Self-control and impulsivity in children: multiple behavioral measures.
Abstract: The present experiment investigated the relationship between laboratory measures of self-control and delay of gratification in children and explored several other factors that may influence self-control In the self-control paradigm, 30 four-year-old children repeatedly chose between three reinforcers received after a delay and one reinforcer received immediately A self-imposed delay modification allowed participants to reverse their choices to the smaller, less delayed reinforcer during the delay to the larger reinforcer. In the delay-of-gratification paradigm, the children received three reinforcers if they waited 20 min until the experimenter returned or one reinforcer if they terminated the trial by ringing a bell A strong positive correlation between the proportion of self-control choices in the self-control paradigm and the wait times in the delay-of-gratification paradigm was found, suggesting concurrent validity between the two measures. In addition, the exposure to visual food cues had no consistent effect across participants on choice in either measure.

Key words: children, self-control, impulsivity, delay of gratification, food cues
Article Type: Report
Subject: Impulse (Research)
Psychological tests (Research)
Self-control (Research)
Self-control (Measurement)
Authors: Forzano, L.B.
Michels, Jennifer L.
Carapella, R.K.
Conway, Patrick
Chelonis, J.J.
Pub Date: 06/22/2011
Publication: Name: The Psychological Record Publisher: The Psychological Record Audience: Academic Format: Magazine/Journal Subject: Psychology and mental health Copyright: COPYRIGHT 2011 The Psychological Record ISSN: 0033-2933
Issue: Date: Summer, 2011 Source Volume: 61 Source Issue: 3
Topic: Event Code: 310 Science & research
Accession Number: 265302081
Full Text: Impulsivity, which can be conceptualized as lack of self-control (Meichenbaum & Goodman, 1971; Mischel & Ebbesen, 1970; Spira & Fischel, 2005), is featured in a number of childhood and adult disorders, including attention-deficit/hyperactivity disorder (ADHD; American Psychiatric Association, 1994; Gomez, 2003; Spira & Fischel, 2005), substance abuse (Coffey, Gudleski, Saladin, & Brady, 2003; Dom, De Wilde, Hulstijn, van den Brink, & Sabbe, 2006), borderline personality disorder (American Psychiatric Association, 1994; Chapman, Leung, & Lynch, 2008), and impulse-control disorders such as gambling (Alessi & Petry, 2003).

Given the broad use of the term impulsivity, it is not surprising that a wide range of definitions and measures have been developed for the construct of impulsivity, with researchers differentiating between two (Dickman, 1990; Swann, Bjork, Moeller, & Dougherty, 2002) or three (Dougherty, Marsh, Mathias, & Swann, 2005) subtypes of impulsivity. For example, according to Dougherty et al. (2005), impulsivity can be divided into at least three main categories, including (a) response initiation, (b) response inhibition, and (c) consequence sensitivity or reward delay.

In response initiation, impulsivity is defined as responding before full evaluation of stimuli has been completed (Dougherty et al., 2005). Typical measures are the Immediate and Delayed Memory Tasks, which are variants of the Continuous Performance Test (CPT; Rosvold, Mirsky, Sarason, Bransome, & Beck, 1956). In these tasks, stimuli are presented in rapid succession (i.e., every 1-2 s), and the individual is to respond only when a specific character appears. In this paradigm, commission errors (responding to stimuli other than the target stimulus) are considered a measure of impulsivity (Dougherty et al., 1998).

In response inhibition, the inability to inhibit a response that has already begun is defined as impulsivity (Dougherty et al., 2005). An example of measurement is the stop-signal paradigm in which individuals are instructed to respond on one key if they see an "X" and on another key if they see an "O" (Logan, Schachar, & Tannock, 1997). However, when there is an auditory tone, the individual is to inhibit the response. During the session, as the tone is introduced and removed, the reaction times (latencies) to stop responding and to begin responding again are recorded. In this paradigm, those who have longer "stop" reaction times than "go" reaction times are said to be impulsive (Logan et al., 1997).

Soreni, Crosbie, Ickowicz, and Schachar (2009) found no significant correlations between performances on the stop-signal task and commission errors in the Conners' (2004) CPT task in children with ADHD. This work supports the notion that impulsivity is multifaceted and supports the inclusion of each of these tests in their respective categories--response inhibition and response initiation. However, Avila, Cuenca, Felix, Parcet, and Miranda (2004) found a significant correlation (r=.39, p < .01) between performance on the stop-signal task and commission errors in the CPT task (AX version) in a larger sample of boys with and without ADHD. Finally, Floyd and Kirby (2001) found a significant correlation in performance on the "snack delay" task (which fits within the response-initiation category) and the "pinball" task (which fits within the response-inhibition category). These studies demonstrate that the boundary between the response-initiation and response-inhibition categories may require further definition.

In a third impulsivity category, the consequence-sensitivity/reward-delay category, self-control can be defined as the choice of a larger, more delayed reinforcer over a smaller, less delayed reinforcer, whereas impulsivity is the choice of the smaller, more immediate reinforcer over the delayed but larger reinforcer (Rachlin & Green, 1972). Within this category, measurement paradigms include the two-choice delayed reward (Cherek & Lane, 1999), single key impulsivity (Mathias et al., 2002), delay discounting (Mazur, 1987), delay of gratification (Mischel & Ebbesen, 1970), and self-control (Ainslie, 1974; Logue, 1988).

Considering that the above-mentioned definitions, measures, and procedures all purport to reflect the constructs of self-control and impulsivity, a number of researchers have treated the measures as though they are equivalent (see Rachlin, 2000, and Reynolds & Schiffbauer, 2005, for reviews). However, only a few have directly compared measures and in most cases have not observed high degrees of concordance. For example, Olson (1989) administered three performance tasks to 79 children. The Kansas Reflection-Impulsivity Scale for Preschoolers (KRISP; Wright, 1971) was given as a "cognitive task." Similar to the matching-familiar-figures task, the KRISP can be classified as a response-initiation task. The draw-a-line-slowly and walk-a-line-slowly tasks (Maccoby, Dowley, Hagen, & Degerman, 1965) were administered as "motor" measures of impulsivity and can be classified as response-inhibition tasks. Finally, a modified delay-of-gratification task (Arend, Gove, & Sroufe, 1979) was used as a "delay" task and fits in the consequence-sensitivity/reward-delay category. Correlations between the three measures of impulsivity were low (ranging from.05 to.26), and Olson concluded that impulsivity is a "multidimensional construct" that cannot be measured by any one test (Olson, 1989, p. 181).

