Cross-cultural evaluation of learning and memory using a consonant-vowel-consonant trigram list.

OBJECTIVE: Word list-learning tasks are commonly used to evaluate auditory-verbal learning and memory. However, different frequencies of word usage, subtle meaning nuances, unique word phonology, and different preexisting associations among words make translation across languages difficult. We administered lists of consonant-vowel-consonant (CVC) nonword trigrams to independent American and Italian young adult samples. We evaluated whether an auditory list-learning task using CVC nonword trigrams instead of words could be applied cross-culturally to evaluate similar learning and associative memory processes. PARTICIPANTS AND METHODS: Seventy-five native English-speaking (USA) and 104 native Italian-speaking (Italy) university students were administered 15-item lists of CVC trigrams using the Rey Auditory Verbal Learning Test paradigm with five study-test trials, an interference trial, and short- and long-term delayed recall. Bayesian t tests and mixed-design ANOVAs contrasted the primary learning indexes across the two samples and biological sex. RESULTS: Performance was comparable between nationalities on all primary memory indices except the interference trial (List B), where the Italian group recalled approximately one item more than the American sample. For both nationalities, recall increased across the five learning trials and declined significantly on the postinterference trial, demonstrating susceptibility to retroactive interference. No effects of sex, age, vocabulary, or depressive symptoms were observed. CONCLUSIONS: Using lists of unfamiliar nonword CVC trigrams, Italian and American younger adults showed a similar performance pattern across immediate and delayed recall trials. Whereas word list-learning performance is typically affected by cultural, demographic, mood, and cognitive factors, this trigram list-learning task does not show such effects, demonstrating its utility for cross-cultural memory assessment.

The Italian version of the Virtual Dementia Tour: Manual translation and an analysis of consistency, validity, and reliability of its pre- post-experience survey.

Introduction: Clinical indications on how to approach caregiving with a person living with dementia underline the need "to have an empathic attitude" requiring the caregiver to view the world from the perspective of the person with dementia. However, it is not easy for the caregiver to understand the perspective their patients have on day-to-day experiences. To put the caregivers in the person with dementia's shoes, the Virtual Dementia Tour (VDT) was developed in 2001, and has been administered to millions of health professionals, community leaders, and family caregivers. Method: In this paper we present the Italian version of the VDT and discuss its internal validity and test-retest reliability for the pre-post experience survey defined by the VDT procedure. Results: An Italian sample (N = 419; mean age = 44.8; standard deviation 14.2) completed the tour and a 5-item survey provided before and after the experience revealed the disposition toward people with dementia changed. Discussion: The VDT Italian version wasrevealed to be valid in supporting a positive perspective change in the perception of dementia as is seen in the original VDT used in English-speaking countries. Highlights: Empathy predicts a higher quality of caregiving for the person living with dementia.The Virtual Dementia Tour (VDT) provides an experience from the person living with dementia's perspective and supports empathy.We present the first Italian version of VDT and its manual translation and validation.Italian VDT internal consistency and test-retest reliability were calculated.Results confirms the reliability and validity of the Italian VDT for empathy.

Take the First-Person Perspective to Become Dementia-Friendly: The Use of 360° Video for Experiencing Everyday-Life Challenges With Cognitive Decline.

The current spread of dementia is engendering an emergency that is not limited to the medical issues but also involves its social dimension. Accordingly, it is necessary to promote a perspective change about the disease that supports a more inclusive view of people with dementia. To ensure this, Dementia-Friendly Communities (DFCs) have recently been developed. Nonetheless, it is not always effortless to deal with people with dementia in an inclusive way because of misconceptions about how they perceive everyday contexts and react in everyday situations. We asked 170 individuals (aged between 13 and 75) to "put themselves in the shoes of a person with dementia" for a few minutes, facilitating this through the use of a 360° video, and to try to experience how activities such as going shopping feel from the first-person perspective. Before and after the experience, participants expressed their opinions about the needs and the autonomies that are deemed to be granted to a person with dementia. The results revealed changes to social perspective after having experienced firsthand what living with dementia could be like. A deeper comprehension of what it is like to live with dementia appeared to be gained, and participants' beliefs about the needs and daily autonomies of those with dementia were modified after the experience. It is possible to conclude that, through the change of perspective, people are more willing to be inclusive toward people with dementia, as is wished for in the DFC approach, although a wider formative intervention on how to be really inclusive still seems to be required.

