Perception of the Ebbinghaus illusion in four-day-old domestic chicks (Gallus gallus)

In the Ebbinghaus size illusion, a central circle surrounded by small circles (inducers) appears bigger than an identical one surrounded by large inducers. Previous studies have failed to demonstrate sensitivity to this illusion in pigeons and baboons, leading to the conclusion that avian species (possibly also nonhuman primates) might lack the neural substrate necessary to perceive the Ebbinghaus illusion in a human-like fashion. Such a substrate may have been only recently evolved in the primate lineage. Here, we show that this illusion is perceived by 4-day-old domestic chicks. During rearing, chicks learnt, according to an observational-learning paradigm, to find food in proximity either of a big or of a small circle. Subjects were then tested with Ebbinghaus stimuli: two identical circles, one surrounded by larger and the other by smaller inducers. The percentage of approaches to the perceptually bigger target in animals reinforced on the bigger circle (and vice versa for the other group) was computed. Over four experiments, we demonstrated that chicks are reliably affected by the illusory display. Subjects reinforced on the small target choose the configuration with big inducers, in which the central target appears perceptually smaller; the opposite is true for subjects reinforced on the big target. This result has important implications for the evolutionary history of the neural substrate involved in the perception of the Ebbinghaus illusion.     

The use of spatial and local cues for orientation in domestic chicks (Gallus gallus)

Animal Cognition - Birds have been widely used to study spatial orientation. However, since different birds rely on different types of visual information to find goal locations (such as spatial...     

Affiliation and aggression as related to gender in domestic chicks (Gallus gallus).

Social discrimination in male and female domestic chicks (Gallus gallus) was investigated by using (a) latencies of approach response, (b) simultaneous free choice, and (c) intersubject aggressive-pecking tests. In approach-response tests, females showed shorter latencies when tested with cagemates than when tested with strangers, whereas males showed shorter latencies when tested with strangers than when tested with cagemates. In simultaneous-choice tests, females spent more time near a cagemate, whereas males spent more time near a strange chick. In aggressive-pecking tests, both sexes pecked more at strangers than at cagemates; aggressive pecking at strangers, however, was higher in males than in females. It is argued that gender effects in social discrimination can be accounted for in terms of stronger social attachment in females and aggressive responses in males.     

Preference for symmetry is experience dependent in newborn chicks (Gallus gallus)

Spontaneous pecking preferences toward symmetric or asymmetric stimuli were tested in newborn chicks (Gallus gallus). A preference for asymmetric patterns was found in na?ve chicks (either 24 or 48 hours old), although a preference for symmetry appeared at retest after chicks had experienced standard rearing conditions (Experiments 1 and 2). Only food-experienced chicks preferred symmetric patterns; food-deprived and hand-fed chicks did not show any preference (Experiment 3). A key factor that allowed for the emergence of a preference for symmetry may relate to the improving of pecking sensorimotor skills occurring during active food manipulation. Possible explanations are discussed for the late emergence of the preference for symmetry and for the preference for asymmetry found in na?ve chicks.     

Geometric modules in animals' spatial representations: a test with chicks (Gallus gallus domesticus)

Recent work has shown that in place-finding tasks rats rely on the geometric relations between the goal object and the shape of the environment. We tested young chickens (Gallus gallus domesticus) on similar tasks in a reference memory paradigm to determine whether differences exist between species in the ability to use geometric and nongeometric spatial information. The main findings were that chicks: (a) encoded and used both geometric and nongeometric (featural) information; (b) did not use the overall spatial arrangement of the features; (c) relied primarily on nongeometric cues when faced with contradictory information. Two mechanisms are evident in chicks' spatial representations: a metric frame for encoding the spatial arrangement of surfaces as surfaces and a cue-guidance system for encoding conspicuous landmarks near the target. The possibility of hierarchical organization and species differences in these two mechanisms are discussed.     

Searching for the center: spatial cognition in the domestic chick (Gallus gallus)

Chicks learned to find food hidden under sawdust by ground-scratching in the central position of the floor of a closed arena. When tested inan arena of identical shape but a larger area, chicks searched at 2 different locations, one corresponding to the correct distance (i.e., center) in the smaller (training) arena and the other to the actual center of the test arena. When tested in an arena of the same shape but a smaller area, chicks searched in the center of it. These results suggest that chicks are able to encode information on the absolute and relative distance of the food from the walls of the arena. After training in the presence of a landmark located at the center of the arena, animals searched at the center even after the removal of the landmark. Marked changes in the height of the walls of the arena produced some displacement in searching behavior, suggesting that chicks used the angular size of the walls to estimate distances.     

Naturalistic psychophysics: thresholds of ducklings (Anas platyrynchos) and chicks (Gallus gallus) to tones that resemble mallard calls

Neonatal ducklings and chickens were tested for responsiveness to a pulsing pure tone that was as similar as possible to the mallard maternal alarm call. It is known that ducklings momentarily cease vocalizing when they hear the alarm call and that chicks do the same when they hear pure tones. The duration of peep suppression can thus be used as a measure of whether subjects of either species heard the stimulus. Chicks might not be as sensitive as ducklings to a mallard alarm call because the signal is less significant to them. An adaptive or staircase procedure was used to estimate absolute thresholds, and group psychometric functions were reconstructed for each species from the trial-by-trial data. Ducklings had lower thresholds than chickens as well as steeper psychometric functions to this stimulus. The results suggest that more sensitive and consistent behavioral responses can be elicited by naturalistic sounds than by more arbitrary acoustic stimuli.     