Reynolds and Stark (1986) studied 132 children in Grades 4 to 6 who were divided into two groups based on teacher referrals (the referred children were said to lack self-control and behave impulsively). The children completed the Children's Perceived Self-Control Scale (Humphrey, 1982) and performed the matching-familiar-figures test, which assesses reflection impulsivity, a type of response-inhibition task (Block, Block, & Harrington, 1974). Also, for each child, two teachers filled out the Self-Control Rating Scale and the Teacher's Self-Control Rating Scale (SCRS and TSCRS; Kendall & Wilcox, 1979). Finally, both parents and teachers completed the Conners' Rating Scales (CRS; Conners, 1969), which include questions about oppositional behavior, inattention, hyperactivity, and other ADHD symptoms. None of the rating scales significantly correlated with performances on the matching-familiar-figures test, and neither the parent nor the child rating scales distinguished between teacher-referred and nonreferred children. The authors concluded that these measures suggested "considerable construct confusion" (Reynolds & Stark, 1986, p. 13).

More recently, Nichols and Waschbusch (2004) conducted a metaanalysis of studies of six laboratory tasks that are used to assess symptoms of ADHD. Studies assessing response inhibition used the traditional CPT (DuPaul, Anastopoulos, Shelton, Guevremont, & Metevia, 1992), the Gordon Diagnostic System (GDS; Gordon, 1991), the stop-signal task (Logan, Cowan, & Davis, 1984), and the Children's Checking Task (CCT; Margolis, 1972). Studies assessing consequence sensitivity/reward delay used traditional delay-of-gratification tasks (Mischel & Ebbesen, 1970) and the choice-delay task (Sonuga-Barke, Taylor, Sembi, & Smith, 1992). Performance in these tasks was compared to parent ratings and behavioral observations. None of the six tasks demonstrated all types of validity tested (convergent, discriminant, and predictive), perpetuating the confusion about the definition of impulsivity (Nichols & Waschbusch, 2004).

We propose three possible explanations for the difficulty in demonstrating agreement between measures of impulsivity in these studies. First, the measures used were in different categories of impulsivity (i.e., response initiation, response inhibition, and consequence sensitivity/reward delay). A second explanation is that the measures used were in different modes, such as questionnaires (including self-, parent, or teacher report), hypothetical choices (such as those in computer tasks), and real choices (such as those in which children receive tangible reinforcers). Finally, some procedures used an externally imposed delay task and others used a self-imposed delay task (Karniol & Miller, 1981). Externally imposed delay tasks, precommitment procedures, or commitment-choice procedures, as they are commonly called, present participants with choices between larger, more delayed and smaller, less delayed reinforcers (Rachlin & Green, 1972). Once the participant makes an initial choice to wait for the larger item, the participant is committed to that choice until the next trial (i.e., the participant cannot make a change in choice to the more immediate reinforcer). Hence, the preference for the larger, more delayed reinforcer involves only the initial choice of the alternative and not the inhibition of the response for the smaller, less delayed reinforcer. In contrast, in self-imposed delay tasks, such as the delay-of-gratification procedure, participants who originally choose the more delayed reward can at any time change their choice and terminate the delay period. In other words, both externally imposed and self-imposed delay tasks involve a choice component, but only self-imposed delay tasks involve sustaining that choice or inhibiting the response for the smaller, less delayed reinforcer (Reynolds & Schiffbauer, 2005). Precommitment procedures have been found to result in increases in self-control (Chelonis, Logue, Sheehy, & Mao, 1998; Schweitzer & Sulzer-Azaroff, 1988).

For the present experiment, to address the first issue (i.e., measures used were in different categories of impulsivity), two tasks from the same impulsivity category (consequence sensitivity/reward delay) were chosen. Using food as the reinforcer for both measures, we compared children's performances in a self-control task to that in a delay-of-gratification task. A self-control task involves presenting alternatives differing in amount and delay of the reinforcer and having the child repeatedly choose between larger, more delayed and smaller, less delayed reinforcers (Forzano, Szuba, & Figurilli, 2003). Self-control is measured as the proportion of responses for the larger, more delayed reinforcer. In a delay-of-gratification task, the child is shown two different amounts of the same item and told that they can have the larger amount if they are able to wait for the experimenter to return (Mischel & Ebbesen, 1970; Mischel, Ebbesen, & Zeiss, 1972). Children are classified as more impulsive if they terminate the delay period before the experimenter returns, thus forgoing the larger amount and settling for the smaller amount (Mischel & Ebbesen, 1970; Mischel et al., 1972). Hence, wait time is the measure of self-control in this task. To address the second issue (i.e., measures used were in different modes), the two measures in the present study are in the same mode; that is, they are both direct measures of the child's behavior. Finally, to address the third issue (i.e., measures differed in externally imposed and self-imposed delays), similar to self-control studies with nonhumans (Chelonis et al., 1998; Logue & Peha-Correal, 1984), we modified the original self-control paradigm so that the delay time could be self-imposed (i.e., even after a participant initially chose the more delayed, larger reinforcer, the participant could change her choice to the smaller amount received more immediately), therefore making the task more similar to the self-imposed delay-of-gratification task.

In addition to addressing the limitations in previous studies, in the current experiment we also examined additional factors that have been shown to affect performance in both the self-control and the delay-of-gratification tasks. First, visual food cues were manipulated. Forzano et al. (2003) found that although 3-year-olds overall were not influenced by the presence or absence of food cues, for some children, the presence of food cues facilitated self-control, whereas for others the absence of food cues facilitated waiting. In Mischel and Ebbesen's (1970) delay-of-gratification experiment, voluntary waiting time in children between the ages of 3.5 and 5.7 years was substantially increased when rewards were absent versus visible. In addition, Forzano and Corry (1998) and Forzano et al. (2010) showed that exposure to visual food cues influenced many adult women's impulsivity.

Finally, results of studies on the effect of gender on self-control have been mixed. Various self-control and delay-of-gratification studies have demonstrated greater self-control in girls (Funder, Block, & Block, 1983; Kanfer & Zich, 1974; Logue & Chavarro, 1992; Sonuga-Barke, Lea, & Webley, 1989). Others have shown more self-control in boys (Forzano et al., 2003), and still others have shown no gender effect (Logue, Forzano, & Ackerman, 1996, Peake, Hebl, & Mischel, 2002). We therefore included both boys and girls in the present experiment.

