Percentage of syllables stuttered (%SS) was calculated as the number of stuttered syllables divided by the total number of syllables produced, multiplied by 100. Repetitions, prolongations, syllable repetitions, tense pauses and pre-speech sound blocking were defined as moments of disfluency. Whole-word and whole-phrase repetitions were included in the total syllable count but were not counted as stuttered syllables.Video recordings have been used in assessment procedures and pre-speech sound blocking identified by postural fixations. For both reading and speaking measures, the first 300 syllables were used for analysis (syllable count ranged from 139-490 syllables).

It measures stuttering severity in the following four areas of speech behavior: (1) frequency, (2) duration, (3) physical concomitants, and (4) naturalness of the individual's speech. Frequency is expressed in percent syllables stuttered and converted to scale scores of 2-18. Duration is timed to the nearest one tenth of a second and converted to scale scores of 2-18. The four types of Physical Concomitants (Distracting Sounds, Facial Grimaces, Head Movements, and Movements of the Extremities) are converted to scale scores of 0-20. Naturalness is ranked on a scale from 1 (Highly Natural Sound Speech) to 9 (Highly Unnatural Sound Speech). Overall naturalness is ranked at the discretion of the clinician. Scaled scores of Frequency, Duration, and Physical Concomitants are added together to derive a Total Score, Percentile Rank, and Severity Equivalent.

The Overall Assessment of the Speaker's Experience of Stuttering - Adult Version (OASES-A) is a self-assessment instrument that requires approximately 20 minutes to complete and is organized into four sections: General Information, Reactions to Stuttering, Communication in Daily Situations, and Quality of Life. It consists of 100 items scored on a 5-point Likert scale ranging from 1 to 5. For each item, higher scores indicate a greater negative impact of stuttering, while lower scores indicate less impact. Impact scores for each section range from a minimum of 20 (if the respondent answers 1 for every item) to a maximum of 100 (if the respondent answers 5 for every item). The total score ranges from 100 (minimum) to 500 (maximum), with higher scores indicating a greater negative impact of stuttering. Scores are reported as scores on a scale.

The Overall Assessment of the Speaker's Experience of Stuttering - Adult Version (OASES-A) is a self-assessment instrument that requires approximately 20 minutes to complete and is organized into four sections: General Information, Reactions to Stuttering, Communication in Daily Situations, and Quality of Life. It consists of 100 items scored on a 5-point Likert scale ranging from 1 to 5. For each item, higher scores indicate a greater negative impact of stuttering, while lower scores indicate less impact. Impact scores for each section range from a minimum of 20 (if the respondent answers 1 for every item) to a maximum of 100 (if the respondent answers 5 for every item). The total score ranges from 100 (minimum) to 500 (maximum), with higher scores indicating a greater negative impact of stuttering. Scores are reported as scores on a scale.

Total of all reporting groups

Race and Ethnicity were not collected from any participant.

One passage was selected from eleven passages in the 2019-2020 Turkish Ministry of National Education curriculum per session. Participants read while video recorded. A speech-language pathologist analyzed the recordings. Repetitions, prolongations, syllable repetitions, tense pauses, and pre-speech blocking were counted as disfluencies. Whole-word and whole-phrase repetitions were included in total syllables but not as stuttered. Pre-speech blocking was identified via postural fixations. %SS = stuttered syllables ÷ total syllables ×100. The first 300 syllables were analyzed (range: 139-490).

Two of three pre-determined topics were selected based on participant interests. Participants spoke while video recorded. A speech-language pathologist analyzed the recordings. Repetitions, prolongations, syllable repetitions, tense pauses, and pre-speech blocking were counted as disfluencies. Whole-word and whole-phrase repetitions were included in total syllables but not as stuttered. Pre-speech blocking was identified via postural fixations. %SS = stuttered syllables ÷ total syllables ×100. The first 300 syllables were analyzed (range: 139-490).

