Education and Training in Developmental Disabilities, 2008, 43(2), 198-216
© Division on Developmental Disabilities
Comparison of PECS and the use of a VOCA: A Replication
Ann R. Beck, Julia B. Stoner, and Stacey J. Bock
Illinois State University
Tom Parton
McLean County Unit 5 Schools
Abstract: This study compares use of the Picture Exchange Communication System (PECS) and a Voice Output
Communication Aide (VOCA) with four preschool children who were either non-speaking or limited in their
ability to speak and did not use an AAC system to communicate functionally. An alternating treatment single
subject design was used to measure participants’ preferences for each system and the verbalizations of the
participants during system use. Results indicated that participants learned PECS in a relatively short time
period, preferences for one mode of communication are not predictable, and the influence of the communication
systems on each participant’s verbalizations varied.
Many children with autism and other developmental disorders can not express themselves
functionally through spoken language (Sigafoos & Drasgow, 2001). For these children,
augmentative and alternative communication
(AAC) systems often provide the means by
which they can communicate with other individuals in their lives. Family members and
interventionists seeking to provide an appropriate AAC system for a child with complex
communication needs are faced with a wide
variety of AAC systems from which to choose.
These options range from unaided systems
(those that do not require anything external
to the body in order to communicate) to
aided systems (those that require something
external to the body in order to communicate;
Mirenda, 2001). Aided systems vary from simple picture boards to digitized electronic devices to highly sophisticated computerized
techniques.
One aided, picture based system is the Picture Exchange Communication System
(PECS). PECS was developed by Bondy and
Frost (1994) to teach children with complex
communication needs how to initiate communication. Its use with these children has been
supported by a large body of anecdotal literaCorrespondence concerning this article should
be addressed to Ann R. Beck, 4100 College of Arts
and Sciences, Illinois State University, Normal, IL
61790-4100. Email: [email protected]
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ture (Mirenda, 2001) and by several controlled, empirical investigations (CharlopChristy, Carpenter, Le, LeBlanc, & Kellet,
2002; Hanley, 2003). There are six training
phases in the PECS protocol. The first one
teaches a child to exchange a picture for a
tangible positive reinforcer. The following
phases teach the child to travel some limited
distance to get the picture to exchange, to
discriminate between two or more pictures, to
use a sentence strip beginning with “I want,”
to respond to direct questioning, and to comment (Bondy & Frost).
Another aided approach to AAC intervention is the use of voice output communication
aids (VOCAs). Mirenda (2001) discusses several advantages for the use of VOCAs that
include the facts that “because they provide
speech output, they have the potential to be
easily integrated into everyday environments
with unfamiliar people” (p.146) and their use
can “facilitate natural interpersonal interactions and socialization by virtue of the speech
output they provide” (p. 147). The use of
VOCAs with children who have complex communication needs has been described in clinically oriented literature (e.g., Burkhart, 1993;
Goossens’, Crain, & Elder, 1992) and has been
supported by a few empirically controlled investigations (e.g., Bock, Stoner, Beck, Hanley,
& Prochnow, 2005; Romski & Sevcik, 1996;
Schepis, Reid, Behrmann, & Sutton, 1998).
Although both PECS and the use of VOCAs
Education and Training in Developmental Disabilities-June 2008
have been documented as being useful with
children who are candidates for AAC interventions, there continues to be a need for literature specific to AAC application and its efficacy that can guide the selection of an
appropriate AAC system (Ogletree & Harn,
2001). Furthermore, as Schlosser (2003) indicates “once it has been demonstrated that
individual interventions are efficacious in
their own right, practitioners are often interested in knowing whether another approach
might be even more efficacious” (p.554).
Thus the need exists not only for additional
studies of the efficacy of specific AAC systems,
but also for comparative studies of the efficacy
of two or more AAC systems.
To address these needs, Bock et al. (2005)
conducted a study utilizing a single-subject,
alternating treatments design to compare children’s learning and use both of PECs and a
GoTalk (a digitized VOCA). Both techniques
were taught using the protocol suggested by
Bondy and Frost (1994). Participants were six
preschool children who were non-speaking.
Their results indicated that within the relatively short time frame of 6-weeks, all their
participants learned to initiate a request spontaneously using both PECS and the GoTalk.
During generalization probes done following
the study, all children showed some evidence
of maintaining the behaviors learned during
the intervention sessions. Additionally, 3 of
the 6 participants demonstrated a preference
for PECS during generalization, 2 of the 6
demonstrated a preference for the GoTalk
during generalization, and 1 showed no preference. Bock et al. interpreted these results to
suggest that both PECS and VOCA can be
efficient methods of communication for children with complex communication needs and
that, at this time, the data do not support the
use of one in exclusion to the other.
Son, Sigafoos, O’Reilly, and Lancioni (in
press) also used an alternating treatments design to compare how children with complex
communication needs learned the use of a
picture exchange system versus the use of a
VOCA. Their findings were consistent with
those of Bock et al. (2005). All 3 of Son et al.’s
participants learned to use both the pictureexchange system and a VOCA relatively
quickly and easily. When given an opportunity
to choose which mode of communication they
preferred following training, all children expressed a preference: one child preferred the
VOCA and two children preferred picture exchange.
