ABSTRACT
<p><b>OBJECTIVE</b>To investigate the possibility of subjective rate, primary task evaluation and psychophysiology evaluation as methods for mental workload assessment of mental arithmetic on visual display terminal (VDT).</p><p><b>METHODS</b>The indexes including Cooper-Harper scale score, correct rate, speed in answering questions, heart rate variability, pupil size and blink rate were recorded during the performance of three different difficult tasks.</p><p><b>RESULTS</b>With the variable number of formula increasing, the Cooper-Harper scale score increased, the right rate decreased, the speed decreased, pupil size increased, and blink rate significantly decreased. In comparison with rest, the value of TP, VLF, LF, LFnorm, LF/HF decreased remarkably in the mental arithmetic task, the value of HFnorm, HF/TP, rMSSD increased. However, the difference was not significant among three groups.</p><p><b>CONCLUSION</b>With the variable number of formula increasing, the participant's mental workload increases. Every method of mental workload evaluation can assess the mental workload information for three tasks at various different levels in a way. Multi-indexes may be appropriate for mental load assessment.</p>