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Infants' pitch perception: Masking by low- and high-frequency noises
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INFANTS’ PITCH PERCEPTION: MASKING BY LOW- AND HIGH-FREQUENCY
NOISES
E. Christine Rogers, Marsha G. Clarkson, and Sheridan G. Miciek Department of Psychology Georgia State University Atlanta, GA 30303-3083 Although infants can hear the pitch of the missing fundamental for harmonic tonal complexes (HTCs), the cues they use to assign pitch remain unclear. Adults hear the pitch of the missing fundamental even in the presence of a low-frequency noise masker that overlaps the frequency of the missing fundamental. This finding suggests that adults’ perception of the missing fundamental is based on the harmonics in the sound and not on nonlinear, combination tones. The present experiment investigated infants’ abilities to hear the pitch of the missing fundamental in the presence of low- and high-frequency noise maskers. In a conditioning procedure, 7-month-old infants learned to turn their heads when the pitch of pure tones or HTCs changed from 160 to 200 Hz (or vice versa). Infants who discriminated HTCs were presented spectrally-varying HTCs (each containing 6 harmonics) and were required to categorize them according to the pitch of the missing fundamental. Finally, HTCs were presented in combination with a low-frequency (60-260 Hz) or a high-frequency (260-2600 Hz) noise masker. The low-frequency masker overlapped the combination tones equivalent to the missing fundamental; whereas the high-frequency masker overlapped the harmonics in the HTCs. Infants who discriminated pure tones also heard them in combination with the low- or high-frequency noise masker. In these instances, only the low-frequency masker overlapped the pure tones. Sound pressure levels were 50 dBA for the stimuli and 65 dBA for the maskers and were determined based on a preliminary study with adult listeners. An ANOVA on the number of trials on which infants turned in the last five signal and no-signal trials for the discrimination and masking stages yielded a significant stage X trialtype X stimulus (tone vs HTC) X masker (low vs high frequency) interaction (p < .05). In the discrimination stage, infants turned more often on signal than on no-signal trials regardless of the stimulus. The mean numbers of trials with turns for pure tones were 4.14 (signal) and 0.75 (nosignal); whereas comparable means for HTCs were 4.17 (signal) and 0.67 (no-signal). In the masking stage, infants turned more often on signal trials than on no signal trials only for pure tones in combination with the high-frequency masker (signal &J = 3, no-signal &I = 1) and for HTCs in combination with the low-frequency masker (signal M = 4, no-signal &I = 0). Mean numbers of trials on which infants turned were virtually equivalent for signal and no-signal trials for the tone/low-frequency masker combination (signal = 1.25, no-signal = 1.25) and the HTC/high-frequency masker combination (signal = 1.5, no-signal = 1). These results demonstrate that infants discriminate the pitch of the missing fundamental in the presence of a low-frequency but not a high-frequency masker. Conversely, they discriminate the pitch of pure tones in the presence of a high-frequency masker and not a low-frequency masker. These results are consistent with masking patterns reported for adults and suggest that infants, like adults, do not rely on combination tones to hear the pitch of the missing fundamental.
INFANTS’ PITCH PERCEPTION: MASKING BY LOW- AND HIGH-FREQUENCY
NOISES
E. Christine Rogers, Marsha G. Clarkson, and Sheridan G. Miciek Department of Psychology Georgia State University Atlanta, GA 30303-3083 Although infants can hear the pitch of the missing fundamental for harmonic tonal complexes (HTCs), the cues they use to assign pitch remain unclear. Adults hear the pitch of the missing fundamental even in the presence of a low-frequency noise masker that overlaps the frequency of the missing fundamental. This finding suggests that adults’ perception of the missing fundamental is based on the harmonics in the sound and not on nonlinear, combination tones. The present experiment investigated infants’ abilities to hear the pitch of the missing fundamental in the presence of low- and high-frequency noise maskers. In a conditioning procedure, 7-month-old infants learned to turn their heads when the pitch of pure tones or HTCs changed from 160 to 200 Hz (or vice versa). Infants who discriminated HTCs were presented spectrally-varying HTCs (each containing 6 harmonics) and were required to categorize them according to the pitch of the missing fundamental. Finally, HTCs were presented in combination with a low-frequency (60-260 Hz) or a high-frequency (260-2600 Hz) noise masker. The low-frequency masker overlapped the combination tones equivalent to the missing fundamental; whereas the high-frequency masker overlapped the harmonics in the HTCs. Infants who discriminated pure tones also heard them in combination with the low- or high-frequency noise masker. In these instances, only the low-frequency masker overlapped the pure tones. Sound pressure levels were 50 dBA for the stimuli and 65 dBA for the maskers and were determined based on a preliminary study with adult listeners. An ANOVA on the number of trials on which infants turned in the last five signal and no-signal trials for the discrimination and masking stages yielded a significant stage X trialtype X stimulus (tone vs HTC) X masker (low vs high frequency) interaction (p < .05). In the discrimination stage, infants turned more often on signal than on no-signal trials regardless of the stimulus. The mean numbers of trials with turns for pure tones were 4.14 (signal) and 0.75 (nosignal); whereas comparable means for HTCs were 4.17 (signal) and 0.67 (no-signal). In the masking stage, infants turned more often on signal trials than on no signal trials only for pure tones in combination with the high-frequency masker (signal &J = 3, no-signal &I = 1) and for HTCs in combination with the low-frequency masker (signal M = 4, no-signal &I = 0). Mean numbers of trials on which infants turned were virtually equivalent for signal and no-signal trials for the tone/low-frequency masker combination (signal = 1.25, no-signal = 1.25) and the HTC/high-frequency masker combination (signal = 1.5, no-signal = 1). These results demonstrate that infants discriminate the pitch of the missing fundamental in the presence of a low-frequency but not a high-frequency masker. Conversely, they discriminate the pitch of pure tones in the presence of a high-frequency masker and not a low-frequency masker. These results are consistent with masking patterns reported for adults and suggest that infants, like adults, do not rely on combination tones to hear the pitch of the missing fundamental.