Spatial and Ocular Trajectories for the Early Diagnosis of Alzheimer's Disease.

Group 1: Cognitively healthy subject: After signing the consent form, during the only visit of the study, the investigator will administer to cognitively healthy subjects two cognitive screening tests to ensure that they meet the criteria for group 1. If performance on the cognitive scales prove to be borderline or below current standards (Montreal Cognitive Assessment ≥ 26/30 and MacNair Cognitive Difficulties Self-Rating Scale ≥15) for at least one of the 2 tests, the participant will prematurely end the study and may be offered an in-depth cognitive assessment as part of routine care. Group 2: Patients suffering from Alzheimer's disease: After signing the consent form, during the only visit of the study, the investigator will administer to patients the Montreal Cognitive Assessment to assess cognitive status.

For every participants (group 1 and 2): During the only visit of the study and after the intervention 1, the participants will answer questionnaires about: * Demographic data such as age, gender, weight, height, education level; * Lifestyle habits such as usual mode of transport, sense of direction, use of GPS device, and video game practice; * Quality of sleep over the previous month and the previous night; * Cognitive reserve questionnaire from Rami et al., 2011; * Concomitant treatment and comorbidities.

For every participants (group 1 and 2): During the only visit of the study and after interventions 1 and 2, the participants will complete the spatial navigation task with eye-tracking. The participants will play the Sea Hero Quest video game and take on the role of the captain of a small boat that has to find its way through an aquatic environment. At the start of each level, the player is shown a map of the environment, with the boat's initial position and the buoys it must reach as quickly as possible in a set order. Once the map has been memorised, it disappears and the navigation begins. Participants will play 6 levels of Sea Hero Quest (two training levels and four different navigation levels). This intervention will be proposed by a trained team member and participants will play on a digital tablet connected to an eye-tracker. The total duration of the task is 30 min (training phase + assessment sequences).

For every participants (group 1 and 2): During the only visit of the study and after interventions 1, 2 and 3, a state-qualified nurse will take venous samples from 3 tubes of 4ml each. These blood samples will be frozen and stored until the end of the study when they will be analysed: * Sample 1: plasmatic Quanterix p-tau217 assay; * Sample 2: apolipoprotein E genotyping; * Sample 3: measurement of plasmatic creatinine levels. Neither the cognitively healthy subjects, nor the patients, nor the clinicians in charge of the patients included will be informed of the results of these biological assays (absence of clinical interest established at the present time of the APOE genotype and the p-tau217 protein level, absence of modification of the care pathway, in adequacy to the bioethics law of August 02, 2021. Creatinine level is used in this study as an adjustment variable to interpret the p-tau217 protein level and will not be used for clinical interpretation.