Mand Variability Article

RESEARCH ARTICLE
Effects of a Lag Schedule with Progressive Time Delay on Sign Mand
Variability in a Boy with Autism
Bryant C. Silbaugh1 & Terry S. Falcomata2
Published online: 18 September 2018
# Association for Behavior Analysis International 2018
Abstract
For some children with autism, mand training can produce highly repetitive manding unless the environment is arranged in a
manner that promotes mand variability. Prior research demonstrated that mand training using a lag schedule and progressive time
delay increased variability in vocal manding in children with autism. Whether lag schedules have similar effects on sign mand
topographies is unknown. The current study evaluated the effects of mand training with a Lag 1 schedule of reinforcement and
progressive time delay (TD) on topographical variability and the development of a sign mand response class hierarchy in a boy
with autism. The results suggest independent use of all sign mand topographies occurred, a mand response class hierarchy was
developed, and topographically variant sign manding increased under the Lag 1 + TD schedule compared to a Lag 0 schedule of
reinforcement. Implications for practitioners, limitations, and directions for future research are discussed.
Keywords Lag schedule . Mand . Operant variability . Response class hierarchy . Time delay
During mand training for individuals with language delays or
deficits (e.g., autism), a response such as saying “juice” is
taught by presenting a relevant establishing operation (EO;
e.g., giving access to salty popcorn and withholding juice)
and using prompting, rapid prompt fading, and differential
reinforcement to transfer control over the target response from
the prompt to the EO and contingent access to juice (Sundberg
& Partington, 1998; see Shafer, 1994, and Wallace, 2007, for
reviews of common procedures and concepts). However, unless the environment is arranged to support a variety of requests from the speaker, procedures commonly used in mand
training for some children with autism can produce invariant
(i.e., repetitive) manding (e.g., Carr & Kologinsky, 1983;
Silbaugh, Falcomata, & Ferguson, 2017).
Behavioral variability is critical for contacting reinforcement in a changing environment (e.g., Sidman, 1960).
Invariant manding may disadvantage a speaker when reinforcement mediated by a listener requires saying something
differently by either (a) failing to obtain reinforcement or
(b) exhibiting resurgence of challenging behavior as the
listener withholds reinforcement for invariant responding
(e.g., Volkert, Lerman, Call, & Trosclair-Lasserre, 2009).
At least two general types of invariant manding are commonly observed.
First, invariance may occur across mands, such as when a
child repeatedly emits mands for only one of multiple reinforcers concurrently available. For example, in the presence of
playdoh, juice, and a book, invariant manding may take the
form of the child repeatedly asking only for the playdoh across
trials. Alternatively, invariance may occur within a given
mand response class for a single reinforcer. For example, a
child may invariantly emit the vocal mand topography
“playdoh” across repeated instances of taking turns playing
with playdoh with a peer. For some children, topographically
invariant instances of a mand emitted over time may be due to
extinction of alternative mand topographies during training or
to a lack of sufficient response exemplars incorporated into
training (Lee, Sturmey, & Fields, 2007; Rodriguez &
Thompson, 2015). For example, to establish a topographically
variant mand response class, instead of only teaching the child
to say “playdoh,” the child may benefit from being simultaneously or sequentially taught to say “want,” “toy,” or
* Bryant C. Silbaugh
[email protected]
1 Department of Interdisciplinary Learning and Teaching, College of
Education and Human Development, University of Texas at San
Antonio, One UTSA Circle, San Antonio, TX 78249, USA
2 Department of Special Education, University of Texas at Austin,
Austin, TX, USA
Behavior Analysis in Practice (2019) 12:124–132
https://doi.org/10.1007/s40617-018-00273-x
“playdoh” under the control of the EO for access to
playdoh, with contingencies that support variation across
instances of turn taking. Wolfe, Slocum, and Kunnavatana
(2014) proposed general guidelines for increasing operant
variability in children with autism, but specific procedures
and guidelines for reinforcing mand variability in practice
requires more research.
