Figure 7: Behavioural indices recorded in Experiment 2.

(a) maintenance, (b) perseverance and (c) switches, in 17 healthy participants under three conditions of pharmacological manipulation. Histograms represent mean values and standard deviation under placebo, DA antagonist (risperidone), and DA precursor (L-Dopa). Markers represent mean values per participant, grouped so to represent measures recorded under the condition of either low or high values (squares and circles, respectively). Boxplots represent the distribution in quartiles of within subject differences between measures recorded under placebo and DA antagonist: the two conditions have been selected to establish a comparison with experiment 1. Each measure reports the distribution of differences across value condition (left), and under either high (centre) or low (right) value separately. Two-way repeated measures 3 × 2 ANOVA indicates the presence of a trend in the interaction between pharmacological and reward conditions for the measure of switches (F = 2.501, p = 0.098). Follow-up analysis reveals a main effect of the pharmacological manipulation (F = 5.296, p = 0.035), irrespective of the associated reward, when comparing the measure of perseverance recorded under placebo and DA antagonist condition (b, right). Finally, two-way repeated measures 2 × 2 ANOVA confirms the presence of an interaction effect for the index of switches when comparing behaviour under DA antagonist with either placebo (c) or DA precursor (F = 3.121, p = 0.096 and F = 6.492, p = 0.021). In particular, the distribution of within subject differences (Placebo -DA antagonist, c, right), recorded under high reward condition, shows the predicted increase in terms of number of switches per luminance pattern under the low DA drive pharmacological manipulation. Statistical significance in the figure, relative to the preliminary 3 × 2 ANOVA is expressed as follows: ^T for 0.10 > p > 0.05; ^(ns) for not significant.