Human auditory sustained potentials. I. The nature of the response

In response to a sustained toneburst a negative baseline shift can be recorded from the human fronto-central scalp regions with an onset latency of approximately 150 msec. This auditory sustained potential is distinct both in its scalp distribution and in its stimulus relationships from the transient response occurring at the onset or offset of the toneburst. It differs from the contingent negative variation in that it can occur in the absence of attention or during sleep. Attention to the auditory stimulus can increase the amplitude of the sustained potential, possibly through the addition of an extra negative potential related to auditory expectancy or uncertainty.