JOURNAL OF APPLIED BEHAVIOR ANALYSIS
ELIMINATION OF BEDTIME THUMBSUCKING IN HOME
SETTINGS THROUGH CONTINGENT READING’
MARTHA F. KNIGHT AND HUGH S. MCKENZIE
UNIVERSITY OF VERMONT
Reading stories at bedtime was made contingent upon nonthumbsucking for girls 3, 6,
and 8 yr old. According to their mothers, all had been persistent thumbsuckers since
infancy. Two had accompanying dental disorders. During baseline conditions, con-
tinuous noncontingent reading occurred. During experimental conditions, reading
terminated on each occasion thumbsucking was observed and resumed immediately
when thumbsucking ceased. High percentages of thumbsucking occurred during baseline
conditions when reading was noncontingent, and low percentages occurred during ex-
perimental conditions when reading was contingent. Bedtime thumbsucking was elimi-
nated for all three girls.
Forty-six per cent of the child population
from birth to 16 yr of age are reported thumb-
suckers (Traisman and Traisman, 1958). The
desirability of eliminating this habit is indicated
by its apparent social inappropriateness, its as-
sociation with dental malocclusion, and con-
tinuing efforts to develop procedures for its
Thumbsucking has been associated with open
bite, overjet, and closed bite dental malocclu-
sions (Norton and Gellin, 1968). In a large
group of children ranging in age from birth to
16, malocclusions were observed in 10% of the
thumbsuckers and in 7% of the nonthumb-
suckers (Traisman and Traisman, 1958). In
another group of primary grade children, over-
jet malocclusion was observed in 30% of the
thumbsuckers and in 9%0 of the nonthumb-
suckers (Murray and Anderson, 1969).
The home has been a preferred setting for
1The authors wish to express their appreciation to
mothers June Nye and Ann Egner for their precision
in recording and reading contingently, to the teachers
and staff of the Burlington Day Care Center for their
assistance and cooperation, and to orthodonist Edward
Marceau and pedodontist Robert Watson for the use
of their professional libraries. Reprints may be ob-
tained from Martha F. Knight, Consulting Teacher
Program, University of Vermont, Burlington, Ver-
implementing procedures to control thumbsuck-
ing. Management procedures sometimes recom-
mended for use in the home include sucking
natural shaped bottle feeding nipples (Picard,
1959), sucking pacifiers such as the Nuk Sauger
exerciser (Meach, 1962), wearing special con-
straining mittens (Benjamin, 1967), prolonged
sucking from the breast or bottle (Spock,
1968), wearing thumb splints, adhesive ban-
dages, restraints, or applying bitter-tasting
chemicals to the thumb (Watson, 1969), and
giving parental attention contingent upon non-
thumbsucking and ignoring thumbsucking
(Haryett, Sandilands, and Davidson, 1968).
The effects of the above procedures have not
been reliably measured.
Management procedures have also been im-
plemented outside the home by dentists, teach-
ers, and behavioral scientists. One such pro-
cedure involves cementing a stainless steel
spurred bar to the upper molars (Haryett, Han-
sen, and Davidson, 1970). This bar extends
across the palatal arch and prevents sucking
action. For a group of 59 children, mothers
reported that thumbsucking was arrested for 11
of 18 children after three months of palatal
bar placement, for 17 of 19 children after six
months, and for all of a group of 22 children
after 10 months of bar placement. Thumbsuck-
1974, 73, 33-38 NUMBER 1 (SPRING 1974)
MARTHA F. KNIGHT and HUGH S. McKENZIE
ing resumed for six of these children within
2 yr after removal of the palatal bar, including
one from the three-month group, three from the
six-month group, and two from the 10-month
A procedure implemented in a classroom was
associated with reduced thumbsucking behavior
in three third-grade girls (Skiba, Pettigrew, and
Alden, 1971). This procedure made teacher at-
tention and praise contingent upon writing and
folding hands, behaviors considered incompat-
ible with thumbsucking. The effectiveness of
this procedure was verified through an ABAB
design for two of the three subjects. Neither
continuance nor generalization of the reduced
thumbsucking was reported.
In a laboratory, presentation of filmed car-
toons contingent upon nonthumbsucking was
alternated with periods of uninterrupted car-
toons for one boy (Baer, 1962). For two addi-
tional boys, cartoons were contingent for one and
yoked for the other. The yoked child was pre-
sented with cartoons only when the other child
was not thumbsucking. This was alternated with
periods of uninterrupted cartoons for both boys.
In all cases, thumbsucking decreased only during
the conditions in which the cartoons were pre-
sented contingent upon nonthumbsucking.
The present paper reports a procedure to help
parents reduce thumbsucking in the home.
Baer’s procedure was adapted such that parents’
reading of stories was made contingent upon
nonthumbsucking and withdrawal of reading
was contingent upon thumbsucking. The bed-
time hour was selected because it is a high-
probability time for occurrence of thumbsuck-
ing (Gesell and Ilg, 1943). Besides having the
advantage of being readily carried out in the
home, this procedure allows the parent to be-
come a signal for nonthumbsucking behaviors.
