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  • ItemOpen AccessPublished version Peer-reviewed
    Anodal tDCS over Primary Motor Cortex Provides No Advantage to Learning Motor Sequences via Observation.
    (Hindawi Publishing Corporation, 2018) Apšvalka, Dace; Ramsey, Richard; Cross, Emily S
    When learning a new motor skill, we benefit from watching others. It has been suggested that observation of others' actions can build a motor representation in the observer, and as such, physical and observational learning might share a similar neural basis. If physical and observational learning share a similar neural basis, then motor cortex stimulation during observational practice should similarly enhance learning by observation as it does through physical practice. Here, we used transcranial direct-current stimulation (tDCS) to address whether anodal stimulation to M1 during observational training facilitates skill acquisition. Participants learned keypress sequences across four consecutive days of observational practice while receiving active or sham stimulation over M1. The results demonstrated that active stimulation provided no advantage to skill learning over sham stimulation. Further, Bayesian analyses revealed evidence in favour of the null hypothesis across our dependent measures. Our findings therefore provide no support for the hypothesis that excitatory M1 stimulation can enhance observational learning in a similar manner to physical learning. More generally, the results add to a growing literature that suggests that the effects of tDCS tend to be small, inconsistent, and hard to replicate. Future tDCS research should consider these factors when designing experimental procedures.
  • ItemOpen AccessPublished version Peer-reviewed
    The missing link? Testing a schema account of unitization.
    (Springer Science and Business Media LLC, 2018-10) Tibon, Roni; Greve, Andrea; Henson, Richard; Henson, Rik [0000-0002-0712-2639]
    Unitization refers to the creation of a new unit from previously distinct items. The concept of unitization has been used to explain how novel pairings between items can be remembered without requiring recollection, by virtue of new, item-like representations that enable familiarity-based retrieval. We tested an alternative account of unitization - a schema account - which suggests that associations between items can be rapidly assimilated into a schema. We used a common operationalization of "unitization" as the difference between two unrelated words being linked by a definition, relative to two words being linked by a sentence, during an initial study phase. During the following relearning phase, a studied word was re-paired with a new word, either related or unrelated to the original associate from study. In a final test phase, memory for the relearned associations was tested. We hypothesized that, if unitized representations act like schemas, then we would observe some generalization to related words, such that memory would be better in the definition than sentence condition for related words, but not for unrelated words. Contrary to the schema hypothesis, evidence favored the null hypothesis of no difference between definition and sentence conditions for related words (Experiment 1), even when each cue was associated with multiple associates, indicating that the associations can be generalized (Experiment 2), or when the schematic information was explicitly re-activated during Relearning (Experiment 3). These results suggest that unitized associations do not generalize to accommodate new information, and therefore provide evidence against the schema account.
  • ItemOpen AccessAccepted version Peer-reviewed
    The Prospective Role of Cognitive Appraisals and Social Support in Predicting Children's Posttraumatic Stress.
    (Springer Science and Business Media LLC, 2015-11) Hitchcock, Caitlin; Ellis, Alicia A; Williamson, Paul; Nixon, Reginald DV; Hitchcock, Caitlin [0000-0002-2435-0713]
    Although both social support and cognitive appraisals are strong predictors of children's posttraumatic adjustment, understanding of the interplay between these factors is limited. We assessed whether cognitive appraisals mediated the relationship between social support and symptom development, as predicted by cognitive models of posttraumatic stress disorder (PTSD). Ninety seven children (Mean age = 12.08 years) were assessed at one month and six months following a single incident trauma. We administered self-report measures of cognitive appraisals, social support, and a diagnostic interview for PTSD. Results indicated that cognitive appraisals at one month post-trauma mediated the relationship between social support at one month post-trauma, and PTSD severity at follow-up. Differences in this relationship were observed between child-reported social support and parent-rated ability to provide support. Firm evidence was provided for the application of cognitive models of PTSD to children.
  • ItemOpen AccessPublished version Peer-reviewed
    A comparison of MEmory Specificity Training (MEST) to education and support (ES) in the treatment of recurrent depression: study protocol for a cluster randomised controlled trial.
