Raju P. Sapkota

How does aging affect the types of error made in a visual short-term memory 'object-recall' task?

This study examines how normal aging affects the occurrence of different types of incorrect responses in a visual short-term memory (VSTM) object-recall task. Seventeen young (Mean = 23.3 years, SD = 3.76), and 17 normally aging older (Mean = 66.5 years, SD = 6.30) adults participated. Memory stimuli comprised two or four real world objects (the memory load) presented sequentially, each for 650 ms, at random locations on a computer screen. After a 1000 ms retention interval, a test display was presented, comprising an empty box at one of the previously presented two or four memory stimulus locations. Participants were asked to report the name of the object presented at the cued location. Errors rates wherein participants reported the names of objects that had been presented in the memory display but not at the cued location (non-target errors) vs. objects that had not been presented at all in the memory display (non-memory errors) were compared. Significant effects of aging, memory load and target recency on error type and absolute error rates were found. Non-target error rate was higher than non-memory error rate in both age groups, indicating that VSTM may have been more often than not populated with partial traces of previously presented items. At high memory load, non-memory error rate was higher in young participants (compared to older participants) when the memory target had been presented at the earliest temporal position. However, non-target error rates exhibited a reversed trend, i.e., greater error rates were found in older participants when the memory target had been presented at the two most recent temporal positions. Data are interpreted in terms of proactive interference (earlier examined non-target items interfering with more recent items), false memories (non-memory items which have a categorical relationship to presented items, interfering with memory targets), slot and flexible resource models, and spatial coding deficits.

Object — Position Binding in Visual Short-Term Memory for Sequentially Presented Unfamiliar Stimuli

The effect of spatial position on visual short-term memory (VSTM) for sequentially presented objects has been investigated relatively little, despite the fact that vision in natural environments is characterised by frequent changes in object position and gaze location. We investigated the effect of reusing previously examined spatial positions on VSTM for object appearance. Observers performed a yes – no recognition task following a memory display comprising briefly presented 1/f noise discs (ie possessing spectral properties akin to natural images) shown sequentially at random coordinates. At test, single stimuli were presented either at original spatial positions, new positions, or at a fixed central position. Results, interpreted in terms of appearance and position preview effects, indicate that, where original spatial positions were reused at test, memory performance was elevated by more than 25%, despite that spatial position was task-irrelevant (in the sense that it could not be used to facilitate a correct response per se). This study generalises object – spatial-position binding theory to a sequential display scenario in which the influences of extrafoveal processing, spatial context cues, and long-term memory support were minimised, thereby eliminating the hypothesis that object priming is the principal cause of the ‘same-position advantage’ in VSTM.

Manual tapping enhances visual short‐term memory performance where visual and motor coordinates correspond

Visuo-manual interaction in visual short-term memory (VSTM) has been investigated little, despite its importance in everyday tasks requiring the coordination of visual perception and manual action. This study examines the influence of a manual action performed during stimulus learning on a subsequent VSTM test for object appearance. The memory display comprised a sequence of briefly presented 1/f noise discs (i.e., possessing spectral properties akin to natural images), wherein each new stimulus was presented at a unique screen location. Participants either did (or did not) perform a concurrent manual action (spatial tapping) task requiring that a hand-held stylus be moved to a position on a touch tablet that corresponded (or did not correspond) to the screen position of each new stimulus as it appeared. At test, a single stimulus was presented, either at one of the original screen positions, or at a new position. Two factors were examined: the execution (or otherwise) of spatial tapping at a corresponding or non-corresponding position, and the presentation of test stimuli either at their original spatial positions, or at new positions. We find that spatial tapping at corresponding positions elevates VSTM performance by more than 15%, but this occurs only when stimulus positions are matched from memory to test display. Our findings suggest that multimodal attentional focus during stimulus encoding (incorporating visual, spatial, and manual components) leads to stronger, more robust memory representations. We posit several possible explanations for this effect.

The impact of extrafoveal information on visual short-term memory for object position

The role of extrafoveal information in visual short-term memory has been investigated relatively little, and, in most existing studies, using verbalisable stimuli susceptible to the recruitment of long-term memory (LTM). In addition, little is known about the impact of extrafoveal information available pre- and posttarget foveation, as it is typical to provide extrafoveal information prior to the foveation of memory targets. In this study, two object-position recognition experiments were conducted (each with two conditions) to establish the impact of extrafoveal information provided before and after the foveation of memory targets. Stimuli comprised 1/f noise discs that minimised the recruitment of LTM by eliminating verbal and semantic cues. Overall, a greater hit rate was found where extrafoveal information was available; however, performance analyses in which extrafoveal information was considered relative to the temporal lag at which target stimuli were foveated reveals both costs and benefits. A beneficial effect arose only where extrafoveal information was provided after the target had been foveated, but not prior to target foveation. Findings are discussed in terms of recency and extrafoveal perception effects, incorporating a postfoveation object-file refresh mechanism.

