Fig. 1: Experimental Design.

A In the sequence learning experiment, the participants saw a sequence of 5-7 images in a fixed order. Each image was presented for 1.5 s followed by an ISI of 0.5 s. During the image presentation period (1.5 s), an image was presented at the center of the screen, flanked by gray placeholders. During the ISI period, a placeholder replaced the central image, and all the placeholders moved in the clockwise direction. At the end of the ISI period, the central placeholder was replaced by the next image in the sequence. B An example of a 5-image sequence. The sequence was repeated 60 times in each experimental session. C For each neuron (N = 452) we determined the image that elicited the most spikes. This image was designated as the preferred image for that neuron. Stimulus preference was verified with a cross-validation analysis (see Methods). The images before and after the preferred image in the sequence were designated as the preceding and following images, respectively. The preferred image had the highest firing rate; the responses to the preceding and following images were not significantly different from each other (p = 0.8 paired t-test, two-sided). In the box and whisker plots, the central mark indicates the median firing rate across cells, the notch reflects the 95% confidence interval for the median, and the box reaches from the first to the third quartile (interquartile range). D Anticipatory responses observed during sequence learning. The mean firing response across all cells (N = 452) is plotted as a function of time. Time = 0 is the onset of the preferred stimulus for each cell, time = −2 s is the onset of the preceding stimulus and time = 2 s is the onset of the following stimulus. The blue, pink and yellow shaded areas correspond to the stimulus periods of the preceding, preferred and following stimuli. The white regions between stimuli are inter-stimulus intervals. Mean firing activity was corrected by subtracting baseline activity before the preceding stimulus (−2.5 s to −2 s). Note the anticipatory firing prior to the onset of the preferred stimuli, as a gradual increase of activity during the preceding stimulus⁶.