Stage 2 1000 1200 1400 1000 1250 1500 1750 2000 Trial Mean  RT (ms) Experiment 1 (n=109) 2 (n=59) 3 (n=213) A B C 0 10 20 30 40 * * * Significant in Mixed Effects Model Lattice vs. Random Modular vs. Lattice Graph Comparison Modular vs. Random = RT Difference (ms) D Lattice Modular Random E 0 Stage 1 0 P earson's ρ  =  0.34 p  <  0.001 0 50 100 150 0.00 0.25 0.50 0.75 1.00 Scaled Learning Rate Nov el Edge Ef fect (ms) n=109 0 50 100 150 0.00 0.25 0.50 0.75 1.00 Scaled Learning Rate Novel Edge Effect (ms) Stage G raph Modular (n=30) Lattice (n=43) Random (n=36) n=70 n=72 n=71 Figure 3. Learning Rate and Edge Surprisal. Impact of new edges on reaction time. (A) Mean RT increases in stage 2 when new edges are added to the graph (trials 1501-2000). Included for comparison are Experiments 2 and 3, where – respectively – only the walk or a subset of edges were changed. In both cases the increase in RT is much smaller. (B) Per-subject learning rate correlated with the novel edge effect, defined as the mean difference in reaction time for a subject learning the second graph when responding to a novel edge versus a familiar edge (see Methods; n=109). Learning rate, the model coefficient for log(trial), was scaled amongst all subjects to the range [0,1]. The blue line is the least squares fit, with the gray envelope indicating the 95% confidence interval. (C) Individual correlations shown for the three types of graphs trained on in the first stage. Subjects exposed to the modular and lattice graphs show a significant relationship ( p < 0 . 01 , n = 30 and p < 0 . 03 , n = 43, respectively), while those exposed to the random graph do not ( p < 0 . 2 , n = 36). Solid lines represent least squares fits, and gray envelopes represent the respective 95% confidence intervals. (D) Differences in reaction time by graph type, across graphs learned in sequence. Each bar shows the number of milliseconds by which the modeled effect for the top listed graph is faster. The increase in RT from lattice to modular, and from random to modular graphs, are both significant to p = 0 . 02 and p = 0 . 001, respectively (See Supplementary Table 5). Error bars indicate standard error as estimated in the mixed effects model. Asterisks indicate significance in the mixed effects model. Group sizes: Lattice-Random: n=70, Modular-Lattice: n=72, Modular-Random: n=71. (E) Examples of the graph types. 11/29