1. When is it cluttering? And when is it cluttering-plus?
Lisa R. LaSalle, Ph.D., CCC-SLP
Board Recognized Specialist-Fluency Disorders
Dept. of Communication Sciences & Disorders
University of Wisconsin-Eau Claire
[read slide] So…I am excited to participate in this online cluttering workshop for a few reasons – I so enjoy working with Judy Kuster. She has such a passion for the topics of fluency disorders – for serving people with fluency disorders, and our students who are our pre-professionals, as well as involving international colleagues in this among many previous such online conferences, an exciting use of technology. Secondly, Lesley Wolk and I, both doctoral classmates once under Ed Conture’s mentoring at Syracuse University in the early 1990s, presented recently at the International Fluency Association on the topic of phonological complexity and stuttering, cluttering and stuttering-cluttering, and we have turned that presentation into a publication submission. (Ed Conture used to say in those days, and I think rightly so, “cluttering, schmuttering, show me the data…” and I think now in 2010, the data are starting to trickle in and we are finally starting to make some sense of the data. ASHA has recently reported that about 2/3 of school-based SLPs have at least one clients who clutter on their caseload, so we know that this is an important topic in our country, as well as in many other countries.
Also, I was fortunate enough to participate in the ISAD conference in October 2009, and presented on the topic of treatment of cluttering. However, in this brief talk, I would like to take a step back and focus more on some larger questions of assessment. I think the particular fact that cluttering is (more often that not) a concomitant communication disorder is what makes it complex and difficult to study, and thus, I chose to attempt to answer this question for the practitioner: “When is it cluttering? And when is it cluttering-plus?”

2. Working definition of cluttering (St
Working definition of cluttering (St.Louis, Myers, Bakker & Raphael, 2007)
Cluttering is a fluency disorder characterized by a rate that is perceived to be abnormally rapid, irregular or both for the speaker (although measured syllable rates may not exceed normal limits). These rate abnormalities further are manifest in one or more of the following symptoms: a) an excessive number of disfluencies, the majority of which are not typical of people who stutter; b) the frequent placement of pauses and use of prosodic patterns that do not conform to syntactic and semantic constraints; and inappropriate (usually excessive) degrees of co- articulation among sounds, especially in multisyllabic words. (pp )” Scaler Scott & St Louis (2009) ask us to be “purists in evaluation and diagnosis of cluttered speech (p. 48).”

3. Recent historical highlights
Weiss (1964) identified cluttering as coexisting with primary stuttering, and emphasized the “central language imbalance.”
Freund (1952; 1970): Differentiate “common stuttering” vs. “neurogenic stuttering” vs. “hysterical”/psychogenic vs. “cluttering”
Van Riper (1982) Track II subgroup (n = 44 followed longitudinally):
“Late talkers”
Rapid, irregular repetitions
Word/sound fears were quite mild: Unaware
[read slide] As cited in Bloodstein, O. & Bernstein Ratner, N. (2008). A Handbook on Stuttering (6/e). Clifton Park, NY: Thomson Delmar.
We can of course, go further back in history: Weiss was an Austrian clinical author, and almost a century before that, a German by the name of Kussmaul (1877) brought the concept of a speaker’s unawareness to the forefront.

4. Now, we are in a virtual Cluttering Renaissance!
International Cluttering Association;
Many more publications;
This first online cluttering conference, etc…
[read slide] So, for example, regarding Weiss’ (1964) premise that cluttering is a central language imbalance, Luchsinger and Landolt (1955, as cited in Bloodstein & Bernstein Ratner, 2008) found that EEG was normal in stutterers but abnormal in clutterers and clutterer-stutterers. Contrast that with currently – we now have evidence from Yvonne Van Zaalen (2009) and her colleagues that in 13 R-handed adults who clutter (AWC) compared to 13 R-handed adults who stutter (AWS), based on fMRI data derived during tasks that involved speaking words of increasing complexity, AWC showed higher activity in right hemisphere precentral gyrus, inferior frontal gyrus and left insula. Whereas AWS showed higher activation in right primary motor cortex, temporal lobe and globus pallidus. Findings tentatively suggest deficits in different parts of the brain are responsible for cluttering and stuttering.

