Effect of Stimulus Intensity and Contrast on the Pattern ERG

Abstract

Stripe patterns of varying spatial frequency were presented in the onset-offset mode. At a high contrast the amplitude of the onset response showed a spatial selectivity which occurred with a high intensity at a higher spatial frequency than with a low intensity. The offset response showed only a monotonic decrease in amplitude at both intensities. Contrast sensitivity functions were derived at different levels of contrast. The spatial selectivity of the onset response occurred at a constant spatial frequency and was more pronounced with low contrasts. The amplitude of the offset response was spatially selective only at low contrasts; with increasing contrast a gradual shift to a non-selective behavior was noted.

Computation of the luminance and pattern components of the bar pattern electroretinogram

“…Our observations of low spatial frequency PERGs have not shown a consistent or systematic latency change with reduced contrasts. This appears to agree with the work of Korth and Rix (1984).…”

“…Our own experimental observations together with other investigators, most notably Korth and Rix (1984), confirm the assumed linearity of the low spatial frequency PERG with contrast. However we recognized the limitation imposed by the available series of grating spatial frequencies on which the retinal illuminance contribution was based.…”

“…In our experiments we have been unable to find any systematic latency variation of low spatial frequency PERGs at different contrast levels, and therefore the subtraction was undertaken at a fixed latency. Indeed it appears from the data of Korth and Rix (1984) that reduced contrast does not alter the latency of the PERG to stimuli of tow spatial frequency, The result of the subtraction is displayed in the final column. The nature of the subtraction reveals a more pronounced spatial tuning.…”

“…Therefore the response amplitude to retinal illuminance changes evoked by gratings of higher spatial frequencies might be expected to be directly related to the attenuation of temporal contrast. The PERG in response to low spatial frequencies (or local ERG in the ultimate case of one element modulating in the entire screen) also has a linear relationship with contrast (Korth and Rix, 1984;Hess et al, 1986). The low spatial content of the stimulus means the response must be dominated by illuminance processing.…”

Spatial Selectivity of Pattern Electroretinogram Components

“…Thus, decrease in luminance affects the onset and offset response in a way different to that which occurs by a decrease in con trast. Using a stripe pattern, spatial tuning for onset responses was at 3.67 cycles/degree (50.119 Td) and at 1.8 c/degree (457 Td) [9], Using a checkerboard stimulus, a similar change was presently observed from 20 min of arc (at 45 cd/m2, corresponding to about 700 Td) to 50 min of arc (at 4.5 cd/m2). The study recommends the application of pattern stimuli in an onset-offset mode for studying antagonistic receptive field properties in the human ERG.…”