Table 3.
Summary of studies reviewed (*results which were marked significant changes in the study).
| Study characteristics |
Intervention |
Outcome |
||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Article | Study design | Sample size | Age (years) and description of the participant(s) | Intervention duration | Intervention content | Speech task | fo | Frequency and intensity range | Formant frequencies | Self-perception and satisfaction | Listener ratings | Level of evidence |
| Bralley et al. (1978) | Prospective | 1 | 49 Male transsexual |
7 sessions, one hour each | Increasing habitual pitch and pitch range, tasks ranging from production of a single monosyllable to conversational speech. Prevention of vocal abuse in the new mode of production was also of primary concern. | Conversational speech |
Habitual pitch in conversational speech (median) Pre: 145 Hz Post: 165 Hz* Fundamental frequency range during conversational speech: Pre: 30 Hz Post: 70 Hz* |
Pitch range: Pre: 100-425 Hz Post: no results |
N/A | The client expressed satisfaction with the results attained. More self confidence |
15 judges who were instructed to rate the voices on a l-to-7 scale (1 representing very masculine and 7 representing a very feminine). Control cis female and male samples were included. Pretreatment: 3.7, last session: 4.6* | V |
| Carew et al. (2007) | Prospective | 10 | 40 (25–64) Male-to-female transsexuals |
5 sessions, weekly, 45 minutes each | Targeting oral resonance: lip spreading and increased forward tongue carriage, ranging from isolated vowels to conversation, homework sheets. | The Rainbow Passage | Median pitch during the passage: Pre: 115.2 Hz Post: 129.3 Hz* Mean pitch during the passage: Pre: 119.4 Hz Post: 133.3 Hz* |
N/A | Extracted vowels /a/, /i/, and /ʊ/: Higher F1* during /a/ and /ʊ/, F2* during /a/ and F3* for all three vowels |
Higher femininity and higher satisfaction* Obtained by VASs |
8 speech pathology student raters, mixed results due to poor interrater reliability. 70% achieved general increases in the perception of femininity (VAS) | V |
| Dacakis (2000) | Retrospective | 10 | 44.5 (32.2–58) Male-to-female transsexuals |
10–90 sessions | Increasing the mean fundamental frequency, no further details. | 2 minutes of spontaneous speech (monologue) | Mean fundamental frequency: Pre: 125.5 Hz* Post: 168.1 Hz* Follow-up: 146.5 Hz* Significant correlation between number of interventions and maintenance of fo increase. |
N/A | N/A | Visual analogue scale (0–100, not at all satisfied – extremely satisfied) Mean results at discharge: 78 (52-100) Mean results at follow up: 80 (49-100) |
N/A | V |
| Gelfer and Tice (2013) | Prospective | 5 5 cis male and 5 cis female control participants, providing speech samples for analysis and listening experiment |
46.5 (42.5–52.3) Male-to-female (MTF) transgender (TG) clients |
15.4 sessions (8 weeks, two times a week, 60 minutes each) | Group therapy, starting with their target pitch on /m/, /n/, /l/, /r/-initiated consonant-vowel syllables to habituate their new SFF and help facilitate good oral resonance, building up to focusing on pitch, quality, intonation, and pitch range during sentences and spontaneous speech. | Isolated sustained vowels /a/, /i/, /u/, The Rainbow Passage, spontaneous speech, 10 semi spontaneous Q/A sets |
Semi-spontaneous Q/A sets (mean): Pre: 126 Hz* Post: 210 Hz* Follow-up: 171 Hz* Spontaneous speech: Pre: 119 Hz* Post: 178 Hz* Follow-up: 138 Hz* Rainbow Passage: Pre: 123 Hz* Post: 194 Hz* Follow-up: 155 Hz* |
N/A |
Semi-spontaneous Q/A sets: F1 /i/ Pre: 267 Hz Post: 335 Hz Follow-up: 280 Hz F2 /i/ Pre: 2373 Hz Post: 2562 Hz Follow-up: 2561 Hz F3 /i/ Pre: 3029 Hz Post: 2977 Hz Follow-up: 3140 Hz Higher F1 during sustained vowel /i/* No significant changes in sustained vowels /a/ and /u/ |
