Diagnostic Performance of an Eye-Tracking Assisted Visual Inference Language Test in the Assessment of Cognitive Decline due to Alzheimer's Disease.

BACKGROUND: The assessment of language changes associated with visual search impairment can be an important diagnostic tool in the Alzheimer's disease (AD) continuum. OBJECTIVE: Investigate the performance of an eye-tracking assisted visual inference language task in differentiating subjects with mild cognitive impairment (MCI) or AD dementia from cognitively unimpaired older adults (controls). METHODS: We assessed a group of 95 older adults (49 MCI, 18 mild dementia due to AD, and 28 controls). The subjects performed the same task under multiple experimental conditions which generate correlated responses that need to be taken into account. Thus, we performed a non-parametric repeated measures ANOVA model for verbal answers, and a linear mixed model (LMM) or its generalized version for the analysis of eye tracking variables. RESULTS: Significant differences were found in verbal answers across all diagnostic groups independently of type of inference, i.e., logic or pragmatic. Also, eye-tracking parameters were able to discriminate AD from MCI and controls. AD patients did more visits to challenge stimulus (Control-AD, -0.622, SE = 0.190, p = 0.004; MCI-AD, -0.514, SE = 0.173, p = 0.011), more visits to the correct response stimulus (Control-AD, -1.363, SE = 0.383, p = 0.002; MCI-AD, -0.946, SE = 0.349, p = 0.022), more fixations on distractors (Control-AD, -4.580, SE = 1.172, p = 0.001; MCI-AD, -2.940, SE = 1.070, p = 0.020), and a longer time to first fixation on the correct response stimulus (Control-AD, -0.622, SE = 0.190, p = 0.004; MCI-AD, -0.514, SE = 0.173, p = 0.011). CONCLUSION: The analysis of oculomotor behavior along with language assessment protocols may increase the sensitivity for detection of subtle deficits in the MCI-AD continuum, representing an important diagnostic tool.

Impact of Cognitive Demand on Eye Movement Pattern in Patients with Alzheimer's Disease.

BACKGROUND: Eye-movement behavior has been used as a reliable tool to identify cognitive and behavioral patterns in individuals with different neuropsychiatric disorders including Alzheimer's disease (AD). Most studies in the field have been dedicated to evaluating eye-movement behavior during cognitive tasks in different protocols using multiple parameters. OBJECTIVE: We aimed to evaluate the differences of eye-movement behavior in healthy subjects, subjects with mild cognitive impairment (MCI), and those with AD in a simple color task with and without cognitive demand. METHODS: 91 subjects: 18 AD, 47 MCI, and 26 healthy controls had their oculomotor parameters assessed during baseline (no cognitive demand involved) and during a simple computational color memory task using an eye-tracker. RESULTS: Baseline showed statistically different and heterogeneous results between normal cognition and MCI groups. Familiarization phase of the task could not discriminate between groups in any of the analyzed parameters. AD subjects made longer fixations and visits on distractors, and more frequent fixations and visits on the target areas than other groups during the response phase. CONCLUSION: Eye-tracking time-related parameters differentiate AD subjects from other groups under cognitive demand even in a simple color memory task.

Impact of cognitive demand on eye movement pattern in patients with alzheimer’s disease

Background: Eye-movement behavior has been used as a reliable tool to identify cognitive and behavioral patterns in individuals with different neuropsychiatric disorders including Alzheimer’s disease (AD). Most studies in the field have been dedicated to evaluating eye-movement behavior during cognitive tasks in different protocols using multiple parameters. Objective: We aimed to evaluate the differences of eye-movement behavior in healthy subjects, subjects with mild cognitive impairment (MCI), and those with AD in a simple color task with and without cognitive demand. Methods: 91 subjects: 18 AD, 47 MCI, and 26 healthy controls had their oculomotor parameters assessed during baseline (no cognitive demand involved) and during a simple computational color memory task using an eye-tracker. Results: Baseline showed statistically different and heterogeneous results between normal cognition and MCI groups. Familiarization phase of the task could not discriminate between groups in any of the analyzed parameters. AD subjects made longer fixations and visits on distractors, and more frequent fixations and visits on the target areas than other groups during the response phase. Conclusion: Eye-tracking time-related parameters differentiate AD subjects from other groups under cognitive demand even in a simple color memory task.

