The relationship between locus of odor cues and double-alternation responding in the rat

In two experiments, rats traversed a runway in the presence of odor cues from odor-donor rats (stimulus odor). These odors were established in the start and run sections of a runway. As in previous work, these odors were shown to be influential determinants of behavior There is an indication that odors of reward and nonreward may be different for different rats, and that these different odors can be used to form complex discriminations.     

Approach and escape to conspecific odors of reward and nonreward in rats

A three-compartment box was used, and a reward odor, or nonreward (extinction) odor, produced by another rat, was present in the middle compartment. Two control odor procedures were also used. The results showed that rats will approach a location in which another rat has previously been given reward more rapidly than they will escape from that location, but showed the opposite effect when the odor was produced by a rat undergoing extinction. The mere presence of an odor associated with another rat had the effect of producing much slower locomotion as compared to a no-odor control condition.     

The learned function of food-deprivation cues: A role for conditioned modulation

Rats trained in one context to use stimuli arising from food deprivation as discriminative signals for shock were tested in other contexts to assess the basis of conditioned responding (i.e., freezing or behavioral immobility). In Experiment 1, discriminative control by 24-h food-deprivation cues failed to promote transfer responding in a test context that had no association with shock. This indicated that food deprivation cues had little direct excitatory power. However, transfer of behavioral control by 24-h food-deprivation cues was obtained in a context paired with shock only when the rats were 19 h water deprived. This finding agrees with the idea that food-deprivation cues become conditioned modulators of the capacity of external stimuli to activate their association with an unconditioned stimulus. In Experiment 2, rats trained to use 24-h food-deprivation cues as signals for shock exhibited significantly greater transfer performance when the transfer context had undergone partial extinction relative to when the transfer context had undergone only simple excitatory training. This finding with deprivation cues and transfer contexts (1) paralleled earlier results obtained with discrete (auditory and visual) conditioned modulators and transfer targets, and (2) posed difficulties for associative summation and generalization interpretations of transfer performance.     

Odors of individuality originating from the major histocompatibility complex are masked by diet cues in the urine of rats

Male Long-Evans rats were trained to discriminate between the urine odors of two congenic strains of rats (PVG and PVG.R1) in an olfactometer on a go/no-go operant task with water reinforcement. These odor donors differ genetically at only one locus of the major histocompatibility complex (MHC). The ability of the subjects to transfer their training to discriminate between novel individuals of the same MHC strain on the same and different diets was then examined. The subjects correctly generalized their original training to new samples from previously undiscriminated individuals of the same MHC type on the same diet without a significant drop in performance. A change in diet disrupted the perception of the MHC-related odor. In a second experiment, rats were trained to discriminate between the odors of pairs of genetically identical PVG or PVG.R1 rats on different diets and were tested for generalization using the odors of rats of the other strain (PVG.R1 or PVG) maintained on the same diet. Changing the strain of the odor donor did not disrupt the learned discrimination. The results of these two experiments confirm the ability of the MHC to generate constant cues in the urine but also reveal that variable diet cues disrupt the perception of these cues. The relationship between the MHC, diet, and other factors in determining individual odors is discussed.     

The influence of cue type and configuration upon radial-maze performance in the rat

The influence of cue type and cue configuration on radial-maze performance in rats was examined in two experiments. In the first experiment, it was found that rats provided with both salient intramaze and extramaze cues acquired the task faster than rats given only one set of cues. No difference in acquisition was found between a group trained with intramaze cues alone and a group trained with extramaze cues alone. In a cue-preference test, it was found that groups that had been trained with extramaze cues, intramaze cues, or both sets of cues relied on extra-maze cues to avoid visited arms when given both types of cues concurrently. When all groups were transferred to intramaze-cue-alone trials, only the group that had been originally trained with extramaze cues alone showed any disruption. Also, during the second half of the intramaze-cue-alone trials, the arrangement of these cues was randomly changed on each trial. This disruption in cue configuration did not deleteriously affect performance in any of the three groups; all remained above chance performance, although the performance of the group originally trained with extramaze cues alone was inferior to that of the other two groups. In Experiment 2, groups of rats were trained on daily alternating trials under intramaze-cue-alone and extramaze-cue-alone conditions. For one group, the configuration of intramaze cues was altered randomly on each trial; the other group had intramaze cues always presented in the same configuration over trials. It was found that acquisition was more rapid on intramaze trials in the group given static configurations. Also, acquisition of the extramaze task was faster than the intramaze task in the group given variable intramaze cue configurations. No difference was found between the intramaze and extramaze conditions in the group given static intramaze cue configurations. These data suggest that a static cue configuration may influence radial maze performance, but is not a necessary condition for such performance.     

