The integration of habits maintained by food and water reinforcement through stimulus compounding.

In Experiment 1, a light and a tone were correlated independently with water reinforcement of bar pressing by rats. With different naive subjects in Experiment 2, one of these stimuli was correlated with food and the other with water reinforcement (counterbalanced). In both experiments the absence of tone and light signaled extinction. Tests of stimulus-reinforcer independence in Experiment 2 indicated that tone and light controlled behavior whose rate was specifically affected by deprivation state. In the stimulus-compounding tests of both experiments, response rates were higher to tone-plus-light than to tone or light presented alone (additive summation). This is the first report of additive summation produced through compounding stimuli paired with different reinforcers. The results are discussed in the context of the effects of incentive motivation on operant performance.     

The effects of delay on neonatal retention of habituated head-turning

Recovery of neonatal head orientation following auditory habituation was used to examine the effects of intertrial delay. One of two words served as stimuli with criterion orienting and habituation established before the delay. Fifty-six full-term neonates were assigned randomly to one of four delay groups: 10 (control), 55, 100, or 145 s. The percentage of head-turns toward the sound source (with one turn per trial) for blocks of three trials served as the principal dependent variable. Recovery of localized head-turning increased as length of delay increased, with the 100- and 145-s groups showing greater recovery than the 10- and 55-s groups. Infants presented with control trials systematically turned away from the sound source following habituation. Selective sensory adaptation, spontaneous recovery, and short-term memory interpretations of these data are considered.     

Anatomically based measurement of facial expressions in simulated versus hypnotically induced affect

In an attempt to determine whether hypnotically induced affect could be reliably discriminated from simulations, three hypnotically trained female undergraduate subjects were presented with posthypnotic cues to either experience or simulate varying degrees of anxiety and pleasure. Facial expressions generated by subjects in response to these cues were recorded on videotape and coded by means of the Facial Action Coding System (FACS). It was hypothesized that simulated emotional expressions, requiring greater cortical processing, would be marked by longer onset latencies and greater irregularity or fluctuation in muscular contraction than the presumably automatic changes in facial behavior accompanying posthypnotic emotions. Statistical analyses confirmed both expectations. The results were viewed as reflecting support for the validity of posthypnotically cued affect.     

Internal stimuli enhance feeding behavior in the mollusc Aplysia

The hypothesis that subsatiating levels of internal food stimuli can arouse and potentiate feeding behavior was examined in the mollusc Aplysia californica. Animals were fed a small quantity of seaweed and their latencies to show biting responses were determined after food arousal was permitted to partially decay. Control animals were stimulated with food, but were not permitted to ingest it, or were fed nonnutritive glass-fiber filter paper. Compared to controls, animals that were fed showed significantly shorter latencies to respond when tested up to 80 min after previous exposure to food. These results indicate that internal stimuli can function like external stimuli to enhance responsiveness to food and suggest the hypothesis that satiation may be viewed as an interactive process involving the interplay of excitatory and inhibitory influences arising from the alimentary system.     

Compounding discriminative stimuli controlling free-operant avoidance

The performances of three rats were stabilized on a multiple schedule that maintained responding by a free-operant avoidance schedule during independent presentations of tone and light. The simultaneous absence of these stimuli signalled shock-free periods and controlled response cessation. Subsequently, test sessions were administered consisting of independent presentations of each stimulus and these stimuli compounded (tone-plus-light). During an extinction test, additive summation was observed to the compounded stimuli, i.e., more responses were emitted to the compound than to either tone or light. During a series of 28 maintenance-test sessions in which the shock schedule remained operative, the compounded stimuli produced a generally enhanced response rate and fewer pauses terminating with shock than either single stimulus condition. These results extend the generality of free-operant additive summation to responding maintained by aversive control. In addition, a comparison of the present study with previous experiments reporting additive summation of positively reinforced responding indicates that similar variables—rate and aversive differences between training stimulus conditions—should be considered in accounting for response distributions during stimulus compounding when responding is controlled by either positive or negative contingencies.     

Concurrent schedules of reinforcement: effects of gradual and abrupt increases in changeover delay

Pigeons' pecks were maintained on concurrent variable-interval 1-min variable-interval 3-min schedules of reinforcement, with a changeover delay of 2 sec. When changeover delay was increased successively to 5.0, 7.5, and 12.5 sec (Exp. I) the actual relative rate of reinforcement for the variable-interval 3-min key decreased progressively for two birds, abruptly for two other birds, and the subjects devoted proportionately less of their time and responding to that key. However, the relative performance measures (relative time and relative responding) approximated the actual relative rate of reinforcement, with a maximum discrepancy of 11%, over all changeover delay values investigated. Experiment II attempted to lengthen response-run durations on the variable-interval 3-min key so that they were long enough to meet the changeover delay requirement at each new changeover delay value, by progressively increasing the changeover delay by 0.5-sec increments. With this procedure the actual relative rate of reinforcement approximated more closely the scheduled relative rate as changeover delay increased. As in Exp. I, relative performance measures approximated the actual relative reinforcement rate (maximum discrepancy 17%).