Tracking selective attention in a musical cocktail

The cocktail party effect refers to mankind’s ability to focus attention on a single sound within noisy or complex auditory environments, in order to extract the most behaviourallyrelevant information present. To investigate this cognitive phenomenon in a precise manner, we used frequency-tagging to separate and identify neural auditory steady-state responses (ASSRs), which are specific to the driving frequency of their respective auditory sources, from a mixture elicited by multiple simultaneous stimuli. Participants directed attention to one out of a few musical streams as we examined how top-down selective attention to the pitch and timing of frequency-tagged musical tones influences the corresponding ASSR. In addition, bottom-up attention towards musical tones was also manipulated with salient changes in pitch. Using magnetoencephalography, we showed that the attentional enhancement of the ASSR can already be observed at general sensor level. Distributed source analyses revealed multiple ASSR sources distributed across the frontal, parietal and temporal cortices, with each of these areas modulated to different extents by selective attention. Notably, we uncovered the existence of ASSR attentional modulation in the frontal, parietal and insular lobes, which has not been previously reported in literature. Our results indicated that the ASSR enhancements from top-down and bottom-up attention were strongest at the frontal and temporal lobes respectively. The ASSR and its attentional modulation also displayed sensitivity towards individual musicality, demonstrating positive correlations with musical sophistication. Surprisingly, we discovered stark differences in cortical representation as well as character between the ASSR during and after the stimulation period. The ASSR during, but not after, stimulation was affected by the stimulus properties, selective attention, and participants’ level of musical sophistication. Moreover, the ASSR during stimulation was generated primarily from temporal sources whereas the post-stimulus ASSR originated mainly from the frontal cortex. We also assessed how the complexity of the stimulus cocktail affects the ASSR by comparing ASSRs elicited from simultaneous musical streams with ASSRs generated by streams that were completely separated in time. With two simultaneous streams, suppression of the ASSR power was observed, which furthermore varied across the cortical space. This caused a shift in the ASSR source distribution from temporal-dominance (separated streams) to proportionally stronger activity in the frontal and centro-parietal cortices (simultaneous streams). With the accumulation of evidence highlighting the differences between ASSR sources in the frontal and temporal regions, our results collectively advocate that these sources are characteristically unique, functionally distinct and largely independent from one another. Taken together, this thesis revealed new aspects of the ASSR and ways to effectively extract the effect of selective attention and its interaction with individual auditory experiences such as musical training. Importantly, this work advocates a novel ‘beyond the temporal cortex’ perspective on ASSR modulation and advances the study of human cognition towards more complex and naturalistic soundscapes using frequency-tagging. LIST OF SCIENTIFIC PAPERS I. Manting, C. L. ; Andersen, L. M. ; Gulyas, B. ; Ullén, F. ; Lundqvist, D. , Attentional modulation of the auditory steady-state response across the cortex. NeuroImage 2020, 217, 116930. II. Manting, C. L. ; Gulyas, B. ; Ullén, F. ; Lundqvist, D. , Auditory steady-state responses during and after a stimulus: Cortical sources, and the influence of attention and musicality. NeuroImage 2021, 233, 117962. III. Manting, C. L. ; Gulyas, B. ; Ullén, F. ; Lundqvist, D. , Selective Attention to Frequency-tagged Concurrent Melodies: The Interplay between Suppression, Topdown and Bottom-up Attention. Manuscript in Preparation Scientific papers not included in the thesis Vinding, M. C. ; Eriksson, A. ; Manting, C. L. ; Waldthaler, J.; Ferreira, D. ; Ingvar, M. ; Svenningsson, P.; Lundqvist, D. , Different features of the cortical sensorimotor rhythms are uniquely linked to the severity of specific symptoms in Parkinson’s disease. medRxiv 2021, 2021.06. 27.21259592. pre-print