ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
Acoustic Properties of Laughter in
Individuals with Williams Syndrome
Diana Culp
Vanderbilt University
1
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
2
Abstract
The laughter produced by individuals with Williams Syndrome has not previously
been studied. This work was motivated by the fact that individuals with WS have high
levels of social empathy, despite low intellectual functioning. This study analyzed the
characteristics of laughter produced by participants while watching humorous video
footage. These data were then described and also compared to the laughter of typically
developing adults. The results suggest that the laughter of Williams syndrome reflects a
positive internal state in the producer.
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
3
Introduction
Williams syndrome is a rare genetic disease “caused by the deletion of
approximately 25 genes on chromosome 7q1 1.23,” (Mervis & John, 2008, p. 970). This
section of chromosome seven contains the genetic code corresponding to the elastin gene.
As a result, Williams syndrome (WS) is characterized by weak ligaments, heart disease,
growth deficiency and connective tissue abnormalities. Cognitively, this disease is
marked by weak visuospatial skills. Individuals with Williams syndrome therefore have
difficulty seeing pieces being part of a larger whole. For instance, when asked to draw a
bicycle by arranging given pieces, the patient will draw each piece separately, (Mervis &
Klein-Tasman, 2003). Additionally, these individuals have mild to moderate intellectual
impairment and slow language acquisition. This neurodevelopmental disease has a
prevalence of 1 in every 7500 (Stromme, Bjomstad, & Ramstad, 2002). Individuals with
Williams syndrome have distinctive, “elfin” facial features. More specifically, they
typically have a “broad brow, full cheeks, stellate iris, flat nasal bridge, full nasal tip,
long filtrum, prominent lips and ear lobes, small, widely spaced teeth, and wide mouth,”
(Rvinen-Pasley et al., 2008, p. 2). Though Williams syndrome has many effects the most
interesting qualities are arguably its associated social characteristics.
Individuals with Williams syndrome are extremely gregarious. They frequently
approach total strangers in order to start a conversation with them, which is reinforced by
their exquisite, although late developing, linguistic skills. These individuals are typically
described as being hypersocial since they are so unreserved in group situations. As
children, Williams syndrome patients focus almost entirely on the faces of the people
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
4
around them, ignoring their surroundings, specifically toys (Rvinen-Pasley et al., 2008).
This is due to these patients’ high level of sociability. Furthermore, when faced with a
visuospatial task, these patients perform markedly better when the task has a social
meaning. For example, when asked to insert missing facial expressions based on social
cues within the scene, Williams syndrome patients were much more successful than in
tasks for which they were asked to complete a drawing of a socially irrelevant object
(Santos et al., pg. 561). These individuals are also extremely emotional, easily influenced
by the emotions and behavior of others, and are often overly anxious and irritable.
Now that the characteristics of Williams Syndrome have been discussed, we turn
our attention to laughter. Bachorowski, Smoski and Owren (2001) described laughter in
terms of its basic acoustic characteristics. Their laughter samples were recorded from 139
undergraduate students while watching humorous video clips. The recorded laughter was
defined as either voiced or unvoiced, with a subcategory of unvoiced grunts and snorts.
Voiced laughter is characterized by a “harmonically rich, vowel-like structure,”
(Bachorowski, Smoski & Owren, 2001, p. 1583). This type of laughter is song-like and
its frequency changes rapidly. Unvoiced laughter is marked by more noisy, atonal
sounds. Grunts, including breathy pants and cackles, were classified as “unvoiced grunt”
type laughter, in addition to snorts.
After classifying the recorded laughter, it was then broken up into bouts and calls
for purposes of acoustic analyses. A laughter bout is an entire laugh utterance or laugh
episode. After being separated into bouts, laughs were then separated into calls, or
discrete acoustic units that make up a laugh bout and tend to be quite short in duration.
After each bout and call was classified, they were analyzed and compared on the basis of
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
5
temporal features, production modes, and source- and filter-related effects. These are the
effects the vocal production branch and respiration track have on laughter.
It was found that more unvoiced (47.6%) laughter was produced than voiced
laughter (30%). The remaining 22.5% was comprised of mixed bouts. This was an
outcome trend that was found throughout the sample and was not based on individuals’
specific laughter style. Laugh bouts had a mean duration of 0.87 seconds with a standard
deviation of 0.77. Females produced more voiced bouts than males, while males laugh
bouts were longer than females. Call durations had a mean of 0.17 seconds with a
standard deviation of 0.14. Calls were 45.2% unvoiced, 34.2% voiced, and 13% mixed
(Bachorowski, Smoski & Owren, 2001). This study also found that voiced laughter is
associated with self-reported positive affect on the part of laughers.
