Spatial and directional tuning of serial dependence for tracking eye movements
An attractive influence of past sensory experience on current behaviour has been observed in many domains, such as for perceptual decisions and motor responses. However, it is unclear what sort of information is integrated across trials, and the limits of this integration, especially for oculomotor behavior. Here we provide a detailed and systematic investigation of the spatial and directional tuning of serial dependence for oculomotor tracking. In a series of experiments, we measured oculomotor responses to sequences of movements: the first movement (the prior) could move at different velocities (5 or 15 deg/s), and could additionally vary in its spatial location or direction relative to the following movement. The second movement (the probe) always moved at the same velocity (10 deg/s) and was constant across all experiments. We observed that eye velocity for the probe movement was faster when following the fast prior compared to following the slow prior, replicating attractive serial dependence. Importantly, this effect stayed consistent for distances of up to 30 deg between probe and prior, strongly suggesting a retinotopic coordinate frame. When we manipulated the direction of the prior, we observed that the strength of the serial dependence on eye velocity as well as eye direction was modulated by the relative angle between prior and probe. We observed stronger serial dependence for prior directions more similar to the probe direction. The strength of the effect on eye velocity and eye direction was correlated, suggesting a shared mechanism controlling these effects. Across all experiments, we observed that even when the prior moved in the opposite direction to the probe, there was a residual attractive effect. This suggests that serial dependence for oculomotor tracking consists of two components, one retinotopic, direction-tuned component and one more general component that is not direction-specific.