Effect of Methylphenidate on Time Perception in Children With Attention-Deficit/Hyperactivity Disorder

Experimental and Clinical Psychopharmacology
Copyright 2004 by the American Psychological Association, Inc.
2004, Vol. 12, No. 1, 57– 64
1064-1297/04/$12.00
DOI: 10.1037/1064-1297.12.1.57
Effect of Methylphenidate on Time Perception in Children With
Attention-De?cit/Hyperactivity Disorder
Ronald L. Baldwin
John J. Chelonis
University of Arkansas for Medical Sciences—Arkansas
University of Arkansas for Medical Sciences—Arkansas
Children’s Hospital
Children’s Hospital, University of Arkansas at Little
Rock, and National Center for Toxicological Research
Rebecca A. Flake
Mark C. Edwards and Charles R. Feild
University of Arkansas at Little Rock
University of Arkansas for Medical Sciences—Arkansas
Children’s Hospital
Julie B. Meaux
Merle G. Paule
University of Central Arkansas
University of Arkansas for Medical Sciences—Arkansas
Children’s Hospital and National Center for Toxicological
Research
The effects of methylphenidate (MPH) on performance of a time-production task were
studied in 17 children with attention-de?cit/hyperactivity disorder who participated in 1 test
session on and 1 off MPH. Participants held a response lever down for at least 10 but no
longer than 14 s. Administration of MPH had no effect on the number of correct responses
or on the mean duration of lever holds. MPH administration signi?cantly decreased timing
response variability, increased holds of 10- to 11-s duration, and decreased lever holds of
extremely short durations. These results indicate that administration of MPH resulted in more
precise timing performance without changing the mean duration of lever holds, suggesting an
enhancement in working memory.
Attention-de?cit/hyperactivity disorder (ADHD) is one
(see American Academy of Pediatrics, 2000; Jaska, 1998)
of the most common neurobehavioral disorders in childhood
and is characterized by developmentally inappropriate lev-
els of inattention, impulsivity, and hyperactivity that are
pervasive in several settings. Children with ADHD are
unable to respond to cues from the behavior of others, are
Ronald L. Baldwin, Mark C. Edwards, and Charles R. Feild,
Department of Pediatrics, University of Arkansas for Medical Scienc-
inept at taking turns, and have an impaired sense of time
es—Arkansas Children’s Hospital. John J. Chelonis, Department of
(Barkley, Koplowitz, Anderson, & McMurray, 1997; Kerns,
Pediatrics, University of Arkansas for Medical Sciences—Arkansas
McInerney, & Wilde, 2001). They often exhibit a decreased
Children’s Hospital; Department of Psychology, University of Arkan-
ability to learn from previous experience and typically ex-
sas at Little Rock; and Division of Neurotoxicology, National Center
hibit impulsive behavior, poor decision making, and risky
for Toxicological Research, Jefferson, Arkansas. Rebecca A. Flake,
behavior (Barkley, Fischer, Edelbrock, & Small?sh, 1990;
Department of Psychology, University of Arkansas at Little Rock.
Julie B. Meaux, Department of Nursing, University of Central Ar-
DiScala, Leschohier, Barthel, & Li, 1998; Gittelman, Man-
kansas. Merle G. Paule, Department of Pediatrics, University of
nuzza, Shenker, & Bonagura, 1985; Milberger, Biederman,
Arkansas for Medical Sciences—Arkansas Children’s Hospital, and
Faraone, Chen, & Jones, 1997).
Division of Neurotoxicology, National Center for Toxicological Re-
One of the signi?cant impairments that children with
search.
ADHD exhibit is compromised time perception (Barkley et
Some of the data reported in this article were presented at the
al., 1997; Kerns et al., 2001; Meaux & Chelonis, 2003).
meeting of the Association for Behavioral Analysis, Toronto,
This can lead to signi?cant problems given that most activ-
Ontario, Canada, May 2002, and at the meeting of the Behavioral
Toxicology Society, Research Triangle Park, North Carolina, April
ities in which children engage are temporally based. For
2002. We thank Jimmie Birdsong and Johnathan Kennedy for
example, classes and activities begin and end at particular
assistance in identifying and recruiting participants; Shannan
times, and the child must manage his or her time with
Stewart for assistance in conducting the experiment; Donna Blake,
respect to schoolwork, homework, chores, and other activ-
LenEll Kelley, Joe Meehan, Jim Parker, and Martin Jackson for
ities. It has been suggested that children with ADHD have
their assistance in managing the data; and Richard Rassmussen for
dif?culty with behaviors that are time-based because they
maintenance of the apparatus.
perceive time intervals as lasting longer than they really do
Correspondence concerning this article should be addressed
(Barkley et al., 1997; Kerns et al., 2001). Also, given that
to Ronald L. Baldwin, Department of Pediatrics, University of
children with ADHD have dif?culty learning from previous
Arkansas for Medical Sciences—Arkansas Children’s Hospi-
tal, 800 Marshall Street, Little Rock, AR 72202. E-mail:
experience (see Barkley et al., 1997), it is likely that they
baldwinronaldL@uams.edu
would be unable to adjust their timing abilities to compen-
57

