Beyond Heart Rate in the Cardiac Psychophysiological Assessment of Mental Effort: The T-Wave Amplitude Component of the Electrocardiogram

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Abstract
The paper begins with an argument for going “beyond” heart rate for greater specificity in the measurement of mental effort. The added measure must reflect sympathetic nervous system (SNS) influences more clearly than does heart rate, which is predominantly influenced by parasympathetic factors. In considering what the human factors practitioner is seeking in the SNS measure, I discuss three requirements, the issue of convenience, and two marginally relevant considerations. The characteristics of T-wave amplitude (TWA) are then examined in this light. Recent evidence for the utility of TWA used jointly with heart rate as a psychophysiological index is then reviewed in terms of reactive sensitivity, specific sensitivity, complementary utility, and physiological utility. There follows a section that considers difficulties and confounding possibilities concerning TWA. The paper concludes that, although controversial, TWA appears to provide a promising psychophysiological path for using cardiac performance measures to aid in the measurement and understanding of the psychological process of mental effort.