Basilar-membrane Activity and Loudness

Buus and Florentine (ISP meeting 2001) presented evidence that basilar-membrane velocity growth functions are proportional to the square root of loudness functions derived from temporal and spectral integration. Although it is not possible to directly measure basilarmembrane activity in humans, it is likely that tone-burst otoacoustic emission input-output functions, at least at low and moderate levels, are closely related to the amount of basilarmembrane activity. To further examine this relation, tone-burst otoacoustic emissions are compared with loudness functions derived from a combination of data from temporal integration of loudness and spectral loudness summation, as well as loudness functions that are more directly measured using cross-modality matching. Tone-burst otoacoustic emission input-output functions show a strong correspondence to loudness measured using all these methods. These findings support the idea that loudness is closely related to basilarmembrane activity and that tone-burst otoacoustic emissions may provide rapid, non-invasive insight into cochlear activity. A non-invasive method for understanding basilar-membrane activity in humans would be invaluable for understanding how the active portion of the cochlea functions. At the 2001 ISP meeting, Buus and Florentine presented evidence that human loudness growth is proportional to the square of basilar-membrane velocity measured in chinchillas (Ruggero et al., 1997). Withnell and Yates (1998) first suggested that otoacoustic emissions might be a suitable tool for examining basilar-membrane nonlinearity. Epstein and Florentine (2005(1)) confirmed that loudness measured using temporal and spectral summation is proportional to tone-burst otoacoustic emissions (TBOAEs). However, these experiments rely on loudness models and do not directly assess loudness. Therefore, a follow-up experiment in which loudness is assessed using a cross-modality matching procedure is presently compared with TBOAEs.