A Comparison of Speech Sound Discrimination in Man and Monkey
Joan M. Sinnott, David Branch Moody, William C. Stebbins · The Journal of the Acoustical Society of America · 1974
Enhanced discrimination between speech sounds across phoneme boundaries relative to discrimination within phoneme categories based on identification defines categorical perception. The present experiment compared man and Old World monkey on speech sound discrimination and particularly on the ability to perceive categorically. Difference thresholds for three humans and four monkeys were determined on a synthetic speech sound continuum from “BA” to “DA.” Humans were instructed and monkeys conditioned with food reinforcement to indicate a stimulus change from a repetitive “BA” in a direction towards the other phoneme “DA,” or, from “DA” towards “BA.” In addition to percent correct discrimination data, reaction times to stimulus change were recorded. Thresholds, defined as 50% correct discrimination between speech sounds, were typically smaller for humans than for monkeys and tended to occur intraphonemically for humans, but at phoneme boundaries for monkeys. Human reaction times, however, were longer near threshold than were those for monkeys, presumably due to increased time required for discriminating within a phoneme category. In this experiment, therefore, the reaction time data provided better evidence for categorical perception in humans than did percent correct discrimination data. [Research supported by grants from NIH and University of Michigan.]