19- and 13-in. televisions with a viewing distance of approximately 60-100 cm. Each film showed one of two events: (I) an actor sitting at a desk hears a phone ring in the hallway and gets up to answer it, or (2) an actor enters a room and sits down in a chair. Videos of Event I included two shots (see Figure 2). Videos of Event 2 in- cluded three shots. In the first shot, an actor walks through a previ- ously closed door and passes the camera. The second shot shows a wide angle view of the actor walking toward a chair at the front of a classroom while sidestepping other chairs. The final shot is a close- up of the actor sitting in the chair. In each video, the actor initially in the scene changes to a different actor across a cut. (In videos of Event 2, the actor changes between the second and third shots.) Two differ- ent pairs of actors were filmed in each event, and separate fi Ims were made, with each actor of a pair changing into the other. Each pair of actors was matched for gender, race, hair color, and glasses, and wore globally similar, but not identical, clothing. Each of the eight films was viewed by 5 different subjects who were simply asked if they would be willing to watch the video before par- ticipating in another study in the same laboratory. They were given no other instructions. The subjects completed the experiment individu- ally. After viewing one of the videos, a subject was given a response sheet that asked him/her to please write a brief description of the video you saw. The experimenter then took the response sheet from the subject. If a written response did not mention the change from one actor to another, the experimenter directly asked the subject if he or she had noticed the person change. For example. subjects viewing event A were asked Did you notice that the person who was sitting at the desk was a different person than the one who answered the phone? Responses to the follow-up question were marked on the re- sponse sheet by the experimenter. Results and Discussion Viewers were surprisingly oblivious to the substitution of one actor for another, even though the person portrayed by the actors was the central object in the film. Only 33\% of the 40 subjects reported that one actor had changed into another. The subjects who failed to notice the change had clearly attended to the films; they produced rich descrip- tions of clothing, the environment, and the motions of the actors. For example, one subject wrote Man in light blue shirt & tee shirt was sitting at cluttered desk, turned to- ward camera & walked toward it. [He] walked outside into hall and picked up the telephone on the wall, In this par- ticular video, the first actor was wearing an unbuttoned, blue, long-sleeve shirt with a T-shirt underneath. The sec- ond actor was wearing a gray long-sleeve shirt which was fully buttoned and had no T-shirt underneath. Of those who did not mention the change in their descriptions, only 2 claimed to have noticed it when asked. CHANGES TO OBJECTS IN MOTION PICTURES 505 EXPERIMENT 2B Although pretesting had shown that people familiar with the actors in the films used in Experiment 2 imme- diately noticed the change from one actor to another, we nonetheless empirically controlled for the possibility that the pairs of people in the films were simply too sim- ilar to allow detection ofthe changes. In this experiment, a different set of subjects viewed all of the actor-change videos from Experiment 2A intermixed with a set of videos with no actor changes. The subjects were asked to indicate which films contained a change. Method A total of 10 Cornell undergraduates participated as subjects in this study in exchange for candy or course credit. The materials and pro- cedure used in this experiment were identical to those of Experi- ment 2A with the following exceptions: (I) Eight new videos con- taining no actor substitutions were added to the 8 actor-change videos from Experiment 2A, for a total of 16 videos. (2) Each subject viewed all 16 films shown in one of two orders (the first was randomly gen- erated and the second was a reversal of the first). (3) The subjects were forewarned that changes would take place in some of the films and were asked to circle change or no change on a worksheet for each film. They were also instructed to be especially careful, because de- tecting the change might be more difficult than it sounded. (4) They were informed of the nature of events shown in films of Events I and 2 (see Experiment 2A) using crudely drawn schematic illustrations of each shot in the two videos (i.e., a roughly drawn sketch similar to the panels shown in Figure 2 with stick figures depicting the actors and arrows indicating the direction of motion). and in the case of Event 2 were told that the changes would occur between the second and third shots. Other than the schematic illustration of the cuts, all instructions were given verbally. Results Unlike the subjects in Experiment 2A, subjects in this experiment had little difficulty in differentiating the ac- tors. On the average, they made fewer than I mistake each. The inability to notice changes to the central object in the scene cannot be attributed solely to the physical similar- ity of the objects before and after the change. GENERAL DISCUSSION Taken as a whole, these