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Rick J. Brown, T. Rowan Candy, Anthony M. Norcia; Development of Rivalry and Dichoptic Masking in Human Infants. Invest. Ophthalmol. Vis. Sci. 1999;40(13):3324-3333.
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purpose. To examine the development of rivalry, dichoptic masking, and binocular
interactions in infants more than 5 months of age using the visual
evoked potential (VEP).
methods. VEPs were recorded in 35 infants between 5 and 15 months of age and 23
adults between 13 and 59 years of age. Counterphasing, sinusoidal, 1
cycle/deg gratings were presented dichoptically. Responses from each
eye were isolated by “tagging” each half-image with a different
temporal frequency (5 or 7.5 Hz). Observers were presented with fixed
80% contrast gratings in each eye in experiment 1. Rivalry was
detected on the basis of a negative correlation between the
simultaneously measured response amplitudes at the second harmonics of
the two eye-tagging frequencies. In a second analysis of the same data,
response amplitudes recorded under dichoptic viewing conditions were
compared to those obtained in a monocular control condition (dichoptic
masking). In experiment 2, a 40% fixed-contrast grating was presented
to one eye, whereas the other eye viewed a grating that was swept in
contrast from 1% to 67%. Dichoptic masking was measured as the
reduction in the fixed-grating response caused by the variable contrast
results. Experiment 1: although adults showed evidence of VEP amplitude
alternations between the eyes for cross-oriented half-images
(physiological rivalry), infants did not. This immature response to
rivalrous stimuli occurred despite the presence of responses at
nonlinear combination frequencies recorded with gratings of the same
orientation in each eye, a definitive indication of binocular
interaction. In addition, both iso- and cross-oriented half-images
produced less dichoptic masking in infants than in adults in this
experiment. Experiment 2: dichoptic masking in the infants was
equivalent to that seen in adults with parallel gratings in the two
eyes; however, masking with cross-oriented configurations was
approximately five times weaker in the infants relative to the adults.
conclusions. The authors have identified a set of stimulus conditions under which
infants between 5 and 15 months of age fail to demonstrate
physiological rivalry despite the presence of binocular interactions.
The observed lack of binocular rivalry may be the result of a specific
immaturity in dichoptic, cross-orientation
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