FIG 1.

Sample stimuli used to measure acuity in Experiments 1 (a), 2 (b) and 3 (c). Observers had to identify the direction of the central target’s tilt, viewed at 6.5 degrees of eccentricity. In some conditions, the surrounding, distractors were absent. When present, the distractors could have the same or different colour, direction of drift or temporal frequency as the target. When search efficiency was measured, all elements were parallel. Observers decided whether any one of them had a unique colour, direction of drift or temporal frequency.