Individual differences in sequence learning and auditorypattern sensitivity as revealed with evoked potentialsElisabet Tubau,1,2Carles Escera,2Vanessa Carral2and Marı´a-Jose´Corral21Department of Basic Psychology, Faculty of Psychology, University of Barcelona, Pg de la Vall d’Hebron, 171, 08035 Barcelona,Catalonia, Spain2Cognitive Neuroscience Research Group, Department of Psychiatry and Clinical Psychobiology, Faculty of Psychology,University of Barcelona, 08035 Barcelona, Catalonia, SpainKeywords: action control, auditory action effects, explicit and non-explicit learners, mismatch negativity, sequential actionAbstractResearch on motor sequence acquisition has shown significant differences between learners. Learners who develop explicitknowledge respond faster than non-explicit ones and they show larger amplitude in event-related brain potentials to sequencedeviants. There is evidence that memory span correlates with the amount of sequence learned, but the specific mechanismssubserving such differences are still unknown. Recently, it has been observed that performance of explicit learners, but not of non-explicit ones, improves when presented with auditory action effects. Accordingly, differences between learners might be related todifferences in auditory rhythm perception. To test this hypothesis, the mismatch negativity (MMN)-evoked potential elicited to stimuliviolating stimulus alternation (i.e. low pitch, high pitch) was recorded in explicit and non-explicit sequence learners. Results confirmedour prediction: explicit learners showed larger amplitude of the MMN to the violation of the auditory rhythm, suggesting newtheoretical implications to account for individual differences in sequential action control.IntroductionSequential activities, such as music or sports, require controlling boththe order of the actions and the precise timing in which they have to beperformed. The problem of how serial order is acquired andrepresented in the brain (Lashley, 1951) has nowadays receivedspecial interest in the serial reaction time (RT) task. In this task, asequence of button presses has to be carried out as responses to certainmandatory stimuli (e.g. visual signals at corresponding spatiallocations). By repeating the sequence, responses are performed faster,especially if participants learn the sequential pattern explicitly (e.g.Hoffmann & Koch, 1997; Eliassen et al., 2001; Ru¨sseler et al., 2003;Tubau & Lo´pez-Moliner, 2004).Interestingly, several studies have shown that sequential perform-ance improves if each response determines the occurrence of a specificsound (Hoffmann et al., 2001; Sto¨ cker & Hoffmann, 2004; Tubauet al., 2007), suggesting that response-contingent sounds enhance thechunking of individual actions into larger units as in rhythmicmelodies. However, Tubau et al. (2007) showed that auditory actioneffects did not facilitate the acquisition of the serial order but theprecise timing control. That is, the percentage of participants wholearned the order (explicit learners) was the same with and withoutauditory effects, but performance of explicit learners, differing fromnon-explicit ones, improved when presented with response-contingentsounds (Tubau et al., 2007). Could these individual differences berelated to differences in neural representation of auditory rhythms?The present study aimed at answering this question using event-related brain potentials (ERP). For that purpose, we used the MMNauditory ERP (Na¨a¨ta¨nen & Escera, 2000), which has been proposed asa good indicator of the accuracy of central sound representation(Na¨a¨ta¨nen & Winkler, 1999) and, accordingly, of behaviouralperceptual performance (i.e. Tiitinen et al., 1994; Amenedo & Escera,2000). The MMN is elicited, with no task requirements, byoccasionally ‘deviant’ sounds occurring in a sequence of repetitive(‘standard’) stimuli (Na¨a¨ta¨nen et al., 2001). When the brain’s responseto the standard stimuli is subtracted from that to the deviant one, theMMN can be seen at 100–200 ms from stimulus-change onset. TheMMN can be elicited by any perceptible physical change, i.e. pitch orduration, or by contrasting more complex sound features such asabstract invariances (Carral et al., 2005), tone patterns (Atienza et al.,2003) and phonemes (Na¨a¨ta¨nen et al ., 1997). Critically, the brain’sneurophysiological response to deviant stimuli implies that a neuralrepresentation of the preceding repetitive stimulus features has beenformed (Na¨a¨ta¨nen & Winkler, 1999; Na¨a¨ta¨nen et al., 2001). Hence, ifmotor sequence acquisition and auditory rhythm perception correlate,MMN differences between explicit and non-explicit learners should beobserved. Specifically, we expected that learners showing bettertiming control of the motor sequence (explicit group) would showlarger MMN responses to auditory pattern deviants than non-explicitlearners.Materials and methodsWe replicated one of the sequence learning conditions of Tubau et al.(2007), which showed high differences between explicit and non-explicit learners regarding their sensitivity to auditory action effects.Correspondence: Dr E. Tubau,1Department of Basic Psychology, as above.E-mail: [email protected] 26 February 2007, revised 14 May 2007, accepted 17 May 2007European Journal of Neuroscience, Vol. 26, pp. 261–264, 2007 doi:10.1111/j.1460-9568.2007.05637.xª The Authors (2007). Journal Compilation ª Federation of European Neuroscience Societies and Blackwell Publishing LtdEighteen students at the University of Barcelona were presented withan incidental learning task. Participants were instructed to respond asfast and as accurately as possible, pressing a left or right buttonaccording to the spatial location of a visual mark (X) on the screen.The stimulus location followed six continuous repetitions per block ofthe sequence: right–left–right–right–left–left–right–left, unknown bythe participants. Responses were executed with the left and right indexfor left and right buttons, respectively. The stimulus was on the screenuntil response. The temporal interval between the response and thenext stimulus was 250 ms. Additionally, different 100-ms tones(200 Hz and 440 Hz) were presented as effects of left and rightresponses, respectively. Participants were informed that the soundswere irrelevant and that they had to respond only to the location ofthe X. After the learning task (formed by 11 blocks), participants