Italian Version of the Scale of Body Connection: Validation and Correlations with the Interpersonal Reactivity Index.

In recent years there has been considerable research on body awareness, which is believed to arise from interoceptive and from exteroceptive signals. In addition, body awareness may be related to empathetic disposition during social interaction. In this paper we assess the psychometric properties of the Italian version of the Scale of Body Connection (SBC). We also examine SBC correlations with the Interpersonal Reactivity Index, a measure of empathy. An Italian sample (N = 576) aged from 17 to 72 years old (M = 30.43; sd 9.41) completed these surveys online. The SBC Italian translation was validated by confirmatory factor analysis showing a good model fit. The two-scale SBC factor structure was confirmed. The SBC was positively associated with the Iterpersonal Reactivity Index (IRI), demonstrating convergent validity between these two scales. Specifically SBC-Bodily Dissociation was positively correlated with IRI-Personal Distress subscale and SBC-Body Awareness was positively correlated with IRI-Emotional Concerns, -Fantasy and -Perspective Taking subscales.

Enacting Space in Virtual Reality: A Comparison Between Money's Road Map Test and Its Virtual Version.

In the field of spatial cognition research the mutual relationship between perception and action that brings out spatial orientation was lately investigated. Besides, the sameness between creating a cognitive map from the exploration of a not simulated environment, from the use of an allocentric (survey-like) sketched map, and from the interaction with egocentric (route-like) 3D virtual environments, is generally contrived. To understand if different embodied affordances could provide different knowledge organization during wayfinding through the use of distinct spatial simulations, the same group of 61 healthy subjects experienced both the classical version of the Money's Road Map test (M-RMT) and a virtual reality version of the Road Map test (VR-RMT). The M-RMT requires a allocentric to egocentric right/left reasoning to explore a stylized city provided in a survey perspective. The VR-RMT is a 3D version of the same environment through which participants can actively navigate by choosing egocentric-based right/left directions in a route perspective. The results showed that the different embodiments afforded by the two environments and the increasing complexity in turn types provides different spatial outcomes. Results were discussed according to the sensorimotor coupling theory provided from the enactive cognition approach and significances for spatial cognition research were provided.

The Neuropsychiatric Inventory-Diary Rating Scale (NPI-Diary): A Method for Improving Stability in Assessing Neuropsychiatric Symptoms in Dementia.

BACKGROUND: In health-care settings, the use of the Neuropsychiatric Inventory-Nursing Home (NPI-NH) may not always be consistent with the authors' guidelines, which affects its reliability. To avoid this bias, a diary version of the NPI (NPI-Diary) was developed. AIMS: This study aimed to evaluate the psychometric properties (internal consistency and reliability) of the NPI-Diary, and examined its convergence with the NPI-NH. METHODS: Two raters administered the NPI-NH and NPI-Diary to 40 participants with Alzheimer's disease, selected randomly from a hospital's weekly turnover. RESULTS: The NPI-Diary exhibited adequate internal consistency (total: α = 0.581) and test-retest reliability (total: ρ = 0.711; p < 0.01). The interrater reliability values (ICC) for the NPI-NH and NPI-Diary differed significantly (Total: NPI-NH ICC = 0.506, NPI-Diary ICC = 0.879; Frequency: NPI-NH ICC = 0.51, NPI-Diary ICC = 0.798; Severity: NPI-NH ICC = 0.491, NPI-Diary ICC = 0.809). The convergent validity between the two inventories was also significant (total: ρ = 0.48; p < 0.01). CONCLUSIONS: The NPI-Diary showed more appropriate validity and reliability compared to the NPI-NH, when administered in a highly variable sample, as is generally the case in the current health-care setting.

Two new virtual reality tasks for the assessment of spatial orientation Preliminary results of tolerability, sense of presence and usability.

