Melbourne School of Psychological Sciences - Theses
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Individual differences in perceptual and cognitive decision-making in response to near identical options
Every day people deal with the “exploration/exploitation dilemma”: Deciding when to stay with the current option or move to a new one. Most research in the literature focuses on the influence that external variables exert on people’s decisions (e.g., punishments/rewards). However, little is known about how people deal with identical or nearly identical options in the absence of external bias. The general assumption present in both human and animal models is that, in the absence of obvious cost, individuals would naturally explore. This thesis directly tests this assumption in six experimental studies by examining people’s behaviour when facing identical or nearly identical options, both in perceptual and behavioural tasks. Despite the obvious differences existing between behavioural and perceptual tasks, people are essentially making similar decisions (to explore a different option; or to exploit the current option). Hence, the broad hypothesis under investigation is that similar tendencies should be found within the same person, across domains. Furthermore, because the impact of external bias was minimal in the tasks used, any differences in people’s explorative tendencies should be attributed to stable factors, such as personality traits. To this end, we individuated two broad personality frameworks (the Big Five Model and the Schizotypy construct). In Study 1-4 we examined how people deal with the trade-off between exploration and exploitation from a perceptual perspective, by using binocular rivalry (where an observer is faced with identical, and equally valid, perceptual solutions). In Study 1 we demonstrated that people high in the Openness to Experience trait significantly differed from other people in the way they flexibly explored and combined basic visual stimuli. In Study 2 we looked at whether differences existed in people’s tendencies to explore perceptual solutions following changes in transient emotional state (i.e., arousal) and found that general changes in one’s mood, but not specific type of mood, have a significant impact. In Study 3 we examined whether changes in alternations (i.e., fast or slow) between perceptual solutions were associated with stable personality traits and found that slower alternations were associated with Conscientiousness, characterised by self-control and determination. In Study 4 we examined whether abnormalities in the way perceptual stimuli are “flexibly” processed in people with schizophrenia can be similarly found in a non-clinical population. We found that increased schizotypy was associated with an increase of mixed percept during binocular rivalry. Study 5-6 examined how people deal with the trade-off between exploration and exploitation from a behavioural perspective, by using the Virtual Environment task, which was designed and developed specifically for this aim. The Virtual Environment task was inspired by the animal literature (i.e., the optomotor maze; van Swinderen, 2011) where flies need to choose between identical turning points to advance in the maze. Study 5 presents the findings from the six pilot task. Each version was sequentially developed to rule out potential confounding variables, which might have been responsible for the “unusual” stereotypical behaviour that emerged. That is, people displayed exclusively exploitative tendencies, with no exploration. Study 6 presents the findings from the virtual environment task. Here people showed variability in their explorative tendencies, however, against our prediction an increase of exploration was linked to those personality traits capturing self-discipline (Conscientiousness), rather than flexibility and the tendency to engage with possibilities (Openness to Experience). This was the first evidence of important similarities between perception and behaviour in the way people deal with the trade-off between exploration and exploitation. For example, in relation to the number of decisions, or sampling, of the environment. Our findings also highlighted two important issues in the exploration/exploitation literature. First, they cast doubt on the assumption that humans have a “natural drive to explore” in the absence of rewards. As shown in the difficulties to design appropriate stimuli to observe a balance between exploration/ exploitation in the first place. Second, because our findings did not replicate data from the animal literature, they represent a cautionary tale in interpreting findings from the animal model to be considered valid for humans.
