To resolve the uncertainty and disagreement that currently exists in the field of mental workload, a unified research approach is required. It is argued that a promising path would be to identify the various dimensions of mental workload and then to develop a metric for each of these. The present study focused on the dimension of mental effort. In particular, the validity of spectral analysis of sinus arrhythmia as a measure of mental effort was investigated using a psychomotor task. The strong correlation observed between the physiological measure and subjective ratings of effort suggest that spectral analysis of sinus arrhythmia is an accurate measure of operator effort. Results also indicate that the intensity of effort invested by subjects could not be inferred from objective task difficulty or performance. Thus, it is important that a measure of effort be included in experiments investigating mental workload. Future research will be directed at developing a continuous measure of operator effort by implementing the physiological measure on-line.
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