Browsing by Author "Martin, Randi C"

Now showing 1 - 6 of 6
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    Genetic Links among Ideology, Cognitive Style, Big Five Personality, and Executive Functions
    (2015-04-21) Ksiazkiewicz, Aleksander Jan; Alford, John R; Wilson, Rick K; Stevenson, Randolph T; Martin, Randi C; Krueger, Robert F
    This dissertation provides novel insights into the role of genes in political attitudes and behaviors by examining the role of genes in political traits over time and by uncovering two novel sets of potential mediators between genes and politics. Chapter 1 provides an exhaustive review of the biopolitics literature, lays out a theoretical framework for the study of biopolitics, and reviews twin study methodology. Chapters 2 and 3 report results from twin study analyses that rely on an original survey of twins that was conducted in the fall of 2012 in cooperation with the Minnesota Center for Twin and Family Research. Chapter 2 conducts one of the first genetically-informative panel studies of political traits. It finds that genetic factors are the primary contributors to trait stability over a four year period in mid-life, but that only environmental factors contribute to trait change over the same period. Chapter 3 conducts the first ever behavioral genetic analysis of three measures of cognitive style—the need for cognition, the need for cognitive closure, and the need to evaluate. It then shows that the correlations between cognitive style and political traits are driven, in most cases, primarily by genetic factors. This finding suggests that cognitive style variables may mediate the role of genes in politics, a possibility that is left open for future research. Chapter 4 utilizes an original online panel, collected via Amazon Mechanical Turk, to examine whether individual differences in executive functions are related to political traits. The results suggest that updating, a form of executive function, is related to several political traits. Moreover, because individual differences in executive functions are highly heritable, updating may mediate the genetic effect on politics. Chapter 5 summarizes the main contributions of this research, which include evidence of the role of genes in political trait stability in mid-life, the heritability of widely-studied cognitive style measures, and the possibility that cognitive style and executive functions mediate the role of genes in politics. The final chapter also lays out a research agenda for the biopolitics field. In short, this dissertation strongly supports integrating genes into political science theory.
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    How do word frequency and semantic diversity affect selection of representations in word processing?
    (2019-04-18) Chapman, Curtiss Anthony; Martin, Randi C
    The frequency at which words are encountered has long been considered an important factor in language processing, with higher frequency speeding word comprehension and production. That is, many theories claim that word representations are stronger for words encountered more often. However, some recent work has claimed that, rather than word frequency, the factor determining the strength of the representation of words (and accounting for previous effects of word frequency) is the word’s semantic diversity (SemD) – i.e., the variety of contexts in which a word is found (Adelman et al., 2006; Jones et al., 2012). Other recent approaches have suggested that SemD may play a more nuanced role in language processing—helping in certain situations and harming in others. That is, when a specific word meaning must be accessed without sufficient context, greater SemD may lead to more effortful processing, sometimes even minimizing or reversing typical frequency effects (Hoffman et al., 2011, 2013). More effortful processing would occur because one has to distinguish a single meaning from among all of the contextually-associated meanings to which a word may be potentially related. A mechanism that distinguishes a target meaning from among potential meanings would be an important one in language processing generally, but the presence of such a mechanism and its relationship to SemD have not been deeply explored. This dissertation explores the relationship and influence of word frequency and SemD in language processing, including whether SemD explains typical word frequency effects and whether SemD creates a need to distinguish from among competing contextual meanings. Part one explores effects and interactions of word frequency and SemD across a variety of large mega-study databases of language processing tasks. Part two attempts to manipulate the mechanism that resolves competition between word meanings to examine its impact on effects of SemD and language processing more generally. Results indicate that both frequency and SemD are important qualities affecting word processing, but little evidence is found for the role of a meaning selection mechanism that responds to SemD. The impact of these results on current theories of language processing is discussed.