    (Springer Science and Business Media LLC, 2014-07-22) Dalgleish, Tim; Bevan, Anna; McKinnon, Anna; Breakwell, Lauren; Mueller, Viola; Chadwick, Isobel; Schweizer, Susanne; Hitchcock, Caitlin; Watson, Peter; Raes, Filip; Jobson, Laura; Werner-Seidler, Aliza; Dalgleish, Tim [0000-0002-7304-2231]; Bevan, Anna [0000-0003-4256-2530]; Hitchcock, Caitlin [0000-0002-2435-0713]; Watson, Peter [0000-0002-9436-0693]
    BACKGROUND: Depression is a debilitating mental health problem that tends to run a chronic, recurrent course. Even when effectively treated, relapse and recurrence rates remain high. Accordingly, interventions need to focus not only on symptom reduction, but also on reducing the risk of relapse by targeting depression-related disturbances that persist into remission. We are addressing this need by investigating the efficacy, acceptability and feasibility of a MEmory Specificity Training (MEST) programme, which directly targets an enduring cognitive marker of depression - reduced autobiographical memory specificity. Promising pilot data suggest that training memory specificity ameliorates this disturbance and reduces depressive symptoms. A larger, controlled trial is now needed to examine the efficacy of MEST. This trial compares MEST to an education and support (ES) group, with an embedded mechanism study. METHODS/DESIGN: In a single blind, parallel cluster randomised controlled trial, 60 depressed individuals meeting diagnostic criteria for a current major depressive episode will be recruited from the community and clinical services. Using a block randomisation procedure, groups of 5 to 8 participants will receive five weekly sessions of MEST (n = 30) or education and support (n = 30). Participants will be assessed immediately post-treatment, and at 3- and 6-months post-treatment (MEST group only for 6-month follow-up). Depressive symptoms at 3-month follow-up will be the primary outcome. Secondary outcomes will be change in depressive status and memory specificity at post-treatment and 3-months. The 6-month follow-up of the MEST group will allow us to examine whether treatment gains are maintained. An explanatory question will examine variables mediating improvement in depression symptoms post-treatment and at 3-month follow-up. DISCUSSION: This trial will allow us to investigate the efficacy of MEST, whether treatment gains are maintained, and the mechanisms of change. Evidence will be gathered regarding whether this treatment is feasible and acceptable as a low-intensity intervention. If efficacy can be demonstrated, the results will support MEST as a treatment for depression and provide the foundation for a definitive trial. TRIAL REGISTRATION: NCT01882452 (, registered on 18 June 2013.
  • ItemOpen AccessPublished version Peer-reviewed
    Autobiographical episodic memory-based training for the treatment of mood, anxiety and stress-related disorders: A systematic review and meta-analysis.
    (Elsevier BV, 2017-03) Hitchcock, Caitlin; Werner-Seidler, Aliza; Blackwell, Simon E; Dalgleish, Tim; Hitchcock, Caitlin [0000-0002-2435-0713]; Dalgleish, Tim [0000-0002-7304-2231]
    We review evidence for training programmes that manipulate autobiographical processing in order to treat mood, anxiety, and stress-related disorders, using the GRADE criteria to judge evidence quality. We also position the current status of this research within the UK Medical Research Council's (2000, 2008) framework for the development of novel interventions. A literature search according to PRISMA guidelines identified 15 studies that compared an autobiographical episodic memory-based training (AET) programme to a control condition, in samples with a clinician-derived diagnosis. Identified AET programmes included Memory Specificity Training (Raes, Williams, & Hermans, 2009), concreteness training (Watkins, Baeyens, & Read, 2009), Competitive Memory Training (Korrelboom, van der Weele, Gjaltema, & Hoogstraten, 2009), imagery-based training of future autobiographical episodes (Blackwell & Holmes, 2010), and life review/reminiscence therapy (Arean et al., 1993). Cohen's d was calculated for between-group differences in symptom change from pre- to post-intervention and to follow-up. We also completed meta-analyses for programmes evaluated across multiple studies, and for the overall effect of AET as a treatment approach. Results demonstrated promising evidence for AET in the treatment of depression (d=0.32), however effect sizes varied substantially (from -0.18 to 1.91) across the different training protocols. Currently, research on AET for the treatment of anxiety and stress-related disorders is not yet at a stage to draw firm conclusions regarding efficacy as there were only a very small number of studies which met inclusion criteria. AET offers a potential avenue through which low-intensity treatment for affective disturbance might be offered.
