Discimination of relative onset time of two-component tones by infants.

A great deal of research has focused on the perception of voice onset time (VOT) differences in stop consonants. Yet, the nature of the mechanisms responsible for the perception of these differences is still the subject of much debate. Recently Pisoni [J. Acoust. Soc. Am. 61, 1352-1361 (1977)] has presented evidence which suggested that the perception of VOT differences by adult listeners may reflect a basic limitation on processing temporal order information by the auditory system. For adults, stimuli with onset differences approximately greater than 20 ms are perceived as successive events (either leading or lagging), while stimuli with onset differences less than about 20 ms are perceived as simultaneous events. Thus, differences in voicing may have an underlying perceptual basis in terms of three well-defined temporal attributes corresponding to leading, lagging, or simultaneous events at onset. The present experiment was carried out to determine whether young infants can discriminate differences in temporal order information in nonspeech signals and whether their discimination performance parallels the earlier data obtained with adults. Discimination was measured with the high-amplitude sucking (HAS) procedure. The results indicated that infants can disciminate differences in the relative onset of two events; the pattern of discrimination also suggested the presence of three perceptual categories along this temporal continuum although the precise alignment of these categories differed somewhat from the values found in the earlier study with adults.