Braddick O J, Birtles D B, Warshafsky J, Akthar F, Wattam-Bell J, Atkinson J, 2006, "Evoked potentials specific to global visual coherence in adults and infants" Perception 35 ECVP Abstract Supplement
Evoked potentials specific to global visual coherence in adults and infants
O J Braddick, D B Birtles, J Warshafsky, F Akthar, J Wattam-Bell, J Atkinson
Coherence sensitivity for patterns of moving dots or oriented elements is increasingly used to assess extrastriate global function in dorsal and ventral streams. We have developed a visual evoked potential (VEP) test of global processing in infants and adults. Coherent and incoherent arrays (contour or motion) alternate at 0.5 - 4 Hz. Local changes at each transition may elicit a second harmonic VEP signal (F2), but a first harmonic (F1) must reflect differential global responses to coherence onset and offset. Supporting this, F1 in adults increases linearly with coherence, while F2 shows little variation. Motion coherence yields larger signals than form, but extrapolating amplitude vs coherence plots suggests similar thresholds for the two systems, consistent with psychophysical results. We have identified global form and motion VEP responses with infants aged 9 - 23 weeks. VEP signals remain constant through this age range for motion, but increase monotonically for form. Adult psychophysical coherence thresholds show only small effects of optical blur, suggesting that immature acuity is not a limiting factor in the development of these responses. These results suggest global integration as a feature of the motion pathway very soon after it emerges in cortical processing, while integrative processes in form processing develop more gradually.
[Supported by MRC programme grant G7908507.]
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