experiments demonstrate that object prop- erties are not automatically used to integrate different views of a scene. Even though we can clearly discriminate individual objects, we apparently do not encode, represent, and use property information to track them over time (Simons, 1996: Xu & Carey, 1996). Our short motion pictures show that even dramatic changes to the very object that is the center of attention often go unnoticed, especially when spa- tiotemporal information suggests continuity. Although previous re- search had demonstrated that attention was necessary for the detection of changes and that changes to central objects were detected more readily (0 Regan et al., 1996; Rensink et al., 1996), interpretations of these results tended to suggest that attention was sufficient for change detection. Along with recent infant work, our studies show that even when we attend to an object, we may not form a rich representation that can be preserved from one view to the next unless the objects properties are intentionally coded. Thus, attending to an object is nec- essary, but not sufficient, for change detection. One potentially problematic aspect of our methodology is that, in a sense, we rely on a memory test to reveal on-line detection of a be- tween-view inconsistency. Given that the observers did not expect the change, our results may reflect the poverty of incidental memory or the difficulty of free recall rather than an inability to detect changes. Al- though our primary purpose was not to test the ability to remember vi- sual details of scenes, this research suggests a variety of interesting is- sues for understanding the relationship between different varieties of memory and change-detection failures. Perhaps a more sensitive test might reveal residual memory for the prechange actor. One possibility is that observers may be able to discriminate the prechange actor from other actors not in the scene when given a recognition or priming task. Although such tasks might reveal the existence of a representation of the prechange actor, such representations probably do not underlie the continuity of our perceptual experience. Presumably, any mechanism underlying a sense of continuity should be tuned toward detecting vi- olations in that continuity. These violations should attract further at- tention, evaluation, and description, both on the response form and af- terwards when observers are directly asked if they had seen the change. Thus, the incidental nature of our task is unlikely to obscure a mecha- nism that is responsible for tracking objects and detecting violations of expected continuity. However, the present studies do not directly as- sess the possible existence of other, less accessible representations that might facilitate the processing of repeatedly viewed objects. Although our findings show that observers often miss surprisingly large changes to central objects, they do sometimes successfully de- tect changes. One explanation for successful change detection in our task is that observers sometimes intentionally encode (e.g., by verbal labeling) a critical object property just before it changes. The actor changes used in our study did not vary several important categorical properties of the person (e.g., race, sex, age). Perhaps changes to such features would consistently register across views. If so, comparing such successes with the failures we have observed could provide use- ful insights into the nature of person concepts. These categorical prop- erties could be registered automatically or they might require effort- ful encoding, but at least for the range of properties manipulated in these studies, change detection seems to require effort and not to be based on automatic domain -general perceptual routines which fully represent the attributes of all attended objects. The visual properties of objects, even attended objects, are not automatically used to inte- grate different views of a scene. REFERENCES BLACKMORE, S. J., BRELSTAFF, G., NELSON, K., & TROSCIANKO, T. (1995). Is the richness of our visual world an illusion? Transsac- cadic memory for complex scenes. Perception, 24, 1075-1081. BRIDGEMAN, B., & MAYER, M. (1983). Failure to integrate visual in- formation from successive fixations. Bulletin of the Psychonomic Society, 21, 285-286. GRIMES, J. (1996). On the failure to detect changes in scenes across saccades. In K. Akins (Ed.), Perception (pp. 89-110). New York: Oxford University Press. HOCHBERG, J. (1986). Representation of motion and space in video and cinematic displays. In K. R. Boff, R. Kaufman, & 1. P. Thomas (Eds.), Handbook of perception and human performance: Vol. J. Sensory processing and perception (pp. 22-1 to 22-64). New York: Wiley. INTRAUB, H. (1981). Rapid conceptual identification of sequentially presented pictures. Journal of Experimental Psychology: Human Perception & Performance, 7, 604-610. IRWIN, D. E., BROWN, J. S., & SUN. J. S. (1988). Visual masking and visual integration across saccadic eye movements. Journal ofEx- perimental Psychology: General, 117,276-287. IRWIN, D. E., YANTIS, S., & JONlDES, J. (1983). Evidence against visual integration across saccadic eye movements. Perception & Psycho- physics, 34, 49-57. JONlDES, J., IRWIN. D. E., & YANTIS, S. (1983). Failure to integrate in- formation from