---

58
BALDWIN ET AL.
sate for any de?ciencies. Previous research has found that
Given the problems in time production exhibited by chil-
children with hyperactivity and ADHD exhibit impaired
dren with ADHD and the therapeutic effect of methylpheni-
performance on tasks of time production or time reproduc-
date (MPH) to enhance performance of a variety of execu-
tion when compared with control children (Barkley et al.,
tive functions in children with ADHD (Barkley et al., 1997;
1997; Capella, Gentile & Juliano, 1977; Kerns et al., 2001;
Chelonis et al., 2002), it is important to evaluate how MPH
Meaux & Chelonis, 2003). In one study by Capella et al.
might affect time production in children with ADHD. Stim-
(1977), children were asked to indicate (produce) time in-
ulant medications have been found very effective in con-
tervals of 15, 30, and 60 s. The experimenter ?rst dropped
trolling the target symptoms of inattention, impulsivity, and
a ball to signal the start of the time interval and then the
hyperactivity that characterize ADHD (see Barkley et al.,
children dropped a ball after they believed the desired time
1997). One line of evidence suggesting that stimulant med-
interval had passed. In a second study by Capella et al.
ication would affect both time production and estimation in
(1977) children were asked to indicate time intervals of 7,
children with ADHD is derived from work on scalar timing
15, and 30 s. The experimenter asked the child to press a
theory. Scalar timing theory is a physiological model of
switch to begin a time interval and then to press the same
switch to signal the end of the interval. In both studies,
time perception that suggests that an internal clock and
children with hyperactivity were found to produce time
reference memory are key to time perception (Fetterman &
intervals that were longer than those targeted (overproduce)
Killeen, 1990; Meck, 1996). This theory postulates that the
compared with control children. In experiments by Barkley
speed of the internal clock is determined by a pacemaker,
et al. (1997), a time-reproduction task was used during
which continuously emits pulses at regular intervals. It is
which children with ADHD viewed a red light that was
hypothesized that the rate of accumulation of these pulses
illuminated for varying durations. The children were then
determines the perceived amount of time that has passed. If
required to turn on a ?ashlight for the same duration that the
the rate of pulse emission from the internal clock (i.e., clock
red light had been illuminated. Children with ADHD were
speed) is increased, more pulses would accumulate in a
found to make signi?cantly larger absolute errors in time
shorter period of time, hence time production would be
reproduction than were control children, and most of these
shorter and estimation would be longer. If the rate of pulse
errors were manifest as errors in overproduction of the
emission (clock speed) is decreased, time production would
targeted time intervals.
be longer and estimation would be shorter. Reference mem-
However, research using a time-estimation (vs. a time-
ory is postulated to store the initial setting of the internal
production) procedure failed to ?nd differences in timing
clock. This value would then be used for determining the
ability between children with and without ADHD. Speci?-
length of the interval being timed. Instability in reference
cally, Senior, Towne, and Huessy (1979) attempted to rep-
memory is hypothesized to lead to random errors in timing
licate the Capella et al. (1977) studies by comparing the
ability (Meck, 1983).
ability of children with ADHD, children with emotional
It is possible that different stages of temporal processing
disturbances, and children with cognitive impairment to
could involve separate brain regions and could be modi?ed
verbally estimate a time interval. The results indicated that
by different neurotransmitter systems (Meck, 1996). For
there were no signi?cant differences between groups of
example, the internal clock used to time durations in the
children on this time-estimation task (Senior et al., 1979).
seconds to minutes range appears to be linked to dopami-
However, only 6 hyperactive children participated in that
nergic function in the basal ganglia (Meck, 1983, 1996).
study, thus limiting the power. Another explanation for the
Dopamine agonists, such as the amphetamines, have been
disparity of ?ndings between the Senior et al. and other
found to result in the underproduction of time intervals in
studies is that the Senior et al. study only required children
rats and pigeons (Mayorga, Popke, Fogle, & Paule, 2000;
to verbally estimate time intervals, whereas other studies
Meck, 1983, 1996; Paule et al., 1999). Therefore, it has been
required children to produce responses of speci?c durations.
postulated that these agents increase the rate of pulse emis-
Recent research conducted by Meaux and Chelonis (2003)
sions, thus increasing clock speed. Alternatively, in nonhu-
used a time-reproduction task in which children were asked
man primates (rhesus monkeys) performing a time-produc-
to view a light for a period of time, verbally estimate the
tion task, neither amphetamine nor cocaine produced any
amount of time the light was on, and then reproduce that
dramatic or systematic changes in their production of time
interval by holding down a response lever for the targeted
intervals. Speci?cally, neither drug produced a lengthening
duration. It was demonstrated that performance on the time-
of the duration of the targeted lever holds (which would
estimation component of this task, in which children ver-
have supported a role in slowing clock speed), and only one
bally reported the time interval, was similar for children
of several doses of each drug evidenced a shortening of
with ADHD and control children. Both children with and
targeted holds (suggestive of speeding up the clock). In
without ADHD overestimated time intervals and became
monkeys, the dopamine antagonist, chlorpromazine, in-
less accurate as interval durations increased; however, chil-
creased the rate of production of correct-duration lever
dren with ADHD signi?cantly underproduced time intervals
holds, decreased the production of incorrect-duration holds,
in relation to children without ADHD. Similar ?ndings have
and slightly shifted hold durations toward shorter values.
been reported in which teenagers with ADHD have demon-
These ?ndings suggest that dopaminergic blockade in pri-
strated impairments in time reproduction but not estimation
mates may alter time-production performance by increasing
(Barkley, Edwards, Laneri, Fletcher, & Metevia, 2001).
internal clock speed (Paule et al., 1999). However, none of

