Effect of Speech Rate on Neural Tracking of Speech.

Jana Annina Müller,Dorothea Wendt,Thomas Brand,Birger Kollmeier,Stefan Debener

doi:10.3389/fpsyg.2019.00449

Abstract

Speech comprehension requires effort in demanding listening situations. Selective attention may be required for focusing on a specific talker in a multi-talker environment, may enhance effort by requiring additional cognitive resources, and is known to enhance the neural representation of the attended talker in the listener’s neural response. The aim of the study was to investigate the relation of listening effort, as quantified by subjective effort ratings and pupil dilation, and neural speech tracking during sentence recognition. Task demands were varied using sentences with varying levels of linguistic complexity and using two different speech rates in a picture-matching paradigm with 20 normal-hearing listeners. The participants’ task was to match the acoustically presented sentence with a picture presented before the acoustic stimulus. Afterwards they rated their perceived effort on a categorical effort scale. During each trial, pupil dilation (as an indicator of listening effort) and electroencephalogram (as an indicator of neural speech tracking) were recorded. Neither measure was significantly affected by linguistic complexity. However, speech rate showed a strong influence on subjectively rated effort, pupil dilation, and neural tracking. The neural tracking analysis revealed a shorter latency for faster sentences, which may reflect a neural adaptation to the rate of the input. No relation was found between neural tracking and listening effort, even though both measures were clearly influenced by speech rate. This is probably due to factors that influence both measures differently. Consequently, the amount of listening effort is not clearly represented in the neural tracking.

Highlights

Speech comprehension in difficult listening environments can be very demanding and effortful
The Bonferroni corrected t-test as post hoc analysis showed that the speech reception threshold for 80% (SRT80) of the SVO sentence structure was significantly lower than the SRT80 of the OVS (p = 0.03, mean difference −1.26, 95%-CI [−2.41, −0.12]) and ambiguous object-verb-subject (ambOVS) (p = 0.02, mean difference −1.51, 95%-CI [−2.83, −0.195]) sentence structure
Since selective attention showed an influence on neural tracking, we investigated whether listening effort caused by linguistic complexity and speech rate and quantified by subjective ratings and pupillometry is reflected on neural tracking as well (H5)

Summary

Introduction

Speech comprehension in difficult listening environments can be very demanding and effortful. The necessity to selectively steer attention may require more cognitive resources and enhance listening effort Factors such as attention influence listening effort, and result in a stronger representation of the attended speech in the listener’s neural response (e.g., Mesgarani and Chang, 2012; O’Sullivan et al, 2014). Increasing background noise and decreasing intelligibility result in an increase in pupil dilation, indicating greater listening effort (Zekveld et al, 2010, 2011) This is only the case until a certain point: recent studies show signs that listeners “give up” at performance levels below 50% correct recognition, i.e., the peak pupil dilation decreases at low performance rates (Wendt et al, 2018). The review shows a lack of consistency and standardization across studies that measured listening effort

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Conclusion