The presence of a social other motivates to invest effort while listening to speech-in-noise

Background: Mental effort has been gaining attention as an important facet of listening. A relevant factor influencing mental effort is motivation, which in turn can be influenced by reward. Reward has been found to enhance the mental effort that is spent while listening, as shown by an increased peak pupil dilation. Furthermore, social interactions have been suggested to be rewarding and may also increase the motivation to spend effort while listening. However, how social aspects influence listening effort has not been examined until now. In this study, we examined the influence of a social presence on listening effort.

Objectives: The aim of this study was to modify existing speech-in-noise paradigms to assess whether a social presence influences the amount of effort spent while listening. More specifically, we aimed to assess if doing a speech-in-noise task together with another individual, rather than alone, affected the task-evoked pupil dilation response. Furthermore, we examined if any potential effects were influenced by the difficulty of the task and the requirement to repeat the sentence.

Method: 34 Young, normal-hearing participants (10 males, 24 females) listened to Dutch sentences that were masked with a stationary noise masker and presented through a loudspeaker. The participants’ task alternated between repeating sentences (active condition) and not repeating sentences (passive condition). The participant did this either alone or together with another individual in the booth. When together, they repeated sentences in turn. The participant and the other individual did not know each other before the study. Participants performed the task at three intelligibility levels (20%, 50% and 80% sentences correct) in a blockwise fashion. During testing, pupil size was recorded as an objective outcome measure of listening effort.

Results: Both task difficulty and doing the task in the presence of another individual significantly increased peak pupil dilation (PPD). There was no interaction between task difficulty and the presence/absence of another individual on PPD. Furthermore, PPD was significantly lower in the passive conditions. This effect interacted with intelligibility. Lastly, performance on the listening task was affected by task difficulty, but not the physical presence/absence of another individual.

Conclusion: Increased PPD values suggest an increase in mental effort during listening when another participant is present, but only in the active condition (i.e. when the participants had to repeat the sentence). The effect of a social presence on pupil dilation seems to be independent of task difficulty.