The Stuttering Severity Instrument-Fourth Edition (SSI-4) (Riley, 2009) was used to assess overall stuttering severity. Participants completed reading and spontaneous speech tasks that were video recorded and scored by a trained speech-language pathologist according to standardized SSI-4 procedures. The total SSI-4 score is calculated by summing scores for frequency of stuttering events, duration of the three longest events, and physical concomitants. Total scores range from 4 to 56, with higher scores indicating more severe stuttering (worse outcome).

Participants were video recorded during reading and spontaneous speech tasks. A trained speech-language pathologist identified stuttering events, including repetitions, prolongations, and blocks. The duration of the three longest stuttering events was measured in seconds using video playback tools. Average duration was calculated by summing the three longest events and dividing by three. Longer durations indicate more severe stuttering.

Participants were video recorded during reading and spontaneous speech tasks. A trained speech-language pathologist evaluated physical concomitants, including head movements, disturbing sounds, facial expressions, and hand and foot movements. Each behavior was scored from 0 (none) to 5 (severe). Total score was calculated by summing individual item scores. Higher scores indicate more pronounced physical involvement accompanying stuttering.

Participants were video recorded during reading and spontaneous speech tasks. A trained speech-language pathologist rated speech naturalness using a 9-point Likert scale, where 1 represents extremely natural speech and 9 represents extremely unnatural speech. Ratings were based on prosody, rhythm, speech rate, and smoothness. Lower scores indicate more natural speech (better outcome).

The Overall Assessment of the Speaker's Experience of Stuttering - Adult Version (OASES-A) is a self-assessment instrument used to evaluate the psychosocial impact of stuttering. The total score is calculated by summing responses across all four domains: general perceptions of stuttering, reactions to stuttering, communication difficulties in daily situations, and quality of life. Each item is rated on a 5-point Likert scale. Total OASES-A scores range from 100 to 500, with higher scores indicating a greater negative impact of stuttering and representing a worse outcome.

This domain includes 20 items about the individual's perception of stuttering. Participants rate statements on a Likert scale from 1 (least negative) to 5 (most negative). Domain score was calculated by summing item scores according to OASES-A guidelines. Total scores range from 20 to 100, with higher scores indicating more negative perceptions.

This domain includes 30 items related to the speaker's affective, behavioral, and cognitive reactions to the act of stuttering. Participants rate each item on a Likert scale from 1 (least negative) to 5 (most negative), with higher scores indicating stronger negative reactions. Domain score was calculated by summing item scores according to OASES-A guidelines. Total scores range from 30 to 150.

This domain includes 24 items assessing the speaker's communication in daily settings. Participants rate each item on a Likert scale from 1 (least difficulty) to 5 (most difficulty), with higher scores indicating greater communication difficulties. Domain score was calculated by summing item scores according to OASES-A guidelines. Total scores range from 24 to 120.

This domain includes 25 items evaluating the impact of stuttering on social, emotional, and occupational aspects of life. Participants rate each item on a Likert scale from 1 (least negative impact) to 5 (most negative impact), with higher scores indicating greater negative impact. Domain score was calculated by summing item scores according to OASES-A guidelines. Total scores range from 25 to 125.

In the sham condition, the same electrode placement will be used, during which the current will be increased for 15 seconds, kept at 1 mA for 15 seconds, decreased for 15 seconds and terminated, and the 20 minute session duration will be performed with 45 seconds of real stimulation accompanied by speech with a metronome.

Percentage of syllables stuttered (%SS) was calculated as the number of stuttered syllables divided by the total number of syllables produced, multiplied by 100. Repetitions, prolongations, syllable repetitions, tense pauses and pre-speech sound blocking were defined as moments of disfluency. Whole-word and whole-phrase repetitions were included in the total syllable count but were not counted as stuttered syllables.Video recordings have been used in assessment procedures and pre-speech sound blocking identified by postural fixations. For both reading and speaking measures, the first 300 syllables were used for analysis (syllable count ranged from 139-490 syllables).

