The Acoustic Characteristics of Ataxic

Dysarthria

The Department of Speech, Language and Hearing Sciences

University of Florida

Karessa White

Rahul Shrivastav, Ph.D

John Rosenbek, Ph.D

1

Abstract

A number of studies have focused on the acoustic and perceptual characteristics of ataxic to help differentiate these speakers from those with normal speech. Many studies have also suggested that such differences may be used clinically to differentially diagnose cerebellar based from other dysarthrias. This study compares the accuracy of a small number of acoustic measures of ataxic dysarthria in differentiating ataxic speakers from a group of age- matched controls. Differences in the magnitude of shimmer and jitter percentages, Pairwise

Variability Index, Proportion of Vocalic Index, and Scanning Index are compared in a group of

17 ataxic and 17 age matched controls. Results show that Scanning Index is the best measurement for detecting the differences between ataxic speech and normal speech.

2

Introduction

Motor neurons are essential for voluntary muscle functions that are used in daily activities such as walking, breathing, and speaking. These neurons excite cells in the brainstem and spinal cord which further relay messages to the lower motor neurons, finally resulting in the execution of a particular motor movement. Disruption to the neural control anywhere in this pathway can impair motor movement. The exact nature of this disruption is often dependent upon the location and extent of the injury to the neural circuitry that controls movement. One sub-type of motor movement disorders resulting from neurodegenerative conditions affecting the is called ataxia.

Ataxia is characterized by irregular or abnormal muscular control and includes movements such as kinetic (intention) or static (postural) tremor and incoordination, where patients need visual information in order to sustain from swaying and falling. The latter is due to the abnormal speed and delay in intentional movements (Mariotti, 2005). There are various types of ataxia which may be inherited or acquired. A number of different causes have been identified including developmental, trauma, and degeneration, to name a few. Among other things, ataxic patients develop difficulty in the precise movements of the articulators needed in speech, resulting in “ataxic dysarthria”.

3 Characteristics of Ataxic Dysarthria

Previous studies have described the speech of patients with ataxic dysarthria to have frequent disturbances in shimmer and jitter during sustained phonation; irregular stress patterns in syllables (Kent, Duffy, and Weismer, 2000), disturbances in rhythm and prosody (Liss, 2002), explosive staccato, scanning vocalization, wavering modulation (Ogawa, 2010), and increased number of inappropriate pauses (Rosen, 2003). Patients with ataxic dysarthria exhibit abnormalities in timing due to impairment in muscular force and incoordination of the muscles of the vocal tract. Other deficits include agrammatism, which is simplified speech that lacks function words and other grammatical features of language (Ackermann, Mathiak, and Riecker,

2007). As the disorder progresses, speech and language errors may increase, causing difficulty in producing intelligible speech (Mariotti, 2005). Ataxic dysarthria is often described as “slurred speech” (Ackermann, 2007), having explosive staccato, scanning vocalization and wavering modulation (Ogawa, 2010). Other evidence of cerebellar lesions includes slowness of reaction time and changes in syllable length and reduced task complexity (Spencer and Rogers, 2005).

Cerebellar ataxia is rarely a disorder with only damage to the cerebellum but has damage in other areas and tracts that interact with the cerebellum as well. Trojano (2005) studied the possible influences of motor speech disturbances in the articulatory loop. Ataxic patients have a deficit in the immediate verbal memory and this further causes a deficit in the short-term memory. Ataxic speakers were observed to show a decrease in information processing speed and therefore took longer to pronounce words (Trojano, 2005). Many patients with ataxic dysarthria also exhibit cognitive deficits that resemble symptoms related to frontal lobe lesions. This is

4 most commonly seen in patients with certain types of spinocerebellar ataxia (SCA1, SCA2 and

SCA3; Suenaga 2008).

