Electrophysiological evidence implicates automatic low-level feature detectors in perceptual asymmetry.

Perceptual asymmetry has been demonstrated behaviorally using frequency modulated (FM) stimuli: a modulated tone is easier to detect among unmodulated distracters than the converse. We demonstrate perceptual asymmetry for FM tones in the mismatch negativity (MMN) component of the event-related potential, regardless of whether the participant attends to the tones. These results suggest that perceptual asymmetry reflects the automatic activation of low-level feature detectors in the auditory system.