Investigation of the optimal time interval between task-irrelevant auditory probes for evaluating mental workload in the shortest possible time.

Event-related brain potentials (ERPs) elicited by auditory stimuli unrelated to a current visual-cognitive task (i.e., task-irrelevant auditory probes) can be used to evaluate the level of mental workload. Towards the evaluation of workload in the shortest possible time, the present study with a multiple-stimulus paradigm (Takeda and Kimura, 2014, Int. J. Psychophysiol.) examined whether manipulating time intervals between probes could improve the temporal resolution in evaluating workload. Probes were presented in four interval conditions as a combination of two mean interval lengths [long (600 ms) vs. short (300 ms)] and two interval variabilities [variable (five levels) vs. fixed], while participants were performing a driving game at slow and fast speeds (i.e., imposing low and high workload, respectively). For each interval condition, the minimum data length required to obtain a significant difference in the amplitude of ERPs (i.e., auditory N1 and P2) between the slow and fast driving tasks was estimated. The N1 difference was significant in all four interval conditions but the required minimum data lengths to observe this difference did not greatly differ across the interval conditions (about 60-90 s). The P2 difference was significant only in the long-variable condition and the required minimum data length was about 120 s. These results suggest that, at least with a multiple-stimulus paradigm, manipulations of time intervals between probes did not greatly improve the temporal resolution in evaluating mental workload; at present, long-variable intervals would be optimal for evaluating mental workload in detail.

Attenuation of auditory N2 for self-modulated tones during continuous actions.

Event-related potentials elicited by tones generated by one's own discrete actions (e.g., button presses) are attenuated compared to those elicited by tones generated externally. The present study investigated whether ERP attenuation would occur when the timing or pitch of tones is modulated by continuous actions, as for such actions, a weak association between actions and their auditory consequences is assumed. In a modulation condition, participants modulated the time interval between tones (Experiment 1) or the pitch of tones (Experiment 2) by turning a steering wheel. In a listening condition, participants listened to the same tones as in the modulation condition without any action. The results revealed that the amplitude of N2 elicited by tones decreased in the modulation compared to listening conditions, consistently in the two experiments, suggesting relatively higher-order auditory processing can be mainly influenced by the prediction of action consequences when continuous actions modulate features of auditory stimuli.

Increased visual task difficulty enhances attentional capture by both visual and auditory distractor stimuli.

Previous studies using a three-stimulus oddball task have shown the amplitude of P3a elicited by distractor stimuli increases when perceptual discrimination between standard and target stimuli becomes difficult. This means that the attentional capture by the distractor stimuli is enhanced along with an increase in task difficulty. So far, the increase of P3a has been reported when standard, target, and distractor stimuli were presented within one sensory modality (i.e., visual or auditory). In the present study, we further investigated whether or not the increase of P3a can also be observed when the distractor stimuli are presented in a different modality from the standard and target stimuli. Twelve participants performed a three-stimulus oddball task in which they were required to discriminate between visual standard and target stimuli. As the distractor stimuli, either another visual stimulus or an auditory stimulus was presented in separate blocks. Visual distractor stimuli elicited P3a, and its amplitude increased when visual standard/target discrimination was difficult, replicating previous findings. Auditory distractor stimuli elicited P3a, and importantly, its amplitude also increased when visual standard/target discrimination was difficult. This result means that attentional capture by distractor stimuli can be enhanced even when the distractor stimuli are presented in a different modality from the standard and target stimuli. Possible mechanisms and implications are discussed in terms of the relative saliency of distractor stimuli, influences of temporal/spatial attention, and the load involved in a task.

Aftermath of 3/11: earthquakes and involuntary attentional orienting to sudden ambient sounds.

Due to the Great East Japan Earthquake on 11 March 2011 and the following long-term earthquake swarm, many people living in the earthquake-affected areas have developed mental stress, even though clinically-diagnosable symptoms may not be apparent. Concurrently, many unusual reports have emerged in which persons complain of abnormally increased sensitivity to sudden ambient sounds during their daily lives (e.g., the sound of the washing machine on spin cycle). By recording event-related potentials to various sudden ambient sounds from young adults living in the affected areas, we found that the level of earthquake-induced mental stress, as indexed by the hyperarousal symptoms of posttraumatic stress disorder, was positively related to the magnitude of P3a to sudden ambient sounds. These results reveal a strong relationship between mental stress and enhanced involuntary attentional orienting in a large majority of trauma-exposed people without diagnosable symptoms.