Infants' localization of sounds in the median vertical plane: estimates of minimum audible angle |
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Authors: | B A Morrongiello P T Rocca |
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Institution: | Departments of Otolaryngology, Neurobiology and Behavior, Cognitive Sciences, and Biomedical Engineering, University of California at Irvine, Irvine, CA, USA |
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Abstract: | Infants 6, 9, 12, 15, and 18 months of age were seated in a dark room directly facing an array of nine loudspeakers positioned along the median vertical plane. One loudspeaker was positioned at ear level, 0 degree, and four others each were positioned above and below 0 degree. To examine infants' resolution of auditory space in the median vertical plane we sought to determine the smallest angular shift in the vertical location of a sound that infants could reliably detect (i.e., minimum audible angle). A two-alternative forced-choice procedure was used in which a sequence of white noise bursts was presented initially at 0 degree, and then shifted vertically (i.e., above or below 0 degree) and continued to be presented until the infant made a directional response; correct responses were visually reinforced. The smallest angular shift in vertical location that was reliably detected systematically decreased with increasing age between 6 months (15 degrees) and 18 months (4 degrees), suggesting a finer partitioning of auditory space along the vertical axis over this age range. By 18 months infants' performance matched that of a group of adults tested under the same circumstances. |
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