TY - JOUR T1 - Normalization Models Applied to Orientation Masking in the Human Infant JF - The Journal of Neuroscience JO - J. Neurosci. SP - 4530 LP - 4541 DO - 10.1523/JNEUROSCI.21-12-04530.2001 VL - 21 IS - 12 AU - T. Rowan Candy AU - Ann M. Skoczenski AU - Anthony M. Norcia Y1 - 2001/06/15 UR - http://www.jneurosci.org/content/21/12/4530.abstract N2 - 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. ER -