Mismatch negativity to slight pitch changes outside strong attentional focus.

The mismatch negativity (MMN) component of the auditory event-related potential (ERP) is elicited by infrequent, physically deviant stimuli in a sequence of frequent homogeneous stimuli ("standards"). It has been suggested that the MMN is generated by an automatic (attention-independent) neural mismatch process between the sensory input and a memory trace encoding the physical features of the standard stimulus. The MMN independence of attention was addressed in the present study. Standard stimuli and two types of deviant stimuli, differing from standards in frequency either "widely" (5%) or "slightly" (3%) were dichotically presented in random order at a very rapid rate. The subject attended either to left- or right-ear stimuli, counting the number of "slight deviants" in that ear. A reading condition with the same stimuli was also included. Even in the present attend conditions with very strong attentional focus, the MMN was elicited by the slight deviants in the unattended input stream. Furthermore, its amplitude was similar to that of the MMN elicited by the equivalent deviant stimuli during reading. The results suggest that auditory frequency is fully analyzed even in the absence of attention.