Neuroplasticity research yields mixed results for the differential contribution of perilesional and contralesional brain areas to language recovery in aphasia. This paper will outline variables that mediate the presence and degree of right hemisphere activity and may account for some of the inconsistent research findings. Factors include the site and size of left hemisphere lesions, the phase of recovery, and the language task type and complexity. The performance accuracy of tasks also will be explored to further qualify the nature of homologous activity. Results found right hemisphere activation to be modulated by the damage and preservation of specific brain areas as well as by the presence of large left hemisphere lesions. Right hemisphere activity also was more consistently evident in the acute phase of recovery and returned to the left hemisphere in the chronic stage. Additionally, homologous areas tended to be more active during comprehension-based language tasks and during tasks of greater difficulty. In qualifying the nature of contralesional mechanisms, the activity appears to be more linguistic-oriented in less-recovered individuals with aphasia and more related to cognitive effort in well-recovered individuals. The nature of homologous activation depends on the brain’s ability to reactivate left hemisphere language networks. / text

This study proposed an experimental test of theoretical models related to emotion and space representation in the brain. Previous research has established that emotion is represented, processed, expressed, and regulated largely by the right hemisphere. Furthermore, there is evidence from experimental paradigms and clinical case reports to suggest that the same hemisphere plays a dominant role in the processing of external space. A conceptual difficulty of clinical and neural network overlap arises when right hemisphere disorders of emotion are compared with those of spatial representation. The current experiment tested some of these hypotheses about emotion regulation and spatial representation in the right hemisphere using nonclinical subjects under a cortical stress paradigm designed to mimic the conditions of cortical duress. An additional goal was an extension of a previous study that examined emotional influence on spatial orientation. Results did not support our initial hypotheses. Subsequent analyses did provide some evidentiary support for some theories related to emotion and brain function. Additionally, patterns of subject performance were observed that support traditionally held theories of differential hemispheric function with regard to emotion and spatial behavior. These findings are discussed within the context of theories of emotion, spatial function, and disorders secondary to right hemisphere damage. / Doctor of Philosophy / This is a study examining the role of emotion and stress on the allocation of attention in the individual’s external environment. Further examined was the role that brain systems involved in attention, emotion, and spatial representation and the correlation with brain damage and syndromes that result in disruption to these systems. Conceptual difficulties regarding overlapping brain areas that contribute to different functions serve as the foundation for understanding both how these systems work and the behavioral manifestations of their dysfunction. Finally, further elucidating the role of these neural systems in contributing to self-awareness, emotion regulation, and the representation of external space was the ultimate objective of this study.

Stroke is the leading cause of serious, long-term disability and nearly half of older stroke survivors experience moderate to severe disability. A common impairment following stroke is impaired discourse production. Functional outcome studies have proposed that the recovery of discourse abilities is critical to achieving a good quality of life. Communication impairments often persist into the chronic stages of recovery and can cause individuals to withdraw from social situations. Discourse production deficits may not be apparent in basic communication interactions, but become more obvious during complex conversations following non-aphasic brain injury (NABI) or right hemisphere stroke (RHD). The purpose of this three-part dissertation was to examine discourse production deficits following NABI and the current practices of speech-language pathologists in the assessment and treatment of discourse deficits. The first study examined the macrolinguistic processes of discourse, which included local coherence, global coherence and cohesion, following NABI. Ten individuals with NABI and 10 heathy controls, closely matched for age, gender, and education, provided a narrative recount of an event. Discourse samples were analyzed for local coherence, global coherence, and cohesion. Results indicated that individuals with NABI demonstrated impaired global coherence compared to healthy controls with