5. Definitions: When is it Cluttering?
When three features are present:
(1) rapid and/or irregular articulatory rate
(2) intelligibility is reduced due to over- coarticulation (weak syllable deletion and imprecise articulation;
(3) disfluencies especially of the non-stutter type, are frequent
Low awareness characteristic: When a listener points out the unintelligibility or the low intelligibility of the speaker who clutters, the speaker can often improve intelligibility and/or fluency by conscious, effortful slowing down.
tachyphemia
Citations are many:
(1) a rapid and/or irregular articulatory rate (e.g., Daly, 1993; St. Louis, Raphael, Myers & Bakker, 2003; Weiss, 1964); Important to note that Medical term for cluttering is “tachyphemia”/”tachylalia” “tachy” = “rapid” and “phemia” or “lalia” = “speech” (Freund, 1970)
(2) a higher than average frequency of normal (nonstutterlike) disfluencies (e.g., St. Louis et al., 2003) and
(3) reduced intelligibility due to exaggerated coarticulation (deletion of syllables or sounds in multi-syllabic words) and imprecise articulation (e.g., Ward, 2006; Weiss, 1964). Telescopes or condenses words (Daly & Burnett, 2006)
Youtube clip to provide the example 
Stuttering among persons with intellectual disabilities: Aware but unconcerned about their own disfluencies (Bonfanti & Culatta, 1977), and Stansfield (1990) reported that 6.3% of 800 adults with learning difficulties showed features of stuttering-cluttering, or “idiopathic disfluency.” an Borsel, Jozefien, Charlotte, Rijke, EvyVan, & Tineke (2006) found the prevalence of stuttering was four times higher in the Special Educational Needs classes than in regular classes. (as cited in Bloodstein & Bernstein Ratner, 2008)

6. Why use the “cluttering-plus” term?
Authors refer to those who stutter and have a concomitant disorder as “stuttering plus.”
Most common concomitant disorder(s) with stuttering are articulation, phonological, language, and/or learning disorders/ disabilities (e.g., Arndt & Healey, 2001).
It is cause for concern that the definition of cluttering shares features with “stuttering-plus.”

7. Cluttering shares at least one feature with stuttering: Disfluencies
Especially re: advanced stuttering. Consider how “mazing” is the same surface behavior as “stalling/filling” (i.e., between-word disfluencies)

8. To keep it simple: Stuttering = loss of control over sound production
disfluencies
Fast rate in fluent segments
Cluttering
Presumably, (1) makes no sense to measure the rate of phones or syllables per second when a speaker is producing a disfluency, and (2) PWS are known to produce fluent speech that is slower than normal.
Both sets of speakers make up for lost time.

9. Perhaps changing the lens from “stuttering plus” to “stuttering vs
Perhaps changing the lens from “stuttering plus” to “stuttering vs. cluttering?” and then to “cluttering plus” will help illuminate our path…
Stuttering…
Cluttering…

10. Cluttering-plus... Cluttering weak syllable deletion
Phonological / articulation disorder
Cluttering
imprecise articulation
As Van Zaalen (2009, p ) has stated, “PWC experience difficulties in making themselves understood in conversations, but many are able to produce correct syllable and word structures in restricted situations
(Weiss, 1964; ...Ward, 2006; St. Louis et al., 2007…). To produce intelligible syllable or word structures, the speaker must exercise appropriate levels of speech motor control…”
LaSalle & Wolk (2009) found that phonologically sparser words are more likely to be stuttered than fluent across individuals who clutter, stutter, and clutter-stutter. However, initial consonant cluster words are also more likely to be stuttered in a case of an adolescent who only stutters, and this was not the case for the three clutterers in our study. So we are talking about different aspects of

