Stimulus discrimination by horses under scotopic conditions.

The research work investigates the ability of horses to visually differentiate between geometric shapes in varied light conditions – from twilight to the dark night.

Research Objective and Methodology

• The primary aim of this research was to understand the extent of scotopic vision (night vision) in horses. In simpler terms, it sought to measure the ability of horses to distinguish between specific geometric figures like circles and triangles under a variety of light conditions.
• The study was conducted in a controlled environment, inside an enclosed building using four horses.
• The brightness levels within the building mimicked the conditions ranging from twilight in open country lands to a dense forest on a dark moonless night.
• A Sky Quality Meter was used to capture brightness measurements ranging between 10.37 to 24.12 magnitudes per square arcsecond, signifying different light conditions from twilight to a dark night.

Research Findings

• The four horses were able to solve the discrimination problems up to a brightness level of 23.77 magnitudes per square arcsecond, providing evidence of their superior night vision.
• Moreover, they navigated their way around obstacles that were in the test area under conditions of extremely dim light, which were too dark for the human experimenters to see. This means that horses have better night vision as compared to humans.
• The conclusions drawn from the study support the existing physiological data that suggests horses have a rod-dominated visual system. Rod cells in the eyes are responsible for vision under very low light conditions.
• The findings also verify the observations suggesting active equine activity during the night.