ERP and EOG responses elicited by deviant tones when presented with and without standard tones to reading subjects.

Event-related potentials (ERPs) and horizontal electro-oculograms (HEOGs) were recorded in 11 subjects to infrequently presented spatially deviant tones (oddball-deviants) embedded in a series of frequently presented standard tones and also to these deviant tones when presented without the standard tones (alone-deviants). Subjects were instructed to read a self-selected book during the stimulus presentation. The mismatch negativity (MMN), a component of the ERP, was elicited by the oddball-deviants, whereas ERPs to the alone-deviants were characterized by a prominent N1. In an additional counting condition (subjects counting the oddball-deviants), the MMN to the oddball-deviants was followed by the P3b. Although the effects of pre-attentive and attentive processing of the oddball-deviants were evident in the ERPs, HEOGs were affected by these stimuli in neither reading nor counting condition. In contrast, robust HEOG responses were elicited by the alone-deviants in the reading condition. The results suggest that reading is a sufficiently demanding task to enable the subject to effectively ignore the oddball-deviants but not the alone-deviants.