Article Figures & Data
Figures
- Figure 1.
Experimental setup. A, The approximate times of divergence for the three taxonomic orders studied (Springer et al., 2003). B, Rats and tree shrew training took place in an identical test chamber, where a nose poke interrupted a photocell indicating a response. The same stimulus/response panel was used for the monkeys, except they were seated in a primate chair and used their hand to make a response. C, The stimulus configuration consisted of a flickering (15 Hz) target and two constantly illuminated distractors. Initially, in the high-contrast condition, the luminance of the distractors was much lower than that of the target. Following acquisition, animals were transferred to progressively more difficult contrast conditions until they received final training in the minimum-contrast condition. Note that the luminance of the target never changed.
- Figure 2.
Learning dynamics. A, To facilitate visual comparison between species, we calculated the discounted performance (see text). The results for a representative animal from each species is shown for the four contrast conditions used. The shading of the markers denotes contrast condition. Note, only rats received training in the intermediate-contrast condition. B, The nondiscounted learning curves for the same animals, except the humans, are shown for the four contrast conditions. The slopes of the linear regression lines plotted in B provide a measure of learning rate.
- Figure 3.
Behavioral performance. A, Mean performance over the first 5 d of training for all species shown. Initially, all species are at a similar level of performance and begin to diverge on day 3. At day 5, the monkeys and tree shrews are still equivalent, while the rats have fallen behind. B, We calculated the maximum performance for each condition by averaging the best 3 d for each animal for that condition. Asterisks denotes significance (*p < 0.05, **p < 0.01, ****p < 0.001). C, To quantify transfer, we compared the mean of the final three sessions of the prior contrast condition to the first three sessions of the subsequent contrast condition. Mean and SEM performance values are shown for a representative animal of each species. The pie charts illustrate the number of cases of transfer observed in that species, i.e., the number of transfer conditions multiplied by the number of subjects for each species. For statistics and description of transfer conditions, see text.
- Figure 4.
Behavioral strategy. A, The spatial bias index (see text) for the three species is shown for the three contrast conditions. B, The probability of remaining at the three response locations following a reward, or following no reward is shown for each species and training stage. C, The mean values for win stay and lose stay for the center position over the different contrast conditions are shown. D, Ratio of win stay/lose stay (WS/LS) versus behavioral performance at the center position for each of the species. Only for rats is WS/LS ratio correlated with behavioral performance, suggesting that they are able to sustain good behavioral performance using reward to counteract their spatial bias against the center nose poke.
Tables
Case M1(SEM) M2 (SEM) T1 (df = 2) T2 (df = 2) p1 p2 M1 H-L 91 (2.9) 68 (3.4) 41.2 21.6 0.0006* 0.002* M2 H-L 83 (0.8) 54 (5) 14.7 8.7 0.004* 0.01* M1 L-M 81 (2.5) 48 (1.9) 68.7 16.9 0.0002* 0.003* M2 L-M 77 (1.8) 59 (4.7) 8 12 0.01* 0.007* TS1 H-L 82 (7) 50 (4.12) 6.2 8.7 0.02* 0.01* TS2 H-L 79 (7.3) 71 (2.6) 2.9 31.5 0.1 0.001* TS3 H-L 82 (8.7) 61 (3.5) 7.6 16.9 0.01* 0.003* TS4 H-L 81 (4.3) 48 (4.2) 14.8 7.7 0.004* 0.01* TS5 H-L 85 (4.9) 42 (0.3) 19.3 69.8 0.002* 0.0002* TS6 H-L 82 (1.1) 52 (4.1) 18.6 9.6 0.003* 0. 01* TS1 L-M 46 (2.5) 61 (2.1) -10.4 28.5 0.009* 0.001* TS2 L-M 76 (3) 56 (4.4) 27.8 11.3 0.001* 0.007* TS3 L-M 78 (3.8) 66 (0.8) 5.7 82.7 0.03* 0.0001* TS4 L-M 65 (4.9) 64 (5.6) 0.2 11.9 0.9 0.007* TS5 L-M 63 (3.6) 64 (1.2) -0.43) 54.2 0.7 0.0003* TS6 L-M 79 (3.8) 72 (4.6) 1.8 17.7 0.2 0.003* R1 H-I 67 (2) 54 (10.7) 3.1 4.2 0.09 0.053 R2 H-I 75 (2.9) 74 (3.2) 0.22 27.6 0.81 0.001* R3 H-I 74 (3.2) 53 (12.3) 2.9 3.5 0.1 0.07 R4 H-I 63 (8) 43 (1.15) 4.6 22 0.04* 0.002* R1 I-L 82 (2.6) 44 (4.8) 13.4 5.0 0.005* 0.03* R2 I-L 74 (5.9) 47 (2.2) 7.2 13.9 0.02* 0.005* R3 I-L 70 (8) 53 (5.2) 6.1 7.9 0.03* 0.015* R4 I-L 76 (5.2) 57 (5.4) 5 9.4 0.04* 0.01* R1 L-M 52 (0.5) 31 (3.4) 11.2 -1 0.008* 0.4 R2 L-M 46 (2.8) 30 (3.5) 7 -1.8 0.02* 0.2 R3 L-M 49 (5.2) 29 (5.13) 4.1 -1.6 0.056 0.2 R4 L-M 58 (6.8) 36 (2.1) 9.3 3.1 0.01* 0.09 The mean behavioral performance pre- and post-transfer (M1,M2) and related SEM values are shown for all transfer cases for each individual animal of all three species (M, monkey; TS, tree shrew; R, rat) and transfer condition (H, high contrast; I, intermediate contrast; L, low contrast; M, minimal contrast); i.e., row TS4 H-L provides information on tree shrew 4 on the transfer from high- to low-contrast condition. Statistics for paired t tests are shown for t test T1, testing M1 against M2, as well as t test T2, testing M2 against chance performance (33%). Triangles denote transfer type (compare Fig. 3C), with full, partial, and no transfer denoted by purple, yellow, and gray, respectively.
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