The Effect of Movement Speed on Mental Workload During a Simple Visually Guided Task

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Mental workload (MW) is a subjective measure of the cognitive effort required to complete a task. Factors such as task speed and the use of feedback can affect the perceived MW and ability to correctly perform an activity. PURPOSE: 1) Determine the effect of task speed on perceived MW during a wrist movement pattern guided by visual feedback (VF); and 2) Determine if MW is different for those who correctly perform the task (Performer: P) compared to those who do not (Non-performer: NP). METHODS: Twelve healthy young subjects were recruited and asked to flex and extend their right wrist to match two different speeds of a target sine wave: 0.7 Hz (FAST) or 1.0 Hz (SLOW). VF of wrist movement and the target pattern were provided concurrently on a screen. Five 20-second trials with two-minute rest intervals were completed at each speed. During rest periods the Raw NASA-TLX (RTLX), a tool used to assess perceived workload, was administered. RTLX categories representing purely MW include: mental demand (MD), temporal demand (TD), and frustration (FR). Cross-correlation analysis of task performance was computed for each subject’s 5th trial at both speed conditions in order to categorize individuals as either P (r > 0.8) or NP (r < 0.8). 2x2 mixed model ANOVAs compared the change in perceived MD, TD, and FR from trial one to five between speed conditions (FAST vs. SLOW) and the two groups (P vs. NP). Post hoc Tukey HSD tests were used to compare differences. Positive changes in MD, TD, and FR denote improvements in MW. RESULTS: Significant speed x group interactions were observed for MD (p=0.008) and TD (p=0.005). No significant interaction or main effects were found for FR (p=0.204). Post hoc tests revealed significant differences in changes in MW between FAST and SLOW speeds among P (MD FAST: 31.4, SLOW: 11.4, p=0.027; TD FAST: 30.0, SLOW: -0.71, p=0.022) and between P and NP during the FAST speed (MD P: 31.4, NP: -2.0, p=0.044; TD P: 30.0, NP: -8.0, p=0.031). CONCLUSIONS:P and NP showed similar changes in MW from trial one to five during the SLOW speed, whereas only P experienced improved MW during the FAST speed. These results suggest MW is affected by movement speed in accordance with subject performance.