Evaluating a Universal Social Information Processing Skills Program for Girls: The Friendship Saver Program
This thesis presents an evaluation of the Friendship Saver Program, a universal program designed to be gender-specific, aimed to improve the social information processing skills of girls. Specially, the program aims to teach social information processing skills as defined by the Social Information Processing Model (SIP) (Crick & Dodge, 1994). The 12-week universal program was delivered to 214 middle-primary school age girls, by trained facilitators from their schools. An implementation quality questionnaire was used to track the fidelity of implementation, and indicated satisfactory to very good delivery of the program across the four schools involved. To evaluate program impact multiple measures were included, using a pre- and post-intervention design. An innovative interactive software program What Next? (Ainley & Ainley, 2006) was used to directly measure participants’ social information processing skills, and the widely-used Strengths and Difficulties Questionnaire (SDQ) (Goodman, 1997) was used to measure general social and behavioural functioning as rated by parents and teachers. The What Next? program measured participants interpretation of cues, response construction and response decision after viewing a video scenario of relational aggression. Due to the novel nature of using software and video footage to assess social information processing skills, participant engagement was also assessed. The engagement results offered strong evidence that the participants were highly engaged by the video scenarios, and maintained their engagement throughout their experience with the software. A pre-post intervention comparison indicated that following participation in the Friendship Saver Program, participants identified significantly more subtle cues indicative of hostile intent, and provided more response constructions and response decisions that were adaptive, with fewer maladaptive responses post-intervention. Hence, these results offered evidence of positive change following the Friendship Saver Program on girls’ social information processing skills. Parent and Teacher SDQ ratings indicated that this sample was a high functioning group at commencement of the project. Teacher ratings on the SDQ demonstrated no change in general social or behavioural functioning post-intervention, while parent ratings indicated fewer externalizing problems post-intervention. In concluding, the findings demonstrate the importance of gender-specific programs for teaching social skills to girls, and the advantages of using software and video technology to measure these skills. The results also demonstrate the potential of the SIP model to inform a targeted intervention for girls, and to be a relevant framework for investigating the social skills of girls.
The low statistical power of psychological research: Causes, consequences and potential remedies
This dissertation examines two major issues in psychological research: formal sample size planning and reporting biases. It is organized into three main parts. The first part examines the history of formal sample size planning and reporting biases in the psychology research literature, outlining the history of the dominant approach to statistical analysis (Chapter 2), demonstrating the implications of low statistical power and reporting biases on research literatures (Chapter 3), and examining the history of statistical power analysis as represented in the psychology research literature (Chapter 4). The second part of this dissertation examines psychologists’ research and publication practices. Chapter 5 presents a meta-analysis of previous power surveys and finds that the average statistical power of psychology research at Cohen’s small and medium effect size benchmarks was lower than typical goal levels and that this value remained approximately constant from the 1960s to 2014. Chapter 6 presents an analysis of more than 130,000 effect size estimates from over 9,000 articles published in 5 APA journals from 1985 to 2013 and finds that the average effect size reported in this body of psychological research decreased over time. Together Chapters 5 and 6 suggest that the average statistical power of psychological research remained stable or may even have decreased over time. In order to investigate why this is the case, Chapter 7 presents the results of a survey of researchers from across fields of psychological research about their research planning practices. This survey highlights the most important barriers that prevent researchers from using formal sample size planning during the design phase of their research and shows that while most researchers believe statistical power is important for their research purposes, practical constraints act to limit achieved sample sizes in most studies. The final part of this thesis examines the implications of low statistical power and reporting biases on scientific research and provides suggestions on how research planning methods could be improved. Bringing together all of the previous large-scale replication projects that have been conducted in the behavioral sciences, Chapter 8 shows that effect sizes in replication studies are, on average, considerably lower than those reported in original studies, and quantifies the substantial heterogeneity in this value across replication projects. Finally, Chapter 9 examines sample size planning efforts reported in recent Psychological Science articles and uses this to illustrate a guide to effect size selection for formal sample size planning. Together, this dissertation shows that low statistical power and reporting biases remain serious problems for the behavioral sciences research literature. Contrasting the long history of efforts to improve the statistical power of psychology research with the lack of change in the average power of research from 1962 to 2014, I argue that new methods of avoiding the negative impact of low statistical power and reporting biases are necessary. Several recent publication and methodological developments, namely (a) preregistration, (b) pre-prints and data repositories, (c) the registered reports publication format and (d) the increasing use of large scale collaborative research projects, provide possible mechanisms with which to reduce the negative impact of low statistical power and reporting biases on the published scientific literature.
