Pupillometry is a promising method for assessing mental workload and couldbe helpful in the optimization of systems that involve human–computerinteraction. The present study focuses on replicating the studies by Ahern(1978) and Klingner (2010), which found that for three levels of difficultyof mental multiplications, the more difficult multiplications yielded largerdilations of the pupil. Using a remote eye tracker, our research expands uponthese two previous studies by statistically testing for each 1.5 s interval of thecalculation period (1) the mean absolute pupil diameter (MPD), (2) the meanpupil diameter change (MPDC) with respect to the pupil diameter during thepre-stimulus accommodation period, and (3) the mean pupil diameter change rate(MPDCR). An additional novelty of our research is that we compared the pupildiameter measures with a self-report measure of workload, the NASA Task LoadIndex (NASA-TLX), and with the mean blink rate (MBR). The results showed thatthe findings of Ahern and Klingner were replicated, and that the MPD and MPDCdiscriminated just as well between the lowest and highest difficulty levels as didthe NASA-TLX. The MBR, on the other hand, did not differentiate between thedifficulty levels. Moderate to strong correlations were found between the MPDCand the proportion of incorrect responses, indicating that the MPDC was higher forparticipants with a poorer performance. For practical applications, validity could beimproved by combining pupillometry with other physiological techniques.
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