Intraindividual Reaction Time Variability to Visual Stimulus in Binocular and Dominant or Non-Dominant Monocular Vision

Reaction time measures have considerable potential to aid neuropsychological assessment in a variety of healthcare settings. One such measure, the intra-individual reaction time variability is of particular interest as it is thought to reflect neurobiological disturbance. The present study aimed to investigate the intra-individual changes in reaction time to visual stimuli in dominant or non-dominant binocular and monocular vision.

This descriptive-analytical study was conducted on 12 volunteers with an average age of 30.08±1.448 years in 2021. The subjects consisted of the students and staff of Golestan University of Medical Sciences (5 female and 7 male). The reaction time was recorded automatically by the hand reaction time device of Danesh Salar Iranian Company based on the time of presentation of visual stimulation on the computer screen and the person's reaction, i.e. pressing the buttons of the handles by each of the two hands. All experiments were performed between 10 and 11 am and following at least 2 hours of fasting. Data collection was done following training trials for correct performance of the 2-choice reaction time test. After completing the reaction time tests for each volunteer, the dominant eye was determined by the hole-in-card method.

In 4 volunteers, the dominant eye was left and in the rest of the volunteers, the dominant eye was right. The dominant eye did not differ between men and women. The number of reaction times recorded in right monocular vision left monocular vision and binocular vision were 902, 911 and 893, respectively. The mean reaction time in right monocular vision, left monocular vision and binocular vision was 306.81±3.310, 304.28±3.339 and 312.95±4.569, respectively, and the range of reaction times in these three states was between 194-1750, 178-1587, and 155-1797 ms, respectively. Intra-individual reaction time variability in the dominant left eye and left hand were significantly lower compared to the dominant right eye and right hand, respectively (P<0.05). No difference was observed between the reaction time of the right monocular vision, left monocular vision, and binocular vision.

The alignment of the dominant left side in the eye and hand reacts faster than the dominant right side in the eye and hand. The mechanism of this phenomenon may be related to the overall process that determines the dominant left hemisphere in approximately 90% of the population.