Fig. 11.

Impact of prestimulus modulation on neuronal response latency and poststimulus attentional effects. A: averaged latency as a function of %contrast is plotted in the unattended condition, separately for the subpopulation of cells with (yellow) and without (black) a reliable baseline shift. Each point represents the average (mean ± SE) across neurons. B: time course of prestimulus modulation. Attentional modulation is calculated before stimulus onset in 100-ms windows, shifted by 25 ms, for 4 artificially sorted subpopulations of trials. Two subpopulations have been separated by selecting trials with high prestimulus firing (solid lines) and low prestimulus firing (dashed lines), separately for the unattended condition (blue lines) and attended condition (red lines). C: time course of the modulation effects exerted by the presence of high vs. low prestimulus baseline activity is shown separately for the attended (In; red line) and unattended (Out; blue line) conditions. The pattern of poststimulus activity in the low-firing condition is compared with the high-firing condition in a 20-ms window, shifted by 1 ms (see materials and methods). Slope values of the regression lines calculated within each window are plotted as a function of time; thin lines mark 95% confidence intervals computed using the subsampling procedure (see materials and methods). Note that despite the strong difference in firing patterns before stimulus onset (B), the time course of modulation does not replicate the poststimulus attentional effects shown in Figs. 3, 4, and 10.