11. Also… Language / Learning disorder Cluttering
Mazing types of disfluencies
Language / Learning disorder
Cluttering
problems in
expression, reading aloud and writing
We believe from the writings of many authors (e.g., St. Louis, et al. 2007) that people who clutter have problems in expression, reading aloud and writing…

12. “Due to a lack of differential diagnostic criteria between cluttering, stuttering and language/ speech impairment related to a learning disability, cluttering is often detected later in life, or not at all. This has the undesired result that therapy results are very limited and communicative skills of affected persons remain poor (van Zaalen, 2009, p. 16).”

13. What is our diagnostic task
What is our diagnostic task? Are we assessing a speaker who presents with:
Pure cluttering?
Fast, irregular rate; often unintelligible and/or disfluent
But the speaker reports experiencing control over sound production and an increase in fluency and/or intelligibility when they at least temporarily increase self-awareness
Pure stuttering?
Disfluent especially in terms of “stutter”/within- word disfluency frequency and reports experiencing loss of control over sound production

14. If it is cluttering, is it cluttering plus:
An articulation/phonological disorder beyond weak syllable deletion and general imprecision?
A documented language-learning disorder?
Other communication disorders (i.e., auditory processing disorder)
Other types of disorders diagnosed by non- SLP professionals (e.g., ADHD; autism; syndromes)
Stuttering? Weiss (1964) – Does stuttering stem from cluttering? Case history re: onset
I had the opportunity to hear Joe Duffy speak in 2008 & 2009: imitation of hypokinetic dysarthria = slurring quality

15. To do this, we need to ask about:
Prevalence of stuttering vs. cluttering vs. their co-occurrence
Prevalence of concomitant disorders compared to the pure existence of each disorder type
Tools of the trade:
Diagnostic materials
Observational skills
Acoustic measures needed (e.g., phones per second; pause loci and duration)
Some have argued that the exact prevalence of cluttering is unknown; some authors report prevalence
rates lower than those for stuttering, whereas others suggest it is approximately 5%; Many have called for a repository of samples from those who clutter. This would help us even perceptually – thanks to research from Healey and colleagues we know that listeners tend to react to an elongation of a continuant C or vowel that exceeds a duration of 445 ms as being a [A] – we need these same perceptual boundaries for the intelligibility, irregular rate, abnormal pausing from clutterers.

16. Preliminary prevalence data
The prevalence of cluttering among disfluent speakers has varied reports: Is cluttering just as prevalent as stuttering (i.e., ~1%), or is it even more prevalent than that?
Unanswered question: Is there an incidence of cluttering to compare to the 5% incidence of stuttering?
That is, do individuals ever spontaneously recover from cluttering?
Weiss (1964) suggested stuttering stems from cluttering; could we infer a core complex?

17. Stutter-Clutter (23/42 = 55%)
Van Zaalen (2009) subjective judgments + objective measurements (n = 54 individuals, 6- to 47 yr-olds, who self-referred or whose parents referred them for fluency disorders)
Undecided (12/54 = 22%)
Decided (42/54 = 78%)
Even with the added measures of disfluency ratio (NS/S), errors, and rate is sps, these cases represent lack of clarity in exact Dx
Stutters (9/42 = 21%)
Clutters (10/42 = 24%)
Stutter-Clutter (23/42 = 55%)

18. If evaluating a person with a fluency disorder suspected to be cluttering:
Determine if facilitating a slow speech rate facilitates greater fluency and/or greater intelligibility/speech precision. Slow via one of the following options:
Delayed auditory feedback (DAF, e.g.,
pacing board and/or
choral reading and rote lists (days of the week)
In other words, is the fluency disorder and/or low intelligibility secondary to speaking faster than the speech production system can handle?
Can the speaker pass a basic apraxia / dysarthria battery?
We need agreement on what defines abnormally fast and abnormally irregular articulatory rate. It is hypothesized that there are persons who clutter who maintain a high articulatory rate in a more demanding speaking situation,
and their speech-language system can not handle such fast speed. Due to speech motor or language planning problems in a high articulatory rate, intelligibility problems or disfluencies occur (Daly, 1992).
The presumable difference between apraxia and dyarthria versus cluttering is that correct syllable and word structures do occur for clutterers in controlled situations (Damste, 1984; Van Zaalen & Winkelman, 2009; Ward, 2006; Weiss, 1964).