successive fixations. Science, 222, 188. KULESHOV, L. (1987). Lev Kuleshov: Fifty years in films. Moscow: Raduga. (Original work published 1920) MCCONKIE, G. W, & CURRIE, C. B. (1996). Visual stability across sac- cades while viewing como lex pictures. Journal ofExperimental Psychologv: Human Perception & Performance, 22, 563-581. MCCONKIE, G. W., & ZOLA,D. (1979). Is visual information integrated 506 LEVIN AND SIMONS across successive fixations in reading? Perception & Psycho- physics, 25, 221-224. NEISSER, U. (1967). Cognitive psychology. New York: Appleton- Century-Crofts. OREGAN, J. K., RENSINK, R. A., & CLARK, J. J. (1996). Mud splashes render picture changes invisible. Investigative Ophthalmology & Visual Science, 37,5213. PASHLER, H. (1988). Familiarity and visual change detection. Percep- tion & Psychophysics, 44, 369-378. POTTER, M. C. (1976). Short-term conceptual memory for pictures. Journal of Experimental Psychology: Human Language & Mem- ory, 2, 509-522. RENSINK, R. A., OREGAN, J. K., & CLARK, J. J. (1996). To see or not to see: The need for attention to perceive changes in scenes. Investiga- tive Ophthalmology & Visual Science, 37, 5213. SIMONS, D. 1. (1996). In sight, out of mind: When object representa- tions fail. Psychological Science, 7, 301-305. SPELKE, E. S., KESTENBAUM, R., SIMONS, D. J., & WEIN, D. (1995). Spa- tiotemporal continuity, smoothness of motion and object identity in infancy. British Journal ofDevelopmental Psychology, 13, 113-142. TARR, M., & AGINSKY, V. (1996, July). From objects to scenes: Specu- lations on similarities and differences. Paper presented at the Scene Recognition Workshop, Max-Planck-Institut fur Biologische Ky- bernetik, Tubingen, Germany. Xu, E, & CAREY, S. (1996). Infants metaphysics: The case of numerical identity. Cognitive Psychology, 30,111-153. APPENDIX Description of the Video in Experiment 1 The film used the following six shots to depict a conversation between two actors: Shot I: A side view of the two actors (Figure IA). The actors are sitting at a table with bright red plates, cups, and soft drink bottles on it. The plate in front of actor A (Figure lB) has food on it. Actor As right hand is resting on the table and she is wear- ing a colorful scarf. Actor Bs hands are crossed with her el- bows resting on the table. The table, both actors, and all of the objects are visible. Shot 2: A medium shot depicting actor A (Figure lB) from over the shoulder of actor B. The back of actor Bs head and part of her right shoulder are visible. The plates, food, and uten- sils are visible as well. Actor A is no longer wearing a scarf. Shot 3: A medium shot of actor B (Figure 1C) from over the shoulder of actor A. The back of actor As head and part of her shoulder are visible. Her right arm is visible as well. Again, the plates, food, and utensils are visible. Actor As scarf has re- turned and actor Bs hand is now on her chin. Shot 4: A full side view of both actors (as in Shot 1). The plates on the table are now white (rather than red) and actor Bs arms are again crossed with elbows resting on the table. Shot 5: A medium shot of actor A. The plates are red again, and actor As right hand now rests on her lap rather than on the table. Shot 6: A medium shot of actor B. The food previously on actor As plate is now on actor Bs plate, and actor As right hand again rests on the table. (Manuscript received September 5, 1996; revision accepted for publication April 21, 1997.) Journal of the History of the Behavioral Sciences, Vol. 35(1), 1 – 22 Winter 1999 q 1999 John Wiley & Sons, Inc. CCC 0022-5061/99/010001-22 JHBS — WILEY RIGHT INTERACTIVE short standard Base of DF Top of ID Base of 1st line of ART 1 JOHN D. GREENWOOD is professor of philosophy and psychology at City College and the Graduate School of the City University of New York. Educated at the Universities of Edinburgh and Oxford, his teaching and research interests are in the philosophy and history of social and psychological science. His most recent works include Realism, Identity and Emotion: Reclaiming Social Psychology (1994) and (as editor) The Mark of the Social: Invention or Discovery? (1997). Address for correspondence: De- partment of Philosophy, City College, 138th Street & Convent Avenue, New York, NY 10031. E-mail: [email protected] UNDERSTANDING THE “COGNITIVE REVOLUTION” IN PSYCHOLOGY JOHN D. GREENWOOD In this paper it is argued that the “cognitive revolution” in psychology is not best repre- sented either as a Kuhnian “paradigm shift,” or as a movement from an instrumentalist to a realist conception of psychological theory, or as a continuous evolution out of more “liberalized” forms of behaviorism, or as a return to the form of “structuralist” psychology practiced by Wundt and Titchener. It is suggested that the move from behaviorism to cognitivism is best represented in terms of the replacement of (operationally defined) “intervening variables” by genuine “hypothetical constructs” possessing cognitive “surplus meaning,” and that the “cognitive revolution” of the 1950s continued a cognitive tradition that can be traced back to the 1920s. q 1999 John Wiley & Sons, Inc. In this paper I provide a characterization of a recent historical episode that I believe has been much misunderstood: the so-called “cognitive revolution” in