Contrast adaptation in retinal and cortical evoked potentials: No adaptation to low spatial frequencies

Abstract

Contrast adaptation occurs in both the retina and the cortex. Defining its spatial dependence is crucial for understanding its potential roles. We thus asked to what degree contrast adaptation depends on spatial frequency, including cross-adaptation. Measuring the pattern electroretinogram (PERG) and the visual evoked potential (VEP) allowed separating retinal and cortical contributions. In ten subjects we recorded simultaneous PERGs and VEPs. Test stimuli were sinusoidal gratings of 98% contrast with spatial frequencies of 0.5 or 5.0 cpd, phase reversing at 17 reversals/s. Adaptation was controlled by prolonged presentation of these test stimuli or homogenous gray fields of the same luminance. When adaptation and test frequency were identical, we observed significant contrast adaptation only at 5 cpd: an amplitude reduction in the PERG (-22%) and VEP (-58%), and an effective reduction of latency in the PERG (-0.95 ms). When adapting at 5 cpd and testing at 0.5 cpd, the opposite effect was observed: enhancement of VEP amplitude by +26% and increase in effective PERG latency by + 1.35 ms. When adapting at 0.5 cpd and testing at 5 cpd, there was no significant amplitude change in PERG and VEP, but a small effective PERG latency increase of +0.65 ms. The 0.5-cpd channel was not adapted by spatial frequencies of 0.5 cpd. The adaptability of the 5-cpd channel may mediate improved detail recognition after prolonged blur. The existence of both adaptable and nonadaptable mechanisms in the retina allows for the possibility that by comparing the adaptational state of spatial-frequency channels the retina can discern between overall low contrast and defocus in emmetropization control.

Oculomotor inhibition covaries with conscious detection

“…Such adaptation selectively reduces perceptual sensitivity for stimuli with orientations similar to the adaptor, especially when both have high spatial frequency (Blakemore and Campbell 1969;Heinrich and Bach 2002). We therefore reasoned that if microsaccadic inhibition relies on similar detection mechanisms as explicit perception, then it should also be weakened in response to stimuli with adapted orientations, in particular for high SFs.…”

Blur adaptation: Contrast sensitivity changes and stimulus extent

“…However, the origin and underlying mechanisms may not be the same as the judgment of perceived focus occurs in the visual cortex whereas contrast adaptation may occur at various earlier stages in the visual processing. There are also reports suggesting that the contrast adaptation occurs at the level of the retina (Heinrich & Bach, 2002;Ohlendorf & Schaeffel, 2009). If the contrast adaption occurs mainly in the retina, there may not be a transfer to the fellow eye or spread to periphery, which is in agreement with our results.…”

Visual evoked potentials in migraine: Is the “neurophysiological hallmark” concept still valid?

“…For instance, in some studies the amplitude reduction is considered a result of sensory adaptation (Heinrich and Bach, 2001;Heinrich and Bach, 2002). The relative effect of sensory adaptation and habituation cannot be separated with the methods commonly applied in migraine habituation studies (Omland et al, 2011).…”