Psychology 2115A/B Lecture Notes - Illusory Contours, Olympic Symbols, Retina

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Published on 20 Apr 2013
School
Western University
Department
Psychology
Course
Psychology 2115A/B
Chapter 5 Review: Object Perception
By the end of this section, you should know:
- Why “the whole differs from the sum of its parts”
- How “rules of thumb” help us
- How we distinguish objects from their background
- Why even the most sophisticated computers are unable to match a person‟s ability to perceive objects
We usually think about vision is as though it works as a camera we have a static visual image of the
world that comes in on the retina and then the retinal image is processed
But in fact, this camera analogy breaks down once you get past the retina
Human vision is actually a 3D view of the world
One of the keys to human vision is invariance our ability to see the world as it actually is vs. how it
is represented in an image
Our visual world in human vision is invariant to a wide range of changes that span changes in levels
of light, changes in size, and changes in shape
Not simply recording images, our vision is actually transforming the simple property of light into
mental constructs of a 3D world in which we all live
Doing this transformation of what is physically present on the retina and what is mentally represented
in our mind, this is the trick and this is what we cannot get computers to do
Our minds are transformational and creative (fills in missing pieces)
Need to think of vision as holistic, not separate pieces
The Challenge of Object Perception
Stimulus is ambiguous on the receptors
o Lots of different objects can create the same image on the retina
o Different objects from the same viewpoint are ambiguous
o The way we resolve the ambiguity is to try to manipulate the object and observe it from lots of
different viewpoints
Objects can be hidden or blurry
o We can recognize objects even if part of them is hidden or obscure
o We still recognize the object as what it is even though a large part of the object is obscure or
hidden
o We use our knowledge of what objects are supposed to look like computers have not been able
to do this
o Are able to recognize objects that are not in good focus computers find this a relatively
difficult task computers looking for certain points on the face whereas humans do much more
shows the difficulty of the visual task that we deal with every day
Objects look different from different viewpoints
o The basic problem is that images of the same object are continually changing as we change our
viewing angles
o Suggests we are not deconstructing the visual world and then putting it back together like our
physiology suggests
Gestalt Psychology
Gestalt = a configuration or idea
o Before Gestalt psychology, it was thought that all of our sensations that we experience sum up to
create perception structuralism: the idea we can break down our perception of the world into
its constituent bits and pieces and then we can put all those pieces back together again to create
perception
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Strategies of perceptual organization
o Despite the fact that objects are hidden, blurry, changing from different viewpoints, etc. this
suggests that it cant all be about sensation, it has to be something more than this
o Gestalt school was formed believed that perception that creates our understanding of form is
not a property of the object itself but rather it represents some sort of organization that we
impose upon those sensations in the brain
o Suggesting that the representation of the 3D form is really created by organizing our sensations
into stable patterns of perception perceptual constancies
o In order to create these, our brain has to make specific assumptions about how the world or have
certain expectations about our perceptual experience partially derived from how our brain is
organized physiologically (rate of neural firing) but also from our experiences form the everyday
world (we learn about how the world is supposed to be)
o „The 5 phenomenon‟/„apparent motion phenomenon‟: dots can appear to move even though there
is no actual movement therefore, it can‟t just be about sensations since there is no sensation
between the dots but we still perceive them as actually moving
Wertheimer vs. Structuralism
The whole differs from the sum of its parts
o It must be more than a summation of all the senses that are going on, but it must be some sort of
organization what we are adding to it as well
Apparent motion
Illusory contours: contours that are not present in the stimulus but are still perceived
o Imposing lines that don‟t actually exist
o It must be more then sensation on our receptors because the receptors aren‟t receiving stimuli
from contours
Laws of Perceptual Organization
Pragnanz, “good figure” or “simplicity
o Every pattern that we encounter should be seen in such a way so that the resulting pattern is the
most simple one possible
o Classic example: the Olympic rings simpler to view them as five circular rings intertwined
them all the separate bits of objects stuck together
Similarity: similar things tend to be grouped together
Continuation: lines tend to be seen in such a way that they follow the smoothest path
Proximity: we tend to perceive dots that are closer together as belonging to the same object
o Things that are near each other are grouped together
Common fate: objects that have a similar end outcome are likely to be grouped together
Familiarity: things that are familiar tend to be grouped together
o Using previous knowledge of what objects ought to be like as a means of recognizing what the
object is
Figure and Ground
Winner-take-all strategy:
o “Our eyes are accustomed to fixing on specific objects. The moment this happens everything
around is reduced to background… The human eye and mind cannot be busy with two things at
the same moment, so there must be a quick and continual jumping from one side to another” –
M.C. Escher
o One object is the one that we focus on and that is the object that becomes the „figure‟ of the
image and the rest of the picture becomes the „background‟ or „ground‟
o We cant attend to two objects at the same time only one have one figure at a time
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Document Summary

By the end of this section, you should know: Why the whole differs from the sum of its parts . How we distinguish objects from their background. Why even the most sophisticated computers are unable to match a person s ability to perceive objects. We usually think about vision is as though it works as a camera we have a static visual image of the world that comes in on the retina and then the retinal image is processed. But in fact, this camera analogy breaks down once you get past the retina. Human vision is actually a 3d view of the world. One of the keys to human vision is invariance our ability to see the world as it actually is vs. how it is represented in an image. Our visual world in human vision is invariant to a wide range of changes that span changes in levels of light, changes in size, and changes in shape.

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