Lateralization in Squirrel Monkeys Using Time and Intensity Cues

Abstract

Four squirrel monkeys were trained to make right or left lever responses to trains of clicks presented binaurally with varying differences in the interaural time, interaural intensity, and the over-all click level. Time and intensity differences and over-all level were varied in 20 μsec, 2 dB, and 10 dB steps, respectively. For any given daily session, either the time or the intensity parameter alone was varied at only one of three over-all click levels. A modified Block up-down procedure was used. Percent-correct lateral judgments were plotted as a function of interaural time and intensity differences for three click levels. Criterion performance of 85% correct lateral judgments was achieved at time differences ranging from 60 to 120 μsec and at intensity differences ranging from 6 to 10 dB that varied both with the individual monkey and the over-all click intensity. End point for lateralization was also examined for time differences. Performance fell below the criterion level between 2.0 and 3.5 msec depending upon the intensity level used. [Supported by NINDS grant.]