Figure 1.

Iconic memory paradigm

(A) Sperling’s experiment. The subjects saw a display with 12 letters for a short amount of time. In the partial report version of the paradigm, an auditory cue indicated which row had to be reported.

(B) Stimulus design. The monkeys made eye movements to one of six purple targets, organized in pairs. The actual stimulus consisted of white curves on a gray background (as in D). The contour elements shown as black solid lines are always visible (skeleton), and a subset of the gray dashed contour elements (discriminant segments) are only displayed briefly. In this example stimulus, the RF (green rectangle) fell on one of the discriminant segments.

(C) Example configurations. On each trial, one of the discriminant segments is shown per pair so that only one of the purple circles of that pair is connected to the branch point.

(D) Stimulus sequence. After the monkey had maintained gaze at the fixation point for 300 ms, the skeleton was visible for 250 ms. Next, the three discriminant segments were shown for a variable duration (58, 105, 152, 200, or 247 ms). After the discriminant segments disappeared, a meta-contrast mask was displayed for 100 ms on half of the trials, whereas the skeleton was displayed in the other half of the trials. At a delay of 750 ms after the onset of the discriminant segments, a central cue appeared (see inset), probing one of the pairs. At this moment, the fixation point became green, cueing the monkey to make an eye movement to the purple circle that had been connected to the branch point of the cued pair. The green rectangle denotes the RF of the recorded neurons and was not visible to the monkey.