Abstract
Motion in distant locations beyond the extent of classical V5/MT receptive fields (CRF) influences motion processing for within CRF stimuli (Allman, Meizin, McGuinness, 1985). Here, we report two experiments investigating the characteristics of such long range motion interaction in humans. In a first, behavioral experiment, we showed a congruency effects in direction of motion discrimination for a peripheral, target random dot pattern (RDP) when a distractor RDP (with similar noise level to target) was displayed in the symmetrical location across the vertical meridian (RDP size: 8 degrees; center-to-center distance: 20 degrees). In a second experiment, this congruency effect was eliminated by the application of transcranial magnetic stimulation (TMS) on human V5/MT if (1) early TMS (120ms after motion onset) was applied over the hemisphere contralateral to the distractor or (2) late TMS (160ms after motion onset) was applied over the hemisphere ipsilateral to the distractor. This result confirms that interactions between left and right human V5/MT are necessary for motion integration across the vertical meridian. Moreover, they argue for separable temporal stages for integration of motion signals within and between hemifields.