Figure 1.

Stimuli and task. A, Example event-related fMRI trial. Subjects decided whether a noisy stimulus represented a house or a face, without knowing how they would indicate their response. Following a delay, subjects received a specific motor preparation instruction for either an eye or hand movement. Star and house symbols indicated faces versus houses, respectively (counterbalanced across subjects). During the response stage, subjects indicated their face or house decision by either saccading to the remembered target location in eye trials (up, down, left, or right), or pressing the corresponding button on a diamond-shaped button box in hand trials. A red fixation cross indicated the start of the response period. Subjects maintained fixation at all times of the trial, except during eye movement responses. Fixation was used as baseline in-between trials (jittered duration, see Materials and Methods). B, Example face and house stimuli at high or low levels of sensory evidence (low or high levels of noise, respectively). Note that these levels were adjusted for each subject individually, based on performance during training and after each run in the scanner. Face and house stimuli and levels of sensory evidence were pseudo-randomized across trials. C, Possible motor plans for the motor preparation stage. Eye and Hand trials as well as target locations were pseudo-randomized across trials. F_Hi, H_Hi, High sensory evidence for faces and houses, respectively; F_Lo, H_Lo, low sensory evidence for faces and houses, respectively.