Cortisol and behavioral responses to separation in mother and infant guinea pigs

In Experiment 1, lactating guinea pigs 3 days postpartum exhibited an elevation of plasma levels of cortisol when their litters were taken from the home cage and placed out of auditory range for 30 min. If pups were left within auditory range during the period of separation, or if the litter was disturbed but not removed, no increase in plasma cortisol levels was observed. In Experiment 2, 11/12- and 18/19-day-old guinea pig pups placed alone in a novel environment for 30 min displayed levels of plasma cortisol and vocalizations that were greater than those of pups tested in the same environment but with their mother. Pups tested with littermates but not with their mother exhibited plasma cortisol levels that were as great as those of pups tested alone. Pups tested with littermates vocalized much less than pups tested alone but more than pups tested with their mother. These results indicate that brief mother-infant separation can activate the pituitary-adrenal system in mother as well as infant guinea pigs and they provide further evidence for the existence of a reciprocal mother-infant attachment in this species.     

Orangutans (Pongo abelii) and a gorilla (Gorilla gorilla gorilla) match features in familiar and unfamiliar individuals

Great apes can perceive images as representative of corresponding real-life objects. Coupled with the potential advantages of identifying specific members of one’s species and mounting evidence for individual recognition in other non-humans, it seems likely that great apes would have the ability to identify conspecifics in photographs. The ability of four orangutans and a gorilla to match images of individuals of their own and a closely related but unfamiliar species was examined here for the first time. First, the subjects matched photographs of familiar conspecifics taken at various time points in a delayed matching-to-sample procedure (Experiment 1). Second, they matched different photographs of unfamiliar individuals of a different species (Experiment 2) at above chance levels. These results suggest that the subjects matched photographs by matching physical features, not necessarily by recognizing the identity of the individuals depicted. However, they also quickly learned to select photographs of familiar individuals when these photographs were paired with photographs of unfamiliar individuals of their own species (Experiment 3), and three subjects showed transfer to novel images of familiar and unfamiliar individuals. Thus, the findings support the idea that subjects attended to physical features to identify individuals that they could categorize on the basis of familiarity.     

Social interaction modifies learned aversions, sodium appetite, and both palatability and handling-time induced dietary preference in rats (Rattus norvegicus)

In a series of four experiments, I examined the extent to which socially transmitted diet preference could counteract the effects of a learned aversion (Experiment 1), a palatability-based diet preference (Experiment 2), a polyethylene glycol 20,000-induced sodium appetite (Experiment 3), and a handling-time induced dietary preference (Experiment 4). I found that rats poisoned after eating a novel diet ate very substantial amounts of the averted diet following interaction with conspecifics that had eaten the averted diet. Following interaction with conspecifics that had eaten an unpalatable diet, rats offered a choice between palatable and unpalatable diets ate more than twice as much unpalatable diet as did controls lacking social experience. Sodium-deficient rats offered a choice between sodium-enriched and sodium-adequate diets ate less than half as much sodium-enriched diet, following interaction with conspecifics that had eaten sodium-adequate diet as did control rats lacking social experience. Rats offered a choice between isocaloric, roughly equipalatable foods with long and short handling times (e.g., sunflower seeds with and without shells) chose the food having the longer handling time after interacting with conspecifics eating that food. These findings suggest that social influence is a major factor in guiding diet selection by rats.     

An investigation into blocking of filial imprinting in the chick during exposure to a compound stimulus

The occurrence of "blocking" was investigated in jungle fowl chicks (Gallus gallus spadiceus B.) in an imprinting situation. In Experiment 1, chicks were simultaneously exposed to two stationary coloured cylinders, either two red cylinders (Group RR), a yellow and a red cylinder (YR), or two yellow cylinders (YY). After six days of exposure, the cylinders were removed from the cages and replaced by a yellow and a blue cylinder (i.e. YB) for each chick. This second phase of the experiment lasted for seven days. When the blue cylinder was presented alone during tests at different stages in Phase 2, the RR birds spent significantly more time with this cylinder and emitted fewer shrill calls than the chicks in the YR and YY groups. In Experiment 2, RR and YY birds were reared as in Experiment 1, except that in the second phase of the experiment they were exposed to a blue cylinder only. In this experiment the development of an attachment to the novel blue cylinder proceeded similarly in the RR and YY birds. In Experiment 3, it was found that chicks that were reared with a yellow and a red cylinder preferred the latter stimulus. Thus, although in the first phase of Experiment 1 the RR birds had been exposed to a more attractive stimulus, in tests during the second phase they spent more time with a novel stimulus (B) than the YY birds. These results are consistent with the suggestion that imprinting to a novel stimulus is "blocked" to some extent when that stimulus is presented in compound with another stimulus to which the animal has previously been exposed.     