Multiple studies have evaluated procedures that increase
variability or novelty across concurrently available reinforcers
(i.e., across mands) during mand training for individuals with
intellectual disability (e.g., Duker & van Lent, 1991) or autism
(Bernstein & Sturmey, 2008; Betz, Higbee, Kelley, Sellers, &
Pollard, 2011; Brodhead, Higbee, Gerencser, & Akers, 2016;
Carr & Kologinsky, 1983; Drasgow, Martin, Chezan, Wolfe,
& Halle, 2015; Sellers, Kelley, Higbee, & Wolfe, 2015). For
example, Bernstein and Sturmey (2008) compared the effects
of continuous and intermittent schedules of reinforcement on
the emission of alternative mands by two children with autism
and vocal manding repertories. A single high-rate mand was
placed on an intermittent schedule of reinforcement (e.g.,
FR10 or FR25), whereas all other mands were reinforced on
an FR1 schedule in the presence of four different reinforcers
for both children. Relatively higher total counts of alternative
mands emitted within sessions were observed when the intermittent schedules were in effect. Although prior research demonstrated procedures that can be used to predict and control
topographical variation across mands, other procedures may
be needed to establish a topographically variant mand response class, which is one focus of the current study.
Operant variability can be brought under discriminative
control and reinforced (Page & Neuringer, 1985). Lag schedules of reinforcement can increase operant variability by delivering reinforcement for a response if it differs from n prior
instances, with n equal to the value of the lag. For example,
under a Lag 3 schedule, a response is reinforced if it differs
from the preceding three responses (e.g., Susa & Schlinger,
2012). Potential advantages of using lag schedules over other
procedures that increase mand variability is that they may
facilitate generalization through the reinforcement of multiple
response exemplars (Silbaugh et al., 2017) and may mitigate
challenging behavior when treatment involves reinforcing
mand variability (e.g., Adami, Falcomata, Muething, &
Hoffman, 2017). A growing body of applied research has
demonstrated that lag schedules reinforce variability in verbal
behavior for individuals with developmental disorders (Wolfe
et al., 2014), and three studies have shown lag schedules can
increase variability in manding.
Brodhead et al. (2016) combined script training with lag
schedules of reinforcement to bring variability in manding for
edible items under discriminative control for three children
with autism. Sessions during the treatment evaluation included three different concurrently available edible reinforcers,
which were alternated across sessions based on the results of
preference assessments. During baseline, all mands were reinforced on an FR1 schedule of reinforcement. Following baseline, script training was used to teach participants to independently use new mand frames, such as “May I have [reinforcer]?” and “I would like [reinforcer].” Also during script training, discriminative control over mand frame variability was
established by alternating conditions with two different colored place mats. A green place mat was correlated with reinforcement for varying mand frames under a Lag 2 or Lag 3
schedule, and a red place mat was correlated with reinforcement for repeating the mand frame (i.e., “I want [reinforcer].”)
that existed in each participant’s repertoire before treatment.
Discriminated mand frame variability was the dependent variable and the dependent measure was the number of different
mand frames emitted per session. The results showed that
participants emitted relatively more different mand
frames per session under a lag schedule. However, the
dependent measure may have been insensitive to the variant dimension of manding because it differed from the
response dimension on which reinforcement was contingent under the lag schedule (De Souza Barba, 2012a, b).
That is, reinforcement was not contingent on the number
of different mand frames emitted within session, but
rather mand frames that differed from n different mand
frames emitted within session. Additionally, the use of
multiple types of reinforcers in a concurrent-operants arrangement does not allow for the assessment of variations in functionally equivalent manding (i.e., multiple
topographies or stimulus selections maintained by a single reinforcer).
