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Janette Atkinson, Deirdre Birtles, John Wattam-Bell, Andrew Wilkinson, Oliver Braddick; Direction-reversal VEP's are delayed in development of premature infants: early dorsal-stream vulnerability?. Journal of Vision 2007;7(9):544. doi: https://doi.org/10.1167/7.9.544.
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VEP responses to direction reversal have a consistently later onset than orientation reversal responses, in the early months of infant development (Braddick et al, Vision Research, 45, 3169 (2005)). Here we examine the effects of very premature birth on the development of these two cortical responses.
16 neurologically normal premature infants, ([[lt]]33 weeks gestation with normal brain ultrasound), were tested between 2–4 months post-term age for steady-state VEP responses to (a) orientation reversals between opposite oblique gratings at 8 reversals/sec; (b) reversals of horizontal motion direction in a dot pattern at 2 reversals/sec. In each case the reversals were embedded in a sequence of stimulus changes to exclude local spatio-temporal contrast changes as a source of signals at the reversal frequency. The premature group was compared with 26 term-born infants matched for post-term age.
VEPs were assessed by signal:noise ratio (S:N) at the reversal frequency. For orientation reversal, the VEP signal:noise ratio (S:N) at the reversal frequency showed flat regression with age, and no difference between the groups. Direction-reversal S:N showed a linear increase with age, and was at a significantly lower level for the premature compared to the term group, implying approximately 4 weeks' delay in development of the directional response in the preterms.
We conclude that (a) the additional visual experience of healthy preterms provides no advantage in cortical development; (b) motion processing provides a sensitive indicator of deleterious effects of preterm birth on the visual brain. This may reflect the sensitivity of the motion system to subtle white-matter anomalies, not readily detectable by ultrasound but possibly observable on MRI. We discuss this result in the context of the ‘dorsal stream vulnerability’, shown by relative impairment of global motion compared to form processing, in a range of neurodevelopmental disorders (hemiplegia, Williams Syndrome, autism, dyslexia, fragile-X).
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