---

EFFECT OF METHYLPHENIDATE ON TIME PERCEPTION
59
the previous research on monkeys examined how dopamine
man & Kaufman, 1990); (b) their achievement scores in reading,
agonists and antagonists affected precision (variability) in
arithmetic, and spelling were 70 or below, as measured by the
timing behavior.
Wide Range Achievement Test (WRAT-3; Wilkinson, 1993); or
Although it is known that central nervous system stimu-
(c) they were diagnosed with schizophrenia, major depressive
disorder, or pervasive developmental disorder, as measured by the
lants that are able to augment dopaminergic function in
Child Symptom Inventory (CSI; Gadow & Sprafkin, 1997).
humans (e.g., MPH and amphetamine) clearly enhance a
All children participated in two experimental sessions that were
variety of executive functions in children with ADHD (Bark-
separated by at least 2 weeks but not more than 6 weeks. Children
ley et al., 1997; Chelonis et al., 2002), it is unknown how
participated in one test session after they had taken their prescribed
they might affect timing behavior in this population. In
dose of MPH more than 1 but less than 2 hr prior to testing (on
studies using a time-reproduction paradigm, Barkley et al.
MPH). For the other test session at least 18 hr had to have elapsed
(1997) used ?ve different time durations to test the effect of
since children took their last prescribed dose of MPH (off MPH).
three different doses of MPH (compared with placebo) in 12
The order of these sessions was randomly assigned; 11 children
children with ADHD. Children with ADHD became less
participated in their ?rst session off MPH and the other 6 partic-
accurate than did control children as targeted durations
ipated in their ?rst session on MPH. Children received either 5 mg
(n
5), 10 mg (n
7), 15 mg (n
2), or 20 mg (n
3) MPH
increased and when distractions were added. Further, MPH
preparation prior to the test session. The mean dose was 0.32
did not signi?cantly enhance timing performance in chil-
mg/kg with a range of 0.12 to 0.62 mg/kg.
dren with ADHD. These results were surprising given that
MPH has been shown to improve a variety of other execu-
tive functions in children with ADHD (Ahmann, Waltonen,
Apparatus
& Olson, 1993; Barkley, 1990; Barkley, Koplowitz, &
Participants performed the temporal response differentiation
McMurray, 1991).
(TRD) task in a small sound-attenuated room that was 2.4 m
The purpose of the present study was to examine the
long
2.4 m wide
2.4 m high. A ?uorescent ceiling light
effects of MPH on timing ability in children with ADHD
illuminated the room throughout the entire TRD task. The child’s
using a prospective time-production task that used a single-
behavior could be continually monitored during test sessions by
target interval of 10 to 14 s. Participants repeatedly pro-
the experimenter through a one-way mirror located on one of the
duced this interval during each test session. None of the
walls of the room. A table with a television monitor was positioned
other studies of children used a procedure that provided for
against the center of the wall that was opposite the one-way mirror.
the production of enough trials to provide a meaningful
Audio and visual directions were played on this monitor prior to
measure of the variability (precision) of timing responses.
starting the task. The experimental apparatus was attached to the
center of the wall adjacent to the monitor. The apparatus consisted
The present procedure allowed for an examination of the
of a large wooden cabinet that was 182 cm tall
60.8 cm
effects of MPH on both accuracy and precision of time
wide
50.4 cm deep, a response panel, and nickel dispenser. The
production. We hypothesized that MPH would decrease
response panel and nickel dispenser were mounted on the surface
variability in a time-production procedure because previous
of the cabinet. Figure 1 shows the response panel that was located
research has demonstrated that MPH signi?cantly enhances
on the front of the apparatus 60.8 cm above the ?oor. The response
short-term memory in children with ADHD (Chelonis et al.,
panel was 65.4 cm high
55.6 cm wide. A round speaker, 6 cm
2002). Because MPH enhances short-term memory, accord-
in diameter, was located 7.3 cm below the top edge of the panel.
ing to scalar timing theory it would also enhance timing
White noise was delivered through this speaker to mask extraneous
precision.
