Echo suppression in the human cortex is affected by the spatial and temporal proximity of the primary sound and echo

Echo suppression in the human auditory cortex was studied with auditory middle latency evoked potentials (AMEP) using virtual reality acoustic stimuli, including distance and elevation cues, presented by earphones. The purpose of the study was to assess the effect of proximity of the source sound and echo on the degree of echo suppression. Sixteen subjects were presented with source-echo pairs in which the preceding source sound was always at the vertex, and the echo varied among ten positions on the coronal plane. Positions varied in elevation, distance and time lag between source and echo. The psychoacoustic location judgment of the fused source-echo pair was closer to the source sound (more echo suppression) the nearer the echo drew to the source in its elevation and time. The equivalent dipole magnitudes of the cortical components of AMEP were significantly reduced (more suppression) with shorter echo lags and when echo elevation was similar to that of the source sound. The distances used in this study did not significantly affect echo suppression. These results indicate that echo suppression in the auditory cortex is more pronounced the closer are the primary sound and echo in locational attributes and timing. As source sound and echo draw apart, echo suppression in the cortex decreases and the perceived localization of the fused source-echo is more biased toward the echo.