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Lecture 13

PSY3108 Lecture 13: Perception
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by OneClass779527 , Fall 2016
3 Pages
97 Views
Fall 2016

Department
Psychology
Course Code
PSY 3108
Professor
Charles Collin
Lecture
13

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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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Description
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 Temporal halves (close to temples) capture light from nasal half and send it to ipsilateral side of brain (same side) Fovea is not split with each half carried to separate hemispheres. Instead, it is represented in both hemispheres. Evidence- foveal sparing (continued visual function in fovea after loss of visual hemisphere due to stroke Two pathways from eye to cortex: Geniculocortical- LGN (lateral geninucleate nucleus) of thalamus to V1 (90% of rgc outputs) Tectopulvinar pathway- superior colliculus (tectum) to pulvinar nucleus to visual cortex (10% rgc) LGN- thalamus nuclei for vision. Kneww shaped. 6 layered structure. Early visual processing (center-surround rfs). Organized in layers and columns. Has left and right halves receiving signal from eyes. Layers 2,3,5 from ipsilateral. Layers 1,4,6 from co
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