sounds during testing. The panel contained two types of response
manipulanda and a variety of stimulus lights. The response ma-
nipulanda used in the TRD task was the leftmost of four retractable
Method
response levers that were located 35.5 cm from the bottom edge of
the speaker. Each response lever was 5 cm wide and extended 3 cm
Participants
from the apparatus. The response levers were centered in a hori-
zontal row, each 3.5 cm apart. Positioned 22 cm below the re-
The participants in this study consisted of 17 children (12 boys
sponse panel and 15 cm from the left edge of the apparatus was a
and 5 girls) who were 7 to 13 years of age and were recruited from
tray in which reinforcers (nickels) were delivered. The tray was 15
outpatient clinics at the Arkansas Children’s Hospital in Little
cm wide
10 cm deep
7.5 cm tall. The stimulus lights and the
Rock, Arkansas. Informed consent was obtained from the parents,
other manipulanda on the response panel were not used during the
and assent was obtained from each child. Children were included
TRD task. The activation and presentation of the left retractable
in this study if they had a t score greater than 65 on the Hyperac-
lever and recording of responses were automated using a comput-
tive subscale of the parent’s version of the Conners’ ADHD/
erized system developed at the National Center for Toxicological
DSM–IV Scale (CADS; Conners, 1997) and had a current prescrip-
Research.
tion from a physician for MPH for the treatment of ADHD. Fifteen
children also had a t score of greater than 65 on the Inattention
subscale of the CADS; the other 2 had a score of 64. All children
Procedure
met Diagnostic and Statistical Manual of Mental Disorders (4th
ed.; DSM–IV; American Psychiatric Association, 1994) criteria for
Before testing, the experimenter requested that the parents com-
ADHD on the basis of interviews by a child psychologist, psychi-
plete several forms regarding their demographics and the physical
atrist, or pediatrician that were conducted as part of the child’s
and educational history of the child. The child was escorted into
evaluation prior to treatment. Children were excluded from this
the testing room (described above) by the experimenter. The child
study if (a) their full-scale intelligence score was 70 or below, as
was told that he or she would play ?ve games (tasks) and that the
measured by the Kaufman Brief Intelligence Test (KBIT; Kauf-
instructions for each game would be shown on the television

---

60
BALDWIN ET AL.
Figure 1.
Diagram of the apparatus. Only the left response lever was used for the temporal
response differentiation task. The tube and tray are where nickel reinforcers were dispensed.
monitor before each game began. After introducing the child to the
very hard game [the narrator presses down the extended
testing room, the experimenter left the room to start the videotaped
response lever again]; so don’t give up if you don’t do well
instructions that were used for the standardization of instructions
right at ?rst. Keep trying and you’ll get it right. Remember,
for all participants and to eliminate the large amount of time
hold the lever down for at least 10 seconds, but not anymore
needed to train children to perform the task. Before the TRD task,
than 14 seconds, and then let it up [the narrator stops pressing
down the response lever and receives a nickel]. We hope you
the following instructions were presented on the television monitor
do well at this game. Remember, it’s a hard game, so don’t
to the child:
give up.
You will notice on the panel in front of you [the narrator
When the videotaped instructions ended, the experimenter re-
points to the row of response levers on the panel], that at the
entered the room and asked the child whether he or she understood
bottom there are four levers. In this game, the lever at the far
left, here [the narrator points to and touches the lever at the far
the instructions. All children indicated that they understood the
left], will come out of the machine [the response lever on the
instructions and required no further explanation of the task. After
far left extends from the machine]. To receive a nickel, you
the child stated that he or she understood the instructions, the
must hold the lever down like this [the narrator presses down
experimenter left the testing room, closed the door, and initiated
the extended response lever, and receives a nickel]. This is a
the task.