relatively intact local coherence and cohesion. Although global coherence deficits were identified in the discourse of individuals with NABI, empirical evidence suggests that speech-language pathologists do not routinely assess or treat discourse production deficits. The second study explored the current practices of speech-language pathologists in the assessment and treatment of individuals with NABI with a specific focus on discourse production deficits using a phenomenological approach. Nine speech-language pathologists participated in semi-structured 1:1 interviews. Results indicated that speech-language pathologists do not routinely assess and treat discourse production deficits due to competing internal values and external or environmental demands. However, speech-language pathologists reported that discourse deficits are present following NABI and are characterized by impaired topic maintenance or global coherence. Participants reported that they were routinely assessing and treating the underlying cognitive process of attention in hopes that it would generalize to improved topic maintenance or global coherence. However, little is known about the relationship between selective attention and global coherence. The third study examined the maintenance of global coherence across discourse tasks and explored the relationship between selective attention and global coherence. Eleven participants with non-aphasic brain injury secondary to right hemisphere stroke participated in the study. Participants provided discourse samples in response to five discourse tasks in a single-task and dual-task condition. Additionally, participants completed the Stroop test to examine selective attention abilities. Results indicated that mean global coherence scores differed across discourse tasks, and that mean global coherence scores for stories was significantly higher than for simple recount and single picture description tasks. To examine the relationship between selective attention and global coherence, mean global coherence scores in the single-task and dual-task condition were compared. Mean global coherence scores were lower in the dual-task condition for all five discourse tasks. Mean global coherence scores for the complex recount task were significantly lower in the dual-task condition. This suggests that the maintenance of global coherence is influenced by attention abilities. There was no significant correlation between performance on the Stroop task and the maintenance of global coherence for any of the five discourse tasks.

Several studies have focused on the contribution of the right hemisphere brain to the emotional aspects of communication, raising evidence that it is specialized in the emotional processing of faces. Right hemisphere brain damage (RHBD) may cause disturbances in the function mentioned, affecting social interactions since they depend on facial emotion recognition. This research aimed to contribute to the study of the possible impairment in the ability to identify facial expressions in 4 RHBD patients in order to elucidate whether those interfere with the performance of two emotion recognition instruments expressed by faces images. From a comparison between the RHBD group, 4 patients with left hemisphere brain damage (LHBD) and 8 subjects in the control group, we found 22 statistically significant or borderline statistical associations results (p≅0,05) only to the stimuli of the instrument Facial Expression Brazilian Task (FERBT), including the analysis of the emotional valences between LHBD and RHBD groups. Of these, 13 showed superiority of the control group in relation to clinical groups, and 9 showed superiority the LHBD group compared to the RHBD group. From this study, we can infer that FERBT is more congruent in relation to Emotion Recognition Index (ERI) concerning the hypothesis of brain asymmetry in facial expression recognition. The results of FERBT partially agrees with the hypothesis of emotional valence, since significant differences between clinical groups were found, favoring the LHBD group to the sum of emotion scores of negative valence at 500 milliseconds (ms), 1 second (s) and overall score of FERBT, adding up all the emotions in different times. However, it should be noted that borderline statistical associations differences favoring the LHBD group were found only for the emotion of fear (200ms and the total time) and anger (total time) with no significant differences for emotions of positive valence. This study helped to assess neuropsychological deficits after right hemisphere brain damage, since there is a significant gap in this diagnostic area. Through research, we can improve our knowledge about impairments caused by right hemisphere lesion by increasingly developing accurate assessment techniques and rehabilitation methods. / Vários estudos têm enfocado a contribuição do hemisfério cerebral direito para os aspectos emocionais da comunicação, levantando evidências de que