Alzheimer's Disease, Visual Search, and Instrumental Activities of Daily Living: A Review and a New Perspective on Attention and Eye Movements

Visual short-term memory binding and attentional processes during object-scene integration are preserved in mild cognitive impairment

Binding, a critical cognitive process likely mediated by attention, is essential for creating coherent object representations within a scene. This process is vulnerable in individuals with dementia, who exhibit deficits in visual working memory (VWM) binding, primarily tested using abstract arrays of standalone objects. To explore how binding operates in more realistic settings across the lifespan, we examined the impact of object saliency and semantic consistency on VWM binding and the role of overt attention. Using an eye-tracking change detection task, we compared younger adults, healthy older adults, and individuals with Mild Cognitive Impairment (MCI). Participants were presented with naturalistic scenes and asked to detect changes in the identity and/or location of objects that were either semantically consistent or inconsistent with their scene context. Across all age groups, semantically inconsistent objects were prioritised during encoding, leading to better change detection than consistent objects. Highly salient objects decreased the inconsistency advantage while being detrimental to detection accuracy when inspected at longer latencies to the first fixation. Longer fixation durations on the critical object were beneficial for recognition. In contrast, delayed initial inspection or frequent subsequent fixations on other objects were detrimental to detection, regardless of age or cognitive impairment. These findings challenge the notion of generalised semantic memory impairment in the prodromal stages of dementia and highlight the importance of efficient attentional control in supporting VWM binding, even in the face of cognitive decline. Overall, preserved low-level and high-level mechanisms of object-scene integration can compensate for age-related cognitive decline, enabling successful binding in naturalistic contexts.

Distinct eye movement patterns to complex scenes in Alzheimer's disease and Lewy body disease

Background

Alzheimer's disease (AD) and Lewy body disease (LBD), the two most common causes of neurodegenerative dementia with similar clinical manifestations, both show impaired visual attention and altered eye movements. However, prior studies have used structured tasks or restricted stimuli, limiting the insights into how eye movements alter and differ between AD and LBD in daily life.

Objective

We aimed to comprehensively characterize eye movements of AD and LBD patients on naturalistic complex scenes with broad categories of objects, which would provide a context closer to real-world free viewing, and to identify disease-specific patterns of altered eye movements.

Methods

We collected spontaneous viewing behaviors to 200 naturalistic complex scenes from patients with AD or LBD at the prodromal or dementia stage, as well as matched control participants. We then investigated eye movement patterns using a computational visual attention model with high-level image features of object properties and semantic information.

Results

Compared with matched controls, we identified two disease-specific altered patterns of eye movements: diminished visual exploration, which differentially correlates with cognitive impairment in AD and with motor impairment in LBD; and reduced gaze allocation to objects, attributed to a weaker attention bias toward high-level image features in AD and attributed to a greater image-center bias in LBD.

Conclusion

Our findings may help differentiate AD and LBD patients and comprehend their real-world visual behaviors to mitigate the widespread impact of impaired visual attention on daily activities.

Eye-tracking paradigms for the assessment of mild cognitive impairment: a systematic review

Mild cognitive impairment (MCI), representing the 'transitional zone' between normal cognition and dementia, has become a novel topic in clinical research. Although early detection is crucial, it remains logistically challenging at the same time. While traditional pen-and-paper tests require in-depth training to ensure standardized administration and accurate interpretation of findings, significant technological advancements are leading to the development of procedures for the early detection of Alzheimer's disease (AD) and facilitating the diagnostic process. Some of the diagnostic protocols, however, show significant limitations that hamper their widespread adoption. Concerns about the social and economic implications of the increasing incidence of AD underline the need for reliable, non-invasive, cost-effective, and timely cognitive scoring methodologies. For instance, modern clinical studies report significant oculomotor impairments among patients with MCI, who perform poorly in visual paired-comparison tasks by ascribing less attentional resources to novel stimuli. To accelerate the Global Action Plan on the Public Health Response to Dementia 2017-2025, this work provides an overview of research on saccadic and exploratory eye-movement deficits among older adults with MCI. The review protocol was drafted based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Electronic databases were systematically searched to identify peer-reviewed articles published between 2017 and 2022 that examined visual processing in older adults with MCI and reported gaze parameters as potential biomarkers. Moreover, following the contemporary trend for remote healthcare technologies, we reviewed studies that implemented non-commercial eye-tracking instrumentation in order to detect information processing impairments among the MCI population. Based on the gathered literature, eye-tracking-based paradigms may ameliorate the screening limitations of traditional cognitive assessments and contribute to early AD detection. However, in order to translate the findings pertaining to abnormal gaze behavior into clinical applications, it is imperative to conduct longitudinal investigations in both laboratory-based and ecologically valid settings.