The first objective of the current experiment was to establish concurrent validity between two measures of self-control in 4-year-olds. Despite previous research comparing impulsivity measures, there has been no direct comparison of self-control and delay-of-gratification tasks. These two measures were chosen because they are similar in at least three respects. First, they are both behavioral measures, which are well-suited for laboratory measurement. Second, they involve actual reinforcers, as opposed to hypothetical reinforcers. Finally, they are both delayed-reward models in which the ability to wait for a larger reward is considered, rather than the ability to initiate or disinhibit responses. Because of these similarities, we hypothesized that performance on the two measures would be positively correlated. The second objective of the current experiment was to explore a major difference between the self-control task and the delay-of-gratification task. The self-control task uses an externally imposed delay, whereas the delay-of-gratification task uses a self-imposed delay. The delay-of-gratification task is likely more generalizable to real-life situations. For example, one could decide to get up early to go to work, only to find oneself pressing the snooze button the next morning (Logue, 1995). We therefore implemented an additional choice in the self-control task that allowed participants to change their choice from the self-control choice to the impulsive choice before the end of the trial period. A similar modification was used with pigeons (Logue & Peha-Correal, 1984) and rats (Chelonis et al., 1998). We hypothesized that the self-control results would more closely match between the two tasks when participants could self-impose the delay. The third objective was to examine the effects of visual food cues on choice in the two tasks, and the final objective was to explore gender differences in the two tasks.

To examine these four objectives, 4-year-old boys and girls participated in a within-subjects design in which they performed the self-control task in four experimental sessions and the delay-of-gratification task in two experimental sessions. In all sessions, mini M&Ms were used as the reinforcers, children made choices between one and three M&Ms, and visual food cues were alternately present and absent.

Method

Participants

Participants were 30 four-year-old children (M = 53.6 months), including 17 boys and 13 girls. Eight of these children were recruited from the Brockport Child Care Center on The College at Brockport, State University of New York campus via letters sent home to their parents. The remaining 22 participants were recruited through posted fliers and advertisements placed in local newspapers. None of the children had diagnoses of ADD/ADHD or a learning disability, as indicated by their parents. None of the children required additional special educational services.

For children at the Brockport Child Care Center, experimental sessions were scheduled such that participants had not had anything to eat or drink for at least 2 hours prior to the session. For the remaining participants, each child's parents were asked to ensure that their child had not had anything to eat or drink for at least 2 hours prior to each session. Compliance with this instruction was checked at the start of each session, and sessions were rescheduled if the participant had eaten or drank anything in the last 2 hours.

Parents of the children from the child care center received $10 for attending the first session. Parents of the remaining children attended every session and received $7 per session.

Apparatus

Self-control and delay-of-gratification sessions were conducted in a small room containing a table, which held the self-control apparatus, a child-sized table where participants sat during the delay-of-gratification tasks, and a cabinet. When the self-control apparatus was not in use in a session, it was covered with a large white sheet. On one wall of the room was a small hole, which was unnoticed by participants and used by the experimenter to observe the child during the delay-of-gratification sessions.

Self-control apparatus. For the self-control sessions, the apparatus was identical to the apparatus used in previous research (Forzano & Logue, 1995; Forzano et al., 2003; Logue & Chavarro, 1992; Logue et al., 1996). The apparatus was a wooden box (76 cm wide x 80 cm high x 47 cm deep) with an open back (adapted from Schweitzer & Sulzer-Azaroff, 1988). On the front of the box was a picture of Mickey Mouse (see Figure 1). Mickey's nose was a white light that could be turned on or off by the experimenter. Below Mickey's face was a food-cue box with a clear Plexiglas front (4 cm wide x 7 cm high). This box protruded from the front of the apparatus (by 4.5 cm) and contained M&Ms for the food-cues-present conditions. The box was empty for the food-cues-absent conditions.

[FIGURE 1 OMITTED]

Two lights were positioned 1 cm below the bottom left and right corners of the food-cue box. The light on the left could be illuminated green, and the light on the right could be illuminated red. Located 10 cm below each light was a drawer (each 11 cm wide x 19 cm deep x 6 cm high). The left drawer was green inside, and the right drawer was red inside. During reinforcement, the drawer emerged 13.5 cm from the panel, allowing the participant to open the lid of the drawer and remove the reinforcers (mini M&Ms). At all other times the drawers remained closed, flush with the front of the apparatus. In front of each drawer was a button that when pushed by the participant activated feedback clicks.

The participant sat in a chair in front of the apparatus. Behind the apparatus, electromechanical switches and timers controlled the events of the experiment. The experimenter sat behind the apparatus, operated the apparatus, and recorded the participant's responses.

Delay-of-gratification apparatus. For the delay-of-gratification sessions, a desk bell and a white, plastic, three-sectioned plate (24 cm in diameter) containing four mini M&Ms of the same color were set in front of the child on the table. The M&Ms were positioned such that three were on the child's right and one was on the left. An opaque cake tin (25 cm in diameter) covered the sectioned plate before the M&Ms were presented to the child. In another room, while observing the child, the experimenter used two digital electronic timers to keep track of wait time.

Procedure

At the beginning of the first session, after the experimenter obtained informed consent from parents and assent from children, children participated in either a self-control testing session or a delay-of-gratification testing session. To assess order effects, children assigned to Order 1 or 2 were exposed to the self-control sessions first, followed by the delay-of-gratification sessions, whereas children assigned to Order 3 or 4 received the delay-of-gratification sessions first, followed by the self-control sessions.

Self-control testing sessions. For the first self-control session (a training session), the child was seated in front of the self-control apparatus, and instructions were given to the child that were identical to those used in Forzano and Logue (1995), Forzano et al. (2003), and Logue et al. (1996). These instructions are included in Appendix A.

If needed, the experimenter allowed the child additional practice before beginning the session. The session did not begin until the child could press both buttons, open the drawers, take out the food items, and eat them without the experimenter's prompts. The experimenter then obtained the child's assent with the following prompt:

The experimenter then sat on a chair behind the apparatus. There was no further communication between the experimenter and the child once the session began, unless the experimenter had to prompt the child to attend to a certain task (a very rare occurrence).

