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PSYC 2390 Study Guide - Sound Intensity, Transient Response, Stapedius Muscle


Department
Psychology
Course Code
PSYC 2390
Professor
Lana Trick

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Sensation and Perception Notes for Final Exam 3/21/2013 9:40:00 AM
Depth Perception
Tricky to get depth information because we have a 3D world (distal
stimulation), but the information we receive on the back of the
retina is only 2D
Proximal cue = visual angle actual size OR how far away in
depth an object is
o Dimensional ambiguity
Binocular Depth Cues
30% more accurate with both eyes
important for close tasks
left and right eyes have different perspectives (slightly different
angles)
binocular cues rely on comparing the left and right images to
determine depth
o larger difference when an object is closer
o look at how different left and right eye images are =
binocular depth perception
Can create sense of 3-dimensionality by having 2 images that are just
slightly different
Random dot stereograms
When you look at the images so one eye sees one side and the
other sees the other, you will see a square floating over another
square
Different views in different eyes; as a result, you see a square
floating up
How is Depth Information Derived from Stereopsis?
Solving the stereo-correspondence problem
How do I match things on one eye with the other
Need find the thing on one eye that matches with the same thing
on the other eye‟s image
Find corresponding parts in left and right eye images
More complicated…
Sometimes the visual system solves the “stereo-correspondence
problem” incorrectly!
o Error in solving the problem

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o Leads to an illusion of depth (they will appear either further
away or much closer)
o Auto-stereograms: magic eye pictures! [you can see them
because of an incorrectly solved stereo-correspondence
problem]
Can get auto-stereograms from looking at repetitive wallpaper/patterns
Retinal Disparity (a.k.a. binocular disparity)
Disparity = difference
ITEMS ON THE HOROPTER
The horopter is the fixation plane = the distance away that you are
focusing/fixating your eyes
Zero disparity = position of object on left and right eyes is the
SAME
ITEMS IN FRONT OF THE HOROPTER
Object is closer than where you are fixating
Object goes on opposite sides of the reference point (see diagram
on CourseLink) = crossed disparity
o e.g. both fall on temporal side
ITEMS BEHIND THE HOROPTER
Object is further away than where you are fixating
Light rays fall on the SAME side of the reference point on both
eyes, but at slightly different positions on each eye = uncrossed
disparity
o e.g. both on nasal side, but at different distances from the
reference point
Binocular depth is a good cue up to ~ 30 METRES
There is a range beyond that where you cannot use binocular information for
depth perception
There is also a distance that is too CLOSE for you to use binocular
information
PANUM‟S FUSION AREA
Area around the horopter in which you can take the differences in
information from left AND right eyes and form ONE image
If they are too far away double images (quickly suppressed by
the brain)

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If they are too close double images (more noticeable, but also
suppressed)
How is Stereo-depth Information Derived in the Brain?
*Interesting observation about tilt after-effect*
You can adapt one eye to left-tilted lines and then look at straight
lines with your OTHER eye… and the illusion crosses over to the
other eye!
One set of receptors that takes information from BOTH eyes
Receptors get tired out from looking at lines with one eye
receptors still tired when you look at straight lines with the other
eye!
There are binocular cells in the brain that take information from
BOTH eyes
*recall* from striate cortex (back of brain received information
from both eyes): hypercolumns (80% of cells responsive to
information from BOTH eyes)
If you do single-cell recordings (wire into individual neuron), you
will find disparity-sensitive cells = respond differently depending on
HOW DIFFERENT images are in left and right eyes
o e.g. there are cells that respond best to 30 minutes of arc
(vs. 0 minutes or 15 minutes or 45 or 60) looking for a
particular depth!
respond better to one depth than others
Bottom line is that, just as there are some cells that respond best
to a certain orientation, there are cells that respond best to
different disparities (e.g. different depths; crossed or uncrossed
disparity, etc.)
Binocular cells will not develop unless you have certain kinds of
experiences during critical periods
Critical periods = when a baby is developing, he/she must get
certain kinds of stimulation in order for different processes to
develop properly
Studies on kittens kittens are born blind
4 weeks 4 months = critical periods
Must have certain visual experiences in order for binocular depth
perception to develop properly
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