Infant psychometric functions: Asymptotic performance.

Abstract

Psychometric functions have been obtained for detection of repeated, short (16-ms) tone bursts [L. A. Werner and G. C. Marean, Assoc. Res. Otolaryngol. (1991)] and for single, long (300-ms) tone bursts [J. Y. Bargones and L. A. Werner, Assoc. Res. Otolaryngol. (1992)] from infants and adults. Infant functions for these stimuli are similar: they tend to have shallower slopes and lower upper asymptotes than those of adults. Best infant performance for both stimuli is about 85% correct. Infant thresholds are also worse than those of adults, but this may result partially from the fact that thresholds were estimated using methods that assume an upper asymptote of 100%. However, most studies of infant threshold present a series of long duration, repeated stimuli. In the current study, upper asymptotic performance for this more optimal stimulus was examined. The observer-based psychoacoustic procedure [Olsho etal., Devel. Psychol. 23, 627–640 (1987)] was used to test 6- to 9-month-old infants. The stimulus consisted of 1-kHz tone bursts, with 500-ms duration. The tone was presented about 25 dB above previously estimated threshold for a similar stimulus. Asymptotic performance was predicted for this stimulus. On signal trials, the tone burst was repeated four times, with 500 ms between bursts. No-signal trials consisted of 4 s of silence. A 30-trial block, consisting of 15 signals trials and 15 no-signal trials, was obtained from each infant to estimate p(C)max. These data were used to estimate the effect of reduced upper asymptote on infant threshold estimates. [Work supported by NIH Grant No. DC00396.]