A classic study on the perceptual characteristics of dysarthria was reported by Darley,

Aronson and Brown (1969) and found ataxic dysarthria to be characterized by “irregular articulatory breakdown”, “excess and equal stress”, prolongation of phonemes and intervals as well as a slower speaking rate. Kinematic analyses of patients with ataxia revealed that ataxia speakers showed greater variability in the movements related to the opening of the mouth than normal controls (Forrest, 1991). Some ataxic patients tend to shorten the onset of the vowel in the presence of an unvoiced stop. It is speculated that this may be related to the greater complexity of producing voiced stops which require coordination between the laryngeal and the vocal tract musculature (Ackermann, 1999).

a. Brain Imaging and Speech Production

During speech production, neural imaging (PET scans) revealed that there was a reduction of blood flow in the cerebellar hemispheres of ataxic patients (Sidtis, 2010), meaning that there is less activity in these regions during certain speech tasks (Schmahmann, 2004;

Mariotti, 2005; Ackermann, 2007; Spencer and Slocomb, 2007; Ogawa, 2010; and Sidtis, 2010).

Some brain imaging techniques determine the level of activity by blood-oxygen level dependent contrasts. Increased blood supply to a particular area signifies increased neural activity in that area. Since ataxic patients have cerebellar degeneration, reduced oxygen consumption in these areas may be expected. Spencer and Slocomb (2007) noted that the right cerebellar hemisphere was also activated during speech tasks such as the planning of articulation and language processing. These results have also shown different speech tasks being associated with different

5 areas of the cerebellum such as bilateral activation for literal speech, increasing with more complex tasks (speech planning and processing), and right hemisphere activation for figurative speech and processing of articulation and working memory tasks.

b. Alternating Motion Rates/ Diadochokinesis

Ozawa (2001) examined six individuals with ataxic dysarthria by measuring their alternating motion rates (AMRs), or diadochokinesis (DDK), which consists of the participant repeating a single syllable as many times as possible in a certain amount of time. AMR values may have some indication of the differences and severity of neurological disorders affecting speech because it identifies variation in articulation rate and accuracy. Results show that in ataxic speakers, fewer syllables are produced in AMR tasks due to an increase in the number of pauses. This method also revealed problems in the control of muscle force and timing. Ziegler and Wessel (1996) studied DDK tasks among three different groups, cerebellar atrophy,

Friedrich’s ataxia, and normal speakers. Results revealed that the normal subjects generally had the shortest syllable duration; which was significantly lower than that in populations with difficulty in muscular control, timing, and coordination. An interesting result was that the

Friedrich’s ataxia group was the least dysarthric, even though they have had the disease longer than the cerebellar atrophy group (Ziegler and Wessel, 1996). This may indicate differences between the characteristics exhibited by each type of cerebellar disorder.

Wang (2008) used an automatized program, Motor Speech Profile Program (MSP) to evaluate DDK for clinical assessment of ataxic patients. The DDK computed automatically was compared against manually obtained counts. Twenty-one participants were asked to repeat syllables ‘pa’, ‘ta’, and ‘ka’ as quickly as possible in a single breath. A seven second sample

6 was used for the MSP program. Wang (2008) found that the MSP algorithm were not accurate in automatically calculating DDK. The main issue with the MSP program was that one-third of the samples could not be analyzed because the energy in the vowels was lower than the amplitude peak for the consonants, thereby making the DDK calculations incorrect. This is a result of articulatory breakdown, which is very common in ataxia. Automatic analysis of this data would often lead to incorrect results.

c. Pause Duration

Ataxic patients tend to have a longer duration of pauses between syllables and syllable prolongation. Pause durations have been measured in sentences, passage readings, and spontaneous speech. Results of these measurements have revealed that ataxic patients show significantly greater pauses between words. These pauses appear to result from difficulties in respiration because at the end of the utterance, the ataxic patients often exhibit rapid exhalation.

Unpredictability in pause duration (Rosen, Kent, and Duffy, 2003), as well as a high occurrence of pauses (Lowit, 2010), and greater pause durations (Schalling, 2007) are typical in patients with ataxia.

d. Vowel Duration, Syllable Duration and Speaking Rate

Vowel and syllable duration are important measurements used to distinguish ataxic patients. Hertrich and Ackermann (1999) found vowel length in ataxic patients to be of similar magnitude as that for controls. This was assumed to reflect that the control of speech duration was independent of cerebellar control. However, Ackermann (1999) observed that the voicing duration of vowels segments is reduced in speech. Schalling et.al. (2007) noted that the high

7 variability of syllable durations may be an important indicator for diagnosing ataxia early when speech is fairly normal and other signs are not yet prevalent.

