Rationale <p>Cross-modal conflict control (CMCC) refers to the ability to prioritize information from one sensory modality while suppressing interference from another when presented with incongruent stimuli. Patients with substance use disorder (SUD) often exhibit CMCC deficits, but it has not been clarified whether this deficit occurs at the perception or response level.</p> Objectives <p>This study investigated whether CMCC deficits in patients with SUD originate at perception or response levels and examined the modulatory role of the left dorsolateral prefrontal cortex (DLPFC) using transcranial direct current stimulation (tDCS).</p> Methods: <p>28 male patients with SUD completed a 2:1 mapping paradigm dissociating perception (PIC) and response level conflicts (RIC) under three tDCS conditions (anodal, cathodal, and sham). The paradigm required attending to visual or auditory stimuli while ignoring incongruent inputs from the other modality, with the left DLPFC as the stimulation target.</p> Results <p>At the perception level, patients with SUD exhibited no significant difference between the degree of visual interference with auditory and auditory interference with visual. At the response level, visual interference with auditory was greater than auditory interference with visual in patients with SUD. Furthermore, anodal tDCS applied to the left DLPFC reduced auditory interference with visual perception at the perception level and diminished audiovisual cross-modal interference intensity at the response level.</p> Conclusions <p>Patients with SUD show dissociable CMCC deficits, with visual interference dominating at the response level but not at the perception level. Anodal stimulation of the left DLPFC enhanced perceptual-level attention and reduced response-level conflict, whereas cathodal stimulation had little effect. These results underscore the key role of the left DLPFC in such deficits and support the therapeutic potential of anodal tDCS for addiction.</p>