Abstract
Amplitude modulations in the speech convey important acoustic information for speech perception. Auditory steady state response (ASSR) is thought to be physiological correlate of amplitude modulation perception. Limited research is available exploring association between ASSR and modulation detection ability as well as speech perception. Correlation of modulation detection thresholds (MDT) and speech perception in noise with ASSR was investigated in twofold experiments. 30 normal hearing individuals and 11 normal hearing individuals within age range of 18–24 years participated in experiments 1 and 2, respectively. MDTs were measured using ASSR and behavioral method at 60 Hz, 80 Hz, and 120 Hz modulation frequencies in the first experiment. ASSR threshold was obtained by estimating the minimum modulation depth required to elicit ASSR (ASSR-MDT). There was a positive correlation between behavioral MDT and ASSR-MDT at all modulation frequencies. In the second experiment, ASSR for amplitude modulation (AM) sweeps at four different frequency ranges (30–40 Hz, 40–50 Hz, 50–60 Hz, and 60–70 Hz) was recorded. Speech recognition threshold in noise (SRTn) was estimated using staircase procedure. There was a positive correlation between amplitude of ASSR for AM sweep with frequency range of 30–40 Hz and SRTn. Results of the current study suggest that ASSR provides substantial information about temporal modulation and speech perception.
Highlights
Speech acoustics have multiple temporal characteristics [1] among which temporal envelope conveys important acoustic cues for speech understanding
Auditory steady state response (ASSR)-modulation detection thresholds (MDT) was determined by obtaining the minimum modulation depth at which the ASSR could be recorded
Short time Fourier transform (STFT) analysis confirmed the ability of the auditory system to code sweeping modulation, which provides the physiological evidence for envelope tracking ability of auditory system
Summary
Speech acoustics have multiple temporal characteristics [1] among which temporal envelope conveys important acoustic cues for speech understanding. Temporal envelope of speech can be considered as a complex amplitude modulation, which is a sum of many modulators. Modulation sensitive neurons present in upper brainstem constitute this modulation filter bank [10]. Any process that affects the sensitivity of these neurons will lead to poor coding of temporal envelope and may lead to speech perception difficulties. It is necessary to assess the sensitivity to different modulation frequencies independently as different neurons respond to different modulation frequencies. Sensitivity to these modulations can be psychophysically assessed by measuring modulation detection thresholds (MDTs). MDT is obtained by estimating minimum modulation depth required to detect the presence of amplitude
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