The contributions of eye gaze fixations and target-lure similarity to behavioral and fMRI indices of pattern separation and pattern completion.

Pattern separation and pattern completion are generally studied in humans using mnemonic discrimination tasks such as the Mnemonic Similarity Task (MST) where participants identify similar lures and repeated items from a series of images. Failures to correctly discriminate lures are thought to reflect a failure of pattern separation and a propensity toward pattern completion. Recent research has challenged this perspective, suggesting that poor encoding rather than pattern completion accounts for the occurrence of false alarm responses to similar lures. In two experiments, participants completed a continuous recognition task version of the MST while eye movement (Experiments 1 and 2) and fMRI data (Experiment 2) were collected. In Experiment 1, we replicated the result that fixation counts at study predicted accuracy on lure trials (consistent with poor encoding predicting mnemonic discrimination performance), but this effect was not observed in our fMRI task. In both experiments, we found that target-lure similarity was a strong predictor of accuracy on lure trials. Further, we found that fMRI activation changes in the hippocampus were significantly correlated with the number of fixations at study for correct but not incorrect mnemonic discrimination judgments when controlling for target-lure similarity. Our findings indicate that while eye movements during encoding predict subsequent hippocampal activation changes for correct mnemonic discriminations, the predictive power of eye movements for activation changes for incorrect mnemonic discrimination trials was modest at best.

Cognitive control in obsessive-compulsive disorder (OCD): Proactive control adjustments or consistent performance?

Cognitive control is often parsed into proactive and reactive control components. In proactive control, task- and goal-relevant information is utilized in a top-down manner to improve performance, while reactive control is a late-response corrective mechanism that occurs after conflict or errors. We tested whether people with obsessive-compulsive disorder (OCD) would show specific proactive control dysfunction in 31 individuals with OCD and 30 psychiatrically-healthy controls. We employed two tasks that differentiate proactive and reactive cognitive control processes: the cued-Stroop and the AX version of a continuous performance task (AX-CPT). There was a 1s or 5s delay between the cue and probe for both tasks to allow for implementation of proactive control processes. Participants also completed a neuropsychological test battery and mood and symptom severity self-report questionnaires. Although there were group-level differences in OCD severity and depression/anxiety symptoms, there were no significant differences in response times (RT) and error rates between groups for delay or condition for the cued-Stroop or for the AX-CPT, indicating similar performance in implementing proactive control strategies. There were also no significant differences between OCD and control participants on neuropsychological test performance. Results suggest a convergence of evidence wherein individuals with OCD are not showing disproportionately altered proactive control abilities.

Repetition of Computer Security Warnings Results in Differential Repetition Suppression Effects as Revealed With Functional MRI.

Computer users are often the last line of defense in computer security. However, with repeated exposures to system messages and computer security warnings, neural and behavioral responses show evidence of habituation. Habituation has been demonstrated at a neural level as repetition suppression where responses are attenuated with subsequent repetitions. In the brain, repetition suppression to visual stimuli has been demonstrated in multiple cortical areas, including the occipital lobe and medial temporal lobe. Prior research into the repetition suppression effect has generally focused on a single repetition and has not examined the pattern of signal suppression with repeated exposures. We used complex, everyday stimuli, in the form of images of computer programs or security warning messages, to examine the repetition suppression effect across repeated exposures. The use of computer warnings as stimuli also allowed us to examine the activation of learned fearful stimuli. We observed widespread linear decreases in activation with repeated exposures, suggesting that repetition suppression continues after the first repetition. Further, we found greater activation for warning messages compared to neutral images in the anterior insula, pre-supplemental motor area, and inferior frontal gyrus, suggesting differential processing of security warning messages. However, the repetition suppression effect was similar in these regions for both warning messages and neutral images. Additionally, we observed an increase of activation in the default mode network with repeated exposures, suggestive of increased mind wandering with continuing habituation.