The development of ordinal numerical competence in young children

Two experiments assessed ordinal numerical knowledge in 2- and 3-year-old children and investigated the relationship between ordinal and verbal numerical knowledge. Children were trained on a 1 vs 2 comparison and then tested with novel numerosities. Stimuli consisted of two trays, each containing a different number of boxes. In Experiment 1, box size was held constant. In Experiment 2, box size was varied such that cumulative surface area was unrelated to number. Results show children as young as 2 years of age make purely numerical discriminations and represent ordinal relations between numerosities as large as 6. Children who lacked any verbal numerical knowledge could not make ordinal judgments. However, once children possessed minimal verbal numerical competence, further knowledge was entirely unrelated to ordinal competence. Number may become a salient dimension as children begin to learn to count. An analog magnitude representation of number may underlie success on the ordinal task.     

Development of a frequency dimension in chickens (Gallus gallus)

Multidimensional scaling is used to examine the consistency of neonates' responses to frequency changes. Chickens at 0 and 4 days of age were presented with all possible transitions between pairs of five pure tones at 500, 525, 551, 578, and 608 Hz. Subjects were habituated to one stimulus, and the duration of an unconditioned delay in their otherwise ongoing peeps was measured after the frequency of the stimulus was changed. Durations of these delays can be used as measures of how different animals perceive two frequencies to be. Scaling solutions show that a nonrandom, adult-like ordering of frequencies emerges between 0 and 4 days of age.     

Reinforcer quality matters: A test of the Mathematical Principles of Reinforcement with domestic hens (Gallus gallus domesticus)

This study evaluated the ability of Killeen's (1994) Mathematical Principles of Reinforcement to account for the effects of changes in reinforcer quality on hens' rates of responding on fixed‐ratio schedules. Hens were trained to peck a key on a fixed‐ratio schedule of reinforcement and then experienced an ascending series of ratio values in two separate conditions. In different conditions, the food reinforcer was either wheat or puffed wheat. Response rates initially increased with increases in ratio requirement before eventually decreasing at larger ratios. Quantitative fits of the model accounted for the data well. The fits revealed that different foods were systematically associated with changes in the specific activation parameter, a, and these were consistent with previous reports of preference for those food items.     

Audience effects on alarm calling in chickens (Gallus gallus)

The male domestic chicken (Gallus gallus) has been found to modulate the production of vocal signals in response to the presence or absence of a suitable audience. We investigated effects on alarm calling by presenting overhead predator models to cockerels in the presence of a variety of social companions. The production of aerial predator calls in response to hawk silhouettes varied with the presence or absence of a member of the same species. The kinds of audience investigated included the mate, unfamiliar females, other females and males with which subjects had had prior visual and auditory contact, and broody hens with and without young. Domestic chicks, unrelated to the subjects, were almost as effective an audience as conspecific adults. A member of another species, however, failed to potentiate alarm-call production. The subjects gave more alarm calls when they were in the presence of either a male or a female audience than when they were alone. By manipulating the visibility of overhead predator models to the subjects and to the audience, we showed that the subjects were not cued by alarm and escape behaviors of the audience. Comparisons with food calling indicate that, in deciding whether to emit a signal in response to the appropriate referent (e.g., food or predators), chickens respond to subtle differences in the nature of the audience with behaviors that vary from one communicative context to another.     

Leap orders in male chickens (Gallus gallus domesticus): longitudinal evidence

Leap orders in pairs of male chickens were traced in a longitudinal study from near hatching to about 11 weeks of age. Birds were given a series of 39 day-long social separations, each followed by a day-long reunion. Tests for aggression occurred during the first 5 min of reunion. Pecks were frequent early in the test series, but soon diminished; leaps supplanted pecks as the most frequent response at about midseries, and abated in turn. To account for this dual pattern of the waxing and waning of aggressive responses, it was hypothesized that leap orders had formed in midseries, thus obviating further agonistic behavior. Support for the hypothesis was found: Early peck orders did not predict later leap orders, but early leap orders did predict subsequent leap and peck orders.     

Sex differences in social reinstatement motivation of the domestic chick (Gallus gallus) revealed by runway tests with social and nonsocial reinforcement

Male and female chicks (Gallus gallus) were trained at 4 days old to run along a corridor to reach a goal box that contained either cagemates (social reinforcement) or food (nonsocial reinforcement). Females ran faster when social reinforcement was used, whereas males ran faster with nonsocial reinforcement. When social reinforcement was used with a V-shaped runway, in which chicks had to proceed toward the goal object in an indirect fashion, sex differences were reversed. The results may be due to stronger social reinstatement tendencies in females than in males: Higher levels of social motivation facilitate behavioral performance when the task is easy (straight runway) and inhibit it when the task is difficult (V-shaped runway).     

Relative salience of species maternal calls in neonatal gallinaceous birds: a direct comparison of Japanese quail (Coturnix coturnix japonica) and domestic chickens (Gallus gallus domesticus)

Differential-approach tendencies of individual incubator-hatched chickens and Japanese quail were assayed using one exemplar of each of the species maternal calls in a simultaneous-choice paradigm. Within 24 hr after hatching, the birds received several short periods of exposure to rotating mounts of an adult female chicken and quail, which emitted the species-appropriate call. All birds were then tested with calls alone over the following 2 to 4 days. The test stimuli were played from speakers located behind pressure-sensitive panels so that approach behavior was recorded when a bird pushed against one of the panels. Both the chickens and the quail, as groups, spent significantly more time attempting to approach the exemplar of their own species maternal call, although there was considerable variation in the magnitude of the approach difference among individuals within each species. Sources of variation in preference scores are analyzed, and a simulation is used to interpret individual differences in response scores. This type of preference test is useful for a number of applications, notably for studying the behavior of quail-chick nervous system chimeras.