Early detection of cognitive decline in Alzheimer's disease using eye tracking

Background

Patients with Alzheimer's disease (AD) are known to exhibit visuospatial processing impairment, as reflected in eye movements from the early stages of the disease. We investigated whether the pattern of gaze exploration during visual tasks could be useful for detecting cognitive decline at the earliest stage.

Methods

Sixteen AD patients (age: 79.1 ± 7.9 years, Mini Mental State Examination [MMSE] score: 17.7 ± 5.3, mean ± standard deviation) and 16 control subjects (age: 79.4 ± 4.6, MMSE score: 26.9 ± 2.4) participated. In the visual memory task, subjects memorized presented line drawings for later recall. In the visual search tasks, they searched for a target Landolt ring of specific orientation (serial search task) or color (pop-out task) embedded among arrays of distractors. Using video-oculography, saccade parameters, patterns of gaze exploration, and pupil size change during task performance were recorded and compared between AD and control subjects.

Results

In the visual memory task, the number of informative regions of interest (ROIs) fixated was significantly reduced in AD patients compared to control subjects. In the visual search task, AD patients took a significantly longer time and more saccades to detect the target in the serial but not in pop-out search. In both tasks, there was no significant difference in the saccade frequency and amplitude between groups. On-task pupil modulation during the serial search task was decreased in AD. The number of ROIs fixated in the visual memory task and search time and saccade numbers in the serial search task differentiated both groups of subjects with high sensitivity, whereas saccade parameters of pupil size modulation were effective in confirming normal cognition from cognitive decline with high specificity.

Discussion

Reduced fixation on informative ROIs reflected impaired attentional allocation. Increased search time and saccade numbers in the visual search task indicated inefficient visual processing. Decreased on-task pupil size during visual search suggested decreased pupil modulation with cognitive load in AD patients, reflecting impaired function of the locus coeruleus. When patients perform the combination of these tasks to visualize multiple aspects of visuospatial processing, cognitive decline can be detected at an early stage with high sensitivity and specificity and its progression be evaluated.

Does physical exercise improve the capacity for independent living in people with dementia or mild cognitive impairment: an overview of systematic reviews and meta-analyses

OBJECTIVE

To summarise existing systematic reviews which assessed the effects of physical exercise on activities of daily living, walking, balance and visual processing in people with dementia or mild cognitive impairment.

METHODS

In this overview of systematic reviews and meta-analyses, seven electronic databases were searched to identify eligible reviews published between January 2015 and April 2021.

RESULTS

A total of 30 systematic reviews were identified and included in the overview. The most frequent type of exercise for the intervention group was multimodal exercises. Mind-body exercises, exergames, dance intervention and aerobic exercise were other exercise types. Most of the reviews reported that exercise is significantly effective for improving activities of daily living (SMD 95%CI, from 0.27 to 1.44), walking (SMD 95%CI, from 0.08 to 2.23), balance (SMD 95%CI, from 0.37 to 2.24) and visuospatial function (SMD 95%CI, from 0.16 to 0.51), which are among the most leading determinants of independent living in individuals with dementia or mild cognitive impairment.