A randomized group experiment comparing the effect of two different intervention
procedures, PECS and the Responsive Prelinguistic Milieu Teaching (RPMT), on the frequency of nonimitative spoken communication and the number of different nonimiative
words spoken by children with autism was conducted by Yoder and Stone (2006). Results of
this study indicated that there was an advantage of PECS over RPMT on both dependent
variables after 6 months of treatment. This
advantage, however, disappeared when the
dependent variables were measured again 6
months after the cessation of treatment. At
this time, children in both treatment groups
evidenced strong growth on both measures of
functional spoken language. When the children’s initial level of object exploration was
considered, however, a difference in children’s performance was apparent. “PECS facilitated the number of different nonimitated
words used in children with initially high object exploration. RPMT benefited children
with initially low object exploration” (p. 708).
Another study utilizing a single subject alternating treatments design was conducted by
Tincani (2004) with two school-aged children
with autism to compare the efficacy of PECS
compared to sign language training. Results
indicated that both treatments increased word
vocalizations, with a greater increase during
sign language training.
Thus the results of Bock et al. (2005), Son
et al. (in press), Tincani (2004), and Yoder
and Stone (2006) all indicate that the use of a
picture exchange system with children with
complex communication is a viable means of
providing children with an appropriate means
of requesting desired objects or events. Furthermore, all of these studies indicated that
another intervention technique (either use of
a VOCA, sign language, or RPMT) could also
be effective. Yoder and Stone’s results indicated that children’s initial level of object exploration could be a factor that would indicate
which technique would be more effective in
obtaining the intervention goal of increasing
verbal output in children with autism. Bock et
al. and Son et al. indicated that children dem-
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onstrated individual preferences for one
means over another that could not be determined by children’s performance during the
intervention, and Tincani reported an advantage of sign language over PECS. The question of what intervention technique is most
appropriate to use to increase the functional
communication of children with complex
communication needs remains an important
one that requires further investigation.
One of the limitations Bock et al. (2005)
cited of their study was the fact that they did
not audio or videotape sessions. They, therefore, could not document any changes that
might have occurred in their participants’ verbalizations or compare the effects of the use of
VOCA and PECS on verbalizations. Given results from previous studies indicating that
both the use of PECS and of VOCAs have
potential for stimulating speech (Bondy &
Frost, 1994; Ganz & Simpson, 2004; Kravits,
Kamps, Kemmerer, & Potucek, 2002, Schwartz,
Garfinkle, & Bauer, 1998; Romski & Sevcik,
1996), and that children demonstrate individual preferences for one system over another
(Bock et al.; Son et al., in press), the influence
of VOCAs and PECS on the verbal output of
children with complex communication needs
should continue to be investigated.
The purposes of the current study, therefore, were to conduct a replication of Bock et
al. (2005) with different preschool-aged participants to increase the ability to generalize
their 2005 findings and to audio-tape the participants’ sessions to document any changes in
verbalizations with intervention using either
PECS or a VOCA. The specific questions asked
were: (a) Which intervention approach is
more efficacious with children with complex
communication needs, the use of PECS or the
use of a VOCA? and (b) How does the use of
PECS influence children’s verbalizations as
compared to the use of a VOCA?
Method
Participants
The participants were four preschool children
who were either non-speaking or limited in
their ability to speak and did not use an AAC
system to communicate functionally. Children
were drawn from an Autism Summer School
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offered through a school district located in a
city with a population of approximately
150,000 in central Illinois. The students were
attending due to extended school year recommendations from their Individualized Education Plans. After obtaining consent for Educational Experimentation from the local school
district’s administration, the children’s teacher
and school speech-language pathologist were
asked to recommend children they believed
would be appropriate for the study. All participants were white Caucasian children from
middle-class homes who were being educated
in a preschool setting six hours daily for four
days a week during 4-weeks of the summer
school session. All children could physically
manipulate and visually locate a laminated 2
in. x 2 in. picture, and none used a formal,
functional AAC system. Three were males
(one set of identical twins) and one was a
female. The twins (Mitchell and Brad, not
their real names) were diagnosed with autism
and were not able to communicate functionally. The female (Susan, not her real name)
had a diagnosis of Speech and Language Impaired and exhibited symptoms of apraxia.
Her phonological-articulation skills had a significant negative impact on the intelligibility
of her limited speech such that she also was
not able to communicate functionally. The
other male (Derek, not his real name) had a
diagnosis of Pervasive Developmental Disorder – Not Otherwise Specified (PDD-NOS).
This child used some limited speech that consisted primarily of echolalic phrases.
Materials
For both the VOCA and PECS interventions,
the symbols used were 2 in. x 2 in. laminated
colored pictures with the name of the picture
printed above it. These pictures were produced with Boardmaker Version 5.1.8 software. Velcro was attached to the back of each
picture. The concrete referent to which each
picture corresponded (e.g. a toy train for the
picture of a toy train) was also used in both
the VOCA and the PECS interventions. The
VOCA interventions used a GoTalk, a lightweight, digitized AAC device with a built-in
handle and nine static locations separated by a
keyguard. Velcro was attached to each of the
location sites on the GoTalk. The PECS inter-
Education and Training in Developmental Disabilities-June 2008
ventions included the use of a 1 in. three-ring
binder with a Velcro strip attached to the
front.
Coded data sheets, identical to those used
by Bock et al. (2005), were utilized in the
current study. These data sheets had a prepared format that allowed for documentation
of correct responses per session for each treatment phase for both PECS and VOCA. Additionally, if a response was incorrect, data
sheets allowed for the documentation of what
aspect of the response was incorrect (e.g., if
the child needed a gestural or physical
prompt to pick up or to release a PECS picture). Prepared format sheets were also utilized to assess procedural fidelity. Sessions
were recorded on a Professional Marantz
CDR300 CD recorder.
