Ψ Sensation & Perception

Psychophysical Methods Electrophysiological Methods Ψ -Discussion Section- Session 2 – Methods Psychophysical Methods Electrophysiological Methods

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

BACKGROUND

The concept of the receptive field A receptive field is that part of the visual field that a neuron responds to by changing it’s firing rate if a stimulus is in it. It’s part of the external world but a property of a neuron.

Model: RF Overlap Convergence Eccentricity World PR in retina Neuronal layer 1 Neuronal layer 2

The receptive field map Size scales with Eccentricity Cortical hierarchy 1 degree of visual angle = roughly 1.5 * the area of the thumbnail at arm’s length http://redwood.ucdavis.edu/bruno/psc129/handouts/useful-numbers/useful-numbers.html

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.

Spatial Frequency in cycles per degree of visual angle High Contrast Low Low Spatial Frequency High

Orientation 0, 180 45, 225 90, 270 135, 315

(Orientation) Tuning curves Firing rate in Hz Orientation in degrees Tuning width in degrees Watkins & Berkley (1974)

Length summation in V1 RF

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.

Now for the real thing…