For all additional self-control testing sessions, the children's ability to operate the apparatus was confirmed by asking the following questions: "Do you remember how to play the Mickey Mouse game?" and "What are you going to do when Mickey's nose lights up?" For each question the experimenter waited for the child to respond with a correct answer or demonstrate that he or she understood the instructions.

Each self-control testing session consisted of 14 discrete trials, similar to previous self-control studies (Forzano & Logue, 1995; Forzano et al., 2003; Logue & Chavarro, 1992). The intertrial intervals (ITIs) were adjusted so that there was 1 min between the start of each trial. If 1 min passed due to a slow response from the child, the next trial was begun immediately after the child made a choice, experienced the delay, and received the reinforcer. This procedure ensured that reinforcement frequency remained as close to one reinforcer per minute as possible and ensured that session time stayed constant at 14 min.

In all self-control sessions, the first four trials were forced-choice trials, meaning the child had only one choice available. This procedure ensured that children were exposed to the contingencies for both left and right button pushes. These forced-choice trials alternated between the left and right button, beginning with the left. If a child continually pressed the ineffective button, the experimenter prompted the child to try the other button. The remaining 10 trials were free-choice trials, meaning the child could choose whichever button he or she preferred.

At the beginning of a free-choice trial, Mickey's nose was illuminated, which signaled that the child could make a response (press either left or right button). If the child pressed the left button, a feedback click was produced, Mickey's nose darkened, and the green light above the left button came on. This began the reinforcer delay period. After the delay, the child received a reinforcer (a drawer below the green light slid out from the apparatus, and the participant then took out the food items and ate them). After the child had removed the food items and shut the drawer completely, the experimenter pulled the drawer back so that it was again flush with the apparatus and turned the green light off. The child ate the food items immediately after removing them from the drawer. The next trial began when the ITI expired and was signaled by the illumination of Mickey's nose. If the child selected the button on the right, the sequence of events was the same as those for the left button, except that the red light above the right button would be illuminated and the right drawer would slide out. The sequence of events for forced-choice trials was the same, except that only a response on one button was functional.

For the training condition (Self-Control Session 1), pressing either button resulted in a 15-s delay followed by two reinforcers. In the experimental conditions (Self-Control Sessions 2-5), for one choice a 30-s prereinforcer delay was followed by access to three mini M&Ms (the self-control alternative), and for the other choice a 0-s prereinforcer delay was followed by access to one mini M&M (the impulsive alternative). In similar studies, preschool children have shown sensitivity to these reinforcement parameters (Logue & Chavarro, 1992; Logue et al., 1996). To control for position and color biases, half of these conditions programmed the self-control alternative for the left choice and half for the right choice (Forzano et al., 2003).

In addition, the children were exposed to two food-cue conditions for two sessions each. For the food-cues-present condition, visual food cues were present (i.e., the small wooden box with a clear Plexiglas front panel contained a plastic box filled with M&Ms). For the food-cues-absent condition, the visual food cues were absent (i.e., the plastic box did not contain M&Ms).

To account for order effects, those assigned to Order 1 and Order 3 had food cues present in Self-Control Sessions 2 and 3 and food cues absent in Self-Control Sessions 4 and 5. Those assigned to Order 2 and Order 4 had food cues absent in Sessions 2 and 3 and food cues present in Sessions 4 and 5. (Recall that participants in Orders 1 and 2 completed their self-control sessions before completing the delay-of-gratification sessions, and the reverse for Orders 3 and 4.)

To make the self-control testing sessions similar to the delay-of-gratification testing sessions, a self-imposed delay modification was made to the standard self-control procedure (see Chelonis et al., 1998; Logue & Pena-Correal, 1984, for a similar modification). In a self-imposed delay procedure, children can reverse, that is, change, their choice to the smaller, less delayed reinforcer during the delay to the larger reinforcer. More specifically, if a participant initially presses the button for the larger, more delayed reinforcer (i.e., waiting 30 s for three food items), he or she could then reverse or change that choice by pressing the other button, which would result in termination of the delay, turning off the delay light for the larger reinforcer and immediately turning on the delay light for the smaller reinforcer, thus resulting in receipt of one food item. Therefore, two major self-control values were generated for each session: an initial self-control proportion (i.e., the proportion of button presses initially for the larger, more delayed reinforcer) and a final self-control proportion (i.e., the proportion of button presses for the larger, more delayed reinforcer after participants reversed their choice and terminated the delay).

Delay-of-gratification testing sessions. The procedure and instructions given for the delay-of-gratification testing session were similar to previous research (Mischel & Ebbesen, 1970; Mischel et al., 1972). The child sat at a table with a desk bell that the child could press if he or she decided to end the waiting period. The participant was given instructions by the experimenter on how and when to operate the bell (see Appendix B).

For the food-cues-absent condition, the plate with M&Ms in front of the child remained covered. For the food-cues-present conditions, the cover was removed from the room as the experimenter left the room. The experimenter then set a timer and observed through a small hole in the wall. The session was terminated if the child chose one M&M when the experimenter was giving instructions, did not understand the instructions, showed any sign of distress, rang the bell, or waited the entire 20 min. Wait time and mode of termination were recorded.

As with the self-control sessions, children were assigned to different orders of conditions. Children assigned to Orders 1 and 3 were exposed to the food-cues-present condition first, followed by the food-cues-absent condition. Children assigned to Orders 2 and 4 received the food-cues-absent condition followed by the food-cues-present condition.

One session was scheduled per day. The mean time to complete the entire experiment was 27.3 calendar days (SD= 13.9).

Results

Self-Control

All of the participants learned how to operate the apparatus during the first few minutes of the first session (with less than 6% of the trials lasting longer that the programmed I min due to long response latencies). All participants ate the reinforcers as soon as they were received. Eighty percent of the participants made verbalizations or gestures indicating their awareness of the food-cues manipulation.

All self-control analyses were performed using the data from the 10 free-choice trials for each of the experimental sessions (Sessions 2 through 5). The dependent variables consisted of four response measures, including (a) the initial proportions of self-control responses (i.e., the proportions of button presses initially for the larger, more delayed reinforcer), (b) the final proportions of self-control responses (i.e., the proportions of button presses for the larger, more delayed reinforcer after participants reversed their choice and terminated the delay), (c) the proportions of alternating responses (Le., the proportions of button presses in which a button press in a given trial was the opposite of the button from the previous trial), and (d) the decrease in self-control proportions from initial and final choices, which accounts for trials in which children initially made the self-control choice but then reversed to the impulsive choice within the trial time.

