Unexceptional sharpness of frequency tuning in the human cochlea

Abstract

The responses to sound of auditory-nerve fibers are well known in many animals but are topics of conjecture for humans. Some investigators have claimed that the auditory-nerve fibers of humans are more sharply tuned than are those of various experimental animals. Here we invalidate such claims. First, we show that forward-masking psychophysical tuning curves, which were used as the principal support for those claims, greatly overestimate the sharpness of cochlear tuning in experimental animals and, hence, also probably in humans. Second, we calibrate compound action potential tuning curves against the tuning of auditory-nerve fibers in experimental animals and use compound action potential tuning curves recorded in humans to show that the sharpness of tuning in human cochleae is not exceptional and that it is actually similar to tuning in all mammals and birds for which comparisons are possible. Third, we note that the similarity of frequency of tuning across species with widely diverse cochlear lengths and auditory bandwidths implies that for any given stimulus frequency the ''cochlear amplifier'' is confined to a highly localized region of the cochlea.auditory nerve ͉ basilar membrane ͉ masking ͉ compound action potential ͉ psychophysical tuning curve

Empirical and biophysical estimations of human cochlea’s psychophysical tuning curve sharpness

“…The results obtained from the mechanical model support Ruggero et al's findings of unexceptional human cochlear tuning sharpness at low frequencies, 10 and corroborate Shera et al's work on SFOAE, giving exceptionally sharp frequency tuning of the human cochlea at high frequencies. 7,11 The findings from all three approaches provide useful conclusions on the relative FTS of the human cochlea in different frequency regions.…”

“…11 Ruggero et al concluded that the human cochlear tuning sharpness is similar to those of these mammals and to that of squirrels, monkeys and cats. 10 However, Shera et al's results revealed sharper cochlear frequency tuning in humans 7,11 and macaque monkeys 12 compared with cats, guinea pigs and chinchillas, which is inconsistent with the work by Ruggero et al 10 Both Ruggero et al and Shera et al measured the ANF responses indirectly using unknown transformation functions. These attempts at defining a species-invariant rapidly varying function to describe the transform between the CAP-and the SFOAE-ANF Q-value require several species to provide reliable data.…”

“…These attempts at defining a species-invariant rapidly varying function to describe the transform between the CAP-and the SFOAE-ANF Q-value require several species to provide reliable data. 10 was more accurate at lower frequencies, where the Q 10 of the SM CAP TC was small (see Fig. 2(a)).…”

“…Verschooten et al estimated the range of human ANF tuning with three rapidly varying first-order SMCAP-to-ANF Q-value transform functions, which were derived using ANF and SM CAP measurements of gerbils, rats, mice, guinea pigs, and chinchillas. 10 Shera et al developed a method of calculating ANF FTS using the delay of stimulus-frequency otoacoustic emission (SFOAE). 7 Rapidly varying functions to transform the SFOAE delay to ANF Q-values have been obtained from ANF and SFOAE measurements of cats, guinea pigs and chinchillas.…”

Human neural tuning estimated from compound action potentials in normal hearing human volunteers

“…The sharpness of cochlear frequency tuning in humans is debated. Evoked otoacoustic emissions and psychophysical measurements suggest sharper tuning in humans than in laboratory animals [15], but this is disputed based on comparisons of behavioral and electrophysiological measurements across species [14]. Here we used evoked mass potentials to electrophysiologically quantify tuning (Q 10 ) in humans.…”