Abstract
A unique sound that deviates from a repetitive background sound induces signature neural responses, such as mismatch negativity and novelty P3 response in electro-encephalography studies. Here we show that a deviant auditory stimulus induces a human pupillary dilation response (PDR) that is sensitive to the stimulus properties and irrespective whether attention is directed to the sounds or not. In an auditory oddball sequence, we used white noise and 2000-Hz tones as oddballs against repeated 1000-Hz tones. Participants' pupillary responses were recorded while they listened to the auditory oddball sequence. In Experiment 1, they were not involved in any task. Results show that pupils dilated to the noise oddballs for approximately 4 s, but no such PDR was found for the 2000-Hz tone oddballs. In Experiments 2, two types of visual oddballs were presented synchronously with the auditory oddballs. Participants discriminated the auditory or visual oddballs while trying to ignore stimuli from the other modality. The purpose of this manipulation was to direct attention to or away from the auditory sequence. In Experiment 3, the visual oddballs and the auditory oddballs were always presented asynchronously to prevent residuals of attention on to-be-ignored oddballs due to the concurrence with the attended oddballs. Results show that pupils dilated to both the noise and 2000-Hz tone oddballs in all conditions. Most importantly, PDRs to noise were larger than those to the 2000-Hz tone oddballs regardless of the attention condition in both experiments. The overall results suggest that the stimulus-dependent factor of the PDR appears to be independent of attention.
Highlights
The evidence obtained from sophisticated analysis of the MMN and P300 components (e.g., Escera et al, 1998; Polich, 2007) suggests that the acoustic novelty and change are detected through different underlying mechanisms such as the transient-detector mechanism that is related to preattentiveperceptual processing and revealed in N1 component, the change-detector mechanism that is related to stimulus-driven attention orienting and revealed in MMN and/or novelty P3a responses, and the attention mechanism that is related to subsequent memory processing in P3b response
Results showed that the mean pupillary dilation response (PDR) was larger for the noise oddballs than for the tone oddballs in all experiments [t(9) = 4.30, p = 0.002 in Experiment 1; F(1, 7) = 10.88, p = 0.013 in Experiment 2; F(1, 17) = 19.94, p < 0.001 in Experiment 3]
Whether and how the PDR for visual oddballs differed between the oddball types depended on the attention condition, as well as whether or not the visual oddballs were presented synchronously with the auditory oddballs
Summary
Pupillary responses under constant illumination are known to reflect emotional arousal (Partala and Surakka, 2003; Bradley et al, 2008) and cognitive functions such as attention (Privitera et al, 2010; Gabay et al, 2011; Binda et al, 2013; Eldar et al, 2013), memory (Goldinger and Papesh, 2012; Naber et al, 2013), processing load (Kahneman and Beatty, 1967; Beatty, 1982; Koelewijn et al, 2015), preference (Yoshimoto et al, 2014), and decision makingPupillary Dilation Response to Auditory Oddballs (Einhäuser et al, 2008, 2010; Preuschoff et al, 2011; Lavin et al, 2014). One major function of norepinephrine is to modulate the “fight-or-flight” response of the organism. In order for it to do so, the sympathetic nervous system needs to monitor any change in the environment, i.e., it must be sensitive to novel signals (e.g., Dayan and Yu, 2006). It is hypothesized that pupillary responses, reflecting the norepinephrine modulation, are sensitive to novel signals. The evidence obtained from sophisticated analysis of the MMN and P300 components (e.g., Escera et al, 1998; Polich, 2007) suggests that the acoustic novelty and change are detected through different underlying mechanisms such as the transient-detector mechanism that is related to preattentiveperceptual processing and revealed in N1 component, the change-detector mechanism that is related to stimulus-driven attention orienting and revealed in MMN and/or novelty P3a responses, and the attention mechanism that is related to subsequent memory processing in P3b response
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