Grasso, P. A., Làdavas, E., Bertini, C., Caltabiano, S., Thut, G., & Morand, S.
Decoupling of early V5 motion processing from visual awareness: a matter of velocity as revealed by transcranial magnetic stimulation
Journal of Cognitive Neuroscience, 30(10), 1517–1531
Motion information can reach V5/MT through two parallel routes: one conveying information at early latencies through a direct subcortical route and the other reaching V5 later via recurrent projections through V1. Here, we tested the hypothesis that input via the faster direct pathway depends on motion characteristics. To this end, we presented motion stimuli to healthy human observers at different velocities (4.4°/sec vs. 23°/sec) with static stimuli as controls while applying transcranial magnetic stimulation (TMS) pulses over V5 or V1. We probed for TMS interference with objective (two-alternative forced choice [2AFC]) and subjective (awareness) measures of motion processing at six TMS delays from stimulus onset (poststimulus window covered: ∼27–160 msec). Our results for V5–TMS showed earlier interference with objective performance for fast motion (53.3 msec) than slow motion (80 msec) stimuli.