Perceived Coherence of Global Motion is Higher in Periphery than in Central Vision

Perceptual sensitivity to global motion depends on many factors including stimulus eccentricity. Little research has investigated how the appearance of global motion stimuli varies across the visual field. This study compared the perceived coherence of global motion between central and peripheral vision and examined the potential association between apparent coherence and motion sensitivity. Participants viewed random dot kinematogram stimuli consisting of 120 dots moving in a 10° circular field (contrast: 60%, speed: 6°/s, lifetime: 50 ms). There were four global motion directions: left, right, up and down, and seven coherence levels varying between 5% and 95%. The stimuli were either presented at the central fixation or 10° to the left or right of fixation with a duration of 300 ms. The participants first judged the direction of global motion, followed by a judgement of motion coherence in comparison to two learned reference levels (low: 5% and high: 95%) in a bisection task. There were considerable individual differences in motion sensitivity as measured by coherence threshold in direction judgment, some participants having lower but others having higher sensitivity in the periphery compared to central vision. Despite the variability in sensitivity, all participants reported a higher level of perceived motion coherence in the periphery compared to central vision, as indicated by the bisection point in coherence judgment. The higher perceived coherence in the periphery was consistent with faster reaction time and with the self-reported relative ease of direction judgment for peripherally presented stimuli. However, there was not a systematic association between perceived coherence and motion sensitivity across participants. The findings suggest that the perceived coherence of global motion stimuli and the sensitivity to such stimuli might be governed by distinct mechanisms. The higher perceived coherence in the periphery is attributable to a smooth motion prior applied where the visual resolution is low.