Two additional papers by Bachorowski and Owren discuss the affect of voiced
laughter. The first work determined that voiced laughter has a more positive effect on the
listener than does unvoiced laughter. This conclusion was reached through five
experiments in which participants listened to pre-recorded laugh tracks and then rated
their internal emotional state, their interest in meeting the laugher and the laugher’s level
of attractiveness (Bachorowski and Owren, 2001). In a second paper, Bachorowski and
Owren (2003) argue that laughter is produced in order to “influence the affective states of
listeners, thereby also affecting their behavior.” In other words, laughter does not
communicate a specific message based on its acoustic features but instead functions to
affect the listener’s emotional response system. One implication is that laughers will be
more likely to produce voiced, rather than unvoiced, laughter if it is advantageous for
them to elicit positive emotions in listeners.
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
6
Since individuals with Williams syndrome have such unique social
characteristics, we hypothesized that their laughter would also be different. Specifically,
their laughter should contain more voiced laughter than that of a typically developing
adult. The acoustics of their laughter might also differ between the properties of voiced
and unvoiced laughter.
Method
Participants
A total of 15 subjects participated in this study. They were between 20 and 30
years of age (n = 8 males); all were Caucasian and from the United States and Canada.
These participants were in attendance at a summer camp for individuals with Williams
Syndrome held in Vanderbilt University’s Kennedy Center in June of 2007. This camp is
musically based since most Williams syndrome patients are extremely gifted in this art
form (Martens, M & Williams, S, 2008).
Stimuli and Apparatus
The stimulus used to promote laughter was an 208 second video segment of
slapstick comedy using animals. This video was selected due to the participants’ high
level of empathy, as is a characteristic of Williams Syndrome patients, (Skwerer et al.,
2008). Using slapstick comedy that involved the minor harm of humans could potentially
have an opposite effect on the participants. For example, instead of laughing when
someone accidently falls in a hole, as typically developing adults do, these individuals
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
7
might instead be concerned over the person’s wellbeing and so the display vignette would
be unlikely to elicit laughter.
While viewing the footage of multiple comedic exchanges of animals, the
participants’ vocal responses were recorded using a small microphone attached to their
shirt fronts. This type of microphone was used in order to avoid calling unnecessary
attention to the device in order to make the situation as normal as possible. The
participants’ laughter was recorded for later analysis, in addition to any speech that may
have been produced.
Design and Procedure
Laughter data was recorded in a laboratory in the Kennedy Center. Participants
were seated in a chair and faced a small television set approximately six feet away. The
research assistant began the experiment by greeting the participant by name and then
beginning a simple script describing the procedure. The assistant then started the footage
and left the room. The film ended and the participant was thanked and led from the room
by the assistant, who had not been present at any time during the experiment, but had
monitored the experiment through the headphone output of the voice recorder.
Laugh Selection and Coding
Laughter was defined as being any sound that would be considered a laugh if heard in
everyday circumstances, as in agreement with the method used by (Bachorowski et al.,
2001). Laughter intermixed with speech was not considered for analyses because of the
difficulty isolating laugh from speech components. Laughter recordings were categorized
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
8
at bout and call levels using Praat software (http://www.fon.hum.uva.nl/praat/). At the
bout level, laughs were categorized as either “voiced,” “unvoiced,” or “mixed.” If there
were the same amount of calls of each type, then the total duration of each type of
laughter is the deciding factor for the categorization of the bout. The duration of and the
number of calls in each bout were also measured.
Results
Laugh types and durations
Bout-level descriptive outcomes
A total of 414 bouts from 11 participants were analyzed (see Table 1 for
descriptive outcomes). The laughter produced by four participants was thrown out due to
recording errors. Of these, 49.5% were voiced, 35.5% were unvoiced, and 15% were
mixed. Examples of these bouts types are shown in Figure 1. Two subjects (18.2%) only
produced two types of laughter, whereas the remaining 9 (81.8%) producing all three
types. Bouts were an average of 0.885 seconds long and contained an average of 4.857
calls. However, there was substantial variability in bout duration and call production. The
shortest bout was 0.13 seconds and contained two calls, whereas the longest consisted of
24 calls and was 2.77 seconds long.
