Vocal Sound Pressure Level and Self-Perception of Speech and Voice in Men and Women With Idiopathic Parkinson Disease
Publication: American Journal of Speech-Language Pathology
Volume 6, Number 2
Pages 85-94
Abstract
This study compared vocal sound pressure level (SPL) and self-perception of speech and voice in men and women with idiopathic Parkinson disease (PD) and in healthy men and women. Thirty subjects with PD (15 men, 15 women) and 14 healthy comparison (HC) subjects (7 men, 7 women) participated in the study. They performed a variety of speech and voice tasks and carried out perceptual self-ratings of nine speech and voice characteristics. To assess performance stability, subjects repeated the data collection procedures on 3 different days. Results revealed that subjects with PD were statistically significantly lower in vocal SPL (2.0–4.0 dB SPL; 30 cm) during speech and voice tasks than HC subjects. Repeated measures across sessions revealed that subjects with PD were not significantly more unstable than HC subjects in their day-to-day performance for all variables examined. In addition, subjects with PD rated themselves as statistically significantly more severely impaired than HC subjects on all nine self-rated perceptual variables examined. These data provide additional descriptive information on speech and voice characteristics in people with PD and may be useful in assessment and treatment planning for this population.
Parkinson disease (PD) is a degenerative condition resulting from a nigrostriatal dopamine deficiency (Hornykiewicz, 1966; Hornykiewicz & Kish, 1986). Approximately 75% of people with PD have speech and voice characteristics that affect their communication abilities (Canter, 1965; Hartelius & Svensson, 1994; Logemann, Fisher, Boshes, & Blonsky, 1978; Ramig, Bonitati, Lemke, & Horii, 1994). Perceptual characteristics, such as reduced loudness, reduced pitch variability, imprecise articulation, and rate disturbances have been reported frequently (Critchley, 1981; Darley, Aronson, & Brown, 1969a, 1969b); however, corresponding acoustic descriptions remain incomplete. In addition, descriptive variables, such as self-perception of speech and voice, and sex-related differences have not been considered. The purpose of this study was to describe vocal SPL and self-perception of speech and voice in order to provide a more comprehensive understanding of speech and voice characteristics in people with PD. These descriptive data may be of clinical value in assessment and treatment planning for this population.
The acoustic variable of vocal SPL, as a measure of vocal loudness, is of particular interest. Recently, a speech treatment program that focuses on increasing vocal loudness in people with PD has been developed (Ramig et al., 1994). Efficacy data from this program, referred to as the Lee Silverman Voice Treatment (LSVT), has documented increased vocal SPL in subjects with PD who received the LSVT (Countryman, Ramig, & Pawlas, 1994; Dromey, Ramig, & Johnson, 1995; Ramig, 1992, 1995; Ramig et al., 1994; Ramig, Countryman, O’Brien, Hoehn, & Thompson, 1996; Ramig, Countryman, Thompson, & Horii, 1995; Ramig & Dromey, 1996). Although reduced vocal loudness is a commonly reported perceptual characteristic in people with PD (Critchley, 1981; Logemann et al., 1978), results from studies of vocal SPL have been inconsistent in their findings. Some studies have demonstrated reduced vocal SPL among subjects with PD during reading tasks (Illes, Metter, Hanson, & Iritani, 1988), whereas others have shown no difference between subjects with PD and healthy comparison (HC) subjects during reading tasks or production of monosyllables (Boshes, 1966; Canter, 1963, 1965; Metter & Hanson, 1986). Given that the LSVT has documented increased vocal SPL in subjects with PD posttreatment, it is of considerable interest to compare vocal SPL between people with PD and healthy individuals.
The explanation for differences in findings among previous studies of vocal SPL is unclear. It is important to note, however, that each of the studies included a limited sampling of speech and voice performance abilities. Samples were collected using either repetition of monosyllables or reading (Boshes, 1966; Canter, 1963, 1965; Illes et al., 1988; Metter & Hanson, 1986). In an effort to clarify whether group differences in vocal SPL exist between subjects with PD and HC subjects, it may be important to elicit a range of speech and voice abilities by sampling a variety of speech and voice tasks. Such tasks could include those used commonly for assessment and training as well as tasks that may be more representative of typical conversational speech.
People with PD have been reported to be variable in their speech and voice performance abilities, especially when they are in clinical testing situations (Weismer, 1984). In addition, the potential for variability may increase when tasks are effort-dependent, such as maximum duration sustained vowel phonation tasks (Kent, Kent, & Rosenbek, 1987; King, Ramig, Lemke, & Horii, 1994). By examining day-to-day performance through repeated data collection sessions, the magnitude and nature of instability of speech and voice performance exhibited by people with PD could be assessed. Understanding this potential for instability would be important for clinical assessment of people with PD. If large day-to-day fluctuations exist, clinicians may need to consider assessing people with PD on more than one day to assure an accurate sampling of speech and voice performance abilities.
