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Previous studies showed that emotional pictures capture attention. Further, this effect was decreased by manipulating spatial attention. In contrast, studies produced mixed findings for effects of perceptual load on attention to emotional pictures. Emotional pictures can be phobic or nonphobic. Because phobia might be an evolutionary adaption, it is possible that effects of phobic pictures on attention differ from effects of nonphobic emotional pictures. The present thesis aimed at investigating attention in spider phobia. Attention to emotional pictures was operationalized as event-related potentials (ERPs) (P1, early posterior negativity [EPN,] and late positive potential [LPP]). Two research questions were formulated. First, do phobic pictures evoke larger ERPs than what can be expected from arousal and valence? Second, are effects of spatial attention and perceptual load on ERPs the same for phobic and nonphobic emotional pictures? To investigate this, phobic and nonphobic negative pictures were presented to spider phobic and nonphobic participants. To determine effects of spatial attention on ERPs, participants were instructed to divert attention to a single letter that was presented in the periphery. To determine effects of perceptual load on ERPs, participants were instructed to perform a letter discrimination task on one, two, or three letters that were presented in the periphery. Study 1 showed enhanced LPP amplitudes to phobic pictures independent of arousal and valence. Further, this effect was present in both phobic and nonphobic participants. Study 2 showed that there was no effect of perceptual load on LPP to phobic pictures. Study 3 showed that spatial attention reduced LPP amplitudes, and to a similar extent for both phobic and nonphobic pictures. Further, perceptual load did not reduce EPN or LPP amplitudes to either phobic or nonphobic pictures. To conclude, the results suggest that phobic pictures evoke larger ERP amplitudes than nonphobic pictures. Still, ERPs to phobic and nonphobic pictures are moderated similarly by spatial attention and perceptual load. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 3: Manuscript.</p>

Semantic richness is a multidimensional and dynamic construct that can be defined as the amount of semantic information a word possesses. In this thesis, the semantic richness dimensions of number of associates, number of semantic neighbours, and body-object interaction were investigated. Forty-eight young adults were randomly assigned to perform either lexical decision (LDT) or semantic categorization tasks (SCT). The goal of this thesis was to investigate behavioural and electrophysiological differences (using the Event-Related Potential technique) between semantically rich words and semantically impoverished words. Results revealed that the amplitude of the N400 ERP component was smaller for words with high number of associates and high number of semantic neighbours compared to words with low number of associates or low number of semantic neighbours, respectively, but only during LDT. Behavioural results, however, only showed an accuracy and reaction time advantage (during item analyses) for words with many associates. In contrast, N400 amplitudes did not differ for words with high body-object interaction rating when compared to words with low body-object interaction rating in any of the tasks, although a behavioural reaction time advantage was observed in item analyses of the LDT. These results suggest that words with many associates or semantic neighbours may be processed more efficiently and be easier to integrate within the neural semantic network than words with few associates or semantic neighbours. In addition, the N400 effect was seen in the LDT but not in the SCT, suggesting that semantic richness information may be used in a top-down manner in order to fulfill the task requirements using available neural resources in a more efficient manner.