Contemporary methods for identifying and leveraging expertise in collective decision-making
From company board committees to grand juries to political parties, decision making often involves a group of individuals with differing views on what the best decision may be. Individuals have different views, in part, because some individuals have more knowledge than others. In theory, decision makers can make better decisions by leveraging the expertise of individuals in the crowd by identifying those who have more knowledge than others. Unfortunately, it is often difficult to identify and leverage expertise in practice. Decision makers often have no records of individuals' past performance from which they can estimate expertise, and subjective measures such as confidence and self-ratings of expertise are often considered as unreliable. In this thesis, I demonstrate how individuals' meta-predictions -- predictions about what other individuals will predict -- can be used to identify and leverage expertise in the crowd on 'single-question' problems, where records on individuals' past performance are unavailable. I first examine how a recent algorithm in the literature can be used to distinguish between subsets of high-performing and low-performing individuals in the crowd on binary decision problems. I show that this algorithm is in fact weighting individuals by the absolute difference between an individual's vote and their meta-prediction about the votes of others, and thus this weighting metric can be used to identify and leverage expertise in the crowd. I develop an improved weighting approach that uses individuals' probabilistic forecasts and their meta-predictions about the average probability forecast of others, and show that this outperforms the top alternative probabilistic aggregation approaches in the literature on a large range of decision problems. Furthermore, I demonstrate that this improved weighting approach provides a superior measure of expertise than existing single-question approaches to identifying expertise in the literature. As an additional test, I compare this single-question approach with cross-domain weighting -- weighting by individuals' performance on problems on unrelated domains -- and show that cross-domain weighting is favoured over single-question approaches in cases where it is possible to obtain individuals' past performance on problems -- even if those questions are from unrelated domains. In general, our results demonstrate the potential for using individuals' meta-predictions and performance on problems from unrelated domains to identify expertise in cases where other approaches might be ineffective or unavailable.
Volumetric Measures of the Medial Temporal Structures and their Neuropsychological Correlates in Alzheimer’s Disease
Diagnosing Alzheimer’s disease (AD) in its earliest phases is difficult. A combination of standardised cognitive testing with AD-related biomarkers such as medial temporal atrophy observed on neuroimaging scans has been proposed to improve the diagnostic process of AD detection. The availability of automated volumetric segmentation software presents as a promising avenue for the incorporation of quantitative volumetric measures into routine clinical workup. However, the performance of these automated protocols in a clinical context remains to be clarified. This thesis aimed to examine the use of automated segmentation in a “real-world” clinical setting against the gold standard of manual segmentation, assess the difficulties surrounding reliable automated measurements, and evaluate the relationship between volume, diagnosis, and memory function. Methods utilised to address the research questions included a review of the diagnostic accuracy of various diagnostic tools, in-depth examination of structural variations that could undermine automated segmentation efforts, a series of validation studies, and assessment of medial temporal volumes and memory function in samples of clinical and healthy controls. The results indicate that a multimodal approach to diagnosis that includes a combination of cognitive assessment and other biomarkers would likely yield a more accurate diagnosis. Although automated segmentation of the medial temporal structures was promising for the hippocampus, the entorhinal and transentorhinal cortices were inherently more challenging to delineate and produced much poorer reliability measures. Medial temporal structural volumes contributed little beyond what was already provided by comprehensive memory assessment for distinguishing between the clinical and healthy control samples. Taken altogether, these findings highlight the need for additional refinement of automated algorithms and further investigation into the ideal combination of cognitive testing and other biomarkers.
Organizational Neuroscience with Applications to Stress Management
This thesis was on organizational neuroscience with applications to stress management. Section 1 developed an organizational neuroscience model of occupational stress that integrated the health impairment process of the job-demands resources model of occupational stress with the (biologically-grounded) allostatic load model of stress. In doing so, this section developed a series of propositions that integrated each model through a job demands-allostatic load pathway. Resilience training was discussed as a potential moderator of this pathway with a focus on mindfulness meditation, physical activity, and multi-modal interventions that comprise each of these practices completed concurrently. In Section 2 of this thesis, specific methodological, interpretational, and philosophical concerns that arise when adopting an organizational neuroscience approach to research were discussed across two critical essays. This included a focus on the appropriateness of statistical