Figure 5: Rule selectivity of neurons in the NCL.

(a) Percent-explained variance (PEV) by the factors ‘cue modality’ and ‘behavioural rule’ for the entire population of recorded neurons, calculated in a 300 ms-sliding window using the ω² statistic. At the beginning of the Delay2, there was a strong sensory influence by the cue modality. At the end of the Delay2 period, the abstract behavioural rule was the strongest variable accounting for the variance in firing rates. Vertical lines mark transitions between task periods, dashed lines show s.e.m. (b) k-Nearest-Neighbor classification: the feature space, spanned by the firing rates of all neurons in a late window. To reduce dimensionality, only the first two principal components (PC1 and PC2) are shown. Each trial is assigned the same label as the majority vote of its k-nearest neighbours in the training set. Neighbours are those trials with the smallest Euclidean distance in the feature space. Blue dots represent trials where the ‘match’ rule was shown, pink dots represent trials where the ‘nonmatch’ rule was shown. An example test trial is marked with a black circle, its nearest neighbours are marked with grey circles. Since the majority of the neighbours belong to the pink class (‘nonmatch’ rule), the test trial would be classified (correctly) as belonging to the pink class. (c) Performance of a k-Nearest-Neighbor classifier predicting the behavioural rule in each trial from the firing rates of all recorded neurons (green). Performance of a second k-Nearest-Neighbor classifier predicting the cue modality in each trial from the firing rates of all recorded neurons (grey). Dashed line indicates chance level. Vertical lines mark the beginning of the rule-cue period, end of the rule-cue period and end of the Delay2 period.