This dissertation consists of a review of the N2 component of the ERP and five experiments investigating the role of complex visual object categorization in modulating the N2 and two other ERP components: the P300, and a late prefrontal positivity. In the review, we focus on paradigms that elicit N2 components with an anterior scalp distribution, namely cognitive control, novelty, and sequential matching, arguing that the anterior N2 should be divided into separate control- and mismatch-related subcomponents. The experiments manipulated categorical typicality and the presence of conflicting information as participants categorized multi-featured artificial animals. In Experiments 1 and 2, rule-irrelevant features were correlated with particular categories during training. During transfer, participants applied a one- dimensional rule to stimuli with category-congruent, category-incongruent, or novel rule-irrelevant features. Category-incongruent and novel features delayed RT and P300 latency, but had no effect on the N2. Experiment 3 used a two-dimensional rule to create conflict between rule-relevant features. Conflict resulted in prolonged RTs, P300 latency, and larger amplitudes of a prefrontal positive component, but had no impact on the N2. Novel features did enhance the N2 relative to frequent features. In Experiments 4 and 5, participants categorized stimuli using a more complex three dimensional rule. Conflicting stimuli shared two features with one prototype and one feature with a second prototype while prototypes contained no conflicting information. A third category contained stimuli with either common or novel features. Again, perceptual novelty, but not conflict, increased the amplitude of the N2. Compared to prototypes, stimuli with conflicting information slowed reaction times but had no effect on P300 latency, instead enhancing a late prefrontal positive component. These results suggest limitations on the generality of the N2's sensitivity to conflicting information, while confirming its sensitivity to attended visual novelty. We suggest that, while P300 latency tracks stimulus evaluation time, application of a complex categorization rule requires a later stage of evaluation involving prefrontal cortex. In very complex rules, computations indexed by the P3 may be terminated early in favor of computations in PFC.

The aim of this PhD thesis was to explore the way in which recognition memory changes over time. Of particular interest was how forgetting and systems level consolidation processes alter the qualitative nature of recognition judgments and the impact this has on event related potentials (ERPs) recorded during recognition. An emerging body of fMRI and animal work has started to suggest that changes to the neural basis of memory can be observed after intervals in the order of days and weeks. Although much research has examined the ERP correlates of recent recognition, there has been little attempt to compare this to remote recognition. This gap in the literature is investigated in the present PhD thesis over five ERP and two behavioural experiments. The first set of experiments investigated recognition success i.e. the subjective awareness that a stimulus has been encountered before. Previous work has associated familiarity-based recognition with an early midfrontal ERP effect whereas recollection-based recognition has been linked to a later onsetting parietal ERP effect. These effects were compared for recently studied stimuli and stimuli studied 1 week earlier. Results revealed an attenuation of the late parietal effect. This quantitative difference suggests that the neural networks underlying the ERPs for recent and remote recollection remain the same after a 1 week delay but may be less active after a period of forgetting. Behavioural work linked this to a drop in strength and episodic detail for remote recollection. Examining the midfrontal effect over time produced a more complex pattern of results. The effect was not reliable in Experiment 1 for remote familiarity judgments. In follow up experiments, however, midfrontal effects were reliable for week old memories but were not modulated by either delay or memory strength manipulations. These findings do not permit strong conclusions regarding the way familiarity memory and midfrontal ERPs vary over time, other than to say that the midfrontal effect is not a short lived correlate of recognition memory. A second set of experiments investigated how the length of the delay between study and test impacts on retrieval orientation and retrieval effort. Retrieval orientation refers to the way in which participants strategically alter how a memory cue is processed based on current task demands. Results showed ERP differences when remote memories were cued compared to when recent memories were cued. However, these differences were eliminated when recent and remote memory was matched for performance. This finding indicated that effort required at retrieval rather than memory age per se influenced differential cue processing. A follow up experiment supported this claim but found that participants may utilise delay information during recognition in a very general sense. In this experiment, ERPs indicated different cue processing when participants knew the age of the memories they were trying to retrieve compared to when they did not. Taken together, the results suggest that memory age does not influence the ERP correlates of recognition in a direct manner. More important are the indirect changes occurring over time, such as reduced memory strength, reduced episodic detail, slower reaction times and increased effort at retrieval. These variables, and possibly a range of others, should be controlled as far as possible in studies aiming to explore neural changes driven by systems consolidation. Prospective studies, where the learning phase can be controlled makes this aim feasible, as some of the experiments in this thesis have shown. Future work might benefit from focusing more on variations at encoding, rather than large differences in the length of the retention interval, as has been the traditional approach to this issue.

