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W.V. Good, C. Hou, A.M. Norcia; Contour Integration in Typically Developing Children Measured With the VEP . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3153.
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© ARVO (1962-2015); The Authors (2016-present)
Contour integration is an important visual function that involves the integration of local orientation information along object contours. It is affected in amblyopia, dyslexia and schizophrenia. Here we tested the sensitivity of children to a synthetic contour–in–noise display using the Visual Evoked Potential (VEP).
VEPs were recorded from 10 normal vision children between 6–10 years of age at three electrode sites (O1, Oz and O2) referenced to Cz. The stimuli consisted of several Gabor–defined contours embedded in a background of randomly–oriented Gabor patches. Gabor–defined contours (targets) were imaginary circles with the patch orientations rotating between being either tangent to the circle (circle configuration) or offset by 60° (pinwheel configuration) at 3Hz (F1). Background Gabor patches (noise) were rotated randomly between 0° and 180° at 3.6Hz (F2). We varied the spatial frequency (4 and 6 cpd) of the Gabor patches and the spacing (3 and 5 carrier wavelengths; lam) of the contours. Throughout each 17–second trial, the ratio of noise spacing to contour spacing (delta) increased in logarithmic steps from 0.45 to 1.0 for 5 lam spacing contours and from 0.76 to 1.0 for 3 lam spacing contours (contours invisible to visible). VEP amplitude was measured at integer harmonics the two driving frequencies (F1 and F2).
The first harmonic responses to the contours (1F1) increased with increasing ratios of noise spacing to contour spacing (delta) across all recording sites. The VEP thresholds for contour detection were about 0.6 delta for 5 lam spacing contours for both 4 and 6 cpd. The responses were saturated for 3 lam spacing contours at both 4 and 6 cpd because the response was highly significant at the lowest value of delta that could be displayed. The 1F1 response amplitudes were higher for 3 lam contours than for 5 lam contours, but there was no significant difference between contour–element spatial frequencies.
VEP contour detection thresholds and response functions derived from contour–in–noise displays can be measured readily in children and may prove to be useful as measures of long–range feature integration. The response functions of children approach the sensitivity achieved by adults viewing the same displays (Norcia, Sampath and Pettet, VSS 2003).
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