Melbourne School of Psychological Sciences - Research Publications

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    Global semantic similarity effects in recognition memory: Insights from BEAGLE representations and the diffusion decision model
    Osth, AF ; Shabahang, KD ; Mewhort, DJK ; Heathcote, A (ACADEMIC PRESS INC ELSEVIER SCIENCE, 2020-04)
    Recognition memory models posit that false alarm rates increase as the global similarity between the probe cue and the contents of memory is increased. Global similarity predictions have been commonly tested using category length designs where it has been found that false alarm rates increase as the number of studied items from a common category is increased. In this work, we explored global similarity predictions within unstructured lists of words using representations from the BEAGLE model (Jones & Mewhort, 2007). BEAGLE differs from traditional semantic space models in that it contains two types of representations: item vectors, which encode unordered co-occurrence, and order vectors, in which words are similar to the extent to which they are share neighboring words in the same relative positions. Global similarity among item and order vectors was regressed onto drift rates in the diffusion decision model (DDM: Ratcliff, 1978), which unifies both response times and accuracy. We implemented this model in a hierarchical Bayesian framework across seven datasets with lists composed of unrelated words. Results indicated clear deficits due to global similarity among item vectors, but only a minimal impact of global similarity among the order vectors. We also found evidence for a linear relationship between global similarity and drift rate and did not find any evidence that global similarity differentially affected performance in speed vs. accuracy emphasis conditions. In addition, we found that global semantic similarity could only partially account for the word frequency effect, suggesting that other factors besides semantic similarity may be responsible.
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    Beyond Pattern Completion with Short-Term Plasticity
    Shabahang, KD ; Yim, H ; Dennis, SJ (Cognitive Science Society, 2020-01-01)
    In a Linear Associative Net (LAN), all input settles to a single pattern, therefore Anderson, Silverstein, Ritz, and Jones (1977) introduced saturation to force the system to reach other steady-states in the Brain-State-in-a-Box (BSB). Unfortunately, the BSB is limited in its ability to generalize because its responses are restricted to previously stored patterns. We present simulations showing how a Dynamic-Eigen-Net (DEN), a LAN with Short-Term Plasticity (STP), overcomes the single-response limitation. Critically, a DEN also accommodates novel patterns by aligning them with encoded structure. We train a two-slot DEN on a text corpus, and provide an account of lexical decision and judgement-of-grammaticality (JOG) tasks showing how grammatical bi-grams yield stronger responses relative to ungrammatical bi-grams. Finally, we present a simulation showing how a DEN is sensitive to syntactic violations introduced in novel bi-grams. We propose DENs as associative nets with greater promise for generalization than the classic alternatives.
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    Early life stress alters pituitary growth during adolescence-A longitudinal study
    Ganella, DE ; Allen, NB ; Simmons, JG ; Schwartz, O ; Kim, JH ; Sheeber, L ; Whittle, S (PERGAMON-ELSEVIER SCIENCE LTD, 2015-03)
    The pituitary gland is integral in mediating the stress-response via its role in hypothalamic-pituitary-adrenal (HPA) axis function. Pituitary gland volume (PGV) is altered in stress-related psychopathology, and one study to date has shown stress to be associated with age-related PGV change during adolescence. The current study investigated the effects of a number of different types of early life (i.e., childhood and adolescent) stress (including childhood maltreatment, stressful life events, and maternal affective behavior) on PGV development from mid- to late adolescence using a longitudinal design. The influence of PGV development on depressive and anxiety symptoms was also investigated. Ninety one (49 male) adolescents took part in mother-child dyadic interaction tasks when they were approximately 12 years old, reported on childhood maltreatment and stressful life events when they were approximately 15 years old, and underwent two waves of structural magnetic resonance imaging (MRI) scans, when they were approximately 16 and 19 years old. Results revealed that childhood maltreatment predicted accelerated PGV development in females, and maternal dysphoric behavior predicted accelerated PGV development in the whole sample. PGV development was not associated with depressive or anxiety symptoms. These results suggest an effect of early life stress on altered HPA axis function across mid- to late adolescence. Further research is required to assess functional implications and whether these changes might be associated with risk for subsequent psychopathology.