Despite the enormous complexity inherent to language, almost all humans acquire and use their native language with apparent effortlessness, simply from being immersed in a normal social environment. It has been hypothesized that conscious processes play only a limited role in language, which may explain how language can be acquired and processed with so little effort. Using event-related potentials, this dissertation addresses this hypothesis by investigating the contributions of implicit and explicit neural mechanisms to different aspects of language. In the first study, the neural mechanisms mediating semantic and syntactic processing of word pairs were examined, using the attentional blink (AB) to manipulate awareness of target words. In the semantic condition, correctly reported target words elicited an N400 effect, while missed target words did not elicit an N400. These results provide evidence that awareness plays a critical role in semantic processing. In the second study, the neural mechanisms that support syntactic processing of full sentences were investigated, using a cross-modal AB to manipulate awareness of syntactic violations. Syntactic violations that were not consciously detected nonetheless elicited a left anterior negativity, indicating that syntactic processing is subserved by implicit neural mechanisms. In the third study, the neural mechanisms underlying semantic acquisition were examined, using a task in which the meanings of novel pseudowords were learned through context. Novel pseudowords elicited a robust N400 effect after remarkably little exposure but only during an explicit task and only when word meanings could be explicitly recognized, indicating that vocabulary acquisition is primarily mediated by explicit neural mechanisms. In the fourth study, the neural mechanisms that support the acquisition of second language (L2) syntax were investigated, using a language-learning task in which participants were trained either implicitly or explicitly. Regardless of training condition, learners who successfully learned the novel L2 syntactic rules showed P600 effects, suggesting that explicit mechanisms play a crucial role in acquiring L2 syntax. Taken together, results from these studies suggest that awareness plays a critical yet constrained role in language processing, yielding new insight into how language is spoken and understood so effortlessly. This dissertation includes previously published and co-authored material. / 10000-01-01

We live in a busy and complex world, so the ability to focus our attention on relevant information at the expense of the irrelevant is essential in allowing us to avoid distraction. However, it is also important that our attention be captured by external stimuli that, although irrelevant to the task at hand, may nevertheless provide information about important changes to our immediate environment. This capture/orienting of attention is an involuntary, fundamental, and biological mechanism necessary for survival. The present thesis employed event-related potentials (ERPs), the minute responses of the brains electrical activity, to examine how changes in the acoustic environment can lead to the capture of attention. Study 1 examined an ERP component, the P3a, which is associated with the processes that lead to the forced capture of attention by external stimuli. This intrusion into consciousness can be studied using an auditory sequence, the oddball paradigm, which consists of a frequently occurring and homogenous ‘standard’ stimulus. At times, a feature of the standard is changed to form a rarely occurring ‘deviant’. If the extent of change between standard and deviant is large enough, processes associated with attention capture may be activated. Study 1 of this thesis employed a more time-efficient multi-feature optimal paradigm, which allows for the presentation of numerous deviants in one auditory sequence. The standard stimulus was a pure tone. Four of the six deviants were created by changing a single feature of the standard (frequency, duration, increase and decrease in intensity), while the remaining two deviants varied on more than one feature from the standard (environmental sounds, white noise). Results revealed that only the environmental sounds (i.e. animal sounds, human voices, musical instruments) and white noise bursts, elicited the P3a, while the other four deviants did not. Studies 2 and 3 determined whether the attention capture processes associated with the P3a could be observed during the sleep onset and sleep periods, where awareness of the external environment is diminished. For sleep to be of benefit it needs to remain as undisturbed as possible, without constant awakenings by irrelevant external input, however, the sleeping organism must still have the ability to become conscious of possibly relevant input that requires immediate action. In Study 2, a P3a was elicited again following only the environmental sound and white noise deviants across wakefulness and the sleep onset period. Surprisingly, during definitive sleep, the environmental sounds continued to elicit a P3a suggesting that attention capture processes may still remain active during sleep. Nonetheless, only the first 30 minutes of sleep were examined. Study 3 was then conducted to examine the P3a across the entire night. Results revealed that the environmental sounds did, in fact, elicited a P3a during both NREM and REM sleep. The present thesis demonstrates that attention capture mechanisms, observed during wakefulness, are also active during sleep onset and sleep when awareness of the external environment is diminished. This is especially critical because the sleeping organism may be vulnerable to external danger, requiring the immediate ability to orient attention to incoming information, leading to awaking and conscious awareness.

