414 Frontal Lobe Contributions to Perception of Rhythmic Group Structure An EEG Investigation PHILIP G. HARRIS, RICHARD B. SILBERSTEIN, GEOFF E. NIELD, AND ANDREW PIPINGAS Brain Sciences Institute, Swinburne University of Technology, 400 Burwood Road, Hawthorn, 3122, Victoria, Australia KEYWORDS: Frontal lobe; Group structure; Interonset interval; Perception of group structure; Rhythmic group structure Substantial research supports the salience of relatively longer interonset intervals (IOIs) in determining rhythmic group structure, 1–4 yet little is understood about the neural underpinnings of the perceptual grouping process. Gestalt-based interpreta- tions of perceptual processes underlying rhythmic groupings have been proposed 5 and converge with orienting response theory, which proposes enhanced neural sen- sitivity following a change in IOI. 6 In support of this, enhancement of the N1-P2 component of event-related potential (ERP) responses to the first sound in short rhythmic groups has been demonstrated. 7 The current study investigated cortical re- sponses to perception of rhythmic group structure by examining changes in EEG re- sponses associated with participants’ active and passive perception of pitch/rhythm patterns. The study used the steady state visually evoked potential (SSVEP) to ex- amine ongoing changes in 13-Hz EEG responses while participants listened to pitch/ rhythm patterns. Forty-three females, aged 18–42 years (mean = 23.0, SD = 5.6) with a wide range of musical training (mean = 4.0, SD = 7.0, range = 0–32) performed two tasks while their EEG was recorded. Pitch memory was tested with a probe recognition task, which required participants to actively memorize 10-note pitch/rhythm patterns for subsequent recognition. A passive task required participants to detect the rare play- ing of two-note pitch pairs among a single-note pitch/rhythm series. Stimuli in both tasks consisted of diatonic pitch series at 600 ms IOI with a semirandom ( p = 0.15) doubling of IOI to 1200 ms. Neither task placed explicit demands on perception of rhythmic structure of the pitch series. Brain electrical activity was recorded from 64 scalp electrodes, including all International 10–20 positions, referenced to linked ear lobes with nose as ground. The SSVEP was elicited by a 13-Hz flicker delivered to Address for correspondence: Philip G. Harris, Brain Sciences Institute, Swinburne University of Technology, 400 Burwood Road, Hawthorn, 3122, Victoria, Australia. Voice: +61-3- 92148832; fax: +61-3-92145525. pharris@bsi.swin.edu.au