Proportions of self-control (initial and final). There were no significant differences in the self-control data obtained between sessions in which the self-control choice was on the left and those in which the self-control choice was on the right for the food-cues-present condition for both initial self-control proportions, t(29) = -1.54, p =.134, d = 0.282, and for final self-control proportions, t(29) = -1.494, p =.146, d = 0.273. Likewise, there were no significant differences in the self-control data between the left/right conditions for the food-cues-absent condition for both initial self-control proportions, t(29) = -0.564, p =.577, d = 0.103, and final self-control proportions, t(29) = -0.189, p =.851, d = 0.035. In other words, there were no statistically significant position or color biases. Therefore, for all further analyses, the left and right data were combined. Hence, the proportion of self-control responses (i.e., number of free-choice self-control responses divided by 10 free-choice trials) was averaged across Sessions 2 and 3 and Sessions 4 and 5. Table 1 and Figure 2 display the initial and final self-control proportions for each participant for the food-cues-present and food-cues-absent conditions.

[FIGURE 2 OMITTED]

A 4 x 2 x 2 mixed-design ANOVA was performed with order and gender as the between-subjects independent variables and proportions of self-control in the food-cues-present and food-cues-absent conditions, both initial and final (after reversals were made), as the within-subjects repeated dependent variables. There was no main effect of food cues for both initial self-control proportions, F(l, 22) = 0.031, p = .861, [[eta].sub.2] = .001, and final self-control proportions, F(1, 22) = 0.001, p = .971, [[eta].sub.2] = .000. There was also no main effect of order for initial self-control proportions, F(3, 22) = 0.810, p = .502, if = .099, or final self-control proportions, F(3, 22) = 0.663, p = .583, [[eta].sub.2] = .083. There was no main effect of gender for either initial self-control proportions, F(l, 22) = 1.33, p = .260, [[eta].sub.2] = .057, or final self-control proportions, F(1, 22) = 0.140, p = .712, [[eta].sub.2] = .006. No significant 2-way or 3-way interactions were found.

Of the 17 boys, nine participants demonstrated higher initial proportions of self-control in the conditions in which food cues were absent than in conditions in which food cues were present. In contrast, six of the boys demonstrated higher proportions of initial self-control in the conditions in which food cues were present than in conditions in which food cues were absent. The self-control proportions for two boys appeared to be unchanged by this manipulation.

Of the 13 girls, four participants demonstrated higher initial proportions of self-control in the conditions in which food cues were absent than in conditions in which food cues were present. In contrast, four of the girls demonstrated higher proportions of initial self-control in the conditions in which food cues were present than in conditions in which food cues were absent. The self-control proportions for five girls appeared to be unchanged by this manipulation.

Proportion of alternating responses. A 4 x 2 x 2 mixed-design ANOVA was performed with order and gender as the between-subjects independent variables and proportion of alternating responses in the food-cues-present and food-cues-absent conditions as the within-subjects (repeated-measures) dependent variable. The main effect of food cues was not significant, F(l, 22) = 0.011, p = .917, [[eta].sub.2] = .001. The main effect of order was not significant, F(l, 22) = 1.929, p = .154, [[eta].sub.2] = .208. The main effect of gender was nearly significant, with mean proportion of alternations of.671 for girls and.498 for boys, F(l, 22) = 3.918, p = .060, [[eta].sub.2] = .151. There was a significant interaction between proportion of alternating responses and order, HI, 22) = 6.02, p = .004, [[eta].sub.2] = .451. However, post-hoc tests did not demonstrate significant differences. No other 2-way or 3-way interactions were found to be significant.

Effect of reversed responses. A 4 x 2 x 2 mixed-design ANOVA was performed with order and gender as the between-subjects independent variables and self-control proportions before and after reversal responses (i.e., initial and final self-control proportions) as the within-subjects (repeated-measures) dependent variable. For the food-cues-present condition, there was a significant main effect of reversal responses (i.e., there was a significant decrease in self-control proportions between the initial and final responses), F(l, 22) = 5.495, p = .029, [[eta].sub.2] = .200. There was no main effect of order, F(3, 22) = 0.844, p = .485, [[eta].sub.2] = .103, or gender, F(l, 22) = 0.206, p = .655, [[eta].sub.2] = .009. There was no significant interaction with order, F(1, 22) = 0.575, p = .638, [[eta].sub.2] = .073, nor with gender, F(1, 22) = 1.853, p = .187, [[eta].sub.2] = .078. There was no significant 3-way interaction.

A 4 x 2 x 2 mixed-design ANOVA was performed with order and gender as the between-subjects independent variables and proportion of self-control before and after reversal responses (for the food-cues-absent condition) as the within-subject dependent variable. Again, there was a significant main effect of reversal responses (i.e., self-control proportions decreased between the initial and final responses), F(l, 22) = 7.27, p = 013, [[eta].sub.2] = .248. There was no main effect of order, F(3, 22) = 0.500, p = .686, [[eta].sub.2] = .064, or gender, F(l, 22) = 1.162, p = .293, [[eta].sub.2] = .050. There was nearly a significant interaction between reversal self-control proportions and gender, F(l, 22) = 3.931, p = .060, [[eta].sub.2] = .152. A repeated measures t test was used to compare the number of reversals made by boys and girls, and the result was significant, t(28) = 2.536, p = .020, d = 0.827. The boys reversed their choices from the self-control choice to the impulsive choice in 4.4% of the trials, whereas girls reversed their choices in only 0.90% of the trials. Finally, there was no interaction with order, F(l, 22) = .574, p = .638, if = .073. There were no other significant 2-way or 3-way interactions.

A repeated measures t test was used to compare the number of reversals made when food cues were present and absent. The number of reversals made in sessions with food cues present (M = 3.5% of trials) was not significantly different than the number of reversals made in sessions with food cues absent (M = 4.9% of trials), t(29) = .0.379, p = .707, d = 0.080.

Delay of Gratification

The delay-of-gratification procedure was explained to each of the 30 participants (see Appendix B). In total, 21 of the 30 participants completed the task by either waiting the full 20 min or ringing the bell to summon the experimenter in both the food-cues-present and food-cues-absent conditions. In the food-cues-present condition, 22 participants completed the task in this manner. In the food-cues-absent condition, 26 participants completed the task in this manner. Of the 60 delay-of-gratification sessions (30 participants x 2 food-cue conditions), there were 16 in which the child waited for the entire 20-min period. Five of the 30 children waited the entire 20-min period in both conditions.