---

EFFECT OF METHYLPHENIDATE ON TIME PERCEPTION
61
The task began with the response lever on the far left end of the
with ADHD on and off MPH. Children initiated a similar
row of response levers extending from the panel. A trial was
number of trials on and off MPH, t(16)
0.13, p
.90.
initiated when the child pressed the response lever and ended when
Children made more correct lever holds when on MPH than
it was released. If the child held the response lever in the depressed
when off; however, this difference was shown to be only a
position for 10 to 14 s, a nickel was dispensed. If the lever was
trend according to a two-tailed repeated measures t test,
held in the depressed position for less than 10 s or greater than
t(16)
1.79, p
.09.
14 s, a nickel was not dispensed. The next trial began as soon as
the response lever was depressed again. The TRD task lasted
Figure 3 shows the means and standard errors for the
for 10 min, or until 30 nickels were earned.
mean duration of lever holds and standard deviations of the
Each testing session consisted of ?ve tasks presented in the
duration of lever holds for children on and off MPH. The
following order: progressive ratio, conditioned position respond-
mean and standard deviation of the duration of lever holds
ing, TRD, delayed matching-to-sample, and incremental repeated
was calculated for each child on and off medication. MPH
acquisition (see Paule, Cramner, Wilkins, Stern, & Hoffman, 1988,
did not signi?cantly alter the mean lever-hold durations,
for a description of each task). Although ?ve tasks were performed
t(16)
0.84, p
.42. Further examination of the data
each session, only the TRD data are being reported here. A 1- to
revealed that for 7 children, administration of MPH de-
2-min break occurred between tasks, during which the experi-
creased their mean lever-hold duration, and for 10 children,
menter replenished the supply of nickels and presented the instruc-
administration of MPH increased their mean lever-hold
tions for the next task. The experimenter observed the participants
during portions of each of the ?ve tasks and completed the Con-
duration. Administration of MPH signi?cantly decreased
ners’ parent questionnaire at the end of the testing session. It took
response variability (i.e., standard deviation of lever holds),
approximately 55 min for the children to complete all ?ve tasks.
t(16)
2.63, p
.05. Administration of MPH decreased
Each participant’s nickels were counted at the end of the testing
the variability of lever-hold durations in 13 and increased
session. Children could earn a maximum of $8 for correct re-
variability in 4 of the children tested. Further analysis re-
sponses during the entire session. The experimenter supplemented
vealed a small and nonsigni?cant correlation between re-
the child’s earnings as necessary so that each child received a
duction in standard deviation and MPH dose, r(16)
minimum of $5. Following completion of the ?ve tasks, the verbal
0.24, p
.38.
and matrices sections of the KBIT were administered to the child,
Figure 4 shows the means and standard errors for the
after which the child was escorted back to his or her parent(s) in
number of lever holds in each 1-s bin for children on and off
the waiting room, and completed questionnaires were collected.
Parents received a $5 gift certi?cate to Wal-Mart as compensation
MPH. The lever-hold durations were divided into 21 sepa-
for bringing their child in for each session.
rate time bins by truncating each value for lever-hold du-
ration to create an integer value. Children off MPH exhib-
Results
ited a less well-de?ned peak at the 10-s time bin (i.e., made
less responses at the mode) than when on MPH. Further,
Figure 2 shows the means and standard errors for the
they consistently made more lever holds at each time bin at
number of trials (lever holds) initiated during the TRD task
the extreme ends of the distribution when off medication
and the number of correct-duration lever holds by children
than when on. Speci?cally, there were no instances in which
the mean number of responses across children off medica-
tion was less than when on medication in the 0- to 4-s time
bins and in the 14-s and greater time bins, which is signif-
icantly less than would be expected by chance. Repeated
measures t tests were conducted to determine whether ad-
ministration of MPH affected the number of lever holds for
each of the 1-s bins for children with ADHD. Administra-
tion of MPH signi?cantly decreased the number of lever
holds that were less than 1 s, t(16)
2.97, p
.01, and
signi?cantly increased the number of lever holds in the 10-s
bin, t(16)
2.45, p
.03.
Discussion
The results of the present study show that MPH signi?-
cantly improved the timing performance of children with
ADHD. This was evidenced by signi?cant decreases in the
variability of lever-hold durations, decreases in the number
of very short (less than 4 s) lever holds, and increases in
lever holds of correct (reinforced) duration, especially in the
10-s time bin. These results suggest that the administration
of MPH increased the precision of timing behavior by
Figure 2.
Means and standard errors for the total number of
decreasing the spread of lever holds within the target inter-
trials initiated and the total number of correct lever holds for
children with attention-de?cit/hyperactivity disorder on and off
val and by decreasing the number of inappropriate re-
methylphenidate.
sponses at time intervals that were distant from the target

