Effect of behavioral history on subsequent responding: experiments using rotary fixed-ratio schedules

The present study proposes a novel experimental approach to examine the effect of previous schedule history on subsequent responses. College students used a three-button device to indicate their choice of response. We performed two experiments. Each experiment consisted of three phases. In experiment I, fixed-ratio 10 (FR 10) reinforcement schedule was employed in phases 1 and 3. Phase 2 employed "Rotary-FR 10" schedule: after obtaining a point produced by pressing one of three specified buttons in a triangular array 10 times, the effective button changed to another in a clockwise direction. Optimal response pattern for Rotary-FR 10 was analyzed. Two types of behavior, referred to as "consecutive" and "scatter" were observed in phase 1. The mean number of optimal responses in consecutive type was significantly higher than scatter type in phases 2 and 3. In experiment II, two schedules were used in phase 1, and the same protocol used in experiment I was followed. We found that the reinforcement schedule used in phase 1 affected acquisition of the optimal response in phase 2. These results suggest that the earlier behavioral tendencies play an important role in determining subsequent behavior and that such behavioral tendency can be modified by specifically designed protocols.     

Nicotine-evoked conditioned responding is dependent on concentration of sucrose unconditioned stimulus

Previous studies have shown that the interoceptive nicotine conditional stimulus (CS) functions similarly to exteroceptive CSs such as lights or environments. For instance, the appetitive conditioned response (CR) evoked when nicotine is repeatedly paired with sucrose presentations (the unconditioned stimulus; US) is sensitive to changes in training dose (CS salience) and the contiguity between the CS effects and sucrose. The current study was conducted to extend this research by examining the possible role of US intensity in CR acquisition and maintenance. Rats were trained using one of four sucrose concentrations: 0, 4, 16, or 32% (w/v). On nicotine sessions (0.4 mg base/kg), rats received 36 deliveries (4 s each) of their assigned concentration intermittently throughout the session; sucrose was withheld on saline sessions. In all groups, an appetitive goal-tracking CR was acquired at a similar rate. However, the asymptotic CR level varied with sucrose concentration. The magnitude of the CR was increased in rats trained with higher sucrose US concentrations. These findings are consistent with previous Pavlovian conditioning research, and extend the conditions under which the nicotine state functions as an interoceptive conditional stimulus.     

Selective stimulus control in discrimination of lateral mirror images by pigeons

Four monocularly and two binocularly viewing pigeons were trained to peck a key when it displayed one stimulus (S+) but not to peck when it displayed another stimulus (S−). S+ and S− were a lateral mirror-image pair of two-coloured stimuli. When tested for transfer with the untrained eye open, two of the monocular birds pecked more during S− than S+, the other two continuing to favour S+. During generalization tests on the wavelength dimension all monocular birds pecked much more often during one S+ colour than during the other. The colour controlling pecking was that displayed on the side of the key facing the open eye during S+ presentations. Both binocular birds developed asymmetrical responses to the key, one favouring the left, the other the right side of the key. Generalization tests on the wavelength dimension showed selective control by the colour displayed on the favoured side of the key during S+ presentations. The results are interpreted as supporting the view that pigeons learn to discriminate lateral mirror images by developing asymmetrical observing responses that convert the left-right difference between the mirror images into a difference more easily discriminable.     

Simple and multiple schedule responding and behavioral contrast when pigeons press treadles

Positive behavioral contrast has been observed when pigeons press treadles on multiple schedules for high rates of reinforcement, but not for low rates. Negative treadle-press contrast has been observed for low rates of reinforcement. Two experiments showed that differences between response rates emitted during simple and multiple schedules appear and fail to appear under similar conditions. The experiments showed that the rate of pressing during the less favorable component of a multiple schedule was less than the rate of pressing during a comparable simple schedule (negative contrast). The rate of treadle–pressing during the more favorable component was not greater than the rate of pressing during a comparable simple schedule, when the schedules provided a low rate of reinforcement (absence of positive contrast), but it was when the schedules provided a high rate of reinforcement (positive contrast). These results help to clarify the definition of behavioral contrast by showing that simple schedules may be appropriate baselines from which to define and measure contrast.     

Modeling and simulation of deformation of hydrogels responding to electric stimulus

A model for simulation of pH-sensitive hydrogels is refined in this paper to extend its application to electric-sensitive hydrogels, termed the refined multi-effect-coupling electric-stimulus (rMECe) model. By reformulation of the fixed-charge density and consideration of finite deformation, the rMECe model is able to predict the responsive deformations of the hydrogels when they are immersed in a bath solution subject to externally applied electric field. The rMECe model consists of nonlinear partial differential governing equations with chemo-electro-mechanical coupling effects and the fixed-charge density with electric-field effect. By comparison between simulation and experiment extracted from literature, the model is verified to be accurate and stable. The rMECe model performs quantitatively for deformation analysis of the electric-sensitive hydrogels. The influences of several physical parameters, including the externally applied electric voltage, initial fixed-charge density, hydrogel strip thickness, ionic strength and valence of surrounding solution, are discussed in detail on the displacement and average curvature of the hydrogels.     