Overshadowing of environmental cues by an odor in toxicosis-based conditioning in rats

It was demonstrated that an odor presented to rats in a distinctive environment can interfere with toxicosis-based conditioning to the environmental cues. Rats poisoned when they drank unflavored water in a black compartment odorized with oil of eucalyptus exhibited no suppression of water intake when they were subsequently tested in the same compartment minus the odor. In contrast, rats poisoned in the same compartment minus the odor later exhibited reduced water consumption in that environment. Oil of eucalyptus proved to be as effective an overshadowing stimulus as a taste cue (a 1.5% NaCl solution).     

Imitative learning in Japanese quail (<Emphasis Type="Italic">Coturnix japonica</Emphasis>) using the bidirectional control procedure

In the bidirectional control procedure, observers are exposed to a conspecific demonstrator responding to a manipulandum in one of two directions (e.g., left vs. right). This procedure controls for socially mediated effects (the mere presence of a conspecific) and stimulus enhancement (attention drawn to a manipulandum by its movement), and it has the added advantage of being symmetrical (the two different responses are similar in topography). Imitative learning is demonstrated when the observers make the response in the direction that they observed it being made. Recently, however, it has been suggested that when such evidence is found with a predominantly olfactory animal, such as the rat, it may result artifactually from odor cues left on one side of the manipulandum by the demonstrator. In the present experiment, we found that Japanese quail, for which odor cues are not likely to play a role, also showed significant correspondence between the direction in which the demonstrator and the observer push a screen to gain access to reward. Furthermore, control quail that observed the screen move, when the movement of the screen was not produced by the demonstrator, did not show similar correspondence between the direction of screen movement observed and that performed by the observer. Thus, with the appropriate control, the bidirectional procedure appears to be useful for studying imitation in avian species.     

Extending the generality of the odor hypothesis: Double-alternation responding in the wood rat (Neotoma floridana osagensis)

In an attempt to extend the generality of the odor hypothesis, two studies using wood rats (Neotoma floridana osagensis) as subjects were conducted. Experiment 1 demonstrated that this species was capable of establishing appropriate odor-based double-alternation patterning in the straight runway. The results of Experiment 2 indicated that albino rats were capable of using odor cues exuded by wood rats, and vice versa.     

Flavor aversions and deprivation state

In the first four experiments, it was found that aversions to saccharin solution produced by contingent poisoning were similar regardless of whether the rats had been trained under the test deprivation or under a different deprivation; the two deprivation states used were thirst and satiety. In Experiment 5, rats were poisoned after drinking grape juice while hungry or poisoned after drinking milk while thirsty, but they were not poisoned after grape-thirst or milk-hunger combinations. In abstract terms, poisoning occurred after AX and BY stimulus combinations, but did not occur after AY and BX combinations. There was some learning under these discrimination conditions.     

The sensory basis of spatial memory in the rat

Rats were given three stages of training on an eight-arm, elevated radial maze with food reward at the end of each arm. In Stage 1, rats were allowed to choose freely among the arms from the beginning of a trial. In Stage 2, three initial forced choices were followed by a series of free choices. In Stage 3, the central platform of the maze was rotated with the rat on it between the initial forced choices and the free choices. Following testing on these three stages, the animals were divided into four groups and deprived of selected senses. One group was made blind, a second anosmic, a third blind and anosmic, and a fourth was left normal. The same three stages of testing that had been conducted preoperatively then were run again post-operatively. Throughout these tests, the possible use of auditory cues was tested by presenting white noise on alternate trials. Finally, two further tests were carried out, the multiple rotations test and the removal-replacement test. The results indicated that visual cues, but not olfactory or auditory cues, played a critical role in the rat’s ability to avoid previously entered alleys. There was evidence also that rats used internal cues from kinesthetic and/or vestibular receptors when visual cues were absent.     

A reexamination of the effects of motivational state on utilization of conspecific odors in the rat

Two previous studies suggested that rats are unable to use conspecifics’ odors when the motivational state of the donor rats is different from their own (Davis et al., 1974; Davis, Prytula, Noble, & Mollenhour, 1976). The effects of motivational conditions on the utilization of such odors were further evaluated in the present study. In Phase 1, test rats were given training either with donors in the same motivational state or with donors in a different state. Differential responses to donors’ odor emissions occurred only when the motivational states of donors and test subjects were the same, thus confirming earlier findings. However, when test subjects’ motivational conditions were changed in Phase 2, discriminations that had been present in Phase 1 were maintained even though the motivational states of these test subjects and their respective donors no longer matched. Thus, any constraint on the rat’s ability to use odors from conspecifics in a different motivational state is not absolute.     

