The Effect of Darkness on Visual Reaction Time and its Physiological Basis

Abstract

Car accidents are a leading cause of death that primarily occur at night. There are many characteristics of night time driving that have been proposed to explain this phenomenon. Our group set out to determine if reaction time was one of the factors that were affected by darkness. Darkness has been known to cause stress and result in a sympathetic arousal that can enhance various physiological variables. Specifically, we predicted there would be increased heart rate, respiration rate, and sweat production while in dark conditions compared to light conditions. This increase in physiological response, we hypothesize, would result in a quicker reaction time in the dark compared to in the light. Subjects performed a reaction time test, under light and dark conditions, while their respiration rate, sweat production, and heart rate were measured. After testing twenty individuals (n=20) our results showed that there was no significant difference in the mean reaction time or any of the physiological variables when going from light to dark. Our results suggest that darkness alone is not sufficient to elevate the physiological responses associated with a sympathetic response and does not change reaction time, indicating that other factors are responsible for elevated car accidents at night.