Lawrence Ward

 
Prospective Graduate Students / Postdocs

This faculty member is currently not actively recruiting graduate students or Postdoctoral Fellows, but might consider co-supervision together with another faculty member.

Professor

Research Classification

Neuronal Systems
Cognition
Stochastic Processes
Electrophysiology

Research Interests

cognitive neuroscience of consciousness, perception, memory, spontaneous thought
computational neuroscience of neural oscillations, brain regional networks
effects of noise in the brain
brain plasticity and cultural learning

Relevant Degree Programs

 

Research Methodology

EEG, MEG, phase locking analysis, transfer entropy analysis, independent component analysis
simulation of solutions to stochastic differential equations

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2019)
Brain network dynamics of auditory change detection and working memory in recreational cannabis users (2019)

There are concerns that cannabis use leads to increased risk of mental illness and neurocognitive impairment. However, empirical findings into the deleterious effects of cannabis use on cognition have been mixed and the underlying brain processes are poorly understood. The present research examined auditory cognitive processes putatively related to psychosis and cannabis use. Groups of cannabis users (CU) and non-users (NU) are compared on two novel tasks that examine electroencephalographic (EEG) measures of early somewhat pre-attentional (MMN) and later attentional (P300) auditory change detection and P300 response in auditory working memory. Additionally, sophisticated EEG source localization was used to interrogate underlying oscillatory activity and brain network connectivity. Chapter 2 introduced the novel roving dual oddball task, and revealed an asymmetry between easy and difficult task conditions, possibly due to increased attentional demands as evidenced by an interplay between dorsal and ventral attentional systems. Chapter 3 compared CU and NU on the same dual oddball task and revealed slower response times and increased P300 latency for CU on the more difficult condition. Theta-band network connectivity suggested that CU engaged in a stimulus driven strategy that became less effective in the more difficult condition due to a breakdown of fronto-temporal connectivity. Groups did not differ in early auditory processes (MMN). Chapter 4 unexpectedly revealed CU to have superior performance on working memory for basic auditory features (pitch and pattern), which was partially reflected in larger P300 amplitudes. Theta connectivity revealed different patterns of brain connectivity. Chapter 5 combined data from Chapters 3 and 4 to examine a local MMN effect across a larger sample along with measures putatively related to impairments associated with heavy cannabis use and psychosis. Again, CU did not show reduced MMN and showed only small differences on various measures. As a whole, this research suggests that proposed auditory impairments due to heavy cannabis use may not generalize to all subsets of cannabis users, and additional research is needed before any definitive conclusions can be reached regarding the impact of frequent cannabis use on cognitive processes.

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Brain connectivity dynamics of reading and dyslexia : typical and perturbed reading networks in adults and children (2018)

Developmental dyslexia is a language-based learning disability characterized by impaired reading speed and accuracy, poor spelling, and poor decoding abilities, despite normal intelligence. Neuroimaging investigations have identified brain regions critical for reading; few studies, however, have characterized how those regions interact to form networks and how those networks are perturbed in individuals with dyslexia. Advances in electroencephalography (EEG) analysis techniques now allow for intricate examination of these networks by focusing on individual frequency bands that comprise the brain signals. This study used EEG across several experiments to examine theta- and gamma-band connectivity patterns—first in the brains of adults, and then in dyslexic and typically-developing children during reading tasks. I investigated: 1) the ways in which the reading networks of typical and dyslexic readers differ, and 2) whether targeted reading interventions reduce these differences over time. Results show that dyslexic children generated greater occipito-temporal connectivity at critical time points in response to words and word-like stimuli, as well as increased engagement of higher-level language areas even for stimuli lacking linguistic content (e.g. consonant strings). After six months, the networks of dyslexic readers resembled those of their typically-developing counterparts for simple orthographic processing, but continued to utilize existing alternative pathways when engaging in higher-level language processes (e.g. phonology). This suggests that performance improvements in dyslexic readers are not necessarily related to changes to the typical left-lateralization of reading networks. These findings are in line with existing frameworks of dyslexia, and highlight the value of connectivity measures in understanding the neural underpinnings of word reading.

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Temporo-frontal phase synchronization supports hierarchical network for mismatch negativity (2011)

Several cortical regions appear active when the mismatch negativity (MMN) scalp potential is evoked automatically in response to detectable auditory changes. It remains debatable whether the activation of regions beyond the auditory cortex is coincidental or functionally significant to the MMN response. We used independent component analysis (ICA) to separate high density EEG data (64-channel) prior to dipole fitting for two reasons: 1) to enhance the spatial resolution of EEG and 2) to provide temporal and frequency information about the cortical sources needed to evaluate their functional relationships during the MMN response. For a group of young adults (n = 12) passively listening to infrequent changes in complex tones while watching a silent movie, event-related activity within sources localized to the orbitofrontal cortex (OFC) and the bilateral superior temporal gyrus (STG) regions accounted for most of the scalp response variance implicating these regions as driving forces in the MMN. For a second group (n = 14) performing both passive and active listening across the same paradigm, cross-coherence (phase synchronization) during the MMN response was consistently found between the OFC and the STG bilaterally. During both paradigms the source in the right inferior frontal gryus (R IFG) was also synchronous with the STG-OFC network. When responding to deviant targets in the active paradigm, synchrony was more bilaterally distributed across the network. For a third group (n = 14) passively listening to infrequent changes in speech syllables, synchrony during the MMN response was found between the STG-OFC again as well as with regions in the R IFG and Broca’s area. This same subject group later attended to the speech syllables responding to deviants and standards with a different button press. Synchrony between the STG-OFC, and Broca’s area was found, as well synchrony with a source in the right anterior cingulate. All paradigms showed synchronous interactions both within and between the temporo-frontal regions that were modulated differentially by deviant and standard stimulus conditions as well as by task demands providing the first evidence of functional coupling within a hierarchical network coinciding with the MMN response evoked at the scalp.