Adami et al. (2017) evaluated the effects of a Lag 1 schedule of reinforcement combined with functional communication training (FCT; Carr & Durand, 1985) on varied nonvocal
manding and challenging behavior in two males with autism
diagnoses. The authors used reversal designs consisting of
three conditions (i.e., baseline, FCT/Lag 0, and FCT/Lag 1),
5-min sessions, and 30-s reinforcer durations for target responses. During baseline, no mand modality equipment was
available and challenging behavior produced the maintaining
consequence identified in a prior functional analysis on a continuous schedule of reinforcement. During FCT/Lag 0, three
different mand modalities were available (i.e., a card to exchange, a microswitch, and a tablet) and the reinforcer was
delivered contingent on the independent selection of any
mand modality. The FCT/Lag 1 condition was similar except
that the reinforcer was contingent on instances of manding in
which the participant selected a mand modality that differed
from the last mand modality selected within the session. For
example, if on Trial 3 the participant used the tablet to mand,
then on Trial 4 he was required to mand by pressing the microswitch or exchanging the card to produce the reinforcer.
The results indicated that FCT with lag schedules replaced
challenging behavior with manding and that the addition of
Behav Analysis Practice (2019) 12:124–132 125
the Lag 1 schedule of reinforcement increased mand
variability across modalities.
Silbaugh et al. (2017) investigated the effects of lag schedules on mand variability in two young children with autism.
For each participant, a mand topography invariance assessment was used to identify two mands emitted invariantly
across trials and to identify two new topographies to target
for each mand during the treatment evaluation. A multiplebaseline design across mands with embedded withdrawal was
used to evaluate the effects of a Lag 1 schedule of reinforcement with progressive time delay (TD) on topographical vocal
mand variability. Sessions were 5 min in duration. During the
Lag 0 condition (i.e., baseline), 25 s of reinforcement was
delivered contingent on any emitted vocal mand topography.
During the Lag 1 condition, 25 s of reinforcement was delivered contingent on independent or prompted variant vocal
mand topographies. A vocal mand topography was variant if
it differed from the immediately preceding vocal mand topography emitted within the session. Specifically, if the participant did not emit an independent variant vocal mand topography within 2 s of the EO (i.e., the onset of a trial), the
experimenter delivered an echoic prompt for a target variant
vocal mand topography. If the participant did not emit a variant vocal mand topography for six consecutive trials under a
given TD (e.g., 2 s), the TD was increased by 2 s on the
seventh trial. Mand variability training increased variability
in multiple functionally equivalent vocal mand topographies
for both participants and all four mands. The results of a post
hoc analysis of relative latencies showed that vocal mand topographies were emitted in a temporally predictably order,
suggesting that mand response class hierarchies (Baer, 1982)
were modified by incorporation of new mand topographies
during treatment. The purpose of the current study was to
extend Silbaugh et al. (2017) by (a) evaluating the effects of
a Lag 1 schedule of positive reinforcement combined with a
progressive TD on the acquisition and variability of multiple
sign mand topographies in a boy with autism and (b) analyzing relative response latencies to assess mand response class
structure formation.
Method
Participants and Setting
Allen was a 5-year-old boy with a diagnosis of autism who
attended a special day school for children with developmental
disabilities and received social and academic instruction using
applied behavior analysis. Based on information collected
during observation and interviews with caregivers and
teachers, Allen was selected for participation in this study
for three reasons. First, he demonstrated a largely deficient
verbal repertoire, consisting mostly of a few spontaneous
vocal mands (e.g., for a preferred stuffed animal) and physically guiding adults by hand to request reinforcers. Second, he
demonstrated good fine motor skills and generalized gross
motor imitation of actions without objects (e.g., clapping)
during an informal clinical assessment by the first author.
Third, his caregivers and teachers indicated that most prior
attempts at expanding Allen’s verbal repertoire had been unsuccessful at establishing mands used spontaneously and consistently. Per their report, he had not received prior instruction
in sign mand training but had received vocal-, picture exchange-, and tablet-based instruction based on Skinner’s analysis of verbal behavior (Skinner, 1957). The study was conducted in the school kitchen, which contained common kitchen appliances, tables, chairs, a piano, and standard research
equipment (e.g., toys, camera), shortly after lunch hours.
