Fig 1.
Illustration of the diffusion model.
The two schematics shown here represent a subset of trials selected from hypothetical results for two conditions. The left image displays a moderate, self-referential drift rate (i.e. positive slope, low absolute value), and the right image displays a strong, non-self-referential drift rate (i.e. negative slope, high absolute value). Overall SRET reaction time is broken down into three components: encoding period, decision phase, and motor response. During the decision phase, evidence accumulation begins at the relative starting point (which varies across subjects) and continues until one of the thresholds is met. The time taken to reach the threshold across all trials is used to determine drift rate. Two drift rates were generated for each individual, one pertaining to decision making for positive adjectives and one for negative adjectives.
Fig 2.
Association between 5-HTTLPR and drift rate for the self-referent encoding task.
The top set of plots (a) show data from Study 1; the bottom set (b) show data from the replication, Study 2. The left plot shows the relationship between the 5-HTTLPR genotype and drift rate for negative adjectives and the right plot shows the relationship between the 5-HTTLPR genotype and drift rate for positive adjectives. The left plot shows that S′-carriers of the 5-HTTLPR polymorphism displayed a larger (less-negative) drift rate, indicating that they had more difficulty categorizing negative words as not self-referential. Points are jittered to so that all observations are presented.
Fig 3.
Association between drift rate and recall for self-referential words on the self-referent encoding task.
The top plot (a) shows data from Study 1; the bottom plot (b) shows data from the replication, Study 2. The scatterplot shows the relationship between drift rate and recall of positive (circles) and negative (triangles) stimuli.
Table 1.
Means (SD) for depressive symptoms and diffusion model parameters presented as a function of 5-HTTLPR genotype.