---

62
BALDWIN ET AL.
control condition in the Barkley et al. (1997) study (vs. the
use of a “no-medication” control condition in the current
study) or to the longer time intervals used in a time-repro-
duction task in the Barkley et al. (1997) studies.
The lack of an MPH-induced shift in peak of the response
duration distributions might also have resulted from the fact
that the children in the present study had extensive experi-
ence in a variety of situations both on and off MPH as part
of their treatment for ADHD. Meck (1983) demonstrated
that with chronic amphetamine exposure, animal subjects
were able to readjust their timing behavior from a shift
toward shorter intervals back to a distribution of timing
responses that was similar to their predrug exposure distri-
bution. Therefore, it is possible that children with ADHD
who have a history of MPH treatment have developed a type
of tolerance to some of its effects on timing ability. The fact
that MPH did signi?cantly decrease response variability in
this task, however, suggests that at least some aspects of
timing behavior do not become tolerant to repeated expo-
Figure 3.
Means and standard errors for the mean and standard
sure to stimulant medication. Previous research has demon-
deviation of lever-hold durations, calculated for each child on and
strated that stimulant medication enhances working memory
off methylphenidate. The asterisk indicates statistically signi?cant
in children with ADHD (Chelonis et al., 2002; Evans,
differences between treatment conditions.
Gualteireri, & Amara, 1986; Gittelman-Klein & Klein,
1975; Sprague, Barnes, & Werry, 1970; Swanson & Kins-
bourne, 1976). If working memory is important for the
interval. These ?ndings are unique because none of the
precision of timing behavior, and MPH improves this aspect
previous research on timing ability in children with ADHD
of memory, then it follows that children with ADHD would
or in nonhuman primates examined the precision (variabil-
exhibit an improvement in timing precision while on MPH.
ity) of responding. The ?nding that MPH decreased vari-
Although it is also possible that participants were expe-
ability in responding is especially interesting given that
riencing mild “withdrawal” symptoms 18 hr after taking
reinforcers were provided for correct responses (typically
their last stimulant medication (i.e., when they were off
not used when assessing timing in humans) and that other
MPH), the data remain relevant for several reasons. Chil-
studies have shown reinforcement alone often decreases
dren undergoing chronic stimulant treatment are often in
response variability (see Schwartz, 1982). The present ?nd-
this exact situation. In addition, withdrawal symptoms as-
ings clearly demonstrate that even in the presence of rein-
forcement, response variability decreased with the admin-
istration of MPH.
Although the results of the present study suggest that
MPH increased the precision of timing behavior, they do not
suggest that MPH affected the time interval at which the
peak lever-hold duration occurred (timing accuracy). In
other words, we are not postulating that the rate of pulse
emission by the internal clock was affected by MPH be-
cause the mean of the lever-hold durations was similar for
children on and off MPH. This ?nding is similar to ?ndings
noted in nonhuman primates (see Paule et al., 1999; Schulze
& Paule, 1990) wherein the dopaminergic stimulants am-
phetamine and cocaine did not systematically shift the mean
of the population of lever-hold distributions in subjects
performing an identical TRD task. Analyses of just the total
trials (lever presses) made and the number of correct lever
holds data (see Figure 2) also revealed no signi?cant effects
of MPH. These observations are similar to those of Barkley
et al. (1997), which showed a lack of signi?cant medication
effect on performance of a time-reproduction task. How-
ever, in the present study there was a clear trend toward
Figure 4.
Means and standard errors for the number of lever
increased correct responses for children on MPH, an effect
holds of speci?c durations blocked into 1-s (1s) intervals for
that was not evident in the Barkley et al. (1997) study. This
children on and off methylphenidate. The asterisk indicates statis-
difference might have been due to the use of a placebo
tically signi?cant differences between treatment conditions.

