Naïve Chicks Prefer Hollow Objects

A cognitive approach to better understand foraging strategies of the adult domestic hen

Foraging is known to be one of the most important activities in the behavioral budget of chickens. However, how these animals adapt different foraging strategies to diverse environmental variations is currently poorly understood. To gain further insight into this matter, in the present study, hens were submitted to the sloped-tubes task. In this task, the experimenter can manipulate the information that enables the hens to find a food reward (visible or not), placed in one of two hollow tubes. First, 12 hens were tested under free-choice conditions (no penalty for exhaustive searching in both tubes). Under these conditions, the hens adopted a non-random, side-biased strategy when the food location was not directly visible. Then, we divided the hens in two cohorts of equal size to study deeper the hens' foraging strategy when faced (1) with a different container, or (2) with a restrictive environmental constraint under forced-choice conditions (no food reward if the unbaited tube is visited first). This latter constraint increased the risk of the hen not receiving food. A change in the containers didn't modify the search behavior of the hens. However, in forced-choice conditions when the location of the food was not directly visible, four out of six hens learned to choose by exclusion. We conclude that hens can selectively adapt their foraging strategy to the point of adopting an exclusion performance, depending on available information and environmental constraints (high or low risk).

Assessing preferences for adult versus juvenile features in young animals: Newly hatched chicks spontaneously approach red and large stimuli

Young precocial birds benefit from staying close to both their mother and their siblings, while prioritising adults, which provide better care. Which features of the stimuli are used by young birds to prioritise approach and eventually attachment to adults over siblings is unknown. We started to address this question in newly hatched domestic chicks (Gallus gallus), focusing on their spontaneous preferences for visual features that systematically vary between adult and juvenile chickens, and that had previously been identified as attractive: size (larger in adults than in juveniles) and colour (darker and redder in adults than in juveniles). Overall, chicks at their first visual experience, that had never seen a conspecific beforehand, were most attracted to the red and large stimuli (two adult features) and spent more time in close proximity with red stimuli than with yellow stimuli. When tested with red large versus small objects (Exp. 1), chicks preferred the large shape. When tested with yellow large and small objects (Exp. 2), chicks did not show a preference. Chicks had a stronger preference for large red stimuli (vs. small yellow objects) than for small red stimuli (vs. a large yellow object) (Exp. 3). These results suggest that the combination of size and colour form the predisposition that helps chicks to spontaneously discriminate between adult and juvenile features from the first stages of life, in the absence of previous experience, exhibiting a preference to approach stimuli with features associated with the presence of adult conspecifics.

Spontaneous biases enhance generalization in the neonate brain

Inductive generalization is adaptive in novel contexts for both biological and artificial intelligence. Spontaneous generalization in inexperienced animals raises questions on whether predispositions (evolutionarily acquired biases, or priors) enable generalization from sparse data, without reinforcement. We exposed neonate chicks to an artificial social partner of a specific color, and then looked at generalization on the red-yellow or blue-green ranges. Generalization was inconsistent with an unbiased model. Biases included asymmetrical generalization gradients, some preferences for unfamiliar stimuli, different speed of learning, faster learning for colors infrequent in the natural spectrum. Generalization was consistent with a Bayesian model that incorporates predispositions as initial preferences and treats the learning process as an update of predispositions. Newborn chicks are evolutionarily prepared for generalization, via biases independent from experience, reinforcement, or supervision. To solve the problem of induction, biological and artificial intelligence can use biases tuned to infrequent stimuli, such as the red and blue colors.

First-sight recognition of touched objects shows that chicks can solve Molyneux's problem

If a congenitally blind person learns to distinguish between a cube and a sphere by touch, would they immediately recognize these objects by sight once their vision is restored? This question, posed by Molyneux in 1688, has puzzled philosophers and scientists since then. To overcome ethical and practical difficulties in the investigation of cross-modal recognition, we studied inexperienced poultry chicks, which can be reared in darkness until the moment of a visual test with no detrimental consequences. After hatching chicks in darkness, we exposed them to either tactile smooth or tactile bumpy stimuli for 24 h. Immediately after the tactile exposure, chicks were tested in a visual recognition task, during their first experience with light. At first sight, chicks that had been exposed in the tactile modality to smooth stimuli approached the visual smooth stimulus significantly more than those exposed to the tactile bumpy stimuli. These results show that visually inexperienced chicks can solve Molyneux's problem, indicating cross-modal recognition does not require previous multimodal experience. At least in this precocial species, supra-modal brain areas appear functional already at birth. This discovery paves the way for the investigation of predisposed cross-modal cognition that does not depend on visual experience.

Parental behavior and newborn attachment in birds: life history traits and endocrine responses

In birds, parental care and attachment period differ widely depending on the species (altricial or precocial), developmental strategies, and life history traits. In most bird species, parental care can be provided by both female and male individuals and includes specific stages such as nesting, laying, and hatching. During said periods, a series of neuroendocrine responses are triggered to motivate parental care and attachment. These behaviors are vital for offspring survival, development, social bonding, intergenerational learning, reproductive success, and ultimately, the overall fitness and evolution of bird populations in a variety of environments. Thus, this review aims to describe and analyze the behavioral and endocrine systems of parental care and newborn attachment in birds during each stage of the post-hatching period.

