Stimulus Variability Affects the Amplitude of the Auditory Steady-State Response

Michael I G Simpson,Gary G R Green,Sam R Johnson,Garreth Prendergast,William P Woods,Stefan J Kiebel

doi:10.1371/journal.pone.0034668

Michael I G Simpson, Gary G R Green + Show 4 more

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https://doi.org/10.1371/journal.pone.0034668

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Journal: PloS one	Publication Date: Apr 3, 2012
Citations: 28	License type: CC BY 4.0

Affiliation: University of York, Swinburne University of Technology

Abstract

In this study we investigate whether stimulus variability affects the auditory steady-state response (ASSR). We present cosinusoidal AM pulses as stimuli where we are able to manipulate waveform shape independently of the fixed repetition rate of 4 Hz. We either present sounds in which the waveform shape, the pulse-width, is fixed throughout the presentation or where it varies pseudo-randomly. Importantly, the average spectra of all the fixed-width AM stimuli are equal to the spectra of the mixed-width AM. Our null hypothesis is that the average ASSR to the fixed-width AM will not be significantly different from the ASSR to the mixed-width AM. In a region of interest beamformer analysis of MEG data, we compare the 4 Hz component of the ASSR to the mixed-width AM with the 4 Hz component of the ASSR to the pooled fixed-width AM. We find that at the group level, there is a significantly greater response to the variable mixed-width AM at the medial boundary of the Middle and Superior Temporal Gyri. Hence, we find that adding variability into AM stimuli increases the amplitude of the ASSR. This observation is important, as it provides evidence that analysis of the modulation waveform shape is an integral part of AM processing. Therefore, standard steady-state studies in audition, using sinusoidal AM, may not be sensitive to a key feature of acoustic processing.

Highlights

The auditory steady-state response (ASSR) is a clinically robust tool [1,2,3], which is used to study the dynamics of cortical following responses to sinusoidally amplitude modulated stimuli, and may be recorded with both EEG [4,5,6] and MEG [7,8,9]
With respect to the locus in the region of interest (ROI) at which we find the significant difference in ASSR between the mixed-width and fixedwidth amplitude modulation (AM), it is at the medial boundary of the STG and MTG, at the Montreal Neurological Institute (MNI) coordinate 46, 226
We find that stimulus variability does affect the amplitude of the auditory steady-state response

Summary

Introduction

The auditory steady-state response (ASSR) is a clinically robust tool [1,2,3], which is used to study the dynamics of cortical following responses to sinusoidally amplitude modulated stimuli, and may be recorded with both EEG [4,5,6] and MEG [7,8,9]. Behavioural studies have shown that preexposure to AM affects AM detection thresholds, with both sinusoidal and non-sinusoidal adapting AM stimuli [10,11,12,13], and that the degree of adaptation is dependent on the waveform shape [11]. Time-reversing asymmetric triangular AM, to generate ‘ramped’ and ‘damped’ AM, results in stimuli that have different behavioural detection thresholds but identical modulation spectra [15,16]. A comparable finding was observed by Prendergast et al [18] using MEG to study the ASSR to different widths of cosinusoidal pulsed AM stimuli, who show that the magnitude of the ASSR is dependent on the waveform shape rather than the modulation spectra, and is selective for the most prevalent waveform shapes in speech [19]

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