o mesmo é especializado no processamento emocional de faces. Lesões de hemisfério direito (LHD) podem acarretar perturbações na função descrita anteriormente, prejudicando as interações sociais, uma vez que estas dependem do reconhecimento de emoções na modalidade facial. A presente pesquisa teve como finalidade contribuir para o estudo dos possíveis comprometimentos na capacidade de identificar expressões faciais em 4 pacientes LHD, buscando elucidar se àqueles acabam interferindo no desempenho de 2 instrumentos de reconhecimento de emoções expressas por imagens de faces. A partir de um comparativo entre o grupo LHD, 4 indivíduos com lesão de hemisfério esquerdo (LHE) e 8 sujeitos controle, foram encontrados 22 resultados com significância estatística ou associações estatísticas limítrofes (p≅0,05) somente para os estímulos do instrumento Facial Expression Brazilian Task (FERBT), incluindo análise da valência emocional entre grupos LHE e LHD. Destes, 13 mostraram superioridade do grupo controle em relação aos grupos clínicos e 9 mostraram superioridade de grupo LHE em relação ao grupo LHD. Infere-se a partir do presente estudo que o FERBT apresenta maior congruência, em relação ao Emotion Recognition Index (ERI), com a hipótese da assimetria cerebral no reconhecimento de expressões faciais. Os resultados do FERBT concordam parcialmente com a hipótese da valência emocional, uma vez que foram encontradas diferenças relevantes entre grupos clínicos, favorecendo o grupo LHE, para o somatório das pontuações de emoções de valência negativa nos tempos de 500 milissegundos (ms), 1 segundo (s) e pontuação geral do FERBT somando-se todas as emoções dos diferentes tempos. Contudo, deve-se ressaltar que associações estatísticas limítrofes, favorecendo o grupo LHE, foram encontradas apenas para a emoção de medo (200ms e total dos tempos) e raiva (total dos tempos), não havendo diferenças significativas para emoções de valência positiva. O presente estudo contribuiu para a avaliação de déficits neuropsicológicos após lesão direita, visto que há importante lacuna nessa área de diagnóstico neuropsicológico. Através da pesquisa, poderemos aprimorar nosso conhecimento sobre as disfunções ocasionadas pela lesão de hemisfério direito, desenvolvendo técnicas cada vez mais precisas de avaliação e métodos de reabilitação.

Viktiga aspekter av kommunikationen styrs från höger hjärnhalva, däribland emotionell prosodi. Forskningen inom detta område har dock hittills varit ganska begränsad. En aspekt, som inte undersökts än, är jämförelse av deltagarens egen och lyssnares skattning av röstens uttrycksfullhet. Syftet med studien vara att undersöka förmågan att uttrycka emotionell prosodi efter stroke i höger hemisfär. Deltagare var tre patienter med stroke i höger hemisfär samt tre kontrollpersoner utan neurologisk sjukdom/skada eller problem med tal eller röst. Sammansättningen i grupperna av deltagare med stroke respektive kontrollpersoner var likvärdig avseende kön, ålder, dialektområde och utbildningsnivå. Emotionell prosodi undersöktes genom flera metoder: akustisk analys av grundtonsvariation samt deltagarnas egen såväl som lyssnares skattning av röstens uttrycksfullhet. I resultaten framkommer tendenser, som indikerar en skillnad mellan deltagarna med stroke i höger hemisfär och kontrollpersonerna. För deltagarna med stroke sågs mindre grundtonsvariation och lägre skattningar av röstens uttrycksfullhet. Då deltagarantalet var litet, bör resultaten tolkas med försiktighet. De tendenser till skillnader mellan försöks- och kontrollpersonerna som ses i resultaten motiverar dock för vidare studier. / Important aspects of communication, including emotional prosody, are regulated from the right hemisphere. However, the research in the area of emotional prosody has so far been rather limited. One of the aspects that have not been examined yet is the comparison of the participant’s own rating of voice expression with ratings by listeners. The aim of the study was to assess expressive emotional prosody after right-hemisphere stroke. Participants were three patients with right-hemisphere stroke and three controls without neurological conditions or problems regarding speech or voice. The groups of participants with stroke and the controls were matched regarding sex, age, dialect and level of education. Emotional prosody was examined using multiple methods: acoustic analysis of variation in fundamental frequency and the participants’ own as well as listeners’ rating of voice expression. The results show tendencies that indicate a difference between the participants with right-hemisphere stroke and the controls. The participants with stroke showed smaller variations in fundamental frequency and lower ratings of voice expression. Due to the small sample size in the present study, results should be treated with caution. However, the tendencies shown in the results regarding differences between subjects and controls would justify further studies.