Patients with Mild Cognitive Impairment Show Lower Visual Short-Term Memory Performance in Feature Binding Tasks

Background: Early cognitive changes in people at risk of developing dementia may be detected using behavioral tests that examine the performance of typically affected brain areas, such as the hippocampi. An important cognitive function supported by the hippocampi is memory binding, in which object features are associated to create a unified percept. Aim: To compare visual short-term memory (VSTM) binding performance for object names, locations, and identities between a participant group known to be at higher risk of developing dementia (mild cognitive impairment [MCI]) and healthily aging controls. Methods: Ten MCI and 10 control participants completed five VSTM tests that differed in their requirement of remembering bound or unbound object names, locations, and identities, along with a standard neuropsychological test (Addenbrooke’s Cognitive Examination [ACE]-III). Results: The performance of the MCI participants was selectively and significantly lower than that of the healthily aging controls for memory tasks that required object-location or name-location binding. Conclusion: Tasks that measure unimodal (object-location) and crossmodal (name-location) binding performance appear to be particularly effective for the detection of early cognitive changes in those at higher risk of developing dementia due to Alzheimer’s disease.


Barriers to diabetes awareness and self-help are influenced by people's demographics: perspectives of South Asians with type 2 diabetes

ABSTRACT Aim: To determine whether barriers to diabetes awareness and self-help differ in South Asian participants of different demographic characteristics (age, gender, and literacy) with type 2 diabetes living in the United Kingdom. Methods: Six focus group discussions (FGDs) were carried out in patients who were categorized according to age (30–60 years, ≥60 years), gender (male, female) and literacy status (literate, illiterate). Data were analysed following the iterative process of thematic analysis techniques. Results: Barriers were demographic-specific. The illiterate groups reported language as the major barrier to improved diabetes awareness and self-help. The literate groups reported that information provided by healthcare providers was general, and not specific to their diet/culture. Major barriers to adherence to the recommended diet for diabetes included: insufficient knowledge/awareness about nutritional content of food (all groups); lack of self-will to resist eating sweets, especially during weddings/festivals (literate older groups/literate younger females/illiterate older males); difficulty cooking separate meals for diabetic and non-diabetic family members (illiterate/literate older females). Other barriers to seeking advice/help ranged from not wanting to disclose their diabetes as it may affect employment/work (literate groups) to fear of being singled out at social gatherings (illiterate groups). General lack of motivation to exercise was reported by all groups. Time constraints and not knowing what/how to exercise was reported by literate younger groups whilst the illiterate older groups reported to not having suitable exercising facilities at local communities. Different barriers were also reported when accessing healthcare; language barriers (illiterate groups), restricted access to doctors’ appointments/difficulty attending specific appointment slots offered by General Practitioners (literate females). Conclusion: Different barriers exist to improved awareness about diabetes and self-help in different patient demographics. Lack of culturally appropriate diabetes educational/awareness programs in the community appeared to be a major barrier in most older and illiterate participants while younger participants reported time constraint.

Need to improve awareness and treatment compliance in high-risk patients for diabetic complications in Nepal

Objective/introduction It is known that knowledge, awareness, and practice influence diabetic control. We compared factors pertaining to healthy lifestyle (exercising, avoiding smoking), self-help (attending appointments, following treatment regimens), and diabetic awareness in high-risk patients for diabetic complications, specifically, those on insulin versus non-insulin treatment, and also those with a longer diabetic duration (≥5 years) versus a shorter duration. Methods 200 consecutive patients with type 2 diabetes (52.0±11.6 years) attending diabetic clinic at a referral hospital in Nepal were recruited. A structured questionnaire explored non-clinical parameters including age, gender, diabetic duration, awareness about diabetes control, self-help, and lifestyle. Clinical data were also measured: HbA1c, fasting blood sugar (FBS), blood pressure, and treatment type (insulin, diet/tablet). Results A significantly higher proportion of patients on insulin (vs non-insulin) or with diabetic duration ≥5 years (vs <5 years) self-reported not doing regular exercise, forgetting to take medicine, and not knowing whether their diabetes was controlled (p≤0.005). HbA1c/FBS levels were significantly higher for patients on insulin or with a longer diabetic duration (p≤0.001). 92% of those on insulin (vs 31% on non-insulin) and 91% with diabetic duration ≥5 years (vs 28% of <5 years) self-reported to seeking medical help due to episodes of uncontrolled blood sugar in the last year (p<0.001). Conclusion Poor self-help/lifestyle and reduced knowledge/awareness about diabetic control was found in patients on insulin or with longer diabetic duration. This is a worrying finding as these patients are already at high risk for developing diabetic complications. The findings highlight need for targeting this more vulnerable group and provide more support/diabetic educational tools.

Change Detection in Visual Short-Term Memory The Relative Impact of Pairwise Switches and Identity Substitutions

Numerous kinds of visual event challenge our ability to keep track of the objects that populate our visual environment from moment to moment. These include blinks, occlusion, shifting visual attention, and changes to objects visual and spatial properties over time. These visual events may lead to objects falling out of our visual awareness, but can also lead to unnoticed changes, such as undetected object replacements and positional exchanges. Current visual memory models do not predict which visual changes are likely to be the most difficult to detect. We examine the accuracy with which switches (where two objects exchange locations) and substitutions (where one or two objects are replaced) are detected. Inferior performance for one-object substitutions versus two-objects switches, along with superior performance for two-object substitutions versus two-object switches was found. Our results are interpreted in terms of object file theory, trade-offs between diffused and localized attention, and net visual change.