Testing the concept of softness imperception: loudness near threshold for hearing-impaired ears

Buus and Florentine [J. Assoc. Res. Otolaryngol. 3, 120-139 (2002)] have proposed that loudness recruitment in cases of cochlear hearing loss is caused partly by an abnormally large loudness at absolute threshold. This has been called "softness imperception." To evaluate this idea, loudness-matching functions were obtained using tones at very low sensation levels. For subjects with asymmetrical hearing loss, matches were obtained for a single frequency across ears. For subjects with sloping hearing loss, matches were obtained between tones at two frequencies, one where the absolute threshold was nearly normal and one where there was a moderate hearing loss. Loudness matching was possible for sensation levels (SLs) as low as 2 dB. When the fixed tone was presented at a very low SL in an ear (or at a frequency) where there was hearing impairment, it was matched by a tone with approximately the same SL in an ear (or at a frequency) where hearing was normal (e.g., 2 dB SL matched 2 dB SL). This relationship held for SLs up to 4-10 dB, depending on the subject. These results are not consistent with the concept of softness imperception.