In models of the response of V1 and MT cells, the gain control signal is taken to be the pooled activity of nearby cells of all direction and orientation preferences (Heeger, 1992; Simoncelli & Heeger, 1998), but the promiscuity of this inhibition has not been directly tested. We studied the stimulus specificity of this signal in MT cells by comparing responses to drifting test gratings presented alone with those measured in the presence of a drifting pedestal grating. Targets were presented at two equally effective locations within the receptive field, and could be either superimposed or separated. When the pedestal grating drifted in the preferred direction of the cell, responses to the test gratings were strongly reduced by the pedestal, regardless of whether the test and pedestal were separated or superimposed. These results support previous work suggesting gain control acts globally over MT receptive fields (Britten & Heuer, 1999; Majaj et al, SFN 2000). When the pedestal grating drifted in the null d...