BIOL ~ ¥ c m A T R Y 1059 1991 ;30:1059- |062 Mismatch Negativity: An Index of a Preattentive Processing Deficit in Schizophrenia A. M. Shelley, P. B. Ward, S. V. Catts, P. T. Michie, S. Andrews, and N. McConaghy Introduction Although there is little doubt that schizophrenics have attentional problems, the precise nature of the deficit remains obscure. Following the dis- tinction between automatic and controlled pro- cesses (Shiffrin and Schneider 1977), some theorists have proposed that schizophrenic at- tention deficits are confined to controlled, or active attentional processes (Caiiaway and Naghdi 1982; Nuechterlein and Dawson 1984), whereas others have postulated an automatic, or preat- tentive dysfunction, such as a failure of inhi- bition (Johnson 1985) or defective filtering (Shagass 1976). Most event-related potential (ERP) studies of schizophrenic attention deficits suggest an impairment in controlled processing indexed by reduced P3 amplitude and an atten- uation of processing negativity (PN) (Michie et al 1990; Ward et al 1991). However, it is pos- sible that dysfunctions in controlled processes may be secondary to defects in preattentive mechanisms. Mismatch negativity (MMN) is an ERP component elicited in the auditory "oddball" paradigm by low probability "deviant" stimuli embedded in a sequence of high probability From the School of Psychology (SA) and Psychiatry (AMS, PBW, SVC, NMcC), University of New South Wales, Kensington, N.S.W., Australia; ~ld the School of Behavioural Sciences, Mac- quarie University, N.S.W., Australia (PTM). Address reprint requests to A.M. Shelley, Psychiatry Department Prince of Wales Hospital, High Street, Randwick, N.S.W. 2031 Australia. Received May 4, 1991; revised June 24, 1991. "'standard" stimuli. The MMN is most clearly evident in conditions in which subjects are asked to ignore auditory stimuli or to perform a distracting task, suggesting that it is an in- dex of preattentive processing. N~it~en (1990) has proposed that the MMN is generated au- tomatically whenever there is a mismatch be- tween the neuronal model of the physical fea- tures of the standard stimulus and the deviant stimulus. At short interstimulus intervals (ISis), all auditory stimuli elicit an N I and P2, but deviants also elicit the MMN, which overlaps NI and P2 (N~i[it~en and Picton 1987) and peaks 100-300 ms after stimulus onset. MI~ amplitude is increased for low probability de- viant stimuli and for larger differences be- tween deviants and standards. The auditory MMN has been observed when stimulus de- viance is defined by changes in pitch, inten- sity, duration, spatial location, and phoneme change (see N~it~inen 1990). The magnetic counterpart of MMN, the mismatch field, has been observed in response to deviations in stimulus frequency, intensity, and duration (see Kaukoranta et al 1989). The present study investigated whether schizophrenics show deficits in preattentive pro- cesses indexed by the MMN. Subjects and Methods Subjects consisted of 11 medicated schizo- phrenics (7 men, 4 women, mean age 29 years, range 18--44 years) diagnosed according to © 1991 Society of Biological Psychiatry 0006-3223/91/$03.50