In recent years, the functional outcomes of patients with right hemisphere stroke (RHS) received considerable attention due to their impact on disability, independent living, quality of life and economic burden. Hemi-inattention (HI) is a complex condition which often accompanies RHS. It is characterised by reduced alertness, attention and low spatial awareness levels. Past studies reported poor outcomes in patients with HI and inconsistent findings in regard to the relationship of HI with functional outcome. Literature review of 13 relevant studies highlighted poor research methodology which complicated interpretation of previous results. Aims: The aim of this study was to address the clinically important question “What is the relationship between early HI status (HI±) and functional change in the 1st six months after right hemisphere stroke?” by improving on research methodology from past studies. Methods: An all-inclusive stroke severity RHS sample (58 with and 35 without HI) were recruited from two stroke units and assessed on motor and cognitive factors with validated measurement tools on four occasions; baseline, hospital discharge, 6 weeks after discharge, and 6 months after stroke. A multi-level modelling approach was used to analyse change in functional progress over time with potential explanatory motor and cognitive factors. Results: HI status was only statistically significant when modelled alone. Its predictive importance greatly diminished when modelled with other factors e.g. stroke severity, time since stroke and age. Conclusion: On average, HI group membership at baseline is unrelated to functional recovery when other influential factors are also considered. The findings extend current knowledge in stroke recovery research and provide suggestions for optimal therapeutic and rehabilitation outcomes. In contrast with traditional methods of regression analysis, multi-level modelling techniques enabled important relationships to be studied in depth. This resulted in new insights into the data which can be used to inform patient management and future research in the field.

This investigation was an attempt to replicate and expand previous research which suggested that laterality of electromyographic biofeedback input had a significant effect in lowering frontalis muscle activity. In 1984 Ginn and Harrell conducted a study in which they reported that subjects receiving left ear only audio biofeedback had significantly greater reductions in frontalis muscle activity than those receiving right ear only or both ear feedback. This study was limited to one biofeedback session and subjects were selected based on demonstration of right hand/ear dominance. The purpose of the present study was to determine whether the left ear effect reported by Ginn and Harrell could be replicated. Furthermore, the current investigation sought to extend the previous finding to left handed subjects and explore the stability of the effect, if found, by adding a second biofeedback session. Subjects were 96 students recruited from undergraduate psychology classes. They were screened for handedness by the Edinburgh Handedness Inventory which resulted in identification of 48 right handers and 48 left handers. Subjects were randomly assigned to one of four groups consisting of left ear feedback, right ear feedback, both ears feedback, and controls. This resulted in eight conditions. Analysis of variance of microvolt changes from baseline found no statistically significant differences between groups. An examination of the rank order of the data reveal a left ear group performance in the same direction as those reported by Ginn and Harrell (1984).

