Narrow-band ripple glide direction discrimination and its relationship to frequency selectivity estimated using psychophysical tuning curves.

The highest spectral ripple density at which the discrimination of ripple glide direction was possible (STRtdir task) was assessed for one-octave wide (narrowband) stimuli with center frequencies of 500, 1000, 2000, and 4000 Hz and for a broadband stimulus. A pink noise lowpass filtered at the lower edge frequency of the rippled-noise stimuli was used to mask possible combination ripples. The relationship between thresholds measured using the STRtdir task and estimates of the sharpness of tuning (Q10) derived from fast psychophysical tuning curves was assessed for subjects with normal hearing (NH) and cochlear hearing loss (CHL). The STRtdir thresholds for the narrowband stimuli were highly correlated with Q10 values for the same center frequency, supporting the idea that STRtdir thresholds for the narrowband stimuli provide a good measure of frequency resolution. Both the STRtdir thresholds and the Q10 values were lower (worse) for the subjects with CHL than for the subjects with NH. For both the NH and CHL subjects, mean STRtdir thresholds for the broadband stimulus were not significantly higher (better) than for the narrowband stimuli, suggesting little or no ability to combine information across center frequencies.