Domenica Bueti¹ (), Alessandro Toso^1,2, Gianfranco Fortunato¹, Chiara Zanonato^1,3, Mathew Diamond¹; ¹SISSA, ²Section Computational Cognitive Neuroscience, Department of Neurophysiology and Pathophysiology, University Medical Center Hamburg- Eppendorf, ³Max Planck Institute for Biological Cybernetics

In humans, the duration processing of a visual event has been shown to entail a wide network of brain areas including primary visual cortex and supplementary motor area. The functional role of these brain regions in temporal computations is far from clear. A simple hypothesis is that V1, conveying the sensory input, encodes stimulus duration while SMA, at the other extreme of a hypothetical hierarchy, decodes it for task-related purposes. Here we used paired pulse transcranial magnetic stimulation (ppTMS) to test this hypothesis. Fifteen healthy volunteers were asked to discriminate the duration of pairs of visual stimuli while ppTMS was applied over right V1, SMA and the Vertex at different timings from the onset of the first stimulus of the pair i.e., 0, 60, 90 and 100% of the total stimulus duration. Compared to vertex stimulation, we observed a significant worsening of temporal discrimination thresholds after ppTMS over V1 at 60% and over SMA at 90% and 100% of the stimulus duration. A second experiment showed that the performance worsening after V1 stimulation was not due to an interference with low-level visual processing. Four different versions of a leaky integrator model were used to fit the data. All models assumed that visual time perception results from the leaky integration of a stimulus’s luminance, with this process being inherently noisy. The models varied in their hypothesized effects of TMS, proposing that these effects could occur either at the perceptual or the input level, by altering the mean or variance of the noisy process. The two winning models suggested that ppTMS influenced the noise variance of the integration process, while V1 and SMA results were best explained by assuming TMS interference at the input and perceptual level, respectively. These results highlight a distinct functional role of V1 and SMA in duration processing.