Baseline pupil size encodes task-related information and modulates the task-evoked response in a speech-in-noise task

Abstract

Pupillometry data are commonly reported relative to a baseline value recorded in a controlled pre-task condition. In this study, the influence of the experimental design and the preparatory processing related to task difficulty on the baseline pupil size was investigated during a speech intelligibility in noise paradigm. Furthermore, the relationship between the baseline pupil size and the temporal dynamics of the pupil response was assessed. The analysis revealed strong effects of block presentation order, within-block sentence order and task difficulty on the baseline values. An interaction between signal-to-noise ratio and block order was found, indicating that baseline values reflect listener expectations arising from the order in which the different blocks were presented. Furthermore, the baseline pupil size was found to affect the slope, delay and curvature of the pupillary response as well as the peak pupil dilation. This suggests that baseline correction might be sufficient when reporting pupillometry results in terms of mean pupil dilation only, but not when a more complex characterization of the temporal dynamics of the response is considered. By clarifying which factors affect baseline pupil size and how baseline values interact with the task-evoked response, the results from the present study can contribute to a better interpretation of the pupillary response as a marker of cognitive processing.

Attention Mobilization as a Modulator of Listening Effort: Evidence from Pupillometry

“…Listeners develop expectations about upcoming listening challenges based on their knowledge of the probabilistic properties of English , the ease of listening to familiar voices (Papesh, Goldinger, & Hout, 2012), cues about upcoming acoustic conditions (e.g., noise that is informative of an upcoming SNR; Seropian et al, 2022), and experience with hearing loss that leads them to expect difficulty in most conversations (Ayasse & Wingfield, 2020). Furthermore, aligned with previous results (Knapen et al, 2016;Relaño-Iborra et al, 2022), baseline pupil size was observed to affect the shape (not just the height) of the pupil response across time. Thus, performing baseline correction on the TEPR without first examining the impact of the listening condition of interest on the pre-stimulus pupil size has the potential to minimize, eliminate, or potentially artifactually reverse expected effects of listening demands on the TEPR.…”

“…The present study examines the relationship between attention mobilization-how individuals prepare their attention in anticipation of an upcoming task-and listening effort allocation-how listeners deploy and use their attentional resources during the task-when listeners can anticipate the difficulty of the upcoming trial. Extending the results of Relaño-Iborra et al (2022), the present study focuses on trial-level variation in attention mobilization for a sustained listening task involving exact stimulus repetitions. Participants listened to three presentations of several 60-s long audiobook passages and were instructed to attend to one of two competing speakers in an easy or difficult listening situation, determined by SNR.…”

“…Recently, Relaño-Iborra et al, (2022) examined the relationship between baseline pupil size and the TEPR, using pupil recordings from a speech intelligibility task with blocked SNRs (Wendt et al, 2018). The authors found that baseline pupil size was not only modulated by timeon-task effects and SNR, but also significantly modulated the shape the shape of the TEPR derived from a growth curve analysis (GCA) model.…”

“…Furthermore, studies that have examined the TEPR as a measure of listening effort have predominantly utilized trial-by-trial baseline pupil size to account for trial-and participant-level variability -either to be subtracted from or to normalize TEPR values (Mathôt et al, 2018). However, as noted, baseline pupil size has been observed to not only affect the height of the TEPR, but also its shape (Knapen et al, 2016;Relaño-Iborra et al, 2022). Previous research has also suggested that baseline pupil size and the TEPR may reflect different processes (Micula et al, 2021;2022).…”

300 Hz transcutaneous auricular vagus nerve stimulation (taVNS) impacts pupil size nonlinearly as a function of intensity

“…During active tasks (i.e., those that elicit behavioral responses to stimuli), the magnitude of the task-evoked pupil response (TEPR) would be expected to be maximal at moderate levels of LC activity, given the nonmonotonic (inverted-U shaped) relationship between LC phasic and tonic activity (Aston-Jones & Cohen, 2005). Phasic peak pupil dilation following VNS onset may likewise be expected to vary as a function of prestimulus baseline pupil size (Johns et al, in press; Relaño-Iborra et al, 2022), which reflects tonic LC activity (Mridha et al, 2021). However, a monotonic relationship between pupil dilation and LC activity might be expected for passive tasks, given evidence from mice that shows pupil dilation to increase monotonically with LC spiking rate (Megemont et al, 2022) as well as iVNS intensity, pulse width, and stimulation rate (Mridha et al, 2021).…”