Perceptual decisions and eye movements are shaped by sensory information and expectations about the environment, reflecting experience-dependent internal models. Yet, they do not always adapt to context in the same way, suggesting they may rely on partly different internal representations.
In direction-biased motion tasks, anticipatory eye movements track the most frequent direction while perceptual discrimination is sometimes biased toward the least frequent one. Less is known about visually-guided eye movements. Here we ask whether perception and eye movements rely on a shared representation of context in a direction-biased random dot kinematogram (RDK) task, or distinct computational strategies.
Thirteen observers (N = 13) performed a direction discrimination task in two conditions, reporting leftward or rightward motion in an RDK in a 2-AFC decision-making paradigm, while eye movements were recorded. The experiment comprised two phases: an adaptive staircase to estimate RDK direction discrimination thresholds, followed by a main task in which motion coherence varied randomly across trials. Crucially, motion direction probabilities shifted from unbiased (50/50) to biased (80/20), either abruptly (JUMP) or gradually (RAMP).
In the JUMP condition, perceptual decisions were robustly biased toward the less frequent direction, a counterintuitive effect that persisted across trials and replicated prior findings, including an independent online experiment (N = 24). This deviates from normative predictions that favor the more frequent direction. Anticipatory eye movements were instead biased toward the more frequent direction, as was early visually guided smooth pursuit, though the latter appeared primarily driven by recent trial history with no clear influence of global probability. In the RAMP condition, the same pattern of oculomotor adaptation was observed, whereas the perceptual bias toward the less frequent direction was reduced, though it remained present. Together, these preliminary findings suggest a partial dissociation between perceptual and oculomotor processes, potentially governed by distinct internal representations of probabilistic context.