Mr. Leek et V. Summers, THE EFFECT OF TEMPORAL WAVE-FORM SHAPE ON SPECTRAL DISCRIMINATION BY NORMAL-HEARING AND HEARING-IMPAIRED LISTENERS, The Journal of the Acoustical Society of America, 94(4), 1993, pp. 2074-2082
A listener's ability to discriminate differences in amplitude spectra
is generally thought to be independent of the temporal waveform shapes
of the stimuli. However, there have been reports of enhanced contrast
between spectral peaks and valleys of harmonic complexes represented
in the temporal firing patterns of auditory-nerve fibers for some comb
inations of component amplitudes and phases [e.g., Horst et al., J. Ac
oust. Soc. Am. 88, 2656-2681 (1990)]. The enhancement has been attribu
ted to nonlinear processing of high-amplitude peaked waveforms. To det
ermine whether such enhancements are observed in psychoacoustic respon
ses of human listeners, subjects were asked to discriminate between ha
rmonic complexes that differed in the frequency location of three form
antlike increments in harmonic amplitude. The stimuli were constructed
to have either a very flat or a very peaked temporal envelope. Over a
range of 1- to 10-dB spectral contrast between elevated harmonics and
background harmonics, discrimination ability was determined as a func
tion of waveform shape and overall amplitude. Performance was measured
for both normal-hearing and hearing-impaired listeners. Normal-hearin
g listeners showed lower thresholds of spectral contrast for peaked wa
veforms at high intensities than for any of the other phase-amplitude
conditions. Although the effect was small (1 to 2 dB), it is consisten
t with an hypothesized enhancement due to nonlinear cochlear processin
g. Hearing-impaired listeners did not demonstrate differential perform
ance across phase or amplitude conditions, perhaps reflecting more lin
ear processing in these damaged ears.