analyses in organizational neuroscience, the implications of the completeness and transparency of reporting research findings, and what kind of causal inferences can be drawn about organizationally-relevant behavior using neuroscience data. These essays served as the statistical and philosophical framework through which the empirical studies conducted in Section 3 were conducted and interpreted. Finally, Section 3 of this thesis was a conceptual evaluation of the resilience training propositions of the theoretical model developed in Section 1. It was a conceptual evaluation in that the sample was one of convenience rather than a working population, specifically. This included three studies conducted within a pilot and feasibility trial that comprised formal mindfulness psychoeducation and aerobic endurance exercise training, completed concurrently. It has been theorized that interventions of this kind exert salutary effects on mental health outcomes through neurobiological mechanisms. To assess this, this intervention was evaluated at multiple levels of analysis to build a comprehensive understanding of its effect on the mind, brain, and physiology. The primary aim of Study I was to investigate the effect of this intervention on self-reported chronic psychosocial stress, and potential mechanisms involving dispositional mindfulness, adaptive and maladaptive emotion regulation strategies, and maximal and submaximal cardiorespiratory fitness. Notably, participation in this intervention was associated with a reduction in chronic psychosocial stress, and an improvement in wellbeing that is considered clinically meaningful with respect to the scale. The primary aim of Study II was to investigate whether the effects of this intervention on mental health outcomes may occur through neural mechanisms, as predicted by theoretical models. This involved a longitudinal voxel-based morphometry study with a focus on gray matter concentration within the hippocampus. This study provided preliminary evidence that this intervention was associated with increases in gray matter concentration within the hippocampus, as well as within regions associated with stress regulation, memory, and sensorimotor processes. The primary aim of Study III was to investigate whether the aerobic endurance training component of this intervention was associated with exercise-induced adaptations to stress-responsive systems. This is of note because these adaptations have been posited to spill over to heterotypic stressors like psychosocial stress, and confer resilience to adversity more broadly. This was evaluated through measuring the cortisol response to a submaximal steady state exercise bout before and after the training period. In this study it was identified that training was associated with an attenuation of cortisol responses, which was indicative of physiological adaptations that enable submaximal exercise workloads to be conducted with greater efficiency and less strain. Limitations and implications for future research were also discussed.
An investigation of within-dimension stimuli in categorization and change detection
This thesis examined the way in which information is combined in order to make decisions. It focused specifically on within-dimension decision-making with spatially separate stimuli. The primary aim was to characterize the underlying organization of processing over time (i.e., identify the processing architecture; whether information processing proceeds in serial, parallel, or is pooled into a single decision-making channel), stopping rules (i.e., whether the process is exhaustive or self-terminating), and the efficiency of processing (i.e., workload capacity). These attributes were assessed through the analysis of response times (RTs) using Systems Factorial Technology (SFT), the Logical-Rules paradigm, and relevant computational modeling. In the first part of the thesis, results from the categorization experiments showed that for the majority of participants, processing occurs coactively (i.e., is pooled into a single decision process). Workload capacity, however, was shown to be limited. This suggests that a violation of context invariance may have occurred and several theories are considered as potential explanations for this finding. In the second part of the thesis, a novel modeling framework for characterizing the time course of change detection based on information held in visual short term memory was presented. Specifically, we sought to answer whether change detection is better captured by a first-order integration model, in which information is pooled from each location, or a second-order integration model, in which each location is processed independently. We conducted two experiments with both disjunctive OR rules and conjunctive AND rules (across locations) using a double factorial paradigm and a redundant target paradigm. These experiments showed that although capacity is generally limited in both tasks, architecture varies from parallel self-terminating in the OR task to serial self-terminating in the AND task. This novel framework allowed for model comparisons across a large set of models, ruling out several competing explanations of change detection. As a whole, this thesis found both differences and similarities in decision-making using within-dimension stimuli across categorization and change detection tasks. The finding of differences in decision-making strategy across categorization and change detection tasks highlights that different perceptual operations can yield a variety of experimental results. It may be expected that other tasks such as visual search, identification, and detection might also diverge. A finding of limited capacity across both task types, however, points to a potential common bottle neck in processing efficiency at an earlier encoding stage.
