title: Normalization models applied to orientation masking in the human infant.
abstract: 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 approximately 5 months of age.
authors.affiliation: Indiana University School of Optometry, Bloomington, Indiana 47405-3680, USA. rcandy@indiana.edu
authors.forename: T R
authors.initials: TR
authors.lastname: Candy
authors.forename: A M
authors.initials: AM
authors.lastname: Skoczenski
authors.forename: A M
authors.initials: AM
authors.lastname: Norcia
mesh_terms: D000328:Adult; D000375:Aging / Q000502:physiology; D015350:Contrast Sensitivity / Q000502:physiology*; D004569:Electroencephalography; D005074:Evoked Potentials, Visual / Q000502:physiology; D006801:Humans; D007223:Infant; D008959:Models, Neurological; D009778:Occipital Lobe / Q000502:physiology; D009949:Orientation / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010470:Perceptual Masking / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D011930:Reaction Time / Q000502:physiology; D012684:Sensory Thresholds / Q000502:physiology; D012815:Signal Processing, Computer-Assisted