The focused sense of self that is central to our experience of consciousness could not exist without human brain's ability to process large amounts of information outside of conscious awareness. The Mismatch Negativity (MMN) is thought to index one such pre-conscious mechanism, a complex novelty detector that compares incoming sounds to rules that it has extracted from the recent acoustic past. Processes that do not require conscious awareness are considered to be "automatic". The automaticity of the MMN, however, has predominantly been studied using very simple stimuli. The present dissertation studied the issue of automaticity using a two-tone alternating pattern (e.g., ABABABAB...) as the "standard" stimuli. MMN-eliciting deviants were rule-violating tone repetitions (e.g., ABABAA&barbelow;AB...). Three studies took complementary approaches to the problem of automaticity. Study 1 tested the automaticity of the detection of rule violations by varying the presumed attentional demands of a visual task, while the auditory pattern was ignored. The MMN was unaffected by visual task difficulty, but it may be impossible for awake, alert subjects to ever fully ignore incoming sounds. Study 2, therefore, studied the MMN during natural sleep, the period of time when the observer is least conscious of the external environment. An MMN was elicited in both the waking state and REM sleep. Interpreted in isolation, these studies might be taken as evidence that the MMN is strongly automatic. Some attention effects, however, have been reported. One proposed mechanism for these attention effects is that attention increases the strength of the memory for the frequently-presented, standard stimuli. Study 3 examined whether the MMN varies with the strength of the memory for the standard by manipulating the number of memory-reinforcing repetitions of the standard that occurred between successive deviants. The results of Study 3 suggest that the amplitude of the MMN is unrelated to the strength of the memory for the standard. Altogether, the results of these studies suggest that even complex, rule-based MMN elicitation is an automatic process, and that studies demonstrating evidence to the contrary should be examined for the influence of other confounding factors.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/30025 |
| Date | January 2010 |
| Creators | Sculthorpe, Lauren Deano |
| Publisher | University of Ottawa (Canada) |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 161 p. |
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