Yes. In a placebo-controlled, double-blind cross-over EEG study in 20 healthy volunteers given oral psilocybin (0.26 mg/kg), P300 amplitude was significantly reduced while mismatch negativity (MMN) was not reliably changed.
The data also showed a decrease in N100, suggesting some impact on early perceptual processing, and the P300 reduction correlated with both subjective intensity and psilocin levels. This pattern points to disrupted attention-dependent, higher-order processing with largely intact automatic, pre-attentive deviance detection.
These results come from a small, experimental study in healthy participants and do not imply clinical effects. Details are in this PubMed report.
Hope this clarifies the finding.