BRAIN RESEARCH 1142 (2007) 169– 177 available at www.sciencedirect.com www.elsevier.com/locate/brainres Research Report Representation of harmony rules in the human brain: Further evidence from event-related potentials Sakari Leinoa,b, Elvira Bratticob, Mari Tervaniemib, Peter Vuustc,d,⁎ aApperception and Cortical Dynamics (ACD), Department of Psychology, P.O. Box 9, FIN-00014 University of Helsinki, Finland bCognitive Brain Research Unit, Department of Psychology, University of Helsinki and Helsinki Brain Research Center, Helsinki, Finland cCenter of Functionally Integrative Neuroscience, Aarhus University Hospital, Denmark dRoyal Academy of Music, Aarhus, Denmark ARTICLE INFO ABSTRACT Article history: In Western tonal music, the rules of harmony determine the order and music-structural Accepted 10 January 2007 importance of events in a musical piece: for instance, the tonic chord, built on the first note Available online 23 January 2007 of the diatonic scale, is usually placed at the end of chord sequences. A brain response termed the early right anterior negativity (ERAN) is elicited when a harmonically Keywords: incongruous chord is inserted within or at the end of a musical sequence. The present Music study was conducted to test whether the ERAN reflects the processing of harmony rather Harmony than the building of a tonal context and whether the ERAN is also elicited by violations of the Event-related potential tuning of the sounds upon which harmony is based. To this aim, ten subjects listened to ERAN musical sequences containing either expected chords only, a harmonically incongruous MMN chord in one of three positions within the cadence, or a harmonically congruous but mistuned chord in one of the three positions. Simultaneously, the electroencephalograph (EEG) was recorded. Incongruous chords violating the rules of harmony elicited a bilateral early anterior negativity, the amplitude of which depended on the degree of the harmony violation. On the contrary, mistuned chords, violating the rule of relations between all the sounds in the sequences, elicited a bilateral fronto-central negativity (the mismatch negativity, or MMN). The MMN was not modulated by the position of the violation within the musical sequence and had a longer peak latency than the anterior negativity elicited by the harmony rule violations. In conclusion, violations of the harmony and tuning rules of Western tonal music were found to generate specific and distinct electric responses in the human brain. © 2007 Elsevier B.V. All rights reserved. 1. Introduction of chords related to the context and induces expectations by activating tonal representations existing in the mind of the When listening to music, a sequence of chords generates listener (Bharucha and Stoeckig, 1987). Expectancies gener- expectancies for notes or chords to follow. Such expectancy is ated by a harmonic context reflect the innate or learned vital to musical experience (e.g., Meyer, 1956). In particular, the mental representation of tonal relationships, or tonality. harmonic context of a chord sequence primes the processing Tonality (also termed musical key) refers to the organization ⁎ Corresponding author. Center of Functionally Integrative Neuroscience, Aarhus University Hospital, Norrebrogade 44, 8000 Aarhus C, Denmark. E-mail address: [email protected] (P. Vuust). 0006-8993/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2007.01.049 170 BRAIN RESEARCH 1142 (2007) 169– 177 of pitches in such a way that one central pitch dominates and Table 1 – Examples of the chord sequences employed in attracts the others and gives name to the key (see e.g., Koelsch et al. (2000) Bharucha, 1984; Bharucha and Krumhansl, 1983; Krumhansl, Position Position Position Position Position 2000). The core of a functional harmonic context is often 1 2 3 4 5 composed of tonic (T), dominant (D), and subdominant (S) Standard T T3 S D T chords. Compared to other chord functions, these three chord Neapolitan TT3SnD T functions are perceived as more closely related to each other at 3rd (Bharucha and Krumhansl, 1983). The dominant is perceived Neapolitan TT3S D Sn as tension-creating, demanding resolution to the stable at 5th position of the tonic, whereas the subdominant reflects an T=tonic, T3=inverted tonic, S=subdominant, D=dominant, intermediate position between these two oppositions. Chords Sn=Neapolitan subdominant. incorporating notes outside the prevailing harmonic context usually demand resolution to more stable harmonies of the system (Bharucha and Krumhansl, 1983). The mental repre- prominent ERAN mainly in position 5 (T) compared to position sentation of tonality may be established by very few notes or 3 (S), might be a consequence of a less well established key in chords (Berent and Perfetti, 1993; Krumhansl and Kessler, position 3 rather than a violation of expectancies based on 1982). Chords breaking these harmonic expectations may be harmony rules of chord succession. Also note that at position