Space-time interference in magnitude judgements revealed by drift-diffusion modelling.

Space and time are strongly interrelated in human cognition: spatial extent can bias temporal judgements, whereas duration can influence perceived spatial extent. However, the mechanisms underlying these reciprocal effects remain debated. We investigated these interactions using psychophysical measures, individual difference analyses and drift-diffusion model (DDM). Participants completed temporal and spatial bisection tasks in separate blocks, judging either the duration or the distance between two successively flashed dots while the irrelevant dimension varied orthogonally. This parametric design enabled the assessment of space-on-time (Kappa) and time-on-space (Tau) effects within the same individuals. Spatial judgements were more precise than temporal judgements, but both tasks showed robust, graded cross-dimensional interference. DDM analyses revealed that relevant and irrelevant magnitudes both modulated the drift rate, indicating that task-irrelevant information influenced evidence accumulation. Individual precision, indexed by the Weber Ratio, predicted drift rate slopes for the relevant dimension but was not systematically associated with susceptibility to interference. Conversely, perceptual bias was closely related to the modulation of the drift rate by irrelevant magnitudes. These findings show that reciprocal space-time interference can be characterized by combining psychophysics and diffusion modelling and suggest that it reflects perceptual, decisional and contextual influences.