Response Definitions and Measurement
The primary dependent variables were (a) variant and (b) invariant manding. We measured independent variant sign mand
topographies, independent invariant sign mand topographies,
and prompted variant sign mand topographies. We collected
count data on instances of sign manding from session video
recordings using a computer-based data-collection program
and converted the count to a rate (i.e., signs per minute) to
enable visual analysis. An independent variant sign mand
topography was defined as an unprompted sign mand topography that differed from the last sign mand topography emitted within the session. For example, if the sign for “toy” was
emitted following the independently emitted sign “want,” then
the sign for “toy” was considered variant. Measurement of
variant sign mand topographies in each session began with
the second emitted sign mand topography because the first
sign mand topography emitted within a session was used by
the experimenter to discriminate between invariant and variant
manding. All distinguishable gestures toward the reinforcer,
other than a reach, were measured (e.g., clap, point). An independent invariant sign mand topography was defined as an
unprompted sign mand topography that did not differ from the
last sign mand topography emitted within the session. A
prompted variant sign mand topography was one that was
evoked by a model prompt provided by the experimenter
and topographically different from the last sign mand topography emitted within the session.
Secondary dependent variables were (a) different acrosssession sign mand topographies and (b) different withinsession sign mand topographies. Different across-session sign
mand topography was defined as a sign mand topography that
differed from all previous sign mand topographies emitted in
prior sessions and was measured by adding each new emitted
sign mand topography during a session to a cumulative total.
Different within-session sign mand topography was defined as
an emitted sign mand topography that differed from all prior
126 Behav Analysis Practice (2019) 12:124–132
emitted sign mand topographies within a session and was
measured by counting the number of different signs emitted
each session.
Interobserver Agreement and Procedural Fidelity
Interobserver agreement (IOA) and procedural fidelity were
assessed by trained observers who viewed videos and independently collected trial-by-trial (i.e., each instance of the programmed EO) data on 33% of sessions randomly selected
across all phases. Data collected on variant, invariant, and
prompted sign mand topographies were assessed using exact
count-per-interval IOA (Cooper, Heron, & Heward, 2007). To
calculate IOA, each recording period was divided into 10-s
intervals, the total number of intervals with exact agreement
was divided by the total number of intervals, and the quotient
was multiplied by 100. Mean IOA was 94% (range 85%–
100%). Mean fidelity for each select procedural component
was calculated by dividing the number correct by the number
correct plus the number incorrect and multiplying the quotient
by 100. Overall mean procedural fidelity was calculated by
dividing the sum of the individual means for each procedural
component implemented correctly by the number of components (i.e., 4) and converting the quotient to a percentage.
Overall mean procedural fidelity was 100% for the immediacy
and duration of reinforcer delivery, response-reinforcer contingency, descriptive praise, and prompt immediacy.
Design and Procedure
Following pretreatment assessment and training, an A-B-A-B
withdrawal design was used to evaluate the effects of sign
mand variability training on variant signs under a Lag 1 +
TD schedule of positive reinforcement (Silbaugh et al.,
2017). Three to four sessions per day were conducted with
the experimenter, approximately two to three days per week.
The participant was given a choice between three different
colors of playdoh every 2 to 3 days to minimize reinforcer
satiation. A treatment evaluation session was terminated and
excluded if no independent sign mand topography was emitted within 1 min of the onset of the first programmed EO of
the session. This occurred only once, during the final Lag 1 +
TD phase. Allen was given a break for 1–2 min consisting of
interaction with the experimenter between sessions of the assessment, training, and the treatment evaluation.
Pretreatment Assessment
The experimenter presented an array of toys and snacks and
conducted an approximately 30-min semistructured play session (a) to identify potentially reinforcing toys or activities and
(b) to briefly assess Allen’s responsiveness to sign mand training. Playdoh was identified as a potential reinforcer based on
Allen’s sustained engagement and repeated reaches for the
playdoh as the experimenter took brief turns. A hand over
hand–to–sign mand stimulus transfer procedure with errorless
prompting, prompt fading (physical, model, no prompt), and
differential reinforcement with reinforcer intervals of 20–30 s
was used to teach Allen “clapping” as an arbitrary mand response topography. Following approximately 20–30 trials,
Allen emitted multiple consecutive independent responses to
brief turns taken by the experimenter. The results of the assessment suggested Allen would rapidly acquire additional
sign mand topographies for playdoh during the treatment evaluation using a motor imitation–to–sign mand stimulus transfer
procedure. The experimenter’s playdoh and associated toys
(e.g., plastic plate, spoons) were not available to Allen between sessions.
