Stephen Rhodes

Ageing and feature binding in visual working memory: The role of presentation time

A large body of research has clearly demonstrated that healthy ageing is accompanied by an associative memory deficit. Older adults exhibit disproportionately poor performance on memory tasks requiring the retention of associations between items (e.g., pairs of unrelated words). In contrast to this robust deficit, older adults’ ability to form and temporarily hold bound representations of an objects surface features, such as colour and shape, appears to be relatively well preserved. However, the findings of one set of experiments suggest that older adults may struggle to form temporary bound representations in visual working memory when given more time to study objects. However, these findings were based on between-participant comparisons across experimental paradigms. The present study directly assesses the role of presentation time in the ability of younger and older adults to bind shape and colour in visual working memory using a within-participant design. We report new evidence that giving older adults longer to study memory objects does not differentially affect their immediate memory for feature combinations relative to individual features. This is in line with a growing body of research suggesting that there is no age-related impairment in immediate memory for colour-shape binding.

Loneliness in Psychosis: A Meta-analytical Review

Loneliness may be related to psychotic symptoms but a comprehensive synthesis of the literature in this area is lacking. The primary aim of the current study is to provide a systematic review and meta-analysis of the association between loneliness and psychotic symptoms in people with psychosis. A search of electronic databases was conducted (PsychINFO, MEDLINE, EMBASE, and Web of Science). A random effects meta-analysis was used to compute a pooled estimate of the correlation between loneliness and psychotic symptoms. Study and outcome quality were assessed using adapted versions of the Agency for Healthcare Research and Quality (AHRQ) tool and GRADE approach, respectively. Thirteen studies were included, providing data from 15 647 participants. A moderate association between psychosis and loneliness was observed (k = 13, N = 15 647, r = .32, 95% CI 0.20, 0.44; I2 = 97.56%; moderate quality evidence). Whether loneliness was assessed by a single-item or a more comprehensive measure had no moderating effect on the estimate. Results indicate that there is a significant positive relationship between loneliness and psychosis. Further studies are needed to determine the causal status of this relationship, but this robust finding should be considered in clinical practice and treatment provision for those with psychotic disorders.

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

ABSTRACT Three experiments investigated younger (18–25 yrs) and older (70–88 yrs) 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; 900/1500 ms), 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 1–3 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 Alzheimers disease.

Healthy Aging and Visual Working Memory: The Effect of Mixing Feature and Conjunction Changes

It has been suggested that an age-related decrease in the ability to bind and retain conjunctions of features may account for some of the pronounced decline of visual working memory (VWM) across the adult life span. So far the evidence for this proposal has been mixed with some suggesting a specific deficit in binding to location, while the retention of surface feature conjunctions (e.g., color-shape) appears to remain largely intact. The present experiments follow up on the results of an earlier study, which found that older adults were specifically poor at detecting conjunction changes when they were mixed with trials containing changes to individual features, relative to when these trials were blocked (Cowan, Naveh-Benjamin, Kilb, & Saults, 2006). Using stimuli defined by conjunctions of color and shape (Experiment 1), and color and location (Experiment 2) we find no evidence that older adults are less accurate at detecting binding changes when trial types are mixed. Further, analysis of estimates of discriminability provides substantial-to-strong evidence against this suggestion. We discuss these findings in relation to previous studies addressing the same question and suggest that much of the evidence for specific age-related VWM binding deficits is not as strong as it first appears.

Locating Temporal Functional Dynamics of Visual Short-Term Memory Binding using Graph Modular Dirichlet Energy

Visual short-term memory binding tasks are a promising early biomarker for Alzheimers disease (AD). We probe the transient physiological underpinnings of these tasks over the healthy brains functional connectome by contrasting shape only (Shape) and shape-colour binding (Bind) conditions, displayed in the left and right sides of the screen, separately, in young volunteers. Electroencephalogram recordings during the encoding and maintenance periods of these tasks are analysed using functional connectomics. Particularly, we introduce and implement a novel technique named Modular Dirichlet Energy (MDE) which allows robust and flexible analysis of the connectome with unprecedentedly high temporal precision. We find that connectivity in the Bind condition is stronger than in the Shape condition in both occipital and frontal network modules during the encoding period of the right screen condition but not the left screen condition. Using MDE we are able to discern driving effects in the occipital module between 100-140ms, which noticeably coincides with the P100 visually evoked potential, and a driving effect in the interaction of occipital and frontal modules between 120-140ms, suggesting a delayed information processing difference between these modules. This provides temporally precise information over a heterogenous population for tasks related to the sensitive and specific detection of AD.Visual short-term memory binding tasks are a promising early marker for Alzheimer’s disease (AD). To uncover functional deficits of AD in these tasks it is meaningful to first study unimpaired brain function. Electroencephalogram recordings were obtained from encoding and maintenance periods of tasks performed by healthy young volunteers. We probe the task’s transient physiological underpinnings by contrasting shape only (Shape) and shape-colour binding (Bind) conditions, displayed in the left and right sides of the screen, separately. Particularly, we introduce and implement a novel technique named Modular Dirichlet Energy (MDE) which allows robust and flexible analysis of the functional network with unprecedented temporal precision. We find that connectivity in the Bind condition is less integrated with the global network than in the Shape condition in occipital and frontal modules during the encoding period of the right screen condition. Using MDE we are able to discern driving effects in the occipital module between 100–140 ms, coinciding with the P100 visually evoked potential, followed by a driving effect in the frontal module between 140–180 ms, suggesting that the differences found constitute an information processing difference between these modules. This provides temporally precise information over a heterogeneous population in promising tasks for the detection of AD.

Informed guessing in change detection

Provided stimuli are highly distinct, the detection of changes between two briefly separated arrays appears to be achieved by an all-or-none process where either the relevant information is in working memory or observers guess. This observation suggests that it is possible to estimate the average number of items an observer was able to retain across a series of trials, a potentially highly informative cognitive characteristic. For each version of the change detection paradigm, for this estimate to be accurate, it is important to specify how observers use the information available to them. For some instantiations of this task it is possible that observers use knowledge of the contents of working memory even when they are in a guessing state, rather than selecting between the response alternatives at random. Here we test the suggestion that observers may be able to use their knowledge of the number of items in memory to guide guessing in two versions of the change detection task. The four experiments reported here suggest that participants are, in fact, able to use the parameters of the task to update their base expectation of a change occurring to arrive at more informed guessing.