N/A | 5 cis male and 5 cis female control participants, 52 college students as listener participants. Female 1.9% of the time in pretest, 50.8% in immediate posttest, 33.1% in long-term posttest (15 months after termination of therapy). Perceived less masculine and more feminine in post tests*. | II |
| Gelfer and Van Dong (2013) | Prospective | 3 3 cis male and 3 cis female control participants, providing speech samples for analysis and listening experiment |
43.1 (32.11–50.5) Male-to-female (MTF) transgender (TG) clients |
12 sessions (6 weeks, 60 minutes each) | Individual therapy, targeting pitch by chanting syllables beginning with /m/, /n/, and /l/,…until spontaneous speech (Vocal Function Exercises, VFE), with a home protocol. | The Rainbow Passage, spontaneous speech, 10 semi spontaneous Q/A sets |
Semi-spontaneous Q/A sets (mean): Pre: 125 Hz Post: 183 Hz Spontaneous speech: Pre: 116 Hz Post: 153 Hz Rainbow Passage: Pre: 122 Hz Post: 177 Hz (no interferential statistics) |
N/A |
Semi-spontaneous Q/A sets: F1 /i/: Pre: 299 Hz Post: 353 Hz F2 /i/: Pre: 2189 Hz Post: 2323 Hz F3 /i/: Pre: 2640 Hz Post: 2987 Hz (no interferential statistics) |
Opinions on the effectiveness of the VFE home protocol, its ease of implementation, overall impressions of therapy. Scale of 1–5. They were generally positive about the addition of VFE to their therapy experience. | 3 cis male and 3 cis female control participants, 27 college students. Identified as male following therapy, although they were rated as less masculine and more feminine*. | II |
| Hancock and Helenius (2012) | Prospective | 1 | 15.3 Male-to-female transgender adolescent |
15 sessions (7 months) | Education and counseling concerning vocal hygiene, posture, breathing patterns. Increasing the habitual pitch and using a fuller sounding voice with more forward resonance and normal vocal quality. Slowing speech rate, blending phonemes, and using upward intonation patterns. characterized by consistent, unconstrained vocal tract. Therapy began with relaxation exercises and laryngeal massage followed by the voice goals. | Sustained vowel /a/, The Rainbow Passage, Cookie Theft Picture, spontaneous speech, four corner vowels in /hVd/, frequency range |
Sustained /a/ (mean): Pre: 205 Hz Post: 209 Hz Follow-up: 209 Hz Rainbow Passage (mean): Pre: 158 Hz Post: 204 Hz Follow-up: 204 Hz Cookie Theft Picture (mean): Pre: 141 Hz Post: 191 Hz Follow-up: 193 Hz Spontaneous speech (mean): Pre: 151 Hz Post: 172 Hz Follow-up: 169 Hz |
Frequency range during spontaneous speech: Pre: 98–330 Hz Post: 104–349 Hz Follow-up: 69–330 Hz Total frequency range: Pre: 87–880 Hz Post: 49–932 Hz Follow-up: 69–392 Hz |
Higher F1 and F2 for all vowels* Pre: between male and female Post: toward female values during treatment, except vowel /u/. |
TSEQ: Pre: 106/120 6 months later: 79/120 2 months after therapy ended: 53/120 Positive change in attitude and self-perception; an overall satisfaction. |
6 cis females and 4 cis males, VAS from masculine to feminine. Increase from 27 to 79 (increase of 192%) for Cookie Theft Picture, 31 to 72 for spontaneous speech (increase of 132%). |
V |
| Hancock and Garabedian (2013) | Retrospective | 25 | 43 (21–60) Male-to-female transgender individuals |
22 sessions (2–77 session, typically once a week) | Increasing fundamental frequency, intonation, resonance, vocabulary, pragmatics, non-verbal communication, reduce phonotraumatic behaviors, vocal hygiene, relaxation techniques and respiration, homework included. | Sustained vowel /a/, The Rainbow Passage, frequency range, spontaneous speech |
Sustained /a/ (mean): Pre: 136 Hz* Post: 184 Hz* Rainbow Passage (mean): Pre: 124 Hz* Post: 156 Hz* Spontaneous speech (mean): Pre: 122 Hz* Post: 150 Hz* |
Total frequency range: Pre: 90–465 Hz Post: 88–579 Hz |
