Dual-task repetition alters event-related brain potentials and task performance

Abstract

Objective

We examined the modulation of event-related brain potentials (ERPs) and the accuracy of sensori-motor coordination on short-term repetition of the concurrent performance of a somatosensory discrimination (oddball) task and a visuo-motor tracking task.

Methods

The subjects concurrently performed visuomotor tracking and somatosensory oddball tasks. In the dual-task condition, the subjects performed the visuomotor tracking and somatosensory oddball tasks concurrently for about an hour. In the oddball-only condition, they performed just the oddball task for the same period.

Results

Tracking performance improved with task repetition. The amplitude of the P300 elicited by somatosensory stimulation in the oddball-only condition decreased significantly with task repetition, whereas in the dual-task condition, it showed a complex pattern of change. The earlier responses were decreased in amplitude in the dual-task condition compared to the oddball-only condition, and gradually decreased with task repetition in both conditions.

Conclusions

Dynamic changes in ERPs and task performance with dual-task repetition support the idea that dual-task repetition produces changes in resource allocation following the automation of stimulus processing in addition to so-called habituation.

Significance

This study also provides evidence for use of ERP amplitudes as physiological indices of functionally different types of resources.

Introduction

Everyday life often requires the performance of two or more tasks simultaneously. A good example comes from driving. A beginner driver can have difficulty performing multiple tasks, e.g., monitoring the road through the windshield, turning the steering wheel, manipulating the gas pedal and brake, and looking at the speedometer. However, a skilled driver can perform multiple sensori-motor tasks smoothly. How then do people learn to perform these complex multiple tasks?

Habituation is one reflection of sensory-motor learning. The P300 of event-related brain potentials (ERPs) (Donchin and Coles, 1988, Katayama and Polich, 1999, Polich, 2007) decreases in amplitude with task or stimulus repetition, i.e., habituation, because the updating of the stimulus environment neural model becomes automated (Polich and McIsaac, 1994, Ravden and Polich, 1998, Ravden and Polich, 1999, Romero and Polich, 1996). The amplitude of the earlier response, the N1, elicited by auditory, visual and somatosensory stimulation is also decreased with stimulus repetition (Budd et al., 1998, Callaway, 1973, Kida et al., 2004c, Kida et al., 2006b, Ritter et al., 1968, Tomberg et al., 1989). According to the orienting response theory (Sokolov, 1960, Sokolov, 1963), habituation reflects the establishment or updating of a neuronal model or template of a stimulus following repeated exposure. In this context, ERP response habituation refers to a decrement in response amplitude resulting from a loss of novelty associated with the building of a neuronal model following repetition of a stimulus (Budd et al., 1998). According to this theory, the development of automatic processing with task repetition in an effortful task leads to an increased amount of resources available for the other task being performed if the resources have a modality-nonspecific feature. These habituation experiments have been, however, carried out mainly in a single-task situation.

Dual-task studies have found that the amplitude of the P300 elicited by target stimuli in an oddball task decreased during the concurrent performance of the other task, and showed a further decrease when the difficulty of the latter task increased. These results have demonstrated that the amplitude of the P300 reflects the amount of perceptual-central resources allocated to a given task (Isreal et al., 1980a, Isreal et al., 1980b, Isreal et al., 1980c, Kida et al., 2004a, Kramer et al., 1983, Kramer et al., 1985, Murray and Janelle, 2007, Sirevaag et al., 1989, Wickens et al., 1983, Wickens, 1980, Wickens, 1991). In general, the P300 is a modality-nonspecific component which can be elicited by stimulation of any sense, especially by infrequent target stimuli in a sequence of frequent standard stimuli. This nonspecific feature of the P300 suggested to us that the resource manifested by the P300 amplitude also shows modality-nonspecific features. Using a dual-task situation across different senses where a visuomotor tracking task and a somatosensory oddball task were performed simultaneously, a previous ERP study found that the amplitude of P300 elicited by somatosensory stimulation reflects modality-nonspecific resources (Kida et al., 2004a). A dual-task experiment using a visual memory search task and a pursuit step tracking task have reported that reductions in the slope of the memory set function with task repetition occurred earlier for P300 latency than for reaction time (RT), assuming that the stimulus evaluation process became automated more rapidly than the response selection components of memory search (Kramer et al., 1991). However, there have been no additional evidence for ERP changes with dual-task repetition, and thus it remains an open question how the ERPs are modulated by dual-task repetition.

In the present study, we examined the effect of repetition of dual task on the somatosensory ERPs (P100, N140 and P300) and task performance in a dual-task situation where we have previously examined a relationship between resource allocation and somatosensory ERPs (Kida et al., 2004a). Two conditions were conducted on separate days. In the dual-task condition, a visuomotor force-tracking task and a somatosensory oddball task were performed concurrently. In the oddball-only condition, the somatosensory oddball task was just performed. Tracking accuracy in the visuo-motor tracking task, and ERPs and reaction time in the oddball task were measured.