  • ItemOpen AccessPublished version Peer-reviewed
    Listeners and Readers Generalize Their Experience With Word Meanings Across Modalities
    (American Psychological Association, 2018-02-01) Gilbert, RA; Davis, MH; Gaskell, MG; Rodd, JM; Gilbert, Becky [0000-0003-4574-7792]; Davis, Matt [0000-0003-2239-0778]
    Research has shown that adults' lexical-semantic representations are surprisingly malleable. For instance, the interpretation of ambiguous words (e.g., bark) is influenced by experience such that recently encountered meanings become more readily available (Rodd et al., 2016, 2013). However, the mechanism underlying this word-meaning priming effect remains unclear, and competing accounts make different predictions about the extent to which information about word meanings that is gained within one modality (e.g., speech) is transferred to the other modality (e.g., reading) to aid comprehension. In two Web-based experiments, ambiguous target words were primed with either written or spoken sentences that biased their interpretation toward a subordinate meaning, or were unprimed. About 20 min after the prime exposure, interpretation of these target words was tested by presenting them in either written or spoken form, using word association (Experiment 1, N = 78) and speeded semantic relatedness decisions (Experiment 2, N = 181). Both experiments replicated the auditory unimodal priming effect shown previously (Rodd et al., 2016, 2013) and revealed significant cross-modal priming: primed meanings were retrieved more frequently and swiftly across all primed conditions compared with the unprimed baseline. Furthermore, there were no reliable differences in priming levels between unimodal and cross-modal prime-test conditions. These results indicate that recent experience with ambiguous word meanings can bias the reader's or listener's later interpretation of these words in a modality-general way. We identify possible loci of this effect within the context of models of long-term priming and ambiguity resolution.
  • ItemOpen AccessAccepted version Peer-reviewed
    Impact of culture on autobiographical life structure in depression.
    (Wiley-Blackwell, 2018-09) Jobson, Laura; Miskon, Nazleen; Dalgleish, Tim; Hitchcock, Caitlin; Hill, Emma; Golden, Ann-Marie; Zulkefly, Nor Sheereen; Mukhtar, Firdaus; Dalgleish, Tim [0000-0002-7304-2231]; Hitchcock, Caitlin [0000-0002-2435-0713]
    OBJECTIVES: Distortions in autobiographical memory have been implicated in major depressive disorder (MDD). Those with MDD demonstrate a 'depressogenic' autobiographical life structure. Research has not examined how culture influences this process. We investigated whether Malay individuals (members of an interdependent culture) with MDD demonstrated a 'depressogenic' autobiographical life structure similar to that of British individuals (members of an independent culture) with MDD. DESIGN: A 2 (Culture; Malay, British) × 2 (Mood; depressed, control) cross-sectional design using a card sort task and self-report measures was used. METHODS: Malay individuals with MDD or no history of MDD completed the life-structure card-sorting task, which provided a novel method for investigating organizational structure of the life narrative. These data were compared to previously collected data in which British individuals with MDD or without MDD had completed the same task within the same experimental protocol. RESULTS: Pan-culturally those with MDD had greater negativity (i.e., used more negative attributes), negative redundancy (i.e., used the same negative attributes repeatedly across life chapters) and negative emodiversity (i.e., had greater variety and relative abundance of negative attributes), and reduced positive redundancy (i.e., used the same positive attributes repeatedly across chapters) in their structuring relative to controls. While the British MDD group had greater compartmentalization (i.e., the negative and positive attributes were clustered separately across different chapters) than British controls, the Malay MDD group had lower levels of compartmentalization than Malay controls. CONCLUSIONS: The findings suggest culture may shape aspects of the autobiographical life structure in MDD. PRACTITIONER POINTS: The majority of the literature investigating depression pertains to individuals from European Western cultures, despite recognition that depression ranks as one of the most debilitating diseases worldwide. This raises questions as to whether current depression models and interventions can be applied universally or whether they are limited to European Western groups. The current study found that pan-culturally those with MDD had similar structuring of their life story relative to controls. However, there were some cultural differences that need to be considered (e.g., Malay individuals provided less detailed, less elaborate and less emotionally diverse life stories and while the British MDD group had greater compartmentalization than British controls, the Malay MDD group had lower levels of compartmentalization than Malay controls). Limitations of the study included group differences in gender and mood at the time of testing. Cultural differences in the number of attributes used may have influenced findings. Only the Malay group completed the individualism-collectivism measure.