psychology. Although it is a matter of debate whether there was a genuine “revolution” in the usual sense in which this term is employed in the history of science (the dramatic overthrow and replacement of prior theories and methods), I believe it is important to recognize that the advent of cognitive theories in the 1950s did mark a fairly radical theoretical discontinuity, and precisely the sort of theoretical discontinuity that is characteristic of many revolutionary episodes in the history of science (Cohen, 1985). My argument, however, is not really intended as a contribution to the general “continuity versus discontinuity” debate about the development of the cognitive revolution. General de- bates about whether significant episodes in the history of science constitute a progressive and continuous development or a discontinuous transformation are not particularly illuminative, as Peter Galison (1997) has forcefully argued. Galison has noted that radical breaks in theo- retical practice have occurred during periods of continuity in experimental or technological practice (and vice versa), and has suggested that the history of a discipline as a whole is better represented as “an irregular stone fence or rough brick wall rather than as adjacent columns of stacked bricks” (1997, p. 19). This seems to be especially true of the history of psychology. Significant historical episodes represent continuities as well as discontinuities, and on a variety of different levels: the task of the historian is to discern their contingent interrelation or “intercalation” (Galison’s term) at different periods. Thus, although the account offered in this paper is critical of competing accounts of the cognitive revolution in terms of continuous development versus radical discontinuity, its main goal is to suggest some neglected discon- 2 JOHN D. GREENWOOD LEFT INTERACTIVEJHBS — WILEY short standard long Top of RH Base of RH Top of text Base of texttinuities and continuities that hopefully improve our understanding of this complex but very significant episode in the history of modern psychology.1 To endorse Galison’s historiographical perspective is not, however, to accept that all putative historical accounts of the cognitive revolution merely describe some aspect of it, and in this paper I reject some traditional, reactionary, and revisionary accounts. Many traditional accounts treat the cognitive revolution as a radically discontinuous break with the hegemony of behaviorism, in which a novel cognitive “paradigm” displaced the previously entrenched behaviorist “paradigm.” Many scholars treat the cognitive revolution in psychology as having essentially evolved out of independent developments in computer science and linguistics, while some have suggested, and others have complained, that it marked a return to the form of “structuralist” psychology practiced by Wilhelm Wundt and Edward B. Titchener in the early decades of the twentieth century. More recent revisionary accounts have argued that the cognitive revolution developed naturally and continuously out of the increasingly liberal attitudes to “internal” cognitive states adopted by later behaviorists. I believe that these ac- counts are seriously flawed, and in this paper I try to explain why. In their place, I offer an2 account of the cognitive revolution (albeit partial and provisional) in terms of a neglected discontinuity between behaviorism and cognitive psychology with respect to the content of theories, and a neglected continuity with a tradition of cognitive theory (distinct from “struc- turalism”) that began in the early decades of the twentieth century. PARADIGMS AND THEORETICAL REALISM The movement from behaviorism to cognitivism that is often characterized as the cog- nitive revolution is not best represented in terms of a Kuhnian “paradigm shift” (Lachman, Lachman, & Butterfield, 1979; Palermo, 1971; Weimer & Palermo, 1973) in which one theoretical paradigm gives way to another under the pressure of an empirical anomaly or set of anomalies (Kuhn, 1970). The various anomalies that eventually faced behaviorism, such3 as the “discovery” of biological limits on conditioning (Breland & Breland, 1961; Garcia & Koelling, 1966), and doubts about the ability of conditioning theory to accommodate linguistic performance (Chomsky, 1959; Lashley, 1951), did not result in the abandonment of the central principles of operant or classical conditioning theories — the core theoretical elements of the behaviorist paradigm. Moreover, behaviorists continued to maintain their in-house journals, their own APA division, and a sizable professional membership (Leahey, 1997). Nor were these recognized anomalies the primary stimulus for the development of cognitive theories in the 1950s, which was provided by outside developments in artificial intelligence and the computer simulation of cognitive abilities (Baars, 1986; Gardner, 1985). 