Effects of caloric, protein, and sodium deprivation on the affiliative behavior of Norway rats (Rattus norvegicus).

The tendency of food-deprived, protein-deprived, and sodium-deprived Norway rats (Rattus norvegicus) and their respective controls to affiliate with conspecifics deprived of either food, protein, or sodium was examined. The authors found that (a) independent of internal state, focal rats offered a forced choice between protein-deprived and protein-replete target rats spent more time near replete than deprived target rats; and (b) both food-deprived and sodium-deprived focal rats offered a forced choice between food-deprived and replete target rats spent less time near fasted rats than did well-fed and sodium-replete focal rats. The data indicate that (a) rats can distinguish both food-deprived and protein-deprived rats from replete rats and (b) the deprivation states of rats can affect their willingness to affiliate with deprived conspecifics.     

Horses (Equus caballus) discriminate body odour cues from conspecifics

Knowledge about social recognition and memory in animals can help us to determine appropriate management and husbandry techniques. In this study, we used a habituation–discrimination procedure to investigate the ability of horses (Equus caballus) to distinguish between the body odour samples of unfamiliar conspecifics. To pick up body odour, we rubbed material on the coat of horses and presented these unknown body odours to 16 different conspecifics of the same sex and similar age. The test consisted of two successive two-min presentations of a sample from one individual (e.g. individual ‘A’) and a simultaneous presentation of samples from individual ‘A’ and a novel individual (e.g. individual ‘B’) during a final third presentation. The results showed that horses, regardless of sex, decreased the time they spent investigating conspecific body odour across the initial two presentations—demonstrating habituation. In the final presentation, the results demonstrated successful discrimination of the previously experienced odour because horses investigated the novel olfactory sample (‘B’) significantly more than the pre-exposed sample (‘A’). Taken together, these findings suggest, for the first time, that horses are able to discriminate two stimuli derived from body odours of unfamiliar conspecifics over short period of time.     

Are consonant intervals music to their ears? Spontaneous acoustic preferences in a nonhuman primate

Humans find some sounds more pleasing than others; such preferences may underlie our enjoyment of music. To gain insight into the evolutionary origins of these preferences, we explored whether they are present in other animals. We designed a novel method to measure the spontaneous sound preferences of cotton-top tamarins, a species that has been extensively tested for other perceptual abilities. Animals were placed in a V-shaped maze, and their position within the maze controlled their auditory environment. One sound was played when they were in one branch of the maze, and a different sound for the opposite branch; no food was delivered during testing. We used the proportion of time spent in each branch as a measure of preference. The first two experiments were designed as tests of our method. In Experiment 1, we used loud and soft white noise as stimuli; all animals spent most of their time on the side with soft noise. In Experiment 2, tamarins spent more time on the side playing species-specific feeding chirps than on the side playing species-specific distress calls. Together, these two experiments suggest that the method is effective, providing a spontaneous measure of preference. In Experiment 3, however, subjects showed no preference for consonant over dissonant intervals. Finally, tamarins showed no preference in Experiment 4 for a screeching sound (comparable to fingernails on a blackboard) over amplitude-matched white noise. In contrast, humans showed clear preferences for the consonant intervals of Experiment 3 and the white noise of Experiment 4 using the same stimuli and a similar method. We conclude that tamarins' preferences differ qualitatively from those of humans. The preferences that support our capacity for music may, therefore, be unique among the primates, and could be music-specific adaptations.     

The effects of cross-fostering on the development of social preferences in meadow voles (Microtus pennsylvanicus)

To determine the role of the parental environment in the formation of species attachments in the meadow vole (Microtus pennsylvanicus), young of this species were fostered to either meadow vole parents (in-fostered young) or to prairie vole parents (M. ochrogaster; cross-fostered young). At 50 to 60 days of age, subjects were tested for social preference in an environment that simulated the conditions of a runway system. The testing design assessed the reaction of fostered animals to a novel species (M. pinetorum) as well as to the parental and biological species. The proportion of total test time spent near stimulus animals did not vary as a function of rearing condition. However, when compared to in-fostered controls, cross-fostered meadow voles displayed increased preference for prairie voles. Novelty did not appear to be a significant factor in test animal choice. These results suggest that in meadow voles, preference for the species of social partner is dependent on postnatal experience with parents.     

