Nabil F. Haddad

Risk-sensitive foraging in rats: the effects of response-effort and reward-amount manipulations on choice behavior.

The literature on risk-sensitive foraging theory provides several accounts of species that fluctuate between risk-averse and risk-prone strategies. The daily energy budget rule suggests that shifts in foraging strategy are precipitated by changes in the foragers energy budget. Researchers have attempted to alter the organisms energy budget using a variety of techniques such as food deprivation, manipulation of ambient temperatures, and delays to food reward; however, response-effort manipulations have been relatively neglected. A choice preparation using a wheel-running response and rats examined risk-sensitive preferences when both response effort and reward amounts were manipulated. Concurrently available reinforcement schedules (FI/60 and VI/60) yielded equivalent food amounts per unit time in all treatments. Two levels of response effort (20 or 120 g tangential resistance) and two levels of reward amount (three or nine pellets) were combined to form four distinct response-effort/reward-amount pairings. Increasing reward amounts significantly shifted choice toward the FI schedule in both response-effort conditions. The incidence of choice preference and the magnitude of shifts in choice were greater for the high response-effort conditions than for the low response-effort conditions. Implications of the significant interaction between response effort and reward amount are discussed in terms of a general energy-budget model.

Wheel-running in discrete trial and operant paradigms under various effort requirements

Two experiments were conducted in which the wheel-running behavior of rats under various effort requirements was investigated. The specific effort requirements were obtained by varying the tangential force required to initiate wheel movement. In the first experiment, a discrete trial preparation was used in which 4 groups of rats received training with high effort levels of 90, 110, 130, and 150 g. The results showed that increasing effort requirements slowed the rate of acquisition, lowered the asymptotic running speeds, and reduced resistance to extinction. In the second experiment, using an operant preparation, running speeds were examined for baseline (nonreinforced) and fixed-interval 1 min schedules of reinforcement at effort levels of 45, 90, and 180 g. The results clearly showed wheel-running to be schedule-induced. However, the effects of effort on FI behavior were less clear due to inconsistencies between subjects. Results are discussed in terms of the potential benefits of bridging operant and discrete trial preparations and methods for studying the effects of effort on animal behavior.

A simple and sensitive method for monitoring running-wheel movement

A running-wheel movement-detection method is described for use with a modified 1350 Commodore mouse and a Commodore 64, is described. The movement-detection method allows for the detection of partial revolutions and direction of movement, but requires no interface equipment. The modified running wheel is discussed as a new technique that may be useful for bridging empirical and theoretical differences between free-operant and discrete-trial runway procedures.

Stimulus control in a simple instrumental task: The role of internal and external stimuli

Abstract Two experiments using rats in a straight alley runway task tested the hypothesis that standard stimuli such as tones and lights (“external” stimuli) and schedule-generated aftereffect stimuli (“internal” stimuli) operate similarly and are similarly subject to the compounding rules specified by R. A. Rescorla and A. R. Wagner (In A. Black & W. Prokasy (Eds.), Classical conditioning II: Current theory and research . New York: Appleton-Century-Crofts, 1972) . The experimental task was an instrumental analog of the classic blocking experiment (L. J. Kamin, In M. R. Jones (Ed.), Miami symposium on the prediction of behavior: Aversive stimulation . Miami: Univ. of Miami Press, 1968) . In Experiment 1, blocking of an external discriminative stimulus by a different asymptotic discrimination was accomplished. In Experiment 2, blocking of an internal stimulus discrimination by an asymptotic external stimulus discrimination was obtained. The present results support the view that internal and external stimuli are indeed similar and function in the same manner with regard to blocking of stimulus control.