Percentage of syllables stuttered (%SS) was calculated as the number of stuttered syllables divided by the total number of syllables produced, multiplied by 100. Repetitions, prolongations, syllable repetitions, tense pauses and pre-speech sound blocking were defined as moments of disfluency. Whole-word and whole-phrase repetitions were included in the total syllable count but were not counted as stuttered syllables.Video recordings have been used in assessment procedures and pre-speech sound blocking identified by postural fixations. For both reading and speaking measures, the first 300 syllables were used for analysis (syllable count ranged from 139-490 syllables).

Percentage of syllables stuttered (%SS) was calculated as the number of stuttered syllables divided by the total number of syllables produced, multiplied by 100. Repetitions, prolongations, syllable repetitions, tense pauses and pre-speech sound blocking were defined as moments of disfluency. Whole-word and whole-phrase repetitions were included in the total syllable count but were not counted as stuttered syllables.Video recordings have been used in assessment procedures and pre-speech sound blocking identified by postural fixations. For both reading and speaking measures, the first 300 syllables were used for analysis (syllable count ranged from 139-490 syllables).

The Stuttering Severity Instrument - Fourth Edition (SSI-4) is a standardized tool measuring stuttering severity based on three components: frequency of stuttering, duration of the three longest stuttering events, and physical concomitants. Each is converted to scaled scores-frequency and duration range from 2 to 18, and physical concomitants from 0 to 20-and summed to produce a Total Score ranging from 4 to 56, where higher scores indicate more severe stuttering. Speech naturalness is assessed separately on a 9-point scale (1 = highly natural, 9 = highly unnatural) and is not included in the Total Score. Scores are reported in scores on a scale.

It measures stuttering severity in the following four areas of speech behavior: (1) frequency, (2) duration, (3) physical concomitants, and (4) naturalness of the individual's speech. Frequency is expressed in percent syllables stuttered and converted to scale scores of 2-18. Duration is timed to the nearest one tenth of a second and converted to scale scores of 2-18. The four types of Physical Concomitants (Distracting Sounds, Facial Grimaces, Head Movements, and Movements of the Extremities) are converted to scale scores of 0-20. Naturalness is ranked on a scale from 1 (Highly Natural Sound Speech) to 9 (Highly Unnatural Sound Speech). Overall naturalness is ranked at the discretion of the clinician. Scaled scores of Frequency, Duration, and Physical Concomitants are added together to derive a Total Score, Percentile Rank, and Severity Equivalent.

The Overall Assessment of the Speaker's Experience of Stuttering - Adult Version (OASES-A) is a self-assessment instrument that requires approximately 20 minutes to complete and is organized into four sections: General Information, Reactions to Stuttering, Communication in Daily Situations, and Quality of Life. It consists of 100 items scored on a 5-point Likert scale ranging from 1 to 5. For each item, higher scores indicate a greater negative impact of stuttering, while lower scores indicate less impact. Impact scores for each section range from a minimum of 20 (if the respondent answers 1 for every item) to a maximum of 100 (if the respondent answers 5 for every item). The total score ranges from 100 (minimum) to 500 (maximum), with higher scores indicating a greater negative impact of stuttering. Scores are reported as scores on a scale.

The Overall Assessment of the Speaker's Experience of Stuttering - Adult Version (OASES-A) is a self-assessment instrument that requires approximately 20 minutes to complete and is organized into four sections: General Information, Reactions to Stuttering, Communication in Daily Situations, and Quality of Life. It consists of 100 items scored on a 5-point Likert scale ranging from 1 to 5. For each item, higher scores indicate a greater negative impact of stuttering, while lower scores indicate less impact. Impact scores for each section range from a minimum of 20 (if the respondent answers 1 for every item) to a maximum of 100 (if the respondent answers 5 for every item). The total score ranges from 100 (minimum) to 500 (maximum), with higher scores indicating a greater negative impact of stuttering. Scores are reported as scores on a scale.

The same electrode placement was used in the sham stimulation study arm, during which the current was increased for 15 seconds, held at 1 mA for 15 seconds and decreased for 15 seconds at the beginning of the session. The 20-minute session duration was 45 seconds of real stimulation accompanied by metronome speech.