Doctor of Philosophy
School of Psychology
McKenzie, David N., Sound representations underlying the duration mismatch negativity (MMN) in a rapid dichotic listening task, Doctor of Philosophy thesis, School of Psychology, University of Wollongong, 2010. http://ro.uow.edu.au/theses/3302
The locus of auditory attention’s influence has been controversial. Mismatch negativity (MMN), a component of the event-related potential (ERP) theorised to reflect an auditory change-detecting comparator, is used to investigate this matter. Some theories place attentive influence prior to this MMN comparator, and cite attentive modulation of the MMN component amplitude as evidence. Other theories argue that attention alters only the comparator output, leaving the inputs unaffected. This thesis aims to test whether attention influences the MMN comp arator input. Duration change MMN is examined in experiments applying robust control of attention through the use of a rapid dichotic listening task. Experiment 1 confirmed the sole existing report of modulation of the duration MMN amplitude by attention. To distinguish whether this modulation reflected change to the comparator inputs or simply to the output, Experiment 2 followed a previous suggestion to investigate whether attention also shifted the threshold for duration MMN elicitation. No threshold shift was found. Seemingly, attention did not affect the MMN comparator inputs. Subsequently, an attention mechanism in which the sensory data of stimuli at the attentive focus was segregated away from all other sensory data, was proposed. For such a mechanism, use of a dichotic listening task paradigm with only two sets of sounds meant that segregation of the attended set of sounds also implied segregation (and hence equivalent attentional benefit) for the other (unattended) set. Experiment 3 demonstrated highly segregated and independently-changeable MMN duration representations. Experiment 4 proposed that presentation of three or more sets of sounds, one set attended, would demonstrate fusion of the multiple unattended sound sets. Evidence for this was found. It was concluded that (1) attention acted prior to the MMN comparator by segregating the attended sound representation; (2) that, despite a high level of independence of the segregated representation, attention did not modify the sensory information of either the attended or unattended sounds, contrary to filtering theories; and (3) a collective representation of multiple unattended sets of sounds arises, even when auditory scene analysis suggests they might segregate.