Inconsistencies between laughter types
In addition to producing differing percentages of laughter types, participants
produced longer voiced laughter bouts that contained correspondingly more calls. On
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
9
average, Williams syndrome patients’ voiced laughter bouts were 1.075 seconds long and
contained 6.229 calls. Conversely, unvoiced laughter bouts produced contained 3.844
calls on average and were 0.818 seconds long. Both of these statistics were statistically
significant in their differences. The mean difference in duration corresponded to a Pvalue of less than 0.001 while the disparity between the average amount of calls per bout
produced a P-value of less than 0.001. This information is contained in Table 2.
Sex differences
Comparisons revealed several sex differences in laugh production. On average,
the five male participants produced bouts that were 1.167 seconds long. Alternatively, the
six female participants’ bouts were 0.795 seconds in length. This was also a significant
difference since it produced a P-value of 0.065. Additionally, there was a statistically
significant difference between the number of total bouts produced by men versus women.
On average, men produced 20.2 total bouts while women produced 52.17 total bouts,
which correspond to a P-value of 0.028. Table 3 shows values for these results.
Comparison to typically developing adult laughter
When comparing Williams syndrome laughter to the typically developing adult
laughter statistics contained in Bachorowski and Smoski (2001), significant differences
were also found. This data is contained in Table 4. The average percentage of unvoiced
and voiced laughter differed between these two groups. Normally developing adult
laughter contains 30% voiced laughter, 47.6% unvoiced laughter and 22.5% mixed
laughter. Conversely, Williams syndrome participants produced 49.5% voiced laughter
39.5% unvoiced laughter and 15% mixed laughter.
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
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Discussion
This study sought to examine some of the basic acoustic features of the laughter
produced by individuals with Williams syndrome. The statistical breakdown of this
information is communicated in Table A and has been described. Specifically, laughter
data was separated into bouts and then classified as voiced, unvoiced, or mixed. The
number of calls per bout and duration was also recorded. Additionally, significant
differences were found between the duration of male and female bouts, the qualities of
voiced and unvoiced laughter, and between individuals with Williams syndrome and the
laughter produced by typically developing adults. These differences can be explained
with the help of Bachorowski and Smoski (2001) and Hudenko, Stone, and Bachorowski
(2009). These studies point out the differences between voiced and unvoiced laughter,
stating that “only voiced laughter is strongly associated with the induction of positive
affect,” (Hudenko, Stone, and Bachorowski, 2009). Also, their findings that “the vocal
expression of emotion in children with autism is closely linked with their internal state,”
can plausibly be applied to adults with Williams syndrome. This conclusion is supported
through the findings of this study, namely the differences between voiced and unvoiced
bouts and the disparities between WS laughter and normally developing adult laughter.
Although anecdotal, one additional finding was the stereotyped nature of each WS
participant’s laughter. Individuals’ laughter analyzed in this study was found to be highly
invariant throughout the laugh recording interval, which also supports the idea that
Williams syndrome laughter reflects a positive internal state. This conclusion is based on
the fact that laughter in typically developing adults is influenced by their social partners,
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
11
and is therefore variable across situations. Namely, voiced laughter produces a more
positive effect on listeners (Bachorowski and Smoski, 2001). Therefore, since WS
laughter is more fixed within a solitary environment, it is more likely to be a reflection of
a positive internal state, instead of a social tool to influence companions.
This study has also produced several avenues for further research, including
exploring the sex differences prevalent in Williams syndrome laughter and the possible
connection between empathy and laughter. Additionally, race and age of the participants
could be examined further.
WS Laughter is linked to internal state
Discrepancies between voiced and unvoiced WS laughter
After analyzing and comparing the average durations and number of calls
between voiced and unvoiced laughter, we concluded that individuals with Williams
syndrome produce longer voiced laughter bouts that contain more calls than the laughter
of typically developing adults. This is an interesting finding since voiced laughter is
unique in the fact that it putatively conveys a positive affect on the part of the laugher and
produces a positive affect in listeners. However, since the participants were alone in the
lab and there were no humans included in the video, no listeners were present. As a
result, the participants didn’t produce more voiced laughter in order to have a positive
effect on their social partners. Instead, it can be suggested that the participants were
conveying a positive internal state through their voiced laughter.
Variance between WS and normally developing adult laughter
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
12
Normally developing adult laughter and Williams syndrome laughter is different:
WS laughter contains more voiced laughter and less unvoiced laughter. This finding
supports the conclusion that Williams syndrome laughter reflects a positive internal state,
since voiced laughter is thought to be a marker of this quality. Again, since the
participants were alone while recording laughter bouts, their laughter was having no
effect on any companion. As a result, the larger percentage of voiced laughter can be
explained by the previously stated conclusion that WS laughter reflects a positive internal
state. This theory is supported by research done by Bachorowski and Smoski (2001) and
Hudenko, Stone, and Bachorowski (2009). Most notably, the Hudenko et al. study
examined the laughter of children diagnosed with autism, who produced almost no
unvoiced laughter. Accordingly, they concluded that “children with autism routinely
produce fewer types of laughs than typically developing children because their laughter is
more closely linked to their internal experience of positive affect,” (Hudenko, Stone, and
Bachorowski, 2009). It then reasonably follows that individuals with Williams syndrome
produce more voiced laughs than any other type due to the fact that their laughter reflects
their emotional condition.