  • ItemOpen AccessPublished version Peer-reviewed
    The Impact of Affective Context on Autobiographical Recollection in Depression.
    (SAGE Publications, 2018-05) Hitchcock, Caitlin; Golden, Ann-Marie J; Werner-Seidler, Aliza; Kuyken, Willem; Dalgleish, Tim; Hitchcock, Caitlin [0000-0002-2435-0713]; Dalgleish, Tim [0000-0002-7304-2231]
    Across two studies we investigated the influence of contextual cues on autobiographical memory recall. In Study 1, participants (N = 37) with major depressive disorder, in episode or in varying degrees of remission, were administered a Negative Autobiographical Memory Task (NAMT) that required them to retrieve negatively valenced memories in response to positive cue words (a positive context). We reasoned that increased depression symptom severity would be associated with a reduced ability to override priming from this disadvantageous context. Consequently, we hypothesized that increased depressive severity would counterintuitively be associated with reduced negativity ratings for retrieved personal memories to positive cues on the NAMT. This hypothesis was supported. Study 2, using a community sample (N = 63), demonstrated that a similar reduction in memory negativity was observed in individuals with lower working memory capacity-an index of executive control. Implications for autobiographical memory and executive training paradigms for depression are discussed.
  • ItemOpen AccessPublished version Peer-reviewed
    A cluster randomized controlled platform trial comparing group MEmory specificity training (MEST) to group psychoeducation and supportive counselling (PSC) in the treatment of recurrent depression.
    (Elsevier BV, 2018-06) Werner-Seidler, Aliza; Hitchcock, Caitlin; Bevan, Anna; McKinnon, Anna; Gillard, Julia; Dahm, Theresa; Chadwick, Isobel; Panesar, Inderpal; Breakwell, Lauren; Mueller, Viola; Rodrigues, Evangeline; Rees, Catrin; Gormley, Siobhan; Schweizer, Susanne; Watson, Peter; Raes, Filip; Jobson, Laura; Dalgleish, Tim; Hitchcock, Caitlin [0000-0002-2435-0713]; Bevan, Anna [0000-0003-4256-2530]; Watson, Peter [0000-0002-9436-0693]; Dalgleish, Tim [0000-0002-7304-2231]
    Impaired ability to recall specific autobiographical memories is characteristic of depression, which when reversed, may have therapeutic benefits. This cluster-randomized controlled pilot trial investigated efficacy and aspects of acceptability, and feasibility of MEmory Specificity Training (MEST) relative to Psychoeducation and Supportive Counselling (PSC) for Major Depressive Disorder (N = 62). A key aim of this study was to determine a range of effect size estimates to inform a later phase trial. Assessments were completed at baseline, post-treatment and 3-month follow-up. The cognitive process outcome was memory specificity. The primary clinical outcome was symptoms on the Beck Depression Inventory-II at 3-month follow-up. The MEST group demonstrated greater improvement in memory specificity relative to PSC at post-intervention (d = 0.88) and follow-up (d = 0.74), relative to PSC. Both groups experienced a reduction in depressive symptoms at 3-month follow-up (d = 0.67). However, there was no support for a greater improvement in depressive symptoms at 3 months following MEST relative to PSC (d = -0.04). Although MEST generated changes on memory specificity and improved depressive symptoms, results provide no indication that MEST is superior to PSC in the resolution of self-reported depressive symptoms. Implications for later-phase definitive trials of MEST are discussed.
  • ItemOpen AccessAccepted version Peer-reviewed
    Factor structure and longitudinal measurement invariance of PHQ-9 for specialist mental health care patients with persistent major depressive disorder: Exploratory Structural Equation Modelling.
