From: AAAI Technical Report SS-92-02. Compilation copyright © 1992, AAAI (www.aaai.org). All rights reserved. The "Philosophical" Case Against Visual Images. A "Crucial" Experiment. Peter Slezak Center for Cognitive Science University of NewSouth Wales P.O. Box 1, Kensington 2033 NSW.,Australia [email protected] s.unsw.oz.au New Focus for Imagery Debate "crucial experiment", since a falsified prediction can always be blamedon one of the auxiliary hypotheses on In their study of reasoning with diagrammatic and non- which any theory depends. Nonetheless, the text-book dia~,rammatic representations, Larkin and Simon(1987) exampleof a "crucial experiment" is the null result of are concerned with external representations and the Michelson-Morleytest of the speed of light, and I explicitly avoid drawinginferences about the bearing of take the null results of our owninvestigations to show their work on the issue of internal, mental that, like the luminiferous ether, the pictorial medium representations. Nonetheless, we mayinfer the bearing does not exist. It is in this sense that the possibility of of their work on internal representations from the reinterpreting visual patterns in mental imagery has theories of Kosslyn, Finke and other ’pictorialists’ who recently emerged as new focus for the long-standing take internal representations to be importantly like controversy. The question of whether, and under what external ones regarding their ’privileged’ spatial conditions, novel information maybe discovered from properties of depicting and resembling their referents. images may shed new light on the debate, since it Thus, Finke (1990) suggests that "perceptual provides a new meansfor testing the properties of the interpretive processes are applied to mental images in conjectured pictorial medium.andthe claimed parallel much the same way that they are applied to actual between imagery and perception. physical objects. In this sense, imaginedobjects can be "interpreted" muchlike physical objects" (1990, p. 18). Elsewhere he suggests that "The image discoveries "Equivalence" of Imagery & Perception which then ’emerge’ resemble the way perceptual Specifically, the possibility of reinterpreting an image discoveries can follow the active exploration and follows as a direct implication of the pictorial theory manipulation of physical objects" (1990, p. 171). which posits an "equivalence" between imagery and After twenty years of controversy, the ’imagery perception. On the pictorial view, a mental image is debate’ concerning the ’format’ of visual mental conceivedto be a "surrogate percept, allowing people to representations is widely regarded as having become detect somepattern or property in a rememberedscene stalled and the impasse has even led some (Anderson that they did not encode explicitly whenthey saw the 1978) to conclude that the issue between pictorialism scene initially" (Pinker and Finke 1980, p. 246). It and the ’tacit knowledge’alternative is undecidable in in this sense that the uninterpreted images in a spatial principle on the basis of behavioral evidence. mediumare themselves supposed to be "functionally At least part of the reason for the persistence of the equivalent to physical objects or events" (Finke, 1980 imagery debate has been the fact that the dispute has p. 113), and cause the same mechanismsto be activated centered upon alternative explanations of the samebody as in actual visual perception itself (ibid, p. 130). of chronometric evidence. The debate has come to Kosslyn (1987, p. 149) explains, one purpose appear intractable because the two contending theories imagery involves "recognition processes" to discover make identical predictions for chronometric evidence information which is not stored explicitly in memory and, accordingly, adducing new evidence of time- and thus we "look" at our images in a way which is dependentmeasures, as has repeatedly been done, cannot analogous to the way we look at external objects in strengthen the case for a pictorial, spatial medium order to inspect them. against the rival tacit knowledge theory. Thus, experiments are needed on which the contending Divergent Predictions accountsdeliver different predictions. Our ownevidence concerns perceptual organization By assimilating imagery so closely with vision, indeed tasks which provide unequivocal criteria of the by claiming their "equivalence", pictorialism is successful rotation, inspection and re-interpretation of committed to predicting closely similar "perceptual" images using "recognition processes" and "shape phenomenain imagery to those found in perception classification" procedures. Despite the demonstratedease itself. It is this deep commitmentto the perceptual of our task under perceptual conditions, naive