Clinical observations of subjects with PD would suggest they have an impaired perception of their own speech and voice abilities. When “soft speaking” subjects with idiopathic PD are questioned about their reduced loudness, a common reply is to say that their loudness is fine, but their spouse has a hearing loss. It has been suggested that impaired self-perceptions are not due to peripheral mechanisms, such as the auditory system, but may be related to an impaired ability to judge self-effort in relation to motor tasks (Solomon, Robin, Lorell, Rodnitzky, & Luschei, 1994). In addition, in a study of perception of dysarthria in subjects with PD, Yorkston, Bombardier, and Hammen (1994) reported that some subjects with PD may not have a full awareness of the extent of their disability. Information regarding how people with PD perceive their speech and voice abilities could be useful in treatment planning. If people with PD do not recognize deficits, such as reduced vocal loudness, they may not be motivated for treatment. Therefore, increasing awareness of such deficits may be a critical component to treatment success.
Sex differences in areas other than speech and voice, such as levels of motor activity (Pantelatos & Fornadi, 1993) and duration of disease in young onset PD (Van Hilten et al., 1993), have been reported in people with PD. However, the literature on speech and voice in people with PD has given little attention to sex differences, and existing speech and voice data are primarily from men (Canter, 1965; Forrest, Weismer, & Turner, 1989; Kent et al., 1994; Metter & Hanson, 1986; Ramig et al., 1994; Solomon & Hixon, 1993). A few studies of speech and voice characteristics of people with PD have reported sex differences in laryngeal phonetic function for speech intelligibility (Kent et al., 1994) and in subharmonic energy in vowel production (Hertrich & Ackermann, 1995).
Given that sex differences have been identified in various aspects of PD and in some speech and voice characteristics, examination of sex differences related to vocal SPL and self-ratings of perceptual characteristics is warranted. This information may provide additional insights into the role sex plays in speech and voice data of people with PD. Clinically, awareness of sex differences may be useful for generalization of speech and voice data across men and women with PD. In addition, sex may influence treatment planning if men and women with PD are differentially affected in their speech and voice abilities.
The present study was designed to examine vocal SPL and self-rated perceptual speech and voice characteristics of men and women with PD compared to healthy men and women. Variables examined included vocal SPL in various speech and voice tasks, duration of maximum sustained vowel phonation, and self-rated perceptual characteristics pertaining to speech and voice. Each subject repeated the data collection procedure on 3 different days within a 4-day period. Group, sex, and day-to-day stability were examined for all tasks.
Methods
Subjects
Forty-four subjects from Southern Arizona volunteered to participate in this study. Subjects were recruited primarily from a local Parkinson disease support group and by referral from community neurologists. Thirty subjects with idiopathic PD (15 men, 15 women) and 14 HC subjects (7 men, 7 women) were included. Mean ages of the men and women with PD were 72.5 years (SD = 8.7) and 66.7 years (SD = 11.2), respectively. Mean ages of the men and women in the HC group were 71.7 years (SD = 7.5) and 67.9 years (SD = 7.5), respectively. A one-way analysis of variance revealed no significant differences (α = .05) in age among the four groups (F(3, 40) = 1.16, p = .34).
Subjects with PD did not demonstrate any speech and voice features that were uncharacteristic of PD. The most common speech and voice characteristics displayed by subjects with PD, based on clinical observation by the experimenters, included reduced vocal loudness, hoarseness, and monotone speech. Additional speech and voice characteristics observed in some subjects included imprecise articulation and, in one subject, palilalia. Subjects’ speech and voice abilities ranged from exhibiting very mild signs of dysarthria to severe dysarthria in 3 subjects. However, the majority of subjects were in the mild to moderate range of severity of speech signs. None of the subjects with PD had a history of speech-language treatment prior to participation in the study. In addition, subjects with PD did not report significant cognitive changes in relation to their disease. Cognitive function was not formally tested.
Subjects with PD were examined on additional variables, such as time postdiagnosis and stage of PD (Hoehn & Yahr, 1967). This information was taken from each subject’s most recent medical records provided by his or her neurologist or, if the subject did not have a neurologist, by the primary care physician. Subjects ranged in time postdiagnosis from 1.5 to 20 years with a mean of 8.0 years (SD = 4.9) for men, and 6 months to 19 years with a mean of 7.0 years (SD = 6.3) for women. An independent groups t test revealed no significant difference between men and women with PD for the variable time postdiag-nosis; t(28) = −0.50, p = −.62.