19. Van Zaalen’s (2009) data also points us to the importance of three other areas for diagnosing cluttering:
Observations of cluttering “imprecisions”:
errors in syllable or word structure;
extra (non-linguistic) pausing;
Cluttering, not stuttering:
SSI-3 severity scores were equal or below 2 (no – mild stuttering);
Score on the Brutten speech situation checklist (S- 24) – or a similar scale – is within normal limits.
Cluttering, not LLD, via standardized tests, etc.

20. Measures important for differential Dx
Disfluency ratio: Determine within-word disfluencies or “stutters” (W, S, A, B) and between-word disfluencies or “non-stutters” / mazing-like disfluencies (P, R, I, O) and divide the nonstutters by the stutters:
Person who clutters > 1.0 due to the predominance of nonstutters
Person who stutters < 1.0 due to the predominance of stutters (Van Zaalen, Wijnen & DeJonckere, 2009)
I believe it is also useful to ask the client about sound production control. While the efficiency of this exercise is complicated by the low awareness characteristic in cluttering, it is trial therapy as well.
Findings from van Zaalen, Wijnen & DeJonckere (2009) showed that a diagnosis based on subjective clinical judgment of a SLP specialized in fluency disorders appeared to correspond with the judgment of another SLP specialist in only 50% of all disfluent cases. Of all cases, 15.2 % of diagnoses remained undecided after adding differentiating objective measures to the subjective diagnostic decision.

21. Measuring rate in syllables per second (sps):
Difficulties:
Weak Syllable Deletion (WSD) gives listeners the impression of rapid rate, but sps is average to slow.
Yet measuring phones per second (pps) is time consuming, and phoneme imprecision adds to the same type of problem.
Van Zaalen (2009) found “accelerated bursts” of speech in the midst of disfluent utterances, when disfluencies are excised and yet this is tedious to measure.
Possible Solutions:
Note percent application of WSD (% opportunity)
Note irregularity / festinating = clinical observation (Duffy, 2008)
See Case of T

22. Case study of T (20 yo UWEC student)
Twenty utterances from a monolog (“Tell me about your typical day” and follow-up Qs) were transcribed and coded for disfluencies.
These 20 utterances ranged from 3 to 58 syllables and averaged 25 syllables in length, totaling 496, or 442 fluent syllables.
Fifteen (75%) included one or more disfluencies and the other five (25%) were fluent.
T produced 54 total disfluencies in this sample of 442 syllables, thus he was 12% disfluent overall (9% nonstutters; 3% stutters):
About half (26/54 = 48%) were interjections [I] (“um” “uh”),
About a quarter were revisions [R] (n=12) and phrase repetitions [P] (n=3) (15/54 = 28%),
Remaining quarter (13/54 = 24%) were within-word disfluencies (sound-syllable repetitions [S] n=6; whole-word repetitions [W] n=5; audible prolongation/other [A] [O] n=2).
This calculates to a rate of 232 syllables per minute (spm), with a range of 153 – 420 spm.