Spatial orientation is a cognitive domain frequently impaired in Alzheimer's Disease and can be one of its earliest symptoms. OBJECTIVE: This paper describes the results of tolerability, sense of presence and usability of two immersive virtual reality tasks for the assessment of spatial orientation, using VR headset in adults. METHODS: 31 healthy adults recruited from university and the local community performed two experimental immersive virtual reality tasks of spatial orientation: the SOIVET-Maze for the assessment of allocentric to egocentric spatial abilities and the SOIVET-Route for the assessment of spatial memory and landmark recognition. Participants completed questionnaires about sense of presence, cybersickness symptoms, technology use profile and motion sickness history. Usability measures were assessed by spontaneous feedback from participants. RESULTS: All participants were able to understand the task instructions and how to interact with the system. Both tasks seemed to induce a strong sense of presence, as assessed by the Witmer and Singer Presence Questionnaires (M=128 and 143 for SOIVET-Maze and SOIVET-Route, respectively). The SOIVET-Route had a small numeric advantage over the SOIVET-Maze tolerability scores assessed by the Cybersickness Questionnaire (M=4.19, SD=5.576 and M=3.52, SD=6.418 for SOIVET-Maze and SOIVET-Route respectively). Also, there were no drop-outs on the SOIVET-Route due to tolerability issues, unlike the SOIVET-Maze, which had two drop-outs. However, this difference was not statistically significant (Z= -.901, p= 0.368, Wilcoxon signed-rank test).

A orientação espacial é um domínio cognitivo freqüentemente comprometido na doença de Alzheimer e pode ser um dos primeiros sintomas manifestados. OBJETIVO: Este artigo descreve os resultados de tolerabilidade, sensação de presença e usabilidade de duas tarefas imersivas de realidade virtual para avaliação da orientação espacial, utilizando óculos de RV em adultos. MÉTODOS: 31 adultos saudáveis, ​​recrutados entre estudantes universitários e da comunidade local, realizaram duas tarefas de realidade virtual imersiva para avaliação da orientação espacial: A tarefa SOIVET-Maze para avaliação da capacidade de transposição da orientação alocêntrica para egocêntrica e a tarefa SOIVET-Route para avaliação da memória espacial e reconhecimento de pontos de referência. Os participantes também responderam questionários sobre Sensação de Presença, Sintomas de cybersickness, Perfil de Uso de Tecnologia e Histórico de cinetose. Feedback espontâneo dos participantes foi utilizado como medida de usabilidade. RESULTADOS: Todos os participantes conseguiram compreender as instruções da tarefa e como interagir com o sistema. Ambas tarefas parecem induzir forte sensação de presença, avaliada pelo Questionário de Presença de Witmer e Singer (M=128 e 143 para SOIVET-Maze e SOIVET-Route, respectivamente). A tarefa SOIVET-Route teve uma pequena vantagem numérica em relação à tarefa SOIVET-Maze na pontuação de tolerabilidade avaliada pelo Questionário de Cybersickness (M=4,19, SD=5,576 e M=3,52, SD=6,418 para SOIVET-Maze e SOIVET-Route respectivamente). Além disso, não houve desistências na SOIVET-Route devido a problemas de tolerabilidade, ao contrário da SOIVET-Maze, que teve dois drop-outs. No entanto, essa diferença não foi estatisticamente significativa (Z= -901, p=0,368, teste de postos sinalizados de Wilcoxon).

Disentangling the Contribution of Spatial Reference Frames to Executive Functioning in Healthy and Pathological Aging: An Experimental Study with Virtual Reality.

A growing body of evidence pointed out that a decline in effectively using spatial reference frames for categorizing information occurs both in normal and pathological aging. Moreover, it is also known that executive deficits primarily characterize the cognitive profile of older individuals. Acknowledging this literature, the current study was aimed to specifically disentangle the contribution of the cognitive abilities related to the use of spatial reference frames to executive functioning in both healthy and pathological aging. 48 healthy elderly individuals and 52 elderly suffering from probable Alzheimer's Disease (AD) took part in the study. We exploited the potentiality of Virtual Reality to specifically measure the abilities in retrieving and syncing between different spatial reference frames, and then we administrated different neuropsychological tests for evaluating executive functions. Our results indicated that allocentric functions contributed significantly to the planning abilities, while syncing abilities influenced the attentional ones. The findings were discussed in terms of previous literature exploring relationships between cognitive deficits in the first phase of AD.