Subjects and Settings
Sara was 3 yr old, with her mother reporting
that she had been a thumbsucker since infancy.
She sucked her right thumb, curled her right
index finger around her nose and often held a
favorite blanket in her left hand. Sara attended
a day care center where she spent most of the
day in a large room with 15 other children. The
noon lunch time was followed by toilet activi-
ties and a 1-hr nap on the room’s carpeted floor.
The initial 20 min following Sara’s lunch was
the daily session time and took place in the
lunch room on a low cot. The first author was
the experimenter and primary observer and the
second author was a second observer during oc-
Rosie was 6 yr old and sucked her thumb at
bedtime, when watching TV, and when holding
soft, fuzzy objects. Rosie’s thumbsucking was
the object of teasing by older siblings. Rosie’s
mother was the experimenter and her older
brother the second observer. The 10-min daily
session took place on the mother’s bed.
Jennifer was 8 yr old, and according to her
mother, sucked her thumb at bedtime, while
watching TV, and when holding a soft blanket
she called “Sucky”. She did not suck her thumb
when peers were present; e.g., in school. Her
parents also reported that she was frequently
reminded by both her dentist and orthondondist
to stop thumbsucking. The daily 20-min session
took place in Jennifer’s bedroom from 8:30 to
9:00 p.m. Jennifer’s mother was the experi-
menter and the first author the second observer.
Response Measures and Reliability
On each occasion a subject inserted her
thumb into her mouth such that a portion of
the thumb was placed posterior to the lips, the
experimenter activated a stopwatch, measuring
the cumulative time the thumb remained in this
position. (Finger sucking was never observed
in these children.) Percentages of thumbsucking
were calculated by dividing thumbsucking time
by total session time and multiplying by 100.
Total session time was the difference between
start and stop time. Session times for Sara were
approximately 20 min in length, with 91 of the
sessions from 17 to 23 min in duration and six
ELIMINATION OF BEDTIME THUMBSUCKING
sessions from 13 to 16 min. The varying session
lengths allowed for stories chosen by Sara to be
completed during the session. Stories were con-
tinued from day to day for Jennifer and Rosie
so that session lengths remained constant.
Reliability of measurement was provided by
the second observers who sat from six to 14 ft
from the subject and recorded in the same man-
ner as the experimenter. Observers were in-
structed to conceal stopwatches from obvious
view and to attend only to the thumbsucking
response when recording, rather than the read-
ing or measuring behaviors of the experimenter.
The clicking sound of the stopwatch may have
been audible during infrequent quiet periods,
but neither experimenters nor observers re-
ported hearing stopwatch clicks other than their
An index of reliability of measures was cal-
culated by dividing the lower recorded percent-
age by the higher and multiplying by 100.
Further reliability was provided by placing the
measures of the experimenter and observer on
the same graph and comparing the two func-
tions. Cofunctional reliability occurs when the
measures of the two observers form similar
functions (Goldiamond, 1968, p. 117). For
instance, the experimenter may observe thumb-
sucking during 90% of the session time and the
second observer 70%. When contingent reading
is introduced, thumbsucking is observed 40%/
and 30% of the time. When reading is no
longer contingent, observations are 95% and
65%. The two functions thus formed are sim-
ilar, indicating cofunctional reliability.
Baseline and Contingent Reading Conditions
Each child was asked to choose books or
stories that were read by the experimenter dur-
ing sessions. During baseline conditions, the ex-
perimenter read continuously to the subject,
whether thumbsucking occurred or not.
During contingency conditions, the experi-
menter stopped reading and was silent for the
duration of the thumbsucking interval. Experi-
menters were instructed to ignore questions or
any other responses made by the child and to
look directly at the book and only peripherally
at the child. When the subject removed her
thumb from her mouth, reading was immedi-
Experimenter measures for Sara (Figure 1)
are indicated by solid points. During Baseline I,
when the experimenter read continuously, the
mean percentage was 82 and the range 70 to
95%. For Contingent Reading I, when reading
was discontinued during thumbsucking inter-
vals, the mean was 18 and the range was zero
to 50. The mean for Baseline II was 70 and the
range 1 to 95%. For Contingent Reading II,
the mean was 11 and the range 0 to 74%.
Second observer measures are indicated by
open circles. The mean index of reliability be-
tween observers was 93%. Experimenter and
observer data indicated cofunctional reliability.
Rosie’s patterns of thumbsucking (Figure 2)
were highly similar to Sara’s. During Baseline I
and II, mean percentages for Rosie were 60 and
22%; during Contingent Reading I and II, 8
and 0.8%,. Ranges for Baseline I and II were
50 to 80 and 5 to 70%, and for contingency
conditions 0 to 15 and 0 to 5%, respectively.
The mean index of reliability was 96%, with
cofunctional reliability as indicated.