Startle responding and context conditioning. Naloxone pretreatment and stimulus intensity

The possibility that acoustic startle stimuli could support a conditional response (freezing) to contextual stimuli was investigated. Rats were exposed to three acoustic startle stimuli on the first day, and one on the second day. On day 1, 20 rats received naloxone pretreatment and another 20 received saline (placebo) pretreatment. Half of each group received a high-intensity acoustic stimulus, the other half a low-intensity acoustic stimulus. Both the higher stimulus intensity and the naloxone pretreatment led to greater freezing behavior during the 3-minute test period before the single startle stimulus on day 2. These findings support the notion that increased actual or perceived intensity of the acoustic startle stimulus increases conditioning to contextual stimuli as indexed by freezing behavior.     

Overshadowing of responding on ratio and interval schedules by an independent predictor of reinforcement

This experiment replicated previous demonstrations that interposing a brief stimulus between reinforced responses and the presentation of the reinforcer reduces responding maintained by intermittent reinforcement schedules. Furthermore, we could find no significant difference between the relative size of the reduction during training on ratio and interval schedules when the predictive significance of the response and stimulus was controlled by a yoking procedure.     

Homing behaviour of pigeons disturbed by application of an olfactory stimulus

Summary Experiments designed to test the olfactory hypothesis of pigeon navigation by application of odorous substances to the birds' beaks and nostrils had shown until now variable results which have been interpreted differently. Using a new procedure, we were able to obtain consistent results. In each of the ten experiments performed, pigeons treated with -pinene were randomly oriented whereas control birds were not. Increase of homing time in experimental birds was also confirmed.This work was supported by a grant from the Consiglio Nazionale delle Ricerche.     

Bombesin effects on responding maintained by a fixed interval schedule of food reinforcement

The present experiment examined rats' responding maintained by a fixed interval two-min schedule of food reinforcement following IP injections of bombesin (4, 6, 16, 32 μg/kg). The results showed that bombesin's effects were rate dependent where the responses per minute emitted during the early portion of the fixed interval were reduced, but responding during the latter portion was unaffected. Bombesin did not reduce overall session responses per minute, pause after reinforcement, or amount of water consumed in the test chamber. The results are in accord with prior research examining the effects of bombesin and cholecystokinin on operant behavior. Together, the data challenge the notion that bombesin affects food-motivated behavior generally; rather, the results indicate that bombesin's effect may interact with the demands required of the animal for reinforcement.     

Baseline training history and effects of methamphetamine on performance of pigeons on an interval-bisection task

Length of baseline training influences how methamphetamine disrupts temporal performance under a peak interval schedule. Acute methamphetamine produces overestimation of time following relatively brief training, but following extended training, methamphetamine produces more general loss of stimulus control. The current study extends the study of training length on the effects of methamphetamine to an interval-bisection procedure. Six pigeons responded under a psychophysical choice procedure in which responses to one key color were correct after presentation of four shorter sample durations and responses to another key color were correct after presentation of four longer sample durations. One group of three pigeons received briefer baseline training (45 sessions), while another group received more extended training (223 sessions) prior to methamphetamine administration. There was no evidence of overestimation of time or generalized loss of stimulus control in either group. Sensitivity (precision of timing) was higher in the group with more extensive training and was disrupted by methamphetamine.     

Homing behavior of pigeons not disturbed by application of an olfactory stimulus

Summary In a second attempt to repeat recently published experiments that appear to support an hypothesis that olfactory cues play an important role in pigeon navigation, we have conducted 15 experiments in which-pinene in vaseline was applied to the birds' beak and nostrils prior to release, a procedure reported by Benvenutiet al. (1973) to cause a decrement in homing performance. Our results show no consistent difference between the experimental and control birds in any of the three parameters (initial orientation, rapidity of orientation, homing speed) measured by Benvenutiet al. We thank our colleagues Timothy Larkin, Marilyn Yodlowski, and Lindsay Goodloe for their help in conducting the releases. This research was supported by Grant BMS 72-02198-AO2 from the National Science Foundation.     

Effect of between-category similarity on basic level superiority in pigeons

Children categorize stimuli at the basic level faster than at the superordinate level. We hypothesized that between-category similarity may affect this basic level superiority effect. Dissimilar categories may be easy to distinguish at the basic level but be difficult to group at the superordinate level, whereas similar categories may be easy to group at the superordinate level but be difficult to distinguish at the basic level. Consequently, similar basic level categories may produce a superordinate-before-basic learning trend, whereas dissimilar basic level categories may result in a basic-before-superordinate learning trend. We tested this hypothesis in pigeons by constructing superordinate level categories out of basic level categories with known similarity. In Experiment 1, we experimentally evaluated the between-category similarity of four basic level photographic categories using multiple fixed interval-extinction training (Astley and Wasserman, 1992). We used the resultant similarity matrices in Experiment 2 to construct two superordinate level categories from basic level categories with high between-category similarity (cars and persons; chairs and flowers). We then trained pigeons to concurrently classify those photographs into either the proper basic level category or the proper superordinate level category. Under these conditions, the pigeons learned the superordinate level discrimination faster than the basic level discrimination, confirming our hypothesis that basic level superiority is affected by between-category similarity.