Pattern of modulation for collinear (A–D) and parallel (E–H) S1 conditions.

<p>(A) Combined time course of SOA-dependent significant facilitation (p<0.05) from 2288 SOA conditions of 208 collinear S1 stimuli. Normalized frequency of significant epoch is color-coded according to the color map shown on the right. Out of 2288, 208 (9.09%) SOA conditions included more than one temporal epoch with significant facilitation. (B) Time course of significant suppression combined from the same collinear S1 configurations. In 611 of 2288 (26.70%) SOA conditions, more than one temporal epoch showed significant suppression. (C) Normalized marginal frequency of significant facilitation from A (red) and suppression from B (blue) against peristimulus time. (D) Normalized marginal frequency of significant facilitation (A, red) and suppression (B, blue) during the poststimulus time period from 0 to 300 ms against SOA. Normallized marginal frequency was derived from marginal sum divided by the number of data points. (E–H) Similar plots as A–D combined from 572 SOA conditions of 52 parallel configurations. Out of 572 SOA conditions, 96 (16.78%) and 71 (12.41%) SOA groups showed significant facilitation and suppression, respectively. Thus, suppression was relatively common with collinear S1, and the relative ratio of facilitative modulation was higher with the parallel configuration. This was true even after the distance between S1 and S2 was taken into account (by subdividing S1 configuration conditions into two distance groups, one or two RF diameter away from RF center). Note that suppressive modulation was concentrated at around 100 ms after S2 onset time (C, G), whereas facilitative modulation was relatively more dispersed and dominant after around 200 ms after S2 onset, especially in the parallel configuration. Also note that collinear S1 tended to suppress at short SOA and facilitate at long SOA (D), whereas this dissociation was relatively weak with parallel S1 (H).</p>