The influence of novelty and complexity on exploratory behavior in 12-month-old infants

This study investigated the influence of the novelty of the environment and the novelty and complexity of the objects (toys) it contained on the exploratory behavior of 12-month-old infants. Each infant was given a choice between novel and familiar toys located in two adjacent rooms (toy rooms). The novelty of the objects was manipulated by allowing the infants to play with one set of toys during a 5-min familiarization trial prior to the choice trial. The novetly of the environment was manipulated by allowing some infants to see, enter, and remain in the toy rooms during the familiarization trial. Finally, the complexity of the objects was manipulated by varying the number of familiar and novel toys; some Ss had four toys in each set (complex array) and some had only one (simple array). The results indicate that all three factors influenced the infants' exploratory behavior. Ss first approached, and spent more time manipulating, the novel than the familiar toys; they spent more time in the toy rooms if they were novel; and they spent more time manipulating the complex array of toys than the simple array.     

Heart-rate responses of infant rats and guinea pigs to stimulus onset and offset: tests of the generality of a bidirectional effect

To test the generality, across modality and across species, of a bidirectional effect of photic stimulation in infant rats found in previous experiments, two experiments examined the effects on heart rate (HR) of onset and offset of auditory stimulation in rats and of photic stimulation in guinea pigs. Experiment 1 demonstrated a unidirectional, decelerative response in rats 17 and 21 days of age to the onset and offset of a 1-kHz tone, at both low (80 dB) and high (100 dB) intensity levels and at 14 days to the onset of the high-intensity tone. Experiment 2 demonstrated that infant guinea pigs, which unlike infant rats are precocial and not nocturnal, responded to the offset but not to the onset of light, and that this response was decelerative. These results indicated a lack of generality of the bidirectional HR effect, and were discussed in terms of the orienting/defensive reflex distinction.     

Developmental flavor experience affects utilization of odor, not taste in toxiphobic conditioning

Feeding experiences were varied in developing rats and the effects upon flavor neophobia and lithium chloride-induced flavor aversions were observed. In Experiment 1, nursing experience of neonate rats was reduced by artificial feeding via intragastric cannula; the rats then were tested with apple juice paired with lithium chloride injection at weaning or maturity. Conditioned aversions were not affected, but neophobia to novel apple juice was attenuated in artificially-reared rats tested at maturity. In Experiment 2, rats received enriched feeding experience after weaning, which consisted of (a) obtaining many complex flavors, a few of which were paired with poisoning, effortlessly in the home cage, or (b) foraging for various foods on an elevated maze. No dramatic effects on neophobia or conditioned taste aversion for saccharin water were apparent. In Experiment 3, rats were given experience after weaning with vanilla-scented water either paired or unpaired with quinine water, and then tested with the odor of almond or that odor compounded with saccharin water for neophobia and lithium-induced aversions. Flavor-experienced rats exhibited more pronounced odor conditioning and more resistance to extinction of the odor aversion after both simple and compound conditioning. In contrast, saccharin taste aversions were relatively unchanged. Apparently, enriched feeding and drinking experience facilitates the utilization of odor more than taste cues.     

Rehousing periadolescent male guinea pigs (Cavia porcellus) apart from their mothers for 24 hours increases maternally directed sexual behavior and plasma testosterone

Periadolescent male guinea pigs (Cavia porcellus) housed continuously with their mother displayed little or no sexual behavior when they were tested with her in a novel environment. However, if males were rehoused without their mother for 24 hr before testing, they frequently directed courtship and sexual behavior toward her. This effect occurred whether the mother was isolated or not during the rehousing period. In addition, rehousing without the mother produced a significant rise in the plasma testosterone levels of the males. It appears that continuous housing with the mother inhibits sexual and courtship behavior directed toward her, as well as gonadal activity, in periadolescent male guinea pigs. These effects may serve to prevent inbreeding.     

