Early attention effects in human auditory-evoked potentials JÖRG HOORMANN, MICHAEL FALKENSTEIN, and JOACHIM HOHNSBEIN Institut für Arbeitsphysiologie an der Universität Dortmund ~ IfADo!, Dortmund, Germany Abstract A fundamental question in attention theory concerns the earliest processing stages that can be modulated by selective attention. A series of experiments is reported in which very early attention effects are found under specific conditions in the frequency-following potential ~ FFP!, a brain stem response to low-frequency tone stimuli. In two experiments, stimuli of two different modalities were applied, and attention directed to one of the modalities. In two further experiments, only auditory stimuli were presented. In the first of these last two experiments, a dichotic paradigm with sustained attention to one ear was used, in the second a monotic paired-stimuli paradigm was used, in which the first stimulus served as reference for the second one. Only in the last experiment significant attention effects were found in the latency, but not in the amplitude of the FFP. The results show that a very early attention effect on the latency of the FFP can be demonstrated, but only under highly specific conditions. The size and preconditions of the attention effect suggest that it reflects subtle intramodal tuning mechanisms in the cochlea or in the lower brain stem. Descriptors: Brain stem, Evoked potentials, Frequency-following potential, FFP, Attention Peripheral Sensory “Gating” It has been long known from animal studies that efferent neurons can modulate activity within afferent pathways, even at the level of the sensory receptor ~Granit, 1955; Hernandez-Peon, Scherrer, & Jouvet, 1956!. On the basis of these data, Hernandez-Peon ~1966! proposed the “peripheral filter” model, which assumes that a de- scending tonic inhibition can modulate sensory neurons. In fact, the hardware for such a filter exists, at least in the auditory system of mammals, namely the olivocochlear bundle ~OCB!. The OCB consists of two subsystems, a medial and a lateral subsystem ~Guinan, 1988!. In the medial OCB, efferent fibers arise from cell bodies in the superior olivary complex and terminate in the co- chlea. This OCB appears to modulate the active micromechanical properties of the outer hair cells ~ Mountain, 1980; Siegel & Kim, 1982!. Scharf, Quigley, Aoki, Peachey, and Reeves ~1987!, who conducted psychophysical studies, postulated that this modulation is an active process to control specifically those frequencies that are task relevant. Hence it is reasonable to assume that early at- tention effects can be mediated by efferent pathways such as the olivocochlear bundle. Indeed, classical animal studies have dem- onstrated effects of auditory attention at the level of the acoustical nerve ~Oatman, 1976; Oatman & Anderson, 1977! and the brain stem ~Gabriel, Saltwick, & Miller, 1975; Olesen, Ashe, & Wein- berger, 1975!. In humans, evoked otoacoustic emissions ~ EOAEs! have been used recently to demonstrate attention effects, because these emissions are sensitive to mechanical alterations of the outer hair cells. The evidence of the studies on otoacoustic emissions is not uniform. Earlier studies ~Avan & Bonfils, 1991; Freedman, Adler, Waldo, Patchman, & Franks, 1990; Froehlich, Collet, Cha- nal, & Morgon, 1990; Meric & Collet, 1992, 1993; Puel, Bonfils, & Pujol, 1988! suffered from methodological problems, that is, comparison of passive with discrimination conditions. This criti- cism does not apply to two more recent studies by Giard, Collet, Bouchet, and Pernier ~1994! and Michie, LePage, Solowij, Haller, and Terry ~1996!. However, whereas Giard et al. ~1994! did find a small ~average of 0.5 dB! but consistent effect of attention on otoacoustic emissions in a narrow frequency band around the evok- ing frequency, Michie et al. ~1996! did not find such an effect. In sum, from animal studies there is ample evidence for pe- ripheral gating even at the cochlear level, although attempts to demonstrate such gating for humans in recent psychoacoustical studies have been doubtful. To clarify this issue, since the early 1970s electroencephalographic data were used to study early at- tention effects, which led to the results summarized in the following. Electrophysiology of Sensory Gating The physiological and psychological mechanisms of selective at- tention can be analyzed in humans by recordings of event-related potentials ~ ERPs! from the scalp. Attention effects have been ob- served consistently for long-latency auditory ~and visual! ERPs. The most prominent attention-related phenomenon is a negative We thank Michael Smieja for his support with the hardware develop- ment, Ludger Blanke for developing the software for EEG processing and presentation, Brigitta Voss for her helpful assistance with the data evalu- ation, Christiane Westedt for producing the figures, and Carl R. Cavonius for checking the manuscript. We also thank Steven Hackley for most valu- able comments and discussions during the preparation of this paper. Address reprint requests to: J. Hoormann, Institut für Arbeitsphysiolo- gie an der Universität Dortmund, Ardeystr. 67, D-44139 Dortmund, Ger- many. E-mail: hoormann@arb-phys.uni-dortmund.de. Psychophysiology, 37 ~2000!, 29–42. Cambridge University Press. Printed in the USA. Copyright © 2000 Society for Psychophysiological Research 29