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    Rethinking the Behavioral Patterns that Dissociate Semantic Dementia and Comprehension-Impaired Stroke Aphasia
    (2016-10-28) Chapman, Curtiss; Martin, Randi C
    Researchers have proposed that semantic processing involves both stored semantic knowledge and mechanisms used to access and manipulate this knowledge. Support for this distinction has come from a contrast of the patterns of behavior in comprehension-impaired stroke patients (SA) and patients with semantic dementia (SD). Specifically, SD patients are argued to have a loss of amodal semantic representations whereas SA patients have an impairment of executive control used to access and manipulate these representations (Jefferies & Lambon Ralph, 2006). However, the conclusions of these researchers are based on incomplete and sometimes vague evidence. They have used questionable executive function measures, have failed to fully test semantic dementia patients on measures of executive function, and have provided only weak evidence for a role of executive function in semantic deficits for stroke patients. The current study re-examines the difference between these patient groups and the nature of their deficits using a set of tasks to measure semantic and executive function abilities and the relationship between them. Our results show that the two patient groups are not as distinct as previously claimed. The SD group shows frequency effects only by some measures, while the SA group shows normal frequency effects; both groups show similar item consistency, correlations of semantic task performance regardless of task demands, and some consistent executive deficits. Additionally, we tested stroke patients who showed executive deficits but not semantic deficits, which calls into question the relation of "access" deficits to executive function. We also examined this relationship based on semantic-executive correlations. While our findings do not rule out the possibility of a distinction between knowledge of and access to semantic knowledge, they do call into question some of the main empirical claims used to support this distinction.
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    Role of Features and Categories in Representing Object Knowledge
    (2015-04-21) Geng, Jingyi; Schnur, Tatiana T.; Martin, Randi C; Fischer-Baum, Simon; Cox, Steven; Hernandez, Arturo
    Understanding how our knowledge about the world is organized can help us understand how we are able to access that knowledge to easily identify objects and communicate with others. One general view of object knowledge organization assumes that object knowledge is represented by how we perceive and interact with objects (for example features like the color or shape we see and touch) (i.e., feature view; e.g., Allport, 1985; Barsalou, 1999, 2008; Gallese & Lakoff, 2005; Tyler & Moss, 2001). In contrast, an alternative view hypothesizes that in addition to features from different modalities (e.g., visual, motor, and tactile), taxonomic (e.g., dog and rabbit are animal) and thematic category information (e.g., eating theme: a dog is chewing a bone) is also critical for representing object knowledge (i.e., feature-plus-category view; e.g., Crutch & Warrington, 2005, 2010; Patterson et al., 2007; Schwartz et al., 2011; Mirman & Graziano, 2012). In order to examine these two general views of object knowledge organization, I investigated whether feature and category information is activated when people access the meaning of words using both behavioral (i.e., response times and errors; Experiments 1 and 2) and functional magnetic resonance neuroimaging measures (Experiment 3). Consistent with the feature-plus-category view, Experiments 1 and 2 showed that when people access the meaning of words, this access was affected (slower/faster) by manipulating visual features (e.g., shape), taxonomic and thematic category information associated with objects. In support of the feature-plus-category view, Experiment 3 revealed that action features (e.g., cutting) associated with objects (e.g., saw) activated the motor brain region (i.e., primary motor cortex) and the taxonomic and thematic categories recruited the bilateral anterior temporal lobes and left temporo-parietal junction respectively. Taken together, my dissertation provides converging evidence from both behavioral and neuroimaging perspectives showing that both feature and category information play a key role in representing object concepts.
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    Sublexical, lexical and phonological short-term memory processes: Evaluating models of speech perception and short-term memory
    (2016-08-12) Dial, Heather Raye; Martin, Randi C
    The current research examined the processes involved in speech perception and the relation of speech perception to phonological short-term memory (pSTM). Contrary to traditional models which assume that sublexical processing necessarily precedes lexical processing (e.g., McClelland & Elman, 1986; Norris, 1994), several studies have demonstrated that patients may perform better on lexical than sublexical speech perception tasks (e.g., Miceli, Gainotti, Caltagirone, & Masullo, 1980). These findings have led to proposals of separate sublexical and lexical routes in speech perception (dual route models; e.g., Hickok & Poeppel, 2000). However, studies demonstrating these dissociations did not closely match the phonological similarity of targets and distractors or task demands between sublexical and lexical tasks. Experiment 1, which rectified these design problems, demonstrated a close correspondence between sublexical and lexical processing across several speech discrimination tasks for brain damaged patients and supported obligatory sublexical processing models of speech perception. Experiment 2 sought to provide converging evidence by tracking patients’ eye movements while they performed sublexical and lexical identification tasks. As in Experiment 1, there was evidence a) of a close correspondence between sublexical and lexical processing and b) for obligatory sublexical processing. However, there were some dependent measures that failed to support the obligatory sublexical processing framework. Dual route models additionally claim that pSTM depends on the brain regions involved in perception, including a sensory-motor interface region involved in rehearsal (e.g., Hickock & Poeppel, 2000). In contrast, traditional models of pSTM assume a phonological maintenance buffer separate from perceptual processes (Martin & Breedin, 1992). In Experiment 3 we found behavioral and structural neuroimaging (lesion-symptom mapping) support for the buffer approach, though no significant results were found in attempts to localize sublexical and lexical processing.