1. It is, of course, an episode that continues to develop, and in historically interesting ways. Some have claimed that the development of “connectionist” challenges to traditional “rules and representations” theories of cognition in the 1980s amounted to a second cognitive revolution (Rumelhart & McClelland, 1986; Schneider, 1987). Others have suggested that developments in connectionist theory and more recent dynamical systems theory have marked a return to earlier forms of associationist psychology (Haselager, 1997). I do not find either of these claims at all convincing, but consideration of them is beyond the scope of the present paper, which is focused on the initial development of the cognitive revolution. However, these important later developments will need to be accommodated by any comprehensive historical account of the progress of the cognitive revolution. 2. References for these different historical accounts are provided at the points that they are considered in the text. 3. As is well known, Kuhn himself thought that psychology was “pre-paradigmatic.” 3UNDERSTANDING THE “COGNITIVE REVOLUTION” IN PSYCHOLOGY JHBS — WILEY RIGHT INTERACTIVE short standard long Top of RH Base of RH Top of text Base of textCertainly, the relation between behaviorism and cognitive psychology is not best rep- resented as a conflict between competing and exclusive theoretical paradigms, on analogy with historical conflicts between, for example, the physical theories of Newton and Einstein in the early twentieth century, or between wave and particle theories of light in the early nineteenth century. The evidence that favored and led to the adoption of Einstein’s theory and the wave theory of light appeared to demonstrate the general inadequacy of Newtonian theory and the particle theory of light, and thus led to their complete rejection by most scientists. Yet nobody — not even dedicated cognitivists — seriously imagined that either the anomalies noted above, or their theoretical biological and cognitive resolutions, demonstrated the general inadequacy of theories of classical or operant conditioning. These recognized4 anomalies, and their theoretical biological and cognitive resolutions, only led to a delimitation of the scope of explanations in terms of conditioning (albeit long overdue), and the extension of underdeveloped biological and cognitive explanations to those domains for which condi- tioning theory had proved to be inadequate. It was only because too many behaviorists grossly overestimated the scope of condi- tioning explanations, and presumed that conditioning theory enabled us (in principle, if not in practice) to explain virtually all forms of animal and human behavior, including complex forms of human behavior such as language, that behaviorism faced these empirical problems and challenges. Behaviorists were not always so intellectually imperialistic, and biological5 limits on learning and the possible inability of conditioning (or “habit”) theories to explain higher cognitive processes were recognized by the early pioneers of conditioning theory, such as Conwy Lloyd Morgan (1896), who conceived of such laws of learning as covering only a limited range of human behaviors. Indeed, one useful consequence of the cognitive revolution was to return conditioning theory — and comparative psychology in general — to the much more reasonable position advocated by Lloyd Morgan in the 1890s (B. F. Skinner and his “radical behaviorist” followers aside), which recognized possible qualitative differences be- tween human and animal psychological processing, as well as obvious continuities between them. In fact, some neobehaviorists were already returning to that position, as the cognitive revolution was emerging, and as they began to engage more complex behaviors such as language or symbolic behavior (Kuenne, 1946; Miller, 1959; Osgood, 1957; Spence, 1937). “Morgan’s Canon” (Morgan, 1894) was originally merely a caution against overestimating the application of cognitive explanations in the animal kingdom, transformed by theorists such as Edward L. Thorndike, John B. Watson, Clark L. Hull, and B. F. Skinner into an effective prohibition against cognitive explanations in both the animal and human realm. The cognitive revolution is also not best represented as a revolution in terms of a par- adigm shift with respect to attitudes towards theories, in the sense of a shift from an instru- 4. Because of this feature, the de facto maintenance of theories of classical and operant conditioning by contem- porary behaviorists in the midst of the cognitive revolution does not itself represent a serious historical anomaly— as if there continued to be many supporters of the Newtonian theory in the midst of the “Einsteinian revolution” in physics. What would be historically anomalous is any behaviorist who still maintained that classical and operant conditioning can explain every form of animal and human behavior— he or she would be like a contemporary physicist who believed that Newton’s theory is about to make a comeback and displace Einstein’s theory. 5. See, for example, Clark L. Hull, who maintained in the Preface of Principles of Behavior (1943a, p. v): . . . that all behavior, individual and social, moral and immoral, normal and psychopathic, is generated from the same primary laws: that the differences in the objective behavioral manifestations are due to the differing conditions under which habits are set up and function. 