Figure 6.

Attention increases the effect of manipulating V1 activity on the activity of MT units. A, Microstimulation was delivered for 50 ms pulses at 200 Hz during a randomly selected 50% of stimulus presentations in each trial. B, Example peristimulus time histograms from two example MT units. Attention increased the efficacy of microstimulation during the 100 ms period after V1 microstimulation (green shaded period). C, Average microstimulation efficacy (difference in firing rate during the 100 ms period shaded in B between stimulated and unstimulated visual stimulus presentations) for each attention condition for 183 units in 16 recording sessions. The difference in the response to microstimulation was significantly higher when the animal attended to the stimulus that overlapped the receptive fields of the microstimulated V1 units (mean increase, 1.67 sp/s, Wilcoxon signed-rank test, p = 0.008).