PSY 310: Sensory and Perceptual Processes 1

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1 Wilhelm Wundt Gestalt Psychology PSY 310 Established the first true psychology laboratory in 1879 University of Leipzig (Germany) Greg Francis Tried to identify basic elements of perception Similar to approaches in chemistry/physics Find basic elements of matter (molecules) Find basic elements of molecules (atoms) Find basic elements of atoms (protons, electrons) Find basic elements of. Lecture 14 This is a real object! Along the way you learn about how the basic elements combine to have different properties The basic idea is the perception is based on sensations Cold, sweet, crisp Look at the title of your textbook and this class! Sensations are supposed to be simpler responses to stimuli If you take a bite of an apple, you might describe its basic sensations as It would be a mistake to refer to it as apple Sensations are identified by introspection Looking inward to identify the basic elements of the experience If you could do this for lots of people and lots of stimuli, you might identify the basic sensory elements of many different perceptual experiences Some seem problematic for the structuralist approach In structuralism, are built of up sensations Different people report different basic sensory elements What about a stimulus like this? No set of basic sensory elements seemed to cover lots of different perceptual experiences Scientific reductionism It never really worked out Other problems So sensations must be necessary to produce percept The goal of reduction is still a strong part of perception, but not along these lines What sensation contributes to the perception of the illusory contour? 1

2 Other problems Likewise, there are stimuli where presumably sensations are being gathered, but they do not give rise to a percept Motion Induced Blindness movie For that matter, one seems to get entirely new kinds of perceptual experiences from some stimuli Apparent motion (demo) Presumably they produce the same sensations, but different Presumably they produce the same sensations, but different Find the man playing the flute There are thousands of stimuli that can be interpreted in Presumably they produce the same sensations, but different Find the Dutch girl Presumably they produce the same sensations, but different It s not just clever drawings Much of perception involves ambiguity More than you realize Motion nowobbleglobe.mov Gestalt Psychology The structuralists recognized these kinds of problems for their approach, but they thought one could eventually deal with them Other people advocated an entirely different approach German scientists (Wertheimer, Koffka, Kohler) Gestalt is a German word that roughly means whole Gestalt psychologists suggested that understanding perception could not be done by breaking it down into parts, but by considering the whole experience The whole is different than the sum of its parts. One task of perception is to identify how to organize different parts of a visual scene How to identify objects? 2

3 Perceptual organization What about the image or the visual system allows you to correctly group different parts of the scene into objects? Similarity Can isolate effects Similarity: color, texture, orientation Position Familiarity Gestalt laws of perceptual organization Position Can isolate the effect Familiarity Having seen this image before, your perceptual organization is different than the first time 3

4 Common fate Motion in a common direction is one example Can be more complicated than just direction Biomot.mov Good figure Law of simplicity Pragnanz The percept you see should be the simplest interpretation of the scene Gestalt Laws They are not really laws, but suggestions about what the visual system might be doing Most people do not really believe them in the same way we believe the laws of physics or the law of natural selection In fact, it is fairly easy to show that the Gestalt laws are not anywhere near a complete description of perceptual organization What is the percept of this image? Is this good figure? This is a photograph of a real object Do you see it in the simplest way possible? 4

5 This is a photograph of a real object Do you see it in the simplest way possible? Conclusions Structural psychology Gestalt psychology Rules of perceptual organization Next time Perceiving objects Figure-ground relationships 5