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Ann M. Skoczenski, Alice D. Nelson, Haley S. Surti; Crowding in infants' VEP vernier responses. Journal of Vision 2001;1(3):451. doi: 10.1167/1.3.451.
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Introduction. Visual crowding refers to a reduction of visual sensitivity for targets presented with flanking stimuli. Crowding occurs in various spatial vision tasks (e.g. orientation discrimination, spatial localization), but its mechanisms are unclear. We measured crowding effects on vernier acuity responses in infants, to determine if infants, like the adult periphery, show more extensive crowding than adults' central vision. Methods. We recorded steady-state visual evoked potentials (VEPs) in 16 infants aged 4 to 9 months, and in 3 adults. Vernier offsets were presented in 80% contrast squarewave gratings, which varied in spatial frequency (SF) across conditions. Each infant was tested on 3 carrier SF conditions, ranging from 0.7 to 4 c/deg, and adults were tested on several carrier SFs ranging from 1 to 16 c/deg. Offsets appeared and disappeared at a rate of 5 Hz, and offset size was fixed at 7 or 10 arc minutes for infants and 1 arc min for adults. We recorded the amplitude, phase and variability of the first harmonic (5 Hz) component of the evoked response, previously shown to be the vernier pattern response. Each observer's responses were averaged over 4–6 trials per condition. In addition, we measured VEP grating acuity. Results. We estimated crowding as the reduction of VEP amplitude compared to the peak amplitude. In adults, crowding occurred above 8 c/deg, 3.75x below grating acuity. In young infants (4–5 months) as well as older infants (7–9 months), crowding occurred above 2 c/deg, 6× below grating acuity of younger infants and 9x below grating acuity of older infants. Discussion. Crowding effects extend to lower SFs in infants compared to adults, indicating that crowding extends over greater distances during infancy. Infant/adult differences in crowding are not predicted by grating resolution. Developmental changes in crowding may be attributed to maturation of lateral interactions or attentional resolution.
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