Next, the experimenter selected three novel sign mand topographies to be targeted during the treatment evaluation. The
form of each sign was modified from American Sign
Language to minimize response effort. The sign “want” was
defined as extending one arm with palms up and bringing the
hand toward the body while forming a half fist once or repeatedly. The sign “playdoh” was defined as extending one arm
out, hand flat, palm down, and moving the hand toward and
away from one’s own body once or repeatedly. The sign “toy”
was defined as orienting one arm at approximately a 90-
degree angle toward the ceiling and tucking the thumb between pointer and middle finger with the tip of thumb pointing
up, then twisting the hand clockwise or counterclockwise
once or repeatedly. Reasonable approximations of the signs
were reinforced throughout the treatment evaluation. Allen’s
right hand was targeted for sign acquisition.
Pretreatment Sign Mand Training
After the pretreatment assessment was complete, a series of 5-
min training sessions were conducted to teach Allen to independently mand for playdoh using the sign “want.” Clapping
and poorly articulated vocalizations were placed on extinction. During each session, the experimenter repeated the training procedures described in the prior assessment. The exit
criterion for training was a single independent instance of
the sign “want” within a training session. Allen met the exit
criterion at the beginning of Training Session 4. The session
was immediately terminated, and baseline (i.e., Lag 0) data
collection for the treatment evaluation began.
Experimental Conditions
Lag 0 (Baseline) Allen was provided with free access to the
playdoh for 30 s prior to the start of the first session each day,
with the exception of the first session, which began immediately after he met the exit criteria for pretreatment sign mand
training. The experimenter initiated the session by
Behav Analysis Practice (2019) 12:124–132 127
removing access to the playdoh. Throughout the session,
20-s access to playdoh plus descriptive praise (e.g.,
“Playdoh! Nice job asking!”) was immediately provided
on a Lag 0 schedule of positive reinforcement contingent
on independent signs for “want.” Attempts to leave the
table were blocked with the least amount of physical
prompting possible by the experimenter.
Lag 1 Procedures in this condition were similar to Lag 0 with
some exceptions. Access to playdoh was delivered for 20 s
immediately contingent on the first independent sign mand
topography emitted in each session. For the remainder of each
session, 20-s access to playdoh plus descriptive praise was
immediately provided contingent on prompted and independent variant sign mand topographies. Only the three target
sign mand topographies (i.e., “want,” “toy,” “playdoh”) were
eligible for reinforcement, and importantly, the participant had
no exposure to sign mand training targeting the topographies
for “toy” or “playdoh” prior to this phase. The lag schedule
was combined with a progressive TD procedure to transfer
control over the “toy” and “playdoh” sign mand topographies
from model prompts to the EO and programmed reinforcer. If
Allen did not emit a variant sign mand topography during the
2-s TD, the experimenter delivered a model prompt (sometimes paired with a verbal prompt, “Do this,” to increase
prompt effectiveness) for a target variant sign mand topography selected nonsystematically by the experimenter (i.e., best
attempt at random choice of variant topography). Thus, Allen
was permitted to sign repeatedly during the TD until a variant
sign mand was emitted (i.e., within 2 s) or evoked (i.e., by a
prompt). The experimenter continued to deliver the prompt at
2-s intervals until the prompt evoked the target variant sign
mand topography. The length of the TD would have increased
by 2 s every six consecutive trials that Allen failed to emit a
variant sign mand topography, although this was not necessary for any sessions.