    (Elsevier BV, 2017-09) Guo, Boliang; Kaylor-Hughes, Catherine; Garland, Anne; Nixon, Neil; Sweeney, Tim; Simpson, Sandra; Dalgleish, Tim; Ramana, Rajini; Yang, Min; Morriss, Richard; Dalgleish, Tim [0000-0002-7304-2231]
    BACKGROUND: The Patient Health Questionnaire-9 (PHQ-9) is a widely used instrument for measuring levels of depression in patients in clinical practice and academic research; its factor structure has been investigated in various samples, with limited evidence of measurement equivalence/invariance (ME/I) but not in patients with more severe depression of long duration. This study aims to explore the factor structure of the PHQ-9 and the ME/I between treatment groups over time for these patients. METHODS: 187 secondary care patients with persistent major depressive disorder (PMDD) were recruited to a randomised controlled trial (RCT) with allocation to either a specialist depression team arm or a general mental health arm; their PHQ-9 score was measured at baseline, 3, 6, 9 and 12 months. Exploratory Structural Equational Modelling (ESEM) was performed to examine the factor structure for this specific patient group. ME/I between treatment arm at and across follow-up time were further explored by means of multiple-group ESEM approach using the best-fitted factor structure. RESULTS: A two-factor structure was evidenced (somatic and affective factor). This two-factor structure had strong factorial invariance between the treatment groups at and across follow up times. LIMITATIONS: Participants were largely white British in a RCT with 40% attrition potentially limiting the study's generalisability. Not all two-factor modelling criteria were met at every time-point. CONCLUSION: PHQ-9 has a two-factor structure for PMDD patients, with strong measurement invariance between treatment groups at and across follow-up time, demonstrating its validity for RCTs and prospective longitudinal studies in chronic moderate to severe depression.
  • ItemOpen AccessPublished version Peer-reviewed
    Language Problems and ADHD Symptoms: How Specific Are the Links?
    (MDPI AG, 2016-10-21) Hawkins, Erin; Gathercole, Susan; Astle, Duncan; The Calm Team; Holmes, Joni; Gathercole, Susan [0000-0001-6618-586X]; Astle, Duncan [0000-0002-7042-5392]; Holmes, Joni [0000-0002-6821-2793]
    Symptoms of inattention and hyperactivity frequently co-occur with language difficulties in both clinical and community samples. We explore the specificity and strength of these associations in a heterogeneous sample of 254 children aged 5 to 15 years identified by education and health professionals as having problems with attention, learning and/or memory. Parents/carers rated pragmatic and structural communication skills and behaviour, and children completed standardised assessments of reading, spelling, vocabulary, and phonological awareness. A single dimension of behavioural difficulties including both hyperactivity and inattention captured behaviour problems. This was strongly and negatively associated with pragmatic communication skills. There was less evidence for a relationship between behaviour and language structure: behaviour ratings were more weakly associated with the use of structural language in communication, and there were no links with direct measures of literacy. These behaviour problems and pragmatic communication difficulties co-occur in this sample, but impairments in the more formal use of language that impact on literacy and structural communication skills are tied less strongly to behavioural difficulties. One interpretation is that impairments in executive function give rise to both behavioural and social communication problems, and additional or alternative deficits in other cognitive abilities impact on the development of structural language skills.
  • ItemOpen AccessAccepted version Peer-reviewed
    Flexible, capacity-limited activity of posterior parietal cortex in perceptual as well as visual short-term memory tasks.
    (Oxford University Press (OUP), 2008-08) Mitchell, Daniel J; Cusack, Rhodri; Mitchell, Danny [0000-0001-8729-3886]
    It has recently been shown, using functional magnetic resonance imaging with a change detection paradigm, that activity in posterior parietal cortex (PPC) correlates with the limited number of objects held in visual short-term memory (VSTM). We replicate this finding and extend it to tasks that use similar stimuli, but without explicit memory requirements. As well as a perceptual task used previously (detecting an item at fixation), 2 additional tasks were designed to increase attentional demands across space (searching for a red item anywhere in the array) and across both space and time (detecting a staggered offset after prolonged viewing of the array). During the VSTM task, a capacity-limited set-size effect was seen in PPC as well as occipital and frontal regions. However, the PPC showed similar activity during 2 of the tasks not requiring VSTM. These findings cannot easily be explained by behavioral performance measures or memory demands alone, suggesting a role of the PPC in processing a limited number of discrete object representations, whether in the current perceptual scene or working memory. The differential influence of item load across perceptual tasks is consistent with task requirements affecting the form of these representations.
  • ItemOpen AccessPublished version Peer-reviewed
    Automatic analysis (aa): efficient neuroimaging workflows and parallel processing using Matlab and XML.
