47 th European Conference on Visual Perception 2025, Mainz, Germany, 24 – 28 August 2025

The SNARC effect is typically described as a compatibility between Response hand and Numerical magnitude (R/ N-SNARC), with faster responses using the left hand for small numbers and the right hand for large numbers. In contrast, the compatibility between Stimulus location and Numerical magnitude (S/N-SNARC) has been largely over- looked. Here, we disentangle the contributions of R/N- and S/N-SNARC effects for peripheral targets, either task-relevant or task-irrelevant, when response latency is further modulated by Simon-like compatibility (i.e., faster responses when the response hand is compatible with the stimulus side). To this end, we conducted two experi- ments based on a Posner cueing paradigm for exogenous covert attention, in which we manipulated the target pos- ition (left/right), the cue validity (valid/neutral/invalid), and the response hand (Simon-compatible/incompatible). The experiments involved two tasks: a localization task (Experiment 1, with task-irrelevant targets) and a magni- tude judgment task (Experiment 2, with task-relevant tar- gets). We employed a novel chronometric framework to decompose response latency into three components: reflexive attention (a shift toward the cue), voluntary atten- tion (a shift toward the target), and response selection. Results showed that S/N-SNARC was driven by voluntary attention in the localization task (Experiment 1), as it was modulated by cue validity, varying from present to absent between the invalid and the valid cue condition. Conversely, in the magnitude judgment task (Experiment 2), S/N-SNARC was driven by the response-selection com- ponent and inhibited by voluntary attention, decreasing progressively from the valid to the invalid cue condition. A similar, though weaker, pattern emerged for the R/ N-SNARC. Interestingly, voluntary attention enhanced Simon-like compatibility in the magnitude task, whereas it suppressed it in the localization task. Our findings suggest that spatial-numerical associations rely on different under- lying mechanisms depending on task demands, and that spa- tial compatibility effects can be either inhibited or driven by voluntary attention.