Abstract
The predictability of the visual environment allows not only to promptly respond to expected visual events, but also to drive anticipatory movements orienting towards them. Anticipatory smooth eye movements (ASEM) have been previously observed in human observers when the temporal and kinematic properties of a forthcoming visual moving target is fully or partially predictable. ASEM help minimize the delay after which the gaze is aligned with the moving target and matches its speed. However, the precise nature of the internal model of target kinematics which drives ASEM remains largely unknown, as well as its interaction with the contextual predictability. In this study we investigated whether and how predictable target speed and acceleration are taken into account for driving ASEM. We recorded eye movements in twelve healthy human volunteers while they tracked a small visual targets with either constant (v1=11°/s, v2=22°/s or v3=33°/s), accelerating (Va, from 11 to 33°/s in 1s) or decelerating (Vd, from 33 to 11°/s in 1s) speed, keeping the direction fixed. Across experimental blocks, we manipulated the probability of the presented target motion properties, with either 100% probability of occurrence of one speed (blocked sessions), or a mixture of two speeds with different proportions (e.g. v1 in 30% of trials and v3 in 70%). We show that ASEM is modulated by the target kinematic properties. With constant-velocity targets, ASEM velocity scales with target velocity across the blocked sessions, and it follows overall a probability-weighted average in the mixture sessions, in agreement with previous results (Souto et al. VSS, 2008). Target acceleration/deceleration does also have an influence on ASEM, however, results are much more variable across participants, and overall do not support an efficient integration of acceleration information in the internal model of target kinematics subserving pursuit anticipation.