Stimulus novelty differentially affects attentional allocation in PTSD

Background: This study investigated attentional allocation in 39 Vietnam combat veterans, 25 with and 14 without posttraumatic stress disorder, assessing P300 amplitudes and latencies during both three-tone and novelty “oddball” tasks. Methods: The three-tone oddball task consisted of three stimuli: frequent tones (85%), rare target tones (7.5%), and rare distractor tones (7.5%). The novelty oddball task was identical to the three-tone task except that the rare distractor tones were replaced with nonrepeating novel sounds (7.5%). Results: Combat veterans with posttraumatic stress disorder showed significant P300 amplitude enhancements at frontal sites in response to distracting stimuli during the novelty but not during the three-tone oddball tasks. There were no amplitude differences in target tones during either task. Conclusions: The data suggest that combat veterans with posttraumatic stress disorder demonstrate P300 responses consistent with a heightened orientation response to novel, distracting stimuli. This finding is consistent both with the clinical presentation of the disorder and with theoretical notions that individuals with posttraumatic stress disorder demonstrate information-processing biases towards vague or potentially threatening stimuli.