Multidimensional perceptual development: consistency of responses to frequency and intensity in young chickens.

The development of consistent responses to multidimensional acoustic stimuli was investigated in newborn chickens. Young chicks suppress their ongoing peeps when they hear a change in an acoustic stimulus, and the amount of that suppression is related to the amount of change. Durations of suppression can thus be interpreted as perceived differences between pairs of stimuli. The suppressions elicited by all possible transitions between pairs of 5 acoustic stimuli that differed in frequency, intensity, and repetition rate were measured at 2 ages. These data were analyzed with a multidimensional scaling program. Interpretable structure is evident in the results from 4-day-old chicks to a subset of the stimuli that vary in frequency and intensity. Newborn chicks, in contrast, showed inconsistent responses. Neither age group responded with interpretable structure to stimuli that differed in 3 dimensions. Thus, consistent responses to 2-dimensional acoustic stimuli emerge over the first few postnatal days. Perceptual dimensions become associated with the physical dimensions of frequency and intensity as animals mature.