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    Nasal Resistance Is Elevated in People with Tetraplegia and Is Reduced by Topical Sympathomimetic Administration
    Gainche, L ; Berlowitz, DJ ; LeGuen, M ; Ruehland, WR ; O'Donoghue, FJ ; Trinder, J ; Graco, M ; Schembri, R ; Eckert, DJ ; Rochford, PD ; Jordan, AS (AMER ACAD SLEEP MEDICINE, 2016)
    STUDY OBJECTIVES: Obstructive sleep apnea (OSA) is common in individuals with tetraplegia and associated with adverse health outcomes. The causes of the high prevalence of OSA in this population are unknown, but it is important to understand as standard treatments are poorly tolerated in tetraplegia. Nasal congestion is common in tetraplegia, possibly because of unopposed parasympathetic activity. Further, nasal obstruction can induce OSA in healthy individuals. We therefore aimed to compare nasal resistance before and after topical administration of a sympathomimetic between 10 individuals with tetraplegia (T) and 9 able-bodied (AB) controls matched for OSA severity, gender, and age. METHODS: Nasal, pharyngeal, and total upper airway resistance were calculated before and every 2 minutes following delivery of ≈0.05 mL of 0.5% atomized phenylephrine to the nostrils and pharyngeal airway. The surface tension of the upper airway lining liquid was also assessed. RESULTS: At baseline, individuals with tetraplegia had elevated nasal resistance (T = 7.0 ± 1.9, AB = 3.0 ± 0.6 cm H2O/L/s), that rapidly fell after phenylephrine (T = 2.3 ± 0.4, p = 0.03 at 2 min) whereas the able-bodied did not change (AB = 2.5 ± 0.5 cm H2O/L/s, p = 0.06 at 2 min). Pharyngeal resistance was non-significantly higher in individuals with tetraplegia than controls at baseline (T = 2.6 ± 0.9, AB = 1.2 ± 0.4 cm H2O/L/s) and was not altered by phenylephrine in either group. The surface tension of the upper airway lining liquid did not differ between groups (T = 64.3 ± 1.0, AB = 62.7 ± 0.6 mN/m). CONCLUSIONS: These data suggest that the unopposed parasympathetic activity in tetraplegia increases nasal resistance, potentially contributing to the high occurrence of OSA in this population.
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    Motion Extrapolation for Eye Movements Predicts Perceived Motion-Induced Position Shifts
    van Heusden, E ; Rolfs, M ; Cavanagh, P ; Hogendoorn, H (SOC NEUROSCIENCE, 2018-09-19)
    Transmission delays in the nervous system pose challenges for the accurate localization of moving objects as the brain must rely on outdated information to determine their position in space. Acting effectively in the present requires that the brain compensates not only for the time lost in the transmission and processing of sensory information, but also for the expected time that will be spent preparing and executing motor programs. Failure to account for these delays will result in the mislocalization and mistargeting of moving objects. In the visuomotor system, where sensory and motor processes are tightly coupled, this predicts that the perceived position of an object should be related to the latency of saccadic eye movements aimed at it. Here we use the flash-grab effect, a mislocalization of briefly flashed stimuli in the direction of a reversing moving background, to induce shifts of perceived visual position in human observers (male and female). We find a linear relationship between saccade latency and perceived position shift, challenging the classic dissociation between "vision for action" and "vision for perception" for tasks of this kind and showing that oculomotor position representations are either shared with or tightly coupled to perceptual position representations. Altogether, we show that the visual system uses both the spatial and temporal characteristics of an upcoming saccade to localize visual objects for both action and perception.SIGNIFICANCE STATEMENT Accurately localizing moving objects is a computational challenge for the brain due to the inevitable delays that result from neural transmission. To solve this, the brain might implement motion extrapolation, predicting where an object ought to be at the present moment. Here, we use the flash-grab effect to induce perceptual position shifts and show that the latency of imminent saccades predicts the perceived position of the objects they target. This counterintuitive finding is important because it not only shows that motion extrapolation mechanisms indeed work to reduce the behavioral impact of neural transmission delays in the human brain, but also that these mechanisms are closely matched in the perceptual and oculomotor systems.
