FIGURE 1.

Generalization Results Across Groups for Ratings of Perceived Risk of Shock in a Study of Neural Substrates of Overgeneralized Conditioned Fear^a

^a Perceived risk of shock (0=no risk, 1=some risk, 2=high risk) was assessed during conditioned danger cues (CS+), generalization stimuli (GS₃, GS₂, GS₁), and conditioned safety cues (ring-shaped [oCS−] or V-shaped [vCS−]), forming a continuum of similarity between CS+ and CS−. Generalized conditioned fear was evidenced by the main effects of stimulus type in each group (all p values <0.0001), reflecting downward gradients of perceived risk as stimuli differentiated from CS+. Dotted lines indicate hypothetical linear decreases in responding from CS+ to oCS− with which to visualize the deviation of gradients from linearity in each group. Such deviations reflect a significantly stronger linear component in the generalization gradient of posttraumatic stress disorder (PTSD) subjects relative to trauma control subjects (p=0.01) and of subthreshold PTSD subjects relative to trauma control subjects (p=0.04), indicating more gradual, linear declines indicative of overgeneralization in PTSD. To identify the point on the continuum of similarity at which perceived risk ceased to generalize for each group, planned comparisons contrasting oCS− against CS+ and GS₃, GS₂, and GS₁ were computed. Red data points signify stimulus types eliciting increased risk ratings relative to oCS− after applying Hochberg’s adjustment for multiple tests (23). In trauma control subjects, perceived risk was elevated from oCS− to CS+ (p<0.0001) and GS₃ (p<0.0001), but not GS₂ (p=0.06) or GS₁ (p=0.91). By contrast, in PTSD and subthreshold PTSD subjects, perceived risk was elevated from oCS− to CS+ (all p values <0.0001), GS₃ (all p values <0.0001), GS₂ (all p values <0.0001), and GS₁ (all p values ≤0.016). Thus, while trauma control subjects generalized perceived risk only to one degree of differentiation from CS+ (i.e., GS₃), those with PTSD and subthreshold PTSD generalized to three degrees of differentiation (i.e., GS₃–GS₁). Ellipses around the rightmost data points highlight response slopes from CS+ to GS₃ that are more gradual and linear in PTSD and subthreshold PTSD but more steep than linear in trauma control subjects.