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Lecture 13

PSY 3108 Lecture Notes - Lecture 13: Depth Perception, Brodmann Area, Retinotopy

Course Code
PSY 3108
Charles Collin

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Our ability to detect gratings at different spatial frequencies (csf) arises because there
are no RGCs with RFs with Large enough to optimally detect frequencies below 8-10
cycle/degree or small enough to detect frequencies above 60 cycles/degree
Nyquist limit- best acuity one can theoretically have is related to the spacing of
receptors. In our fovea, 60 cones per degree. Our upper sf detection limit is 60
cycles/degree. So we have best possible acuity we can have
Lateral inhibition: adjacent sensory receptors send signals that inhibit one-another in a
complex matrix. Results in center surround rf. In all sensory systems. Aids detection of
perceptual features such as change across space or time. Helps emphasize relative
differences or changes more than absolute values. Ex- we see differences in brightness
better than we see absolute brightness. Differences re important adaptively speaking.
Allows us to deal with large range of absolute values.
Centre surround inhibition emphasizes on relative lightness, rather than absolute
brightness. Results in light consistency and contrast illusion. Also emphasizes on edges
rather than fills for better object detection & Mach Band illusion (exaggerated contrast
between edges between slightly differing shades). Herman grid illusion also arises
(ghost like grey blobs appearing on white borders on black background… Effect can be
(partly) explained by center- surround antagonism.).
Barany cross & White’s illusion: may be due to a combination of lateral inhibition and
gestalt belongingness principle (two Triangles look different colors)
Shadow effects- contrasting changes interpreted as being due to illumination
differences instead of reflectance difference
Chapter 10
Basics of ho we see:
RGC are dot detectors, V1 (primary visual cortex): line orientation, motion, color. V4:
shapes, Temporal lobe: objects and faces
Dorsal and ventral streams
Dorsal- mainly motion processing (where pathway). Ventral- identity processing (what
pathway) takes most of its input from P pathway
Contra laterality- information from left half of visual field goes first to right half of brain &
vice versa (Nott left eye right brain. Based on visual field).
Nasal halves of retinas (close to nose) capture light from temporal half of visual field
and send signals across to contra lateral sides of the brain
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