Figure 3.
Attentional modulation of amplitude of the evoked response and fluctuations at nonstimulus frequencies. Effects of attention were quantified as a contrast index of fMRI signal amplitudes for the two attention conditions: (wedge − fixation)/(wedge + fixation). (A) Attending to the rotating wedge significantly increased the amplitude of the visual response (stimulus frequency, 0.0293 Hz) in early and ventral visual cortical areas, but not in IPS1, IPS2, LO1, or LO2. (B) In contrast, attending to the wedge decreased the strength of endogenous nonstimulus fluctuations (0.0073–0.1 Hz, excluding the stimulus frequency and its harmonics) in every measured topographically organized area except IPS2, V4, and VO1. These attention effects were not observed in a PCC control region. Error bars represent SEMs across pairs of attention-to-wedge and attention-to-fixation runs.
