Abstract:

The present study assessed the behavioral capacity of six chinchillas (Chinchilla villidera) to discriminate complex acoustic differences, like those observed for the first formant (F1) of human speech, using operant methods. In a minimum-uncertainty task, chinchillas discriminated single-formant stimuli with fundamental frequencies of 100 or 200 Hz, 60 Hz (Q6) bandwidths, and center frequencies ranging from 2.5--7.0 Bark (approximately 253--709 Hz) in 0.25-Bark steps. Each trial began with the repeated presentation of a ``target'' stimulus. The chinchillas' task was to discriminate whether this repeating target changed in center frequency or remained constant throughout the trial. The chinchillas completed 20 experimental sessions for each of six conditions in which fundamental frequency and center frequency of the target stimulus were varied. Stimulus characteristics were designed to reveal perceptual consequences of interactions between individual harmonics and overall spectral shape of the single formant. Behavioral sensitivities were estimated by d[sup '] and percent correct. Data will be discussed in the context of human psychophysical performance and observations of single-unit responses in the chinchilla cochlear nucleus from studies utilizing the same stimulus corpus. [Work supported by NSF.]