INFANTS PITCH PERCEPTION - MASKING BY LOW-FREQUENCY AND HIGH-FREQUENCY NOISES

The present research employed an operant conditioning procedure typica lly used with infants to test noise masking of pure tones and tonal co mplexes in adults and in 7-month-old infants. Adults and infants were presented with either pure tones of 160 and 200 Hz or harmonic tonal c omplexes with pitches equivalent to 160 and 200 Hz. The tonal complexe s did not contain energy at the fundamental frequency. After learning these tasks, subjects in the tonal complex group categorized spectrall y varying tonal complexes according to the pitch of the missing fundam ental. Stimuli were subsequently presented in combination with either a low- or a high-frequency noise. Both age groups successfully discrim inated pure tones when combined with a high-frequency noise but not wh en combined with a low-frequency noise in the same frequency range as the pure tone. Infants, Like adults, successfully categorized harmonic tonal complexes based on the pitch of the missing fundamental when th ose stimuli were combined with a low-frequency noise in the range of t he missing fundamental but not when combined with a high-frequency noi se which covered the frequency range of the harmonics themselves. Thes e results suggest that infants rely primarily on a central process and not peripherally generated combination tones to hear the pitch of the missing fundamental. (C) 1997 Acoustical Society of America. [S0001-4 966(97)00112-4].