Tips Of Psychophysical Tuning Curves Research Articles

Relationship between psychophysical tuning curves and critical bandwidths.

In Experiment I, band noises were used as signals and pure tones were used as maskers. The conventional psychophysical tuning curves (PTCs) present the following characteristics depending on the signal level; slopes of the PTC are steeper than those of the auditory nerve fibers frequency threshold curve (FTC). This result from the large effect of the combination tones and, especially, of the off-frequency listening. Bandwidths of PTC do not depend on both signal levels and duration, but they are narrower than the equivalent rectangular bandwidth (ERB) of auditory filters. Masked thresholds at tips of PTC are affected by the temporal integration of signal sound at signal levels of 10- and 20-dB SL, but are not affected at 30-dB SL. This implies a close relation between PTCs and critical bandwidths (CB-widths). In Experiment II, pure tones were used as signals and band noise were used as maskers. The low- and high-frequency slopes were steeper in Experiment I. The flat parts of the masked threshold at the tips of curves become broader as the signal duration increased. No such flattening was found at a 30-dB signal level, irrespective of signal duration. The results of Experiment II coincide with the prediction derived from the excitation-pattern model. Masked thresholds at the tip of PTC were the same as in Experiment I. The conventional PTC represents the psychological frequency selectivity, and its 3-dB bandwidth corresponds to the CB-width. However, the quantitative properties depend greatly upon the bandwidths of the band noises used as signals or maskers.

High-Level Psychophysical Tuning Curves

Forward-masked psychophysical tuning curves (PTCs) were obtained for 1000-Hz probe tones at multiple probe levels from one ear of 26 normal-hearing listeners and from 24 ears of 21 hearing-impaired listeners with cochlear hearing loss. Comparisons between normal-hearing and hearing-impaired PTCs were made at equivalent masker levels near the tips of PTCs. Comparisons were also made of PTC characteristics obtained by fitting each PTC with three straight-line segments using least-squares fitting procedures. Abnormal frequency resolution was revealed only as abnormal downward spread of masking. The low-frequency slopes of PTCs from hearing-impaired listeners were not different from those of normal-hearing listeners. That is, hearing-impaired listeners did not demonstrate abnormal upward spread of masking when equivalent masker levels were compared. Ten hearing-impaired ears demonstrated abnormally broad PTCs, due exclusively to reduced high-frequency slopes in their PTCs. This abnormal downward spread of masking was observed only in listeners with hearing losses greater than 40 dB HL. From these results, it would appear that some, but not all, cochlear hearing losses greater than 40dB HL influence the sharp tuning capabilities usually associated with outer hair cell function.

Frequency resolution at equivalent sound‐pressure levels in normal‐hearing and hearing‐impaired listeners

Forward‐masked psychophysical tuning curves (PTCs) were obtained for multiple‐level 1000‐Hz probe tones from 15 normal‐hearing and 23 hearing‐impaired ears with cochlear hearing loss. Comparisons between normal‐hearing and hearing‐impaired PTC characteristics were made at equivalent masker levels near the tips of PTCs. The low‐frequency slopes of PTCs from hearing‐impaired listeners were not different from those of normal‐hearing listeners, i.e., hearing‐impaired listeners did not demonstrate abnormal upward spread of masking when equivalent masker levels were compared. Only 8 of the 23 hearing‐impaired listeners demonstrated abnormally broad PTCs, due exclusively to abnormally gradual high‐frequency slopes to their PTCs. This demonstration of abnormal downward spread of masking was only observed in listeners with hearing losses greater than 40 dB HL. From these results, it would appear that some, but not all, cochlear hearing losses greater than 40 dB HL influence the sharp tuning capabilities usually associated with outer hair‐cell function. The restriction of abnormal findings in this study to the high‐frequency sides of PTCs alone is likely due to the use of equivalent masker‐level comparisons, and also to the use of flat‐envelope nonsimultaneous maskers rather than fluctuating‐envelope simultaneous masker. [Work supported by NINCDS.]