Dependent Measures
For the PECS intervention the dependent
measure, a correct response, was operationally
defined as exchanging a picture for a desired
item without a gestural or physical prompt.
The dependent measure for the VOCA intervention, also a correct response, was operationally defined as positioning the VOCA correctly by grasping the handle and accessing a
picture to produce digitized speech in exchange for a desired item without a gestural
or physical prompt.
The children’s vocalizations and verbalizations were also recorded during both PECS
and VOCA interventions. Recordings were
transcribed and transcriptions were analyzed
for total number of utterances per session, the
percentage of these utterances that were intelligible, the percentage of intelligible responses that were not imitated responses, and
the total number of different intelligible
words uttered per session.
Data Collectors
Four investigators were present during all intervention sessions. The specific investigators
present each day followed a regular rotation
across the 4-weeks of the study and included
six graduate students in speech language pathology, three doctoral level faculty members
in speech-language pathology or special education, and the speech-language pathologist
who worked in the autism summer school experience. All of the professionals involved in
conducting this study had extensive experience working with children with complex
communication needs. For every session the
lead person was always either one of the certified speech-language pathologists or the special educator. All investigators were trained in
the interventions, data collection procedures,
and procedures to evaluate procedural reliability.
Inter-rater Agreement
Inter-rater agreement was assessed for correct
responses using both the VOCA and PECS
during baseline, intervention, and generalization probes. Two individuals independently
scored each child’s responses for all sessions.
Number of agreements was tallied and divided
by the number of agreements ⫹ disagreements. Inter-rater agreement was 100% for all
children for the VOCA condition and 100%
for Mitchell and Brad for PECS and 99% and
95% for Susan and Derek, respectively.
Inter-rater agreement for the transcription
of the recordings of the sessions was also calculated. Three graduate students in speechlanguage pathology, who were members of
the research team, transcribed the recordings.
First, all recordings were transcribed in their
entirety by dividing the transcripts equally
among the three graduate students who each
transcribed their assigned transcripts. Then,
20% of the sessions were randomly selected,
with the stipulation that the sessions chosen
were representative of the entire length of the
study, to be re-transcribed. The same graduate
students who originally transcribed the sessions also transcribed the randomly selected
sessions, but no student re-transcribed the
same session. That is, 20% of the transcripts
were independently transcribed by two graduate students who were part of the research
team. The unit-by-unit agreement index (i.e.,
the number of agreements divided by the
number of agreements ⫹ disagreements) was
100% for Derek, 93% for Susan, 97% for
Mitchell, and 96% for Brad.
Experimental Design
The same experimental design used by Bock
et al. (2005), an alternating treatment single
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201
subject design (Tawny & Gast, 1984; Zhan &
Ottenbacher, 2001), was implemented in this
study. First, intervention procedures were operationally defined so that in each session a
child would have 10 opportunities or 15 minutes, whichever came first, to request items or
activities using VOCA and 10 opportunities or
15 minutes, whichever came first, to request
items or activities using PECS. Then schedules
were set for counterbalancing the presentation of interventions across time and children
and for the order in which children would
participate each session. If a child started with
PECS followed by VOCA on day one, then the
order was reversed on day two and so on,
counterbalancing the order of intervention
procedure used across children. Additionally,
half the children were randomly selected to
follow the intervention order VOCA/PECS
and the other half followed the order PECS/
VOCA. The order in which children participated rotated so that the child who was seen
first on day one was seen last on day two, the
child who was seen second on day one was
seen first on day two, the child who was seen
third on day one was seen second on day two,
and the child was seen last on day one was
seen third on day two. This rotation was maintained throughout the summer.
General Procedure
All sessions, except for the generalization
probes, were conducted in the same classroom in the school the children were attending. Children were seen on an individual basis
for all sessions. A reinforcement inventory was
conducted on the first day of the study. Baseline data were collected on the second day.
Baselines were conducted on only one day
because alternating treatment single subject
designs do not require baselines (Zhan & Ottenbacher, 2001) and because the time span
of the summer school session was relatively
short. Intervention was then conducted over
the next 3 1⁄2-weeks. Generalization probes
took place in the home one week after the end
of summer school.
Reinforcement inventory. Prior to beginning
any intervention with the children, a reinforcement inventory was conducted for each
child. During the reinforcement inventory,
two to three objects were placed in front of
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the child and researchers documented which
object was preferred per object grouping.
Preference for the object was noted when the
child independently chose to consume an edible or to manipulate an object or a toy. Approximately 10 reinforcing objects were identified for each child. These objects included
food, toys, and activities (e.g., playing with a
See ‘n’ Say or a Barney stuffed animal). For
each child, the reinforcers were randomly divided into two groups of equally desired objects and activities. One group of reinforcers
was randomly chosen for use with the VOCA
intervention and the other with the PECS intervention.
Baseline. The baseline data were collected
to strengthen the conclusions drawn from the
results of the study. During baseline 3-4 items,
the corresponding PECS pictures, and the
VOCA with the appropriate pictures attached
were placed within the child’s reach. The
child was observed for 10 minutes and the
number of times that the child either exchanged a picture with the observer or activated a location on the VOCA as a request for
an item was recorded. The observer did not
interact with the child unless the child engaged in one of the above behaviors or in a
self-injurious behavior.
