This study investigates the effect of virtual reality (VR) motor tasks on functional movement disorders.

The investigators want to investigate how different display modes of virtual hands and the experimental manipulation of the visual representation of virtual hand movements affect (1) the performance of the hand movements (2) the tremor and (3) the subjective perception of the tremor.

There are three groups: Patients with functional tremor (FT), patients with essential tremor (ET) and healthy controls (HC). The study is carried out on one or two consecutive days. The first appointment is only made for patients with ET and FT and is used for the neurological examination and to assess the severity of the tremor. It takes place at the Outpatient Clinic for Movement Disorders at the University Clinic for Neurology in Graz and lasts a maximum of 30 minutes. The second appointment is at the Institute of Psychology at the University of Graz and requires the active participation of the respondent for 2.5 hours. Subjects are asked not to take any tremor-influencing medication on the day of the examination. HC will only attend the appointment at the Institute of Psychology.

First appointment:

• Clinical Global Impression - Severity Scale (CGI-S): 5-point Likert scale, clinicians assess the severity of the condition
• Patient Global Impression of Severity (PGI-S): 5-point Likert scale, patients assess the severity of the condition
• Fahn Tolosa Marin Tremor Rating Scale (FTM): assesses the tremor severity
• Simplified Version of the Functional Movement Disorders Rating Scale (S-FMDRS): assesses the severity of the functional tremor

Second appointment:

1. Questionnaires:

   • Simulator Sickness Questionnaire (SSQ): 4-point Likert scale, assesses nausea, oculomotor and visual disturbances, disorientation (2 timepoints: before and after VR tasks)
   • Edinburgh Handedness Inventory (EDI)
   • Questionnaire about sociodemographic data
   • Technology Usage Inventory (TUI): 7-point Likert scale, acceptance and use of technologies
   • Igroup Presence Questionnaire (IPQ): sense of presence in the VR

2. electroencephalogram (EEG) and surface-Electromyography (surface-EMG) of forearm muscles: run synchronously with the examinations

3. VR-tasks: all tasks are carried out in randomized order

   1. 3x3 matrix: individual fields light up in random order, participants are instructed to touch the fields in the given sequence as quickly as possible. 30 repetitions with a realistic VR-hand model and 30 repetitions with an abstract VR-hand model.
   2. 3x3 matrix: same task as (a) but after each repetition, participants must touch a field labeled "next" to continue the task. 30 repetitions.
   3. apple in a box: a virtual apple is to be placed in a virtual box using the hand with the weaker tremor, while the other hand is left resting on the table. 30 repetitions.
   4. apple in a box: same task as (c) but the resting hand is not visible. 30 repetitions.

Inclusion Criteria:

• diagnosis of functional tremor (FT) or essential tremor (ET) or healthy control persons
• In patients with FT and ET: presence of a constant or intermittent tremor during the neurological examination

Exclusion Criteria:

• unclear tremor syndrome
• essential tremor plus (ET plus)
• conditions that interfere with EEG diagnostic (skin conditions, skin infections, wounds)
• reflex epilepsy
• cervical degeneration or chronic pain syndrome of the cervical spine
• severe somatic illness
• previous cerebral or head surgery
• implanted pacemaker or deep brain stimulation
• persons who are unable to consent