The Impact of Comorbidities and Expectations on Functional Neurological Disorder Symptoms (FND)
Functional Neurological Disorder (FND) is a condition that encompasses a wide spectrum of neurological symptoms that do not have an organic explanation. It is not clear why some patients develop a specific neurological symptom. In our study we considered the most frequent FND sub-types: functional motor disorders (FMD) and non-epileptic seizures (NES). It has been purported that individuals with risk factors, create strong expectations about body sensations based on clinical experiences such as disease, injury or surgery. These expectations would impact the nervous system which in turn lead to functional symptoms. These symptoms are inconsistent in frequency and evolution across time, and they are vulnerable to suggestion. Thus, there are no objective measures that can account for the symptoms. This thesis aims to determine whether previous clinical factors affecting different parts of the body have a relationship with the development of functional motor disorder (FMD) and non-epileptic seizures (NES), and to carry out a preliminary study of a measure capable of identifying perceptual differences in patients with functional weakness, the most reported symptom. In the first study we analysed the medical records of 108 FND patients (52 FMD and 56 NES), and in the second study we applied the Size-Weight Illusion (SWI) to 11 FND patients with functional weakness and 15 healthy controls (HC). It was found that patients with motor symptoms (FMD) had significantly higher rates of clinical factors that affected their limbs prior to the symptom onset than NES. Moreover, contrary to predicted, patients with NES had a similar rate of events that affected their head than FMD. However, NES had a higher rate of clinical factors during their lifetime than FMD, such as dissociative symptoms, suicidal ideation, and being victim of bullying, which affect the mind, and from the patients’ perspective they can be considered as located in the head. In the second study, FND and HC experienced a similar size-weight illusion. The severity and laterality of the symptom did not impact on the strength of the illusion, nor the dominance of the affected side. However, we propose that it is likely to find an effect in FND with a larger sample size. Otherwise, if similar results were found in future studies, the SWI might be a test that provides an objective assessment to confirm FND has a normal perception of weight relative to size.
Using long-wear electroencephalography to ascertain the variability of Lempel-Ziv Complexity (LZc) measures of consciousness
It has been recently claimed that measures of spontaneous electroencephalography (EEG) signal complexity, such as Lempel-Ziv Complexity (LZc), can provide an index of an individual’s level of consciousness. Research and clinical practice are currently limited to unreliable behavioural and physiological measures to indicate consciousness. Therefore, there is significant urgency for an objective, reliable, brain-based measure of consciousness. EEG complexity measures utilise algorithms from Information Theory to quantify the diversity in spontaneous EEG data. These are being used to measure the diverse neural activity which necessarily underlies conscious experience. LZc assesses the complexity of multi-channel EEG data using a compression algorithm. Studies of LZc typically involve comparing conditions of altered consciousness with periods of conscious wakefulness. These studies suggest that the change in complexity observed is reflective of the change in level of consciousness. However, very little is known about how LZc varies, either with or without a corresponding change in consciousness. The present study utilised portable long-wear EEG to record multi-day, continuous EEG data from two participants (a total of 8 days for Participant 1 and 4 days for Participant 2). Data from each participant was analysed independently. A LZc algorithm was used to compute a complexity value for every non-overlapping 10-second segment. Results demonstrated that, as with previous research, LZc during Wake (14-hours during the day, multiple days per participant) is, on average, higher than during sleep (Stage N1, Stage N2, Slow-Wave-Sleep, and REM sleep). However, there is considerable variation surrounding these means. Visualising LZc across Wake revealed a consistent but wide spread of variability around the mean, with a scattering of low LZc values reflected by a negative skew in the data. This also results in a wide range of possible mean LZc values made available from taking samples (between 1 and 120 minutes in duration) during this period. Although this variability reduces with larger samples sizes, even day-to-day, LZc can significantly differ within a person. Regardless of the source of this variability, its presence causes concern due to the overarching clinical motivations and potential practical applications of this measure. These results suggest that LZc may not be indicative of level of consciousness, as previously claimed. The issues raised and addressed in this study are not unique to LZc, but will apply to all complexity algorithms, current and future. With this study, we have shown that long-duration EEG is a successful framework for identifying variability in a complexity measure of consciousness. This information-rich dataset is uniquely capable of exposing and investigating complexity measures, with the additional insight of observing and analysing complexity across time. This study endeavours to redirect discussions of this field and promote the use of this framework to both acknowledge and empirically address all surrounding issues and assumptions. All complexity measures should undergo reliability testing as both a proof of concept and a proof of practice before being utilised in research or clinical applications.