Results
All target sign mands were emitted during the treatment evaluation. Data on specific topographies are not shown. Figure 1
displays the rates of independent variant, independent invariant, and prompted variant sign mand topographies. During
baseline (i.e., Lag 0), moderate rates of independent variant
manding were stable and rates of independent variant
manding were low and steady. Coinciding with the introduction of Lag 1 + TD, a moderate increase in prompted variant
manding occurred along with a moderate decrease in the level
of independent invariant manding and a moderate-to-large
increase in the level of independent variant manding with a
slightly ascending trend. The return to baseline resulted in an
immediate decrease to a zero rate of prompted variant
manding (no prompts occurred), an increase in level and a
shift to ascending trend in independent invariant manding,
and a return to the baseline level of independent variant
manding. Reintroduction of the Lag 1 + TD resulted in replications of the changes in prompted variant, independent invariant, and independent variant manding observed in the first
Lag 1 + TD condition.
Table 1 provides a summary of cumulative different acrosssession sign mand topographies and mean independent different within-session sign mand topographies. Figure 2 provides
session-by-session cumulative different mand topographies.
The cumulative total increased from two in the first session
to five by the end of the first Lag 1 + TD session, and the mean
different within-session sign mand topographies increased
from an overall mean of 1.67 in the Lag 0 conditions to an
overall mean of 2.6 in the Lag 1 + TD conditions.
The first author assessed mand response class structure
using procedures described in prior research (Richman,
Wacker, Asmus, Casey, & Andelman, 1999; Silbaugh et al.,
2017). First, he generated transcripts of within-session sign
mand topographies, including independent and prompted
Fig. 1 Rates of independent variant (top panel), independent invariant
(middle panel), and prompted variant (bottom panel) signing per
session during conditions in which reinforcement was contingent on (a)
any independent target sign mand topography (Lag 0) or (b) variant target
sign mand topographies (Lag 1 + TD)
128 Behav Analysis Practice (2019) 12:124–132
target and nontarget sign mand topographies from session
videos for all sessions. Next, he determined the relative latencies of each independent sign mand topography for each session on a trial-by-trial basis by assigning a ranking of 1 or 2
based on the order in which the two most frequent sign mand
topographies occurred. Last, he calculated the percentage of
trials in which a given independent sign mand topography was
the first response within a session by dividing the number of
trials in which a sign mand topography was given a rank of 1
by the number of trials (i.e., instances of the EO) for the
session and converting the quotient to a percentage. For example, in a session in which an EO was presented 10 times,
the sign mand topography “want” might be emitted first 8
times and the sign mand topography “toy” might be emitted
first 2 times. Therefore, the percentage of trials in which the
sign mand topography was ranked 1 for the session would be
80% for “want” and 20% for “toy.”
Figure 3 displays the percentage of trials per session in
which each of the three most frequently independently emitted
sign mand topographies were ranked first. “Want,” “clap,” and
“playdoh” were emitted in a relatively predictable temporal
order across trials, mostly during Lag 1 + TD sessions. “Want”
was most likely to be emitted first during Lag 0 and Lag 1 +
TD conditions (Lag 0: M = 95% of trials per session; Lag 1 +
TD: M = 83% of trials per session). During the first Lag 1 +
TD condition, “clap” (M = 8% of trials per session) or
“playdoh” (M = 3% of trials per session), in that order, were
the second most likely sign mand topographies to be emitted
first. During the second Lag 1 + TD condition, “playdoh” was
the second most likely sign mand topography to be emitted
first (M = 23% of trials per session).
Discussion
Much behavior-analytic research has demonstrated that mand
training can increase the manding repertoires of individuals
with language delays or deficits (e.g., Shafer, 1994; Sundberg
& Partington, 1998; Wallace, 2007). For some, common mand
training procedures may produce invariant patterns of
manding insensitive to changes in contingencies mediated
by a verbal audience. Procedures that reinforce mand variability may mitigate or replace repetitive manding, but unfortunately such procedures are lacking. Therefore, the current
study aimed to extend prior research on the reinforcement of
mand variability (i.e., Silbaugh et al., 2017) by evaluating the
effects of a Lag 1 + TD procedure on the acquisition of new
sign mand topographies and topographical sign mand variability. Visual analysis of the results depicted in Fig. 1 suggests a largely nonvocal boy with autism acquired and varied
multiple functionally equivalent sign mand topographies
when variant and invariant manding contacted the contingencies that composed the Lag 1 + TD condition. This finding is
consistent with prior research that suggested mand variability
can be directly reinforced (Brodhead et al., 2016; Silbaugh et
al., 2017) and provides additional support for the notion that
lag schedules are a promising approach to establishing adaptive mand variability.
