Abstract: "Biases in information gathering are common in the general population and reach pathological extremes in paralysing indecisiveness, as in obsessive–compulsive disorder (OCD). Here we adopt a new perspective on information gathering and demonstrate an information integration bias whereby there is over-weighting of most recent information via evidence strength updates (ΔES). In a crowd-sourced sample (N = 5,237), we find that a reduced ΔES weighting drives indecisiveness along an obsessive–compulsive spectrum. We replicate this attenuated ΔES weighting in a second lab-based study (N = 105) that includes a transdiagnostic obsessive–compulsive spectrum encompassing OCD and generalized anxiety patients. Using magnetoencephalography (MEG), we trace ΔES signals to a late neural signal peaking at ~920 ms. Critically, highly obsessive–compulsive participants, across diagnoses, show an attenuated neural ΔES signal in mediofrontal areas, while other decision-relevant processes remain intact. Our findings establish biased information weighting as a driver of information gathering, where attenuated ΔES is linked to indecisiveness across an obsessive–compulsive spectrum."