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G. Mirabella, C. Hou, A.M. Norcia; Development of Fusional Suppression in Human Infants . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4823.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: In infants, processes relating to fusion and stereoacuity are not believed to develop until about the third month (Birch et al., 1982, Birch & Petrig, 1996, Braddick et al., 1980). In most infant studies, fusion has been operationalized as a differential visual evoked potential (VEP) or behavioral response to non-disparate targets that are either correlated or anti-correlated between the two eyes. Here we use disparate targets that also evoke a shift in visual directions in adults with normal stereopsis. This phenomenon is also known as "fusional suppression" (McKee & Harrad, 1993, McKee et al, ARVO 2002) because binocular vision suppresses monocular information to in order to obtain single vision. Methods: VEPs were recorded in infants 10 to 15, and 16 to 21 weeks of age, and in normal adults. One eye was presented with a grating containing vernier offsets (10 arcmin) oscillating between alignment and misalignment at 1 Hz. The other eye was presented with one of two static targets (pedestals). One pedestal consisted of collinear vertical bars. When the two half images are fused, the display is seen as a set of bands moving in depth from the fixation plane (0 arcmin disparity) to 10 min of crossed disparity, alternating with static 0 disparity bands. Making and breaking of collinearity is coincident with the appearance and disappearance of depth. The second pedestal consisted of bars that had fixed horizontal offsets in correspondence with the vernier offsets in the other eye. When these two half images are fused, the bands appear to be moving in depth about a 10 arcmin standing disparity. This second stimulus produced no make-break percept. Results: In both infants and adults, stimuli that involved make-break percepts (0 disparity pedestal, monocular and binocular controls) evoked significant odd harmonic response components. These odd harmonic components were reduced by the addition of disparity to the pedestal. Consistent with McKee et al. (2002), we consider this reduction to be the neural correlate of fusional suppression. The strength of fusional suppression increased systematically with age. There were also notable differences in the VEP waveforms between infants and adults, with adult responses being sharper and less variable, with shorter peak latencies. Conclusions: Infants as young as 10 weeks of age show a reduction in VEP amplitude when viewing stereo targets with a standing disparity, and thus show fusional suppression in a manner similar to adults. The present data provide additional evidence for fully functional binocular vision being present no later than 10-15 weeks.
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