PECS Phase I – Picture exchange. Four researchers were involved in PECS intervention
during Phase I. One researcher served as the
communication partner and sat across a table
from the child. The second researcher was the
prompter and sat behind the child. The third
and fourth members of the research team
observed and scored responses.
These roles stayed consistent within a session, but rotated across sessions so that a child
did not learn to communicate with only one
person. A picture was placed in front of the
child and the corresponding desired item was
either placed on the table behind the picture
or was held by the communication partner.
No verbal prompting was provided to the
child to exchange the picture for the object. If
the child tried to pick up the item without
exchanging a picture for it, his or her response was blocked and the prompter used
hand-over-hand to assist the child in accomplishing the exchange. During the time between the presentation of the stimuli and the
child’s final response, the communication
Education and Training in Developmental Disabilities-June 2008
partner held out her open hand giving the
child a gestural prompt to exchange the picture. Once the student placed the picture in
the communication partner’s hand, the partner gave the child the desired item and reinforced the child verbally, stating, for example,
“train, I want train!” All prompting was gradually faded until the child was independently
able to exchange a picture for a desired object
80% of the time for two out of three consecutive days. Once this criterion was reached,
PECS Phase II was begun.
PECS Phase II – Persistence of communication.
The Phase II protocol for PECS consisted of
placing a 1 in., three-ring binder with one
picture attached to the Velcro strip on its
cover in front of the child. The object that
corresponded to the picture was also in the
child’s view. No verbal or gestural prompts
were given to the child by the communication
partner to exchange the picture for the object. If the child tried to access the desired
item without using the picture, then physical
assistance was provided to enable the child to
pick up the picture and exchange it for the
object. Once the child handed the picture to
the communication partner, the partner gave
the child the desired object and verbally reinforced the child as in Phase I. When the child
was able to exchange the picture independently in Phase II, the communication partner
gradually began to move away from the child
until a distance of 6 ft was achieved. The communication partner also began to turn away
from the child. In the final step of shaping
persistence, the communication partner
moved 6 ft away and turned her back to the
child. The child was thus required to become
more persistent in his or her attempts to communicate because he or she had to pick the
picture up, get out of his or her chair, ambulate toward the communication partner, appropriately get the communication partner’s
attention, and finally hand the picture to the
communication partner in order to receive
the desired object. When the child did this
successfully for 80% of the opportunities on 2
out of 3 consecutive days, PECS Phase III was
initiated.
PECS Phase III – Picture discrimination. The
Phase III protocol for the PECS intervention
consisted of placing two pictures on the Velcro strip on the binder, one of a desired item
and one of a neutral item (e.g., a hanger).
The order in which these pictures were placed
on the strip was alternated on a random
schedule. This binder was placed in front of
the child and the desired object was located
behind the binder, but in a position that was
obvious to the child. Again, the communication partner sat across a table from the child
and did not prompt the child in any way to
exchange a picture for the object. The child
had to look at the two pictures, discriminate
between them to select the picture of the desired item, and then hand that picture to the
communication partner in exchange for the
desired item. If the child chose the picture of
the neutral item to exchange, then the child
received the neutral item. If the child rejected
it, then the child was given another chance to
choose between the pictures of the desired
item and the neutral item.
When the child was able to discriminate
between the items on a consistent basis, the
items the child had to choose between were
changed to be equally desirable. Again, the
order in which these pictures were placed on
the strip was alternated on a random schedule. On every fifth trial a correspondence
check was conducted. These checks consisted
of offering the child two items after the picture exchange, asking the child to “Take it”
without specifying what the child should take,
and noting if the child chose the item that
corresponded with the picture he or she had
originally selected. If the child did not choose
the item originally requested, then an error
correction sequence was performed in which
the child was prompted to choose the item
that corresponded to the picture the child
had handed the communication partner. After every successful exchange, the communication partner verbally reinforced the child in
the same way she had in the previous Phases.
VOCA Phase I –Activate picture location. The
protocol used for the intervention with the
GoTalk was identical to that used for the
PECS. The only difference was that the picture of the item was attached to one of the
locations on the VOCA and the name of the
picture (e.g. production of “cookie”) was programmed into the device. To receive the desired object, the child had to grasp the handle
on the upper edge of the GoTalk, lift the top
edge off the table so that the bottom edge of
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203
the GoTalk was still supported on the table,
and activate the location containing the picture. Requiring the child to lift the VOCA
partially off the table was done as preparation
for Phase II training.
VOCA Phase II –Persistence of communication.
Again, the protocol used for the VOCA intervention in Phase II was identical to that of the
protocol followed for the PECS Phase II intervention with the exception that the child had
to pick the GoTalk up by the handle, carry it
to where the communication partner was, get
the communication partner’s attention, brace
the GoTalk on his or her stomach or hip, and
then activate the correct location as a request
for the desired object or event.
VOCA Phase III –Picture discrimination. A
protocol identical to the one used with PECS
Phase III was utilized for the VOCA Phase III
with the exception that the two pictures were
attached to randomly alternated spots on the
GoTalk and the child had to pick the GoTalk
up as in Phase I and activate the location with
the picture of the desired item.
Generalization probes. Generalization probes
were conducted in the children’s homes one
week after the end of treatment. During these
probes, the PECS and VOCA materials were
placed together in a location the child could
access. The family members were instructed to
interact with the children in a typical manner.