N/A | TSEQ: insufficient data, only 4/25 completed the questionnaire at the start and end. Three increased, one remained stable | N/A | V |
| Kalra (1978) | Prospective | 1 | 27 Morphological male transsexual who became a female |
3 months, weekly session of 45 minutes | Pitch elevation: exercises which reinforced resonance and maintained a balance between the vocal generator and supraglottal resonators. As new pitch levels were acquired, Froeschel’s chewing method was used to increase anterior oral resonance. Reducing clavicular breathing patterns and lessen pharyngeal tension. | Spontaneous speech, automatic speech tasks, chewing |
Chewing (mean): Pre: 180 Hz Post: 200 Hz Follow-up: 190 Hz Days of the week while chewing (mean): Pre: 180 Hz Post: 196 Hz Follow-up: 185 Hz Months of the year while chewing (mean): Pre: 160 Hz Post: 190 Hz Follow-up: 185 Hz Spontaneous speech (mean): Pre: 153 Hz Post: 198 Hz Follow-up: 200 Hz No statistical data |
N/A | N/A | N/A | N/A | V |
| Kawitzky and McAllister (2020) | Prospective | 12 19 cis men as control participants |
45.2 (21–71) Transgender women |
1 session | Increasing F2 through biofeedback. Vowels /ae/, /ʌ/, and /ɑ/ were target vowels, into the context of real words, surrounded by voiced plosives. Three conditions: unshifted, shifted-up and shifted down position. Participants were informed of two strategies they might use to manipulate the location ofthe peak: (a) changing the positioning of the tongue in the mouth, and (b) changing the shape of the lips. | Vowels /ae/, /ʌ/, and /ɑ/, target words bud/bad/bod | Fundamental frequency during target words: visual inspection of boxplots does not indicate any reliable patterns of fo differences across conditions. | N/A |
F1: Some differences were observed between shifted-up, shifted-down, and unshifted target conditions, but were generally small in magnitude and showed no clear pattern across vowel targets. Shifted-down was lower dan unshifted*, but shifted-up was not higher than unshifted. F2: Differed consistently across elicitation conditions. Higher F2 during shifted-up*, lower F2 during shifted-down*. F3: No differences between conditions. |
N/A | 26 blinded naïve raters on VAS (definitely male to definitely female). Higher F2 or fo values received higher perceptual ratings of femininity. Best to combine both. Combining F1 or F3 with fo yielded higher femininity ratings* but not on their own. |
II |
| Kaye et al. (1993) | Prospective | 1 | 44 Male-to-female transsexual subject |
12 sessions, 60 minutes each | Raising fundamental frequency, while ensuring that the procedures would not cause laryngeal strain. Correct sound production and resonance were also emphasized. | First two sentences of The Rainbow Passage |
Mean during reading: Pre: 101 Hz Post: 135 Hz Frequency range during reading: Pre: 21 Hz Post: 31 Hz |
N/A | N/A | N/A | 2 cis male, 2 cis female, 1 trans male control participants, 40 student listeners. Two 5-point equal interval rating scales: femininity and masculinity. Perceived as less masculine* and more feminine* after the therapy, even though never labeled as a female. |
V |
| Mészáros et al. (2005) | Prospective | 3 | 23 (20–26) Male-to-Female transsexuals |
9.6 months (8–19 months, one session a week) | Developing a female pitch, high-pitch vocalization by using the first articulation zone, a costo-abdominal breathing technique, decreasing laryngeal muscle tension, and to increase head resonance as compared to chest resonance. Attention was paid to the formation of soft tones, precise articulation and the attainment of a female intonation. | The North Wind and The Sun, voice range profile | Habitual pitch during the North Wind and The Sun (mean of three participants): Pre: 150.6 Hz Post: 191.3 Hz No statistical data |
