Previous research has suggested that infants discriminate many speech sounds according to phonemic category regardless of language exposure, while adults of one language group may have difficulty discriminating nonnative linguistic contrasts. Our study attempted to address directly questions about infant perceptual ability and the possibility of its decline as a function of development in the absence of specific experience by comparing English-speaking adults, Hindi-speaking adults, and 7-month-old infants on their ability to discriminate 2 pairs of natural Hindi (non-English) speech contrasts. To do this, infants were tested in a "visually reinforced infant speech discrimination" paradigm, while a variant of this paradigm was used to test adults. Support was obtained for the above hypotheses. Infants were shown to be able to discriminate both Hindi sound pairs, and support for the idea of a decrease in speech perceptual abilities wih age and experience was clearly evident with the rarer of the 2 non-English contrasts. The results were then discussed with respect to the possible nature and purpose of these abilities.

Previous research has suggested that infants discriminate many speech sounds according to phonemic category regardless of language exposure, while adults of one language group may have difficulty discriminating nonnative linguistic contrasts. Our study attempted to address directly questions about infant perceptual ability and the possibility of its decline as a function of development in the absence of specific experience by comparing English-speaking adults, Hindi-speaking adults, and 7-month-old infants on their ability to discriminate 2 pairs of natural Hindi (non-English) speech contrasts. To do this, infants were tested in a "visually reinforced infant speech discrimination" paradigm, while a variant of this paradigm was used to test adults. Support was obtained for the above hypotheses. Infants were shown to be able to discriminate both Hindi sound pairs, and support for the idea of a decrease in speech perceptual abilities wih age and experience was clearly evident with the rarer of the 2 non-English contrasts. The results were then discussed with respect to the possible nature and purpose of these abilities.

Four experiments were performed to assess the effect of different orientations and direction oflighting on the visual processing of shaded or bipartite disks. In the first two experiments, observers were presented with nine different shading orientations from A"to 180". Targets were detected in a rapid and parallel fashion for shaded disks when the orientation of the shading gradient was not horizontal (90°) or oriented at 67.5". Search asymmetries favoring the detection of "pock" targets over "ball" targets were found for all orientations. The search rates for bipartite disks were similar to the shaded disks at a", 22.5", and 90"but not for intermediate orientations, and no search asymmetries were found. These differences suggest that shaded displays and bipartite displays are processed by different underlying mechanisms. The third experiment showed that the direction of the light source (left or right) had no influence on search asymmetries around the 90"point. Shading gradient orientation affected magnitude estimates of depth in the fourth experiment. These experiments show that the visual system's "assumption" of overhead lighting is broadly tuned.

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List of Tables v List of Figures vi LIST OF FIGURES Figure Page Model of sensory integration resulting from the convergence of specific sensory channels on the association cortex 6 Three stages of sensory differentiation according to Bower • (1974-a) 9 Schematic diagram of display for Experiment I 25 Pulse patterns used in Experiment I 27 Schematic diagram of laboratory arrangement 28 Proportion of looking to right and left 30 Proportion of looking to fast and slow visual displays 31 Schematic diagram of display for Experiment II .... 37 Pulse patterns used in Experiments II & III 39 10 Mean duration of fixation per trial for groups S 1 and NS 1 41 11 Mean duration of fixation per trial for groups S 0 and NS 0. . 45