Two researchers remained in the environment primarily as data collectors and did not
participate in the communication exchanges
unless children initiated the exchange. Every
instance of the child spontaneously selecting
either the GoTalk or a PECS picture and using
it to initiate a request with a person in their
home was documented.
pect of the response was incorrect. Similar
tables were not constructed for PECS because
of the rapid acquisition of PECS behavior.
Bock et al. (2005) referenced Alberto and
Troutman (2003) as indicating that graphic
displays of data should be simple and uncluttered so that a clear picture of progress over
time is given. The graphic display of data used
by Bock et al. therefore departed from what is
usual for alternating treatment designs because “(a) both interventions consisted of
three separate phases and the children progressed through the intervention phases
(PECS and VOCA) at differing rates; thus,
creating an inability to insert intervention
lines between the phases; and (b) data were
collected on each treatment (PECS and
VOCA) each day resulting in multiple overlapping data points” (p. 269). Graphic data on
requesting behaviors from the current study
are displayed in a manner similar to that of
Bock et al. for the same reasons stated by these
authors.
Procedural Fidelity
To ensure that procedures were correctly implemented, procedural fidelity measures were
assessed during the intervention procedures.
On a schedule that was unknown to the person presenting intervention, a scorer documented procedural fidelity for at least one
session in each phase of each intervention for
all children. Procedural reliability was documented on a form that was created for each
phase for both PECS and VOCA. Procedural
reliability was 100% across all phases of each
intervention for each child.
Results
Data Analysis
Data on the acquisition of spontaneous initiations of requests with PECS and with VOCA,
the mean number of utterances spoken per
session, the mean percentage of utterances
per session that were intelligible, the mean
percentage of intelligible words that were not
imitated, and the mean number of different
words spoken per session were graphed and
then visually inspected. Additionally, for incorrect responses utilizing the GoTalk, data
tables were constructed documenting what as-
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Acquisition of Use of PECS and VOCA During
Individual Pull-Out Sessions
On the day baseline data were collected, no
child showed any ability to utilize either PECS
or the VOCA to initiate a request. As shown in
Figures 1-4, Derek and Susan met the criterion to advance through to Phase III with
PECS within the 4-week time frame of the
summer school experience. By the end of the
summer school experience Brad reached criterion to move to Phase II of PECS, but time
Education and Training in Developmental Disabilities-June 2008
Figure 1. Derek’s progress in learning PECS and the VOCA
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Figure 2. Susan’s progress learning PECS and the VOCA
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Education and Training in Developmental Disabilities-June 2008
Figure 3. Mitchell’s progress learning PECS and the VOCA
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Figure 4. Brad’s progress learning PECS and the VOCA
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Education and Training in Developmental Disabilities-June 2008
only allowed for one session to be conducted
with him in Phase II of PECS. Mitchell approached criterion to move to Phase II of
PECS, but did not meet criterion during the
time frame of the study.
Only Susan met criterion to move to Phase
II with the VOCA, but time did not allow
Phase II training to begin. Derek made
progress toward meeting the criterion to move
from Phase I to Phase II training with the
VOCA, but neither Mitchell nor Brad ever had
one fully accurate response using the VOCA.
The steps required for a response with the
GoTalk to be considered correct were that the
child first had to pick the GoTalk up, then had
to point to and press the appropriate picture,
and finally had to release the GoTalk. Each of
these steps was analyzed for each participant.
For Susan, even though it took her until the
end of the study to reach criterion to move to
Phase II with the VOCA, she was able to point
to and press the correct picture and release
the GoTalk with at least 80% accuracy for two
out of three consecutive sessions by the sixth
session. The physical act of picking the GoTalk up was what appeared to be difficult for
her to learn. Similarly, Derek was able to point
to and press the correct picture and release
the GoTalk with at least 80% accuracy for two
out of three consecutive sessions by the sixth
and fourth sessions, respectively. It was not
until the final session that he demonstrated
the ability to pick up the GoTalk consistently.
Brad was able to point to and press the picture
with approximately 50% accuracy either independently or given only a gestural cue from
the sixth session through the remainder of the
study. From the tenth session on he was able
to release the GoTalk with at least 40% accuracy. He never showed any consistent ability to
pick the GoTalk up. Mitchell demonstrated
no consistent ability to perform any of the
steps needed for use of the GoTalk.
Generalization of PECS and VOCA in the Home
Generalization probes of the use of PECS and
the VOCA were held in the home one week
after the end of the summer school experience for Susan and Derek. Susan only demonstrated generalization of PECS behavior one
time and never demonstrated generalization
of the use of the VOCA in her home. Derek,
however, used both modes of communication,
but showed a marked preference for the use
of the GoTalk. Specifically, he demonstrated
generalization of PECS behaviors three times
and of the use of the VOCA 17 times to initiate
a request. Generalization sessions were not
held in Mitchell and Brad’s home due to
scheduling conflicts with the parents.