Stage of disease was determined using the Hoehn & Yahr scale (1967), which categorizes severity of PD into five stages ranging from Stage I, being the least impaired, to Stage V, being the most severely impaired. Stage of disease was available for 10 men and 10 women with PD; thus, significance testing was based on n = 20. Stage of disease ranged from 2.0 to 5.0 with a mean of 2.85 (SD = 1.0) for men, and 1.0 to 4.0 with a mean of 2.40 (SD = 0.8) for women. An independent groups t test revealed no significant difference between men and women with PD for the variable stage of disease; t(18) = −1.11, p = .28.
All subjects with PD were taking anti-Parkinson medications at the time of data collection and did not change medications during this period. Subjects were not always seen at the same time in their medication cycle due to the logistics of scheduling the sessions. Given that medication has been documented to have a limited effect on speech and voice in people with PD (Hanson, Gerratt, & Ward, 1984; Larson, Ramig, & Scherer, 1988, 1994; Solomon & Hixon, 1993), this was judged not to be of great concern. The experimenters recorded the time of each subject’s last medication and next medication at the beginning of each session for reference in the event that large or unusual variability was observed in a subject’s performance from session to session.
HC subjects were free of any known condition that could affect their speech or voice, including neurological disease, speech or voice complaints, or a history of speech-language disorders. This information was determined from screening questions asked during the recruitment process and the initial interview of subjects before data collection procedures.
Videolaryngostroboscopic examinations of the larynx were performed by an otolaryngologist prior to subjects’ participation in the study. This confirmed that both the subjects with PD and HC subjects were free of any laryngeal pathology, such as vocal nodules, polyps, or gastric reflux.
Procedures and Equipment
Each subject participated in three data collection sessions within a 4-day period. Sessions consisted of recording a variety of speaking and voice tasks and completion of a self-rated perceptual scale.
Audio recordings were made with subjects seated in a sound-treated booth. A head-mounted microphone (AKG C410) was fitted to each subject’s head with mouth-to-microphone distance of 6 cm remaining constant throughout the session. A sound-level meter (SLM, Bruel & Kjär 2236) was placed 30 cm in front of the subject’s lips and maintained at that distance throughout the recording session. The microphone and SLM signals were recorded onto a digital audio tape (DAT) 8-channel recorder (Sony PC-208AUC). In addition, the experimenter hand-recorded the peak vocal SPL measures, which were continuously displayed at 1-s intervals from the digital output of the SLM during all speaking and voice tasks. The same experimenter collected all the handwritten vocal SPL data.
Calibration signals were recorded onto the DAT tapes for each subject prior to the recording of speaking and voice tasks and following any adjustments of input levels on the DAT recorder. Standard procedures for recording calibration signals were followed (tone generator and sustained phonation). The distance for calibration signals and all tasks was 30 cm. This distance was monitored constantly throughout the recording session.
Speech and Voice Tasks
To evaluate a range of speech and voice performance abilities, vocal SPL was recorded during four speech and voice tasks. Tasks included commonly used assessment and training tasks, such as maximum duration sustained vowel phonation and reading. In addition, monologue and picture description, which may be more representative of typical conversational speech, were included. Task requirements and instructions were as follows:
Maximum Duration Sustained Vowel Phonation.
Six maximum duration sustained vowel phonations were elicited, four at the beginning of the recording session and two at the end. Subjects were instructed to “take a deep breath and say ‘ah’ for as long as you can.” A clock with a second hand was provided for the subjects to watch, and each subject was encouraged to monitor his or her performance. No instructions for loudness level were given for this task. To facilitate interpretation of vocal SPL as it relates to respiratory and laryngeal interactions in sustained vowel phonation, duration (in seconds) of maximum sustained vowel phonation also was recorded.
Reading.
Subjects were asked to read aloud a phonetically balanced paragraph, “The Rainbow Passage” (Fairbanks, 1960), at a comfortable pitch and loudness level. The reading passage was in large type and placed on a music stand in front of the subjects at a comfortable reading distance.
Monologue.
Samples of spontaneous speech were obtained by asking the subjects to “Give me 30 seconds of monologue on a topic of your choice.” If the subject could not generate a topic, the experimenter provided a cue, such as “Tell me about what you are doing today” or “Tell me about a memorable vacation.” No instructions were given for loudness level.
Picture Description.
Subjects were asked to describe a standard picture, the “Cookie Theft” picture (Goodglass & Kaplan, 1983). The picture was placed on a music stand in front of subjects at a visually comfortable distance. Subjects were instructed to describe the picture for 30 seconds. No instructions for loudness level were given.
