418 Electroencephalography and clinicalNeurophysiology, 86 (1993) 418-427 © 1993 Elsevier Scientific Publishers Ireland, Ltd. 0013-4649/93/$06.00 EEG 92578 Auditory processing in visual brain areas of the early blind: evidence from event-related potentials * K. Alho, T. Kujala, P. Paavilainen, H. Summala and R. N i it inen Department of Psychology, University of Helsinki, SF-O0014 Helsinki (Finland) (Accepted for publication: 11 January 1993) Summary Auditory event-related potentials (ERPs) were recorded in early blind subjects and sighted controls when they attended to stimuli delivered to a designated ear under dichotic conditions. The scalp distribution of the processing negativity (PN), the endogenous negativity elicited by attended stimuli, was in the blind posterior to that in the sighted. This suggests that posterior brain areas normally involved in vision participate in auditory selective attention in the early blind. Furthermore, occasional higher-frequency tones in the to-be-ignored ear elicited a negativity (presumably the mismatch negativity; MMN) that had a posterior scalp distribution in the blind as compared to controls. This suggests that the posterior brain areas of the blind also participate in processing of auditory stimulus changes occurring outside the focus of attention. Key words: Blind; Visual deprivation; Audition; Attention; Event-related potentials Blindness beginning at an early developmental stage modifies processing in the non-deprived sensory modalities. Early binocular deprivation increases the proportion of neurons responsive to tactile stimuli dur- ing a somatosensory task in the occipital (Brodmann's area 19) and parietal (area 7) cortices of the monkey (Hyv~irinen et al. 1981a,b; Carlson et al. 1987). Consis- tent with this, Uhl et al. (1991) found that negative DC potential shifts associated with a tactile task were larger over the occipital scalp in early blind humans than in sighted controls. Early blindness also affects auditory processing. The blind may develop an ability to use echoes in order to perceive spatial positions of objects (e.g., Strelow and Brabyn 1982). Development of such auditory abilities in the blind might be related to changes in the auditory system. For example, Ryugo et al. (1975) found that early visual or somatosensory deafferentation increases the density of dendritic spines in the auditory cortex of the rat. Furthermore, Merzenich et al. (1984) suggested that even in normal development of the auditory sys- tem, the cortical mechanisms for sound localization are Correspondence to: Kimmo Alho, Department of Psychology, P.O. Box 11, University of Helsinki, SF-00014 Helsinki (Finland). Tel.: (3580) 191 3407; Fax: (3580) 191 3443. * This research was supported by the University of Helsinki and the Academy of Finland. The authors wish to thank the anonymous referees for their constructive comments and criticism. dynamically maintained and altered throughout life. This plasticity is necessary because of changes in bin- aural localization cues which occur as a result of fac- tors such as the growth of the head and external ears during development and with hearing loss related to aging. Intracranial recording of evoked potentials in the cat has shown that early auditory deprivation leads to enhanced responsiveness of primary auditory cortex to visual stimuli (Rebillard et al. 1977). Furthermore, Neville et al. (1983) found larger visual event-related potentials (ERPs) over temporal and frontal scalp ar- eas in congenitally deaf human adults than in hearing controls. This suggests that congenital deafness causes enhanced visual processing in brain areas normally participating in audition (see also Neville and Lawson 1987). In early blind humans, the negative N1 deflection (peak at about 100 msec from stimulus onset) and the subsequent positive P2 and P3 deflections of auditory ERPs show shortened latencies and enhanced ampli- tudes (Niemeyer and Starlinger 1981; Woods et al. 1985). However, there has been no indication that cortical areas normally involved in vision participate in auditory processing in the blind. Although Wanet-De- falque et al. (1988) found higher occipital glucose metabolism (measured with positron emission tomogra- phy; PET) in early blind subjects than in blindfolded controls during auditory and tactile discrimination tasks, a similar difference was also found in a resting