contrast sensitivity - mcgill...

contrast sensitivity

Robert.Hess@McGill.CA

Receptive field�The region of retina over �

which a stimulus affects the� electrical activity of a neuron

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bipolar cellin vivo

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ganglion cellin vivo

receptorin vitro

Receptive field of a ganglion cell

1°-10° Light stimulus Light in

RF centre

RF periphery Centre and periphery On-centre neuron

Off-centre neuron 1s

RF centre

RF periphery Centre and periphery

Orientation tuning

A cortical binocular cell

Ocular dominance

Ocular dominance columns

Orientation columns

A sinusoidal grating

contrast

Spatial frequency

A neuron as a spatial filter

Filtering along the pathway

A spatial analysis

Contrast responses

1.0

0.5

Contrast %0.1 0.3 1.0

Sens

itivi

ty

P-cells

threshold saturation

Contrast vs spatial frequency

SPATIAL FREQUENCY (cycles/degree)

CON

TRA

ST S

ENSI

TIV

ITY

Window of visibility

SPATIAL FREQUENCY (cycles/degree)

CON

TRA

ST S

ENSI

TIV

ITY

Spatially-tuned channels

SPATIAL FREQUENCY (cycles/degree)

CON

TRA

ST S

ENSI

TIV

ITY

Temporal response of a neuron

1.0

0.5

Temporal Frequency (hz)1 10 100

Sens

itivi

ty

Human temporal sensitivity

Peripheral sensitivity

Types of retinal ganglion cell

Magno & parvo layers

An isoluminant grating

Colour vs luminance CSF

Robert F Hess

Amblyopia: a new view

McGill Vision Research Unit Dept. of Ophthalmology, McGill University, Canada

The Stimuli

Visual Development

Eileen Birch

Days of recovery

G

ratin

g ac

uity

(c/d

egre

e)

Gaussian size (sd min)

Alig

nmen

t acc

urac

y (m

in)

Monocular deprived cats

Strabismic cats

Gaussian size (sd min) Alig

nmen

t acc

urac

y (m

in)

Unrelated to visibility loss

Positional loss

Acu

ity lo

ss

Cont

rast

sens

itivi

ty lo

ss

Stimuli: positional sensitivity

Amblyopes

Contrast sensitivity ratio (dB)

Alig

nmen

t acc

urac

y ra

tio