The left hemisphere (LH) is accepted as the dominant hemisphere for language processing. There is also evidence confirming the language processing abilities of the right hemisphere (RH), particularly its lexical-semantic processing potential (Chiarello, 1988; Joanette, Goulet, & Hannequin, 1990). The capacity of the RH for language processing is significant to the investigation of language processing following LH lesions. However, the precise neurocognitive mechanisms underlying language processing following lesion remain to be fully elucidated. Subsequently, the overall aim for this thesis is to investigate hemispheric contributions to semantic processing following unilateral lesions, and to explore the significance of the contribution made by the RH. In order to achieve this overall aim, the current thesis firstly explores the hemispheric contributions made to lexical-semantic processing for healthy adults, and then shifts focus to explore the changes in hemispheric processing for participants with unilateral lesions (LH and RH). Comparisons of hemispheric activation between these groups will clarify the underlying hemispheric mechanisms that facilitate language processing following unilateral lesion. This thesis includes four complementary investigations of hemispheric contributions to semantic processing. The first study combined divided visual field (DVF) priming with event-related potentials (ERPs), in order to investigate controlled hemispheric semantic priming for young healthy adults. Two experiments were employed for a between subjects comparison of time-course differences (stimulus onset asynchrony, or SOA, varied between experiments) in hemispheric activation of associated and nonassociated category members. Continuous electroencephalograms were recorded throughout the priming task for each participant, and later analysed with reference to relevant ERP components (N400 and Late Positive Complex). Bilateral N400 priming was revealed for associated category members at both the short and long SOA. There was no significant N400 priming for the nonassociated category member condition. The examination of hemispheric priming of associated and nonassociated category member stimuli over the same time-course was continued in the second study for participants with unilateral LH lesions and matched controls. The second investigation aimed to determine the impact of unilateral LH lesions on controlled hemispheric semantic priming, utilising the DVF priming paradigm with participants following unilateral lesions. This study also aimed to explore associations between hemispheric activation during the online priming task and offline comprehension abilities. Differences in priming were observed between the LH lesion group and the control group, with participants in the LH lesion group requiring the association relationship to elicit priming. Priming also varied for participants as a function of their offline comprehension abilities, with RH priming associated with higher offline scores. The third investigation continued the exploration of hemispheric semantic activation following LH lesion, examining the impact of a LH lesion on interhemispheric control mechanisms, and the modification of hemispheric processing capacities with and without dominant hemisphere control. This investigation again utilised DVF priming with associated and nonassociated category member stimuli, in conjunction with the dual task paradigm. The dual task paradigm is designed to overload one hemisphere’s processing resources in order to remove interhemispheric suppression. Findings indicate that following LH lesions, the RH’s contribution is enhanced under conditions that are designed to overload the LH. The final study shifts from the investigation of participants with LH lesions to the impact of a RH lesion. This exploration of controlled hemispheric semantic priming following RH lesion sought to increase our understanding of the underlying mechanisms for semantic processing following unilateral lesion. The RH’s role in lexical-semantic processing has been documented consistently over approximately the last twenty years, however, there remains limited direct investigation of a RH lesion’s impact on contributions to semantic processing. A single case investigation utilised the same experimental procedure as the second study described. Findings suggest a similar activation pattern between the individual with RH lesion and the control participants, with both exhibiting bilateral activation of the associated and nonassociated category member stimuli. However, a subtle difference was found between the activation of the individual with RH lesion and that of the control group, with the individual with a RH lesion showing increased strategic processing difficulties at the longer SOA. Overall, the current thesis demonstrates the importance of the RH for efficient strategic semantic processing for both healthy adults, and people with unilateral lesions. In addition, this thesis concludes that following a LH lesion, the RH contribution to controlled semantic processing may be associated with successful comprehension, and that RH contributions may be improved with the addition of a secondary task designed to overload LH processing. The present thesis provides evidence to support the use of the DVF priming paradigm in the investigation of hemispheric contributions to semantic processing following unilateral lesion. It is anticipated that these findings will improve the current understanding of the underlying hemispheric contributions to lexical-semantics following a unilateral lesion, and will encourage continuing investigation into the RH’s capacity to impact language recovery.

