Change detection and di¡erence detection of tone duration discrimination Shuntaro Okazaki a , Shin’ichiro Kanoh b , Kana Takaura a , Minoru Tsukada c and Kotaro Oka a a School of Fundamental Science and Technology, Graduate School of Science and Technology, Keio University, Kanagawa, Japan, b Department of Electronic Engineering, Graduate School of Engineering, Tohoku University, Miyagi, Japan and c Faculty of Engineering, Tamagawa University, Tokyo, Japan Correspondence and requests for reprints to Shuntaro Okazaki, School of Fundamental Science and Technology, Graduate School of Keio University, 3-14 -1 Hiyoshi, Kohoku-ku, Yokohama 223- 8522, Japan Tel: + 81 45 5631151 ext. 42345; fax: + 81 45 564 5095; e-mail:okazaki@bpni.bio.keio.ac.jp Sponsorship: This work was supported by the Ministry of Education, Culture, Sports, Science and Technology, Grant-in-Aid for 21st century COE program ‘Understanding and Control of Life’s Function via Systems Biology’. Received 11 January 2006; accepted13 January 2006 An event-related potential called mismatch negativity is known to exhibit physiological evidence of sensory memory. Mismatch negativity is believed to represent complicated neuronal mechan- isms in a variety of animals and in humans. We employed the auditory oddball paradigm varying sound durations and observed two types of duration mismatch negativity in anesthetized guinea pigs. One was a duration mismatch negativity whose increase in peak amplitude occurred immediately after onset of the stimulus di¡erence in a decrement oddball paradigm. The other exhibited a peak amplitude increase closer to the o¡set of the longer stimulus in an increment oddball paradigm. These results demonstrated a mechanism to percept the di¡erence of duration change and revealed the importance of the end of a stimulus for this perception. NeuroReport 17:395^399  c 2006 Lippincott Williams & Wilkins. Keywords: auditory perception, discrimination, event-related potentials, guinea pigs, mismatch negativity Introduction The perception of sound duration change is one of the most primitive brain functions required for survival. To investi- gate this type of perception, a sequence of repetitive frequent (standard) stimuli and infrequent (deviant) stimuli (the oddball paradigm) was employed and elicits an event- related potential (ERP) that is called mismatch negativity (MMN) [1]. MMN is observed not only in humans [2–5], but also in many awake and anesthetized mammals, for example, monkey [6], cat [7,8], rabbit [9], mouse [10], and guinea pig [11,12]. To clarify the neuronal mechanisms of MMN, it is important to establish animal models of the brain response involved in MMN. In fact, the research of animal models has contributed significantly to the under- standing of the neuronal mechanisms of human MMN. Auditory MMN is elicited by a deviance of the stimuli in various physical attributes such as duration, intensity, and frequency of simple tones [13], or of more complex stimuli [14]. Recent studies indicate that auditory MMN is involved in higher-order speech processing (i.e. temporal auditory grouping and speech sound perception [14–17]). Thus, MMN is believed to provide an index of higher order function in auditory processing. Furthermore, it is well known that the amplitude and latency of MMN change depend on the different frequencies of standard and deviant stimuli [18]. Therefore, MMN appears to indicate the brain’s detection of how a difference magnitude between standard and deviant stimuli is (difference detection), in addition to the detection of the stimulus change (change detection). Studies, for example, [19,20] have reported how the difference magnitude of duration change may be represented in MMN and its magnetic counterpart (MMNm). Studies investigating the difference between duration increment and decrement, however, do not exist. Previous studies have reported that duration MMN is triggered by the onset of the stimulus difference (OSD) [10]. On the oddball paradigm in which the duration of the deviant stimuli is shorter than that of the standard stimuli (duration decrement oddball para- digm), the difference of duration between the standard and deviant stimuli is recognized at the OSD. In the duration increment oddball paradigm, difference of duration between standard and deviant stimuli, however, is detected at the offset of deviant stimuli as opposed to the OSD. Noting the different timing of the change detection and the difference detection in duration discrimination, we investigated the event-related potential from varying dura- tions (duration MMN) on anesthetized guinea pigs. In this study, the amplitude and latency of the duration MMN varied according to the direction of the tone duration change (duration increment and decrement). As the guinea pig is an inexpensive and easily available laboratory animal with good audition [21] and its anatomical and electro- physiological attributes are remarkably established, it is an ideal subject for our research. This animal model of MMN has good applicability for future studies on neuronal mechanisms of duration discrimination in humans. AUDITORYAND VESTIBULAR SYSTEMS NEUROREPORT 0959-4965  c Lippincott Williams & Wilkins Vol 17 No 4 20 March 2006 395 Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.