Figure 6. Impacts of short-term and long-term components of correlated activities of V1 neurons. A, The classification success rates in the absence and presence of pure short-term correlations (mean ± SEM). In the presence of pure short-term correlations, the decoding accuracy was slightly improved (p = 0.0044, paired t test, 15 sessions with 134 neurons). Note that the chance level is
, as 16 stimuli were decoded. B, The baseline drifts, which cause long-term correlations, were visualized by the principal component analysis for the average responses to 16 visual stimuli (tuning curves) of the neurons with significant baseline drifts (to be precise, the same neuron pool as in C, right). The average responses for 1st–20th trials (turquoise blue) and 21th–40th trials (green) demonstrate that the entire activities of neurons shift over trials. C, Decoding accuracy in the absence and presence of pure long-term correlations. The cross-validated classification success rates for four types of learning were compared: (1) when trained by former trials and tested by former trials, (2) when trained by former trials and tested by latter trials, (3) when trained by former trials and tested by latter trials after the respective global means were subtracted for detrending (i.e., centering and equating the means of former and latter trials in B), (4) when trained by even-numbered trials and tested by odd-numbered trials. Note that the conventional sampling of odd-numbered 20 trials (1st, 3rd, 5th,
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, 39th) included both former and latter trials as a part and, thus, can be inhomogeneous under baseline drifts. No significant difference was observed among four types of learning in the absence of pure long-term correlations, that is, when both short-term and long-term correlations were absent (left, not significant for all pairs, paired t test, 11 sessions with 77 neurons). The significant decrease at the green bar in the presence of pure long-term correlations demonstrates that the long-term correlations do harm for generalization (right, *p < 0.05, paired t test, 23 sessions with 189 neurons). The recovery of the classification success by the detrending or the conventional inhomogeneous sampling (trained by even-numbered and tested by odd-numbered trials) suggests that the brain can decode stimulus information under changing environments by using a sophisticated decoder (***p < 0.001, paired t test).