An exploration of representation and maintenance in visuo-spatial working memory for simultaneously and sequentially presented information

Multiple lines of evidence have indicated that the system responsible for the short term representation and maintenance of visually presented, non-verbal information - Visuo-Spatial Working Memory - is not unitary. One of the most influential dissociations observed is that between performance on a task requiring memory for patterns within a matrix (visual patterns task) and memory for sequences of locations (Corsi blocks task). A growing body of research suggests the difference of importance between these two tasks is manner of presentation - whether information is simultaneously or sequentially presented. It has been proposed that visuo-spatial working memory can be fractionated into two components - a visual and a spatial subsystem, which are considered to support memory for visual matrix patterns and sequences of locations respectively. The extent to which these components are thought to interact varies between models, and recent questions have been raised over differential use of executive resources. The current thesis investigated whether the same visual information was represented by separate subsystems on the basis of the format in which it was presented. Experiments 1-3 used interference methodology, employed during the retention interval of a recognition task which required the locations of three dots to be remembered. Presentation of primary task stimuli was of either a simultaneous or a sequential format and interference stimuli were designed to target possible visual or spatial subsystems. Passive viewing of simultaneous or sequential interference stimuli was not found to produce a reliable disruption to memory performance. A typical spatial interference task and a novel visual task requiring detection of images were found to disrupt memory for both simultaneously and sequentially presented information. There was, however, no evidence of selective interference. Experiment 4 employed memory for the appearance of a series of items to provide further evidence that the novel visual paradigm affects visuo-spatial memory rather than an imagery strategy. Experiments 5-8 investigated memory for static arrays and sequences consisting of a greater number of locations. It was found that emphasis on retaining order in sequence recall did not exacerbate differences in performance level between memory for arrays and sequences. An individual differences approach including seven other measures revealed recall of simultaneously presented information and recall of sequentially presented information were best predicted by each other, and then by different predictors. The results from the above studies suggest common resources support memory for static arrays and sequences of locations as well as indicating use of different resources. That memory for simultaneously and sequentially presented information was equally disrupted by a primarily visual and a primarily spatial interference task suggests maintenance of information may employ overlapping processes regardless of presentation format. Models of visuo-spatial working memory which advocate sequences of locations are maintained in memory by processes operating separately from those maintaining static arrays of information are hard to reconcile with the current data; it is suggested that a model which proposes separable yet interdependent subsystems provides the best account of both the results obtained and the literature reviewed

Impairment in Theory of Mind in Parkinson’s Disease Is Explained by Deficits in Inhibition

Objective. Several studies have reported that people with Parkinson's disease (PD) perform poorly on tests of 'Theory of Mind' (ToM), suggesting impairment in the ability to understand and infer other people's thoughts and feelings. However, few studies have sought to separate the processes involved in social reasoning from those involved in managing the inhibitory demands on these tests. In this study, we investigated the contribution of inhibition to ToM performance in PD. Methods. 18 PD patients and 22 age-matched healthy controls performed a ToM test that separates the ability to infer someone else's perspective from the ability to inhibit one's own. Participants also completed a battery of standard measures of social and executive functioning, including measures of inhibition. Results. The PD patients performed worse on the ToM test only when the inhibitory demands were high. When the level of inhibition required was reduced, there were no significant group differences. Furthermore, executive impairments in PD patients were limited to measures of inhibition, with disadvantages associated with poorer ToM performance in this group. Conclusions. This study provides convincing evidence that the apparent impairment observed on ToM tests in PD is explained by deficits in inhibition

Suffix interference and processing speed effects in young and older adults' visual feature binding

