Modified spectral tilt affects older, but not younger, infants' native-language fricative discrimination.
OBJECTIVE
It is important to ensure that hearing aid fitting strategies for infants take into account the infant's developing speech perception system. As a way of exploring this issue, this study examined how 6- and 9-month-olds with normal hearing perceive native-language speech in which the natural spectral shape was altered to emphasize either high-frequency (positive spectral tilt) or low-frequency (negative spectral tilt) information.


METHODS
Discrimination was tested using a visual habituation procedure. Forty-eight 6-month-olds and forty-eight 9-month-olds were presented with a fricative contrast, /f/-/s/, in 1 of 3 conditions: (a) as unmodified speech; (b) with a -6 dB/octave tilt; or (c) with a +6 dB/octave tilt.


RESULTS
Six-month-olds showed evidence of discriminating /f/-/s/ in all 3 conditions, but 9-month-olds showed such evidence only in the unmodified condition.


CONCLUSIONS
The findings suggest that the perceptual reorganization that emerges for consonants at the end of the first year affects 9-month-olds' discrimination of native speech sounds. Perceptual reorganization is usually indexed by a decline in the ability to discriminate nonnative speech sounds. In this study, 6-month-olds demonstrated an acoustic-based sensitivity to both modified and unmodified native speech sounds, but 9-month-olds were most sensitive to the unmodified speech sounds that adhered to the native spectral profile.
Beach
Elizabeth Francis
EF
MARCS Auditory Laboratories, University of Western Sydney, New South Wales, Australia. elizabeth.beach@nal.gov.au
Kitamura
Christine
C
D000161:Acoustic Stimulation; D000367:Age Factors; D002663:Child Language; D006801:Humans; D007223:Infant; D007804:Language Development; D008954:Models, Biological; D010700:Phonetics; D013018:Sound Spectrography; D013063:Speech Discrimination Tests / Q000379:methods; D013067:Speech Perception