Surprise response as a probe for compressed memory states
Fig 3
Subject-specific compression parameters extracted by single-trial analysis.
(a) Single-trial P300 AUC responses of a representative subject to standard tones (blue empty circles) and to oddball tones (red, filled circles) as a function of the number of occurrences (n) of the opposite tone in the preceding sub-sequence of N = 11 tones (the fitted N for that subject). The black-edged filled circles show the average response for each n. Single trials: weighted-R2 = 0.230, one-sided permutation test for the R2, 1000 permutations, p-value<0.001, 1145 data points. Mean values: R2 = 0.934 p-value = 3.14x10−7, 12 data points. (b) Single-trial P300 AUC responses to standard tones (blue, empty circles) and to oddball tones (solid red circles) as a function of the optimal IB surprise predictor (N = 11, β = 48.33) for the same subject as in (a). The black-edged solid circles show the average response for each surprise value. Single trials: weighted-R2 = 0.231, one-sided permutation test for the R2, 1000 permutations, P-value<0.001, 1145 data points. Mean values: R2 = 0.939 p-value = 2.22x10−7, 12 data points. (c) color-coded weighted-R2 values of the linear regression analysis for all tested IB compression parameters, for the same subject as in (a,b). The vertical axis denotes the memory window length N. The horizontal axis denotes the representation accuracy parameter β. The pair of model parameters (N, β) that achieved the highest R2 value (marked in black asterisk) was used for the remainder of the analysis. (d) Surprise-related analysis (SRA). The single-trial waveforms were averaged by the IB surprise associated with each trial and are shown color-coded according to the surprise level (shown in the legend). The average SRA waveforms exhibited a gradual increase in the P300 magnitude with the IB surprise level.