Perceptual Self-Rating Task
Subjects were asked to complete a perceptual self-rating scale at each of the three recording sessions. A visual analog scale (Kempster, 1984; Schiffman, Reynolds, & Young, 1981) was used to obtain subject self-ratings on nine variables related to voice (loudness, shakiness, hoarseness, monotone), speech (slur, mumble), and spoken communication (understood by others, participate in conversation, and start conversation). The scale required the subjects to indicate how they perceived their speech to be “most of the time.” Subjects placed a slash through a solid horizontal line that represented a continuum ranging from complete presence of a characteristic, “My voice is always loud enough,” to complete absence of a characteristic, “My voice is never loud enough.” Written instructions were provided for the task. In addition, verbal instructions were provided to further clarify that subjects should rate their own perception of their speech and voice, not their perception of how others, such as spouses, perceive their speech and voice. Any questions subjects had regarding the perceptual rating form were answered by the experimenters. A complete description of this scale has been provided elsewhere (Ramig, 1992; Ramig, Pawlas, & Countryman, 1995). All subjects were able to complete this task on their own.
Data Analysis
Vocal SPL means were calculated using the continuously hand-recorded peak vocal SPL that was displayed at 1-s intervals from the digital output of the SLM during all speech and voice tasks. Given that peak vocal SPL could only be recorded from the SLM during speech output, pauses and hesitations were not included in the analysis. Mean vocal SPL measures derived from hand-recorded second-to-second peak vocal SPL have been reported to be comparable to mean vocal SPL measures derived from a custom-built software program (Countryman & Ramig, 1993; Ramig, Countryman, et al., 1995). Because the computer program incorporates the entire contour of SPL and the hand-recorded method incorporates peak vocal SPL sampled at 1-s intervals, the latter method generates data approximately 1 to 2 decibels greater than the computer method of analysis. Given the large sampling of vocal SPL in this study and the validity of the SPL output from a high quality SLM, use of the hand-recorded peak vocal SPL at 1-s intervals was the preferred method for deriving vocal SPL means. This method of analysis was used for both subject groups and thus would not affect comparisons between groups and tasks.
The vocal SPL means (and SDs) for the maximum sustained vowel phonation task were derived by calculating the mean vocal SPL of the six individual maximum vowel phonations elicited at each session. These data were then used to calculate the overall mean vocal SPL for the maximum sustained vowel phonation task for the three recording sessions. The vocal SPL means (and SDs) for the reading passage, monologue, and picture description were derived by calculating the mean vocal SPL for each speech task for all three recording sessions.
Duration of maximum sustained vowel phonation was analyzed using a custom-built software program employing standard procedures (Ramig, Countryman, et al., 1995). The mean duration was analyzed for the six individual maximum sustained vowel phonations elicited at each session. These data were then used to calculate an overall mean duration of the maximum sustained vowel phonation task for the three recording sessions.
Standard procedure for analysis of visual analog scales was used to examine perceptual data (Boeckstyns & Backer, 1989). The line representing the continuum of presence or absence of a characteristic was measured. The distance of the subject’s slash on the line from one end of the continuum was measured and calculated into a percentage based on the total distance of the line. This percentage represented subjects’ self-perceived presence of a particular characteristic in their speech and voice “most of the time.”
Reliability
Intrasubject reliability was calculated for all measures examined. Vocal SPL, duration of maximum sustained vowel phonation, and self-rated perceptual data from sessions 1, 2, and 3 were correlated, and mean difference scores were calculated. SPL intrasubject reliability resulted in correlation coefficients that ranged from 0.82 to 0.88 and mean difference scores that ranged from 0.28 dB SPL to 0.59 dB SPL. Duration of maximum sustained vowel phonation intrasubject reliability resulted in correlation coefficients that ranged from 0.91 to 0.93 and mean difference scores that ranged from 0.05 to 0.11 s. Intrasubject reliability for self-rated perceptual data resulted in correlation coefficients that ranged from 0.74 to 0.82 and mean difference scores that ranged from 0.59% to 2.54% (0–100% scale). These measures indicated good intrasubject reliability for vocal SPL, duration of maximum sustained vowel phonation, and self-rated perceptual data.
Measurement reliability was calculated for vocal SPL, duration of maximum sustained vowel phonation, and self-rated perceptual scales by reanalyzing 25% of the data. Correlation coefficients and mean difference scores were calculated for all measurement reliability checks. Intermeasurer reliability for vocal SPL was determined by playing the DAT tapes and re-recording by hand peak vocal SPL measures observed at 1-s intervals from the SLM. Calibration signals recorded on the tape at the time of the voice recordings were used as reference measures for setting the SLM at a distance representative of the actual recording session. Vocal SPL measurements by two examiners were highly correlated with a correlation coefficient of 0.93 and a mean difference score of 1.18 dB SPL. Measurement reliability for duration of maximum sustained vowel phonation was also high, with a correlation coefficient of 0.99 and mean difference score of 0.15 s. Interexaminer measurements for perceptual data resulted in a correlation coefficient of 0.99 with a mean difference score of 0.07%.
