PSY270H1 Lecture 7: Perception (Cont) and Attention (Mar. 6, 2017)

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Published on 10 Mar 2017
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This Class: Ch 3 & 4
Next Class: Ch 4 & other
readings posted on Mar 13
Midterm is two weeks - Mar 20
Homework:
Illusions, Unconscious Inference
Gestalt Laws
Dual Visual Pathways and Mirror Neurons
Perception
Allocating Attention and Models
Cognitive and Perceptual Loads
Attention
Lecture Topics:
Room assignments posted on blackboard
Midterm two weeks - Mar 20, 6:10pm-8:10pm
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Pre-Lecture Notes:
Lecture Notes: Perception (Cont) and Attention
Perception
Top-Down Processing Cont: Illusions
One of those are egocentric (self-body) representation - where you find yourself In space
This representation operates despite any other stimuli in the environment
Ex. you don't need to look at your nose to touch it or anywhere else on your body
We represent our world and bodies in various frames of reference
We think of our bodies in a natural position on how it operates
Within this representation, there are anatomical norms that operate
Then vary the onset synchrony (the gap between) of the two buzzing cubes
If you reduce the duration between vibrating very fast, ptp start to make errors
In regular anatomical position, they are quite accurate
If you cross their hands and do the same task, accuracy drastically decreases
Ptp brought into lab, sit down, and given two cubes serving as buzzers and they provide vibration
feedback --> cubes will vibrate and you need to push which one buzzed first
White below represents normal anatomical position
Black below represents crossed arm position
Above is measured with "just noticeable difference" --> amt of time required between the buzzes to
have a 75% change of accurately discriminating that one came before the other
We want to assume normal anatomical position despite knowing our hands being crossed
Visual representation assumes the true position, egocentric wants to believe it's normal
The visual representation (allocentric reference = the environment) overrides, making you
believe visual = egocentric representation --> conflict causes the crossed-hands deficit
Argued that when you are receiving info the hands, we have info coming from our egocentric area
Crossed-Hands Deficit (Shore, Spry, Spence, 2002)
Lecture 7: Mar. 6, 2017
March 6, 2017
6:00 PM
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The same deficit still happens, however
When you walk into a room, visual system immediately creates a visual representation --> so
even if you close your eyes, you keep the representation. The same is with this deficit
Ptp can immediately feel that it's hard --> to compensate, ptp will naturally close their eyes
No visual representation of the room, cubes, or crossed arms --> removes the deficit
Only if you can prevent the representation from being created does this happen
Brought ptp into lab and blindfolded the ptp before they can see anything at all in the room
--> question: is everything egocentric for blind people? No, they have other representations
that could be used to interfere. Providing them the opportunity to feel around could create an
allocentric interference effect, but it won't be to the same degree as vision
Blind people show no deficits because they can't create this allocentric reference
Makes sense bc it reduces amt of cognitive work
Believed that most of our perceptions are the result of unconscious inferences based on likelihood or
statistics --> more we should assume things if they are more likely
However, even if you know c, you would assume a because usually things that are in the
foreground typically block things in the background
This is based on the probability of things being correct
Ex. seeing the b and c below would create the same bottom-up perception as image a
This is a result of unconscious inferences or assumptions based on likelihood
Helmholtz's Theory of Unconscious Inference
Wanted to understand how we understand things and how we perceive the whole environment
If you were to take all the bottom-up stimulation and add it up, it doesn't give you the same
experience that you feel everyday since we're applying top-down information to this
Came up with the idea: the whole is different than the sum of it's part
Proposed rules to explain how small elements of a scene are groups to form larger units
Ex. below shows a dog in the foreground and a tree in the background
We will be focusing on six of the rules
Through studies, they came up with laws of perceptual organization
Gestalt School in Germany
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Tend to see the object below as a square and triangle
Few will see three separate objects (small triangle, large square, small trapezoid
Good Figure: tendency to group things in the easiest method possible
We tend to group things that share a "common goal" such as those that are moving in the
same direction (bricks below are moving in one direction than one in the middle)
Common fate: we tend to group things together if they are bound to a particular fate
Even if line is broken, we connect it together even if they're occluded or blocked
You believe the outline of someone continues behind a table
Good continuation: tend to connect smooth lines and curves
Such a group of friends
Proximity: tend to group things together that exist close by
Such as below which shows two rows of squares, three rows of circles instead of columnds
Similarity: things that look similar tend to be grouped together
You see a rectangle within a square with a triangle above the square, but you would collectively
look at it as a house
Familiarity: tend to group things into familiar objects and shapes
There are certain figures that are more related to one law to another one, eg
Big the obvious answer
Note: SA on the test with Gestalt laws will be very explicit, since laws tend to overlap
Gestalt Laws
Good continuation - water continues ahead of woman
Familiarity - know what people look like
Similarity - the colours of the clothes match those of the surrounding environment
Left image:
Good continuation - would assume the leg is what the arm should be
Good figure - easier to process leg as part of body
Similarity - same skin colour
Right image: Good continuation, good figure
Examples - What Gestalt Principles are at play?
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