    (Frontiers Media SA, 2014) Cusack, Rhodri; Vicente-Grabovetsky, Alejandro; Mitchell, Daniel J; Wild, Conor J; Auer, Tibor; Linke, Annika C; Peelle, Jonathan E; Mitchell, Danny [0000-0001-8729-3886]
    Recent years have seen neuroimaging data sets becoming richer, with larger cohorts of participants, a greater variety of acquisition techniques, and increasingly complex analyses. These advances have made data analysis pipelines complicated to set up and run (increasing the risk of human error) and time consuming to execute (restricting what analyses are attempted). Here we present an open-source framework, automatic analysis (aa), to address these concerns. Human efficiency is increased by making code modular and reusable, and managing its execution with a processing engine that tracks what has been completed and what needs to be (re)done. Analysis is accelerated by optional parallel processing of independent tasks on cluster or cloud computing resources. A pipeline comprises a series of modules that each perform a specific task. The processing engine keeps track of the data, calculating a map of upstream and downstream dependencies for each module. Existing modules are available for many analysis tasks, such as SPM-based fMRI preprocessing, individual and group level statistics, voxel-based morphometry, tractography, and multi-voxel pattern analyses (MVPA). However, aa also allows for full customization, and encourages efficient management of code: new modules may be written with only a small code overhead. aa has been used by more than 50 researchers in hundreds of neuroimaging studies comprising thousands of subjects. It has been found to be robust, fast, and efficient, for simple-single subject studies up to multimodal pipelines on hundreds of subjects. It is attractive to both novice and experienced users. aa can reduce the amount of time neuroimaging laboratories spend performing analyses and reduce errors, expanding the range of scientific questions it is practical to address.
  • ItemOpen AccessAccepted version Peer-reviewed
    Training refines brain representations for multitasking.
    (Proceedings of the National Academy of Sciences, 2015-11-17) Duncan, John; Mitchell, Daniel J; Duncan, John [0000-0002-9695-2764]; Mitchell, Danny [0000-0001-8729-3886]
  • ItemOpen AccessPublished version Peer-reviewed
    Semantic and emotional content of imagined representations in human occipitotemporal cortex.
    (Springer Science and Business Media LLC, 2016-02-03) Mitchell, Daniel J; Cusack, Rhodri; Mitchell, Danny [0000-0001-8729-3886]
    Mental imagery is a critical cognitive function, clinically important, but poorly understood. When visual objects are perceived, many of their sensory, semantic and emotional properties are represented in occipitotemporal cortex. Visual imagery has been found to activate some of the same brain regions, but it was not known what properties are re-created in these regions during imagery. We therefore examined the representation during imagery for two stimuli in depth, by comparing the pattern of fMRI response to the patterns evoked by the perception of 200 diverse objects chosen to de-correlate their properties. Real-time, adaptive stimulus selection allowed efficient sampling of this broad stimulus space. Our experiments show that occipitotemporal cortex, which encoded sensory, semantic and emotional properties during perception, can robustly represent semantic and emotional properties during imagery, but that these representations depend on the object being imagined and on individual differences in style and reported vividness of imagery.
  • ItemOpen AccessAccepted version Peer-reviewed
    The temporal evolution of electromagnetic markers sensitive to the capacity limits of visual short-term memory.
    (Frontiers Media SA, 2011) Mitchell, Daniel J; Cusack, Rhodri; Mitchell, Danny [0000-0001-8729-3886]
    An electroencephalographic (EEG) marker of the limited contents of human visual short-term memory (VSTM) has previously been described. Termed contralateral delay activity, this consists of a sustained, posterior, negative potential that correlates with memory load and is greatest contralateral to the remembered hemifield. The current investigation replicates this finding and uses magnetoencephalography (MEG) to characterize its magnetic counterparts and their neural generators as they evolve throughout the memory delay. A parametric manipulation of memory load, within and beyond capacity limits, allows separation of signals that asymptote with behavioral VSTM performance from additional responses that contribute to a linear increase with set-size. Both EEG and MEG yielded bilateral signals that track the number of objects held in memory, and contralateral signals that are independent of memory load. In MEG, unlike EEG, the contralateral interaction between hemisphere and item load is much weaker, suggesting that bilateral and contralateral markers of memory load reflect distinct sources to which EEG and MEG are differentially sensitive. Nonetheless, source estimation allowed both the bilateral and the weaker contralateral capacity-limited responses to be localized, along with a load-independent contralateral signal. Sources of global and hemisphere-specific signals all localized to the posterior intraparietal sulcus during the early delay. However the bilateral load response peaked earlier and its generators shifted later in the delay. Therefore the hemifield-specific response may be more closely tied to memory maintenance while the global load response may be involved in initial processing of a limited number of attended objects, such as their individuation or consolidation into memory.