The left hemisphere (LH) is accepted as the dominant hemisphere for language processing. There is also evidence confirming the language processing abilities of the right hemisphere (RH), particularly its lexical-semantic processing potential (Chiarello, 1988; Joanette, Goulet, & Hannequin, 1990). The capacity of the RH for language processing is significant to the investigation of language processing following LH lesions. However, the precise neurocognitive mechanisms underlying language processing following lesion remain to be fully elucidated. Subsequently, the overall aim for this thesis is to investigate hemispheric contributions to semantic processing following unilateral lesions, and to explore the significance of the contribution made by the RH. In order to achieve this overall aim, the current thesis firstly explores the hemispheric contributions made to lexical-semantic processing for healthy adults, and then shifts focus to explore the changes in hemispheric processing for participants with unilateral lesions (LH and RH). Comparisons of hemispheric activation between these groups will clarify the underlying hemispheric mechanisms that facilitate language processing following unilateral lesion. This thesis includes four complementary investigations of hemispheric contributions to semantic processing. The first study combined divided visual field (DVF) priming with event-related potentials (ERPs), in order to investigate controlled hemispheric semantic priming for young healthy adults. Two experiments were employed for a between subjects comparison of time-course differences (stimulus onset asynchrony, or SOA, varied between experiments) in hemispheric activation of associated and nonassociated category members. Continuous electroencephalograms were recorded throughout the priming task for each participant, and later analysed with reference to relevant ERP components (N400 and Late Positive Complex). Bilateral N400 priming was revealed for associated category members at both the short and long SOA. There was no significant N400 priming for the nonassociated category member condition. The examination of hemispheric priming of associated and nonassociated category member stimuli over the same time-course was continued in the second study for participants with unilateral LH lesions and matched controls. The second investigation aimed to determine the impact of unilateral LH lesions on controlled hemispheric semantic priming, utilising the DVF priming paradigm with participants following unilateral lesions. This study also aimed to explore associations between hemispheric activation during the online priming task and offline comprehension abilities. Differences in priming were observed between the LH lesion group and the control group, with participants in the LH lesion group requiring the association relationship to elicit priming. Priming also varied for participants as a function of their offline comprehension abilities, with RH priming associated with higher offline scores. The third investigation continued the exploration of hemispheric semantic activation following LH lesion, examining the impact of a LH lesion on interhemispheric control mechanisms, and the modification of hemispheric processing capacities with and without dominant hemisphere control. This investigation again utilised DVF priming with associated and nonassociated category member stimuli, in conjunction with the dual task paradigm. The dual task paradigm is designed to overload one hemisphere’s processing resources in order to remove interhemispheric suppression. Findings indicate that following LH lesions, the RH’s contribution is enhanced under conditions that are designed to overload the LH. The final study shifts from the investigation of participants with LH lesions to the impact of a RH lesion. This exploration of controlled hemispheric semantic priming following RH lesion sought to increase our understanding of the underlying mechanisms for semantic processing following unilateral lesion. The RH’s role in lexical-semantic processing has been documented consistently over approximately the last twenty years, however, there remains limited direct investigation of a RH lesion’s impact on contributions to semantic processing. A single case investigation utilised the same experimental procedure as the second study described. Findings suggest a similar activation pattern between the individual with RH lesion and the control participants, with both exhibiting bilateral activation of the associated and nonassociated category member stimuli. However, a subtle difference was found between the activation of the individual with RH lesion and that of the control group, with the individual with a RH lesion showing increased strategic processing difficulties at the longer SOA. Overall, the current thesis demonstrates the importance of the RH for efficient strategic semantic processing for both healthy adults, and people with unilateral lesions. In addition, this thesis concludes that following a LH lesion, the RH contribution to controlled semantic processing may be associated with successful comprehension, and that RH contributions may be improved with the addition of a secondary task designed to overload LH processing. The present thesis provides evidence to support the use of the DVF priming paradigm in the investigation of hemispheric contributions to semantic processing following unilateral lesion. It is anticipated that these findings will improve the current understanding of the underlying hemispheric contributions to lexical-semantics following a unilateral lesion, and will encourage continuing investigation into the RH’s capacity to impact language recovery.