New insight about mand variability training may be gained
by comparing some differences between the current study and
the procedures described by Silbaugh et al. (2017). First,
Silbaugh et al. (2017) evaluated the effects of the procedures
on topographical vocal mand variability in children with autism. However, the current study demonstrated the procedures
can also increase nonvocal topographical mand variability
Fig. 3 Percentage of trials per session in which a given independent sign
mand topography occurred first during Lag 0 and Lag 1 + TD conditions.
Data are displayed for the three most frequent sign mand topographies
Table 1 Summary of cumulative different across-session sign mand
topographies and mean independent different within-session sign mand
topographies
First Session Final Session
Cumulative different across-session
sign mand topographies
2 5
Lag 0 Lag 1 + TD
Mean independent different
within-session sign mand topographies
1.67 2.6
Fig. 2 Cumulative different sign mand topographies exhibited across
sessions and Lag 0 and Lag 1 + TD conditions
Behav Analysis Practice (2019) 12:124–132 129
(i.e., sign variability). Second, the current study targeted variability within a recently acquired mand with a very brief
reinforcement history, whereas Silbaugh et al. (2017) targeted
mands with a presumably much longer reinforcement history.
This difference may explain why the participants in Silbaugh
et al. (2017) did not emit all target alternative mand topographies prompted during sessions, but Allen did. That is, when
the outcomes of the two studies are compared, it may be inferred that a mand with a brief reinforcement history relative
to a mand with a longer history may be more sensitive to
procedures used to incorporate a variety of topographies into
the response class, thereby establishing a new mand response
class hierarchy. If so, mand variability training may have a
more significant clinical impact when implemented early in
intervention programming targeting manding. Third, the participants in Silbaugh et al. (2017) exhibited clear reductions in levels of invariant manding when variant manding
levels were elevated in Lag 1 + TD conditions, and although prompts were not technically eliminated from the
treatment, prompts were not delivered in many sessions
for both participants, suggesting that the Lag 1 schedule
alone was sufficient to maintain mand variability. In the
current study, Allen exhibited relatively similar levels of
invariant manding across conditions, and prompts were
used in most Lag 1 + TD sessions to evoke a variant
response. Additional research is needed to identify variables that determine levels of invariant manding when
variant manding is reinforced.
Basic variability research (Odum, Ward, Barnes, & Burke,
2006; Stahlman & Blaisdell, 2011; Wagner & Neuringer,
2006) suggests operant variability may be increased by introducing delays to reinforcement following relatively repetitive
baseline responding. In the current study, during Lag 0, the
first instance of sign manding emitted in each trial was immediately reinforced. However, because Allen was permitted to
emit multiple responses in each trial during Lag 1 + TD sessions until the contingency was met, reinforcer delivery was
contingent on variant sign mand topographies but also delayed
in relation to early invariant responses in the trial. Thus, it is
possible that differences in mand variability between phases in
the current study may have been determined by delays to
reinforcement in relation to the first response emitted on trials
rather than the lag schedule. Future research could further
clarify the relative effects of lag schedules and delays to reinforcement on manding by using multiple schedules to compare rates of mand variability across conditions in which (a)
reinforcement is delivered according to the lag schedule described in the current study and (b) reinforcement is delivered
independent of variant responding but following a brief delay
yoked to the average delay to reinforcement under the lag
schedule. Relatively elevated rates under the lag schedule
would provide additional support for the hypothesis that increased variant manding under a lag schedule is attributable to
a dependency between reinforcement and the variant dimension of manding.
Inspection of the data in Table 1 suggests that Allen only
emitted approximately the level of sign mand variability required to produce the reinforcer in Lag 1 + TD phases. This
finding is largely consistent with the results of prior research
(Brodhead et al., 2016; Silbaugh et al., 2017). The cumulative
different across-session sign mand topographies summarized
in Table 1 demonstrate that Allen acquired five new functionally equivalent sign mand topographies across only 19 (i.e., 3
sessions of pretreatment sign mand training and 16 sessions of
sign mand training) 5-min sessions, including the arbitrary
sign acquired during pretreatment assessment (i.e., clapping).