Sensitivity of instrumental responses to an upshift in water deprivation

The role of incentive learning in instrumental performance following an upshift in the degree of water deprivation was analyzed in three experiments. In Experiments 1A and 1B, rats trained to perform an instrumental action reinforced by either sucrose or maltodextrin solutions when in a low-deprivation state were shifted to a high-deprivation state and tested in extinction. This shift in water deprivation increased performance only if the animals had been exposed to the reinforcer in the high-deprivation state prior to testing. In Experiment 2, the role of the instrumental contingency in mediating the preexposure effect observed in the first two studies was examined by training rats to make two instrumental actions for different outcomes. The preexposure experience with the outcomes produced a relative increase in performance of the action reinforced with the incentive preexposed in the high-deprivation state when a choice between the two response alternatives was conducted in that state. These experiments support the conclusion that instrumental performance following revaluation of the reinforcer by an upshift in the level of thirst depends on a process of incentive learning.     

The role of experimenter-odor cues in the performance of object-memory tasks by rats

Two experiments assessed whether odors left on stimulus objects by experimenters who handle them might confound the interpretation of ostensibly visually guided object-memory tasks for rats. In Experiment 1, rats were able to discriminate the relative recency with which an experimenter touched two otherwise identical objects (intertouch interval = 4 sec), presumably on the basis of an odorintensity discrimination. However, after the rats mastered the odor discrimination with no delay between when the second of the two stimulus objects was last touched by the experimenter and when the rats were permitted to attempt the discrimination, their performance dropped to chance levels when this delay was increased to 15 sec. In Experiment 2, rats were trained in two slightly different ways to perform a delayed-nonmatching-to-sample (DNMS) task, one that involved systematic differences in the temporal order in which the experimenter handled the sample and novel stimulus objects and one that did not. There were no significant differences in the rate at which rats mastered the DNMS task with these two procedures, and the performance of rats that were trained according to the former procedure was unaffected when they were switched to the latter procedure. Moreover, rats required considerably fewer trials to master the DNMS task than the rats in Experiment 1 required to master the odor discrimination. These findings demonstrate that, under certain circumstances, rats can discriminate the relative recency with which two objects are handled by an experimenter, but that this ability contributes little to their performance of conventional object-based DNMS tasks.     

Cues for spontaneous alternation by gerbils

Twenty male Mongolian gerbils (Meriones unguiculatus) were tested for spontaneous alternation behavior in a T-maze under five cue conditions: (1) all cues present, (2) only S’s own odor trail, (3) only orientation cues, (4) no cues, (5) only another S’s odor trail. Significant alternation was found only in the first two conditions, indicating that odor trail is the only alternation cue for gerbils under testing conditions which also yield considerable orientation alternation in rats. There was also a tendency for gerbils to “alternate” the odor trail left by the noncagemate, but to follow that of a cagemate. A previous failure to find evidence of alternation in gerbils may have been due to a lack of opportunity for the animals to engage in trail-marking behavior.     

Effect of a conspecific’s presence on deprived rats’ Performance: Social facilitation vs distraction/imitation

The present study investigated effects of (a) conspecific’s “mere presence” and (b) water deprivation on emission of dominant responses by rats. Zajonc (1965) suggests that a conspecific’s presence functions like a physiologically based drive in enhancing performance of dominant responses. Alternative interpretations suggest that a conspecific’s presence impairs performance by distracting the observer or eliciting imitation of “irrelevant” responses. The social facilitation vs distraction/imitation hypotheses were tested in a 2 by 2 design: Barpress-trained rats, deprived of water for 4 or 23 h, barpressed for water in the presence of a naive rat or alone. Results supported social facilitation theory: Performance was significantly higher when the conspecific was present rather than absent and when the responder was 23 h rather than 4 h deprived. In reconciling these data with conflicting results, it was suggested that degree of contact may be important in determining how a conspecific’s presence affects performance of dominant responses.     