There is debate regarding whether or not working memory for bound visual objects is more age-sensitive than that for individual visual features. To investigate this potential ‘age-related binding deficit’, we administered a visual recognition task to young and healthy older adults. In experiment 1, coloured shapes were sequentially presented, either with or without a subsequent, to-be-ignored, coloured shape (suffix). Performance was generally better with the individual shape memory test relative to binding (coloured shape test), although a greater binding deficit was found in older than young adults, regardless of whether or not a suffix had been presented. Additional analyses identified that the deficit was only observable within the lure (test probe absent) trials, suggesting that it is more likely to be observed in circumstances that encourage overwriting of bound objects at test. A second experiment will also be presented, which was aimed at assessing the potential role of processing speed in visual binding. Both age groups performed the task at relatively slow and fast encoding speeds, tailored to each group, allowing us to explore the circumstances that may lead to binding deficits and/or serial position curves in both young and older adults

ECAS A-B-C:alternate forms of the Edinburgh Cognitive and Behavioural ALS Screen

BACKGROUND: The Edinburgh Cognitive and Behavioural ALS Screen (ECAS) is a short assessment by which neuropsychological symptoms can be detected and quantified in people with ALS. To avoid potential practice effects with repeated administration, here we present alternative versions of the ECAS suitable for measuring change over time.  OBJECTIVE: To develop two alternate versions of the ECAS: ECAS-B and ECAS-C.  METHOD: One hundred and forty-nine healthy adult participants were recruited. Thirty participants completed a pilot study in developing the alternate versions. Two groups of 40 participants were administered the ECAS-B or ECAS-C and compared to published data of the original ECAS (ECAS-A) to determine equivalence. An additional 39 participants were administered the ECAS consecutively, either repeating the original version (ECAS-A-A-A) serially or the different versions (ECAS-A-B-C) to determine potential practice effects. Recordings of assessments were scored by a second researcher to determine inter-rater reliability.  RESULTS: No significant differences were found between versions (A, B, C) of the composite performance measures of ALS Specific, ALS Non-Specific, and ECAS Total scores. Repeated serial administration of ECAS-A (A-A-A) produced some practice effects for composite scores, whereas no such effects were found when alternate versions were administered serially (A-B-C). Exceptionally high intra-class correlations were found for all three versions of the ECAS suggesting a high degree of rater agreement.  CONCLUSION: The newly developed alternate forms of the ECAS are both highly equitable to the original ECAS-A and enable avoidance of practice effects, thus supporting their use in measuring cognition and behaviour over time

HIV pre-exposure prophylaxis and early antiretroviral treatment among female sex workers in South Africa: Results from a prospective observational demonstration project.

BACKGROUND: Operational research is required to design delivery of pre-exposure prophylaxis (PrEP) and early antiretroviral treatment (ART). This paper presents the primary analysis of programmatic data, as well as demographic, behavioural, and clinical data, from the TAPS Demonstration Project, which offered both interventions to female sex workers (FSWs) at 2 urban clinic sites in South Africa. METHODS AND FINDINGS: The TAPS study was conducted between 30 March 2015 and 30 June 2017, with the enrolment period ending on 31 July 2016. TAPS was a prospective observational cohort study with 2 groups receiving interventions delivered in existing service settings: (1) PrEP as part of combination prevention for HIV-negative FSWs and (2) early ART for HIV-positive FSWs. The main outcome was programme retention at 12 months of follow-up. Of the 947 FSWs initially seen in clinic, 692 were HIV tested. HIV prevalence was 49%. Among those returning to clinic after HIV testing and clinical screening, 93% of the women who were HIV-negative were confirmed as clinically eligible for PrEP (n = 224/241), and 41% (n = 110/270) of the women who were HIV-positive had CD4 counts within National Department of Health ART initiation guidelines at assessment. Of the remaining women who were HIV-positive, 93% were eligible for early ART (n = 148/160). From those eligible, 98% (n = 219/224) and 94% (n = 139/148) took up PrEP and early ART, respectively. At baseline, a substantial fraction of women had a steady partner, worked in brothels, and were born in Zimbabwe. Of those enrolled, 22% on PrEP (n = 49/219) and 60% on early ART (n = 83/139) were seen at 12 months; we observed high rates of loss to follow-up: 71% (n = 156/219) and 30% (n = 42/139) in the PrEP and early ART groups, respectively. Little change over time was reported in consistent condom use or the number of sexual partners in the last 7 days, with high levels of consistent condom use with clients and low use with steady partners in both study groups. There were no seroconversions on PrEP and 7 virological failures on early ART among women remaining in the study. Reported adherence to PrEP varied over time between 70% and 85%, whereas over 90% of participants reported taking pills daily while on early ART. Data on provider-side costs were also collected and analysed. The total cost of service delivery was approximately US$126 for PrEP and US$406 for early ART per person-year. The main limitations of this study include the lack of a control group, which was not included due to ethical considerations; clinical study requirements imposed when PrEP was not approved through the regulatory system, which could have affected uptake; and the timing of the implementation of a national sex worker HIV programme, which could have also affected uptake and retention. CONCLUSIONS: PrEP and early ART services can be implemented within FSW routine services in high prevalence, urban settings. We observed good uptake for both PrEP and early ART; however, retention rates for PrEP were low. Retention rates for early ART were similar to retention rates for the current standard of care. While the cost of the interventions was higher than previously published, there is potential for cost reduction at scale. The TAPS Demonstration Project results provided the basis for the first government PrEP and early ART guidelines and the rollout of the national sex worker HIV programme in South Africa