  • ItemOpen AccessAccepted version Peer-reviewed
    The neural basis of precise visual short-term memory for complex recognisable objects.
    (Elsevier BV, 2017-10-01) Veldsman, Michele; Mitchell, Daniel J; Cusack, Rhodri; Mitchell, Danny [0000-0001-8729-3886]
    Recent evidence suggests that visual short-term memory (VSTM) capacity estimated using simple objects, such as colours and oriented bars, may not generalise well to more naturalistic stimuli. More visual detail can be stored in VSTM when complex, recognisable objects are maintained compared to simple objects. It is not yet known if it is recognisability that enhances memory precision, nor whether maintenance of recognisable objects is achieved with the same network of brain regions supporting maintenance of simple objects. We used a novel stimulus generation method to parametrically warp photographic images along a continuum, allowing separate estimation of the precision of memory representations and the number of items retained. The stimulus generation method was also designed to create unrecognisable, though perceptually matched, stimuli, to investigate the impact of recognisability on VSTM. We adapted the widely-used change detection and continuous report paradigms for use with complex, photographic images. Across three functional magnetic resonance imaging (fMRI) experiments, we demonstrated greater precision for recognisable objects in VSTM compared to unrecognisable objects. This clear behavioural advantage was not the result of recruitment of additional brain regions, or of stronger mean activity within the core network. Representational similarity analysis revealed greater variability across item repetitions in the representations of recognisable, compared to unrecognisable complex objects. We therefore propose that a richer range of neural representations support VSTM for complex recognisable objects.
  • ItemOpen AccessPublished version Peer-reviewed
    Task Encoding across the Multiple Demand Cortex Is Consistent with a Frontoparietal and Cingulo-Opercular Dual Networks Distinction.
    (Society for Neuroscience, 2016-06-08) Crittenden, Ben M; Mitchell, Daniel J; Duncan, John; Mitchell, Daniel J [0000-0001-8729-3886]; Duncan, John [0000-0002-9695-2764]
    UNLABELLED: Multiple-demand (MD) regions of the human brain show coactivation during many different kinds of task performance. Previous work based on resting-state functional magnetic resonance imaging (fMRI) has shown that MD regions may be divided into two closely coupled subnetworks centered around the lateral frontoparietal (FP) and cingulo-opercular cortex. Here, we used on-task fMRI to test whether this division is apparent during the performance of an executive task. Furthermore, we investigated whether there is a difference in the encoding of task between the two subnetworks. Using connectivity methods, we found that activity across the entire MD cortex is correlated during task performance. Meanwhile, however, there was significantly stronger connectivity within each of the subnetworks than between them. Using multivoxel pattern analysis, we also found that, although we were able to decode task-relevant information from all regions of the MD cortex, classification accuracy scores were significantly higher in the FP subnetwork. These results suggest a nested picture with MD regions as a whole showing coactivation and broad rule representation, but with significant functional distinctions between component subnetworks. SIGNIFICANCE STATEMENT: Multiple-demand (MD) regions of frontal and parietal cortex appear essential for the orchestration of goal-directed behavior and problem solving. Understanding the relative specialization of regions within the MD cortex is crucial to understanding how we can coordinate and execute complex action plans. By examining functional connectivity during task performance, we extend previous findings suggesting that the MD cortex can be divided into two subnetworks centered around the frontoparietal (FP) and cingulo-opercular (CO) cortex. Furthermore, using multivoxel pattern analysis, we show that, compared with the CO subnetwork, the FP subnetwork manifests more differentiated coding of specific task events.
  • ItemOpen AccessPublished version Peer-reviewed
    A Putative Multiple-Demand System in the Macaque Brain.
