Public health
Interactions of visual and cognitive stress

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Abstract

Background

The objective of this research is to assess the ocular and muscular response to long-duration reading under different visual and cognitive difficulty levels.

Methods

Thirty-five subjects, with 20/20 vision and without history of ocular pathology or cognitive deficits, participated in the study. Subjects read under different visual and cognitive difficulty levels for 6 (30-minute) conditions. Upper and lower orbicularis oculi, frontalis, and trapezius muscle activities were recorded using surface electromyography (EMG). Aperture size, pupil diameter, and pulse rate of the subjects were recorded with a video camera, pulse meter, and ISCAN eye tracker (ISCAN Inc.), respectively.

Results

The results show that the texts read with a refractive error caused increased orbicularis oculi EMG power and reduced aperture size (P < 0.001). There was no statistically significant difference between the conditions for pulse rate, pupil diameter, or EMG activity of the frontalis and trapezius muscles with either visual or cognitive stress presented in this experiment.

Conclusion

Visual stress experienced due to reading under an induced refractive error is potentially mediated by a local mechanism, different from the mechanism underlying reading under low contrast or high cognitive demand.

Section snippets

Methods

Thirty-five subjects in the age group of 18 to 30 years were recruited for the study. This sample size achieves 80% power to detect an R2 of 0.24 attributed to the 2 main effects (cognitive stress and visual stress) and interaction using an F test with a significance level of 0.05, assuming that subjects account for approximately 10% of the variance. The Ohio State University Institutional Review Board approved the protocol. Subjects were recruited from The Ohio State University and nearby

Results

Table 3 provides a summary of the control period before the onset of each experimental condition. The intraclass correlation coefficient (ICC) demonstrated varied consistency across baseline conditions depending on the measure evaluated. EMG recordings were quite variable with an average ICC of 0.42. The most reliable measures were OO 0.75 (electrode placement closest to the lower lid) and the frontalis location. The OO factor score combining 3 locations had a modest ICC of 0.38. The aperture

Discussion

Results from this study show that specific conditions of refractive error blur result in increased OO EMG measures and reduced aperture size, both of which indicate an eyelid squint response to refractive error. Such a mechanism seems to be driven by a benefit that results from squinting, in this case, a clearer visual image. For the low-contrast condition, EMG measures from the OO locations do not show any increase compared with good text conditions, indicating that visual stress from low

Conclusions

The objective of the study was to test the effects of visual and cognitive difficulty levels during reading and video viewing conditions on a set of physiologic measures designed to measure local and central mechanisms. The visual stressor (specific refractive error blur) caused eyelid squint, but low-contrast conditions did not show any changes in the OO EMG. Increasing the cognitive load (especially between the reading conditions) resulted in increased palpebral aperture size under all visual

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    Disclosure: This study was supported by a grant from the Microsoft Corporation, Advanced Reading Technologies Group.

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