Context effects in intensity discrimination

Animal studies have shown that auditory neurons adapt their firing rate depending on sound level statistics. This dynamic range adaptation (DRA) has been measured by presenting short segments of noise or tones with some levels being presented more often than others. DRA manifests as a shift of the rate-level function of the neurons toward the most frequently presented levels. It produces a change in sensitivity enhancing the coding of these most probable levels. The aim of this study was to search for a perceptual correlate of DRA in normal hearing participants. Intensity discrimination thresholds were measured for pure-tone and for broadband pulse-spreading harmonic complex test signals embedded in different contexts, with the hypothesis that discrimination thresholds should be lower when the context mean level matches the test signal level. For broadband signals, the results were fully consistent with this hypothesis, while for pure tones, intensity discrimination always degraded with increases in context level, independently from the level of the test signals. Additional experiments suggest that partial masking and confusion may have obscured the effects of DRA for pure tones.