Deconvolution of magnetic acoustic change complex (mACC) Fabrice Bardy a,b,c,d,e,⇑ , Catherine M. McMahon a,b,e , Shu Hui Yau d,e , Blake W. Johnson d,e a HEARing Co-operative Research Centre, VIC, Australia b Department of Linguistics, Macquarie University, NSW, Australia c National Acoustic Laboratories, NSW, Australia d Department of Cognitive Science, Macquarie University, NSW, Australia e ARC Centre of Excellence in Cognition and its Disorders, Australia article info Article history: Accepted 4 March 2014 Available online xxxx Keywords: Magnetoencephalography Overlapping responses Least-squares deconvolution Rapid acoustic change complex highlights  We developed a novel experimental approach to objectively measure discrimination of rapidly chang- ing sounds.  We investigated the feasibility of disentangling three sorts of overlapping cortical responses elicited by synthesized speech sounds in normal hearing adults.  Cortical responses recovered using the LS-deconvolution can potentially be used as biomarker of spectro-temporal processing mechanisms at the level of auditory cortex. abstract Objective: The aim of this study was to design a novel experimental approach to investigate the morpho- logical characteristics of auditory cortical responses elicited by rapidly changing synthesized speech sounds. Methods: Six sound-evoked magnetoencephalographic (MEG) responses were measured to a synthesized train of speech sounds using the vowels /e/ and /u/ in 17 normal hearing young adults. Responses were measured to: (i) the onset of the speech train, (ii) an F0 increment; (iii) an F0 decrement; (iv) an F2 dec- rement; (v) an F2 increment; and (vi) the offset of the speech train using short (jittered around 135 ms) and long (1500 ms) stimulus onset asynchronies (SOAs). The least squares (LS) deconvolution technique was used to disentangle the overlapping MEG responses in the short SOA condition only. Results: Comparison between the morphology of the recovered cortical responses in the short and long SOAs conditions showed high similarity, suggesting that the LS deconvolution technique was successful in disentangling the MEG waveforms. Waveform latencies and amplitudes were different for the two SOAs conditions and were influenced by the spectro-temporal properties of the sound sequence. The magnetic acoustic change complex (mACC) for the short SOA condition showed significantly lower ampli- tudes and shorter latencies compared to the long SOA condition. The F0 transition showed a larger reduc- tion in amplitude from long to short SOA compared to the F2 transition. Lateralization of the cortical responses were observed under some stimulus conditions and appeared to be associated with the spec- tro-temporal properties of the acoustic stimulus. Conclusions: The LS deconvolution technique provides a new tool to study the properties of the auditory cortical response to rapidly changing sound stimuli. The presence of the cortical auditory evoked responses for rapid transition of synthesized speech stimuli suggests that the temporal code is preserved at the level of the auditory cortex. Further, the reduced amplitudes and shorter latencies might reflect intrinsic properties of the cortical neurons to rapidly presented sounds. Significance: This is the first demonstration of the separation of overlapping cortical responses to rapidly changing speech sounds and offers a potential new biomarker of discrimination of rapid transition of sound. Crown Copyright Ó 2014 Published by Elsevier Ireland Ltd. on behalf of International Federation of Clinical Neurophysiology. All rights reserved. http://dx.doi.org/10.1016/j.clinph.2014.03.003 1388-2457/Crown Copyright Ó 2014 Published by Elsevier Ireland Ltd. on behalf of International Federation of Clinical Neurophysiology. All rights reserved. ⇑ Corresponding author at: Australian Hearing Hub, 16 University Avenue, Macquarie University, NSW 2109, Australia. Tel.: +61 2 94 12 68 14; fax: +61 2 94 12 67 69. E-mail address: Fabrice.Bardy@nal.gov.au (F. Bardy). Clinical Neurophysiology xxx (2014) xxx–xxx Contents lists available at ScienceDirect Clinical Neurophysiology journal homepage: www.elsevier.com/locate/clinph Please cite this article in press as: Bardy F et al. Deconvolution of magnetic acoustic change complex (mACC). Clin Neurophysiol (2014), http://dx.doi.org/ 10.1016/j.clinph.2014.03.003