The Modality Specificity of the Slow Negative Wave

Event-related potentials were recorded in a simple reaction time task using a 3-sec interval between S₁ and S₂. The sensory modalities of S₁ and S₂ were varied across 4 conditions to yield all possible combinations of tones and flashes. A negative component which peaked between 600 and 800 msec after S₁ was specific in scalp distribution to the modality of S₁ but not S₂. It was concluded that this negative component is a response to S₁ and not related to processes associated with anticipation of S₂. A slow negative shift which peaked at S₂ was largest at the vertex in all conditions, suggesting its motor origin. A trend for the latter activity to be more negative in posterior recordings when S₂ was visual than auditory leaves open the possibility that the terminal CNV is a combination of motor activities and anticipation of the sensory modality of S₂.