Maternal discrimination and the development of sex differences in exploratory behaviour in infant spiny mice (Acomys cahirinus)

The present paper reports sex differences in exploratory behaviour by infant Spiny Mice, Acomys cahirinus, that may, in part, be related to differences in maternal behaviour towards pups; like some other rodents, mother Acomys differentiate behaviourally between male and female pups. In Experiment 1 infant Acomys were allowed to explore a novel arena. This experiment showed that even by Day 3 (the day of birth=Day 1) female Acomys explored a novel environment more than males; they entered the arena sooner than males and spent more time in contact with a novel object. Experiment 2 showed that infant females were more active than males when observed in the home cage in the presence of their parents and made more approaches to the mother. Mothers, on the other hand, directed more licking behaviour towards males. Experiment 3 focused on the exploratory behaviour of individual pups in the presence of the mother. Given access to a large, complex arena, female pups explored more than males. The results also showed that mothers direct more of their social interactions towards sons than daughters, particularly when pups are about a week old. Some mothers appear to “direct” the movement of their offspring, by blocking their forward movement; this was done more often to male than to female pups. The data suggest that the previously observed changes in exploratory behaviour at this time, and the emergence of sex differences in exploration, may in part depend upon the mothers' reactions to pups by sex.     

The role of phonology in incidental vocabulary acquisition during silent reading

In two experiments, we investigated the role of phonology in learning new words incidentally during silent reading. Participants read sentence pairs containing novel or known words that varied in homophony (whether another word exists with an alternate spelling for the same pronunciation). In Experiment 1, we monitored readers' eye movements to investigate online processes involved in establishing meanings for novel words. In Experiment 2, participants completed cued recall and vocabulary recognition tasks after the reading session to assess the influence of phonological form on word learning. Eye movement results indicate that readers spent the most time reading novel homophones (e.g., skwosh) and surrounding context, indicating that phonological information is activated early during a reader's initial encounter with a new letter string. Retention measures suggest that readers were able to infer a meaning for each novel word type, despite the increased difficulty associated with reading novel words with familiar phonological forms, and that phonology aided the acquisition of orthography.     

Generalization of learning from picture books to novel test conditions by 18- and 24-month-old children

Researchers know little about whether very young children can recognize objects originally introduced to them in a picture book when they encounter similar looking objects in various real-world contexts. The present studies used an imitation procedure to explore young children's ability to generalize a novel action sequence from a picture book to novel test conditions. The authors found that 18-month-olds imitated the action sequence from a book only when the conditions at testing matched those at encoding; altering the test stimuli or context disrupted imitation (Experiment 1A). In contrast, the 24-month-olds imitated the action sequence with changes to both the test context and stimuli (Experiment 1B). Moreover, although the 24-month-olds exhibited deferred imitation with no changes to the test conditions, they did not defer imitation with changes to the context and stimuli (Experiment 2). Two factors may account for the pattern of results: age-related changes in children's ability to utilize novel retrieval cues as well as their emerging ability to understand the representational nature of pictures.     

Novel odors evoke risk assessment and suppress appetitive behaviors in mice

The effects of four novel odors on risk assessment by mice (i. e., flat back approach, stretched attention, immobility) and the suppression of appetitive behaviors were examined in two experiments. When novel odors were presented in a straight runway, subjects spent significantly less time in the odor compartment, relative to controls, when it contained sheep wool, chocolate, or citronella (but not cat fur) odors. Risk assessment behaviors occurred at similar levels among all groups and appetitive behaviors were not suppressed by the novel odors. When odorants were scattered over one half of the subjects' home cage floor in Experiment 2, all novel odors increased the duration of at least on e risk assessment measure and/or suppressed appetitive behaviors (i. e., eating, grooming, rearing). The results clearly reveal that a reasonably wide range of novel odors evoke at least some level of risk assessment which presumably reflects increased fearfulness. The odors of sheep wool and cat fur induced a wider range of such responses than did chocolate or cinnamon suggesting that mammalian odors may be particularly effective stimuli. If so, however, it is clear that predator odors are not uniquely effective in this regard. Experiment 1 also underscores the importance of the testing environment in assessing the behavioral effects of novel odors in mice. © 1993 Wiley-Liss, Inc.     