23. Case study of T (continued)
Fluent speech rate could only be based on the five fluent utterances, and averaged 3.6 sps (range: 3.0 – 4.5 sps).
“Disfluent speech rate,” based on the remaining 15 utterances, averaged 3.95 sps (range: 2.55 – 7.0 sps). (see pp & 267 of Guitar, 2006)
Example 1:40 Well mainly we’re jus’ [R] we’re really bad at the business [b8zn1s] side of things so we can never really [R] an’ we play outside [tse]d] of the cities, like we won this battle of the bands in the cities earlier [6ly5] this year. 1: actual syl/9 sec = 5.33 sps
We could use a logic that goes something like this: (1) Disfluent rate (DR) is a generally a slower average than fluent or articulatory rate (AR) at least from people who stutter (i.e., stuttering takes up time), so (2) if a cluttering client’s DR is faster than the norms for AR, then he must be fast. That is, along with a subjective rating of fast/irregular rate, an objective yet less tedious and more available measure could be added to verify fast and irregular rate. In this case study however, T showed a faster DR than AR, lending either credence to the point made by van Zaalen that the fast spurts occur in the disfluent utternances, presumably to make up for lost time, or there is a bias in the data by not having enough fluent utterances in a clinical assessment situation to compare to the disfluent ones.

24. Case study of T (continued) : N=84 multisyllabic words in this sample.
Of these 84 , 23 were produced with “weak syllable deletion” (e.g., “outside”  “tside” “one o’clock”  “one-clock”).
Thus, percentage of weak syllable deletion application is 23/84 or 27% , which is higher than considered normal at any adult age.
If intended syllables are counted instead of actual ones, speech rate (sps) results would be faster.
This finding, along with the problem of few fluent utterances, makes an articulatory rate measure challenging.

25. Case history / interview Q’s:
Rate, fluency, clarity/intelligibility, language and thought, and self-awareness
Lay definition questions of cluttering v. stuttering:
Cluttering: Is it ok with you that listeners tell you to “slow down”? Do you tend to slow down when told to? Does slowing help your fluency? Does it help you to be better understood? Why? Why not? (i.e., awareness)
Stuttering: When you repeat or prolong sounds/syllables, do you know exactly what word you want to say, but for that split second, you are unable too say it? Describe that moment as best you can. (i.e., loss of control, a core definitional concept)
Medication(s)? Dosage? Effects? (Bernstein & Bloodstein Ratner, 2008)
As Ward (2006) described, PWS seem to have problems producing what is already coded,
while PWC experience problems in coding speech during conversation.
Esp. “self-awareness,” the client’s awareness of whether the listeners are getting it or not, is also important. One differential diagnosis question that is very important is to ask, “If someone tells you to slow down, does that tend to help you to be more fluent, or does that tend to make the problem worse?” If the person answers “Yeah, when someone asks me to slow down, I often will try to do that, and it generally helps my fluency,” that is often the response of a more mature client who clutters. Versus, most of the time for people who stutter, being told to slow down will worsen the problem. In this second case, a lot of attention is being brought to the nature of their speech, and for most individuals who stutter their speech fluency will worsen with the “slow down” instruction.

26. Lay definition of cluttering
“Cluttering is a speech problem in which a person’s speech is either too fast, too jerky, or both. Most people who clutter seem to run their words or sentences together, and they often have many more fillers, hesitations, revisions, or other breaks in their speech than normal speakers do. Their speech sounds ‘cluttered’ as though they do not have a clear idea of what they want to say, and they are often not aware that they have a speech problem.”

27. Lay definition of stuttering
“Stuttering is a speech problem in which a speaker typically repeats or prolongs (draws out) parts of words, or gets stuck or blocked on words. Sometimes stuttering consists of strategies that try to reduce or avoid repeating, prolonging, or blocking. Stuttering is often associated with psychological stress or unpleasant feelings. Finally, the person who stutters often experiences a loss of voluntary control in saying certain words (St. Louis, 2009).”
Then the lay definition of stuttering, just very briefly, is useful for differential diagnosis purposes, or for diagnosing the concomitant disorder of “stuttering-cluttering.” [read slide]
Again I find this useful to include simple language when we describe the problem to our clients.
St. Louis et al. found, when asking respondents to identify if they knew anyone who stutters or clutters, given these lay definitions, that cluttering may be more prevalent than the literature suggests (e.g., St. Louis et al., 2003). So with combined categories of cluttering and stuttering-cluttering almost as prevalent as stuttering. So likely this underestimation of the prevalence of stuttering over the years is in line with the experience many of us have had, that relatively few clients who clutter will cross our clinic doorstep. That is, people who clutter exist, maybe as many as 1 per 100 or 1 per 200, but they often don’t pursue help for their speech. So it’s difficult to get a true estimate of the prevalence of cluttering.