Wellbeing and functioning in emerging adulthood: A longitudinal study of determinants and mechanisms
During the key periods of adolescence and emerging adulthood, individuals can be particularly vulnerable to experiencing suboptimal wellbeing and functioning. With potential long-term impacts on adult trajectories, early wellbeing promotion is critical. This study aimed to further understand wellbeing development across adolescence and into emerging adulthood, by examining the role of a range of individual and environmental characteristics. The individual characteristics examined included temperament, anxiety symptoms, and depression symptoms. Environmental characteristics included parental responses to emotion expression, parental mental health, stressful life events, and maltreatment. The role of emotion regulation strategies were also explored in relation to the characteristics and wellbeing. The study utilised a longitudinal community cohort from the Adolescent Development Study, recruited from schools across Melbourne, Australia. The sample included 245 families who completed questionnaires across three time points. At time 1 (mean age = 12.45), measures of temperament, depression symptoms, anxiety symptoms, parental depression symptoms, parental anxiety symptoms, and parental responses to offspring emotion expression were completed. At time 2 (mean age = 15.01), adolescents completed measures of stressful life events and maltreatment. They completed emotion regulation and wellbeing measures at the final time point (mean age = 18.83). Predictor variables were factor analysed within each domain in order to provide sufficient representation of the structure of the data. A series of path analyses, controlling for gender and SES revealed that temperament traits, neglect, and abuse predicted wellbeing and functioning outcomes. Bootstrap path analyses (using 95% confidence intervals for the indirect effect) revealed significant associations between the emotion regulation strategies of rumination, distraction, mindfulness, cognitive reappraisal, and expressive suppression with the individual and environmental characteristics, and wellbeing and functioning outcomes. Findings suggest that wellbeing development across adolescence and emerging adulthood is associated with individual characteristics (e.g., temperament), as well as environmental experiences that deviate from adaptive ranges (e.g., neglect). The various patterns found in the study reinforce the salience of examining wellbeing as a multifaceted construct, with aspects of wellbeing potentially having different developmental pathways. Furthermore, emotion regulation strategies may be important for wellbeing pathways, with maladaptive strategies (e.g., rumination) being associated with lower wellbeing and adaptive strategies (e.g. mindfulness) associated with higher wellbeing. Therefore, emotion regulation may be a suitable target for optimising youth wellbeing.
Brain and behavioural correlates of emotional voice processing in autism and its broader phenotype
Autism Spectrum Disorder (ASD) is a complex neurodevelopmental condition characterised by impairments in two core domains of social communication deficits and restricted, repetitive behaviours or interests. A milder variant of autism-like characteristics, known as the Broader Autism Phenotype (BAP), is present at higher rates in relatives of individuals with ASD than the general population, indicating a genetic liability for ASD. There is a wealth of social cognitive research documenting theory of mind, empathising, and emotional face processing deficits in ASD and the BAP, which correspond to abnormal brain function in the “social brain”. However, less research has been conducted on the brain and behavioural correlates of emotional voice processing in ASD and the BAP, despite its significance for social cognition. This thesis aimed to profile emotional voice processing abilities in ASD and the BAP in relatives and the general population, specifically relating to non-linguistic vocalisations known as vocal affect bursts (e.g., laughter, cries, screams). This thesis also aimed to identify the neurobiological substrates of emotional voice processing in individuals with ASD and relatives with the BAP. Three studies were performed to address these aims, each using the same purpose-built, web-based and/or functional MRI (fMRI) task to assess behavioural performance and elicit brain activation. Whole-brain activation elicited by the fMRI task was assessed using random- and fixed-effects analyses (RFX and FFX), which allowed inferences to be made on the population and sample levels, respectively. Study 1 examined vocal affect burst recognition and its neurobiological correlates in individuals with high-functioning ASD (n = 16) compared to typically-developing controls (n = 16). The ASD group demonstrated a vocal emotion recognition deficit on the web-based task, where they misclassified neutral non-linguistic voices as expressing basic emotions at a higher rate than controls. RFX analyses revealed no significant group differences in brain activation, whereas FFX analyses revealed that the ASD group demonstrated higher activation relative to controls in widely distributed regions associated with emotional voice processing, executive function, memory, motor and somatosensory processing, and visual processing. These findings enable atypical brain activation to be inferred for this specific ASD cohort, but not for the wider ASD population. Although cohort-specific, such information may facilitate hypothesis generation for future investigations of neurobiological compensation in ASD. Study 2 addressed the same research questions as Study 1 in relatives of individuals with ASD (n = 13) who were determined to have the BAP on clinical assessment. The BAP group demonstrated no vocal emotion recognition