The essential role of stimulus temporal patterning in enabling perceptual learning Shu-Guang Kuai 1,3 , Jun-Yun Zhang 1,3 , Stanley A Klein 2 , Dennis M Levi 2 & Cong Yu 1 Little is known about how temporal stimulus factors influence perceptual learning. Here we demonstrate an essential role of stimulus temporal patterning in enabling perceptual learning by showing that ‘unlearnable’ contrast and motion-direction discrimination (resulting from random interleaving of stimuli) can be readily learned when stimuli are practiced in a fixed temporal pattern. This temporal patterning does not facilitate learning by reducing stimulus uncertainty; further, learning enabled by temporal patterning can later generalize to randomly presented stimuli. Perceptual learning refers to improvement, through practice, in the ability to discriminate fine differences in visual and other sensory features such as contrast 1,2 , orientation 3,4 and Vernier and other positional acuities 5,6 (see refs. 7 and 8 for recent reviews). Many studies have investigated the effects of spatial factors—such as stimulus contrast, spatial frequency and orientation—on perceptual learning. However, the role of stimulus temporal factors in perceptual learning has been largely overlooked. n = 10 Time 92 ms 92 ms C = 0.20 C = 0.30 C = 0.47 C = 0.63 n = 4 Post-training ΔD D = 22.5° D = 67.5° D = 112.5° D = 157.5° Post-training ΔD Pre-training ΔD n = 5 n = 6 Contrast threshold ΔC Post-training ΔC Session Pre-training ΔC SA Direction threshold (deg) Direction threshold (deg) YH 0.03 0.04 0.05 0.06 0.08 0.1 0.2 0.3 Pre-training ΔC 0.03 0.04 0.05 0.06 0.08 0.1 0.2 0.3 0.03 0.04 0.05 0.06 0.08 0.1 0.2 135135135135 Session 135135135135 Session 135135135135 2 3 4 5 678 10 20 Pre-training ΔD 2 3 4 5 678 10 20 Session 135135135135 0.3 f a b c d e g h i j Contrast threshold ΔC 0.03 0.04 0.05 0.06 0.08 0.1 0.2 0.3 0.03 0.04 0.05 0.06 0.08 0.1 0.2 0.3 Post-training ΔC 0.03 0.04 0.05 0.06 0.08 0.1 0.2 0.3 YS ZJ 2 3 4 5 6 8 10 20 2 3 4 5 6 8 10 20 2 3 4 5 6 8 10 20 2 3 4 5 6 8 10 20 Figure 1 Effects of stimulus roving and temporal patterning on perceptual learning of contrast and motion-direction discrimination. (a) Stimuli for contrast discrimination in a two-alternative forced-choice (2-AFC) trial. A fixation cross was followed by two Gabor stimuli (spatial frequency sf ¼ 6 cycles per degree, presented for 92 ms each separated by a 600-ms interstimulus interval; s.d. s ¼ 0.071.) The observers’ task was to judge which stimulus had higher contrast. Discrimination thresholds were measured with a three-down–one-up forced-choice staircase method. (b) Observer SA’s unchanged session-by-session contrast thresholds (DC) for each reference contrast with contrast roving. Throughout: error bars, s.e.m.; solid lines, linear fits. Training sessions were typically 2 h and included 1,000–1,200 trials. (c) Comparison of mean post- and pre-training contrast thresholds obtained with contrast roving showed no significant learning (F 1,3 ¼ 3.26, P ¼ 0.169; data points significantly below dashed diagonal line indicate that learning has taken place). (d) Observer YH’s session-by-session reduction in contrast thresholds during practice with temporally patterned contrasts. (e) Comparison of mean post- and pre-training contrast thresholds obtained with temporal patterning showed significant learning (F 1,9 ¼ 40.8, P ¼ 0.000). (f) Stimuli for motion direction discrimination. A circular window of diameter 81 held 1,000 random dots, all moving in the same direction at a speed of 101 per s. In a 2-AFC trial, two sets of dots (for clarity, fewer dots are shown) were presented for 500 ms each, with a 200-ms interval between presentations. The observers’ task was to judge in which interval the random dots moved more clockwise. (g) Observer ZJ’s session-by-session motion direction thresholds (DD) with direction roving. (h) Comparison of mean post- and pre-training motion direction thresholds showed no significant improvement after practice with direction roving (F 1,5 ¼ 0.007, P ¼ 0.936). (i) Observer YS’s session-by-session lowering of direction thresholds with temporally patterned directions. (j) Comparison of mean post- and pre-training motion direction thresholds showed that significant learning took place under stimulus temporal patterning (F 1,4 ¼ 17.7, P ¼ 0.014). Received 1 August; accepted 23 August; published online 16 October 2005; doi:10.1038/nn1546 1 Institute of Neuroscience, Chinese Academy of Sciences, Shanghai 200031, China. 2 School of Optometry and Helen Wills Neuroscience Institute, University of California, Berkeley, California 94720, USA. 3 These authors contributed equally to this work. Correspondence should be addressed to C.Y. (yucong@ion.ac.cn). NATURE NEUROSCIENCE VOLUME 8 [ NUMBER 11 [ NOVEMBER 2005 1497 BRIEF COMMUNICATIONS © 2005 Nature Publishing Group http://www.nature.com/natureneuroscience