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    Modelling associations between neurocognition and functional course in young people with emerging mental disorders: a longitudinal cohort study
    Crouse, JJ ; Chitty, KM ; Iorfino, F ; Carpenter, JS ; White, D ; Nichles, A ; Zmicerevska, N ; Guastella, AJ ; Scott, EM ; Lee, RSC ; Naismith, SL ; Scott, J ; Hermens, DF ; Hickie, IB (SPRINGERNATURE, 2020-01-21)
    Neurocognitive impairment is commonly associated with functional disability in established depressive, bipolar and psychotic disorders. However, little is known about the longer-term functional implications of these impairments in early phase transdiagnostic cohorts. We aimed to examine associations between neurocognition and functioning at baseline and over time. We used mixed effects models to investigate associations between neurocognitive test scores and longitudinal social and occupational functioning ("Social and Occupational Functioning Assessment Scale") at 1-7 timepoints over five-years in 767 individuals accessing youth mental health services. Analyses were adjusted for age, sex, premorbid IQ, and symptom severity. Lower baseline functioning was associated with male sex (coefficient -3.78, 95% CI -5.22 to -2.34 p < 0.001), poorer verbal memory (coefficient 0.90, 95% CI 0.42 to 1.38, p < 0.001), more severe depressive (coefficient -0.28, 95% CI -0.41 to -0.15, p < 0.001), negative (coefficient -0.49, 95% CI -0.74 to -0.25, p < 0.001), and positive symptoms (coefficient -0.25, 95% CI -0.41 to -0.09, p = 0.002) and lower premorbid IQ (coefficient 0.13, 95% CI 0.07 to 0.19, p < 0.001). The rate of change in functioning over time varied among patients depending on their sex (male; coefficient 0.73, 95% CI 0.49 to 0.98, p < 0.001) and baseline level of cognitive flexibility (coefficient 0.14, 95% CI 0.06 to 0.22, p < 0.001), such that patients with the lowest scores had the least improvement in functioning. Impaired cognitive flexibility is common and may represent a meaningful and transdiagnostic target for cognitive remediation in youth mental health settings. Future studies should pilot cognitive remediation targeting cognitive flexibility while monitoring changes in functioning.
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    Clinical, neurocognitive and demographic factors associated with functional impairment in the Australian Brain and Mind Youth Cohort Study (2008-2016)
    Lee, RSC ; Hermens, DF ; Naismith, SL ; Kaur, M ; Guastella, AJ ; Glozier, N ; Scott, J ; Scott, EM ; Hickie, IB (BMJ PUBLISHING GROUP, 2018-12)
    OBJECTIVES: We sought to determine the unique and shared contributions of clinical, neurocognitive and demographic factors to functional impairment in a large, transdiagnostic, clinical cohort of adolescents and young adults. DESIGN: Cross-sectional baseline data from a prospective, cohort study. SETTING: Help-seeking youth referred from outpatient services were recruited to the Brain and Mind Youth Cohort (2008-2016) in Sydney, Australia. PARTICIPANTS: In total, 1003 outpatients were recruited, aged between 12 and 36 years (mean= 20.4 years, 54% female), with baseline diagnoses of affective, psychotic, developmental or behavioural disorders. INTERVENTIONS: Treatment as usual. PRIMARY OUTCOME MEASURES: Social and occupational functioning was used to index level of functional impairment. Structural equation modelling was used to examine associations between neurocognition, core clinical symptoms and alcohol and substance use, and clinician-rated and researcher-rated functional impairment. Moderator analyses were conducted to determine the potential influence of demographic and clinical factors (eg, medication exposure). RESULTS: Independent of diagnosis, we found that neurocognitive impairments, and depressive, anxiety and negative symptoms, were significantly associated with functioning. The association of neurocognition with social and occupational functioning remained significant even when constraining for age (15-25-year-olds only) or diagnosis (affective disorders only) in the final model. CONCLUSIONS: This study demonstrated that, in a clinically representative sample of youth, the key determinants of functioning may not be disorder specific. Further, evidence of neurocognitive dysfunction suggests that interventions that target cognition and functioning should not necessarily be reserved just for older adults with established illness.
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    The underlying neurobiology of key functional domains in young people with mood and anxiety disorders: a systematic review
    Iorfino, F ; Hickie, IB ; Lee, RSC ; Lagopoulos, J ; Hermens, DF (BMC, 2016-05-23)
    BACKGROUND: Mood and anxiety disorders are leading causes of disability and mortality, due largely to their onset during adolescence and young adulthood and broader impact on functioning. Key factors that are associated with disability and these disorders in young people are social and economic participation (e.g. education, employment), physical health, suicide and self-harm behaviours, and alcohol and substance use. A better understanding of the objective markers (i.e. neurobiological parameters) associated with these factors is important for the development of effective early interventions that reduce the impact of disability and illness persistence. METHODS: We systematically reviewed the literature for neurobiological parameters (i.e. neuropsychology, neuroimaging, sleep-wake and circadian biology, neurophysiology and metabolic measures) associated with functional domains in young people (12 to 30 years) with mood and/or anxiety disorders. RESULTS: Of the one hundred and thirty-four studies selected, 7.6 % investigated social and economic participation, 2.1 % physical health, 15.3 % suicide and self-harm behaviours, 6.9 % alcohol and substance use, whereas the majority (68.1 %) focussed on clinical syndrome. CONCLUSIONS: Despite the predominance of studies that solely examine the clinical syndrome of young people the literature also provides evidence of distinct associations among objective measures (indexing various aspects of brain circuitry) and other functional domains. We suggest that a shift in focus towards characterising the mechanisms that underlie and/or mediate multiple functional domains will optimise personalised interventions and improve illness trajectories.