Two new virtual reality tasks for the assessment of spatial orientation: preliminary results of tolerability, sense of presence and usability / Duas novas tarefas de realidade virtual para avaliação da orientação espacial: resultados preliminares de tolerabilidade, sensação de presença e usabilidade

Abstract Spatial orientation is a cognitive domain frequently impaired in Alzheimer's Disease and can be one of its earliest symptoms. Objective: This paper describes the results of tolerability, sense of presence and usability of two immersive virtual reality tasks for the assessment of spatial orientation, using VR headset in adults. Methods: 31 healthy adults recruited from university and the local community performed two experimental immersive virtual reality tasks of spatial orientation: the SOIVET-Maze for the assessment of allocentric to egocentric spatial abilities and the SOIVET-Route for the assessment of spatial memory and landmark recognition. Participants completed questionnaires about sense of presence, cybersickness symptoms, technology use profile and motion sickness history. Usability measures were assessed by spontaneous feedback from participants. Results: All participants were able to understand the task instructions and how to interact with the system. Both tasks seemed to induce a strong sense of presence, as assessed by the Witmer and Singer Presence Questionnaires (M=128 and 143 for SOIVET-Maze and SOIVET-Route, respectively). The SOIVET-Route had a small numeric advantage over the SOIVET-Maze tolerability scores assessed by the Cybersickness Questionnaire (M=4.19, SD=5.576 and M=3.52, SD=6.418 for SOIVET-Maze and SOIVET-Route respectively). Also, there were no drop-outs on the SOIVET-Route due to tolerability issues, unlike the SOIVET-Maze, which had two drop-outs. However, this difference was not statistically significant (Z= -.901, p= 0.368, Wilcoxon signed-rank test).

Resumo A orientação espacial é um domínio cognitivo freqüentemente comprometido na doença de Alzheimer e pode ser um dos primeiros sintomas manifestados. Objetivo: Este artigo descreve os resultados de tolerabilidade, sensação de presença e usabilidade de duas tarefas imersivas de realidade virtual para avaliação da orientação espacial, utilizando óculos de RV em adultos. Métodos: 31 adultos saudáveis, ​​recrutados entre estudantes universitários e da comunidade local, realizaram duas tarefas de realidade virtual imersiva para avaliação da orientação espacial: A tarefa SOIVET-Maze para avaliação da capacidade de transposição da orientação alocêntrica para egocêntrica e a tarefa SOIVET-Route para avaliação da memória espacial e reconhecimento de pontos de referência. Os participantes também responderam questionários sobre Sensação de Presença, Sintomas de cybersickness, Perfil de Uso de Tecnologia e Histórico de cinetose. Feedback espontâneo dos participantes foi utilizado como medida de usabilidade. Resultados: Todos os participantes conseguiram compreender as instruções da tarefa e como interagir com o sistema. Ambas tarefas parecem induzir forte sensação de presença, avaliada pelo Questionário de Presença de Witmer e Singer (M=128 e 143 para SOIVET-Maze e SOIVET-Route, respectivamente). A tarefa SOIVET-Route teve uma pequena vantagem numérica em relação à tarefa SOIVET-Maze na pontuação de tolerabilidade avaliada pelo Questionário de Cybersickness (M=4,19, SD=5,576 e M=3,52, SD=6,418 para SOIVET-Maze e SOIVET-Route respectivamente). Além disso, não houve desistências na SOIVET-Route devido a problemas de tolerabilidade, ao contrário da SOIVET-Maze, que teve dois drop-outs. No entanto, essa diferença não foi estatisticamente significativa (Z= -901, p=0,368, teste de postos sinalizados de Wilcoxon)

The Role of Baseline Vagal Tone in Dealing with a Stressor during Face to Face and Computer-Based Social Interactions.

Facing a stressor involves a cardiac vagal tone response and a feedback effect produced by social interaction in visceral regulation. This study evaluated the contribution of baseline vagal tone and of social engagement system (SES) functioning on the ability to deal with a stressor. Participants (n = 70) were grouped into a minimized social interaction condition (procedure administered through a PC) and a social interaction condition (procedure administered by an experimenter). The State Trait Anxiety Inventory, the Social Interaction Anxiety Scale, the Emotion Regulation Questionnaire and a debriefing questionnaire were completed by the subjects. The baseline vagal tone was registered during the baseline, stressor and recovery phases. The collected results highlighted a significant effect of the baseline vagal tone on vagal suppression. No effect of minimized vs. social interaction conditions on cardiac vagal tone during stressor and recovery phases was detected. Cardiac vagal tone and the results of the questionnaires appear to be not correlated. The study highlighted the main role of baseline vagal tone on visceral regulation. Some remarks on SES to be deepen in further research were raised.

