Adjunctive behavior in humans on a food delivery schedule

Adjunctive behavior in humans on a food delivery schedule

Physiology & Behavior, Vol. 20, pp. 2 0 3 - 2 0 4 . Pergamon Press and Brain Research Publ., 1978. Printed in the U.S.A. BRIEF COMMUNICATION Adjuncti...

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Physiology & Behavior, Vol. 20, pp. 2 0 3 - 2 0 4 . Pergamon Press and Brain Research Publ., 1978. Printed in the U.S.A.


Department o f Psychology, La Trobe University, Bundoora, Victoria, Australia 3083 (Received 15 May 1977) WALLACE, M., A. SANSON AND G. SINGER. Adjunctive behavior in humans on a food delivery schedule. PHYSIOL. BEHAV. 20(2) 203- 204, 1978. - Adjunctive behavior as indexed by increased activity has been shown previously in adult humans who were performing cognitive tasks or playing games of chance on a fixed interval schedule. In the present experiment with eating as the schedule controlled behavior, the amount of movement unrelated to eating was measured for eight subjects under three conditions. Movement scores were significantly higher when food was available either ad lib or on a FI 60 food delivery schedule than when food was not available. Data showed that with ad lib food, subjects operated on a self imposed schedule. These results establish the first direct comparison between animal and human adjunctive behaviors. Schedule induced

Food Schedules


A NON R E I N F O R C E D increase in activity described as adjunctive behavior has been shown to occur in animals placed on FI or VI schedules [2]. In adult humans, adjunctive behavior, indexed by an increase in movement scores, has been demonstrated during game playing on a FI 60 schedule where a computer console was used to simulate a jackpot machine, similar to those found in gambling casinos [4]. It was also observed in a gambling situation where groups of four subjects played poker dice with their dice throwing restricted to a FI 120 schedule [ 1 ]. Increases in movement scores were shown in individual subjects when a cognitive task which did not involve a contingent monetary reward (maze solving) was schedule controlled [3 I. Whereas most experiments on various animal species involve scheduled food rewards, studies on human subjects have used gambling tasks with monetary reward or cognitive tasks with no extrinsic reward. The present experiment was designed to test whether adjunctive behavior would occur in humans on a food delivery schedule. The paradigm used was essentially the same as that used in animal experiments. Ad lib presentation of food was included as a control condition which also allowed us to determine whether human subjects impose their own eating schedules.

Subjects were ~tested in a high-ceilinged, sound-proofed room, 3m x 8m,.in which stood two tables. On one table was a timer, a response key-board set up to record reaction times on a simple task, and a stopwatch. During scheduled sessions, a Smarties dispenser was placed on the second table: this dispensed Smarties (small sugar-coated chocolate candies) at the rate of one a minute, contingent upon pressing a key. A beeper which could sound once a minute was also present, along with two chairs and a water dispenser. Subjects' movements were scored through a one-way mirror from an observation room. A monitor in this room recorded the number of key presses and Smarties dispensed. A beeper, audible only in the observation room, sounded every 10 sec for scoring purposes.

Procedure Subjects were tested individually in half hour sessions , one session per day and as far as possible on consecutive days. They were told that the purpose of the experiment was to monitor the effect of blood-sugar level on reaction times. Therefore, at the beginning and end of each session, subjects were tested on a simple reaction-time task and their pulses were taken. (Results were not recorded). They were asked not to eat for 2 hr before the session. Subjects were tested on five sessions. On the first and last sessions subjects were asked simply to remain in the experimental room for the half hour between reaction time tasks (no food). On the second session, 30 Smarties were


Subjects Eight non-psychology university students aged between 18 and 21 years served as subjects. They were paid a small amount of money on completion of the experiment. 203



given to the subject in a bowl, to be eaten ad lib lad lib food). On the third and fourth sessions, subjects were told that the dispenser would be used to regulate the rate of intake of Smarties. On the third session they were told that it would not dispense more than one a minute, and to "just press the key when you want o n e " (FI 60 demand). On the fourth session they were asked to maintain their Smarties consumption at the rate of one a minute, and to aid them in this the beeper sounded at one minute intervals (FI 60 forced). Four of the eight subjects were habitual smokers and were tested in two additional sessions, one with ad lib Smarties and one with scheduled Smarties, when smoking was allowed.