28. What’s on your clipboard?
Daly & Cantrell (2006) Predictive Cluttering Inventory. Free download from and supplemental info about its use.
Sample dialog, monolog, and phone calls of spontaneous, connected speech.
Good for excluding those who do not clutter, esp. (Van Zaalen, 2009)
Quick assessment tools for measuring disfluencies per 100 words; we use a 300-word grid based on Conture (2001):
Between-word disfluencies: “Phrase repetitions, Revisions; Interjections; Other” [common in cluttering]
Within-word disfluencies: “Whole-word repetitions, Sound- syllable repetitions, Audible prolongations, Blocks” [less common in cluttering]
Self-Perception task (e.g., Daly & Burnett, 1996)

29. What’s in your clinic room?
Computer, with mic, headphones, speaker, and installed with:
Audacity (v 1.2)
DAF/FAF Assistant (v.1.1)
Cluttering Assessment Program (v. 2.02; Bakker, 2005)
Low-tech options: recorder-playback device (Loquitor™) ; touch pad type stopwatches, calculators
[read slide] Praat is another software program available.
Cluttering software will allow you to assess number of inappropriate sounds inserted per 100 words; Count unfinished or “cut-off” words per 100 words. Count disfluencies per 100 words and determine proportion of between-word types vs. within-word types per total disfluencies.
Audio-recording and playback is almost a necessity when working with individuals who clutter because they are often are not able to identify speech errors online, while speaking, but they can be taught to identify errors offline, and then generalize that back to doing online error prevention and pause-filled self-corrections.

30. What will you do with recorded speech samples?
Count disfluencies per 100 words.
Code for type (W,S,A,B “stutters”/P,R,I,O “nonstutters”).
Divide the number of nonstutters by the number of stutters for a disfluency ratio (Campbell & Hill, 1994), so that the closer to 0-1.0, the more likely, the speaker stutters and does not clutter, and v.v. (Van Zaalen, 2009) .
Determine relative fluency response (%decrease) to “speak slower and more carefully” instruction.
[read slide]
words and determine proportion of between-word types vs. within-word types per total disfluencies.
Re: counting disflu: “2.5. Ratio Disfluencies
Evaluation of disfluencies, as a supplement to the diagnostic criteria based on articulatory
rate and articulatory accuracy was done using Campbell and Hill’s Systematic Disfluency
Analysis procedure (Campbell & Hill, 1994). All disfluencies in samples of spontaneous
speech and speech in story retelling were counted. The percentage of stutter-like
disfluencies and normal disfluencies was calculated. The ratio disfluencies was obtained by
dividing the percentage non-stutter disfluencies by the percentage stutter disfluencies, (for
instance a participant with 20% non-stutter disfluencies and 2% stutter disfluencies had a
ratio of 20/2=10) (Van Zaalen & Winkelman, 2009). It is expected that PWC will have a
higher frequency of non-stutter disfluencies and therefore their ratio will be above one,
while the person who stutters will experience more stutter disfluencies and their ratio will be
below one. It is also expected that the mix group (PWCS) ratios will be either below or
above one.”
If the client is showing signs of cluttering he or she will show more BWDs than WWDs, so no use trying to sample duration of three longest blocks as you would for a stuttering evaluation.