Sensitivity and specificity of the ECAS in Parkinson’s disease and Progressive Supranuclear Palsy

Disentangling Parkinson’s disease (PD) and progressive supranuclear palsy (PSP) may be a diagnostic challenge. Cognitive signs may be useful, but existing screens are often insufficiently sensitive or unsuitable for assessing people with motor disorders. We investigated whether the newly developed ECAS, designed to be used with people with even severe motor disability, was sensitive to the cognitive impairment seen in PD and PSP and able to distinguish between these two disorders. Thirty patients with PD, 11 patients with PSP, and 40 healthy controls were assessed using the ECAS, as well as an extensive neuropsychological assessment. The ECAS detected cognitive impairment in 30% of the PD patients, all of whom fulfilled the diagnostic criteria for mild cognitive impairment. The ECAS was also able to detect cognitive impairment in PSP patients, with 81.8% of patients performing in the impaired range. The ECAS total score distinguished between the patients with PSP and healthy controls with high sensitivity (91.0) and specificity (86.8). Importantly, the ECAS was also able to distinguish between the two syndromes, with the measures of verbal fluency offering high sensitivity (82.0) and specificity (80.0). In sum, the ECAS is a quick, simple, and inexpensive test that can be used to support the differential diagnosis of PSP

Visual feature binding in younger and older adults: Encoding and suffix interference effects

Three experiments investigated younger (18-25) and older (70-88) adults’ temporary memory for colour-shape combinations (binding). We focused upon estimating the magnitude of the binding cost for each age group across encoding time (Experiment 1; 900/1500ms), presentation format (Experiment 2; simultaneous/sequential), and interference (Experiment 3; control/suffix) conditions. In Experiment 1, encoding time did not differentially influence binding in the two age groups. In Experiment 2, younger adults exhibited poorer binding performance with sequential relative to simultaneous presentation, and serial position analyses highlighted a particular age-related difficulty remembering the middle item of a series (for all memory conditions). Experiments 1 to 3 demonstrated small to medium binding effect sizes in older adults across all encoding conditions, with binding less accurate than shape memory. However, younger adults also displayed negative effects of binding (small to large) in two of the experiments. Even when older adults exhibited a greater suffix interference effect in Experiment 3, this was for all memory types, not just binding. We therefore conclude that there is no consistent evidence for a visual binding deficit in healthy older adults. This relative preservation contrasts with the specific and substantial deficits in visual feature binding found in several recent studies of Alzheimer’s disease