One may assume that longer vowel and syllable durations would result in slower rate of speech. However, these breakdowns in duration or a slower speaking rate is not always present, especially in patients exhibiting milder symptoms. Although it has been shown that generally, dysarthric speakers have more variability in temporal and spatial speech characteristics than normal speakers, ataxic speakers can show speaking rates similar to that of normal speaking rate

(Anderson, Lowit, and Howell, 2007). In contrast, other studies such as Lowit et.al. (2010) found ataxic speakers to have significantly reduced rate compared to the control group.

e. Rhythm

Rhythm measurements help to distinguish ataxic speakers from normal controls because ataxic speakers tend to have an abnormal stress pattern. Researchers have used different measurements to test the rhythm of ataxic patients as a way to determine if disturbances in rhythmic might help identify patients with this type of cerebellar disorder (Liss et.al., 2009).

Certain measurements can be used to determine the variability in the rhythm of ataxic speakers.

These measures include Pairwise Variability Index (PVI), Proportion of Vocalic Index (%V),

Scanning Index (SI), and Interstress Interval (ISI). PVI (Low, Grabe, & Nolan, 2000) measures the differences in the duration of successive vowels in a sentence. Proportion of Vocalic Index,

%V, (Ramus, Nespor, & Mehler, 1999) measures the average vowel rate in a given sentence. SI

(Ackermann and Hertirch, 1994) involves the product of successive syllable durations divided by the average of the syllable durations raised to the nth power, where n refers to the number of syllables in the sentence. Finally, ISI (Hartelius et al., 2000) is the standard deviation of the

8 syllable duration squared. Studies on these measurements revealed that the Pairwise Variability

Index and Inter-stress Interval were the two that produced significant differences between ataxic and normal speakers (Henrich, 2006).

f. Intelligibility

Therapy often focuses upon improving the speech of dysarthric patients because of the poor intelligibility in daily communication (Nuffelen, 2009). Perceptual studies are used to determine if listeners can hear differences in the speech of different dysarthric speakers. In a series of studies using the Lexical Boundary Error (LBE) analyses, Liss and her colleagues (Liss et al, 1998; 2000; 2002) reported that intelligibility deficits in ataxic dysarthria are strongly influenced by the inappropriate and variable stress patterns and prosody seen in these patients.

They also observed modest gains in intelligibility for ataxic speakers following familiarization to their speech. However, the patterns of error based on LBE analyses remained consistent despite familiarization.

Treatment

Dysarthria can continue for many years without any or little improvement and although there is no cure for ataxic dysarthria, symptoms of the disorder can be addressed through a variety of treatment.

a) Diet and Nutrition

Perlman (2000) suggests that poor diets in ataxic patients can cause heightening of symptoms due to lack of certain nutrients and weight gain. Diets should be regulated and if there

9 are issues with swallowing, this should be addressed through appropriate treatment. In the most severe cases, a feeding tube may be needed. Some vitamin, mineral and herbal treatments are used but these have not always proven to be beneficial and excesses of minerals can lead to damage and even atrophy of the neural cells (Perlman, 2000).

b. Medication and Surgery

According to a review by Perlman (2000), some medications have been proposed as a treatment but results from clinical trials vary depending on the type of medication used. Most of these pharmacologic treatments act by influencing the neurotransmission mechanism.

Thalamotomy and thalamic stimulation are also used in patients with severe tremor and associated difficulty in mobility and other daily activities (Perlman, 2000).

c. Therapy

Physical therapy focuses on improving mobility and the fatigue that often occurs in ataxic patients whereas speech therapy helps improve some dysarthric characteristics in ataxic patients.