The average wait time in the food-cues-present condition was 537.3

s (SD = 569.4 s). In the food-cues-absent condition, the average wait time was 508.9 s (SD = 541.7 s). Table 1 and Figure 3 display the wait times for each participant for the food-cues-present and food-cues-absent conditions.

A 2 x 4 x 2 mixed-design ANOVA was performed with gender and order as the between-subjects independent variables and the wait times as the within-subjects (repeated-measures) dependent variable in the food-cues-present and food-cues-absent conditions. There was no main effect of food cues on wait times, F(l, 13) = 0.071, p = .794, [[eta].sub.2] = .005, or gender on wait times, F(l, 13) = 0.033, p =.955, [[eta].sub.2] = .000. There was a main effect of order on wait times, F(3, 13) = 5.072, p = .015, [[eta].sub.2] = .539. Collapsed across food-cue conditions and gender, wait times were significantly longer in Order 4 participants (i.e., when delay-of-gratification sessions were completed before self-control sessions) than in Order 1 participants (i.e., when self-control sessions were completed before delay-of-gratification sessions), t(14) = 5.364, p = .002, d = 2.82. There were no significant 2-way or 3-way interactions.

Mischel and Ebbesen's (1970) participants, who participated in the same delay-of-gratification paradigm in one session, waited an average of 11.29 min (SD = 6.84) when food cues were absent and an average of 1.03 min (SD = 2.39) when food cues were present. in the present experiment, participants waited 8.48 min (SD = 9.03) when food cues were absent and 8.95 min (SD = 9.49) when food cues were present. When food cues were absent, participants' wait times in the current experiment were not significantly different from those in the Mischel and Ebbesen study, t(32) = 0.808, p = .426. When food cues were present, the current participants waited significantly longer than those in the Mischel and Ebbesen study, t(32) = 2.316, p = .027, d = 0.963.

[FIGURE 3 OMITTED]

In order to perform a more accurate comparison of results between the two studies, we reduced all current wait times that exceeded 15 min to 15 min, to match the maximum wait time in the Mischel and Ebbesen (1970) study. In addition, we only considered wait times for participants in the present study who participated in Orders 3 and 4, since they completed the delay-of-gratification tasks before the self-control tasks and therefore their behavior would not have been influenced by the self-control tasks. Finally, we only considered the first delay-of-gratification session for each participant in order to mimic Mischel and Ebbesen's single-session/betwecn-subjccts design. Five children participated in the food-cues-prescnt condition in their first session, whereas seven participated in the food-cues-absent condition. Even with these changes, the wait times in the current study in the food-cues-present condition were still significantly longer than those in the Mischel and Ebbesen study, t(11) = 2.858, p = .008, d = 0.570. In the food-cues-absent condition, the wait times between the two studies were not significantly different, t(13) = 1.106, p = .278, d = 0.518.

Self-Control and Delay of Gratification

The relationship between participants' self-control proportions in the self-control task and wait time in the delay-of-gratification task was analyzed with Pearson correlations. For the food-cues-present condition, the correlation between self-control proportions and wait times was significant for both initial self-control proportions, r(20) = .556, p = .007, and final self-control proportions, r(20) = .613, p = .002. For the food-cues-absent condition, significant positive correlations were also found between the initial self-control proportions and wait times, r(24) = .430, p = .028, and between final self-control proportions and wait times, r(24) = .438, p = .025. Collapsed across the food-cue conditions, the relationship between self-control proportions and wait times was r(20) = .652, p = .001 for initial self-control proportions and r(20) = .642, p = .002 for final self-control proportions.

Discussion

The first study objective, to establish concurrent validity between two different measures of self-control, was demonstrated by the large significant positive correlation between self-control proportions in the self-control task and wait times in the delay-of-gratification task. This is the first demonstration, in humans, of a strong positive correlation between two measures within the consequence-sensitivity/reward-delay category of impulsive behavior (see Reynolds, De Wit, & Richards, 2002, for an experiment with rats that found a significant relationship using delay discounting and delay-of-gratification tasks), and it supports the inclusion of the self-control and delay-of-gratification tasks in this category by Dougherty et al. (2005).

Our next objective was to explore a modification to the self-control task that allowed participants to change their choices within a trial in order to create a situation more like that in the delay-of-gratification task (see Logue & Pena-Correal, 1984, and Chelonis et al., 1998, for similar modified procedures using pigeons and rats, respectively). First, we found a significant difference between initial, externally imposed choices in the self-control task (which reflects the traditional procedure) and final choices (after self-imposed reversal of choices were made). That is, participants' proportions of self-control decreased significantly when they were allowed to change their choices from the self-control alternative to the impulsive alternative in order to obtain the reinforcer immediately. This indicates that there is an absolute difference in self-control (or impulsivity) between the two types of delay imposition. However, in both cases, performance in the self-control task was significantly and strongly correlated with performance in the delay-of-gratification task.

We also compared the rate at which our participants changed their choices to the impulsive choice in the self-control task to previous studies featuring this self-imposed delay. In Logue and Pena-Correal's (1984) experiment, pigeons could change their choices to receive access to grain more quickly, but this choice reduced the amount of time they had access to the grain from 6 s to 2 s. In their study, subjects reversed their choices in 49% of the trials, generating a significant decrease in the final self-control proportions (Logue & Pena-Correal, 1984). In the Chelonis et al. (1998) study, in which rats were allowed to change their choices during the delay, subjects demonstrated very little reversing, such that the authors did not report the final self-control proportions.

In the present study, the children reversed their choices on 4.2% of the trials, significantly fewer than the pigeons in Logue and Pena-Correal (1984) experiment, who reversed choices on 49% of the trials, t = 5.844, p < .001. This finding is consistent with Tobin and Logue's (1994) meta-analysis that concluded that self-control is greatest in humans, lower in rats, and lowest in pigeons, which some have interpreted as a function of species differences (Rodriguez & Logue, 1988; Sonuga-Barke et al., 1989) and others have attributed to procedural differences (Forzano & Logue, 1994; Jackson & Hackenberg, 1996).

Next, in the current study there was no overall effect of the presence or absence of visual food cues on self-control in the self-control task, nor did food cues affect wait times in the delay-of-gratification task. The former result is consistent with the self-control experiment of 3-year-olds in the Forzano et al. (2003) study, in which there was also no main effect of food cues.