subjects character of imagery which is the source of its have generally been unable to succeed in the tasks under vulnerability to such asymmetriesas those of Chambers imagery conditions as would be predicted on the and Reisberg (1985) and our ownresults. pictorial theory. Thus, Kosslynsuggests that "imageinterpretation is Of course, as historians and philosophers of science at the heart of the role of imagery in cognition (if one well know, there can be strictly no such thing as a cannot inspect imaged patterns, they are useless)" 12 (1988, p. 249). He says "The recognition mechanisms Finke and Slayton (1988) have extended this work, [of vision] can be usedin imageryas a wayof accessing providingfurther evidence"that people are capableof stored information"(1988, p. 264)and his modelentails makingunexpected discoveries in imagery" and that that "imagesdepict visual information, and that this novel patterns can "emerge" from within imaged informationis interpreted by someof the samesorts of patterns. classificatory proceduresused in classifying sensory input during vision" (1980, p. 32). Kosslynexplains Response by Finke, Pinker and Farah. further that "the purposesof imagery,in large part, parallel those of vision" and "onemay ’recognize’ parts Most recently, Finke, Pinker and Farah (1989) have and properties of imagedobjects that had not been soughtto reinforce these claims with newexperiments previouslyconsidexed" through the "use of recognition which also purport to showthat subjects can inspect processes" (1987, p. 149). The significance and reinterpret their images by "applying shape reinterpreting imagesas a crucial test of the pictorial classification proceduresto the informationin imagery" theoryis evidentin Kosslyn’sexplicit predictions: (1989,p. 51). This latter workis of particular interest becauseit has beenspecifically designedto counter the Theimage is formedby forcing a changeof state in skeptical conclusionswarranted by the negativeresults the visual buffer in the attended region, whichcan of Chambersand Reisberg and sets the scene for our then be reprocessedas if it wereperceptual input (e.g., owninvestigation. Thus,it is in the light of this clash the shape could be recategorized), thereby of experimentalresults and theoretical claims that our accomplishingthe purposesof imagerythat parallel own experiments are to be understood: Our new those of perception.(1987, p. 155; emphasisadded) experimentsavoid the specific objections by Finke et al. and by falsifying entailmentsof the pictorial theory By contrast with these implications of the quasi- in a different manner,our results can be seen as further illuminating the precise conditions under whichsuch perceptual, pictorial mediumtheory, the ’tacit knowledge’ account would predict that the re- seeminglycontradictory results can be obtained. interpretation of imagesis difficult becauseit assumes that the mentalrepresentations are very abstract output "Philosophical" &"Strictly Empirical" of ’higher’ cognitive processes, - encodings of However,it is ultimately fruitless for the protagonists conceptualizationsor beliefs and, in this sense, already in the imagery debate to continue counterposing meaningfuland not requiring interpretation, - nor empiricalresults as if these speakfor themselves.The susceptible of easy re-interpretation (Pylyshyn1973, cloudinessof the presentsituation and the intractability 1978). of the debate is symptomaticof fundamentalconceptual problemsrather than straightforwardempirical issues. Chambers& Reisberg Negative Results Finke (1989) passes over such "philosophical" This questionof reinterpreting visual imageshad been problemsand the principal alternative theory (Fodor brought into sharp relief with the workof Chambers 1975) implyingtheir relative unimportanceand saying and Reisberg (1985) who found that subjects were that "this is strictly an empiricalquestion" whichhas uniformlyunable to reverse their mental imagesof the been decidedby the evidencethat "mentalimages can be familiar ambiguousfigures such as the duck/rabbitand reinterpreted" (1989, p.129). Thecited data of Finke, Neckercube. Chambersand Reisbergsee their results as Pinker and Farah undoubtedlyshow that "imagescan be supporting the "philosophical" argumentsfor taking reinterpreted", but this cannot "refute" Chambersand imageryto be moreconceptual and cognitive, in the Reisbergsince it only begs the central question: What sense that they are intrinsically interpreted symbols is the reasonfor the discrepancy? whichdo not ne, ed, and do not easily permit, further TheChambers and Reisberginvestigation derives its interpretation. Since the close parallel, indeed significance from showing the inability of image "equivalence" of imagery with the mechanismsof