Fig. 1.

Top, Spatial layout of the display. The screen was 36 × 25 cm (70 × 50° at the usual distance of 25 cms), of uniform red, with mean luminance of 14 cd/m². The bar, usually vertical and equiluminant green (but sometimes black), could be displayed at any position. The ruler, when used as a reference, appeared 500 msec after completion of saccade. Bottom, Time course of the presentation. The black fixation circle (F₀) stayed on for the duration of the experiment. After a warning, a similar black circle appeared atF₁, to which observers saccaded as quickly as possible. The stimulus (in this case a single vertical bar at position0°) was briefly displayed for one frame (8 msec) at some arbitrary time after the saccadic target appeared. In the first series of experiments, observers simply reported the apparent position of the bar relative to the ruler. In others, they had to report the apparent offset of two half-bars or the number of bars seen in a multiple display.