Results
SPL Data
Mean vocal SPL (and SD) for all subject groups, sessions, and tasks are summarized in Table 1. This table illustrates differences in vocal SPL for groups, sex, and sessions. A repeated measures analysis of variance (ANOVA) with two within-subject factors (session and task) and two between-subject factors (group and sex) was conducted on the vocal SPL data to determine significance (α = .05) of any vocal SPL differences. Data were entered into a statistical analysis computer program (SAS, 1995), and a Type IV SS (sum of squares) was used for hypothesis testing as an estimated function to correct for the unbalanced design. A significant difference was identified for the main effect of group (F(1, 4) = 9.79, p = .035). No other significant main effect or interaction effects were identified (Fs(1, 4) < 3.94, ps > .11).
| Group | Sustained Phonation | Rainbow Passage | Monologue | Picture Description | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Session 1 | Session 2 | Session 3 | Session 1 | Session 2 | Session 3 | Session 1 | Session 2 | Session 3 | Session 1 | Session 2 | Session 3 | |
| PD Men | 69.11 (4.55) | 69.53 (4.41) | 70.19 (5.45) | 71.71 (3.90) | 72.64 (2.92) | 72.71 (4.08) | 70.24 (4.29) | 69.84 (3.75) | 70.10 (4.52) | 69.80 (5.98) | 70.53 (4.52) | 71.35 (4.61) |
| PD Women | 67.60 (4.15) | 68.54 (4.92) | 68.78 (5.45) | 69.96 (3.27) | 70.17 (3.18) | 70.35 (3.33) | 68.01 (2.80) | 68.75 (3.56) | 68.24 (4.05) | 68.86 (4.78) | 68.39 (3.56) | 68.38 (4.10) |
| HC Men | 73.30 (4.55) | 74.59 (5.41) | 75.06 (7.05) | 73.64 (3.62) | 73.45 (3.18) | 74.20 (3.73) | 72.39 (4.79) | 71.56 (4.04) | 72.45 (5.50) | 72.22 (3.99) | 72.46 (4.48) | 73.15 (4.48) |
| HC Women | 72.33 (5.14) | 71.18 (5.26) | 71.73 (5.98) | 73.30 (1.23) | 73.74 (1.13) | 73.43 (1.63) | 71.42 (1.74) | 71.44 (1.60) | 72.31 (2.40) | 71.00 (2.36) | 71.66 (2.42) | 71.94 (2.98) |
Note: PD Men (n = 15); PD Women (n = 15); HC Men (n = 7); HC Women (n = 7). Complete data available for all subjects except one man with PD who did not have session 3 data.
Group differences for overall mean vocal SPL across tasks, with sex and session data pooled, were calculated and are displayed in Figure 1. On average, the HC subjects produced speech that was 2.00–4.00 dB SPL greater than the subjects with PD. Examination of group mean differences revealed that the greatest difference in SPL between the subjects with PD and HC subjects was with maximum sustained vowel phonation, followed by monologue, picture description, and the reading passage.
Duration of Maximum Sustained Vowel Phonation
Mean duration (and SD) of maximum sustained vowel phonations with the simultaneously generated vocal SPL measures for subject groups across sessions are provided in Table 2. These duration measures can provide useful information for the interpretation of vocal SPL data in the sustained vowel phonation task. A repeated measures ANOVA with one repeated factor (session) and two between-subject factors (group and sex) was conducted for significance testing (a = .05) of duration differences. No significant differences were identified for the main effect of group (F(1, 38) = .28, p = .736), sex (F(1, 38) = .28, p = .602), or session (F(2, 76) = .02, p = .984), or for any of the related interactions (Fs(1, 38) < 1.12, ps > .33). Duration of maximum sustained vowel phonation ranged from 5.74 to 34.85 s for subjects with PD and from 8.47 to 26.23 s for HC subjects.
| Group | Session 1 | Session 2 | Session 3 | |||
|---|---|---|---|---|---|---|
| Time | SPL | Time | SPL | Time | SPL | |
| PD Men (n = 15) | 17.98 (7.14) | 69.11 (4.55) | 18.06 (3.77) | 69.53 (4.41) | 18.46 (5.87) | 70.19 (5.45) |
| PD Women (n = 15) | 15.02 (7.91) | 67.60 (4.15) | 14.67 (6.54) | 68.54 (4.92) | 15.74 (8.60) | 68.78 (5.45) |
| HC Men (n = 7) | 17.27 (6.94) | 73.30 (4.55) | 17.38 (5.57) | 74.59 (5.41) | 16.07 (5.12) | 75.06 (7.05) |
| HC Women (n = 7) | 17.62 (4.74) | 72.33 (5.14) | 17.82 (3.90) | 71.18 (5.26) | 17.94 (5.01) | 71.73 (5.98) |
Note: Complete data available for all subjects except one man with PD who did not have session 3 data.