Increased effort requirements and risk sensitivity: a comparison of delay and magnitude manipulations

Reward magnitude and delay to reward were independently manipulated in two separate experiments examining risk-sensitive choice in rats. A dual-running wheel apparatus was used and the tangential force resistance required to displace both wheels was low (50g) for half of the subjects, and high (120g) for the remaining subjects. Concurrent FI30-s and FI60-s schedules delivered equivalent amounts of food reward per unit time (i.e. 5 and 10 pellets of food, respectively), and these conditions served as the baseline treatment for all subjects. Variability, either in reward magnitude or delay, was introduced on the long-delay (60s) schedule during the second phase. All subjects were returned to the baseline condition in the third phase, and variability was introduced on the short-delay (30s) interval schedule during phase four. The subjects were again returned to the baseline condition in the fifth and final phase, ultimately yielding a five-phase ABACA design. Original baseline performance was characterized by a slight short-delay interval preference, and this pattern of performance was recovered with each subsequent presentation of the baseline condition. Overall, the data obtained from the reward magnitude and delay-to-reward manipulations were indistinguishable; subjects experiencing low-response effort requirement behaved in a risk-indifferent manner and subjects experiencing high-response effort requirement preferred the variable schedule. Implications for the daily energy budget rule on risk-sensitive foraging are discussed in light of these findings.

The Rescorla-Wagner Theory of Conditioning: A Review of the Literature

A comprehensive literature review of the published articles which have tested, evaluated, or modified the conditioning theory specified by Rescorla and Wagner (1972) is presented. Following a description and presentation of the formal properties of the model, five basic classes of studies are reviewed. The classes are comprised of reviews of studies which have (a) tested the model’s basic assumptions, (b) manipulated the salience of conditioned stimuli, (c) manipulated the potency of unconditioned stimuli, (d) investigated background stimuli or commom»elements between stimuli, and (e) introduced refinements or modifications of the original model. Finally, a brief discussion of the theory’s impact and future is presented.

Monitoring running-wheel movement using a serial mouse and an IBM-compatible system

A running-wheel-movement-detection system is described for use with an IBM-compatible system and a serial mouse. It is an adaptation of a system developed for use on a Commodore 64. The IBM-compatible system provides obvious advantages in speed, memory, data storage, and programming ease over the earlier Commodore 64 system.

Blocking Effects in Two-Choice Discrimination Tasks in Rhesus Monkeys Macaca Mulatta

The present experiments investigated blocking effects in rhesus monkeys (Macaca mulatta) in a discrimination learning paradigm using a single stimulus modality. Two experimental chambers were used. In one the monkeys were required to operate a joystick in order to manipulate a Pacman figure to consume one of two stimuli (S+ and S-) appearing on a video screen. In the other the monkeys were required to press Plexiglas panels mounted in front of the screens to indicate their choice of the stimuli. Correct responses resulted in the delivery of marshmallows. Results indicated (a) consistent occurrence of blocking, (b) no unblocking due to increased magnitude of reward, and (c) no differences due to task requirements in the two different chambers. These studies extend our knowledge of blocking effects to monkeys and provide novel procedures for using monkeys in basic learning research.

Specific and nonspecific transfer: Effects of nonreward, delay of reward, and punishment sequences on persistence

Two experiments were conducted to test the effects of training with different aversive events on rats’ subsequent persistence of responding. In Experiment 1, it was found that training with the same aversive event (nonreward) as that encountered during extinction (specific transfer) resulted in higher resistance to extinction than did training with different combinations of non-reward, punishment, and delay (nonspecific transfer). Experiment 2 indicated that these effects are controlled primarily by sequential variables and that persistence effects generated by the same or different aversive events as those encountered during extinction summate. A theoretical framework emphasizing the role of generalization decrement and sequential variables was invoked to account for these results.

N-length shifts and successive contrast effects

The present experiment was designed to investigate the effects of successive shifts in N-length in a simple instrumental task. A recent theory (Capaldi, Note 1) predicts positive contrast effects due to a shift from a longer to a shorter N-length and negative contrast resulting from the opposite shift. Two groups of rats were given seven trials per day, four of which were rewarded, in a straight alley. One group was trained using an N-length of three, and the other using an N-length of one. After 20 days, one-half of each group was shifted to the opposite N-length for an additional 20 days, while the remainder of the animals continued as in the first phase for this period. Finally, all four groups received 5 days of extinction. There was no evidence for either positive or negative contrast. In addition, there were no group differences during the extinction phase. The data did not support the predictions generated by the rein-forcement level theory.