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    Neuropsychological and functional outcomes in recent-onset major depression, bipolar disorder and schizophrenia-spectrum disorders: a longitudinal cohort study
    Lee, RSC ; Hermens, DF ; Naismith, SL ; Lagopoulos, J ; Jones, A ; Scott, J ; Chitty, KM ; White, D ; Robillard, R ; Scott, EM ; Hickie, IB (NATURE PUBLISHING GROUP, 2015-04-28)
    Functional disability is the lead contributor to burden of mental illness. Cognitive deficits frequently limit functional recovery, although whether changes in cognition and disability are longitudinally associated in recent-onset individuals remains unclear. Using a prospective, cohort design, 311 patients were recruited and assessed at baseline. One hundred and sixty-seven patients met eligibility criteria (M=21.5 years old, s.d.=4.8) and returned for follow-up (M=20.6 months later, s.d.=7.8). Two-hundred and thirty participants were included in the final analysis, comprising clinically stable patients with major depression (n=71), bipolar disorder (BD; n=61), schizophrenia-spectrum disorders (n=35) and 63 healthy controls. Neuropsychological functioning and self-rated functional disability were examined using mixed-design, repeated-measures analysis, across diagnoses and cognitive clusters, covarying for relevant confounds. Clinical, neuropsychological and functional changes did not differ between diagnoses (all P>0.05). Three reliable neuropsychological subgroups emerged through cluster analysis, characterized by psychomotor slowing, improved sustained attention, and improved verbal memory. Controlling for diagnosis and changes in residual symptoms, clusters with improved neuropsychological functioning observed greater reductions in functional disability than the psychomotor slowing cluster, which instead demonstrated a worsening in disability (P<0.01). Improved sustained attention was independently associated with greater likelihood of follow-up employment (P<0.01). Diagnosis of BD uniquely predicted both follow-up employment and independent living. Neuropsychological course appears to be independently predictive of subjective and objective functional outcomes. Importantly, cognitive phenotypes may reflect distinct pathophysiologies shared across major psychiatric conditions, and be ideal targets for personalized early intervention.
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    Neuropsychological profile according to the clinical stage of young persons presenting for mental health care.
    Hermens, DF ; Naismith, SL ; Lagopoulos, J ; Lee, RSC ; Guastella, AJ ; Scott, EM ; Hickie, IB (Springer Science and Business Media LLC, 2013)
    BACKGROUND: Clinical staging of mental disorders proposes that individuals can be assessed at various sub-syndromal and later developed phases of illness. As an adjunctive rating, it may complement traditional diagnostic silo-based approaches. In this study, we sought to determine the relationships between clinical stage and neuropsychological profile in young persons presenting to youth-focused mental health services. METHODS: Neuropsychological testing of 194 help-seeking young people (mean age 22.6 years, 52% female) and 50 healthy controls. Clinical staging rated 94 persons as having an 'attenuated syndrome' (stage 1b) and 100 with a discrete or persistent disorder (stage 2/3). RESULTS: The discrete disorder group (stage 2/3) showed the most impaired neuropsychological profile, with the earlier stage (1b) group showing an intermediate profile, compared to controls. Greatest impairments were seen in verbal memory and executive functioning. To address potential confounds created by 'diagnosis', profiles for those with a mood syndrome or disorder but not psychosis were also examined and the neuropsychological impairments for the stage 2/3 group remained. CONCLUSIONS: The degree of neuropsychological impairment in young persons with mental disorders appears to discriminate those with attenuated syndromes from those with a discrete disorder, independent of diagnostic status and current symptoms. Our findings suggest that neuropsychological assessment is a critical aspect of clinical evaluation of young patients at the early stages of a major psychiatric illness.