Summary Dysfunctional perception and attention often accompanies and predates the onset of psychiatric illnesses including obsessive-compulsive and anxiety disorders. Many of these dysfunctional responses appear in the context of perceived threat and danger. The neurobiology of visual and attention systems has been extensively characterized in animal models, resulting in extensive mechanistic knowledge ranging from the molecular to the systems and behavioral levels. The proposed research aims to provide new empirically-based, quantitative, and objective markers of specific perceptual and attention processes associated with obsessive-compulsive and anxiety psychopathology. We aim to establish a dimension spanning from hypervigilance to perceptual avoidance, hypothesized to discriminate between diagnostic categories but also predictive of transdiagnostic variables such as severity and comorbidity. We will measure well-validated markers of sensory processing (visual evoked potentials) and competition/attention (frequency-tagged steady state potentials). These data will then be related to clinical data collected in a large sample of individuals presenting with symptoms on the obsessive-compulsive and anxiety spectrum. A mechanistic computational model of perception and attention will be used to aid in data reduction and to heighten reliability. Finding reliable and valid biomarkers of visuocortical reactivity has the potential of transforming diagnostic assessment by providing continuous indices of specific dysfunction. If the goals of this application are met, then reliable and valid indices of dysfunctional perception and attention may help to significantly shift clinical practice. In assessment, objective measures of fear conditioning could be used, for example, to objectively identify patients with hypervigilance, versus those with avoidant dispositions. These inter-individual differences may also be relevant in the context of exposure-based treatments and may represent novel means of assigning patients to individualized treatment protocols as well as predicting treatment outcome.