Professor Greg Francis 8/14/12 PSY 200: Intro. to Cognitive Psychology 1 Purdue University Mental imagery PSY 200 Greg Francis Lecture 24 Is a picture in your head like a picture in the world? Purdue University Mental representation  How do you mentally represent knowledge?  concepts (prototypes, exemplars)  propositions  mental images, maps Purdue University Perception  We have knowledge about, and memories of, perceived stimuli  sights  smells  touches  sounds  Are these converted into propositions, or concepts  or is there something else? Purdue University Images  When we see this image how do we represent the information in the image?  analog: copy of image in head and we can retrieve it  symbology: convert to propositions/concepts Purdue University Images  I can remember the image on the previous slide and it feels like I picture the image in my head  but is it really?  could it be a proposition? Runs to girl ball wears shorts Purdue University Images  If you ask me questions about the previous slide, my answers would not necessarily identify the representation Runs to girl ball wears shorts There was a girl running to a soccer ball. She wore red shorts. Mental ObservableProfessor Greg Francis 8/14/12 PSY 200: Intro. to Cognitive Psychology 2 Purdue University Pure propositions  Let’s look at the arguments for a purely propositional representation  Look at this picture, I’ll ask you questions about it Purdue University Working with images  If this image was printed on a piece of paper, you would have no problem answering the questions about it  If you had an exact copy of the image in your head, you would expect you could “look” at the copy and make all kinds of judgments  but you cannot  how you interpret the image to a large extent determines what you 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 images Purdue University Another example  Answer these questions:  Which is further North, Seattle, Washington or Montreal, Canada?  Which is further East, Detroit, Michigan or Indianapolis, Indiana?  Which is further South, Boston, Massachusetts or New York City, New York?  Which is further West, Reno, Nevada or San Diego, California? Purdue University Another example  How did you do? Purdue University Propositions  So this suggests that mental images are not exactly like real images  and something like propositional information likely influences reports that are ostensibly based on mental images or mental maps California California is west of Nevada West relation Nevada object Reno is in Nevada in relation Reno agent San Diego object San Diego is in California in relation agent agent Purdue University Propositions  It is clear that propositional information influences mental imagery  but is it all propositions?  are there mental images, as we tend to experience them?  Is there any reason to believe that mental images are at all analogous to real images?  yesProfessor Greg Francis 8/14/12 PSY 200: Intro. to Cognitive Psychology 3 Purdue University Representation of mental images  Imagine you have a mental image of a lion  If the mental image is a description (set of propositions), then it should include descriptive information (head, mane, ears, whiskers,, tail,…) » size of body parts shouldn’t matter much (except as information in the proposition) Purdue University Representation of mental images  Imagine you have a mental image of a lion  If the mental image is a depiction, then it should include factors such as head, mane, ears, and their sizes and relative positions » self reports of mental images suggest the depicted version, but how to measure experimentally? Purdue University Representation of mental images  Kosslyn (1976)  Ask subjects to quickly answer questions like: » Does a lion have a head? (big body part) » Does a lion have claws? (small body part)  subjects in two groups » 1) form a mental image of a lion » 2) think about a lion, but without a mental image  Subjects forming a mental image respond more quickly to the head question than the claw question » presumably because the head is bigger in the mental image 02004006008001000120014001600SmallpartBig partImageryNo imageryReaction time (ms) Purdue University Representation of mental images  Subjects that did not form a mental image respond more quickly to the claws question than the head question  presumably because the propositions about a lion having claws are more accessible in some network of propositions  So, different ways of thinking about a lion can lead to different patterns of access to information  which implies mental images are different than propositions 02004006008001000120014001600SmallpartBig partImageryNo imageryReaction time (ms) Purdue University Mental rotation  Shepard & Metzler (1971)  3-D shapes  rotated in plane  or in depth  decide if shapes are same are different  measure time to decide Purdue University Mental rotation  CogLab experiment  163 participants  The more rotated the stimuli are, the longer it takes to make a response  close to linear increase in RTProfessor Greg Francis 8/14/12 PSY 200: Intro. to Cognitive Psychology 4 Purdue University Mental rotation  This type of experiment has been taken as strong evidence that mental images are not just propositions  imagined movement of the mental image (rotation) resembles actual movement  It takes time to mentally move through a mental space » The CogLab data suggests it is about 100 degrees/second » 10 milliseconds for each degree  no reason why propositions would give data that incorporate spatial and temporal relations between aspects of the mental images Purdue University Vividness  There are individual differences in reports of mental image vividness  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%)  Nevertheless, people all do basically the same on