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The Journal of Neuroscience, June 15, 2001, 21(12):4530-4541

Normalization Models Applied to Orientation Masking in the Human Infant

T. Rowan Candy¹, Ann M. Skoczenski², and Anthony M. Norcia³

¹ Indiana University School of Optometry, Bloomington, Indiana 47405-3680, ² Eunice Kennedy Shriver Center, University of Massachusetts Medical School, Waltham, Massachusetts 02452, and ³ Smith-Kettlewell Eye Research Institute, San Francisco, California 94115

Human infants can discriminate the orientation of lines within the first week after birth (Atkinson et al., 1988; Slater et al., 1988) but have immature orientation-selective pattern masking until after 6 months of age (Morrone and Burr, 1986). Here the development of orientation processing is further examined using a visual-evoked potential paradigm and normalization models of pattern masking. Contrast response functions were measured for 1 cycle per degree (cpd) gratings, counterphase-reversed in contrast at either 3.3 or 5.5 Hz. A second 1 cpd, 20% contrast, 8.3 Hz grating of either the same or orthogonal orientation was added as a mask. Evoked responses associated with the test grating, the mask, and intermodulation between the two were individually extracted using spectral analysis of the scalp-recorded EEG. Adults exhibited orientation selectivity in the masking of their test component responses and in nonlinear intermodulation between the test and mask stimuli. Infants <5 months old, however, demonstrated nonselective masking or a reversed selectivity in their responses to the test component, with adult-like orientation selectivity in their intermodulation responses. Within the context of a normalization model of pattern masking, the results are consistent with the existence of oriented filters early in life the responses of which are normalized immaturely until ~5 months of age.

Key words: visual development; pattern masking; orientation selectivity; human infant; visual-evoked potentials; visual cortex; normalization models

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Copyright © 2001 Society for Neuroscience  0270-6474/01/21124530-12$05.00/0

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