Effect of Interventions on Verbalizations
Tables 1, 3, 5, and 7 display data regarding
verbalizations produced during the use of
PECS and during the use of the VOCA for the
first 2-weeks of intervention, for the second
2-weeks of intervention, and for the entire
4-weeks of intervention. Each child’s mean
number of total utterances per session, mean
percentage of intelligible utterances per session, mean percentage of spontaneous intelligible utterances, and mean total number of
TABLE 1
Means of Derek’s utterances per session for PECS vs. VOCA
PECS
1st 2 weeks
2nd 2 weeks
total
VOCA
1st 2 weeks
2nd 2 weeks
total
Total
utterances
% intelligible
utterances
% spontaneous
intelligible utterances
Total number of
different words
16.4
18.3
17.5
55.6
73.0
65.8
92.2
81.6
86.0
12.0
11.4
11.7
15.6
19.3
17.8
57.2
85.6
73.8
93.4
97.4
95.8
11.4
16.0
14.1
PECS vs VOCA: A replication
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209
different words spoken are given for each of
the above listed time frames. As an illustration
of each child’s verbalizations, Tables 2, 4, 6,
and 8 record intelligible utterances spoken
during PECS and VOCA interventions for
sample sessions at the beginning and at the
end of the 4-weeks of intervention.
As shown in Table 1, during both the PECS
and VOCA interventions, Derek’s mean number of total utterances per session and the
mean percentage of intelligible utterances
spoken per session increased from the first to
the second 2 week time period. His mean
percentage of spontaneous intelligible utterances spoken per session decreased from the
first to the second 2 week period of PECS, but
remained high and stable for the VOCA intervention. Derek’s mean number of different
words spoken did not change during the
course of the 4-weeks for PECS, but increased
with the VOCA. A Comparison of data between the PECS and VOCA sessions for the
total 4-weeks indicates that Derek’s mean
number of utterances was not different for
PECS and VOCA, but all other verbalization
measures were higher for VOCA than PECS.
Table 2 lists intelligible utterances produced
by Derek for PECS and VOCA sessions in the
beginning of the intervention and at the end
of the intervention. Inspection of this Table
indicates that there was little change in the
complexity of the type of utterances produced
by Derek in either condition.
Data regarding Susan’s verbalizations are
contained in Tables 3 and 4. Inspection of
Table 3 indicates that for mean number of
utterances per session there was a slight increase for PECS and a decrease for VOCA
from the first to the second 2 week time period. There was also an increase in mean percentage of intelligible utterances spoken per
session for VOCA. No other notable changes
were noted for any of the other measures of
Susan’s verbalizations. Comparing Susan’s
data on verbalizations for the PECS and the
VOCA treatments indicated that there was an
advantage of PECS for the mean number of
utterances per session, and an advantage for
VOCA for the mean percentage per session of
the intelligibility of those utterances. No other
differences were noted. Inspection of Table 4
illustrates the similarity in her utterances in
210
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TABLE 2
Sample utterances for Derek
7/7/05
7/28/05
VOCA
Truck, truck
Sit please
Give to me
Farmer in the Dell
Okay
PECS
I want truck, please
Want bus
Other bus, other bus please
I want the farm
Done
I want crackers, please
Okay
VOCA
Very good, ok
I want pretzel
I want See ‘n’ Say
Drum
PECS
Cracker, you want cracker.
This is me
This, hanger
You want hanger
Yes . . . want train
I want train, please
bus
Give to me, cracker, See ‘n’ Say
You want See ‘n’ Say
Cracker
Picture
Hanger
both conditions from the beginning to the
end of the 4-week session.
As shown in Table 5, Mitchell had an increase over the course of the 4-weeks in both
the PECS and VOCA conditions in his mean
number of utterances per session, mean percentage of utterances that were intelligible
per session, and mean number of different
words spoken per session. The percentage of
intelligible utterances that were spontaneous
stayed fairly high and consistent across the
entire 4-weeks for both conditions. Comparing his verbalizations for PECS and VOCA
indicates that his mean percentage of intelligible utterances, while low for both PECS and
VOCA conditions, was greater for VOCA than
PECS. All other measures were comparable
Education and Training in Developmental Disabilities-June 2008
TABLE 3
Means of Susan’s utterances per session for PECS vs. VOCA
PECS
1st 2 weeks
2nd 2 weeks
total
VOCA
1st 2 weeks
2nd 2 weeks
total
Total
utterances
% intelligible
utterances
% spontaneous
intelligible utterances
Total number of
different words
27.2
29.6
28.4
48.2
47.0
47.6
91.8
98.8
95.3
4.4
2.8
3.6
25.2
21.0
23.3
58.0
65.0
61.3
97.5
100.0
98.6
3.5
4.4
3.9
for PECS and VOCA conditions. Table 6 illustrates the increase in verbalizations for Mitchell across the duration of the intervention.
As shown in Table 7, Brad had a decrease in
all utterance measures from the first to the
second 2 week time period for PECS and
VOCA. The only exception to this was mean
percentage of spontaneous intelligible utterances per session for VOCA, which did not
change during the intervention. Table 8 illustrates this change in Brad’s verbalizations.
Conclusions
Acquisition and Generalization of Use of PECS
and VOCA
Within the relatively short time span of the
current study, two participants (Derek and
TABLE 4
Sample utterances for Susan
7/7/05
7/28/05
VOCA
Yeah, yeah
Done
No
PECS
Yeah, yeah, yeah
No, no
VOCA
Yeah, yeah
No, no, no, no, no
PECS
Yeah
D (naming letter)
S (naming letter)
L (naming letter)
Susan) learned through Phase III of PECS, 1
through Phase I of PECS (Brad), and the
remaining participant (Mitchell) was making
good progress toward attaining criterion to
move to Phase II of PECS. These findings
support those of Bock et al. (2005) that indicate that children are able to learn at least the
first stages of PECS in a relatively short period
of time.
