The aim of the present study is to investigate potential cognitive mechanisms contributing to working memory impairment in Alzheimer's disease and vascular dementia. The investigators consider a new hypothesis suggesting that difficulties in mobilizing maintenance strategies of information could explain this working memory deficit. More specifically, the investigators assume that patient groups will have difficulties in employing both refreshing and elaborative strategies during a working memory task (i.e., complex span task), as compared to a control group.

Working memory is considered as a central hub in human cognition. Good working memory capacities are fundamental for daily life. However, previous research has indicated that patients with Alzheimer's disease or vascular dementia have significant working memory impairment. Currently, there is no consensus on the cognitive mechanisms responsible for this deficit. Prior findings have highlighted that patients with Alzheimer's disease and/or vascular dementia demonstrate specific difficulties in dual-task situations. In this context, the investigators hypothesize that the continuous alternation between maintenance and processing phases involved in working memory could be impaired for these patients. Thus, the aim of the present study is to investigate if patients with Alzheimer's disease and/or vascular dementia can use maintenance strategies of information in working memory, as typically observed in individuals without cognitive impairments.

To this end, the investigators propose a short working memory task in which they manipulate the opportunities to use refreshing strategies and elaborative strategies. The investigators expect that patients with Alzheimer's disease, vascular dementia, or mixed dementia will benefit less than healthy older adults from the increased opportunities to employ refreshing and elaboration. These difficulties could account for the impaired working memory performance associated with these diseases.

In a second step, the investigators formulate distinctive hypotheses between patient sub-groups:

• On the one hand, Alzheimer's disease is characterized by salient impairment of episodic long-term memory. Consequently, the investigators hypothesize that the working memory decline could be related to this deficit in long-term memory. Specifically, patients with Alzheimer's disease would have greater difficulty in implementing elaboration strategies. Thus, these patients' recall performance should benefit less from semantic links between the to-be-remembered items compared to patients with vascular dementia.
• On the other hand, vascular dementia is characterized by a significant impairment of executive functioning. Thus, the investigators hypothesize that the working memory decline could be related to difficulties in implementing refreshing strategies (i.e., voluntary control of attention). Thus, the recall performance of these patients should benefit less from increased free time during the task, compared to patients with Alzheimer's disease.
• Finally, very few studies have been carried out on patients with mixed dementia (from both Alzheimer's disease and vascular dementia). The investigators assume that the recall performance of these patients will benefit less from elaborative opportunities compared to patients with dementia vascular, and less from refreshing opportunities compared to patients with Alzheimer's disease.

Inclusion Criteria:

• For patient and control groups: Adults ≥ 65 years of age
• For patient and control groups: Native French speaker
• For patient and control groups: Vision for easy reading
• For patient and control groups: Hearing for easy instruction understanding
• For patient and control groups: Back span ≥ 3 during the "Digit Span Backward" subtest (WAIS-IV)
• For patient and control groups: Formulation of the non-opposition to participate in this study
• For patient group only: Consultation in Grenoble University Hospital (Centre de Gérontologie Sud - Gerontology center) for clinical neuropsychological assessment due to suspected cognitive impairment
• For patient group only: Diagnosis of Alzheimer's disease, vascular dementia, or mixed dementia (i.e., Alzheimer's disease and vascular dementia)
• For patient group only: Have undergone a neuropsychological assessment at the day clinic, less than 6 months old.
• For patient group only: Have obtained a medical opinion stating that there is no contraindication to participate in this study and no concurrent pathology that could impair the patient's cognitive abilities.
• For patient group only: Absence of praxis and language disorders thath might prevent the carrying out of the experimental task.
• For patient group only: MMSE score between 18 and 25 included
• For control group only: External visitor/carer of a patient/resident of Grenoble University Hospital or volunteers at Grenoble University Hospital.
• For control group only: MMSE score ≥ 26

Exclusion Criteria:

• For patient and control groups: People under guardianship or deprived of their freedom
• For patient and control groups: Diagnosis of severe psychiatric disorders
• For patient and control groups: Suspicion of pathologies related to alcohol dependence
• For patient and control groups: No French social security coverage
• For patient and control groups: Refusal to voluntarily participate in this study
• For patient and control groups: People covered by articles L1121-5 to L1121-8 of the French Public Health Code
• For patient group only: Suspicion of another neurodegenerative disease, such as fronto-temporal dementia, Parkinson's disease, Lewy body disease.
• For patient group only: Clinical neuropsychological assessment did not reveal any cognitive impairment.

The population of this study will consist of patients performing a neuropsychological assessment at Grenoble-Alpes University Hospital. These patients consult because of cognitive disorders. The patients are dividied into these three subgroups according to their medical diagnosis of Alzheimer's disease, vascular dementia, or mixed dementia (diagnostic criteria : Dubois et al. (2021) for Alzheimer's disease; VASCOG diagnostic criteria : Sachdev et al., 2015 for vascular dementia; and diagnostic criteria : DSM-V (APA, 2013) for mixed dementia due to Alzheimer and vascular etiology). The population of this study will also include healthy participants (carers/visitors of patients at the Gerontology centre or volunteers at Gerontology centre).