Perceptual Data
Mean percentage ratings (and SD) of self-rated perceptual speech and voice characteristics for groups across sessions with sex data pooled are provided in Table 3. Complete data from 12 men and 13 women with PD and 6 men and 7 women in the HC group were used. A repeated measures ANOVA with one within-subject factor (session) and two between-subject factors (group and sex) was conducted to determine significance (α = .05) of any self-rated perceptual differences. Since individual repeated measure ANOVAs were performed for each of the nine perceptual variables, a Bonferroni correction (.05/9) of p ≤ .006 was used to identify statistically significant differences (Keppel, 1991). Statistically significant group differences were identified for all nine perceptual variables (Fs (1, 33) > 12.62, ps < .006), for which the subjects with PD rated themselves as more severely impaired than the HC subjects. Group differences with sex and session data pooled are illustrated in Figure 2. No other statistically significant main or interaction effects were identified (Fs < 4.78, ps > .01).
| Group | Loud 1 | Loud 2 | Loud 3 |
|---|---|---|---|
| PD | 51.62 (12.89) | 57.33 (15.97) | 57.80 (16.78) |
| HC | 80.38 (14.02) | 81.77 (12. 15) | 84.54 (11.12) |
| Shaky 1 | Shaky 2 | Shaky 3 | |
| PD | 59.43 (20.13) | 62.14 (17.43) | 63.19 (20.06) |
| HC | 86.08 (10.71) | 85.85 (12.31) | 87.08 (9.76) |
| Hoarse 1 | Hoarse 2 | Hoarse 3 | |
| PD | 51.63 (17.16) | 56.21 (18.38) | 58.33 (18.90) |
| HC | 88.17 (9.88) | 82.08 (12.95) | 84.92 (11.21) |
| Monologue 1 | Monologue 2 | Monologue 3 | |
| PD | 60.21 (19.65) | 62.00 (20.20) | 64.70 (18.36) |
| HC | 86.31 (10.96) | 85.46 (11.20) | 85.77 (11.57) |
| Slur 1 | Slur 2 | Slur 3 | |
| PD | 61.39 (18.41) | 66.11 (21.29) | 69.19 (18.09) |
| HC | 88.77 (9.55) | 87.25 (11.17) | 88.00 (8.16) |
| Mumble 1 | Mumble 2 | Mumble 3 | |
| PD | 62.67 (19.05) | 64.85 (19.53) | 63.48 (15.76) |
| HC | 84.92 (10.00) | 84.69 (8.62) | 82.50 (9.06) |
| Understand 1 | Understand 2 | Understand 3 | |
| PD | 54.71 (13.99) | 56.50 (17.41) | 56.96 (18.21) |
| HC | 83.00 (10.72) | 82.23 (8.58) | 83.69 (9.16) |
| Participate 1 | Participate 2 | Participate 3 | |
| PD | 57.64 (19.40) | 61.50 (18.69) | 61.44 (20.21) |
| HC | 82.92 (11.01) | 81.77 (13.66) | 76.77 (13.37) |
| Start 1 | Start 2 | Start 3 | |
| PD | 56.22 (16.38) | 58.75 (17.82) | 55.15 (17.28) |
| HC | 72.85 (17.11) | 75.08 (12.75) | 73.15 (15.77) |
Note: Scale ranges from 0 to 100%. Lower percentage scores represent a more severely impaired self-rating of a particular variable.
Summary
Results of this study identified a statistically significant group difference for vocal SPL between subjects with PD and HC subjects, in which subjects with PD were, on average, 2.0–4.0 dB SPL lower than HC subjects across tasks. No significant differences for sex, session, or related interactions for vocal SPL were found. In addition, no statistically significant differences for duration of maximum sustained vowel phonation were identified for group, sex, sessions, or related interactions. Examination of perceptual self-ratings of speech and voice characteristics revealed statistically significant differences between subjects with PD and HC subjects for all nine perceptual variables. Subjects with PD consistently rated themselves as more severely impaired that the HC subjects for these variables. No other significant differences for sex, session, or related interactions were identified.
