Emerging Self-Representation Presents a Challenge for Perspective Tracking in Infancy

The capacity to track another’s perspective is present from early in life, with young infants ostensibly able to predict others’ behaviour even when the self and other perspective are at odds. Yet, infants’ abilities are difficult to reconcile with the well-documented challenge that older children face when they need to ignore their own perspective. Here we provide evidence that it is the emergence of self-representation, from around 18 months, that likely creates a perspective conflict between self and other. Using mirror self-recognition as a measure of self-awareness and pupil dilation to index conflict processing, our results show that mirror recognisers perceive greater conflict than non-recognisers when viewing a scenario in which the self and other have divergent perspectives, specifically when the conflict between self and other is salient. These results suggest that infants’ perspective tracking abilities may benefit from an initial absence of self-representation.

Task-Induced Mental Fatigue and Motivation Influence Listening Effort as Measured by the Pupil Dilation in a Speech-in-Noise Task

Objectives: Listening effort and fatigue are common complaints among individuals with hearing impairment (HI); however, the underlying mechanisms, and relationships between listening effort and fatigue are not well understood. Recent quantitative research suggests that the peak pupil dilation (PPD), which is commonly measured concurrent to the performance of a speech-in-noise task as an index of listening effort, may be informative of daily-life fatigue, but it remains unknown whether the same is true for task-induce fatigue. As fatigue effects are known to manifest differently depending on motivation, the main aim of the present study was to experimentally investigate the interactive effects of task-induced fatigue and motivation on the PPD. Design: In a pre-/post- fatigue within-subject design, 18 participants with normal hearing (NH) engaged in a 98-trial-long speech-in-noise task (i.e., a load sequence, approximately 40 min. long), which either excluded or included additional memory demands (light vs. heavy load sequence). Before and after the load sequence, baseline pupil diameter (BPD) and PPD were measured during shorter probe blocks of speech-in-noise tasks. In these probe blocks, if participants correctly repeated more than 60% of the keywords, they could win vouchers of either 20 or 160 Danish krones worth (low incentive vs. high incentive). After each probe block, participants reported their invested effort, tendency for quitting, and perceived performance. Results: The BPD in anticipation of listening declined from pre- to post-load sequence, suggesting an overall decrease in arousal, but the decline did not scale with the magnitude of the load sequence, nor with the amount of monetary incentive. Overall, there was larger pre- to post-load sequence decline in PPD when the load sequence was heavy and when the monetary incentives were low. Post-hoc analyses showed that the decline in PPD was only significant in the heavy-load sequence-low reward condition. The speech-in-noise task performance, self-reported effort, and self-reported tendency to quit listening did not change with the experimental conditions. Conclusions This is the first study to investigate the influence of task-induced fatigue on BPD and PPD. Whereas BPD was not sensitive to the magnitude of previous load sequence and monetary incentives, the decline in PPD from pre- to post- load sequence was significant after the heavy load sequence when the offered monetary incentives were low. This result supports the understanding that fatigue and motivation interactively influence listening effort.

Comparison of Pupil Dilation Responses to Unexpected Sounds in Monkeys and Humans

Pupil dilation in response to unexpected stimuli has been well documented in human as well as in non-human primates; however, this phenomenon has not been systematically compared between the species. This analogy is also crucial for the role of non-human primates as an animal model to investigate neural mechanisms underlying the processing of unexpected stimuli and their evoked pupil dilation response. To assess this qualitatively, we used an auditory oddball paradigm in which we presented subjects a sequence of the same sounds followed by occasional deviants while we measured their evoked pupil dilation response (PDR). We used deviants (a frequency deviant, a pink noise burst, a monkey vocalization and a whistle sound) which differed in the spectral composition and in their ability to induce arousal from the standard. Most deviants elicited a significant pupil dilation in both species with decreased peak latency and increased peak amplitude in monkeys compared to humans. A temporal Principal Component Analysis (PCA) revealed two components underlying the PDRs in both species. The early component is likely associated to the parasympathetic nervous system and the late component to the sympathetic nervous system, respectively. Taken together, the present study demonstrates a qualitative similarity between PDRs to unexpected auditory stimuli in macaque and human subjects suggesting that macaques can be a suitable model for investigating the neuronal bases of pupil dilation. However, the quantitative differences in PDRs between species need to be investigated in further comparative studies.

