title: The influence of probe level on the tuning of stimulus frequency otoacoustic emissions and behavioral test in human.
abstract: BACKGROUND
  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. 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.
  
  
  METHODS
  The 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.
  
  
  RESULTS
  The 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.
  
  
  CONCLUSIONS
  Probe 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.
authors.affiliation: Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, 100084, China.
authors.forename: Yao
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, 100084, China. gongqin@mail.tsinghua.edu.cn.|Research Center of Biomedical Engineering, Graduate School at Shenzhen, Tsinghua University, Shenzhen, 518055, China. gongqin@mail.tsinghua.edu.cn.
authors.forename: Qin
authors.initials: Q
authors.lastname: Gong
authors.affiliation: Tsinghua National Laboratory for Information Science and Technology (TNList), Tsinghua University, Beijing, 100084, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Zhang
mesh_terms: D000328:Adult; D000067290:Behavior Rating Scale; D005260:Female; D006801:Humans; D008297:Male; D017084:Otoacoustic Emissions, Spontaneous; D055815:Young Adult
keywords: Frequency selectivity (FS); Probe level; Psychophysical tuning curves (PTCs); Stimulus frequency otoacoustic emission suppression tuning curves (SFOAE STCs)