Commonly used speech therapy techniques are as follows:

i. Rate Reduction

Rate reduction techniques have sometimes been designed to help in the improvement of ataxic dysarthria. It is assumed that slowing the speech rate in dysarthric patients may allow more time to properly articulate and improve intelligibility. However, the results have been mixed. Pilon (1998) showed that when the rate of speech was reduced the intelligibility of some participants increase (2 out of 3. In contrast, a slow rate actually resulted in poorer intelligibility for one patient who had the least severity of the dysarthria (Pilon, 1998). Thus, rate reduction

10 techniques may only be beneficial for more severe dysarthric speakers. Van Nuffelen (2009) evaluated the effects of speech rate modifications on speaking, articulation, and intelligibility.

Nineteen ataxic patients and twenty controls were told to speak at half the rate that they normally would, use the alphabet board, pacing board, perform hand tapping and delayed auditory feedback at 50ms, 100ms, and 150ms. The reading samples consisted of 20 passages with simple sentences. Participants were asked to read for at least 2 minutes. The recordings were then rated for intelligibility by a speech language pathologist experienced in the field of dysarthria. Results showed that none of the rate control methods significantly increased intelligibility for the group tested but did result in improvements for some individuals. The rate control methods that helped the most in improving intelligibility are voluntary rate control, alphabet board, hand tapping, and pacing board. Overall, the reduction in speaking and articulation rate did not improve intelligibility and improvements were only observed in 5 out of 19 subjects.

ii. Lee Silverman Voice Treatment

A treatment created for Parkinson’s disease patients called the Lee Silverman Voice

Treatment (LSVT) is sometimes used for ataxic patients to enhance their intelligibility. The

LSVT is a treatment that helps to increase loudness in speaking for better intelligibility. A particular task used in the LSVT treatment called Smooth Speech is a technique that helps with speech coordination and has been previously used to successfully treat neurologically based speech disorders. Stocks (2009) reported on a participant who underwent treatment using

Smooth Speech and found that the participant did not have significant changes in coordination but did exhibit overall improvement in communication abilities. Loud phonation gives speech clarity because it causes more precision in articulation and enhanced naturalness. Sapir (2003)

11 reported that the naturalness of speech and accuracy of articulation improved after LSVT treatment in a participant with ataxic dysarthria.

The present study attempted to determine which of the many acoustic measures of ataxic dysarthria reported previously might be most successful in discriminating ataxic speakers from age matched controls. Kent, Duffy, and Weismer (2000) reported that ataxic speakers typically have higher shimmer and jitter than normal speakers. Anderson, Lowit & Howard (2007) reported greater variability in speech segment duration for ataxic speakers, often accompanied by a reduced overall rate of speech (Lowit, 2010). “Scanning” speech or other errors in the rhythm are commonly reported in ataxic patients. Different measures to capture these differences (e.g.

PVI, %V, and SI) have been reported previously and may help in differentiating ataxic dysarthria from normal speech or other dysarthrias (Liss, 2009). In the present experiment, the accuracy of each of these measures in discriminating ataxic speech from normal was evaluated.

Methods

a. Participants

Nineteen participants, diagnosed with ataxia and cerebellar disease by a neurologist at the

University of Florida’s Movement Disorders Clinic were tested in this study. The ataxic participants’ ages ranged from 22 to 90 and consisted of 7 male subjects and 10 female subjects.

There were originally 19 participants but 2 participants’ recordings were damaged in transferring samples into database, subsequently 17 ataxic participants were tested here. The characteristics of the participants for this study are presented in Table 1 below.

12 Participant Age Gender Diagnosis

1 60 M Freidriech’s Ataxia

2 29 M

3 56 M Freidriech’s Ataxia

4 30 F Unknown

5 90 F Deterioration of Cerebellum

6 46 M

8 22 F SCA-3

9 45 M

10 66 F Sporadic Ataxia

11 42 F SCA-2

12 64 F SCA

13 74 F SCA-2

15 68 F Cerebellar Ataxia

16 59 M SCA-2

17 55 F SCA-6

18 73 F SCA-6

19 41 M

Table 1.Characteristics of Ataxic Participants.

