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Abstract

Improper body water regulation contributes to physiological changes, affects mood states, and impacts regulation of behavioral responses. With improvements in eye tracking technology (fixation duration and pupil diameter), the ability to quantify focal points and mental effort has expanded greatly. PURPOSE: To examine the effects that fatigue states and hydration, (euhydrated (Eu) vs. hypohydrated (Hypo)), has on average fixation duration and pupil diameter using five separate low cognitive load hydration stimuli. METHODS: Six college aged males underwent two trials of active fatigue/dehydration in an environmental chamber at 35℃ until 2% body water loss was achieved. Fluid restriction and ad-libitum consumption was counterbalanced across trials. Participants viewed 5 stimuli, pre and post fatiguing protocol in a randomized order, consisting of 5 still-image hydration images consisting of commercially available water and carbohydrate-electrolyte drink images. Eye tracking was utilized to quantify mental effort (ME) through observed change in fixation duration and pupil diameter while viewing low cognitive load still image stimuli. Prior to trials, participants underwent familiarization of all stimuli. RESULTS: Pre-post Hypo and Eu trial fixation durations (ms) were 965 ± 923 to 987 ± 777 (p=0.999) and 1210 ± 848 to 903 ± 659 (p=0.953) respectively. Pre-post Hypo and Eu trial pupil diameters (mm) were 3.07 ± .305 to 3.21 ± .346 (p=0.010) and 3.14 ± .352 to 3.12 ± .335 (p=0.982) respectively.  CONCLUSION: While significant changes in ME in both hydrated states were not seen for fixation duration, pupil diameter in Hypo trials revealed trends toward significance that appear to be attenuated by fluid consumption during the Eu trials.   Acknowledging the limitations of our small sample size, and as fixation duration is well established in ME literature, it seems plausible that changes in ME while utilizing low cognitive load stimulation may be less sensitive to detection in fixation duration, as compared to pupil diameter across hydration states. Future research should investigate possible thresholds of detection for ME across various levels of cognitive load stimuli.

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