Does Cognitive Load Affect Measures of Consciousness?

Measures of consciousness based on signal diversity of spontaneous or perturbed EEG are not affected by cognitive load, whereas the P300b event-related potential is. In 12 participants, EEG was recorded during passive attention to sensory stimuli and during a demanding working memory task. The P300b, which reflects conscious awareness of auditory deviance, was significantly reduced by the concurrent memory task. In contrast, several signal diversity measures, including the perturbational complexity index, were unchanged. These findings suggest that signal diversity measures may remain reliable for assessing consciousness in clinical settings where attention, sensory processing, or command following are impaired.

Study at a glance

Abstract

Developing and testing methods for reliably measuring the state of consciousness of individuals is important for both basic research and clinical purposes. In recent years, several promising measures of consciousness, grounded in theoretical developments, have been proposed. However, the degrees to which these measures are affected by changes in brain activity that are not related to changes in the degree of consciousness has not been well tested. In this study, we examined whether several of these measures are modulated by the loading of cognitive resources. We recorded electroencephalography (EEG) from 12 participants in two conditions: (1) while passively attending to sensory stimuli related to the measures and (2) during increased cognitive load consisting of a demanding working memory task. We investigated whether a set of proposed objective EEG-based measures of consciousness differed between the passive and the cognitively demanding conditions. The P300b event-related potential (sensitive to conscious awareness of deviance from an expected pattern in auditory stimuli) was significantly affected by concurrent performance on a working memory task, whereas various measures based on signal diversity of spontaneous and perturbed EEG were not. Because signal diversity-based measures of spontaneous or perturbed EEG are not sensitive to the degree of cognitive load, we suggest that these measures may be used in clinical situations where attention, sensory processing, or command following might be impaired.