Fig. 8.

A, 0–25 Hz filtered averaged evoked potentials. We performed a Quade test and Conover procedures on the averaged evoked potential, computed over 100 msec time windows regularly shifted by 20 msec. Two successive effects can be found. They are plotted on the figure as dots or barsindicating the center of the 100 msec time window on which an effect has been found. A first effect occurs on all of the electrodes between 200 and 300 msec; it corresponds to potentials more negative for the illusory triangle than for the two others (dots). The second effect concerns a more limited set of electrodes and appears between 300 and 400 msec. It corresponds to a greater positivity in response to the real triangle than the two others (bars). B, Topography of the 0–25 Hz averaged evoked potential (grand average across subjects) at two latencies (250 and 380 msec) in each condition. At 250 msec, the response to the illusory triangle shows a more pronounced negativity at occipital and parietal electrodes. At 380 msec, the real triangle elicits a more positive response than the two others on the right side of the scalp.