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C Hou, V Sampath, TR Candy, AM Norcia; Development of the Spatial Organization and Dynamics of Short-Range Lateral Interactions in Human Visual System . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4703.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To study how the visual system combines orientation information across dynamic borders and how the rules of this combination change during early development. Methods:VEP responses were measured under 5 stimulus conditions: a random array of 1 c/deg grating patches, (square shaped, 0.6 deg on a side) counterphase reversed at 4.52 Hz (target test alone), an arrangement with target abutting the end-zone of flank modulated at 2.58 Hz ( collinear configuration ), an arrangement with target abutting the side-zone of flank ( non-collinear configuration), an arrangement where flank orthogonally abutted the end-zone of target ( orthogonal end-zone configuration) and an arrangement where flank orthogonally abutted the side-zone of target ( orthogonal side-zone configuration). VEPs to these stimuli were recorded from 24 infants between 8-24 weeks of age and 14 adults between 18-59 years of age. VEP amplitude and phase were measured at the second and fourth harmonics of each component part and at four intermodulation (IM) frequencies (mF1+nF2) where m, n=1, 2 and F1=4.52 and F2=2.58 Hz. Results:The second and fourth harmonic responses to target and flank were smaller when target and flank were presented together than when they were presented separately in both infants and adults. Masking was equal for the iso-oriented (collinear and non-collinear) and orthogonally-oriented (end-zone and side-zone) arrangements. On the other hand, infants showed only second order (F1+F2), but not fourth order (2F1+2F2) intermodulation responses in the iso-oriented configurations and no intermodulation in the orthogonally-oriented configurations. Adults showed both second and fourth order terms in the iso-oriented configurations and fourth order terms but not second order terms in the orthogonally-oriented configurations. Conclusion:Infants and adults showed similar lateral masking effects for both iso-oriented and orthogonally-oriented organizations and no spatial and orientation selectivity, suggesting that lateral masking interactions are adult-like both in terms of their strength and their spatial organization by 24 weeks of age. The intermodulation components, on the other hand are immature both in terms of their strength and spatial organization. These components must therefore reflect different neural mechanisms than those associated with lateral masking.
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