No food


Ad rib food FI 60 food Session 3 : FI 60 Demand] Session 4:FI 60 Forced J


8O Scoring Scoring of movement in all sessions was based on 10-sec time samples. Subjects were scored as either quiet, moving, eating or smoking. Scores on the latter two categories were deleted and percentage movement scores were calculated as the percentage of the remaining samples on which the subject was moving. The number of Smarties consumed, the number of key presses and the number of cigarettes smoked and puffs taken were also recorded. RESULTS

z LU ~E

60 laJ t9


Data from Sessions 1, 2 and 5 show that the presence of ad lib food (Session 2) increases movement scores when compared with scores obtained when no food is present (Sessions 1 and 5) t = 3.27 df 3, p<0.05 (no food vs ad lib food) (Fig. 1). There was no significant difference in movement scores when the ad lib food condition was compared with the two food schedule conditions (Sessions 3 and 4). These findings may be the result of a self imposed eating schedule on ad lib sessions, since three of the four subjects showed eating responses on more than 16 separate occasions on which the time samples were taken and these responses are distributed over the whole 30 min period. Only one subject ate all his Smarties during the first three min of the session and he had the lowest movement score. There was no difference in movement scores between the FI 60 demand schedule and the FI 60 forced schedule (t < 1). The data indicate that subjects schedule their eating responses under the demand condition, since all subjects under this condition obtained at least 24 Smarties and spread their eating over the whole 30 min session. Since for subjects who are smokers the ability to smoke or to abstain may influence eating as well as movement, the movement scores for the smokers under smoking and non-smoking conditions were comi0ared; no significant difference was found. DISCUSSION

Human subjects on a food delivery schedule show adjunctive behavior (an increase in unreinforced movements) as do other species. The present finding extends the occurrence of atljunctive behavior in humans beyond situations where gambling or cognitive tasks are scheduled, It



2 3 4 5 SESSIONS FIG. 1. Percentage movement scores for 4 non-smoking subjects under 3 conditions: no food, ad lib food and scheduled food. also weakens the claim that only animals which are reduced in body weight develop adjunctive behavior [2}. The presence of food available ad lib during test sessions also resulted in an increase in movement scores over baseline. Inspection of the data showed that subjects appeared to operate on a self imposed schedule which could be reconstructed from the data and was close to a VI 120 or a FI 120 schedule. This self imposed schedule was also shown when subjects were in a demand feeding condition without a warning signal. In this latter situation, subjects again scheduled their own eating. The fact that humans self impose schedules which lead to increased activation has interesting implications for the occurrence and maintenance in humans of adjunctive behaviors such as doodling, grooming and sipping drinks when food is available. Self imposed scheduling has not been observed in other species. These findings lead to the question of whether eating itself may become an adjunctive activity when some other behavior is schedule controlled, a question which could have relevance for some types of overeating in humans. Smoking did not have a significant effect on movement scores. This is in accordance with our previous findings [3 ].


1. Clarke, J., M. Gannon, 1. Hughes, C. Keogh, G. Singer and M. Wallace. Adjunctive behavior in humans in a group gambling situation. Physiol. Behav. 18: 159-161, 1977. 2. Falk, J. L. The nature and determinants of adjunctive behavior. Physiol. Behav. 6: 577-588, 1971.

3. Wallace, M. and G. Singer. Adjunctive behavior and smoking induced by a maze solving schedule in humans~ Physiol. Behav. 17: 849-852, 1976. 4. Wallace, M., G. Singer, M. J. Wayner and P. Cook. Adjunctive behavior in humans during game playing. Physiol. Behav. 14: 65l--654, 1975.