The neuroimaging study used a similar paradigm (see Figure S1A available online). Confidence data were used to plot ROCs to assess overall performance and separate the contributions of state- and strength-based perception. Confidence-based ROCs were plotted for each individual, and aggregate ROCs are shown in Figure 2B (see Table S1 for response times). Overall accuracy was computed for each participant by quantifying the area this website under

the ROC curve (Macmillan and Creelman, 2005). Overall accuracy was significantly lower for patients (M = 0.67, SD = 0.08) than for controls (M = 0.75, SD = 0.06; t(13) = 2.36, p = 0.02). In order to characterize the nature of this impairment, we assessed the contribution of state- and strength-based perception to performance by examining the ROC parameters ( Aly and Yonelinas, 2012 and Yonelinas, 1994). The degree of curvilinearity in the ROC provides an estimate of perception based on assessments of selleck screening library continuously graded strength information, while the upper x intercept reflects the probability of discrete, state-based perception (Aly and Yonelinas, 2012). The more the ROC curves away from the chance diagonal, the greater the estimate of strength-based perception; the further left the upper x intercept is shifted, the greater the probability

of state-based perception. Visual examination of the aggregate ROCs (Figure 2B) shows that the patients’ ROCs are less curved than

the controls’, whereas the upper x intercepts of the groups are identical. This suggests that MTL damage selectively impairs the ability to make strength-based perceptual judgments, and judgments based on discrete states of perceiving specific differences are preserved. These observations from Thymidine kinase the aggregate ROCs were confirmed in the average parameter estimates (Figure 2C). A 2 (group: patient or control) × 2 (perception: state or strength) mixed-model analysis of variance revealed a significant main effect of group (F(1,13) = 6.27, p = 0.026), a significant main effect of perception (F(1,13) = 12.72, p = 0.003), and a significant group by perception interaction (F(1,13) = 8.53, p = 0.012). The interaction arose because strength-based perception was reduced by more than 50% in the patients compared to controls (0.33 and 0.76, respectively), leading to a statistically significant impairment, (t(13) = 3.24, p = 0.003). In contrast, there was no difference in estimates of state-based perception between patients and controls, t < 1. These results held for patients with selective hippocampal damage as well as patients with more extensive MTL damage (filled and open shapes in Figure 2C, respectively). Both the hippocampal patient group (M = 0.45, SD = 0.08) and the larger MTL lesion group (M = 0.14, SD = 0.20) had reduced estimates of strength-based perception compared to controls (M = 0.76, SD = 0.26).