Discussion
This study was designed to describe vocal SPL and self-perception of speech and voice in people with PD as compared to healthy individuals. The identification of statistically significant group differences for vocal SPL and self-rated perceptual variables suggests that changes related to PD may affect speech and voice performance abilities. These findings provide a clear motivation for considering a treatment program designed to increase vocal loudness, such as the LSVT, as an intervention option for patients with PD who are experiencing communication problems.
Generally, previous studies of vocal SPL have not identified statistically significant group differences between subjects with PD and HC subjects (Boshes, 1966; Canter, 1963, 1965; Metter & Hanson, 1986). These studies differed from the current study in that they included a limited sampling of speech and voice, using either repetition of monosyllables or a reading task during a single voice-recording session. In contrast, the present study did identify a statistically significant group difference in vocal SPL between subjects with PD and HC subjects. It was hypothesized that group differences in vocal SPL may be revealed by examining a variety of speech and voice tasks in this study. While a range of group differences in vocal SPL was identified across tasks (2.0–4.0 dB SPL), these differences did not reach a level of statistical significance. Therefore, the finding of a group difference for vocal SPL may have been related to the inclusion of repeated sessions in this study. Given that speech and voice performance was stable across the 3 sessions in both subject groups, the greater number of observations in each task condition contributed to increased power (decreased type II error) of the statistical design (Keppel, 1991). As a result, the likelihood of identifying a statistically significant group difference in our data was improved.
The greatest difference in vocal SPL between subjects with PD and HC subjects was observed on the maximum sustained vowel phonation task. Examination of the corresponding duration data (in seconds) revealed no statistically significant group differences for this measure. This is not surprising given the considerable individual variability observed in both groups of subjects on this task (PD = 5.74–34.85 s; HC = 8.47–26.23 s). However, the lack of a group difference for duration in conjunction with a significant group difference for simultaneously generated vocal SPL suggests that factors other than respiratory drive may have been contributing to reduced vocal SPL in subjects with PD. Specifically, reductions in vocal fold adduction may have played a critical role.
Subjects with PD have been documented to have incomplete vocal-fold adduction (Perez, Ramig, Smith, & Dromey, 1996; Smith, Ramig, Dromey, Perez, & Samandari, 1995), including bowed vocal folds (Hanson et al., 1984). This condition has been related to reduced vocal loudness and vocal SPL in this population. Given that the task of maximum sustained vowel phonation requires sustained vocal-fold adduction (Dromey et al., 1995), the decreased vocal SPL in subjects with PD may have been related to inadequate laryngeal valving or coordination. When the laryngeal mechanism was driven by the respiratory system, it may have been unable to generate and maintain adduction sufficient to produce vocal SPL levels comparable to the HC subjects. This interpretation is consistent with findings of Dromey et al. (1995) and Ramig and Dromey (1996), who reported increases in maximum flow declination rate (reflecting speed of glottal flow shutoff) and vocal SPL in subjects with PD accompanying improvements in glottal closure pre- to posttreatment. Inadequate laryngeal functioning may also have contributed to the lower vocal SPL for subjects with PD in the reading, monologue, and picture description tasks.
No statistically significant differences were identified across sessions for subjects with PD and HC subjects for the variable of vocal SPL. Although motor performance for limb movements may indeed be highly variable and susceptible to drug fluctuations in subjects with PD, this was not the case for vocal SPL as measured in this study. This consistency of performance for speech tasks, especially effort-dependent tasks, may be related to the extreme care that was taken to elicit comparable effort from subjects across sessions.
Sex did not play a significant role for differences in vocal SPL. Previous studies reporting sex differences in speech and voice characteristics of people with PD examined subtle vocal differences, such as laryngeal phonetic function (Kent et al., 1994) and subharmonic energy in vowel production (Hertrich & Ackermann, 1995). Vocal SPL may not have been as sensitive as these previous measures, which would account for the lack of sex differences identified here.
The descriptive vocal SPL results provided by this study may have considerable clinical value. Given that a statistically significant group difference was identified for vocal SPL between subjects with PD and HC subjects, a treatment program targeted at increasing vocal SPL, such as the LSVT, would be appropriate for people with PD. The stability of vocal SPL for speech and voice tasks across sessions would suggest that when care is taken to elicit comparable effort, a single day of assessment may be sufficient to ensure a representative sampling of vocal SPL in most people with PD. This is important information in today’s health care settings, where repeated-day assessments would not be endorsed by most insurance companies (Higgins, Netsell, & Schulte, 1994). Finally, the lack of sex differences for vocal SPL in this study suggests that performance on comparable speech and voice tasks would be similar across men and women with PD. Therefore, clinicians could expect that most men and women with PD who are reduced in vocal SPL would benefit from similar treatment strategies.
