Pupil dilation during speech production in noise is modulated by masker type
Pupil dilation is affected by both sensory and motor events. In speech perception, pupil dilation can indicate increased listening effort, as induced for instance by decreasing the signal-to-noise ratio. Moreover, a larger pupil dilation has been observed for speech masked by a competing speaker, compared to speech masked by stationary noise. In speech production, pupil dilation has shown to be modulated by language processing, but the literature is sparse. For instance, it is unclear whether masker type similarly affects pupil dilation when speech is produced in noise.
In the current study, twenty-four normal-hearing participants were tasked to read out loud sentences that were presented on a screen. Simultaneously, background noise was played, which consisted of either a competing speaker, speech-shaped stationary or fluctuating noise at similar loudness levels. In a control condition, no background noise was played. Pupil size was recorded for the duration of each trial and acoustic features such as intensity and spectral tilt were extracted from the verbal response.
Our results confirmed previous findings showing that intensity is increased and spectral tilt decreased for speech produced in stationary masking when compared to fluctuating and competing-speaker masking. Conversely, we found larger pupil dilation for competing-speaker masking, similar to results from speech perception studies. Despite larger vocal effort found for stationary masking, pupil dilation was more sensitive to the cognitive effort imposed by the competing speaker. Since pupil dilation has been shown to be affected by movement intensity, this finding appears to indicate that cognitive effects outweigh articulatory effects. The results demonstrate the potential use of pupillometry in speech production studies.