ΨΨSensation

&

Perception

ΨΨ-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:

World PR in retina Neuronal layer 1 Neuronal layer 2

•Overlap

•Convergence

•Eccentricity

RF

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 Frequencyin cycles per degree of visual angle

Low Spatial Frequency High

Hig

h

C

ontr

ast

Low

Orientation

0, 180

45, 225

90, 270

135, 315

(Orientation) Tuning curves

Watkins & Berkley (1974)

Firing rate in Hz

Orientation in degrees

Tuning width in degrees

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…