4 JOHN D. GREENWOOD LEFT INTERACTIVEJHBS — WILEY short standard long Top of RH Base of RH Top of text Base of textmentalist to a realist conception of theories, that is, from the treatment of theories of cognitive and biological states and processes as mere linguistic instruments that facilitate the integration and prediction of empirical laws, to their treatment as theoretical references to putatively real cognitive and biological states and processes. Although this is the usual historical account6 advanced by those in the cognitive science community (Baars, 1986), and popularized by Jerry Fodor (Fodor, 1975), it is of doubtful validity. It is quite clear that Hull (1943b) and Edward C. Tolman (1948), for example, were realists (in the above sense) about biological states (drives) and cognitive states (cognitive maps) respectively. Thus, to quote Tolman, for example: For the behaviorist, “mental processes” are to be identified and defined in terms of the behaviors to which they lead. “Mental processes” are, for the behaviorist, naught but inferred determinants of behavior, which ultimately are deducible from behavior. Be- havior and these inferred determinants are both objectively defined types of entity. (Tol- man, 1932, p. 3) Not even the more radical behaviorists denied the existence of cognitive states. When John B. Watson (1925) equated thoughts with movements of the larynx, his central claim (following the Russian reflexologists Ivan M. Sechenov and Vladimir M. Bechterev) was that cognitive states are motor or behavioral responses rather than centrally initiated states, and thus non-candidates for the explanation of motor or behavioral responses. B. F. Skinner’s objection to cognitive states, the existence of which he never denied, was based upon the redundancy of putative explanatory references to cognitive states (the “second link”), when these are operationally defined in terms of stimulus inputs (the “first link”) and behavioral outputs (the “third link”): The objection to inner states is not that they do not exist, but that they are not relevant in a functional analysis. We cannot account for the behavior of any system while staying wholly inside it; eventually we must turn to forces operating upon the organism from without. Unless there is a weak spot in our causal chain so that the second link is not lawfully determined by the first, or the third by the second, then the first and third links must be lawfully related. If we must always go back beyond the second link for prediction and control, we may avoid many tiresome and exhausting digressions by examining the third link as a function of the first. (Skinner, 1953, p. 35) Conversely, early cognitivists were, in fact, extremely wary about committing them- selves to the existence of cognitive states. Roy Lachman, Janet Lachman, and Earl Butterfield (1979), for example, after reviewing dozens of experimental studies of perception, memory, linguistic processing, and the like, nonetheless concluded that it was too early to say if cog- 6. It ought to be stressed that the term “realist” is employed in this paper only to mark the position that treats theoretical terms as putatively referential, as opposed to the “instrumentalist” position that treats theoretical terms as nothing more than (non-referential) linguistic instruments that facilitate the integration and prediction of empirical laws. It is not employed to mark any of the bewildering variety of different positions that are often also characterized as “realist”: for example, positions in classical debates about the nature of universals, our knowledge of the existence and properties of physical objects in the external world, and in modern debates about whether the history of science demonstrates the general or approximate truth of contemporary scientific theories. The realist versus instrumentalist debate about the putative reference of scientific theories was the type of debate engaged by Andreas Osiander and Christopher Clavius over the status of the Copernican theory in the sixteenth century. Osiander was an instrumentalist who maintained that the Copernican theory was a useful and economical calculation device that did not purport to give a true description of the positions of the planets (and was thus not heretical). Clavius was a realist who maintained that the Copernican theory did purport to describe the true positions of the planets, and was false (and thus heretical). Similar disputes occurred over the status of the atomic and quantum theories in the nineteenth and twentieth centuries. 5UNDERSTANDING THE “COGNITIVE REVOLUTION” IN PSYCHOLOGY JHBS — WILEY RIGHT INTERACTIVE short standard long Top of RH Base of RH Top of text Base of textnitive states really exist! Some cognitive theorists, such as John Anderson (1981), continued to maintain an agnostic view. Some were simply inconsistent: Richard Nisbett and Lee Ross (1980), for example, after having appealed to dozens of experimental studies that they claimed demonstrated that persons regularly make inaccurate judgments about their cognitive states, then declared themselves agnostic on the question of whether there are any cognitive states! THE REAL REVOLUTION: FROM “INTERVENING VARIABLE” TO “HYPOTHETICAL CONSTRUCT” In consequence, it is perhaps natural and tempting to see the move from behaviorism to cognitive psychology as a progressive liberalization of attitudes toward theories, particularly theories postulating intersubjectively unobservable internal states. On this increasingly pop- ular view, cognitive psychology is