Relative time in dangerous and safe places influences one-way avoidance learning in the rat

This paper reports three experiments on one-way avoidance learning in rats which examined the effect of time spent in the safe and dangerous compartments on acquisition, maintenance, and extinction of avoidance. In Experiment 1 time spent in safety was manipulated, and time spent in danger was held constant. Animals spending more time in safety needed fewer trials to reach the acquisition criteria and more trials to reach the extinction criteria; both effects became stronger as the required criteria for acquisition and extinction were increased. In Experiment 2 time spent in safety/danger was manipulated while holding the intertrial interval constant. Groups simultaneously spending more time in safety and less time in danger again needed fewer trials to reach the learning criteria. In Experiment 3 time spent in danger was manipulated, whereas time spent in safety was held constant. Groups spending less time in danger needed fewer trials to reach the learning criteria. These results indicate that the magnitude of the reinforcement or incentive value of the safety compartment is not a linear function of absolute time spent therein, but a function of the ratio between the length of time spent in safety and in danger.     

Selective attention in peacocks during predator detection

Predation can exert strong selective pressure on the evolution of behavioral and morphological traits in birds. Because predator avoidance is key to survival and birds rely heavily on visual perception, predation may have shaped avian visual systems as well. To address this question, we examined the role of visual attention in antipredator behavior in peacocks (Pavo cristatus). Peacocks were exposed to a model predator while their gaze was continuously recorded with a telemetric eye-tracker. We found that peacocks spent more time looking at and made more fixations on the predator compared to the same spatial location before the predator was revealed. The duration of fixations they directed toward conspecifics and environmental features decreased after the predator was revealed, indicating that the peacocks were rapidly scanning their environment with their eyes. Maximum eye movement amplitudes and amplitudes of consecutive saccades were similar before and after the predator was revealed. In cases where conspecifics detected the predator first, peacocks appeared to learn that danger was present by observing conspecifics’ antipredator behavior. Peacocks were faster to detect the predator when they were fixating closer to the area where the predator would eventually appear. In addition, pupil size increased after predator exposure, consistent with increased physiological arousal. These findings demonstrate that peacocks selectively direct their attention toward predatory threats and suggest that predation has influenced the evolution of visual orienting systems.     

Light-dark variation and changes across the lactational period in the behaviors of undisturbed mother and infant guinea pigs (Cavia porcellus)

Lactating guinea pigs (Cavia porcellus) and their litters were observed by videophotography across the light/dark cycle at 1, 11, 21, and 31 days postpartum. The highest level of behavioral activity was seen in the dark, particularly in the hour after light offset. This circadian pattern was evident from Day 1 in mothers and from Day 11 in pups. Contact between mothers and pups was inversely related to activity, occurring more frequently during light. Maternal grooming of pups occurred on Day 1 and then declined: self-grooming by pups increased across days. Intake of solid food and water by pups occurred on Day 1 and increased thereafter. A nearly complete transition from nursing to independent ingestion was observed between 21-31 days of age. Overall, we document several ontogenetic changes in young guinea pigs and demonstrate that under laboratory conditions mother and infant guinea pigs exhibit a nocturnal activity pattern.     

Enhanced defense in adult rats deprived of playfighting experience as juveniles

In an earlier study we found that shock-elicited defensive aggression was intensified in rats that had been deprived of playfighting as juveniles. The three experiments reported here extend this phenomenon to the more naturalistic intruder/resident paradigm for eliciting defense. Rats were reared from 20 to 50 days in one of three conditions: in pairs or in isolation with or without 1 hour of daily playfighting experience. They were rehoused in small groups at 50 days, when the frequency of play is beginning to wane, in order to eliminate the effects of ongoing isolation at the time of testing. They were tested for defense at 80 to 100 days by being placed in a resident's cage for 10 minutes. Our main finding was that play-deprived animals spent significantly more time immobile after they had been attacked than did animals of the other two groups. The increased immobility associated with playfighting deprivation is not caused by baseline differences in emotionality such as those elicited by a novel environment (Experiment 1), the presence of a strange animal (Experiment 2), or nonsocial aversive stimuli (Experiment 3). Furthermore, play-deprived rats were not more reactive when pinched with forceps to stimulate a bite delivered by a conspecific, whether or not another rat was present behind a divider. Thus isolates' greater reactivity may be restricted to situations involving pain coupled with close proximity to and contact with another rat. A secondary finding was that there were no differences in defensive behaviors other than immobility. The appropriate generalization to be drawn from these studies is that early social deprivation facilitates the defensive response to a social threat that happens to be prepotent under the given experimental conditions.