PowerPointPrsentation

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Sensation Perception
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-Discussion Section- Session 2
Methods Psychophysical Methods Electrophysiologic
al Methods
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Presentation 1 Human orientation
discrimination tested with long stimuli
(1984)presented by Michelle Arroyo

Presentation 2 Oblique effect A neural basis
in the vsiual cortex (2003)presented by Hillary
Schiff
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BACKGROUND
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The concept of the receptive field
A receptive field is that part of the visual
field that a neuron responds to by changing its
firing rate if a stimulus is in it.
Its part of the external world but a property of
a neuron.
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Model

• Overlap
• Convergence
• Eccentricity

RF
World
PR in retina
Neuronal layer 1
Neuronal layer 2
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The receptive field map

• Size scales with
• Eccentricity
• Cortical hierarchy

1 degree of visual angle roughly 1.5 the area
of the thumbnail at arms length
http//redwood.ucdavis.edu/bruno/psc129/handouts/u
seful-numbers/useful-numbers.html
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Both papers today deal with V1

• V1 in the monkey Area 17 in Cats/People
• Striate cortex (Cytoarchitectonically)
• Primary visual cortex (Functionally)
• RF sizes small. Generally smaller than 1 degree.
  Foveally smaller than ¼ degree.
• Tuned (Differentially Sensitive) for 6 qualities
  in the receptive field, including Spatial
  Frequency and Orientation.

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Spatial Frequency
in cycles per degree of visual angle
High Contrast Low
Low Spatial Frequency High
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Orientation
0, 180
45, 225
90, 270
135, 315
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(Orientation) Tuning curves
Firing rate in Hz
Orientation in degrees
Tuning width in degrees
Watkins Berkley (1974)
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Length summation in V1 RF
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Perception and Memory

• Introducing memory
• Out of the pan into the fire
• On the next slide, memorize one of the cards but
  keep it a secret.

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Now for the real thing