Within-session changes in key and lever pressing for water during several multiple variable-interval schedules

Rats pressed keys or levers for water reinforcers delivered by several multiple variable-interval schedules. The programmed rate of reinforcement varied from 15 to 240 reinforcers per hour in different conditions. Responding usually increased and then decreased within experimental sessions. As for food reinforcers, the within-session changes in both lever and key pressing were smaller, peaked later, and were more symmetrical around the middle of the session for lower than for higher rates of reinforcement. When schedules provided high rates of reinforcement, some quantitative differences appeared in the within-session changes for lever and key pressing and for food and water. These results imply that basically similar factors produce within-session changes in responding for lever and key pressing and for food and water. The nature of the reinforcer and the choice of response can also influence the quantitative properties of within-session changes at high rates of reinforcement. Finally, the results show that the application of Herrnstein's (1970) equation to rates of responding averaged over the session requires careful consideration.     

Effects of chlordiazepoxide and cocaine on concurrent food and avoidance-of-timeout schedules.

Five rats were trained on a concurrent schedule in which responses on one lever produced a food pellet on a random-interval 30-s schedule during 10 s of food availability associated with distinctive exteroceptive stimuli. Responses on another lever postponed for 20 s the presentation of a 50-s timeout, during which all stimuli were extinguished and the schedule contingencies on the food lever were suspended. The response rates maintained by the random-interval schedule exceeded those maintained by the avoidance contingency, but both provided a stable baseline to assess the behavioral effects of different drugs. Low doses of cocaine hydrochloride (1 and 3 mg/kg) did not affect food-reinforced responding or avoidance response rates. Intermediate doses (5.6, 10, and 13 mg/kg) produced a dose-dependent decrease in food-maintained and avoidance response rates, and both types of responding were virtually eliminated after administration of the highest doses (17 and 30 mg/kg) of cocaine. Low doses of chlordiazepoxide (1 and 3 mg/kg) increased food-maintained and avoidance response rates, and both rates decreased systematically after 10 and 30 mg/kg of this drug. The effects of cocaine and chlordiazepoxide on response rates maintained by avoidance of timeout from food presentation were unlike those reported when subjects responded to avoid shock presentation. The results of this experiment thus provide evidence to suggest that the effects of drug administration on avoidance behavior may be a function of the nature of the consequent event to be avoided.     

Biobehavioral effects of extended salt loading and conflict stress in intact baboons.

Behavioral stressors may inhibit sodium excretion, potentially increasing plasma volume and elevating blood pressure during chronic exposure. Blood pressure regulation may be especially deranged during manipulations that further challenge the kidney, such as a diet high in salt content. The effects on blood pressure and other variables of combined behavioral stress (food/shock conflict) and dietary salt (12 g NaCl per day; 218 mEq Na+ per day) were examined in adult male baboons over the course of 1 year. Mean arterial pressure was not significantly elevated over baseline after 5 months of high dietary salt alone (6 +/- 5 mmHg) but was maximally elevated by an average of 17 (+/- 3 SEM) mmHg after 5 months of combined salt and conflict stress. Control baboons showed no significant trends in mean arterial pressure across the same time period. Individual subjects whose blood pressure was "salt+stress resistant" or "salt+stress sensitive" were differentiated by their degree of pressure diuresis and natriuresis, urinary free cortisol, and a behavioral index of stress sensitivity. The data indicate additive effects of chronic high dietary salt intake and behavioral stressors on blood pressure in nonhuman primates that are dependent on renal function and pituitary-adrenocortical activity.     

DOES PACKAGE SIZE MATTER? A UNIT-PRICE ANALYSIS OF “DEMAND” FOR FOOD IN BABOONS

In a study examining “demand” for food, responding of 8 adult male baboons (Papio c. anubis) was maintained under a fixed-ratio schedule of food reinforcement during daily 23-hr experimental sessions. Completion of the ratio requirement resulted in the delivery of one, five, or 10 1-g food pellets. Supplemental feeding was limited to fruit and a dog biscuit daily. Responding increased as “cost” was increased across a wide range of fixed-ratio values before reaching a maximum and then decreasing. Increasing the number of food pellets per delivery decreased total responding and the number of reinforcements per day. A unit-price analysis, in which intake was converted to grams per day and fixed-ratio values were converted to responses per gram, yielded demand functions that overlapped at lower unit prices. Under one or more multiple-pellet conditions, however, intake decreased more quickly than under the one-pellet condition as the fixed-ratio value was increased in all but 1 baboon. This indicates that even when using unit-price conversions, there was variability in total intake. Although unit-price conversions yielded intake data that were more consistent across conditions, conditions differed in response topography even at the same unit prices: Under the multiple-pellet conditions there were longer pauses in responding, running response rate was slower, and the first eating bout (i.e., “meal”) of the session was smaller than under the one-pellet condition. These findings (a) support the heuristic value of a unit-price analysis for studying responding for and consumption of commodities that have similar attributes, and (b) indicate that different response topographies may result in similar intakes of a commodity.     

