Safety and Acute Effects of tDCS on Vocal Performance in Adolescent Singers

Incidence and Severity of Treatment-Emergent Adverse Events Associated With Transcranial Direct Current Stimulation

Treatment-emergent adverse events will be assessed using a structured checklist documenting the presence and intensity of tingling/itching, warmth or burning sensation, skin redness, headache, dizziness, nausea, fatigue or drowsiness, visual symptoms, and other spontaneously reported symptoms. Symptoms present at baseline will be recorded, and an event will be considered treatment-emergent if it occurs after the start of stimulation or increases in intensity relative to baseline. For each event, severity will be categorized as none, mild, moderate, or severe. Stimulation interruptions, inability to complete the stimulation session, and adverse events requiring additional assessment or care will also be recorded. The number and proportion of participants experiencing each treatment-emergent adverse event, together with its severity, will be reported.

Change in Vocal Performance Scores

Vocal performances will be audiovisually recorded and evaluated by blinded independent expert raters using an adapted analytical vocal-performance rubric based on Gynnild (2015). The rubric evaluates Technique, Language/Text, Musicality, Ability to Communicate, and Choice of Repertoire. Performance grades range from A to F and are converted to numerical values from 5 to 0, with higher scores indicating better vocal performance. Because all participants perform the same standardized repertoire, the Choice of Repertoire domain will not contribute to the primary performance score. The primary vocal-performance score will be calculated as the mean of the four applicable domain scores (Technique, Language/Text, Musicality, and Ability to Communicate), each scored from 0 to 5, resulting in an overall mean score ranging from 0 to 5. Higher scores indicate better vocal performance. Changes over time will be compared between the active and sham groups.

Change in Vocal Performance Scores

Vocal performances will be audiovisually recorded and evaluated by blinded independent expert raters using an adapted analytical vocal-performance rubric based on Gynnild (2015). The rubric evaluates technique, language/text, musicality, ability to communicate, and choice of repertoire. Performance grades range from A to F and are converted to numerical values from 5 to 0, with higher scores indicating better vocal performance. Because all participants perform the same standardized repertoire, the choice-of-repertoire domain will not contribute to the primary performance score. The primary vocal-performance score will be calculated from the applicable rubric domains, and changes over time will be compared between the active and sham groups.

Change in Self-Reported Vocal Performance

Participants will rate their own vocal performance on a numerical rating scale from 0 to 10, where 0 represents the worst possible performance that day and 10 represents the best possible performance that day. Higher scores indicate better self-perceived vocal performance.

Change in Self-Reported Nervousness

Participants will rate their nervousness related to the vocal performance on a numerical rating scale from 0 to 10, where 0 represents no nervousness and 10 represents the highest level of nervousness experienced. Higher scores indicate greater self-reported nervousness.

Change in Self-Reported Confidence

Participants will rate their confidence regarding the vocal performance on a numerical rating scale from 0 to 10, where 0 represents no confidence and 10 represents the highest possible confidence. Higher scores indicate greater self-reported confidence.

Participant Perception of Intervention Allocation

Participants will report whether they believe they received active stimulation, sham stimulation, or whether they do not know which condition they received. Responses will be used to evaluate the effectiveness of participant blinding.