In addition, 17 participants’ with no speech disturbances were selected as controls. These participants were selected from a pre-existing database of normal elderly speakers producing the same set of speech stimuli and recorded using similar equipment and procedures. The participants were selected based on age range that matches that of the ataxic participants.

b. Stimuli and Recording Procedures

The participants were asked to produce vowel sounds /a/, /i/, /u/, /o/, and /ae/ for 5 seconds each, read 22 sentences, and read a standard passage (“The Rainbow Passage”). The data was recorded using a Marantz Professional Solid State Recorder PMD671 in a room away

13 from loud activity to ensure that the recording would not contain significant background noise.

An Artist Series Audio-Technica ATM73a Cardioid Condenser head-worn microphone was placed about 2 inches away from the participant’s mouth to ensure clear communication. The recordings were sampled at 22050 Hz with quantization at 16 bits and stored in the Microsoft wave format.

c. Analyses

Prolongation of the vowel sounds /a/, /i/, and /u/ were reduced to 250 ms of the mid- portion using a MATLAB script. The mid-portion was used to avoid the onset and offset of the vowel because ataxic patients tend to have unusual occurrences of intonation due to respiratory problems. These vowels were analyzed for shimmer and jitter using TF-32 by creating spectrographs and using the automated function. The mean, standard deviation and variance of these values were calculated and compared. Three sentences (“The cut on his knee formed a scab”, “The soup was served in a bowl”, and “The baby slept in his crib”) were used to measure the durations of syllables and vowels using a script in the signal analyses software, Praat. These sentences were chosen because the vowels in the words correspond with the prolonged vowel sounds analyzed. The rhythm measurements Pairwise Variability Index, Proportion of Vocalic

Interval, and Scanning Index were used to determine the differences between the articulation of ataxic and normal speakers. These calculations are described below.

Pairwise Variability Index (PVI) measures the differences in the duration of successive vowels in a sentence. This is important because ataxic speakers tend to have an abnormal rhythm because of variation in vowel duration. Ataxic speakers tend to produce longer vowel sounds when they should be shorter or shorten vowel sounds in certain syllables. Proportion of Vocalic

14 Interval (%V) measures the average vowel rate in a given sentence. In this measurement, the sum of the vowel durations is divided by the duration of the sentence. Scanning Index (SI) involves the product of successive syllable durations divided by the average of the syllable durations raised to the nth power, depending on the number of syllables in the sentence. This measurement can show the variability between syllables that ataxic speakers tend to exhibit. Sometimes the syllable length is unpredictable to the listener and may cause the speech to be unintelligible.

d. Statistical Analysis

All of the values obtained and calculated in this study were statistically analyzed for significance using One-way Analysis of Variance (ANOVA). This was used instead of T-test because more than one factor was present. ANOVA was used to account for differences in various articulatory/acoustic measures between ataxic (independent variable) and normal subjects (dependent), while addressing the differences between male and female speakers (fixed factors).

Results

Vowel Prolongation

The results of the mean, standard deviation, and variance of the sample obtained in this study are presented below in Table 2, Table 3, and Table 4. These numbers were generated automatically in TF-32 and show that there are some numerical differences between the ataxic and normal speakers. Mean fundamental frequency between the 2 groups tend to vary; sometimes the ataxic patients have higher frequencies and sometimes they have lower frequencies. In most cases below, ataxic speakers tended to have higher occurrences of shimmer

15 and jitter in vowel prolongation than normal speakers except in the vowel /u/. This is expected in ataxic speakers due to respiratory and vocal fold dysfunction.

Measurements Ataxic Normal

Mean Standard Variance of Mean Standard Variance of

Deviation Sample Deviation Sample

F0 168.761 71.789 5153.635 152.228 36.829 1356.447

Jitter % 1.541 3.153 9.942 1.055 0.947 0.897

Shimmer % 8.031 15.013 225.384 6.477 5.357 28.699

Table 2. Fundamental Frequency, Jitter, and Shimmer values for Ataxic and Normal Speakers for /a/.

