Responses of low-frequency neurons in the inferior colliculus (IC) of anesthetized guinea pigs were recorded to interaural phase modulation (IPM) before, during, and after iontophoresis of bicuculline, an antagonist to the inhibitory neurotransmitter GABA. Sensitivity to the direction of virtual motion resulting from IPM is an emergent property of neurons at the level of the IC. One model to account for this emergent sensitivity depends on GABAergic inhibition. Blocking GABAergic inhibition with bicuculline substantially increased neuronal discharge rates and increased the extent to which neurons were sensitive to the apparent-motion cues of IPM. The effect of GABA blockade is consistent with the hypothesis that sensitivity to the motion cues of IPM results from a process of adaptation-of-excitation whereby the magnitude of the recent response history influences subsequent neuronal responsiveness. These results indicate that GABAergic inhibition strongly influences the context-dependent processing of low-frequency binaural signals in the IC.