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This paper proposes a scheme for assessing the alertness levels of an individual using simultaneous acquisition of multimodal physiological signals and fusing the information into a single metric for quantification of alertness. The system takes electroencephalogram, high-speed image sequence, and speech data as inputs. Certain parameters are computed from each of these measures as indicators of alertness and a metric is proposed using a fusion of the parameters for indicating alertness level of an individual at an instant. The scheme has been validated experimentally using standard neuropsychological tests, such as the Visual Response Test (VRT), Auditory Response Test (ART), a Letter Counting (LC) task, and the Stroop Test. The tests are used both as cognitive tasks to induce mental fatigue as well as tools to gauge the present degree of alertness of the subject. Correlation between the measures has been studied and the experimental variables have been statistically analyzed using measures such as multivariate linear regression and analysis of variance. Correspondence of trends obtained from biomarkers and neuropsychological measures validate the usability of the proposed metric.

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Continuous and repetitive performance of cognitive tasks is likely to cause a change in the alertness levels of an individual. The present paper investigates the changes in EEG as a marker of alertness during an experiment designed to induce cognitive fatigue in subjects by continuous and repetitive performance of standard neuropsychological tests. Electroencephalogram (EEG), speech data and high-speed ocular images are recorded during the task set comprising of an Auditory Response Test (ART) Psychomotor Vigilance Test (PVT), a Letter Counting (LC) task, and a variant of the Stroop Task. EEG recorded during the ART is analyzed in the present work. Variation in network parameters in brain networks formed from the EEG records using the Motif Synchronization technique is employed to trace the change in alertness levels of subjects due to increase in cognitive fatigue.