Profile analysis in listeners with normal and elevated audiometric thresholds: Behavioral and modeling results.

Profile-analysis experiments measure the ability to discriminate complex sounds based on patterns, or profiles, in their amplitude spectra. Studies of profile analysis have focused on normal-hearing listeners and target frequencies near 1 kHz. To provide more insight into underlying mechanisms, we studied profile analysis over a large target frequency range (0.5-4 kHz) and in listeners with both normal and elevated audiometric thresholds. We found that profile analysis degrades at high frequencies and that the effect of spacing between nearby frequency components differs with frequency. Consistent with prior reports, elevated audiometric thresholds were not associated with impaired performance when stimuli consisted of few distantly spaced frequency components. However, elevated audiometric thresholds were associated with elevated profile-analysis thresholds for stimuli composed of many closely spaced frequency components. Behavioral thresholds from listeners with and without hearing loss were predicted by decoding firing rates from simulated auditory-nerve fibers or simulated modulation-sensitive inferior-colliculus neurons. Although responses from both model stages informed some aspects of the behavioral data, only population decoding of inferior-colliculus responses accounted for the worsening of profile-analysis thresholds at high target frequencies. Collectively, these results suggest that profile analysis involves multiple non-peripheral factors, including multichannel comparisons and midbrain tuning to amplitude modulation.