Subjects with PD rated themselves to be significantly more severely impaired than the HC subjects on all nine perceptual variables, indicating some awareness of speech and voice deterioration. Although people with PD have been reported to have breakdowns in their ability to monitor self-effort in relation to motor tasks and their perceptions of the extent of their dysarthria (Solomon et al., 1994; Yorkston et al., 1994), these breakdowns were not reflected in the perceptual self-ratings of speech and voice in this study. These results were, however, consistent with self-perceptions of dysarthric characteristics in subjects with PD reported by Antonius, Beukelman, and Reid (1996). These authors examined self-ratings of dysarthric characteristics in subjects with PD as compared to ratings by their primary caregivers. The subjects with PD rated themselves as having significantly more dysar-thric characteristics, which again suggests an awareness of deterioration in speech and voice.
The differences in results across self-rated perceptual studies and clinical observations may be related to different internal and external influences on subjects with PD. Internal influences may have included the impaired sense of effort demonstrated by subjects with PD in relation to a motor task (Schneider, Diamond, & Markham, 1986; Solomon et al., 1994). For example, when subjects with PD produce a voice that is measured to be reduced in vocal SPL, they may feel as though they are putting forth the same effort for voice production as they always have. Prior to PD, this amount of effort resulted in adequate vocal SPL. Therefore, reports from “soft-speaking” subjects with PD who deny any reduced loudness may be related to their perceived sense of effort for voice production rather than actual vocal SPL.
External influences on perceptual self-ratings of speech and voice in subjects with PD may have included the experience of family and friends telling subjects that they were not loud enough. Many of our subjects with PD reported daily instances where they were asked to repeat what they said or to speak louder. Even though subjects in this study were directed to complete self-ratings based on their own self-perception of speech and voice and not that of others, these external influences cannot be factored out. These influences may explain why some subjects who reported not feeling reduced in loudness rated themselves as more severely impaired than the HC subjects. In addition to self-ratings of reduced loudness, subjects with PD rated themselves to be less likely to “participate” in conversation or to have “confidence” in their voice. These variables suggest that subjects with PD have experienced a negative impact of speech and voice deterioration on their overall communication abilities.
No statistically significant differences were identified across sessions or sexes for the self-rated perceptual variables. The stability of self-ratings across sessions for subjects with PD is important to note. Given that cognitive function was not formerly tested in subjects with PD, it could have had an influence on their ability to complete this task. However, the stability of self-ratings for speech and voice characteristics across days suggests that subjects with PD had sufficient cognitive function for a reliable performance on this task. The lack of statistically significant differences for sex on the self-rated perceptual variables suggests that men and women with PD may be similar in their self-perceptions of speech and voice deterioration. Thus, self-perception issues would require similar treatment strategies for men and women with PD.
As with vocal SPL, the descriptive information from self-ratings of perceptual speech and voice characteristics has a great deal of clinical value. Given that subjects with PD generally were aware of some speech and voice deterioration, they may be motivated for treatment. Despite this awareness, it has been reported that subjects with PD may not recognize the extent of their disability in terms of speech and voice deficits (Yorkston et al., 1994). Therefore, educating subjects with PD about the degree of their speech and voice deterioration may still be a necessary component for treatment success. Furthermore, Ramig, Pawlas, and Countryman (1995) reported that retraining self-perceptions of appropriate vocal loudness for intelligible speech in people with PD was a key element for successful voice treatment outcomes. They referred to this retraining as “calibration” and noted that only those people with PD who accepted the new vocal loudness level maintained treatment effects over time. The relationships between sensory self-perception, sense of effort, and reductions in vocal loudness and vocal SPL appear to be key issues in understanding and successfully treating speech and voice disorders in PD. Future investigations should focus on clarifying these relationships.
Author Note
This research was supported, in part, by National Multipurpose Research and Training Center Grants P60 DC-00976 and DC-01409 and Research Grant RO1 DC-01150 from the National Institute on Deafness and Other Communication Disorders, and Research Grant 8133G40108 from the National Institute for Disability and Rehabilitation Research. Appreciation and gratitude is extended to all subjects who volunteered their time and energy to participate in this study. The authors would like to thank the following persons for their contributions to this paper: from the University of Arizona-Tucson, Dr. Jeanette Hoit; from the Wilbur James Gould Voice Research Center of The Denver Center for The Performing Arts, Ms. Deborah Huhn and Mr. Geron Coale.
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This work is licensed under a Creative Commons Attribution 4.0 International License .History
- Received: Jul 17, 1996
- Accepted: Mar 19, 1997
- Published in issue: May 1, 1997
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