The effect of flashing lights on speed perception for lateral motion and motion in depth.

Flashing lights are commonly used to enhance visibility and attract attention, but they may influence other perceptual processes such as localization, distance estimation, and motion perception. In this study, we investigated how flashing affects speed perception for stimuli moving laterally and in-depth. On each trial, observers viewed a moving white dot on a stereoscopic display that traveled either laterally or in-depth at one of several speeds (ranging from about 4-17 cm/s) and under one of three flashing conditions (none, 3 Hz, or 6 Hz). During part of the trajectory, the dot was occluded and its speed was perturbed. Speed perception was probed by asking observers to report whether the dot sped up or slowed down during occlusion. Replicating prior findings, speeds for motion-in-depth were generally underestimated relative to lateral motion, especially at higher stimulus speeds. Notably, this motion-in-depth underestimation bias was reduced when the stimulus was flashing. A follow up exploratory analysis on motion-in-depth perception also showed consistent differences between motion toward and away from the observer across both the continuous and flashing conditions. These findings contribute to our understanding of the utility of flashing lights for visual communication and suggest that flashing may specifically alter speed perception for motion-in-depth.