CONCLUSION

Evidence has shown that exercise (especially multicomponent exercise programmes including cognitive, physical and multitasking exercises) with sufficient intensity improves the activities of daily living skills. Exercise also improves walking, balance and visual processing, which can provide a more independent life for people with dementia and mild cognitive impairment. Cognitively impaired people should therefore be encouraged to exercise regularly in order to be more independent.

Supplemental data for this article is available online at http://dx.doi.org/10.1080/13607863.2021.2019192.

Factors associated with dropout in the longitudinal Vogel study of cognitive decline

Dementia, including Alzheimer's disease, is a growing problem worldwide. Prevention or early detection of the disease or a prodromal cognitive decline is necessary. By means of our long-term follow-up 'Vogel study', we aim to predict the pathological cognitive decline of a German cohort (mean age was 73.9 ± 1.55 years at first visit) with three measurement time points within 6 years per participant. Especially in samples of the elderly and subjects with chronic or co-morbid diseases, dropouts are one of the biggest problems of long-term studies. In contrast to the large number of research articles conducted on the course of dementia, little research has been done on the completion of treatment. To ensure unbiased and reliable predictors of cognitive decline from study completers, our objective was to determine predictors of dropout. We conducted multivariate analyses of covariance and multinomial logistic regression analyses to compare and predict the subject's dropout behaviour at the second visit 3 years after baseline (full participation, partial participation and no participation/dropout) with neuropsychiatric, cognitive, blood and lifestyle variables. Lower performance in declarative memory, attention and visual-spatial processing predicted dropout rather than full participation. Lower performance in visual-spatial processing predicted partial participation as opposed to full participation. Furthermore, lower performance in mini-mental status examination predicted whether subjects dropped out or participated partially instead of full participation. Baseline cognitive parameters are associated with dropouts at follow-up with a loss of impaired participants. We expect a bias into a healthier sample over time.

Eye-Tracking Metrics for Figure-Copying Processes in Early- vs. Late-Onset Alzheimer's Disease

Visuospatial dysfunction is a common symptom in patients with Alzheimer's disease (AD). To more focus on copying processes rather than on finally completed figures, we conceptually split the copying processes into three stages: visuoperceptual function, visuoconstructional function, and working memory function. We constructed perceptual and working spaces to investigate the different stages of copying, and then, we compared the number and duration of fixations and saccades and the number of switches across the two spaces. We used eye-tracking glasses to assess eye-tracking metrics in patients with early-onset AD (EOAD), patients with late-onset AD (LOAD), and normal control (NC) participants while they copied the simplified Rey–Osterrieth complex figure test (RCFT). Regarding eye metrics on the perceptual space, the number and duration of fixations were greater in both groups of patients with AD than in the NC participants group (number: EOAD vs. NC: p < 0.001, LOAD vs. NC: p = 0. 003/ duration: EOAD vs. NC: p < 0.001, LOAD vs. NC: p < 0.001). On the working space, the number and duration of fixations were greater in the patients with EOAD than in the patients with LOAD and NC participants (number: EOAD vs. LOAD: p = 0. 007, EOAD vs. NC: p = 0. 001/duration: EOAD vs. LOAD: p = 0. 008, EOAD vs. NC: p = 0. 002). The number of saccades and switching was higher in patients with EOAD than in NC participants (p < 0.001). The eye-tracking metrics from the simplified RCFT correlated with the neuropsychological test scores. Patients with EOAD and LOAD achieved the same level of performance at the simplified and original RCFT scores. However, patients with EOAD than LOAD showed a greater number and duration of fixations on the working space and more frequent switching between the perceptual and working spaces, which may reflect more cognitive efforts to achieve the same level of performance.

