This study investigates whether learning can manifest itself in EEG changes
without explicit awareness of the acquired knowledge and without any motor
requirement (to rule out acquisition of motor skills). Subjects passively
heard particular stimulus combinations interspersed with random combination
s. Immediately after this, stimulus combinations were presented which conta
ined violations of the previously learned regular sequences. These violatio
ns elicited two frontally distributed negative waves peaked at about 250 ms
and 500 ms, respectively. None of the participants could detect any regula
rity of the stimulation. No significant difference between regular vs rando
m stimulus combinations was found during acquisition. These findings indica
te that learning without explicit knowledge does not require motor activity
(i.e. is independent of learning response sequences) and does not depend o
n stimulus probabilities. NeuroReport 11:3327-3331 (C) 2000 Lippincott Will
iams & Wilkins.