Pitch range diminished on average, as evidenced by an elevation in the lower limit of the pitch range. The vocal intensity range reached normal values. | N/A | The degree to which the person’s voice could be used for communication, a subjective scale, 0 = no limitations, 1 = limited communication only in the case of voice loading, 2 = a moderate degree of constant limitation, and 3 = constant severe limitation in everyday communication. All participants went from 3 to 0. | N/A | V |
| Mount and Salmon (1988) | Prospective | 1 | 63 Male-to-female transsexual |
88 sessions (60 minutes each, over 11 months period) | Higher pitch levels while avoiding vocal abuse, and modify tongue carriage to achieve higher resonance characteristics of the vocal tract. Additional: promote a breathy vocal attack, and establish appropriate inflection patterns at higher pitch levels. Homework included. | Conversational speech, sustained vowels, audio and video recorded. |
Sustained vowel /i/ (mean): Pre: 110 Hz Post: 195 Hz Follow-up: 235 Hz Sustained vowel /a/ (mean): Pre: 110 Hz Post: 210 Hz Follow-up: 230 Hz Sustained vowel /u/ (mean): Pre: 110 Hz Post: 210 Hz Follow-up: 200 Hz No statistical data |
N/A |
Pre – post - follow-up (after 5 years): F1 during /i/: 222-278-371 Hz F1 during /a/: 606-829-955 Hz F1 during /u/: 277-322-389 Hz F2 during /i/: 2092-2383-2389 Hz F2 during /a/: 1053-1147-1191 Hz F2 during /u/: 810-1065-1168 Hz F3 during /i/: 3467-3505-3363 Hz F3 during /a/: 2331-2718-2853 Hz F3 during /u/: 1944-2458-2151 Hz No statistical data |
N/A | N/A | V |
| Quinn and Swain (2018) | Prospective | 1 | 17 Transgender individual |
2 60 minutes sessions a day, for two weeks | Vocal health and flexibility, pitch raising through Stemple’s Vocal Function Exercises, oral resonance target through the Katherine Verdolini’s Lessac-Madsen Resonant Voice Therapy program (focus on lip spreading and anterior tongue carriage). Additional: vocal education (gentle onsets), feminine intonation patterns. Homework included. | The Rainbow Passage, The Grandfather Passage, spontaneous speech, frequency range during reading |
Rainbow Passage (mean): Pre: 145 Hz Post: 179 Hz Grandfather Passage (mean): Pre: 146 Hz Post: 166 Hz Spontaneous speech (mean): Pre: 143 Hz Post: 144 Hz No statistical data |
Rainbow Passage: Pre: 73 Hz Post: 80 Hz Grandfather Passage: Pre: 73 Hz Post: 81 Hz Spontaneous speech: Pre: 75 Hz Post: 78 Hz No statistical data |
N/A |
Self-rated femininity and satisfaction (VAS of 10 cm): increase during voice intervention phase and after ceasing intervention (reading and spontaneous speech)*. TVQ: Pre: 100/120 Post: 81/120 Short interview concerning their experiences completing the program: 9/10 on the usefulness of the therapy program, and 7/10 to what degree of change they perceived in their voice. |
7 external raters evaluated femininity (VAS of 10 cm): increase in femininity during voice intervention phase*. Oral resonance was found to have no additional statistically significant impact on outcomes. More feminine in reading than spontaneous speech. No statistically significant difference between listener and self-ratings*. |
V |
| Söderpalm et al. (2004) | Retrospective | 21 | 40 Male-to-female transsexual individuals |
17 sessions (3–45), 45–60 minutes each | Vocal hygiene exercises, pitch raising exercises by gradual climbing, ‘gliding’, precise and more anterior articulation. | A Difficult Case, sustained vowels, interview | Less than half the patients produced a fundamental frequency above 155 Hz at the end of therapy but ten patients had reached this level at follow-up. There was an increase of 20 Hz for 10 patients between baseline and follow-up measures of fundamental frequency*. Increase in mean fundamental frequency is greater for those with more than 14 sessions. |
N/A | N/A | VAS of 10 cm (masculinity/femininity): Pre: 6.6 Follow-up: 8 |
N/A | V |