This study aims to further develop tACS as a tool to improve speech perception, by manipulation of brain-speech synchronisation ("entrainment"), thereby transforming a promising approach into a technique that can benefit to society on a large scale.

Neural oscillations align their phase to the rhythm of speech. This phenomenon is termed neural entrainment and associated with successful speech comprehension. Importantly, we have demonstrated that transcranial alternating current stimulation (tACS) can be used to manipulate how neural activity aligns to speech rhythm, leading to changes in speech perception. The aim of Experiment 1 is to understand how tACS operates on the neural level. This aim will be reached by testing whether tACS produces rhythmic electroencephalography (EEG) responses that outlast the stimulation, indicating an involvement of endogenous oscillatory activity. The aim of Experiment 2 is to increase efficacy of tACS and, consequently, its potential to play an important role in research and everyday life applications. This aim will be reached by using brain imaging (fMRI) to predict optimal stimulation protocols for individual participants. The aim of Experiment 3 is to reveal how tACS can boost speech perception in a multi-speaker scenario. This aim will be reached by using tACS to enhance attended speech or suppress distracting speech, and by comparing these two approaches in their efficacy to boost speech perception. The aim of Experiment 4 is to combine established techniques to create novel opportunities to improve speech perception. This aim will be reached by using neurofeedback to teach participants to enhance their own neural entrainment, applying tACS to support them in this process.

Inclusion Criteria:

• Subject aged between 18 and 50 years old
• informed written consent
• Absence of pro-epileptogenic drugs
• Absence of visual or hearing impairment incompatible with participation in the study

Exclusion Criteria:

• Pregnant or breastfeeding women,
• Persons protected by law adults under guardianship or curatorship
• Persons not affiliated to a Social Security scheme
• Subjects with progressive psychiatric or neurological pathology
• Subjects with a contraindication to tCS or MRI (history of epilepsy, severe head injury or brain/spinal cord surgery, cardiac pacemaker/defibrillator, implanted equipment activated by electrical, magnetic or mechanical system, hemostatic clip carriers of intracerebral aneurysms or carotid arteries, orthopedic implant carriers, claustrophobic, pregnancy).

masking to the conditions of the experiments