Findings of the current study also support
those of Bock et al. (2005) regarding the use
of a VOCA. The use of the GoTalk was more
difficult to learn than was the use of PECS for
all of the children in the current study. For 3
of the 4 children, however, the difficulty in
learning to use the GoTalk appeared to be
primarily due to the physical act of picking it
up by the handle. Both Susan and Derek
quickly learned to point to and press the correct picture and to release the GoTalk and
Brad demonstrated some ability to perform
these two tasks. These three children thereby
showed some understanding of the purpose of
using the GoTalk to request a desired item or
action.
The fourth child, Mitchell, did not demonstrate any ability to utilize the GoTalk appropriately. This was also the child who made the
least amount of progress in learning PECS.
During the first 2-weeks of the study Mitchell
and his twin brother Brad frequently engaged
in off-task and noncompliant (e.g., leaving the
table, sitting on the floor, crying) behaviors.
The other two participants did not display
these types of behaviors. Such behaviors interfere with learning and Mitchell’s and Brad’s
limited progress with PECS and the GoTalk
PECS vs VOCA: A replication
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211
TABLE 5
Means of Mitchell’s utterances per session for PECS vs. VOCA
PECS
1st 2 weeks
2nd 2 weeks
total
VOCA
1st 2 weeks
2nd 2 weeks
total
Total
utterances
% intelligible
utterances
% spontaneous
intelligible utterances
Total number of
different words
8.3
17.4
14.0
5.7
9.2
7.9
100.0
93.3
95.0
1.0
2.7
2.3
11.0
15.4
13.8
4.5
14.0
10.6
100.0
100.0
100.0
1.5
2.5
2.2
during the time frame of this study could well
be due to this interference. Indeed, both boys’
behavior improved during the last 2-weeks of
the study and that is when all of Brad’s
progress with PECS and the GoTalk and most
of Mitchell’s progress with PECS occurred.
The possibility also exists for Mitchell, however, that some aspect of the GoTalk (e.g., the
auditory feedback, the overall appearance of
the device) was aversive to him and that he
might not have learned to use it even with
extended training.
Because of parental scheduling constraints,
generalization data were only collected for
two (Susan and Derek) of the four participants. Generalization occurs when a learned
response is made to stimuli that are similar to
those stimuli used in training (Wilkinson &
McIlvane, 2002). Neither Brad nor Mitchell
demonstrated any evidence that they had
learned to use the GoTalk. On the second to
TABLE 6
Sample utterances for Mitchell
7/6/05
PECS
Ok, ok
VOCA
7/27/06
PECS
One, two, three
Hey, hey, hey
VOCA
I get it
I want
Hey, hey, hey
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the last session, Brad mastered criterion to
move to Phase II of PECS, but Mitchell never
mastered this criterion. Therefore, it is doubtful that these two participants would have
demonstrated generalization of either of
these behaviors even if their parents’ schedule
had allowed generalization sessions to be conducted in their home.
Susan had mastered the criteria to move
through Phase III of PECS and would have
moved to Phase IV if the time frame of the
study had allowed. She also met the criterion
to move to Phase II of the VOCA condition,
but again, time did not allow for this Phase to
be initiated with her. She did not, however,
show any notable generalization of either behavior in the home. This could indicate that
Susan needed more training and that her parents and other family members also needed to
be involved in the training in order for use of
either behavior to generalize to the home.
Derek also mastered the criteria to move to
Phase III of PECS and made progress toward
achieving criterion to move to Phase II of the
VOCA condition. His generalization data indicated a strong preference for use of the
VOCA. Given the fact that he progressed
more rapidly through the stages of PECS than
of VOCA use, this was a somewhat surprising
finding. It is consistent, however, with the
findings of Bock et al. (2005) and Son et al.
(in press) indicating that children express
preferences for one mode of communication
over another that are not predictable from
data on their accuracy when learning the
modes of communication.
Education and Training in Developmental Disabilities-June 2008
TABLE 7
Means of Brad’s utterances per session for PECS vs. VOCA
PECS
1st 2 weeks
2nd 2 weeks
total
VOCA
1st 2 weeks
2nd 2 weeks
total
Total utterances
% intelligible
utterances
% spontaneous
intelligible utterances
Total number of
different words
28.5
14.4
19.4
21.3
9.5
13.8
97.0
75.0
84.4
5.3
2.8
3.9
19.2
8.4
12.9
24.6
13.1
17.9
98.6
100.0
99.0
7.0
1.7
4.7
Verbalizations
Data on verbalizations for the four children
suggested that the influence of the two interventions on verbalizations was different for
each child. Brad showed a notable decrease in
all measures of his verbalizations for both conditions except for mean percentage of intelligible utterances that were spontaneous. These
remained consistent for the VOCA condition.
