Rat orientation discrimination performance increases with target stimulus duration.

(A) The testing chamber is fitted with three photo-interrupter detectors; a central sensor for trial initiation and two flanking sensors equipped with drinking spouts for perceptual report. The rat activates each sensor by breaking the infrared beam with its nose. Trial initiation results in the presentation of visual stimuli on an LCD monitor placed at a 25 cm viewing distance. When the rat selects the correct response port, a liquid reward is delivered at the centre of the corresponding flanking sensor. (B) Trial structure. Rat performance was measured in the absence of a mask across varying target durations. Following a central nose-poke, a blank gray screen was shown for a random period of 350–650 ms. Subsequently, the target grating was visible for 8.3–100 ms, followed by another random period with blank screen. After this period, a tone sounded, signalling that animals could leave the central port and move to a side port to indicate their response. Correct responses were only rewarded if they were made in the allocated response window. (C) Individual and average performance across 7 animals. The dotted line indicates chance performance. For each rat, the target duration where performance became significantly above chance is indicated by an asterisk (*, p<0.05). The black arrows indicate the target duration (16 and 42 ms) selected for subsequent masking experiments. For rat A, data represents a summary of performance across an average of 155 trials/duration and 17 sessions (Rat B– 214 trials/duration; 9 sessions. Rat C– 298 trials/duration; 24 sessions. Rat D– 327 trials/duration; 23 sessions. Rat E– 381 trials/duration; 25 sessions. Rat F– 191 trials/duration; 9 sessions. Rat G– 226 trials/duration; 29 sessions).