Human event-related brain potentials to auditory periodic noise stimuli Christian Kaernbach a, *, Erich Schro ¨ger a , Thomas C. Gunter b a Institut fu ¨r Allgemeine Psychologie, Universita ¨ t Leipzig, Seeburgstrasse 14–20, 04 103 Leipzig, Germany b Max-Planck-Institut fu ¨r neuropsychologische Forschung, Inselstrasse 22–26, 04 103 Leipzig, Germany Received 22 December 1997; accepted 22 December 1997 Abstract Periodic noise is perceived as different from ordinary non-repeating noise due to the involvement of echoic memory. Since this stimulus does not contain simple physical cues (such as onsets or spectral shape) that might obscure sensory memory inter- pretations, it is a valuable tool to study sensory memory functions. We demonstrated for the first time that the processing of periodic noise can be tapped by event-related brain potentials (ERPs). Human subjects received repeating segments of noise embedded in non-repeating noise. They were instructed to detect the periodicity inherent to the stimulation. We observed a central negativity time-locked on the periodic segment that correlated to the subjects behavioral performance in periodicity detection. It is argued that the ERP result indicates an enhancement of sensory-specific processing.  1998 Elsevier Science Ireland Ltd. Keywords: Audition; Event-related potentials; Periodic noise; Auditory sensory memory; Echoic memory Periodic noise as an auditory stimulus was introduced to psychophysics in order to investigate the lower limit of auditory periodicity analysis [4]. There, subjects were pre- sented with periodically recurring iterations of a segment of white noise that were seamlessly connected to each other. For cycle lengths of two seconds or more this sounded per- fectly like homogenous non-repeating white noise. For cycle lengths of one second or less subjects did easily remark the periodic nature of the stimulus due to the percep- tion of recurring faint events such as clanks and beeps; (demonstrations of periodic noise stimuli can be found at http://www.uni-leipzig.de/~psycho/kaernbach/pn/). Whereas this stimulus was originally designed to study periodicity detection, it is of indubitable value to the study of sensory auditory memory (echoic memory) [3]. It has served in numerous psychophysical studies, testing the intra- and inter-subject stability of the perceived faint events [6], studying their temporal and spectral extent [7], varying the spectral shape of the carrier [12], or estimating phase sensitivity [16] or time-constants [2,8] of echoic memory. To our knowledge, however, it has not yet been investigated whether the processing of periodic noise stimuli can be probed by event-related potentials (ERPs). In one approach, auditory sensory memory has been stu- died measuring event-related magnetic fields elicited by repeating sinusoidal tones at varying repetition rates [9]. However, this approach is based on a hypothetical relation between auditory trace strength and the amplitude of the magnetic components. Moreover, it is unclear to what extent the measured effect could be due to adaptation instead of memory. Other studies measured late cognitive change-specific potentials elicited by infrequent changes of repeating tonal patterns [1,10,11,15,17]. This approach clearly studies memory as the measured ERP components result from a comparison of the stimulus with a detailed representation of the standard stimulus (e.g. of time order in [17]). However, all these studies used simple sinusoidal tones or tonal patterns consisting of sinusoidal tones that may have been memorized using a symbolic rather than a sensory representation. This would be different with a per- iodic noise stimulus as the latter does not contain simple Neuroscience Letters 242 (1998) 17–20 0304-3940/98/$19.00  1998 Elsevier Science Ireland Ltd. All rights reserved PII S0304-3940(98)00034-2 * Corresponding author. Tel.: +49 341 9735968; fax: +49 341 9735969; e-mail: chris@psychologie.uni-leipzig.de