This decrease could be due to the fact that as
TABLE 8
Sample utterances for Brad
7/7/05
7/27/06
7/28/06
VOCA
Four, four
Five
No, no, no, no
Yeah, yeah, yeah
Okay
PECS
Five
Yeah, yeah
No, no, no
Vee (naming letter)
Thank you
Mario
Two
VOCA
Baby
Nine
PECS
Drum
VOCA
Yeah
PECS
he began to learn to use PECS to obtain a
desired object, he had less reason to try to
verbalize. His verbalizations prior to intervention did not, however, serve a functional purpose. Therefore PECS and his baseline verbalizations were not functionally equivalent
behaviors and PECS should not have replaced
his speech for that reason. Additionally, because he did not learn to use the GoTalk
independently even through Phase I training,
this explanation would not account for why
his verbalizations also decreased in the VOCA
condition. Another explanation for his decrease in verbalizations could be due to the
concept of working memory, which is necessary for language processing. Many theorists
suggest that “working memory is of limited
capacity (resources) and that there is competition by the processes for this limited capacity” (Wright & Shisler, 2005, p. 109). The possibility exists that Brad’s limited resources in
working memory were allocated to the learning of PECS and VOCA leaving him with insufficient resources to produce voluntary
speech. If this explanation was correct, then
his verbalizations should return to their previous levels, or increase, as he learned to use
PECS and a VOCA and needed to direct fewer
of his cognitive resources to the production of
these behaviors. None-the-less, these data are
cautionary indicators that the verbalizations of
all children might not be advantaged by use of
either PECS or a VOCA.
Results of the interventions on the remaining participant’s verbalizations were more positive. Derek’s verbalization data indicated an
PECS vs VOCA: A replication
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213
advantage of VOCA over PECS for all measures taken. By the end of the study, the percentage of his verbalizations that were intelligible had increased for both conditions, but
more notably so in the VOCA than the PECS
condition. Additionally, the percentage of
these intelligible responses that were spontaneous increased in the VOCA condition, but
actually decreased in the PECS condition.
Given that this child could produce some limited verbal speech before the onset of the
study, the advantage of VOCA over PECS
could be due to the added auditory input
provided by the VOCA.
Mitchell’s total number of utterances increased with both types of interventions.
While the mean of the utterances per session
for the entire 4-weeks was similar for both
PECS and VOCA, the gain in number of utterances spoken was greater for PECS than
VOCA. The increase in the mean percentage
of words that were intelligible, however, was
greater for the VOCA than the PECS condition. Inspection of Table 6 also indicates that
the complexity of his utterances increased for
both conditions, but more so for the VOCA
condition than PECS. The data on Mitchell’s
verbalizations therefore indicated a mixed influence of the two techniques taught. Both
PECS and VOCA had a slight positive influence on his spoken output with a small advantage of PECS over the VOCA condition for
number of utterances spoken and of VOCA
over PECS for intelligibility and complexity of
output. Given the fact that this child demonstrated no consistent ability to perform any of
the steps of using the GoTalk independently,
the fact that the VOCA condition influenced
his speech production at all was unexpected.
Such data suggest that even though he evidenced minimal learning with the VOCA, he
was still attending to the sessions and that
some of the auditory input (e.g., I want) was
registering enough for him to produce it at a
later time.
Susan’s verbalization data also appeared to
indicate a mixed effect of the two techniques.
The mean percentage of her intelligible responses that were spontaneous and the mean
number of different words she spoke per session were consistent throughout the study for
both conditions. In a manner similar to that of
Mitchell, however, her mean utterances per
214
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session increased in the PECS condition and
decreased in the VOCA condition while her
mean percentage of utterances that were intelligible increased in the VOCA condition,
but remained stable in the PECS condition.
For both Mitchell and Susan, the slight advantage found for the increase in mean number
of utterances per session for PECS could potentially have been due to the fact that their
greater ease in learning PECS allowed them to
allocate more of their limited cognitive resources to producing verbal output during the
PECS condition than during the VOCA condition. The slight advantage of the VOCA condition for the intelligibility of their spontaneous utterances could possibly have been due
to the auditory input provided by the VOCA.
Upon inspection of Table 4, however, it
becomes apparent that Susan was essentially
producing the same words at the beginning
and at the end of the study and that the
overall effect of either condition on her verbalizations was minimal. Susan demonstrated
characteristics of apraxia of speech that interfered with her ability to produce intelligible
speech. This child could very well require intervention targeted directly at her motor production of speech in order to show significant
increases in verbalizations.
Limitations and Directions for Future Study
Data on learning of the GoTalk indicate that
the primary difficulty children had in learning
to use this device was in the physical manipulation of it. For children to be able to demonstrate persistence in communication, however, they had to learn to pick the device up
and carry it to where they needed to communicate. This study should be replicated using a
device that does not need such physical manipulations, such as a wrist band device or a
device worn around the waist.
A major limitation of this study was the
limited time frame over which it took place, a
4-week summer school session. This time
frame did not allow three children to move
past Phase I with VOCA and only allowed two
children to move to Phase III of PECS. Furthermore it did not provide time to study the
effects of a fully learned use of PECS or VOCA
on verbalizations or how children would generalize these learned behaviors to other set-
Education and Training in Developmental Disabilities-June 2008
tings and communication partners. This study
should be replicated over a longer period of
time to determine more fully how the learning
of PECS and VOCA compare and the relative
influence each has on verbalizations.
Results of this study, however, are consistent
with those of previous research that indicate
that children can learn PECS in a relatively
short time period, and that various interventions have differential effects on children that
can not always be predicted. Research that
furthers understanding of the relative efficacy
of different AAC intervention techniques continues to be needed in order to offer the best
future possible to children with complex communication needs.
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Received: 25 October 2006
Initial Acceptance: 15 January 2007
Final Acceptance: 15 March 2007
Education and Training in Developmental Disabilities-June 2008