Our latter food-cue result (i.e., no effect of food cues on wait times in the delay-of-gratification task) is not consistent with Mischel and Ebbesen's (1970) result that children ages 3 to 5 years waited significantly longer when food cues were absent than when food cues were present. Although it does not appear that any other delay-of-gratification studies have manipulated food cues, four studies used the same delay-of-gratification task with food cues present only and with children ranging from 1.5 to 6 years old. These studies also had the children choose between a small and large amount of candy, which is similar to the present experiment's methodology of varying the amount of the reinforcer, not the quality (as was done in Mischel and Ebbesen's study). In Jacobsen's (1998) study, the children's average wait times were 5.5 to 11 min, and in Jacobsen, Huss, Fendrich, Kruesi, and Ziegenhain (1997), average wait times were 8.9 min (for 1.5-year-olds) and 9.7 min (for 6-year-olds). These wait times are much more consistent with those in the present study when food cues were present (8.95 min) than with the average wait time of 1.03 min in the Mischel and Ebbesen study. Further, Flynn (1975) and Shipman (1972) reported that 45% and 64-65% of children, respectively, waited for the entire 15 min to obtain the larger amount of candy. Again, these results are more comparable to the result of the present study (i.e., 41% of children waited through the entire delay) than to the Mischel and Ebbesen result of 0%. A clear difference between the Mischel and Ebbesen study and all of these other studies is the nature of the reinforcer choices. In the Mischel and Ebbesen study, the two choices differed in reinforcer quality (a pretzel and a cookie). In contrast, in all of the other studies, including the current experiment, children chose between two amounts of the same reinforcer. It appears that this difference may account for the difference in wait times. Further, it should be noted that the variability in the wait times in the current experiment appears to be greater than that in the Mischel and Ebbesen study, which warrants further research.

An additional effect found on wait times in the delay-of-gratification task was the order of conditions, with wait times being longer for participants who received the delay-of-gratification sessions prior to the self-control sessions than for participants who received the delay-of-gratification sessions after the self-control sessions. Perhaps the shorter delays of the self-control task provided a contrast effect and influenced wait times in the delay-of-gratification task. Experience with prior delays could be investigated in future experimentation.

In addition, future research could examine the effects of a larger number of free-choice trials in the self-control procedure. Similar to previous self-control studies (Forzano & Logue, 1993; Morzano et al., 2003; Logue & Chavarro, 1992), in the current experiment self-control proportions were calculated by averaging the 20 free-choice trials per condition. However, other research with humans in a self-control paradigm have involved more trials (Dixon, Rehfeldt, & Randich, 2003).

The final objective was to explore gender differences in the self-control and delay-of-gratification tasks. No significant relationships were found between gender and the overall measures of self-control in the current experiment (i.e., self-control proportions in the self-control task and wait times in the delay-of-gratification task). This finding is consistent with other self-control and delay-of-gratification studies that have not found a gender effect (Logue et al., 1996; Peake et al, 2002). This finding is also consistent with a meta-analysis, conducted by Silverman (2003), of 33 studies of delay of gratification. Although the overall results favor girls in that analysis, the studies varied in their results, and effect sizes were low.

In addition, the findings in the current study for the self-control task with food cues absent are the same as in Forzano et al. (2003), which used an identical procedure. However, in the food-cues-present condition in the Forzano et al. study, 3-year-old boys demonstrated significantly higher self-control than girls, in contrast to the present experiment, in which no differences were shown. Perhaps the difference in ages of the children between the experiments account for the difference in the results.

A nearly significant gender difference was found in the present experiment, in that boys reversed their self-control choice, from self-control to the impulsive choice, more than girls. This difference in responding may reflect a gender difference in self-control. This phenomenon (behavior that diverged from the practice and forced-choice trials) may be due to the girls' lower probability of deviating from the "rules" of the initial trials. Alternate possibilities are that the boys were more physically active (pressing more buttons altogether) or that they were more impulsive than girls in this paradigm. Again, each of these explanations warrants further research.

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Appendix A

Participant Instructions for Self-Control Sessions

"We're going to play the game now, a fun game with a Mickey Mouse and M&Ms. (Child's name), have a seat right here and I'll show you how to play. When Mickey's nose lights up [point to nose] like this [turn on nose], see Mickey's nose light up [point to nose]? What you have to do is press one of these buttons [point to the left and then right button], whichever one you want, but not both. If you press this button [experimenter presses green button], the green light will come on. See the green light? When the drawer comes out, you will open it up and take out the M&Ms and eat them. If you press this button [experimenter presses red button], the red light will come on. See the red light? When the drawer comes out, you will open it up and take out the M&Ms and eat them."

"Now let's see you try. Can you press this button [experimenter has child press the green button]? Great! See how the green light came on? Now when the drawer comes out, open it up, and what are you going to do with those M&Ms [experimenter waits for child to say "eat them"]? Now let's try the other button. Can you press this button [experimenter has child press the red button]? Terrific! Now when this drawer comes out, open it up, and what are you going to do with those M&Ms [experimenter waits for child to say "eat them"]?"

Appendix B

Participant Instructions for Delay-of-Gratification Sessions

"Sometimes I have to go out of the room, and when I do, you can bring me back. Do you see this bell? Well, if I go out of the room and you ring this bell, you can make me come back into the room. You can make me come back! Let's try it. I'll go out of the room now and shut the door. As soon as I shut the door, you ring the bell and make me come back." [Experimenter has the child practice ringing the bell and making the experimenter return four times. After the fourth bell ring, the experimenter returns with the three-section plate containing the reinforcer.]

"Let's see what's under here. I'll bet it's a surprise. Oh boy, look at that. One M&M and three M&Ms. Can you point to or tell me which one you'd like to eat? You can eat either the one M&M or the three M&Ms [if the child chooses the one M&M the experimenter terminates the session]. Oh, you know what? I have to go out of the room now, and if you wait until I come back by myself then you can eat this right up. But, you know, if you don't want to wait you can ring the bell and bring me back anytime you want to. But if you ring the bell, then you can't have that [experimenter points to the three M&Ms] but you can have this [experimenter points to the one M&M]"

"So, if you ring the bell and bring me back you can't have the three M&Ms, but you can have the one M&M. Can you tell me, which do you get to eat if you wait for me to come back by myself? But if you want to, how can you make me come back? If you ring the bell and bring me back, then which do you get? Would you like to play this game today? Okay, let's start. I have to leave the room now. And if you want to you can ring the bell whenever you want and bring me back."

