Effects of discrimination task difficulty on N1 and P2 components of late auditory evoked potential

The present study investigated the question of whether, in healthy young listeners, increases in discrimination task difficulty will alter the amplitude of either the N1 or P2 components of the late auditory evoked potential (LAEP). Using a stimulus oddball procedure, listeners discriminated changes in the frequency of ongoing tonal stimuli. On different test runs, task difficulty was manipulated by decreasing the size of the frequency differences and/or adding competing speech babble to the nontest ear. Both stimulus procedures produced significant decreases in P2 amplitude but had no effects on N1 amplitudes. This finding of selective effects on later rather than earlier occurring components of the LAEP provides objective evidence that some forms of auditory processing are mediated at more central levels of the system.