Textual Inference Comprehension in Mild Cognitive Impairment: The Influence of Semantic Processing and Verbal Episodic Memory.

Language complaints, especially in complex tasks, may occur in mild cognitive impairment (MCI). Various language measures have been studied as cognitive predictors of MCI conversion to Alzheimer's type dementia. Understanding textual inferences is considered a high-demanding task that recruits multiple cognitive functions and, therefore, could be sensitive to detect decline in the early stages of MCI. Thus, we aimed to compare the performance of subjects with MCI to healthy elderly in a textual inference comprehension task and to determine the best predictors of performance in this ability considering one verbal episodic memory and two semantic tasks. We studied 99 individuals divided into three groups: (1) 23 individuals with amnestic mild cognitive impairment (aMCI), (2) 42 individuals with non-amnestic mild cognitive impairment (naMCI), (3), and (4) 34 cognitively healthy individuals for the control group (CG). A reduced version of The Implicit Management Test was used to assess different types of inferential reasoning in text reading. MCI patients performed poorer than healthy elderly, and there were no differences between MCI subgroups (amnestic and non-amnestic). The best predictors for inference-making were verbal memory in the aMCI and semantic tasks in the naMCI group. The results confirmed that the failure to understand textual inferences can be present in MCI and showed that different cognitive skills like semantic knowledge and verbal episodic memory are necessary for inference-making.

Visual Search Efficiency in Mild Cognitive Impairment and Alzheimer's Disease: An Eye Movement Study.

BACKGROUND: Visual search abilities are essential to everyday life activities and are known to be affected in Alzheimer's disease (AD). However, little is known about visual search efficiency in mild cognitive impairment (MCI), a transitive state between normal aging and dementia. Eye movement studies and machine learning methods have been recently used to detect oculomotor impairments in individuals with dementia. OBJECTIVE: The aim of the present study is to investigate the association between eye movement metrics and visual search impairment in MCI and AD. METHODS: 127 participants were tested: 43 healthy controls, 51 with MCI, and 33 with AD. They completed an eyetracking visual search task where they had to find a previously seen target stimulus among distractors. RESULTS: Both patient groups made more fixations on the screen when searching for a target, with longer duration than controls. MCI and AD fixated the distractors more often and for a longer period of time than the target. Healthy controls were quicker and made less fixations when scanning the stimuli for the first time. Machine-learning methods were able to distinguish between controls and AD subjects and to identify MCI subjects with a similar oculomotor profile to AD with a good accuracy. CONCLUSION: Results showed that eye movement metrics are useful for identifying visual search impairments in MCI and AD, with possible implications in the early identification of individuals with high-risk of developing AD.

Propriedades espaço-temporais da acuidade vernier no córtex visual humano usando potenciais visuais provocados de varredura

Esta pesquisa pretendia estabelecer um mapa espaço temporal das respostas de vernier no córtex visual humano. O uso do potencial visual provocado de varredura (PVPv) proporciona medidas eficientes e sensíveis dos limiares de vernier com os quais se pode começar a examinar as respostas corticais de vernier no âmbito dos parâmetros espaço temporais. As respostas de vernier foram avaliadas em relação à hipótese de que os sinais retinianos provenientes das células ganglionares da via magnocelular e não da via parvocelular compõem o input neural para córtex que é utilizado para gerar as respostas de vernier (tarefas de localização de alta precisão Lee et a., 1990; Lee et al., 1995). Métodos: As respostas de vernier no córtex humano foram medidas por meio do potencial visual provocado de varredura (PVPv). Quebras de vernier foram introduzidas em grades de ondas quadradas de produzindo colunas verticais intercaladas de barras estáticas e móveis. Medidas binoculares da acuidade vernier foram feitas em grades de alto contraste (64%) em função de 3 frequências temporais (3, 6 e 15 Hz) e 2 frequências espaciais (1 e 8 c/g). Medidas utilizando grades de baixo contraste foram feitas em função de 3 frequências temporais (3, 6 e 10Hz) e 3 frequências espaciais (1, 2 e 8c/g) em ambos os protocolos (alto e baixo contraste) as medidas foram feitas utilizando o PVPv. Foi utilizado o sistema POWER DIVA que utiliza a metodologia dos mínimos quadrados recursivos para extrair a amplitude e fase da resposta nos harmônicos selecionados da frequência do estímulo. Foram analisados o primeiro (1F1) e o segundo (2F1) harmônicos neste estudo. Com base em estudos anteriores, assume-se que o primeiro componente harmônico refere-se às respostas ao estímulo de vernier, e o segundo às respostas (...)