    (Society for Neuroscience, 2016-08-17) Mitchell, Daniel J; Bell, Andrew H; Buckley, Mark J; Mitchell, Anna S; Sallet, Jerome; Duncan, John; Mitchell, Daniel J [0000-0001-8729-3886]; Bell, Andrew H [0000-0001-8420-4622]; Buckley, Mark J [0000-0001-7455-8486]; Mitchell, Anna S [0000-0001-8996-1067]; Duncan, John [0000-0002-9695-2764]
    UNLABELLED: In humans, cognitively demanding tasks of many types recruit common frontoparietal brain areas. Pervasive activation of this "multiple-demand" (MD) network suggests a core function in supporting goal-oriented behavior. A similar network might therefore be predicted in nonhuman primates that readily perform similar tasks after training. However, an MD network in nonhuman primates has not been described. Single-cell recordings from macaque frontal and parietal cortex show some similar properties to human MD fMRI responses (e.g., adaptive coding of task-relevant information). Invasive recordings, however, come from limited prespecified locations, so they do not delineate a macaque homolog of the MD system and their positioning could benefit from knowledge of where MD foci lie. Challenges of scanning behaving animals mean that few macaque fMRI studies specifically contrast levels of cognitive demand, so we sought to identify a macaque counterpart to the human MD system using fMRI connectivity in 35 rhesus macaques. Putative macaque MD regions, mapped from frontoparietal MD regions defined in humans, were found to be functionally connected under anesthesia. To further refine these regions, an iterative process was used to maximize their connectivity cross-validated across animals. Finally, whole-brain connectivity analyses identified voxels that were robustly connected to MD regions, revealing seven clusters across frontoparietal and insular cortex comparable to human MD regions and one unexpected cluster in the lateral fissure. The proposed macaque MD regions can be used to guide future electrophysiological investigation of MD neural coding and in task-based fMRI to test predictions of similar functional properties to human MD cortex. SIGNIFICANCE STATEMENT: In humans, a frontoparietal "multiple-demand" (MD) brain network is recruited during a wide range of cognitively demanding tasks. Because this suggests a fundamental function, one might expect a similar network to exist in nonhuman primates, but this remains controversial. Here, we sought to identify a macaque counterpart to the human MD system using fMRI connectivity. Putative macaque MD regions were functionally connected under anesthesia and were further refined by iterative optimization. The result is a network including lateral frontal, dorsomedial frontal, and insular and inferior parietal regions closely similar to the human counterpart. The proposed macaque MD regions can be useful in guiding electrophysiological recordings or in task-based fMRI to test predictions of similar functional properties to human MD cortex.
  • ItemOpen AccessAccepted version Peer-reviewed
    Neural Prediction Errors Distinguish Perception and Misperception of Speech
    (Society for Neuroscience, 2018-07-04) Blank, Helen; Spangenberg, Marlene; Davis, Matthew H; Blank, Helen [0000-0002-5824-0811]; Spangenberg, Marlene [0000-0002-2549-3476]; Davis, Matthew H [0000-0003-2239-0778]
    Humans use prior expectations to improve perception, especially of sensory signals that are degraded or ambiguous. However, if sensory input deviates from prior expectations, correct perception depends on adjusting or rejecting prior expectations. Failure to adjust or reject the prior leads to perceptual illusions especially if there is partial overlap (hence partial mismatch) between expectations and input. With speech, “Slips of the ear” occur when expectations lead to misperception. For instance, a entomologist, might be more susceptible to hear "The ants are my friends" for "The answer, my friend" (in the Bob Dylan song "Blowing in the Wind"). Here, we contrast two mechanisms by which prior expectations may lead to misperception of degraded speech. Firstly, clear representations of the common sounds in the prior and input (i.e., expected sounds) may lead to incorrect confirmation of the prior. Secondly, insufficient representations of sounds that deviate between prior and input (i.e., prediction errors) could lead to deception. We used cross-modal predictions from written words that partially match degraded speech to compare neural responses when male and female human listeners were deceived into accepting the prior or correctly reject it. Combined behavioural and multivariate representational similarity analysis of functional magnetic resonance imaging data shows that veridical perception of degraded speech is signalled by representations of prediction error in the left superior temporal sulcus. Instead of using top-down processes to support perception of expected sensory input, our findings suggest that the strength of neural prediction error representations distinguishes correct perception and misperception.