Task Context Modulates the Selectivity of Macaque Superior Temporal Sulcus Neurons for Partially Occluded Bodies

Abstract

Most single-unit studies of animate object processing in the primate ventral visual stream rely on passive fixation, leaving it unclear whether neuronal selectivity for socially relevant stimuli depends on behavioral context. Here, we tested whether task demands alter the selectivity of neurons in the ventral bank of the superior temporal sulcus (STS) for body pose or viewpoint. Male rhesus monkeys viewed identical body stimuli (monkey avatars) under two conditions: a task in which body pose was behaviorally relevant and a condition in which the same stimuli were irrelevant for obtaining a reward. Task context modulated STS responses: neuronal responses were stronger and more selective when stimuli were task-relevant, yielding improved decoding performance compared with the task-irrelevant condition. These effects were most pronounced for partially occluded bodies, indicating that task demands enhance processing under challenging visual conditions. Despite these modulations, the overall impact of task context was modest relative to the neurons' intrinsic selectivity, and stimulus preference rankings remained largely stable across tasks. For partially occluded bodies, task-dependent effects were observed in both middle and anterior STS, with a tendency for earlier modulation in middle STS, consistent with hierarchical processing. These findings suggest that STS neurons maintain largely stable body selectivity across behavioral contexts, while task relevance enhances response gain and selectivity, particularly when visual information is degraded. More generally, this study helps reconcile previous conflicting reports of task context modulations in the macaque inferior temporal cortex by showing that task effects are present but relatively subtle and depend on stimulus conditions.