... ao movimento relativo dos elementos do estímulo. Esta hipótese foi testada por meio da utilização de protocolos controle para ambos os arranjos de estímulos (alto e baixo contraste) em que foram utilizados os mesmos parâmetros, porém com deslocamentos entre as barras completamente simétricos (elementos da grade jamais se alinhavam). O sistema POWER DIVA calcula para cada segundo de janela de análise (bin) a amplitude local. A amplitude média do ruído nos 10 bins de análise é utilizada para calcular a razão sinal ruído para cada bin. Apenas sinais com razão sinal ruído maior que 3 foram considerados resposta. A média vetorial de 8 tentativas para cada condição de estímulo foi utilizada para determinar os limiares.Resultados: Os dados são consistentes com dados psicofísicos anteriores, especialmente os dados de Bradley & Skottun (1987) que demonstraram decréscimo significativo nos limiares de vernier com o aumento da frequência espacial. Os limiares eletrofisiológicos de vernier obtidos com o presente trabalho mostraram-se paralelos aos dados psicofísicos em função das frequências espaciais em ambos os protocolos. Os limiares no 1F1 também demonstraram redução significativa com o aumento da frequência temporal em altas frequências espaciais

The research was directed at establishing a spatiotemporal map of human cortical vernier responses. The use of swept-parameter, steady state visual evoked potential (sweep VEP, or sVEP) provides efficient and sensitive measurement of vernier thresholds with which to begin to examine cortical vernier responses over the spatio-temporal parameter space. The vernier responses were evaluated in relation to the hypothesis that the magnocellular (M) but not parvocellular (P) ganglion cell retinal output forms the neural input to cortex that is used to derive vernier (high precision localization task - Lee et al., 1990; Lee et al., 1995). Methods: Human cortical vernier responses were measured using the sweep visual evoked potential (sVEP). Vernier offsets are introduced into a square wave grating producing interleaved vertical columns of moving and static bars. Binocular measurements of the vernier acuity were made using high contrast (64%) gratings as a function of 3 temporal frequencies (TF = 3, 6 and 15 Hz) and 2 spatial frequencies (SF = 1 and 8 c/g). Measurements were also made at low contrast (8%) as a function of 3 temporal frequencies (3, 6 and 10Hz) and 3 spatial frequencies (1, 2 and 8c/g) using the sVEP. The POWER DIVA system uses the recursive least squares to extract the response amplitude and phase at selected harmonics of the stimulus frequency. We analyzed the evoked potentials at the first (1F1 fundamental) and second (2F1) harmonics. Based on prior research, we take the 1F1 component to be the specific response to the periodic vernier onset/offset, while the 2F1 component reflects local relative motion responses. We checked this assumption by also measuring sVEPs using a motion control protocol in which equivalent displacement amplitudes were presented in and identical stimulus array, but with the displacements being (...)

... completely symmetrical alternations between two states of misalignment (grating elements were never aligned). To ensure that the amplitude data used for the regression and extrapolation to threshold is really a response to stimulus instead of noise, POWER DIVA calculates, for each 1-second analysis window (time bin), a local noise amplitude. The mean noise amplitude across 10 analysis bins is used to calculate the signal to noise ratio for each time bin. Only signals with a signal to noise ratio > 3 were considered as a response. The vector average of at least 8 trials was used to determine thresholds. Results: The data are consistent with some comparable prior psychophysical data, especially data from Bradley & Skottun (1987) who showed significant decrease in the vernier thresholds with the increase of spatial frequency. Our cortical (sVEP) vernier thresholds paralleled the psychophysical data as a function of SF in both protocols. The 1F1 (vernier) thresholds also exhibited a significant decrease with increase of temporal frequency at high SF