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    The white matter correlates of domain-specific working memory and language processing
    (2022-11-21) Horne, Autumn; Martin, Randi C
    Prior neuropsychological evidence suggests separable, domain-specific working memory (WM) buffers for maintaining phonological (i.e., speech sound) and semantic (i.e., meaning) information. The phonological and semantic WM buffers can be damaged separately from each other, having distinct effects on both language comprehension and production. The phonological WM buffer’s proposed location is the left supramarginal gyrus (SMG), whereas semantic WM has been related to the left inferior frontal gyrus (IFG), middle frontal gyrus (MFG), and angular gyrus (AG). However, less is known about the white matter correlates of phonological and semantic WM and any corresponding relationships to multiword language processing. Here, I report 1) the white matter correlates of phonological and semantic WM, 2) the white matter correlates of multiword language production and comprehension, and 3) evidence that semantic WM can mediate the relation between tract integrity and language processing. These analyses focus on the left hemisphere as there is strong evidence for the involvement of left hemisphere regions in verbal WM and language processing. I also present exploratory analyses of the relations between right hemisphere tracts and both WM and language processing to address the possibility that WM and/or language function reorganizes to the right hemisphere after left hemisphere brain damage. Participants were 45 individuals with left hemisphere brain damage. Each participant was tested on a battery of single word processing, phonological WM, semantic WM, sentence comprehension, and narrative production tasks. T1 and diffusion weighted scans were also obtained for each participant. Virtual dissections were performed for each participants’ arcuate fasciculus (AF), inferior fronto-occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF), middle longitudinal fasciculus (MLF), and uncinate fasciculus (UF). These tracts were chosen because they have terminations in regions that have previously been identified as potential domain-specific WM buffers: the SMG for phonological WM and the IFG, MFG, and AG for semantic WM. In chapter 2, to test the relation between white matter tract integrity and domain-specific working memory, I took a multiple regression approach which allowed us to control for both single word processing and gray matter damage to the regions where each tract terminates. I predicted that the indirect pathway of the left AF would support phonological WM while the left IFOF, ILF, MLF, UF, and direct pathway of the AF would support semantic WM. Further, because semantic WM is critical for multiword language processing, it was predicted that tracts supporting semantic WM should also support multiword language production and comprehension. In line with the predictions, the left ILF, left MLF, left IFOF, and left direct segment of the AF were related to semantic WM performance. Relationships between semantic WM and right ILF and right IFOF integrity were also observed. Phonological WM was related to both the left ILF and MLF. In chapter 3, I used a multiple regression approach to investigate the relation between tract integrity and language processing while controlling for single word processing and gray matter damage. I found that the left AF, IFOF, ILF, and right IFOF were related to language comprehension while the left IFOF and ILF were related to language production. The right IFOF was also related to language comprehension. Further, I used mediation analysis to investigate whether semantic WM fully or partially mediates the relation between left IFOF and left ILF tract integrity and multiple aspects of multiword language processing. Additionally, phonological WM mediated the relation between left ILF integrity and language comprehension. The results of this work inform our understanding of the white matter correlates of both WM and language processing, especially semantic WM, and the neural basis of the relation between semantic WM and language processing, which no previous work has investigated. From a theoretical perspective, this work is also important for adjudicating between alternative buffer theories of verbal WM and should inform future research on neuroplasticity, particularly how the right hemisphere may support cognitive processing after left hemisphere brain damage