Measurements Ataxic Normal

Mean Standard Variance of Sample Mean Standard Variance of

Deviation Deviation Sample

F0 148.878 43.883 1925.711 166.394 41.198 1697.302

Jitter % 0.662 0.762 0.581 0.3494 0.128 0.016

Shimmer % 2.931 3.869 14.975 1.539 0.777 0.604

Table 3. Fundamental Frequency, Jitter, and Shimmer values for Ataxic and Normal Speakers for /i/.

Measurements Ataxic Normal

Mean Standard Variance of Mean Standard Deviation Variance of Sample

Deviation Sample

F0 157.028 45.481 2068.545 152.228 36.83 1356.447

Jitter % 0.821 1.104 1.218 1.269 3.734 13.944

Shimmer % 2.447 2.856 8.158 4.262 10.454 109.293

Table 4. Fundamental Frequency, Jitter, and Shimmer values for Ataxic and Normal Speakers for /u/.

16 Overall, one-way ANOVA results showed that there were no significant differences in the fundamental frequency and the percentage of jitter and shimmer between all ataxic and normal speakers in the vowels /a/, /i/, and /u/. These results are shown in Table 5, Table 6, and

Table 7. There were also no significant differences of the gender of speakers. Kent et.al. (2000) speculated that females tend to have a higher occurrence of shimmer than males and the numbers in ataxic female speakers are generally higher than normal female speakers and male speakers in this study, but these differences are not statistically significant.

Variable F-Value P-Value Shimmer F(1,34) = 0.17 0.68 Jitter F(1,34)= 0.39 0.54 Table 5. One-way ANOVA results of shimmer and jitter in ataxic and normal speakers for vowel /a/. * p<0.1

Variable F-Value P-Value Shimmer F(1,34)= 2.24 0.14 Jitter F(1,34)= 2.94 0.1 Table 6. One-way ANOVA results of shimmer and jitter between ataxic and normal speakers for vowel /i/.* p<0.1

Variable F-Value P-Value Shimmer F(1,34)= 0.5 0.48 Jitter F(1,34)= 0.24 0.63 Table 7. One-way ANOVA results of shimmer and jitter between ataxic and normal speakers for vowel /u/.* p<0.1

Rhythm Measurements for Sentences

The results of the mean and standard deviation for ataxic and normal speakers are shown below in Figure 1, Figure 2, and Figure 3 for the 3 rhythmic measurements used in this study:

PVI, %V, and SI. These measurements were used to measure variation in all 3 sentences

(Sentence 1: “The cut on his knee formed a scab”, Sentence 2: “The soup was served in a bowl”, and Sentence 3: “The baby slept in his crib”). For PVI, ataxic speakers tended to have a lower mean than the normal speakers but for %V the values vary and for SI the mean values were greater in all three sentences for ataxic speakers than for normal speakers.

17 80 70 60 50 40 Normal PVI 30 Ataxic PVI 20 10 0 Sent 11 Sent 13 Sent 15

Figure 1. Mean Pairwise Variability Index (PVI) values for normal and ataxic speakers (in seconds).

0.5 0.45 0.4 0.35 0.3 0.25 Normal %V 0.2 Ataxic %V 0.15 0.1 0.05 0 Sent 11 Sent 13 Sent 15

Figure 2. Mean Proportion of Variability Index (%V) values for normal and ataxic speakers (in seconds).

18 0.8 0.7 0.6 0.5 0.4 Normal SI 0.3 Ataxic SI 0.2 0.1 0 Sent 11 Sent 13 Sent 15

Figure 3. Mean Scanning Index values for ataxic and normal speakers (in seconds).

Scanning Index yielded significant different values for the ataxic and normal speakers for all 3 sentences analyzed. The level of significance (p-values) was consistently below 0.01.

Pairwise Variability Index showed significantly different values between ataxic and normal speakers for one of the three sentences only. For Proportion of Vocalic Interval, One-way

ANOVA results showed that there were no significant differences between ataxic and normal speakers for all 3 sentences, shown below in Table 8, Table 9, and Table 10.

Variable F-Value P-Value PVI F(1,32)=0.97 0.33 %V F(1,32)=0.13 0.72 SI F(1,32)=50.3 <0.01 Table 8. One-way ANOVA results of rhythmic measurements between ataxic and normal speakers for Sentence 1.

