ISCA Workshop on Plasticity in Speech Perception (PSP2005)

Senate House, London, UK
June 15-17, 2005

Infant Discrimination of Spectrally Weighted Speech

Christine Kitamura, Janice Gregory, Stacey Kuan

MARCS Auditory Laboratories, University of Western Sydney, Australia

In this study infant discrimination of spectrally weighted speech was examined using frequency responses typically found in adult hearing aids. We know infants perceive speech differently to adults and children, but we do not know much about how infants process speech with differing degrees and directions of spectral tilt. To date, the only research on spectral tilt discrimination comes from studies using complex tones found in music. Here we tested infants' ability to discriminate normal speech from speech with a positive or negative tilt (6dB and 9dB). In each of the eight groups of infants (N=190) half were aged 24 weeks and half aged 36 weeks. Each group of infants was tested with normal speech and either -6dB,+6dB,-9dB or +9dB. An habituation procedure was used in which the same stimulus was presented until there was an average 50% decrement in looking times over two trials (compared to the average of the first two trials). Once this criterion was met, two no-change control trials followed and then infants were presented with two test trials of the novel stimulus. The order of the habituation and novel stimulus was counterbalanced so that half the infants were habituated with speech with no spectral tilt (hereinafter called 0dB) and tested with one of the 4 spectral tilts (-6dB, +6dB, - 9dB, or +9dB), and for the other half of the infants this was reversed. The results showed no order effects. For the main analyses two (2)x2x2 (trialtype x age x tilt direction) ANOVAs were conducted one for 6dB and one for 9dB experiments. The dependent variable was the average looking time (in the two control versus the two novel trials). For the four 9dB experiments, there was a significant main effect for trial type (p=.000), and no other main effects or interactions. Paired t-tests showed both age groups could discriminate 0dB from positive and negative 9dB (all ps .8) while 24-week-olds did not discriminate 0dB and +9dB (p>.8) but showed a trend to discriminating 0dB and -9dB (p=.09). The emerging sensitivity to spectrally tilted speech will be discussed in relation to the relevant literature.

Full Paper

Bibliographic reference.  Kitamura, Christine / Gregory, Janice / Kuan, Stacey (2005): "Infant discrimination of spectrally weighted speech", In PSP2005, 37-40.