The left hemisphere (LH) is accepted as the dominant hemisphere for language processing. There is also evidence confirming the language processing abilities of the right hemisphere (RH), particularly its lexical-semantic processing potential (Chiarello, 1988; Joanette, Goulet, & Hannequin, 1990). The capacity of the RH for language processing is significant to the investigation of language processing following LH lesions. However, the precise neurocognitive mechanisms underlying language processing following lesion remain to be fully elucidated. Subsequently, the overall aim for this thesis is to investigate hemispheric contributions to semantic processing following unilateral lesions, and to explore the significance of the contribution made by the RH. In order to achieve this overall aim, the current thesis firstly explores the hemispheric contributions made to lexical-semantic processing for healthy adults, and then shifts focus to explore the changes in hemispheric processing for participants with unilateral lesions (LH and RH). Comparisons of hemispheric activation between these groups will clarify the underlying hemispheric mechanisms that facilitate language processing following unilateral lesion. This thesis includes four complementary investigations of hemispheric contributions to semantic processing. The first study combined divided visual field (DVF) priming with event-related potentials (ERPs), in order to investigate controlled hemispheric semantic priming for young healthy adults. Two experiments were employed for a between subjects comparison of time-course differences (stimulus onset asynchrony, or SOA, varied between experiments) in hemispheric activation of associated and nonassociated category members. Continuous electroencephalograms were recorded throughout the priming task for each participant, and later analysed with reference to relevant ERP components (N400 and Late Positive Complex). Bilateral N400 priming was revealed for associated category members at both the short and long SOA. There was no significant N400 priming for the nonassociated category member condition. The examination of hemispheric priming of associated and nonassociated category member stimuli over the same time-course was continued in the second study for participants with unilateral LH lesions and matched controls. The second investigation aimed to determine the impact of unilateral LH lesions on controlled hemispheric semantic priming, utilising the DVF priming paradigm with participants following unilateral lesions. This study also aimed to explore associations between hemispheric activation during the online priming task and offline comprehension abilities. Differences in priming were observed between the LH lesion group and the control group, with participants in the LH lesion group requiring the association relationship to elicit priming. Priming also varied for participants as a function of their offline comprehension abilities, with RH priming associated with higher offline scores. The third investigation continued the exploration of hemispheric semantic activation following LH lesion, examining the impact of a LH lesion on interhemispheric control mechanisms, and the modification of hemispheric processing capacities with and without dominant hemisphere control. This investigation again utilised DVF priming with associated and nonassociated category member stimuli, in conjunction with the dual task paradigm. The dual task paradigm is designed to overload one hemisphere’s processing resources in order to remove interhemispheric suppression. Findings indicate that following LH lesions, the RH’s contribution is enhanced under conditions that are designed to overload the LH. The final study shifts from the investigation of participants with LH lesions to the impact of a RH lesion. This exploration of controlled hemispheric semantic priming following RH lesion sought to increase our understanding of the underlying mechanisms for semantic processing following unilateral lesion. The RH’s role in lexical-semantic processing has been documented consistently over approximately the last twenty years, however, there remains limited direct investigation of a RH lesion’s impact on contributions to semantic processing. A single case investigation utilised the same experimental procedure as the second study described. Findings suggest a similar activation pattern between the individual with RH lesion and the control participants, with both exhibiting bilateral activation of the associated and nonassociated category member stimuli. However, a subtle difference was found between the activation of the individual with RH lesion and that of the control group, with the individual with a RH lesion showing increased strategic processing difficulties at the longer SOA. Overall, the current thesis demonstrates the importance of the RH for efficient strategic semantic processing for both healthy adults, and people with unilateral lesions. In addition, this thesis concludes that following a LH lesion, the RH contribution to controlled semantic processing may be associated with successful comprehension, and that RH contributions may be improved with the addition of a secondary task designed to overload LH processing. The present thesis provides evidence to support the use of the DVF priming paradigm in the investigation of hemispheric contributions to semantic processing following unilateral lesion. It is anticipated that these findings will improve the current understanding of the underlying hemispheric contributions to lexical-semantics following a unilateral lesion, and will encourage continuing investigation into the RH’s capacity to impact language recovery.