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J Atkinson, J Wattam-Bell, O Braddick; Development of Directional and Orientation-Selective VEP Responses: Relative Functional Onset of Dorsal and Ventral Stream Processing in Human Infants . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3992.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: During the first 3 months of life, infants develop VEP responses that are signatures of orientation selectivity and direction selectivity in cortical neurons (Braddick et al, Nature, 1986; Wattam-Bell, Vision Research, 1991). These forms of selectivity represent the initial stages of processing required for ventral and dorsal streams. The aim of this study was to compare the relative onset of these responses in the same individual infants, at comparable frequencies. Methods: A group of infants aged 4-13 weeks post-term age were each tested on orientation-reversal (OR-) and direction reversal (DR-) VEPs, in counterbalanced order. OR-VEPs were elicited with a grating which alternates betweeen 45 deg and 135 deg orientations at 4 reversals/sec, these alternations being embedded in a sequence of random phase shifts at 25 per sec to control for non-orientation-selective responses to local contrast change. DR-VEPs were elicited with a moving random pixel pattern (velocity 5 deg/sec) which reverses direction at 4 reversals/sec, with replacement of the random pattern at 8 per sec to isolate specific responses to direction. The presence of a VEP response at the stimulus frequency with consistent phase was tested with Hotelling's T2 test. Results: Infants throughout the age range showed significant responses to orientation reversal. Almost all infants of 10 weeks and over showed significant responses to direction reversal, but the majority of infants under 10 weeks did not show this response. Conclusion: Direct comparison shows that responses indicating cortical direction selectivity emerge at a later age than do responses indicating cortical orientation selectivity. We conclude that sensitivity to directional motion is a separate, later developing aspect of cortical processing than is sensitivity to pattern. Relation to other reports of directional VEP responses in young infants (del Viva et al, ECVP 2001) will be discussed. Implications of these results for the underlying developmental mechanisms in V1, the establishment of processing in dorsal and ventral streams beyond V1, and the concept of dorsal-stream vulnerability (Atkinson, ARVO 1999) will be considered.
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