Target selection signals causally influence human perceptual decision making.

The ability to form decisions is a foundational cognitive function which is impaired across many psychiatric and neurological conditions. Understanding the neural processes underpinning clinical deficits may provide insights into the fundamental mechanisms of decision making. The N2c has been identified as an EEG signal indexing the efficiency of early target selection, which subsequently influences the timing of perceptual reports through modulating neural evidence accumulation rates. Evidence for the contribution of the N2c to human decision making however has thus far come from correlational research in neurologically healthy individuals. Here, we capitalised on the superior temporal resolution of EEG to show that unilateral brain lesions in male and female humans were associated with specific deficits in both the timing and strength of the N2c in the damaged hemisphere, with corresponding deficits in the timing of perceptual reports contralaterally. The extent to which the N2c influenced clinical deficits in perceptual reporting speed depended on neural rates of evidence accumulation. This work provides causal evidence that the N2c indexes an early, hemisphere-specific process supporting human decision making. This non-invasive EEG marker could be used to monitor novel approaches for remediating clinical deficits in perceptual decision making across a range of brain disorders.Significance Statement Understanding how particular brain processes contribute to decision-making is crucial for our treatment of psychiatric and neurological disorders. This study provides causal evidence linking deficits in speed of visual processing to specific well-delineated EEG signals representing early target selection and evidence accumulation, in individuals with brain lesions. By showing how these lesions disrupt perceptual decisions, this work identifies a potential biomarker for decision-making deficits. This EEG measure offers a promising, non-invasive tool to track and refine treatments aimed at restoring decision-making abilities in affected patients.