Abstract
Patients with Obsessive–Compulsive Disorder (OCD) often struggle to suppress maladaptive habitual behaviours, yet the temporal dynamics of habit–goal arbitration remain unclear. Here we address this question using an intensive four-day training protocol followed by a time-resolved forced-response test, combined with computational modelling. OCD patients and healthy controls (HCs) showed comparable learning trajectories, indicating intact basic associative learning and perceptual–motor speed in OCD. Critically, when previously learned stimulus–response mappings were remapped, OCD patients exhibited a selective increase in habitual errors, but only within an early time window. At longer preparation times, differences disappeared. Computational model comparison showed that OCD patients were more likely than HCs to be best described by a habit model. Within this model, OCD patients showed reduced variability in habitual preparation latency, reflecting more temporally consistent, sharply tuned habit behaviour. Exploratory analyses linked greater symptom severity to more variable goal-directed preparation. Together, these findings suggest that precisely timed habitual responses are more likely to be expressed during early preparation in OCD. This early-expression bias offers a possible account of ego-dystonic compulsions as a biased race in response preparation, without treating the task as a direct test of competition between independent systems