Highly stereotyped laughter
Our conclusion that Williams syndrome laughter is closely linked to individuals’
emotional states is also supported by a unique characteristic of their laughter. This is a
highly stereotyped bout pattern between individuals. Of the 11 participants in this study,
nine of them produced a significantly larger number of their most frequent laughter type
as compared to their second most frequent type. For example, one participant produced
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
13
60 voiced bouts and 26 unvoiced bouts; a statistically significant difference. This
interesting finding supports the hypothesis that Williams syndrome laughter is more
invariant than normally developing adult laughter, and is therefore more likely to be tied
to a positive internal state.
Future Research
Sex differences in WS laughter
The sex differences found in the course of this study were interesting: the male
participants produced laughter bouts that contained more calls than their female
counterparts. This finding was also discovered in the normally developing adult laughter
(Bachorowski and Smoski, 2001) and therefore deserves further research. We did
discover that the male participants were more likely to verbally respond to the humorous
videos than the females. For example, male participants were more likely to comment on
and interact verbally with the video stimulus, making statements such as “Whoa! Crazy
penguin!” and “Watch out kitty!” during the data collection. This is an interesting finding
and inspires a closer examination, especially by varying the content of the video, which
could influence the participants’ reactions.
Empathy and its impact on WS laughter
Williams syndrome patients are unique in their high level of empathy. This is a
characteristic trait of the syndrome and can provide insight into empathy in normally
developing adults. Consequently, the relationship between Williams syndrome laughter
and empathy is one that could have interesting implications in terms of understanding the
affective lives of persons diagnosed with this disorder.
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
Subject
1
2
3
4
5
6
7
8
9
10
11
# of Bouts
50
20
10
35
47
17
38
27
12
95
63
Average # of
Calls
3.66
3
6
4.229
3.851
6.0588
2.184211
2.814815
10.83333
5
8.126984
Average
Duration
0.72578
0.684
1.4343
0.816143
0.8835
1.206824
0.276316
0.895222
2.525167
0.867463
1.020587
Average # of
Bouts
14
# of Voiced
Bouts
15
8
7
26
15
14
4
6
10
60
40
Total Voiced
Bouts
37.63636364
Total # of Bouts
414
205
49.50%
# of
Unvoiced
Bouts
# of Mixed
Bouts
29
12
2
5
28
1
4
17
2
26
21
Total
Unvoiced
Bouts
147
35.50%
6
0
1
4
4
2
30
4
0
9
2
Total Mixed
Bouts
62
15.00%
Table 1
Unvoiced Average # Voiced Average # of
of Calls
Calls
3.844
6.229
t(1, 350) = 6.53, p < .001
Unvoiced Average
Voiced Average
Duration
Duration
0.818 seconds
1.075 seconds
t(1, 350) = 3.47, p < .001
Table 2: Significant differences between laughter types
Male Average
Duration
Female Average Duration
1.167 seconds
0.795 seconds
t(1,9) = 2.10, p = .065
Male Average
Female Average
Number of Bouts
Number of Bouts
20.2 bouts
52.17 bouts
t(1,9) = 2.62, p = .028
Table 3: Sex differences
WS % Unvoiced
39.50%
Typically Developing
% Unvoiced
47.60%
WS % Voiced
49.50%
Typically Developing
% Voiced
30%
Table 4: Differences between WS laughter and typically developing adult laughter
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
Figure Captions
Figure 1. A voiced bout shown using Praat software.
Figure 2. An unvoiced bout shown using Praat software.
15
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
Figure 1
Figure 2
16
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
17
Acknowledgements
This research was performed at Vanderbilt University, under the supervision of
Dr. Jo-Anne Bachorowski: thank you for your help and support. Also, thank you to Dr.
Craig Smith, Director of the Psychology Honors Program for all of your communication
and assistance. Finally, thank you to Elisabeth Dykens for your aid in data collection and
to the individuals who participated in this study.
ACOUSTIC PROPERTIES OF LAUGHTER IN INDIVIDUALS
WITH WILLIAMS SYNDROME
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