---

EFFECT OF METHYLPHENIDATE ON TIME PERCEPTION
63
sociated with chronic stimulant medication, generally stud-
American Psychiatric Association. (1994). Diagnostic and statis-
ied in adult substance abusers, tend to manifest only after
tical manual of mental disorders (4th ed.). Washington, DC:
very long-term administration at relatively high doses. It is
Author.
unknown whether similar sequelae occur in children. In a
Barkley, R. A. (1990). Attention de?cit hyperactivity disorder: A
handbook for diagnosis and treatment. New York: Guilford
review of stimulant drugs and vigilance performance (Koe-
Press.
lega, 1993), it was stated that “Evidence from several stud-
Barkley, R. A., Edwards, G., Laneri, M., Fletcher, K., & Metevia,
ies does not support the hypothesis that improvements are
L. (2001). Executive functioning, temporal discounting, and
only a recovery of withdrawal-induced impairment” (p. 1).
sense of time in adolescents with attention de?cit hyperactivity
The implication here is that the poorer performance ob-
disorder (ADHD) and oppositional de?ant disorder (ODD).
served in subjects in the nondrugged state is not a re?ection
Journal of Abnormal Child Psychology, 29, 541–556.
of disrupted function caused by symptoms brought about by
Barkley, R. A., Fischer, M., Edelbrock, C. S., & Small?sh, L.
or associated with acute drug withdrawal.
(1990). The adolescent outcome of hyperactive children diag-
In addition, recent studies in nonhuman primates have
nosed by research criteria: I. An 8-year prospective follow-up
shown that infant and juvenile subjects are much less sen-
study. Journal of the American Academy of Child and Adoles-
sitive to the behavioral effects of stimulants than are adults
cent Psychiatry, 29, 546 –557.
Barkley, R. A., Koplowitz, S., Anderson, T., & McMurray, M. B.
(Paule, 1997). Thus, the likelihood of young human partic-
(1997). Sense of time in children with ADHD: Effects of dura-
ipants exhibiting withdrawal phenomena appears less than
tion, distraction, and stimulant medication. Journal of the Inter-
that for adults, and the positive effects of stimulant treat-
national Neuropsychological Society, 3, 359 –369.
ment likely are not due to treatment of withdrawal
Barkley, R. A., Koplowitz, S., & McMurray, M. B. (1991). At-
symptoms.
tention de?cit disorder with and without hyperactivity: Clinical
This research is the ?rst to clearly demonstrate differ-
response to three dose levels of methylphenidate. Pediatrics, 87,
ences in timing ability as a result of administration of MPH
519 –531.
in children with ADHD. Administration of MPH was found
Capella, B., Gentile, J. R., & Juliano, D. B. (1977). Time estima-
to signi?cantly decrease variability of lever-hold durations
tion by hyperactive and normal children. Perceptual and Motor
(i.e., increase precision). Although it may be argued that
Skills, 44, 787–790.
these results may be due to practice effects because more
Chelonis, J. J., Edwards, M. C., Schulz, E. G., Baldwin, R. L.,
Blake, D. J., Wenger, A., & Paule, M. G. (2002). Stimulant
children received MPH on the second test session, this is
medication improves recognition memory in children diagnosed
unlikely because of the 6 children who received MPH on the
with attention-de?cit/hyperactivity disorder. Experimental and
?rst session, all but 1 demonstrated a decrease in variability
Clinical Psychopharmacology, 10, 400 – 407.
of lever-hold durations after administration of MPH. Fur-
Conners, C. (1997). Conners’ Rating Scales. Toronto, Ontario,
ther, this study did not control for dose effects of MPH
Canada: Multi-Health Systems.
because a range of doses was used. However, it is unlikely
DiScala, C., Leschohier, I., Barthel, M., & Li, G. (1998). Injuries
that this had much effect on the results because the corre-
to children with attention de?cit/hyperactivity disorder. Pediat-
lation of dose with decreases in variability was small and
rics, 102, 1415–1421.
not signi?cant. Finally, it would be useful to replicate this
Evans, R. W., Gualteireri, C. T., & Amara I., (1986). Methylpheni-
research using placebo control conditions to make this work
date and memory: Dissociated effects in hyperactive children.
more comparable with the Barkley et al. (1997) research.
Psychopharmacology, 90, 211–216.
These ?ndings indicate that variability in responding
Fetterman, J. G., & Killeen, P. R. (1990). A componential analysis
appears to decrease with the administration of MPH. This
of pacemaker– counter timing systems. Journal of Experimental
suggests that administration of MPH might enhance the
Psychology: Human Perception and Performance, 16, 766 –
ability of children with ADHD to more consistently apply
780.
successful strategies in problem solving. These results also
Gadow, K. D., & Sprafkin, J. (1997). Child Symptom Inventory— 4
suggest that de?cits in timing ability noted while off MPH
norm manual. Stony Brook, NY: Checkmate Plus.
are a result of de?cits in working memory and are not due
Gittelman, R., Mannuzza, S., Shenker, R., & Bonagura, N. (1985).
to differences in the speed of a postulated internal clock
Hyperactive boys almost grown up: I. Psychiatric status. Ar-
(i.e., peak time intervals were the same in both the on and
chives of General Psychiatry, 42, 937–947.
off conditions). These ?ndings also suggest that any inter-
Gittelman-Klein, R., & Klein, D. F. (1975). Are behavioral and
psychometric changes related in methylphenidate-treated hyper-
vention that enhances working memory in children with
active children? International Journal of Mental Health, 4,
ADHD would also enhance timing ability in these children.
182–198.
Jaska, P. (1998). Fact sheet on attention de?cit/hyperactivity dis-
References
order. Retrieved July 27, 2002 from http://www.add.org
Kaufman, A. S., & Kaufman, N. L. (1990). Kaufman Brief Intel-
Ahmann, P. A., Waltonen, S. J., & Olson, K. A. (1993). Placebo-
ligence Test. Circle Pines, MN: American Guidance Services.
controlled evaluation of Ritalin side effects. Pediatrics, 91,
Kerns, K. A., McInerney, R. J., & Wilde, N. J. (2001). Time
1101–1106.
reproduction, working memory, and behavioral inhibition in
American Academy of Pediatrics. (2000). Clinical practice guide-
children with ADHD. Child Neuropsychology, 7, 21–31.
line: Diagnosis and evaluation of the child with attention-de?cit/
Koelega, H. S. (1993). Stimulant drugs and vigilance performance:
hyperactivity disorder. Pediatrics, 105, 1158 –1170.
A review. Psychopharmacology, 111, 1–16.

