Figure 3. Brain responses are modulated by local statistics.
The brain response to a given observation is plotted as a function of the recent history of events. We connected the possible extensions from shorter to longer patterns, such that the data are represented as a ‘tree’. Each of these trees corresponds to an experimental condition. At each node of a tree, the circles should be read from left to right and denote the corresponding patterns; for instance, the pattern AAAB shows the activity level elicited by the item B when it was preceded by three As. X and Y denote the pooling of both stimuli in conditions in which both stimuli are equiprobable. In the frequency-biased condition, we report the activity evoked by item B, the most frequent stimulus. Activity levels across sensors were averaged using a topographical filter within a late time window (from 500 to 730 ms) post-stimulus onset. The topographical filters were obtained by contrasting rare and frequent patterns (e.g. XYXX – XYXY in the alternation-biased condition). The filters are shown in Figure 3—figure supplement 1; the small, circled and colored numbers at the bottom of each tree serve as identifiers. We defined and applied the filters using a cross-validation approach to ensure statistical independence (see Materials and methods).
Figure 3—figure supplement 1. Responses to the violation of local patterns used as spatial filters.