Variable F-Value P-Value PVI F(1,32)=11.0 0.00* %V F(1,32)=0.48 0.49 SI F(1,32)=25.4 <0.01 Table 9. One-Way ANOVA results of rhythmic measurements between ataxic and normal speakers for Sentence 2.

Variable F-Value P-Value PVI F(1,32)=2.09 0.16 %V F(1,32)=0.6 0.45 SI F(1,32)=19.2 <0.01 Table 10. One-way ANOVA results of rhythmic measurements between ataxic and normal speakers for Sentence 3.

19 Discussion

Vowel Prolongations

Studies have reported abnormal increase in jitter and shimmer during sustained phonation tasks for ataxic speakers than for normal speakers. Studies have also reported differences in female and male speakers with shimmer and jitter, noting that female speakers have higher occurrences of jitter (Kent et.al, 2000). The results of the present study show large gender differences for shimmer values with ataxic females having 7.47% greater of shimmer in vowel prolongation than normal females and females together having 5.36% more shimmer than male speakers. However, overall ataxic speakers do not have significant differences in the percentage of shimmer and jitter in sustained phonation, indicating that this would not be a reliable source for differential diagnosis of ataxia. It is important to note that the age of onset and the length of disease were controlled for this study.

Rhythm Measurements for Sentences

Ataxic speakers are known to have longer syllable and vowel durations than normal speakers due to difficulty in planning the movement of articulators. Scanning Index appears to be most sensitive to differences between ataxic and normal speakers. The other measurements used vowel durations to determine abnormalities in speech and revealed that there were no statistically significant differences between ataxic and normal subjects except for PVI for one sentence.

These results indicate that vowel production is not the main issue ataxic speakers have in articulation but rather consonant production or consonant-to-vowel boundaries may be more difficult for the ataxic speakers to produce. Scanning Index measures syllable durations which include both vowels and consonants and because the vowel durations were not significantly

20 different from the normal speakers’ vowel durations, the consonant or CV boundaries might be affected.

Proportion of Vocalic Interval values are shown in Figure 2. There were no significant differences between the PVI for speakers with and without ataxia and therefore this would not be a good discriminator of ataxic speech. Reduced or increased vowel duration alone may not be a characteristic of ataxic dysarthria.

The mean values for Scanning Index are presented in Figure 3 and show that the ataxic speakers have significantly higher values than the normal speakers. Ataxic speakers collectively have greater variability in the durational differences between successive syllables than normal speakers. These likely result from dysfunction in motor planning due to damage in the cerebellum. Based on the results of this study, Scanning Index would be a measurement that may help in discriminating ataxic and normal speech. The lack of significant differences in absolute vowel durations between normal and ataxic speakers, in the presence of significant differences in syllable durations across the two groups, suggest that the main problem for ataxic dysarthria might relate to inappropriate co-articulation resulting from poor coordination. This has also been speculated in other studies such as (Ackermann, 1999).

A study by Henrich (2006), on the other hand, found that Pairwise Variability Index was the best rhythm measure but this study only tested 6 spinocerebellar speakers and 6 normal control speakers and thus had less data to really account for variation. In the present study PVI showed significant differences between ataxic and normal speakers for only one sentence and thus may not be considered a consistent measure to differentially diagnose ataxic speech.

21 For increasing clinical use of any of these measures, it is necessary to develop an automatic program to calculate SI for dysarthric speech. Such an algorithm would not only reduce the time in performing these measure but the results and diagnoses would be more accurate than manual calculation. Early diagnosis of ataxia can allow for earlier intervention in treating the symptoms associated with this disease.

Conclusion

Based on the results of this study, Scanning Index is recommended as the best measure for the diagnosing of Cerebellar ataxia because it produced the most consistent results. This measure differs from the other two in that it measures the entire syllable instead of just the vowel. From the results, it seems as though the main problem is not with vowel prolongation and reduction as presumed but that the main focus in treatment should be on consonant production and co-articulation.

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