Abstract
BackgroundFrequency selectivity (FS) of the auditory system is established at the level of the cochlea and it is important for the perception of complex sounds. Although direct measurements of cochlear FS require surgical preparation, it can also be estimated with the measurements of otoacoustic emissions or behavioral tests, including stimulus frequency otoacoustic emission suppression tuning curves (SFOAE STCs) or psychophysical tuning curves (PTCs). These two methods result in similar estimates of FS at low probe levels. As the compressive nonlinearity of cochlea is strongly dependent on the stimulus intensity, the sharpness of tuning curves which is relevant to the cochlear nonlinearity will change as a function of probe level. The present study aims to investigate the influence of different probe levels on the relationship between SFOAE STCs and PTCs.MethodsThe study included 15 young subjects with normal hearing. SFOAE STCs and PTCs were recorded at low and moderate probe levels for frequencies centred at 1, 2, and 4 kHz. The ratio or the difference of the characteristic parameters between the two methods was calculated at each probe level. The effect of probe level on the ratio or the difference between the parameters of SFOAE STCs and PTCs was then statistically analysed.ResultsThe tuning of SFOAE STCs was significantly positively correlated with the tuning of the PTCs at both low and moderate probe levels; yet, at the moderate probe level, the SFOAE STCs were consistently broader than the PTCs. The mean ratio of sharpness of tuning at low probe levels was constantly around 1 while around 1.5 at moderate probe levels.ConclusionsProbe level had a significant effect on the sharpness of tuning between the two methods of estimating FS. SFOAE STC seems a good alternative measurement of PTC for FS assessment at low probe levels. At moderate probe levels, SFOAE STC and PTC were not equivalent measures of the FS in terms of their bandwidths. Because SFOAE STCs are not biased by higher levels auditory processing, they may represent cochlear FS better than PTCs.
Highlights
Frequency selectivity (FS) of the auditory system is established at the level of the cochlea and it is important for the perception of complex sounds
At both low and moderate Lps, the ftip shifted slightly higher than fp for Stimulus frequency otoacoustic emission (SFOAE) suppression tuning curve (STC) whereas the ftip of psychophysical tuning curves (PTC) coincided with fp
The SFOAE STCs were tuned more broadly at the moderate Lp than that at low Lp. For both low and moderate Lps, low-frequency side (LF) slopes for SFOAE STCs were shallower than those for PTCs but high-frequency side (HF) slopes were similar for SFOAE STCs compared with PTCs
Summary
Frequency selectivity (FS) of the auditory system is established at the level of the cochlea and it is important for the perception of complex sounds. Direct measurements of cochlear FS require surgical preparation, it can be estimated with the measurements of otoacoustic emissions or behavioral tests, including stimulus frequency otoacoustic emission suppression tuning curves (SFOAE STCs) or psychophysical tuning curves (PTCs). These two methods result in similar estimates of FS at low probe levels. Frequency selectivity (FS), an ability of decomposing frequency components of a complex stimulus, plays a crucial role in the auditory perception [1] It can be assessed noninvasively in humans by measurements of psychophysical tuning curves (PTCs), where the masked threshold for a fixed tone is tracked across a range of masker frequencies [2,3,4]. Regardless of the uncertainty of the tendency for PTCs’ tuning at higher probe levels, PTCs’ subjectivity remains a limitation for clinical use and an objective method for FS estimate is required
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