characterized as having emerged or evolved continuously out of more liberalized forms of neobehaviorism, which allowed for the introduction of “in- ternal variables” such as “internal” or “mediating” r-s connections, so long as these were operationally defined (Amsel, 1989; Kendler & Kendler, 1975; Leahey, 1992; Miller, 1959). However, while it may be true that later behaviorists might have felt more comfortable and less apologetic about postulating internal states than their earlier fellows (although neither Hull or Tolman appear to have been especially reticent in this respect), this characterization also seems to be seriously flawed. There was a very significant difference between the types of “internal” states postulated by even the most liberal neobehaviorists and by cognitive psychologists from the 1950s onward. It is true that only Watson and Skinner, for their diverse but essentially extreme positiv- istic reasons, were truly antitheoretical with respect to postulated internal states that are not intersubjectively observable. Most other behaviorists and neobehaviorists, and famously Hull and Tolman, allowed for the introduction of theoretical terms, or postulated “intervening variables,” so long as these were, at least ideally, rigidly and exhaustively defined operation- ally, via principles or “laws” relating stimulus inputs to internal states and internal states to behavioral outputs (Bergmann & Spence, 1941; Hull, 1943b; Pratt, 1939; Stevens, 1935; Tolman, 1936). It was Kenneth MacCorquodale and Paul Meehl (1948) who recognized the serious inadequacy of this characterization of theoretical terms. If intervening variables are rigorously and exhaustively defined in terms of empirical laws, they cannot function as sub- stantive (non-vacuous) explanations of empirical laws, or be creatively developed to generate novel empirical predictions. (As noted earlier, this was essentially the basis of Skinner’s justified dismissal of cognitive intervening variables as vacuous — and thus predictively re- dundant — ”explanatory fictions.”) In order to generate substantive explanations and have the potential for further development, genuine theories, or “hypothetical constructs,” must possess “surplus meaning.” Where this “surplus meaning” comes from in psychological science is a7 matter of some dispute, but that genuine theories poses such surplus meaning is not — for this is precisely what accounts for their explanatory power and creative predictive potential. In natural science, this substantive surplus meaning is often created via the exploitation of theoretical models and analogies, as in Niels Bohr’s “planetary” theory of the atom and the “wave” theory of light. The constructive resources of analogy and metaphor enable sci- 7. The notion of “surplus meaning” employed by MacCorquodale and Meehl derives from Hans Reichenbach 1938. 6 JOHN D. GREENWOOD LEFT INTERACTIVEJHBS — WILEY short standard long Top of RH Base of RH Top of text Base of textentists to introduce meaningful descriptions of intersubjectively unobservable phenomena by exploiting, via analogy and metaphor, the semantics of our descriptions of properties of familiar and discriminable systems (Campbell, 1920; Harré, 1970; Hesse, 1966, 1976; Boyd, 1979; Holyoak & Thagard, 1997; Gentner & Markman, 1997). This enables scientists to introduce meaningful theoretical descriptions such as “electric charge” (on analogy with a charge of gunpowder), “curvature of space” (on analogy with curvature of a sphere), “and so on by continuous steps to the most esoteric terminology of modern physics” (Hesse, 1976, p. 8). This account can be extended to theories in cognitive psychology, many of which pos- tulate representational states — such as memories and beliefs — that are held to have some of the semantic and syntactic properties of linguistic structures. Indeed, such an account has been explicitly developed by Richard Boyd, with respect to “computational” theories in cog- nitive psychology: A concern with exploring analogies, or similarities, between men and computational devices has been the most important single factor influencing postbehaviorist cognitive psychology. Even among cognitive psychologists who despair of the actual machine simulation of human cognition, computer metaphors have an indispensable role in the formulation and articulation of theoretical positions. These metaphors have provided much of the basic theoretical vocabulary of contemporary psychology. (Boyd, 1979, p. 360, my emphasis.) It is in precisely this area that we seem to find the very real discontinuity between even “liberalized” forms of neobehaviorist theory and cognitive theories developed from the 1950s onward. Liberalized forms of behaviorist theory never really possessed significant surplus meaning. Concepts such as “drive,” “habit strength,” “divergent habit family hierarchy,” “pure stimulus act,” and the like, and all the internal variables of “mediation theory,” were provided with rigorous operational definitions, no matter how awkward and unwieldy they proved to be. Even those neobehaviorists who rejected the extreme antitheoretical or atheoretical po- sitions of Watson and Skinner maintained that surplus meaning had no place in psychological science. They insisted that “the only meaning possessed by intervening