Jennifer Michels is now at the Department of Neurodevelopmental and Behavioral Pediatrics, University of Rochester Medical Center, Rochester, NY, and at The College at Brockport, State University of New York; Renae K. Carapella is now at the American Foundation for Suicide Prevention, Western New York Chapter, Spencerport, NY; Patrick Conway is now at the Research Institute on Addiction at the State University of New York at Buffalo, Buffalo, NY, and at Corning Community College, Corning, NY; John J. Chelonis is now at the Division of Neurotoxicology, National Center for Toxicological Research, Jefferson, AR.

We thank A. Hoock for assistance in preparing figures.

This document has been reviewed in accordance with United States Food and Drug Administration (FDA) policy and approved for publication. Approval does not signify that the contents necessarily reflect the position or opinions of the FDA, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. The findings and conclusions in this report are those of the author(s) and do not necessarily represent the views of the FDA.

Correspondence concerning this article should be addressed to L. B. Forzano, Department of Psychology, The College at Brockport, State University of New York, 350 New Campus Drive, Brockport, NY 14420. E-mail: lforzano@brockport.edu

L. B. Forzano, Jennifer L. Michels, R. K. Carapella, Patrick Conway and J. J. Chelonis

The College at Brockport, State University of New York
"Would you like to play the Mickey game?" If child says no, "Okay,
  no problem. We're all done playing in here today. Let's go back to
  the front room." If child says yes, "So when Mickey's nose lights
  up, what are you going to do? [Experimenter waits for correct
  response.] Remember, you can press any button you want. Okay, let's
  start. I'm going to sit right back here."


Table 1
Demographics, Proportion of Self-Control for Both Initial and Final
Choices, and Wait Times (s) Demonstrated by Each Participant in Both
the Food-Cues-Present and Food-Cues-Absent Conditions

                                       Food cues absent
Participant    Age     Gender  Order  [SC.sub.initial]   [SC.sub.final]
             (months)

1            54        M       3                 0.50            0.50
2            55        F       4                 0.55            0.50
3            51        M       4                 0.00            0.00
4            49        M       1                 0.45            0.10
6            54        F       3                 0.75            0.75
9            55        M       2                 0.95            0.95
10           50        M       4                 1.00            1.00
11           54        F       2                 0.50            0.45
12           49        F       1                 0.50            0.45
13           52        F       4                 0.60            0.55
14           57        M       3                 0.45            0.45
15           59        F       2                 0.60            0.60
16           55        M       2                 0.50            0.50
17           51        M       4                 0.95            0.85
18           55        M       2                 0.50            0.45
19           53        F       3                 0.45            0.45
20           58        M       1                 0.45            0.40
21           54        M       4                 0.90            0.65
23           52        M       1                 0.45            0.45
24           56        F       4                 1.00            1.00
25           50        F       4                 0.35            0.35
26           48        F                         0.50            0.50
27           58        M       3                 0.85            0.70
28           52        F       2                 0.45            0.45
29           54        M       3                 0.35            0.35
30           53        F       1                 0.45            0.45
31           50        F       4                 0.40            0.40
33           56        M       2                 0.45            0.45
34           56        M       1                 0.60            0.55
35           56        M       4                 1.00            1.00
M            54                                  0.58            0.54
(SE)         0.53                                0.04            0.04

                                       Food cues present
Participant    Age     Gender  Order  [SC.sub.initial]    [SC.sub.final]
             (months)

1            54        M       3                  0.60            0.55
2            55        F       4                  0.80            0.75
3            51        M       4                  0.45            0.25
4            49        M       1                  0.55            0.40
6            54        F       3                  0.85            0.85
9            55        M       2                  0.95            0.70
10           50        M       4                  0.60            0.60
11           54        F       2                  0.50            0.50
12           49        F       1                  0.50            0.45
13           52        F       4                  0.50            0.45
14           57        M       3                  0.40            0.40
15           59        F       2                  0.40            0.40
16           55        M       2                  0.55            0.55
17           51        M       4                  0.85            0.80
18           55        M       2                  0.70            0.35
19           53        F       3                  0.45            0.45
20           58        M       1                  0.75            0.75
21           54        M       4                  0.55            0.45
23           52        M       1                  0.70            0.70
24           56        F       4                  0.80            0.80
25           50        F       4                  0.45            0.45
26           48        F                          0.40            0.40
27           58        M       3                  0.45            0.35
28           52        F       2                  0.45            0.45
29           54        M       3                  0.60            0.60
30           53        F       1                  0.45            0.45
31           50        F       4                  0.50            0.50
33           56        M       2                  0.50            0.50
34           56        M       1                  0.60            0.60
35           56        M       4                  0.80            0.80
M            54                                   0.59            0.54
(SE)         0.53                                 0.03            0.03

                                       Wait times (s)
Participant    Age     Gender  Order   [FC.sub.pres]   [FC.sub.absent]
               (months)

1            54        M       3              1,200            1,200
2            55        F       4
3            51        M       4                  2            1,200
4            49        M       1                 10               10
6            54        F       3              1,200            1,200
9            55        M       2              1,200                5
10           50        M       4              1,145            1,200
11           54        F       2                  1                1
12           49        F       1                  7                1
13           52        F       4                  4              630
14           57        M       3                504                8
15           59        F       2                 47                4
16           55        M       2                 54              536
17           51        M       4              1,200            1,200
18           55        M       2              1,200              559
19           53        F       3                                 124
20           58        M       1                               1,197
21           54        M       4
23           52        M       1                                   2
24           56        F       4              1,200            1,200
25           50        F       4
26           48        F                                           2
27           58        M       3                  3              .02
28           52        F       2                               1,200
29           54        M       3                200              100
30           53        F       1                  1              236
31           50        F       4              1,200
33           56        M       2                137               18
34           56        M       1                106              199
35           56        M       4              1,200            1,200
M            54                               537.3            508.9
(SE)         0.53                             121.4           106.24

Note. [SC.sub.initial] = the self-control proportions demonstrated by
the first choice the child made; [SC.sub.final] = the final
self-control proportions, which include any reversal that occurred from
the self-control choice to the impulsive choice; [FC.sub.pres] = wait
time demonstrated in food-cues-present condition; [FC.sub.absent] =
wait time demonstrated in food-cues-absent condition.
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