How fast can we see? The latency development in human infants to pattern, orientation and direction-reversal visual evoked potentials

The goal of this thesis is to track latency changes in three visual evoked potentials (VEP) stimuli as an indication of overall brain development, in order to provide a nonnative base line to different iate visual and neurological development from pathological processes. VEP- neural electri cal activ ity recorded from the scalp surface and synchronized with visual stimulus transitions- is one of the common techniques in understanding infant vision development. Past work has concentrated on responses to pattern reversal and to the latency of the initial positive peak. Here we compare the ti ming of responses to pattern , orientation, and direction -reversal VEPs, and transient peak latencies to those calculated from the gradient of steady-state phase against reversal rate. The three stimuli were tested in 81 adults at 1- 16 rls and 137 infants (3.6- 79.0 weeks) at 2- 8 rls. Initial responses to orientation and direction were as fast as for contrast- around 100 ms, consistent with other fi ndings that V J is orientation selecti ve. Cortical processing for both OR and DR yielded longer latencies (200 ms) by the calculated method, perhaps reflecting more involvement of higher visual processing in compari son to PRo Orientation and direction latencies also had a del ayed onset and longer developmental period to reach maturity. Infa nts reached adult transient PR latency values by J 5 weeks, for OR by 50 weeks, and for DR by 10 weeks. For the calculated latency, infants reached both adult PR and DR latencies by 30 weeks while OR showed little change across age. We successfully conftrmed that (I) phase-based calculation of latency is effective, easy to use, and taps into a different cortical pathway; (2) motion processing has an additional, faster, subcortical pathway; (3) a parallel processing of initial contrast and orientation; and (4) later visual processing is not only developmentally delayed for all three stimuli but also more vul nerable to perinatal brain damage. These latency diffe rences provided a baseline for cl inical evaluations where identi fication of delayed latencies should aid early diagnosis and guide therapies for adults and infants.EThOS - Electronic Theses Online ServiceGBUnited Kingdo