Figure 1.

Behavioral task. (A) A trial sequence. Following a brief fixation period, a peripheral placeholder would flash white (peripheral cue) or two white bars would simultaneously flash in the upper and lower visual field, directly above or below the corresponding placeholders (neutral cue). After an interstimulus interval (ISI), either noise patches (N) or targets embedded in noise (T+N) would be concurrently presented inside all four placeholders for 30 ms. On any given trial, the response cue location was predetermined and what was presented in all other three locations was randomized. After a 100 ms interval, a response cue appeared at fixation to indicate the location for which the observer had to report whether a Gabor was present or absent. On one third of the trials the response cue pointed to a precued location. On another third of the trials the response cue pointed to a location that was not precued. In the remaining trials, the precue did not indicate any particular location, and the response cue had equal probability of asking for the detection of a target at any location. (B) Stimuli. On half of the trials, only noise was presented at the precued location; in the other half, the target was presented with noise. The noise was filtered white noise, and the target was a vertical Gabor with a randomly chosen phase. (C) Examples of types of trials. In a valid trial the location indicated by the peripheral cue matched the response cue. In an invalid trial the location indicated by the peripheral cue did not match the response cue. In a neutral trial the cue was presented above and below the placeholders in the upper and lower visual field, and the response cue had equal probability of pointing to a location in either the right or left hemifield.