Preserved Extra-Foveal Processing of Object Semantics in Alzheimer's Disease

Alzheimer's disease (AD) patients underperform on a range of tasks requiring semantic processing, but it is unclear whether this impairment is due to a generalised loss of semantic knowledge or to issues in accessing and selecting such information from memory. The objective of this eye-tracking visual search study was to determine whether semantic expectancy mechanisms known to support object recognition in healthy adults are preserved in AD patients. Furthermore, as AD patients are often reported to be impaired in accessing information in extra-foveal vision, we investigated whether that was also the case in our study. Twenty AD patients and 20 age-matched controls searched for a target object among an array of distractors presented extra-foveally. The distractors were either semantically related or unrelated to the target (e.g., a car in an array with other vehicles or kitchen items). Results showed that semantically related objects were detected with more difficulty than semantically unrelated objects by both groups, but more markedly by the AD group. Participants looked earlier and for longer at the critical objects when these were semantically unrelated to the distractors. Our findings show that AD patients can process the semantics of objects and access it in extra-foveal vision. This suggests that their impairments in semantic processing may reflect difficulties in accessing semantic information rather than a generalised loss of semantic memory.

Mesenchymal stem cell-conditioned medium attenuates the retinal pathology in amyloid-β-induced rat model of Alzheimer's disease: Underlying mechanisms

Amyloid‐beta (Aβ) oligomer is known to contribute to the pathophysiology of age‐related macular degeneration. Herein, we aimed to elucidate the in vivo and in vitro effects of Aβ_1‐42 application on retinal morphology in rats. Our in vivo studies revealed that intracerebroventricular administration of Aβ_1‐42 oligomer caused dysmorphological changes in both retinal ganglion cells and retinal pigment epithelium. In addition, in vitro studies revealed that ARPE‐19 cells following Aβ_1‐42 oligomer application had decreased viability along with apoptosis and decreased expression of the tight junction proteins, increased expression of both phosphor‐AKT and phosphor‐GSK3β and decreased expression of both SIRT1 and β‐catenin. Application of conditioned medium (CM) obtained from mesenchymal stem cells (MSC) protected against Aβ_1‐42 oligomer‐induced retinal pathology in both rats and ARPE‐19 cells. In order to explore the potential role of peptides secreted from the MSCs, we applied mass spectrometry to compare the peptidomics profiles of the MSC‐CM. Gene ontology enrichment analysis and String analysis were performed to explore the differentially expressed peptides by predicting the functions of their precursor proteins. Bioinformatics analysis showed that 3‐8 out of 155–163 proteins in the MSC‐CM maybe associated with SIRT1/pAKT/pGSK3β/β‐catenin, tight junction proteins, and apoptosis pathway. In particular, the secretomes information on the MSC‐CM may be helpful for the prevention and treatment of retinal pathology in age‐related macular degeneration.

Visual Search in Behavioral Variant Frontotemporal Dementia

BACKGROUND

Changes to visual search have shown specific patterns in a number of dementia subtypes. The cortical regions involved in the control of visual search overlap with the regions affected in behavioral variant frontotemporal dementia (bvFTD). Previous literature has examined visual search in bvFTD with smaller array sizes.

OBJECTIVE

To examine the pattern of behavior shown by bvFTD patients while undertaking visual search in the presence of larger numbers of distractors to model increased cognitive load.

METHODS

15 bvFTD and 17 control participants undertook three visual search tasks: color, orientation, and conjunction searches. A wide range of array sizes was used, from 16 to 100 items arranged as a square. Behavior was quantified using accuracy, response time, and eye movements.

RESULTS

BvFTD participants displayed a reduction in accuracy and an increased response time across all task types. BvFTD participants displayed an increase in number of objects examined and number of fixations made for color and conjunction tasks. Fixation duration was increased for orientation and conjunction (the more difficult tasks) but not color search. Results indicated the increase in time to response to be due to an increased intercept, with no significant difference in slope for the different tasks.

CONCLUSION

BvFTD participants display a pattern of visual search behavior consisting of a decrease in accuracy, an increase in response time, and a corresponding increase in the number and length of eye movements made during visual search. The pattern seen corresponds to studies of frontal lobe damage, while differing in pattern from that seen in a range of other cognitive conditions.

