Professor Greg Francis 5/27/081Mental imageryIIE 269: Cognitive PsychologyGreg FrancisLecture 24Is a picture in your head like a picture inthe world?Mental representation How do you mentally representknowledge? concepts (prototypes, exemplars) propositions mental images, mapsPerception We have knowledge about, and memoriesof, perceived stimuli sights smells touches sounds Are these converted into propositions, orconcepts or is there something else?Images When we see thisimage how do werepresent theinformation in theimage? analog: copy ofimage in head andwe can retrieve it symbology: convert topropositions/conceptsImages I can rememberthe image on theprevious slideand it feels like Ipicture the imagein my head but do I really? could it be aproposition?Runs togirlballwearsshortsImages If you ask me questions about the previous slide,my answers would not identify the representationRuns togirlballwearsshortsThere was a girl running to a soccer ball. She wore red shorts.MentalObservableProfessor Greg Francis 5/27/082Pure propositions Let’s look at the arguments for a purelypropositional representation Look at this picture, I’ll ask you questions about itWorking with images If this image was printed on a piece of paper, you wouldhave no problem answering questions about it If you had an exact copy of the image in your head, youwould expect you could “look” at the copy and make allkinds of judgments but you cannot how you interpret the image to a large extent determines whatyou know about it Mental images are not exactly like real images this tends to be particularly true for memory of images verbal descriptions dominate memory for imagesAnother example Answer these questions: Which is further North, Seattle, Washington orMontreal, Canada? Which is further East, Detroit, Michigan orIndianapolis, Indiana? Which is further South, Boston, Massachusetts orNew York City, New York? Which is further West, Reno, Nevada or SanDiego, California?Propositions So this suggests that mental images are notexactly like real images and something like propositional information likelyinfluences reports that are ostensibly based onmental images or mental mapsPropositions It is clear that propositional information influencesmental imagery but is it all propositions? are there mental images, as we tend to experience them? Is there any reason to believe that mental imagesare at all analogous to real images? yesRepresentation of mental images Imagine you have a mental image of a lion If the mental image is a description (set ofpropositions), then it should include descriptiveinformation (head, mane, ears, whiskers,, tail,…)» size of body parts shouldn’t matter much(except as information in the proposition)Professor Greg Francis 5/27/083Representation of mental images Imagine you have a mental image of a lion If the mental image is a depiction, then it shouldinclude factors such as head, mane, ears, and theirsizes and relative positions» self reports of mental images suggest thedepicted version, but how to measureexperimentally?Representation of mental images Kosslyn (1976) subjects in two groups» 1) form a mental image of a lion» 2) think about a lion, but without a mentalimage Ask subjects to quickly answer questions like:» Does the lion have a head?» Does the lion have claws? Subjects forming a mental image respond morequickly to the head question than the claw question» presumably because the head is bigger in themental imageRepresentation of mental images Subjects that did not form a mental image respondmore quickly to the claws question than the headquestion» presumably because the propositions about alion having claws is more accessible in somenetwork of propositions So, different ways of thinking about a lion canlead to different patterns of access toinformation which implies mental images are different thanpropositionsMental rotation Shepard & Metzler(1971) 3-D shapes rotated in plane or in depth decide if shapesare same aredifferent measure time todecideMental rotation CogLab experiment The more rotated thestimuli are, the longerit takes to make aresponse close to linear increasein RT 144 paraticipantsMental rotation This type of experiment has been taken asstrong evidence that mental images are notjust propositions imagined movement of the mental image (rotation)resembles actual movement no reasons why propositions would give data thatincorporate spatial and temporal relations betweenaspects of the mental images No real difference for rotations in the plane versusrotations in depth (mental sculptures)Professor Greg Francis 5/27/084Vividness There are individual differences in reports of mental imagevividness some people report their mental images are just like real images others report they are fuzzy and vague some people report no mental images at all (10%) blood flow patterns in occipital cortex are consistent with theseclaims Nevertheless, people all do basically the same on many tasks thatseem to require operating on mental imagesConclusions Mental representations of pictorialinformation There are some things you cannot do withmental images Propositions are important Mental images are not just propositionsNext time Review for exam 2 Exam 2 Start a discussion of language Language as an instinct pidgins and creoles Why we do not have to worry about teaching languagein