Jennifer’s thumbsucking did not markedly de-
crease until after Day 38 (Contingent Reading
I, Figure 3), when her bed was moved to the
center of the room. The move was made because
her mother reported that Jennifer was preoc-
cupied by items on the bookshelves located on
the wall, and it was thought that this preoccupa-
tion might be reducing the effectiveness of con-
tingent reading. After the bed was moved, Jen-
nifer’s patterns of thumbsucking were closely
similar to Sara’s and Rosie’s. Because thumb-
sucking did not decrease until after Day 38,
Baseline III and Contingent Reading III were
implemented to obtain a more conclusive ver-
ification of the effect of contingent reading.
MARTHA F. KNIGHT and HUGH S. McKENZIE
BASELINE I CONTINGENT
BASELINE II CONTINGENT READING It
4 6 12 16 20 24 28 32 36 40 44 40 52 56 60 64
* EXPERIMENTER MEASURES
o OBSERVER MEASURES
Fig. 1. Each point represents the percentage of time Sara sucked her thumb during daily bedtime reading
sessions. Experimenter measures are depicted as solid points and observer measures as open circles.
CONTINGENT READING I
BASELINE II CONTINGENT
I I READING 11
IeS# I 0
0 EXPER IMENTER MEASURES
Fig. 2. Each point represents the percentage of time Rosie sucked her thumb during each daily bedtime read-
ing session. Experimenter measures are depicted as solid points and observer measures as open circles.
EUMINATION OP BEDTIME THUMBSUCKING
Mean percentages for Baseline II and III
were 25 and 68%, with ranges 0 to 52 and 57
to 75%. During Contingent Reading II, thumb-
sucking measures remained at zero, and during
Contingent Reading III, the mean percentage
was 5%, with a range of 0 to 16%1. The mean
index of reliability was 94%/, with cofunctional
reliability as indicated. No thumbsucking was
observed on a post check 25 days after daily
measures were terminated.
The principles of behavior analysis inherent
in the described procedure are the same as in
Baer’s (1962). Differential reinforcement is ap-
plied for all behaviors other than thumbsucking
(DRO) on a continuous schedule, while the
effects of contingent withdrawal of the rein-
forcer punishes thumbsucking and increases the
probability of stable avoidance behavior (non-
thumbsucking). Emotional responses, some-
times reported to be produced by punishment,
were observed in each subject during contin-
gency conditions: e.g., Sara hit the experi-
menter; Jennifer shouted, “Read, I’m getting
mad;” and Rosie said, “I know why you’re not
For Jennifer, behavioral control is demon-
strated by comparison of the four conditions
BII, CRII, BII, and CRII (Figure 3). A
marked decrease in thumbsucking behavior was
observed only during the final six days of CRI,
after Jennifer’s bed was relocated. This reloca-
tion was preceded by reports that Jennifer was
increasingly attending to items on the shelves.
For instance, on Day 37 Jennifer took a news-
paper from the shelf and continued to suck her
thumb while reading the newspaper. In order
to clarify the effects of contingent reading, a
third return to baseline conditions was judged
For Jennifer and Rosie, complete cessation
of thumbsucking was reported for the entire day
BASELINE I B II
CONTINGENT READING I
I CR II I
I I l I
I I I
I I I
* EXPERIMENTER MEASURES
o OBSERVER MEASURES
Fig. 3. Each point represents the percentage of time Jennifer sucked her thumb during daily bedtime
reading sessions. Experimenter measures are depicted as solid points and observer measures as open circles.
The arrow indicates a relocation of the bed away from apparently distracting stimulus materials.
38 MARTHA F. KNIGHT and HUGH S. McKENZIE
within several weeks after the procedures were
terminated and reportedly has not recurred in
the 4 yr since. Mothers of these girls were in-
structed to attend to their daughters (e.g., pa-
rental praise and proximity) when nonthumb-
sucking behaviors occurred and to withdraw
attention (e.g., cease conversation and walk
away) when thumbsucking occurred. However,
whether such instructions were followed or
alone led to complete generalization is ques-
tionable. Perhaps each mother was established
as a stimulus in the presence of which non-
thumbsucking was reinforced, thus facilitating
generalization. Sara’s mother did not carry out
the contingent reading procedures and reported
that Sara did not generalize nonthumbsucking
behaviors from naptime to other situations.
The effectiveness of these procedures is fur-
ther supported by anecdotal reports of two boys,
ages two and four, for whom mothers applied
the contingent reading procedures. For both
boys, generalization was reported to be complete
within several weeks after termination of pro-
cedures. Thumbsucking was reported not to
have recurred during the 5 yr since reading
procedures were terminated.
The use of mother’s contingent reading in
Baer’s paradigm is an effective procedure for
eliminating thumbsucking behavior at bedtime.
Through implementation of these procedures,
generalization may be facilitated by the estab-
lishment of the mother as a stimulus for non-
thumbsucking behaviors. Further advantages are
the adaptability of these procedures to the home
routine and the utilization of readily available
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(Revision requested 2 March 1972.)
(Revision requested 23 October 1973.)
(Final acceptance 27 December 1973.)