Visual exploration patterns of human figures in action: an eye tracker study with art paintings.

Art exploration is a complex process conditioned by factors at different levels and includes both basic visual principles and complex cognitive factors. The human figure is considered a critical factor attracting the attention in art painting. Using an eye-tracking methodology, the goal of this study was to explore different elements of the human figure performing an action (face and body parts in action) in complex social scenes characterized by different levels of social interaction between agents depicted in scenes (individual vs. social). The sample included 44 laypersons, and the stimuli consisted of 10 fine art paintings representing the figurative style of classical art. The results revealed different scanning patterns of the human figure elements related to the level of social interaction of agents depicted in the scene. The agents' face attracted eye movements in social interaction scenes while the agents' body parts attracted eye movements only when the agents were involved in individual actions. These processes were confirmed specifically in participants with high empathic abilities who became immediately fixated on faces to develop a mimetic engagement with other agents. Future studies integrating other measures would help confirm the results obtained and strengthen their implication for embodiment processes.

Detecting early egocentric and allocentric impairments deficits in Alzheimer's disease: an experimental study with virtual reality.

Several studies have pointed out that egocentric and allocentric spatial impairments are one of the earliest manifestations of Alzheimer's Disease (AD). It is less clear how a break in the continuous interaction between these two representations may be a crucial marker to detect patients who are at risk to develop dementia. The main objective of this study is to compare the performances of participants suffering from amnestic mild cognitive impairment (aMCI group), patients with AD (AD group) and a control group (CG), using a virtual reality (VR)-based procedure for assessing the abilities in encoding, storing and syncing different spatial representations. In the first task, participants were required to indicate on a real map the position of the object they had memorized, while in the second task they were invited to retrieve its position from an empty version of the same virtual room, starting from a different position. The entire procedure was repeated across three different trials, depending on the object location in the encoding phase. Our finding showed that aMCI patients performed significantly more poorly in the third trial of the first task, showing a deficit in the ability to encode and store an allocentric viewpoint independent representation. On the other hand, AD patients performed significantly more poorly when compared to the CG in the second task, indicating a specific impairment in storing an allocentric viewpoint independent representation and then syncing it with the allocentric viewpoint dependent representation. Furthermore, data suggested that these impairments are not a product of generalized cognitive decline or of general decay in spatial abilities, but instead may reflect a selective deficit in the spatial organization Overall, these findings provide an initial insight into the cognitive underpinnings of amnestic impairment in aMCI and AD patient exploiting the potentiality of VR.

The role of egocentric and allocentric abilities in Alzheimer's disease: a systematic review.

A great effort has been made to identify crucial cognitive markers that can be used to characterize the cognitive profile of Alzheimer's disease (AD). Because topographical disorientation is one of the earliest clinical manifestation of AD, an increasing number of studies have investigated the spatial deficits in this clinical population. In this systematic review, we specifically focused on experimental studies investigating allocentric and egocentric deficits to understand which spatial cognitive processes are differentially impaired in the different stages of the disease. First, our results highlighted that spatial deficits appear in the earliest stages of the disease. Second, a need for a more ecological assessment of spatial functions will be presented. Third, our analysis suggested that a prevalence of allocentric impairment exists. Specifically, two selected studies underlined that a more specific impairment is found in the translation between the egocentric and allocentric representations. In this perspective, the implications for future research and neurorehabilitative interventions will be discussed.

Virtual reality as allocentric/egocentric technology for the assessment of cognitive decline in the elderly.

Wayfinding ability has a high adaptive value, allowing humans to efficiently explore an environment in order to have a goal-oriented activity. This is done thanks to the capacity of individuals to actively acquire knowledge during interaction. Recently, different studies examined the wayfinding performances of older adults in Virtual Reality. While these studies underlined a greater difficulty with the wayfinding task in the elderly subjects, the effects of age on specific aspects of navigational tasks are less well specified. More, a recent study (Konishi & Bohbot, 2013) suggested that older people who use spatial navigational strategies (navigation is achieved by orientating oneself in relation to an allocentic landmark map) in their everyday lives may have increased gray matter in the hippocampus and enhance their probability of healthy and successful aging. To evaluate this hypothesis we tested 176 subjects (from 20 to 89 years old) in wayfinding ability by using an interactive computer-based evaluation tool - the VR Maze spatial task - that requires the translation of the allocentric spatial knowledge to the corresponding egocentric one and its organization to perform a goal directed wayfinding. More, the study explored the relationships of these abilites with traditional paper and pencil measures of memory, executive and attentive functions. Data show how some aspects of spatial ability impairment are not clearly detectable using classical tests, whereas they become evident using the VR Maze spatial task. This difference is even more marked in the wayfinding ability evaluation of the elderly population. Finally, the VR Maze spatial task appears to be correlated with classical neuropsychological tests.

