Automated measurement of spectral sensitivity of motion vision during optokinetic behavior

Abstract

Optokinetic behavior is a commonly used paradigm to conveniently determine sensitivities of motion vision in animals. The optokinetic reflex (OKR) compensates global image motion on the retina by head and eye movements. It can reliably be elicited without training the test animal. In most OKR behavior experiments the animal is stimulated either with a rotating drum containing a pattern of vertical stripes or with computer monitors displaying a moving stripe pattern. In many of these studies, sensitivity thresholds are measured based on the subjective judgment of the experimenter. In this paper, we describe an alternative method to induce and measure OKR behavior. Our setup consists of a metal drum into which a slide is projected via a 360° panoramic mirror, using a spectrally filtered LED as light source. The slide is mounted on a motor-driven turntable whose rotation leads to a horizontal movement of the stimulus on the drum’s wall, accordingly. By this means a spatial, temporal, and spectral well-defined and flexible panoramic stimulation is achieved. The animal’s head movements are video recorded under infrared illumination and tracked online. We introduce an objective criterion to automatically determine sensitivity thresholds based on the correlation of the animal’s head angle with the stimulus position. We exemplarily used this setup for an experiment that could not be performed with the state-of-the-art setup consisting of four monitors—the measurement of spectral sensitivity thresholds of the OKR behavior in turtles.