Autoshaping as a function of prior food presentations

Young chickens were given 1, 10, 100, or 1000 presentations of grain in a hopper. Subsequently, the key was illuminated before each presentation of grain to study autoshaping of the key-peck response. The number of keylight-grain pairings before a bird first pecked the lighted key was found to be a U-shaped function of the number of prior food-only presentations, with pecks occurring significantly sooner after 100 food-only trials than after any of the other values. Two of five chicks at the 100-trial value pecked on the first illumination of the key. Experiment II showed further that when a series of food-only trials (no keylight) preceded keylight-only trials (no food) 30% of the chicks pecked the illuminated key. Experiment III extended the generality of first-trial pecking to pigeons. After preliminary training with food-only, two of five pigeons pecked on the first illumination of a key. The results suggest a close relationship between autoshaping and pseudo-conditioning.     

On the effects of food deprivation and component reinforcer rates on multiple-schedule performance

Six pigeons were used to investigate the effects of varying body weight and component reinforcer rates in two-component multiple variable-interval variable-interval schedules. In Parts 1 and 3 of the experiment, unequal component reinforcer rates were arranged, and body weights were respectively increased and decreased. At 80% ad lib weight, response-rate ratios were closer to unity than reinforcer-rate ratios, but at 100% or more of ad lib weight, response-rate ratios generally equaled reinforcer-rate ratios. In Part 2, component reinforcer-rate ratios were varied over five conditions with the subjects maintained at 100% or more of their ad lib weights, and response-rate ratios matched reinforcer-rate ratios. The data thus support the empirical finding that response allocation in multiple schedules is a function of deprivation. Although this qualitative result is predicted by three models of multiple-schedule performance, only a model that assumes no direct component interaction adequately describes the data.     

Schedules of food postponement: II. Maintenance of behavior by food postponement and effects of the schedule parameter

In Experiment I, food-deprived, feeder-trained squirrel monkeys pressed a lever to postpone brief electric shocks (Response-Shock=Shock-Shock interval=30 seconds). Forty-one three-hour sessions of shock postponement were followed by 120 sessions of concurrent shock and food postponement. The shock schedule was unchanged and the food schedule was Response-food interval–20 seconds, Food-food interval 10 seconds. After concurrent shock and food postponement, the shock schedule was discontinued and 40 sessions of food postponement ensued, followed by 53 sessions of extinction. After extinction, food postponement was resumed for 11 sessions. Stable responding with low food rates was maintained under food-postponement after the concurrent schedule. Responding decreased to low levels under extinction and recovered immediately to previous levels when the food-postponement schedule was re-instated. In Experiment II, a parameter of the food-postponement schedule was studied sequentially. Using the same subjects, the Response-food–Food-food interval was manipulated from four seconds to 80 seconds with several orders of presentation. Relations of response rates and food rates to the parameter were similar to those seen under shock postponement. Exposure to very short postponement times (four seconds), resulting in very high food rates, decreased but did not abolish subsequent responding at longer postponement times. Results are discussed from the point of view that reinforcing functions of stimuli consequent on responding depend on a prior history of scheduled contact with those stimuli.     

COMBINING STIMULUS FADING,REINFORCEMENT, AND EXTINCTION TO TREAT FOOD REFUSAL

The food refusal of a 6-year-old girl with destructive behavior was treated using stimulus fading, reinforcement, and escape extinction. Intake increased and compliance with prompting procedures remained relatively stable despite the increased consumption requirement.     

A COMPARISON OF SIMULTANEOUS AND DELAYED REINFORCEMENT AS TREATMENTS FOR FOOD SELECTIVITY

This study compared the relative efficacy of providing simultaneous or delayed reinforcement on food acceptance during meals. The participant was a 7-year-old boy with pervasive developmental disorder and a history of food selectivity. Results indicated that both procedures were effective in increasing acceptance; however, the simultaneous reinforcement procedure produced more rapid behavior change and a higher overall percentage of food acceptance.     

THE EFFECTS OF MEAL SCHEDULE AND QUANTITY ON PROBLEMATIC BEHAVIOR

We present 2 case examples that illustrate the effects of meal schedule and quantity on displays of problematic behavior. In the first example, self-injury displayed by a toddler with severe developmental delays was maintained by parent attention, but only when he was satiated for food. When he was food deprived, self-injury decreased but did not appear to be differentiated across low or high social conditions. In the second example, crying and self-injury displayed by an elementary-aged girl with severe disabilities were correlated: Both behaviors were associated with food quantity, and neither behavior was responsive to social stimuli. These results replicate and extend previous findings demonstrating that meal schedule or food quantity can affect problematic behavior. In the present studies, brief functional analyses of aberrant behavior provided useful information for interpreting distinct patterns of behavior displayed by each child. We discuss these results in terms of the concept of establishing operations.