Lateral inhibition and glaucoma: Solving the structure-function discrepancy.

Test 1: Lateral inhibition can be studied in detail with a psycho-physical

phenomenon called "illusion of movement." This phenomenon is based on the

finding that a thin (dark) line between two (sinusoidal and reverse-phased)

alternating in brightness straps on a fixed distance from the line appears to

shift (Gregory and Heard The Quarterly J of Exp Psych 1983). With a variant of

this experiment, lateral inhibition can be measured (Jansonius and Kuiper

1989). The depth of the lateral bands of the psychophysical line spread

function is a measure of lateral inhibition.

Test 2. An alternative psycho-physical test to measure lateral inhibition is

based on the Westheimer function (Westheimer G. J. Physiol. 1967). To

distinguish a stimulus on a background of constant illumination is dependent on

the diameter of the background. With a small diameter a reduced sensitivity is

found because of spatial summation (the stimulus is less visible). When the

diameter increases it fills the receptive field until lateral inhibition starts

to work. The sensitivity will increase again to a balance where both spatial

summation and lateral inhibition are 'saturated' . Endpoint is the difference

in sensitivity between healthy subjects and glaucoma patients measured with a

background in diameter where lateral inhibition is expected.

Test 3. The final way to measure lateral inhibition is based on contrast

sensitivity measurements. Here, we measure a contrast sensitivity function and

our outcome measure is the contrast sensitivity at low spatial frequencies

relative to the contrast sensitivity at medium spatial frequencies, which is a

measure of lateral inhibition.

N/A