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Master's Student Supervision (2010 - 2018)
Map reading under load : sex differences in learning digital maps (2015)

Imagine the following scenario: you’re at an unfamiliar location and you need to catch the bus to get home, however, you don’t know where the bus stop is. What do you do? In the modern world, the typical solution would be to open a map application on your smartphone and use it to determine the best route to your destination. Software developers are constantly improving mapping software with new features and design overhauls, but it is important to take a step back and ask how these factors might affect our ability to learn the information being presented. Are there cognitive factors that may help, or hinder, our ability to learn digital maps? A map reading experiment was devised to test the effect of cognitive load on map learning (Experiment 1). Participants learnt routes and landmarks under both low and high cognitive load. Our results show that high cognitive load hinders males’ ability to learn landmarks, while it hinders females’ ability to learn routes. A second experiment was conducted to determine the robustness of this effect. Map task difficulty was increased and our results show that the original 3-way interaction disappears when the demand on working memory becomes too high. Overall, our findings are in line with the existing literature on sex differences in map reading, and also indicates that 1) cognitive load plays a role in that relationship, and 2) a threshold exists for the effect once task difficulty is increased.

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Search through time is like search through space : behavioural and electrophysiological evidence (2015)

We conducted four experiments comprised of sequential auditory and visual searches in order to further explore the generalizability of the search asymmetry phenomenon to different sensory modalities, and to the sequential presentation of items in search arrays. It has been shown that search time to identify targets that contain features that distractors don’t have (feature-present targets) is faster than search time to identify targets that are missing features that distractors have (feature-absent targets). In Experiment 1 participants listened to auditory oddball sequences, consisting of two types of five-tone runs: the flat run, which consisted of five pure tones of the same frequency (the feature-absent target), and the change run, which consisted of four pure tones of the same frequency, followed by a fifth tone of a different frequency (the feature-present target). In some sequences the change runs were common and the flat runs were rare (the feature-present condition), while in other sequences these roles were reversed (the feature-absent condition). Experiments 2, 3 and 4 used the same protocol, however the visual stimuli consisted of rings (annuli) that differed by some feature (colour in Experiment 2, contrast in Experiment 3, and shade in Experiment 4). In all four experiments participant reaction times (RT) and electrophysiological (P300) responses to rare target patterns were recorded. In Experiments 1, 2 and 3, the reaction time and P300 latencies to identify feature-present targets were significantly faster than those to feature-absent targets, suggesting strong similarities between simultaneous visual search, and sequential auditory and visual search. What’s more, P300 responses to feature-present targets exhibited strong characteristics of both P3a and P3b subcomponents, while feature-absent responses only resembled that of the P3b. By contrast, the results of the fourth experiment were inconclusive. In Experiment 4 the saliency of the feature difference in the change runs was significantly reduced compared to that of the first three experiments, yielding longer reaction times and weaker P300 responses. Implications for the current understanding of search strategies associated with easy (feature-present) and difficult (feature-absent) searches, as well as the locus of the search asymmetry phenomenon, are discussed.

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Connectivity in cortical networks during word reading (2012)

The neural processes underlying word reading remain much of a mystery. In particular, the flow of information within and between language networks during word reading has not been adequately explored. The present study investigated local spectral power changes and functional and effective (causal) connectivity at each stage of word reading. EEG was used to record brain activity from healthy volunteers (n = 15), during a reading task. Independent component analysis yielded multiple sources of activation previously identified with fMRI and PET as being crucial to word reading. A combination of event-related spectral perturbation and phase synchrony analyses was performed on these independent components. Additionally, analyses of transfer entropy were conducted to investigate the possible causal information flow between sites of interest. Results confirm the VWFA as a central hub for word reading, showing a progression of theta band phase synchrony with early visual areas and then later with high-level language processing areas. Transfer entropy analyses largely converged with the theta synchrony results, again emphasizing the VWFA as a crucial node in the reading network, initially receiving information from early visual cortex, and then sending information to high-level areas. These results highlight the interplay between local and long-distance neural dynamics involved at each stage of processing during reading. Additionally, these measures of functional and causal connectivity may be used as a benchmark for comparison with clinical populations (e.g. individuals with certain kinds of dyslexia), such that disturbances in connectivity may provide insight as to underlying neurological problems.

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