All participants with cervical dystonia will be in this group to receive the intervention. After answer three questionnaires (The Mini Mental State Examination, the Revised Toronto Western Spasmodic Torticollis Rating Scale and Psychiatric Screening Tool, Fahn, Tolosa, Marin Tremor Rating Scale), their neck, wrist, and ankle proprioception will be tested respectively. They they will go through the intervention of cervical vibrotactile stimulation. Lastly, their neck proprioception will be tested again.

Healthy people age- and sex- matched with participants with cervical dystonia will be in this group. This group will only be tested on their neck, wrist, and ankle proprioception, to compare with the cervical dystonia group.

The intervention in this study is vibrotactile stimulation with 3 different intensities on 4 combinations of cervical muscles. The three intensity levels are 0.25mm, 0.64mm, and 1.48mm of movement range of the vibrator, when attached to the cervical area. The four muscle combinations (left and right SCM, left and right TRP, left SCM and TRP, right SCM and TRP) are selected as they were shown to be more effective than other combinations in a previous studies. The total number of bouts of stimulation is 12 (3 intensities * 4 muscle combinations). Each VTS application is 2 minutes long, resulting in total stimulation time of 24 minutes. There will be a 5-minute break of no-vibration between each application of vibration.

During the intervention, the participant will remain seated and asked to not interfere voluntarily with dystonic muscle spasms. During breaks, they can adjust their head posture for their comfort. Extra breaks will be given if needed.

The primary outcome measure is the head angle index, which quantifies how much a participant's head posture deviates from a neutral upright position. There are three degrees of freedom for the neck joint (axial rotation, lateral bending, and flexion/extension). For each participant, the degree(s) of freedom with abnormality will be identified at baseline. For any time period during the experiment, the mean absolute neck angle in each abnormal degree of freedom will be calculated and normalized by the typical maximal range of motion in healthy individuals. These normalized values will be averaged to yield the Head Angle Index.

The secondary outcome measure is absolute position matching error, which quantifies the position sense acuity of the participants in each joint. For each tested joint, they will be given a set of target position. The joint will be passively rotated to the target position, and back to the starting position. The participant will then try to reproduce the target position, based on their memory of the position. After repeating for 9 times, the absolute value of the differences between the matched position and the target position will be averaged to get the absolute position matching error.