(A) There was no average change in the decision threshold with either depolarizing or hyperpolarizing stimulation, where the decision threshold reflects the coherence required to reach 80% accuracy. (B) Decision time decreases with increasing coherence, with depolarizing stimulation speeding decision time and hyperpolarizing stimulation slowing decisions. (C) Depolarizing stimulation decreases and hyperpolarizing stimulation increases decision time, but this effect is reduced with increasing coherence. (D) Neural dynamics of the model. The model was run continuously, with the decaying activity of each trial influencing the initial activity at the beginning of the following trial. Depolarizing stimulation delayed the return of this decaying activity to baseline levels, while hyperpolarizing stimulation dampened the overall dynamics of the model and therefore suppressed residual activity. (E) When sorted by the choice made on the previous trial (Left* or Right*), the indecision point (or level of coherence resulting in chance selection of the same choice), shifts. This reflects a bias towards repeating that decision. (F) The positive shift in indecision point is further increased by depolarizing stimulation and decreased by hyperpolarizing stimulation. (G) A logistic regression model was fit to choice behavior with coefficients for coherence and the choice on the previous trial. (H) This analysis confirms a positive value for the influence of the previous choice on the current choice (a1), scaled by the influence of coherence (a2). Depolarizing stimulation increases this ratio, and hyperpolarizing stimulation reduces it. See Figure 2—source data 1 for raw data.