Attractiveness of lactating females' breast odors to neonates

A series of experiments investigated the responses of human infants to olfactory cues produced by lactating females. 2-week-old bottle-feeding girls oriented preferentially to the breast odor (odorized pad) of a nursing woman when paired with such odors from either a nonparturient female or axillary odors from the same lactating female. Responses to axillary odor from a lactating female did not differ from those to a clean (nonodorized) pad. These data indicate that breast odors from lactating females are especially attractive to female infants who are unfamiliar with the stimulus woman and who have had no prior breast-feeding experience.     

Incentive contrast produced by deprivation shifts

Deprivation shifts, using conditions analogous to those which produce strong incentive contrast when reward quantity is changed (extended preshift training, short interval from the last preshift trial to the first postshift trial, large preshift differences in deprivation) resulted in contrast of runway speed and choice behavior. In the first experiment, a downshift of hunger during rats’ runway training produced a slow lessening of speed below that of a group trained continually at low hunger. In the second experiment, rats were trained to traverse a runway to one food-containing goalbox when very hungry and to another, distinctively different food-containing goalbox when not very hungry. The rats were next given a series of choice trials between the two goalboxes. There was a brief preference for the high-hunger goalbox, followed by a preference for the low-hunger goalbox. The results of the second experiment suggest that deprivation affects the strength of conditioning of a cue-reinforcer expectancy, while the slow development of contrast in the first experiment indicates that deprivation also affects the development of either habit strength or a response-reinforcer expectancy.     

Incentive learning and the motivational control of instrumental performance by thirst

The role of incentive learning in instrumental performance following a shift in the degree of water deprivation was analyzed in three experiments. In Experiments 1A and IB, rats trained to perform an instrumental action reinforced with either sucrose or maltodextrin solutions when in a high-deprivation state were subsequently shifted to a low-deprivation state and tested in extinction. This within-state shift in water deprivation reduced instrumental performance only when the animals had been exposed to the reinforcer in the low-deprivation state prior to instrumental training. In Experiment 2, a concurrent training procedure was used to assess whether the change in the value of the reinforcer brought about by preexposurewas mediated by the contingency between the instrumental action and the reinforcer. Preexposure to the reinforcer under the low-deprivation state produced a selective reduction of the performance of the action upon which it was contingent during training when testing was conducted in extinction following a shift from the high- to the low-deprivation state. These experiments provide evidence that animals have to learn about the incentive value of a reinforcer in a particular motivational state through exposure to the reinforcer in that state.     

Taste + odor interactions in compound aversion conditioning

In three experiments with rats, taste + odor interactions in compound aversion conditioning were investigated. In Experiment 1, two odors (0.02% almond and 0.02% orange) were compared on single-element odor aversions, taste (denatonium) potentiated odor aversions, and potentiated odor aversions following taste extinction. Although no odor differences were seen following single-element conditioning, both types of potentiated orange odor aversions were stronger than their almond odor counterparts. These data show that odors of similar conditionability are differentially potentiated by the same taste. To determine whether these differences were due to unique perceptual representations, the effects of elemental extinction or compound extinction on aversions to the compound were investigated in Experiments 2 and 3. In Experiment 2, orange odor extinction weakened responding to the compound significantly more than taste extinction did. In contrast, almond odor extinction and taste extinction produced similar decrements in responding to the compound in Experiment 3. These results suggest that the perceptual representation of these specific taste + odor compounds are different, and they are discussed in regard to configural and within-compound association accounts of potentiation.     

Control of conditional discrimination performance by CS-evoked event representations

The ability of visual CSs previously paired with flavored substances to substitute for those substances as conditional discriminative cues was examined in two Pavlovian appetitive conditioning experiments using rat subjects. In Experiment 1, a visual stimulus was first paired with the delivery of a sucrose solution. Then the rats were trained in conditional discrimination tasks in which sucrose delivery alone served as a conditional cue signaling whether or not a subsequent tone would be reinforced with food pellets. Subjects rapidly acquired discriminative performance to the tones, especially in a feature-negative condition in which sucrose delivery signaled when the tone would not be reinforced. In a subsequent test in which neither food nor sucrose was delivered, presentation of the visual CS also controlled discriminative performance to subsequently presented tones. Experiment 2 showed the ability of a visual CS to substitute for a flavored substance as a conditional cue to be highly stimulus specific. Experiment 2 also showed that a flavored substance was less effective as a conditional cue when it was made to be expected by preceding it with a previously associated visual signal than when it was made to be surprising by preceding it with a visual stimulus signaling another flavored liquid. These results indicate that CS-evoked representations of events can substitute for those events themselves in the control of previously established conditional discrimination performance.