Sensory suppression and increased neuromodulation during actions disrupt memory encoding of unpredictable self-initiated stimuli

Actions modulate sensory processing by attenuating responses to self- compared to externally-generated inputs, which is traditionally attributed to stimulus-specific motor predictions. Yet, suppression has been also found for stimuli merely coinciding with actions, pointing to unspecific processes that may be driven by neuromodulatory systems. Meanwhile, the differential processing for self-generated stimuli raises the possibility of producing effects also on memory for these stimuli, however, evidence remains mixed as to the direction of the effects. Here, we assessed the effects of actions on sensory processing and memory encoding of concomitant, but unpredictable sounds, using a combination of self-generation and memory recognition task concurrently with EEG and pupil recordings. At encoding, subjects performed button presses that half of the time generated a sound (motor-auditory; MA) and listened to passively presented sounds (auditory-only; A). At retrieval, two sounds were presented and participants had to respond which one was present before. We measured memory bias and memory performance by having sequences where either both or only one of the test sounds were presented at encoding, respectively. Results showed worse memory performance — but no differences in memory bias — and attenuated responses and larger pupil diameter for MA compared to A sounds. Critically, the larger the sensory attenuation and pupil diameter, the worse the memory performance for MA sounds. Nevertheless, sensory attenuation did not correlate with pupil dilation. Collectively, our findings suggest that sensory attenuation and neuromodulatory processes coexist during actions, and both relate to disrupted memory for concurrent, albeit unpredictable sounds.

Listening Effort in Cochlear Implant Users: The Effect of Speech Intelligibility, Noise Reduction Processing, and Working Memory Capacity on the Pupil Dilation Response

Purpose: This study aimed to evaluate the effect of speech recognition performance, working memory capacity (WMC), and a noise reduction algorithm (NRA) on listening effort as measured with pupillometry in cochlear implant (CI) users while listening to speech in noise. Method: Speech recognition and pupil responses (peak dilation, peak latency, and release of dilation) were measured during a speech recognition task at three speech-to-noise ratios (SNRs) with an NRA in both on and off conditions. WMC was measured with a reading span task. Twenty experienced CI users participated in this study. Results: With increasing SNR and speech recognition performance, (a) the peak pupil dilation decreased by only a small amount, (b) the peak latency decreased, and (c) the release of dilation after the sentences increased. The NRA had no effect on speech recognition in noise or on the peak or latency values of the pupil response but caused less release of dilation after the end of the sentences. A lower reading span score was associated with higher peak pupil dilation but was not associated with peak latency, release of dilation, or speech recognition in noise. Conclusions: In CI users, speech perception is effortful, even at higher speech recognition scores and high SNRs, indicating that CI users are in a chronic state of increased effort in communication situations. The application of a clinically used NRA did not improve speech perception, nor did it reduce listening effort. Participants with a relatively low WMC exerted relatively more listening effort but did not have better speech reception thresholds in noise.

Early phase of pupil dilation is mediated by the peripheral parasympathetic pathway

Pupil diameter fluctuates in association with changes in brain states induced by the neuromodulator systems. However, it remains unclear how the neuromodulator systems control the activity of the iris sphincter (constrictor) and dilator muscles to change the pupil size. The present study compared temporal patterns of pupil dilation during movement when each muscle was pharmacologically manipulated in the human eye. When the iris sphincter muscle was blocked with tropicamide, the latency of pupil dilation was delayed and the magnitude of pupil dilation was reduced during movement. In contrast, when the iris dilator muscle was continuously stimulated with phenylephrine, the latency and magnitude of rapid pupil dilation did not differ from the untreated control eye, but sustained pupil dilation was reduced until the end of movement. These results suggest that the iris sphincter muscle, which is under the control of the parasympathetic pathway, is quickly modulated by the neuromodulator system and plays a major role in rapid pupil dilation. However, the iris dilator muscle receives signals from the neuromodulator system with a slow latency and is involved in maintaining sustained pupil dilation.