---

64
BALDWIN ET AL.
Mayorga, A. J., Popke, E. J., Fogle, C. M., & Paule, M. G. (2000).
behaviors in animals and humans to detect drug and/or toxicant
Similar effects of amphetamine and methylphenidate on the
effects. Neurotoxicology and Teratology, 21, 491–502.
performance of complex operant tasks in rats. Behavioural
Schulze, G. E., & Paule, M. G. (1990). Acute effects of d-
Brain Research, 109, 59 – 68.
amphetamine in a monkey operant behavioral test battery. Phar-
Meaux, J. B., & Chelonis, J. J. (2003). Time perception differences
macology Biochemistry and Behavior, 35, 759 –765.
in children with and without ADHD. Journal of Pediatric
Schwartz, B. (1982). Reinforcement induced behavioral stereo-
Healthcare, 17, 64 –72.
typy: How not to teach people to discover rules. Journal of
Meck, W. H. (1983). Selective adjustment of the speed of internal
Experimental Psychology: General, 111, 23–59.
clock and memory processes. Journal of Experimental Psychol-
Senior N., Towne, D., & Huessy, D. (1979). Time estimation and
ogy: Animal Behavior Processes, 9, 171–201.
hyperactivity, replication. Journal of Perceptual and Motor
Meck, W. H. (1996). Neuropharmacology of timing and time
Skills, 49, 289 –290.
perception. Cognitive Brain Research 3, 227–242.
Sprague, R. L., Barnes, K. R., & Werry, J. S. (1970). Methyl-
Milberger, S., Biederman, J., Faraone, S. V., Chen, L., & Jones, J.
phenidate and thioridazine: Learning, reaction time, activity and
(1997). ADHD is associated with early initiation of cigarette
classroom behavior in disturbed children. American Journal of
smoking in children and adolescents. Journal of the American
Orthopsychiatry, 40, 615– 628.
Academy of Child and Adolescent Psychiatry, 36, 37– 44.
Swanson, J. M., & Kinsbourne, M. (1976, June 25). Stimulant-
Paule, M. G. (1997). Age-related sensitivity to the acute behavioral
related state-dependent learning in hyperactive children. Sci-
effects of cocaine and amphetamine in monkeys. Neurotoxicol-
ence, 192, 1354 –1357.
ogy and Teratology, 19, 241–242.
Wilkinson, G. S. (1993). Wide Range Achievement Test adminis-
Paule, M. G., Cramner, J. M., Wilkins, D., Stern, H. P., & Hoff-
tration manual. Wilmington, DE: Wide Range.
man, E. L. (1988). Quantitation of complex brain function in
children: Preliminary evaluation using a nonhuman primate
behavioral test battery. Neurotoxicology, 9, 367–369.
Received September 11, 2002
Paule, M. G., Meck, W. H., McMillan, D. E., McClure, G. Y. H.,
Revision received March 27, 2003
Bateson, M., Popke, E. J., et al. (1999). The use of timing
Accepted August 28, 2003

---