Quantifying the effect of natural and arbitrary sensorimotor contingencies on chromatic judgments

When a body movement systematically co-occurs with a stimulus, a change in perception to compensate for this correlation may occur. In Experiment 1 (similar to A. Bompas & J. K. O'Regan, 2006), we induced a correlation between leftward eye saccades and a red stimulus, and rightward eye saccades and a green stimulus. In a subsequent test phase, observers compared the color of two stimuli after leftward and rightward saccades. The major result was that stimuli tended to look greener after a leftward saccade and redder after a rightward saccade (A. Bompas & J. K. O'Regan, 2006). Measured here in meaningful units for the first time, the shift in the point of subjective equality was approximately d' = 0.4, a remarkably large effect for only 40 minutes of eye movement/color exposure. A control experiment ruled out a simple reduction in initial bias as the cause of the effect. In Experiment 2, we hypothesized that the blue of the sky might cause an initial bias to judge spots seen with upward gaze as "yellower"; this expectation was not met, but the basic effect was replicated and extended to other chromaticities and eye movement directions. Experiment 3 substituted listening to tones for the eye movements (a sensorisensory correlation) to explore differences between sensorimotor adaptation and sensory integration; neither effect was found for our task. Sensorimotor adaptation can be a remarkably powerful influence on perception; because it operates in a compensatory direction, it may oppose the effects of sensory integration, depending upon task demands.