The response of V1 neurons is suppressed by annular surrounds that fall well beyond their classical receptive fields. The neuronal basis for surround suppression is unknown although there is evidence that it arises via feedback from extra-striate cortex to V1. We have recently demonstrated a psychophysical analog of this surround suppression in the human periphery (SFN, 2004). High contrast annular surrounds, separated from a Gabor target by more than 3 periods raise contrast thresholds by a factor of 2 - 4. Psychophysically, surround suppression is tightly tuned for orientation, peaking at the orientation of the test target. Here we examine the spatiotemporal characteristics of orientation-specific surround suppression using high-density EEG and distributed source modeling. METHODS Probes consisting of low-contrast Gabor patches were presented either foveally or peripherally. Probes could be presented either (1) alone, (2) surrounded by a high contrast co-oriented annular grating or (3) surrounded by an o...