The slowing down of responses after committing an error in speeded response tasks has been reliably observed over decades, but explanations vary. Post-error slowing (PES) is commonly thought to reflect a proactive mechanism improving response selection or inhibition. Dutilh and colleagues (2012b) used computational modelling to compare accounts of PES, concluding it results from widened response boundaries reflecting increased caution - supporting a proactive account. We used EEG to test three of the five accounts modelled by Dutilh and colleagues to provide direct neural evidence to supplement their simulated data. In a Go/No-Go task administered to healthy young adults ( N = 94, 24.3 ± 4.8 yrs), we mapped ERP parameters to the theoretical drift parameters established by Dutilh and colleagues. Their hypothesis would predict larger N2 after errors and correlation between N2 amplitude and PES magnitude. Our results contradicted these predictions - N2 amplitude was smaller after errors (p = .076) with no correlation to PES ( p = .960). Instead, our findings strongly support a disorienting account where errors disrupt ongoing attentional processing. The post-error anterior N1 was significantly disrupted by errors ( p = .012) and correlated with PES magnitude ( p = .027). We suggest PES is not strategically proactive but primarily the consequence of attentional disruptions that incidentally improve response inhibition by offsetting response execution initiation. Interestingly, even within our young to middle-aged sample (18-40 years), post-error N1 showed slight age-related diminishment, though higher general intelligence effectively mitigated these disruptions ( p < .002), suggesting cognitive ability influences how errors impact attention.