deficit relative to controls (n = 13) on the web-based task. Under FFX analyses alone (not RFX analyses), the BAP group demonstrated significantly higher activation in the left lateral occipital cortex relative to controls. Inferences about the FFX findings are limited to the specific BAP cohort assessed here, and cannot be extended to the wider population of ASD-relatives with the BAP. Nonetheless, these findings may inform new hypotheses exploring endophenotypes (i.e., intermediate phenotypes) of ASD, characterised by a similar expression of neurobiological compensation in ASD and the BAP. Study 3 used the web-based task to assess the association between vocal affect burst recognition and the continuous distribution of BAP traits in the general population of individuals without a family history of ASD. It was hypothesised that lower recognition accuracy for the six basic emotions would correlate with higher self-ratings of BAP traits. In contrast to expectations, higher classification accuracy (and emotional intensity ratings) for angry voices correlated significantly with higher self-ratings of rigid BAP traits. The specific anger-rigid association indicates that enhanced auditory threat detection constitutes an aspect of the BAP in the general population. Further research is recommended to examine whether this relationship is mediated by underlying personality factors like neuroticism or trait anxiety. Overall, different behavioural profiles of emotional voice processing abilities were observed in individuals with ASD (deficit—misclassifying neutral voices as being emotional), relatives with the BAP (no deficit—intact performance), and individuals from the general population with higher levels of BAP traits (advantage—enhanced sensitivity to angry voices). The neuroimaging findings of enhanced activation in the specific ASD and BAP cohorts assessed here may have implications for future research investigating the role of neurobiological compensation for emotional voice processing in their respective populations, potentially including the exploration of endophenotypes of ASD. Such studies would ideally include larger ASD and BAP (relatives) samples that enable the assessment of more homogenous, identifiable subgroups who may be susceptible to increased cognitive demands for emotional voice processing. This thesis extends research on social cognition within the voice modality in ASD and the BAP, and may have wider implications for understanding the genetic aetiology of social communication impairments in ASD.
Is the mental number line a unique model of numerical cognition?
Many theories of number propose that humans possess a ‘mental number line’ (MNL) representation. The MNL is commonly measured with a number-to-position (NP) task, and this task is often used to make inferences about the MNL representation. However, most research on MNL representations to date has made assumptions about the properties of the MNL without considering the role of ordinal relationships between numbers. The research reported in this thesis examined whether the MNL metaphor should be extended to include ordinal relationships, and to examine the nature of these relationships. A pilot study tested whether a linear MNL representation could be shifted with logarithmic training. Adults completed a series of logarithmic feedback sessions, and their NP task performance was assessed at the end of each training block. Findings revealed little to no systematic effect of logarithmic training on NP task performance, despite participants successfully learning the logarithmic function. They also revealed individual differences in the overall impact and learning of the logarithmic feedback. These findings suggested that relationships between numbers may change to allow accurate task performance, which may not be reflected in the NP task. Study 1 tested whether the linear response profile that describes NP performance is specific to number, or whether this pattern of responding is a feature of ordered lists more generally. Adults were given NP and alphabet-to-position tasks. Findings showed that numbers and letters both displayed similar linear trends. This suggested that the linear profiles attributed to number may reflect the way in which ordinal lists of symbols are learned. Studies 2a and 2b investigated whether leaning a list of novel symbols is mediated by the underlying spatial properties of the symbols (e.g., spatial complexity). Novel symbols were used to minimise the overlearned nature of Hindu-Arabic numerals. Study 2a aimed to determine the ideal novel symbol set to use in Study 2b, specifically, one which could be ordered by complexity. Participants made judgements on two novel symbol sets, and their relationship to a range of numerical stimuli. In Study 2b, a paired comparisons training method was used to teach participants the order of a list of novel symbols. Participants were allocated to either a spatial complexity or a random complexity condition, and made judgements regarding which of two symbols was numerically ‘larger’. When novel symbols were ordered by spatial complexity, learning was facilitated. These findings showed that the spatial complexity and relational information of symbols may mediate the construction of ordered representations. This suggests that a common cognitive representation underlies all ordinal lists. Overall, the findings of this research indicate that a more nuanced account of the MNL representation is required, particularly in terms of ordinal relationships between numbers. The findings also suggest that the NP task measures ordinal lists more generally. Arguably, the way in which ordered lists are learned, combined with the relative relationships between symbols, may account for performance on the NP task, and the MNL metaphor should be extended to account for these ordinal relationships.