Figure 6. Visualization of a possible spatial distribution of the ECoG signal sources.

According to this model, inputs from a narrow stimulus (left) give rise to a stimulus-locked response in a relatively small region of cortical input layers; when the stimulus is wider (right) the stimulus-locked response is correspondingly larger. When the response from neighboring stimulus locations gives rise to responses in overlapping cortical locations (dashed red lines), we assume the total neural response is approximately the maximum of the two responses (black lines). The stimulus-locked responses measured by the electrode grow with stimulus size because the area of cortical stimulation under the electrode increases with stimulus size. In contrast, the broadband response from a small stimulus already spans the electrode antenna function. Consequently, the wider stimulus does not produce a much larger response in the electrode than the narrow stimulus. Alternative explanations for why the wider bar could produce a larger response are schematized in Figure S6.