Adjusting fixed-ratio schedules in the squirrel monkey

On an adjusting schedule of reinforcement, a parameter of the schedule is varied as a function of some characteristic of the animal's performance. In Experiment I, the fixed-ratio response requirement was varied as a function of the time that elapsed before the animal started responding in each fixed-ratio (initial pause). When initial pauses were shorter than a specified duration, the response requirement was increased; when they were longer than the specified duration, the response requirement was decreased. Specified durations of 1, 2, 4, 8, and 15 min were studied. The average response requirement maintained by each monkey was directly related to the length of the specified duration of initial pause. In Experiment II, the fixed-ratio response requirement was constant, but reinforcement occurred only when the initial pause was longer than a specified duration. The average durations of initial pauses were directly related to the length of the specified duration and to the response requirement. Meprobamate consistently decreased the average durations of initial pauses.     

Concurrent fixed-ratio and avoidance responding in the squirrel monkey

Squirrel monkeys maintained concurrent performances appropriate to a fixed-ratio schedule of food reinforcement on one lever and an avoidance schedule on a second lever. The overall rate of responding maintained by either schedule was not systematically affected when the other schedule was discontinued and its lever removed.     

Electric shock produced drinking in the squirrel monkey.

Squirrel monkeys were periodically exposed to brief electric tail shocks in a test environment containing a rubber hose, response lever, and a water spout. Shock delivery produced preshock lever pressing and postshock hose biting. Additionally, all subjects displayed licking responses following postshock biting-attack episodes. Further experiments showed that licking was: (1) influenced by hours of water deprivation; (2) drinking behavior; (3) the direct result of shock delivery; and (4) developed spontaneously in naive subjects with or without opportunities for hose biting or lever pressing. Removing the opportunity to attack increased postshock drinking. A noxious environmental stimulus that causes aggression can also produce drinking.     

Effects of d-amphetamine on observing behavior in the squirrel monkey

Four squirrel monkeys were trained to press a lever, which produced stimuli indicating availability or non-availability of reinforcement for pushing a key. Food reinforcements were available for the key response at random intervals with an average rate of 1 per min. When food was available, a single lever response produced a red light behind the key. Reinforcement availabilities and red keylights remained until terminated by a reinforced key response. When reinforcement was not available, each lever response produced a 0.5-sec green light on the key. Except after lever responses, the key remained dark. Under this procedure, lever responses functioned as observing behavior in that they produced discriminative stimuli correlated with the availability or non-availability of reinforcement for key responses. The procedure generated a high rate of responding on the lever, short latencies of the key response after onset of red lights and few responses to the key in the absence of red lights. Intra-muscular d-amphetamine, in doses from 0.125 to 1.0 mg/kg, abolished both observing behavior and key responding for periods that increased as a function of dose. However, both observing and key rates were increased at the smallest dose in two subjects whose performances included responding to the key in the absence of red lights. Results are discussed in relation to previous findings regarding effects of amphetamines on operant behavior and on observing and monitoring performance.     

Responding in the squirrel monkey under fixed-ratio schedules of stimulus termination

Key pressing was maintained under a fixed-ratio schedule in which electric shock was scheduled for delivery at a fixed time (t seconds) after each stimulus onset, and every n^th response terminated the stimulus and initiated a timeout from shock. Under this procedure, the higher the rate of responding, the briefer the duration of the stimulus presentation and the lower the frequency of shock delivery. The effects of several schedule parameters were studied to determine whether the maintenance of responding was dependent on an inverse relation between response rate and shock frequency. Shock rate and shock frequency were made independent of response rate by decreasing the value of t to 0.5 second and delivering shock only during the first presentation of the stimulus after a fixed time, including stimulus and timeout durations, had elapsed since the previous shock. The experiments showed that shock frequency and response rate are inversely related when t is of relatively long duration compared to the value of the fixed-ratio parameter, but that a decrease in shock rate or frequency due to a high rate of responding is not necessary for the maintenance of responding under a fixed-ratio schedule of stimulus termination.     

Responding in the squirrel monkey under second-order schedules of shock delivery

Lever-pressing responses were maintained in the squirrel monkey when the only consequence of responding was the delivery of a response-produced electric shock, or alternatively, a brief visual stimulus that was occasionally followed by an electric shock. When shock was produced by the first response occurring after 8 min (8-min fixed-interval schedule), a period of no responding at the beginning of the interval was followed by a gradual increase in response rate during the interval. Similar rates and patterns of responding were maintained when a 1-sec visual stimulus was produced by the first response occurring after 8 min and shock delivery followed the brief stimulus. Subsequently, patterns of positively accelerated responding were engendered during individual fixed-interval components when the first response occurring after 4 min produced a 1-sec visual stimulus and shock delivery followed the second, and later the fourth, presentation of the 1-sec stimulus. When the duration of the brief stimulus was varied over a 100-fold range from 0.1 to 10.0 sec (1) mean response rates decreased monotonically as stimulus duration increased, and (2) patterns of positively accelerated responding were least variable and response rates during the initial part of each 4-min interval were lowest at a stimulus duration of 1 sec.     

On the use of the squirrel monkey in behavorial and pharmacological experiments

We have found the squirrel monkey to be a useful experimental subject for behavioral and pharmacological experiments. This note presents techniques used for housing, feeding, handling, and administering drugs to these small primates.     

The learning of hand preferences by squirrel monkey

Summary In a reaching task with Squirrel Monkeys stable hand preferences were established by reward training. The use of a particular hand was brought under the control of a colour cue.     

Maternal separation alters later consumption of novel liquids in the squirrel monkey

The consumption of novel, fruit-flavored drinks was measured in juvenile squirrel monkeys that had either had their mother removed from the home cage for 2 h on 80 occasions prior to weaning or had not undergone this separation procedure. Among previously separated animals, males drank more than did females during the first 30 min following presentation, whereas there was no difference in the drinking of nonseparated males and females at this time. Further, the amount of liquid consumed during the 20 h following presentation increased across days of exposure in the nonseparated, but not in the previously separated monkeys. These results show that brief maternal separation can affect the later behavior of squirrel monkeys, and are consistent with findings in rhesus macaques that maternal separation alters later exploratory behavior.