31. What structured tasks will you ask of your client?
Ask for rote speech: “Count, days of the week.”
Imitate multisyllabic words and sentences, phonemically loaded (e.g., Source for Apraxia)
Imitate a sentence with appropriate pausing.
Read and answer questions about the reading (Who, What, When, Why/what if).
Diadochokinesis: “Say /ppp/ as many times as you can as fast as you can.” (Use Audacity or stopwatch).
/pt/ “patty” for young children
/ptk/ “pattycake” for young children
[read slide] Ask them to imitate words like “aluminum” and “anemone”
“Who/What” Questions bring on more fluency, whereas “Why/what if” might bring on more disfluent speech.
Oral diadochokinetic coordination below
expected levels.
Table 2. Items adjusted to factors 1 and 2 according to a factor analyses of the Predictive Cluttering
Inventory (Daly & Burnett, 2006).

32. What other structured tasks might you ask of client?
Oral peripheral examination (e.g., St. Louis & Ruscello, 2000)
Motoric tasks
Audiological evaluation (pure-tone; typanometry; screen for auditory processing
Battery of tests assessing the suspected concomitant disorder(s) (e.g., standardized language measures)
[read slide]

33. References
Arndt, J. & Healey, C. (2001). Concomitant disorders in school-age children who stutter. Language, Speech, and Hearing Services in Schools, 32,
Bloodstein, O. & Bernstein Ratner, N. (2008). A Handbook on Stuttering (6/e). Clifton Park, NY: Thomson Delmar.
Conture, E. (2001). Stuttering (3/e). Englewood Cliffs, NJ: Prentice-Hall.
Daly, D. (1993). Cluttering: the Orphan of Speech-Language Pathology, American Journal of Speech-Language Pathology, 2(2), pp. 6-8).
Daly, D. & Burnett, M. (1996). Cluttering: Assessment, Treatment planning, and case study illustration. Journal of Fluency Disorders, 21,
Daly, D. A. & Cantrell, R.P. (2006). Cluttering characteristics identified as diagnostically significant by 60 fluency experts. Second World Congress on Fluency Disorders Proceedings.

34. Freund, H. (1952). Studies in the interrelationship between stuttering and cluttering. Folia
Phoniatrica, 4,
Freund, H. (1970). Observations on tachylalia. Folia Phoniatrica, 22,
LaSalle, L. & Wolk, L. (2009, August). Stuttering, cluttering, and phonological complexity: Case studies. Paper presented at the 6th World Congress on Fluency Disorders, Rio De Janeiro, Brazil.
Scaler Scott, K. & St. Louis, K. (2009). A perspective on improving evidence and practice in cluttering. Perspectives on Fluency and Fluency Disorders, 19,
St. Louis, K. O. (August, 2009). Global perspectives on cluttering: Research, assessment and treatment. Paper presented at the 6th World Congress on Fluency Disorders, Rio De Janeiro, Brazil.
St. Louis, K. O., Raphael, L. J., Myers, F. L., & Bakker, K. (2003, Nov. 18). Cluttering updated. The ASHA Leader, pp. 4- 5,

35. St. Louis, K. , Myers, F. , Bakker, K. , & Raphael, L. (2007)
St. Louis, K., Myers, F., Bakker, K., & Raphael, L. (2007). Understanding and treating cluttering. In E. Conture & R. Curlee (Eds). Stuttering and related disorders of fluency (3/e). NY, NY: Thieme, pp
Van Riper, C. (1982). The nature of stuttering. Englewood Cliffs, NJ: Prentice Hall.
Van Zaalen, Y. (2009). Cluttering identified: Differential diagnostics between cluttering, stuttering and speech impairment related to learning disability. Dissertation. Utrecht University, Netherlands. Retrieved from /zaalenopthof.pdf  
Van Zaalen, Y., Wijnen, F., & Dejonckere, P.H. (2009). Differential diagnostics between cluttering and stuttering, part one. Journal of Fluency Disorders, 34,
 Weiss, D. (1964). Cluttering. Englewood Cliffs, NJ. Prentice- Hall, Inc.
Ward, D. (2006). Stuttering and cluttering, Frameworks for understanding and treatment. Psychology Press, East Sussex.