perceived as erroneous, and a reinterpretation of the current 5 the Neapolitan chord always followed a dominant chord, tonality may occur (Berent and Perfetti, 1993). which created a strong expectation for a tonic chord. In Recently, several event-related potential (ERP) studies contrast, at position 3 the Neapolitan chord always followed a investigating the violation of harmonic expectations based on chord that created an expectation for a subdominant chord. the rules of Western tonal music have been conducted (e.g., According to Western musical theory, when used to replace a Koelsch et al., 2000, 2005; Loui et al., 2005; Maess et al., 2001). In subdominant chord, the Neapolitan generates a chord pro- these studies, inappropriate chords within or at the end of gression more accepted in the theory of functional harmony harmonic cadences (chord sequences) elicited an event-related than when placed after a dominant chord (Drabkin, 2002). The potential (ERP) component called the early right anterior most appropriate resolution of the dominant is a tonic chord. negativity (ERAN). The ERAN occurs at an early latency (150– When placed after a dominant chord, i.e. replacing the 250 ms after stimulus onset) and is maximal over anterior strongly expected tonic chord, the Neapolitan therefore regions of the scalp with a tendency to be lateralized to the creates an inappropriate chord succession. This is especially right. The ERAN has been most commonly recorded in a semi- true when the chord that is to be replaced is the final chord of attended paradigm, where the subjects’ attention is directed the cadence. The comparison used in the previous studies towards the music by asking them to respond to infrequent between Neapolitan chords at position 3 and at position 5 of a chords played on a deviant instrument. It can also be elicited five-chord cadence is therefore unbalanced as it contrasts preattentively (Koelsch et al., 2002b), however its amplitude is expectations which are formed by either the building of modulated by the attentional load (Loui et al., 2005). The ERAN tonality or by the harmony rules of ordering of musical has been shown to be larger in musical experts than in novices events. Consequently, also the elicitation of a larger ERAN by a (Koelsch et al., 2002c). Utilizing magnetoencephalography Neapolitan in position 5 than in position 3 of the cadence (e.g., (MEG), Maess et al. (2001) localized the sources of the magnetic Koelsch et al., 2000) may be the result of a confound between ERAN response in the Broca’s area (BA44) and its right- the effects of the building of a tonal context and the processing hemispheric homologue with a non-significant tendency of the harmony violation. towards right-hemispheric superiority. The left-hemispheric In our study we wished to separate the effects of tonality Broca’s area is involved in the processing of linguistic syntax establishment within a musical context and the effects of a (see e.g., Friederici et al., 2000). This result has been interpreted violation of harmony rules, which determine the succession to demonstrate an analogy of the rules of harmony in music and music-structural importance of chords within a cadence. with the rules of linguistic syntax since both comprise of To accomplish this, the present study was based on a chord ordered succession of meaningful sound events in time (e.g., sequence containing seven chords instead of five chords as in Koelsch and Siebel, 2005; Patel, 2003). previous ERAN studies (see Table 2 and Fig. 1). Our standard In previous studies, the violation of the rules of harmony chord sequence formed an authentic cadence (T-D-T-T3-S-D-T) was realized by placing an inappropriate chord, the Neapoli- following the rules of Western functional harmony. Three tan subdominant (Sn), into the authentic cadence (see Table types of chord sequences containing Neapolitan chords 1). The Neapolitan subdominant is the first inversion of the addressed the abovementioned problems by reversing the major triad built on the flattened second degree of the scale (in order of expectation. At positions 3 and 7, the Neapolitan chord C major or minor: F-Ab-Db). The Neapolitan chord includes always followed a dominant chord, hence replacing a tonic notes outside of the prevailing tonality (or key) and is used in chord. In this way, according to harmony rules, a very inap- Western classical music as a variation of the subdominant, propriate succession was created. In one case, at position 3, the most often preceding a V-I cadence. In the previous experi- tonality was not yet established and in the other case, at ments, the Neapolitan chord was presented either at position position 7, the tonality was well established and a strong 3 or at the ending position 5 of the cadence. It is noteworthy expectation for the final tonic chord was created (for the that each trial in the previous ERAN studies was performed in prominent role of the last chord of a cadence for evoking a a different key.