Pure‐tone sensitivity of human infants

The ability of 3‐, 6‐, and 12‐month‐old infants to detect pure tones in quiet was tested at frequencies ranging from 250–8000 Hz. Stimuli were presented monaurally via headphone. Signal trials consisted of ten repetitions of a 500‐ms tone burst, with 10‐ms rise‐fall time and 500 ms between bursts; no‐signal trials were 10‐s intervals of quiet. The infant's response to a tone was judged by an observer, who, blind to trial type, decided whether or not a tone had been presented on each trial, based on the infant's behavior. Comparison of infant thresholds, determined using an adaptive rule, to those of adults tested under similar conditions showed a progressive improvement in threshold from 3–12 months. Three‐month‐olds' threshold were relatively poorer at 250 and at 8000 Hz compared to adults. The 6‐ and 12‐month‐olds' thresholds were somewhat closer to those of adults at 4000 and at 8000 Hz than at lower frequencies. Maturation of absolute sensitivity, of frequency resolution, and of nonsensory processing may all contribute to these age‐related changes. [Work supported by NIH.]