Motion prediction at low contrast

Accurate motion prediction is fundamental for survival. How does this reconcile with the well-known speed underestimation of low-contrast stimuli? Here we asked whether this contrast-dependent perceptual bias is retained in motion prediction under two different saccadic planning conditions: making a saccade to an occluded moving target, and real-time gaze interaction with multiple moving targets. In a first experiment, observers made a saccade to the mentally extrapolated position of a moving target (imagery condition). In a second experiment, observers had to prevent collisions among multiple moving targets by glancing at them through a gaze-contingent display or by hitting them with the touchpad cursor (interaction condition). In both experiments, target contrast was manipulated. We found that, whereas saccades to the imagined moving target were systematically biased by contrast, the gaze interaction performance, as measured by missed collisions, was generally unaffected - even though low-contrast targets looked slower. Interceptive actions increased at low contrast, but only when the gaze was used for interaction. Thus, perceptual speed underestimation transfers to saccades made to imagined low-contrast targets, without however necessarily being detrimental to effective performance when real-time interaction with multiple targets is required. This differential effect of stimulus contrast suggests that in complex dynamic conditions saccades are rather tolerant to visual speed biases.