This finding may be considered particularly striking considering that Allen’s team had reported great difficulty with identifying reinforcers that consistently maintained independent
manding and that mand training in other modalities (i.e., vocal, electronic devices, card exchange) had largely been
unsuccessful.
The relative latencies of the three most frequent sign mand
topographies were compared to assess mand response class
structure. The data depicted in Fig. 2 show that although
Allen emitted high rates of independent variant sign manding
during the Lag 1 condition, for the majority of sessions,
“want” was the first sign mand topography emitted, which
suggests that new sign mand topographies were incorporated
into the mand during treatment in a manner that resulted in the
formation of a response class hierarchy. In the first Lag 1 + TD
condition, the second most frequent sign mand form emitted
was the arbitrary clap response established during the pretreatment assessment. By the end of the second Lag 1 + TD condition, the second most frequent sign mand topography emitted was “playdoh,” and differences in relative response
strength (as assessed by indirect measurement using relative
response latencies) between “want” and “playdoh” largely
diminished in the last two sessions. Future studies could focus
more on variables (e.g., lag schedule value, number of mand
topographies targeted, parameters of reinforcement, length of
contact with the lag schedule) that may influence the effects of
mand variability training on the relative response strength of
new members integrated into the response class. That is, such
studies might shed some light on how mands, and perhaps by
analogy socially mediated challenging behavior, come to be
organized probabilistically as new members enter the functional response class.
The current findings may also have theoretical implications
related to the emergence of more complex verbal behavior.
When Allen varied sign mand topographies within a trial under the lag schedule, he typically emitted the response sequence “want” followed by “playdoh,” or “want” followed
by “toy.” Structurally, these response patterns are equivalent
to two-word sentences, suggesting that schedules selective for
verbal operant variability and their associated contexts may
130 Behav Analysis Practice (2019) 12:124–132
play an important role in the development of novel word combinations from the members of an existing repertoire and the
transition to use of longer-mean-length utterances. In natural
environments, the early emergence of mands in the form of
sentences may reflect naturally occurring contingencies of reinforcement selective for topographical variability and the formation of mand response class hierarchies consisting of new
and existing response forms. Any underlying principle may
apply to other verbal operants as well. In some cases, when
individuals with language delays or deficits fail to demonstrate an increased mean length of utterance despite intensive
high-quality behavioral intervention, the outcome may reflect
in part a failure of the program to systematically provide a
verbal environment selective for verbal variability, and future
avenues of research could investigate these possibilities.
The lack of data on maintenance and social validity is a
limitation that should be addressed in future research. In addition, the current study did not evaluate the effects of the Lag
1 condition in the absence of prompts, so additional research
in which prompts are eliminated from the current procedures is necessary to evaluate the effects of a Lag 1
schedule alone. Future research could also examine the
effects of mand variability training targeting topographical variability during the treatment of challenging behavior using FCT (Carr & Durand, 1985) to assess potential
clinical advantages over the traditional approach, which
does not use schedules selective for variability. Last, the
generality of the current findings is unknown pending
replication with additional participants.
Implications for Practice
& Demonstrates how practitioners might combine prompts
with lag schedules to teach and reinforce mand variability
in children with autism;
& Demonstrates increased topographical sign mand variability attributable to a lag schedule with prompting;
& Provides evidence for the development of a new sign
mand response class hierarchy using a lag schedule with
prompting.
Acknowledgements We thank the families for participating in our research, and Samantha Swinnea for her assistance with data collection.
We also thank Allen Neuringer for his helpful insights and comments
on an earlier version of the manuscript.
Compliance with Ethical Standards
Conflict of interest We report no conflicts of interest.
Ethical Approval All procedures performed in studies involving human
participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki
declaration and its later amendments or comparable ethical standards.
Informed Consent Informed consent was obtained from all individual
participants included in the study.
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