Author:
HEINRICH THOMAS STEPHAN,BACH MICHAEL
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.
Publisher
Cambridge University Press (CUP)
Subject
Sensory Systems,Physiology
Cited by
27 articles.
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