Evoked Brain Potentials to Sound Offset in Humans in Conditions of Spatial Masking

The influence of the relative positions of a sound stimulus and a background masker on the components of evoked potentials (EPs) in the human brain in response to sound offset was studied. Sound stimuli were presented dichotically and sound image positions were specified by interaural level differences. The test signal and masker were located at a single point in space or were separated by designed angular distances of 90° or 180°. Coincidence of the positions of the signal and masker led to significant decreases in the amplitudes and increases in the latencies of the N1, P2, and N2 components of offset responses. Separation of the signal from the masker led to increases in response amplitude almost to the level of the response to the signal in silence, along with decreases in the latencies of all response components, which presumptively indicates successful extraction of the stimulus from the background.