Abnormal Functional Connectivity in Cognitive Control Network, Default Mode Network, and Visual Attention Network in Internet Addiction: A Resting-State fMRI Study

Internet addiction (IA) has become a global mental and social problem, which may lead to a series of psychiatric symptoms including uncontrolled use of internet, and lack of concentration. However, the exact pathophysiology of IA remains unclear. Most of functional connectivity studies were based on pre-selected regions of interest (ROI), which could not provide a comprehensive picture of the communication abnormalities in IA, and might lead to limited or bias observations. Using local functional connectivity density (lFCD), this study aimed to explore the whole-brain abnormalities of functional connectivity in IA. We evaluated the whole-brain lFCD resulting from resting-state fMRI data in 28 IA individuals and 30 demographically matched healthy control subjects (HCs). The correlations between clinical characteristics and aberrant lFCD were also assessed. Compared with HCs, subjects with IA exhibited heightened lFCD values in the right dorsolateral prefrontal cortex (DLPFC), left parahippocampal gyrus (PHG), and cerebellum, and the bilateral middle cingulate cortex (MCC) and superior temporal pole (STP), as well as decreased lFCD values in the right inferior parietal lobe (IPL), and bilateral calcarine and lingual gyrus. Voxel-based correlation analysis revealed the significant correlations between the Young's Internet Addiction Test (IAT) score and altered lFCD values in the left PHG and bilateral STP. These findings revealed the hyper-connectivity in cognitive control network and default mode network as well as the hypo-connectivity in visual attention network, verifying the common mechanism in IA and substance addiction, and the underlying association between IA, and attention deficit/hyperactivity disorder in terms of neurobiology.

Search and Match Task: Development of a Taskified Match-3 Puzzle Game to Assess and Practice Visual Search

Background

Visual search declines with aging, dementia, and brain injury and is linked to limitations in everyday activities. Recent studies suggest that visual search can be improved with practice using computerized visual search tasks and puzzle video games. For practical use, it is important that visual search ability can be assessed and practiced in a controlled and adaptive way. However, commercial puzzle video games make it hard to control task difficulty, and there are little means to collect performance data.

Objective

The aim of this study was to develop and initially validate the search and match task (SMT) that combines an enjoyable tile-matching match-3 puzzle video game with features of the visual search paradigm (taskified game). The SMT was designed as a single-target visual search task that allows control over task difficulty variables and collection of performance data.

Methods

The SMT is played on a grid-based (width × height) puzzle board, filled with different types of colored polygons. A wide range of difficulty levels was generated by combinations of 3 task variables over a range from 4 to 8 including height and width of the puzzle board (set size) and the numbers of tile types (distractor heterogeneity). For each difficulty level, large numbers of playable trials were pregenerated using Python. Each trial consists of 4 consecutive puzzle boards, where the goal of the task is to find a target tile configuration (search) on the puzzle board and swap 2 adjacent tiles to create a line of 3 identical tiles (match). For each puzzle board, there is exactly 1 possible match (single target search). In a user study with 28 young adults (aged 18 to 31 years), 13 older (aged 64 to 79 years) and 11 oldest (aged 86 to 98 years) adults played the long (young and older adults) or short version (oldest adults) of the difficulty levels of the SMT. Participants rated their perception and the usability of the task and completed neuropsychological tests that measure cognitive domains engaged by the puzzle game.

Results

Results from the user study indicate that the target search time is associated with set size, distractor heterogeneity, and age. Results further indicate that search performance is associated with general cognitive ability, selective and divided attention, visual search, and visuospatial and pattern recognition ability.

Conclusions

Overall, this study shows that an everyday puzzle game–based task can be experimentally controlled, is enjoyable and user-friendly, and permits data collection to assess visual search and cognitive abilities. Further research is needed to evaluate the potential of the SMT game to assess and practice visual search ability in an enjoyable and adaptive way. A PsychoPy version of the SMT is freely available for researchers.