variables is their relationship to both independent and dependent variables” (Kendler, 1952, p. 271) and that “valid intervening variables . . . are the only kinds of constructs admissible in sound scientific theory” (Marx, 1951, p. 246). In contrast, cognitive theories from the 1950s onwards did possess surplus meaning — despite the frequent rhetorical avowals of a commitment to the operational definition of theories by cognitive psychologists. Such avowals in practice amounted to nothing more than a recognition of the need to provide empirical operational measures of cognitive constructs, and a means of testing predictions derived from them (in conjunction with a variety of aux- iliary hypotheses and background assumptions). Alan Newell, Clifford Shaw, and Herbert Simon (1958), for example, advertised their computational theory of problem solving as a “thoroughly operational theory of human problem-solving.” However, all that Newell, Shaw, and Simon provided was a set of behavioral predictions derived from their theory and a means of empirically assessing them. Neither the axioms of logic described by the theory (adapted from Bertrand Russell and Alfred N. Whitehead [1925]), or the rules of the sentential calculus employed in the derivation of theorems, were defined operationally. While theoretical definitions of the sensory register, attention, long- and short-term mem- ory, depth grammar, cognitive heuristics, visual perception, propositional and imagery coding, episodic and semantic memory, template-matching, procedural networks, inference, induc- 7UNDERSTANDING THE “COGNITIVE REVOLUTION” IN PSYCHOLOGY JHBS — WILEY RIGHT INTERACTIVE short standard long Top of RH Base of RH Top of text Base of text 8. For an early statement of this point, see Kurt Lewin (1940), who complained that although Hull’s theoretical constructs were well defined operationally, they lacked conceptual properties. 9. Thus S.S. Stevens (1935, p. 517), claimed that “a term or proposition has meaning (denotes something) if, and only if, the criteria of its applicability or truth consist of concrete operations that can be performed.” Laurence D. Smith (1986) has convincingly argued that Hull and Tolman essentially developed their theoretical views indepen- dently of the influence of logical positivism (which later came to be called “scientific empiricism”), appealing to the positivist account as a sort of post hoc justification of their cautious theoretical positions. I think there is a fair degree of truth in this (although I believe Smith’s case is somewhat overstated). But, it also seems very clear that the general positions of Hull and Tolman, like the positions of Watson, Skinner, Kendler, Osgood, Miller and just about every other avowed behaviorist or neobehaviorist, are clearly positivist in spirit, insofar as they treated inter- subjectively observable behavior as the bedrock of scientific psychology, and rejected any form of putative theoretical description of unobservables that was not exhaustively defined in terms of observables. It is not essential to my account, however, that the types of theories introduced by neobehaviorists were actually influenced by the logical positivist account— it is sufficient that, as most neobehaviorists (correctly) maintained, their theories did generally satisfy the restrictive criteria of the logical positivist account. tion, and the like have abounded in the cognitive psychological literature, operational defi- nitions — as opposed to specified operational measures — of these phenomena have been virtually non-existent. So there is a significant discontinuity between behaviorist and cognitive theories. To put it bluntly, so-called liberalized neobehaviorist “theories” did not, in general, constitute genuine and substantive psychological theories at all. Cognitive psychological8 theories from the 1950s onward generally did. The neobehaviorist error was to confuse the reasonable requirement for operational mea- sures of postulated theoretical states and processes with the peculiar notion that the meaning of theoretical descriptions must be (can only be) specified in terms of such operational mea- sures — a confusion neobehaviorists inherited from scientific empiricist philosophers of sci- ence such as Rudolph Carnap (1936, 1937). This confusion is very clear in neobehaviorist9 articulations of the supposed rationale for operational definitions, in terms of the need to provide a determinate meaning for theoretical descriptions: It is evident that this equational mode of anchoring symbolic constructs to objectively observable and measurable antecedent and consequent conditions or phenomena is nec- essary, because otherwise their values would be indeterminate and the theory of which they constitute an essential part would be impossible of empirical verification. (Hull, 1943, p. 273) . . . an operational psychology will be one that seeks to define its concepts in such a manner that they can be stated and tested in terms of concrete repeatable operations by independent observers . . . The behaviorism I am going to present seeks, then, to use only concepts which are capable of such concrete operational verification. (Tolman, 1951, p. 89) Although it is, of course, desirable that theories have determinate meaning, their deter- minate meaning …