<p> Accurate face recognition plays a critical role in developing and maintaining social relationships. Typically developing adults show expertise when processing faces, demonstrated by their ability to recognize new faces even after a single exposure. Furthermore, face recognition is superior for highly familiar faces associated with rich semantic information. Although semantic processes mediate familiar face recognition, it is unclear what processes mediate unfamiliar face recognition. The main objective of my thesis was to identify unique neural mechanisms underlying familiar versus unfamiliar face recognition and to detail how these mechanisms change as a result of learning. I used event-related potentials (ERPs) to assess the stages of face processing affected by familiarity.</p> <p> In Chapter 1, I reviewed the literature contrasting familiar and unfamiliar face recognition processes from cognitive and neural perspectives.</p> <p> In Chapter 2, I identified processes involved in unfamiliar face recognition by recording ERPs to repeated presentations of unfamiliar faces in upright and inverted orientations. Inverted faces portray the same structural information as upright faces but with novel orientation that disrupts identity processing. Repeated exposure to an upright face (and not an inverted face) produced repetition priming at an early perceptual stage reflected by the N170 component, suggesting that unfamiliar face recognition is mediated by early perceptual representation.</p> <p> In Chapter 3, I directly tested whether semantic information modifies early perceptual face processing. I recorded ERPs to new faces that were learned over a five-day session with either person-specific or irrelevant information. N170 repetition priming was observed for all faces except those learned with person-specific information, suggesting that relevant semantic information, and not merely perceptual experience, changes early perceptual face processing.</p> <p> In Chapter 4, I assessed the relationship between N170 and N400 recognition processes. Specifically, I examined whether top-down semantic processes reflected by the N400 modulate early identity processes reflected by the N170. I constructed composite faces by combining facial features from different famous individuals; the facial features conveyed incongruous identity information so that when the face was processed as a whole it was perceived to be novel. Both familiar faces and composite faces failed to elicit N170 repetition priming but did elicit a similar N400 response, suggesting that familiar face recognition can be achieved with very little facial information. Moreover, these results suggest that the retrieval of semantically relevant information during familiar face recognition occurs even in the presence of incongruous perceptual information and that such processing modulates early perceptual processes.</p> <p> Together, these results demonstrate the interplay between memory and perception (which I summarize and discuss in Chapter 5), revealing different mechanisms of face recognition as a function of person-specific information. Unfamiliar face recognition takes place at the perceptual stage reflected by the N170 and is revealed through repetition priming. As an unfamiliar face becomes well known, its recognition processes shift to a later semantic stage reflected by the N400 and such semantic processes seem to modulate early perceptual processes. This knowledge has advanced our understanding of face processing at cognitive and neural levels.</p> / Thesis / Doctor of Philosophy (PhD)

Whilst studies on rhythm-keeping and error-related negativity have been conducted, previous studies have given participants auditory or visual cues to indicate the rhythm they are meant to be maintaining. In this electroencephalography study, a novel experiment called the Human Metronome Task was introduced, using healthy university students as participants. The Human Metronome Task tested the participants by having them tap in synchrony with a beat, and then having the beat be removed, with the participants still being supposed to maintain the same beat with their taps, now without any auditory or visual aids. The purpose was to see if deviations in unassisted rhythm keeping are sufficient to elicit error-related negativity. When comparing different deviations of the tap-timing of each participant to their average tap-timing, no significant differences in electroencephalography amplitude were found. It was concluded that the Human Metronome Task is unable to elicit error-related negativity in participants. It seems plausible that this is due to the ambiguity of whether responses are erroneous or accurate. Thus, it seems as if it is necessary for more indications of whether a response is erroneous or not for the elicitation of error-related negativity than was present in the Human Metronome Task.

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