(PP1305) Loudness Perception at and Near Elevated Threshold: Is Soft Still Soft?

Abstract: Two differing models of loudness recruitment (abnormally fast growth of loudness above elevated thresholds) for individuals with sensory hearing loss have been described (Buus & Florentine, 2002; Moore & Glasberg, 2004). The two models provide conflicting data related to perceived loudness at elevated thresholds and loudness growth near threshold in listeners with sensory hearing loss compared to normally hearing listeners. The present study was conducted to gain insight into this discrepancy.

Summary: Objective and Rationale: Two differing models of loudness recruitment (abnormally fast growth of loudness above elevated thresholds) for individuals with sensory hearing loss have been described (Buus & Florentine, 2002; Moore & Glasberg, 2004). The two models provide conflicting data related to perceived loudness at elevated thresholds and loudness growth near threshold in listeners with
sensory hearing loss compared to normally hearing listeners. The present study was conducted to gain insight into this discrepancy.


Design: 29 listeners with normal hearing and 29 listeners with hearing loss participated in a simple yes/no detection task for 4000 Hz tones presented at and near their hearing threshold (at -4, 0, 4, 10, and 16 SL) while their pupil dilation response was recorded as measure of effort and an indirect index of loudness. Pupil dilation response was intended to be used as an indicative measure of the magnitude of the perceived loudness of sounds presented at low sensation level. Participants also completed a subjective rating task to judge the loudness of the same tones and other at higher levels up to 28 dB SL.


Results: A significant difference between groups was seen in the pupil dilation response at threshold (0 SL) and 10 SL conditions. At threshold, pupil dilation in normal hearing listeners initiated earlier and was sustained longer compared to listeners with hearing loss consistent with increased difficulty of sound detection at threshold. Similar response behavior was observed at -4 SL. At 10 SL, pupil dilation in listeners with hearing loss was sustained longer compared to normal hearing listeners. Pupil dilation to tones at other levels (4 and 16 SL conditions) was not different between groups. Both groups subjectively rated the loudness of tones at all levels similarly with similar loudness growth patterns.



Conclusion: Results suggest that normal hearing listeners experienced more difficulty in the sound detection task at threshold, as well as more uncertainty in decision making. This observation may be consistent with a louder perception for tones at threshold in listeners with hearing loss, which supports the softness imperception loudness model put forth by Florentine et al. In general, caution should be exercised when interpreting pupillary responses to directly indicate perceived loudness or psychoacoustic sensation as task induced cognitive processing may also contribute to the response.