From allo- to egocentric spatial ability in early Alzheimer's disease: a study with virtual reality spatial tasks.

The ability to orient in space constitutes a main sign of cognitive impairment in Alzheimer's disease (AD). Presently, a peculiar aspect of topographical disorientation in AD linked with spatial reference frame congruence appears to have been only minimally investigated. We aim to study whether there is a decline in performing the allo- to egocentric translation of spatial knowledge during different types of wayfinding in AD patients. We introduced two virtual reality tasks, the VR-Maze and VR-Road Map tasks, in which we compared 26 AD and 26 healthy, elderly subjects. The results emphasize that there is a specific reduction in performing allo- to egocentric spatial tasks in AD, whereas this reduction is not as evident in equivalent allocentric spatial tasks. The data are consistent with the neurological results regarding the early degeneration of the hippocampus and retrosplenial cortex in AD, which underlies the ability to translate between these two reference frames.

Validation of a Neuro Virtual Reality-based version of the Multiple Errands Test for the assessment of executive functions.

The purpose of this study was to establish ecological validity and initial construct validity of the Virtual Reality (VR) version of the Multiple Errands Test (MET) (Shallice & Burgess, 1991; Fortin et al., 2003) based on the NeuroVR software as an assessment tool for executive functions. In particular, the MET is an assessment of executive functions in daily life, which consists of tasks that abide by certain rules and is performed in a shopping mall-like setting where items need to be bought and information needs to be obtained. The study population included three groups: post-stroke participants (n = 5), healthy, young participants (n = 5), and healthy, older participants (n = 5). Specific objectives were (1) to examine the relationships between the performance of three groups of participants in the Virtual Multiple Errands Test (VMET) and at the traditional neuropsychological tests employed to assess executive functions and (2) to compare the performance of post-stroke participants to those of healthy, young controls and older controls in the VMET and at the traditional neuropsychological tests employed to assess executive functions.

Sleep dysfunctions influence decision making in undemented Parkinson's disease patients: a study in a virtual supermarket.

In the early-middle stages of Parkinson's disease (PD), polysomnographic studies show early alterations of the structure of the sleep, which may explain frequent symptoms reported by patients, such as daytime drowsiness, loss of attention and concentration, feeling of tiredness. The aim of this study was to verify if there is a correlation between the sleep dysfunction and decision making ability. We used a Virtual Reality version of the Multiple Errand Test (VMET), developed using the NeuroVR free software (http://www.neurovr2.org), to evaluate decision-making ability in 12 PD not-demented patients and 14 controls. Five of our not-demented 12 PD patients showed abnormalities in the polysomnographic recordings associated to significant differences in the VMET performance.

Executive functions in a virtual world: a study in Parkinson's disease.

In Parkinson's disease executive functions are altered. We used a Virtual Reality version of the Multiple Errand Test in order to evaluate decision-making ability in 12 patients and 14 controls. Patients with Parkinson's disease, even if not-demented, showed strategies full of errors, suggesting that impulse control disorder, very frequent in course of disease, could precede cognitive dysfunctions.

Implementation of the multiple errands test in a NeuroVR-supermarket: a possible approach.

Our goal was to develop a tool for the assessment of executive functions by customizing a virtual reality (VR) version of the Multiple Errands Test (MET) [Shallice & Burgess, 1991; Fortin et al., 2003]. The MET is an assessment of executive functions in daily life which consists of tasks that abide by certain rules. It is performed in an actual shopping mall-like setting where there are items to be bought and information to be obtained. The specific goal of this study was to conduct a pilot study using the virtual version of MET (VMET) with both control subjects and patients with cognitive impairment derived from stroke.