Form Properties of Moving Targets Bias Smooth Pursuit Target Selection in Monkeys

During natural viewing, we often recognize multiple objects, detect their motion, and select one object as the target to track. It remains to be determined how such behavior is guided by the integration of visual form and motion perception. To address this, we studied how monkeys made a choice to track moving targets with different forms by smooth pursuit eye movements in a two-target task. We found that pursuit responses were biased toward the motion direction of a target with a hole. By computing the relative weighting, we found that the target with a hole exhibited a larger weight for vector computation. The global hole feature dominated other form properties. This dominance failed to account for changes in pursuit responses to a target with different forms moving singly. These findings suggest that the integration of visual form and motion perception can reshape the competition in sensorimotor networks to guide behavioral selection.

Imprintability of Newly Hatched Domestic Chicks on an Artificial Object: A Novel High Time-Resolution Apparatus Based on a Running Disc

In filial imprinting, newly hatched chicks repeatedly approach a conspicuous object nearby and memorize it, even though it is an artificial object instead of their mother hen. Imprinting on an artificial object in a laboratory setting has a clear sensitive period from post hatch days 1–3 in the case of domestic chicks. However, the establishment of imprintability are difficult to investigate because of the limitations of the behavioral apparatus. In this study, we developed a novel behavioral apparatus, based on a running disc, to investigate the learning processes of imprinting in newly hatched domestic chicks. In the apparatus, the chick repeatedly approaches the imprinting object on the disc. The apparatus sends a transistor-transistor-logic signal every 1/10 turn of the disc to a personal computer through a data acquisition system following the chick’s approach to the imprinting object on the monitor. The imprinting training and tests were designed to define the three learning processes in imprinting. The first process is the one in which chicks spontaneously approach the moving object. The second is an acquired process in which chicks approach an object even when it is static. In the third process, chicks discriminate between the differently colored imprinting object and the control object in the preference test. Using the apparatus, the difference in the chicks’ behavior during or after the sensitive period was examined. During the sensitive period, the chicks at post hatch hour 12 and 18 developed the first imprinting training process. The chicks at post hatch hour 24 maintained learning until the second process. The chicks at post hatch hour 30 reached the discrimination process in the test. After the sensitive period, the chicks reared in darkness until post hatch day 4 exhibited poor first learning process in the training. Thus, this apparatus will be useful for the detection of behavioral changes during neuronal development and learning processes.

Steps towards a computational ethology: an automatized, interactive setup to investigate filial imprinting and biological predispositions

Soon after hatching, the young of precocial species, such as domestic chicks or ducklings, learn to recognize their social partner by simply being exposed to it (imprinting process). Even artificial objects or stimuli displayed on monitor screens can effectively trigger filial imprinting, though learning is canalized by spontaneous preferences for animacy signals, such as certain kinds of motion or a face-like appearance. Imprinting is used as a behavioural paradigm for studies on memory formation, early learning and predispositions, as well as number and space cognition, and brain asymmetries. Here, we present an automatized setup to expose and/or test animals for a variety of imprinting experiments. The setup consists of a cage with two high-frequency screens at the opposite ends where stimuli are shown. Provided with a camera covering the whole space of the cage, the behaviour of the animal is recorded continuously. A graphic user interface implemented in Matlab allows a custom configuration of the experimental protocol, that together with Psychtoolbox drives the presentation of images on the screens, with accurate time scheduling and a highly precise framerate. The setup can be implemented into a complete workflow to analyse behaviour in a fully automatized way by combining Matlab (and Psychtoolbox) to control the monitor screens and stimuli, DeepLabCut to track animals' behaviour, Python (and R) to extract data and perform statistical analyses. The automated setup allows neuro-behavioural scientists to perform standardized protocols during their experiments, with faster data collection and analyses, and reproducible results.

Visual Field Analysis: A reliable method to score left and right eye use using automated tracking

Brain and behavioural asymmetries have been documented in various taxa. Many of these asymmetries involve preferential left and right eye use. However, measuring eye use through manual frame-by-frame analyses from video recordings is laborious and may lead to biases. Recent progress in technology has allowed the development of accurate tracking techniques for measuring animal behaviour. Amongst these techniques, DeepLabCut, a Python-based tracking toolbox using transfer learning with deep neural networks, offers the possibility to track different body parts with unprecedented accuracy. Exploiting the potentialities of DeepLabCut, we developed Visual Field Analysis, an additional open-source application for extracting eye use data. To our knowledge, this is the first application that can automatically quantify left–right preferences in eye use. Here we test the performance of our application in measuring preferential eye use in young domestic chicks. The comparison with manual scoring methods revealed a near perfect correlation in the measures of eye use obtained by Visual Field Analysis. With our application, eye use can be analysed reliably, objectively and at a fine scale in different experimental paradigms.

Stability and individual variability of social attachment in imprinting

Filial imprinting has become a model for understanding memory, learning and social behaviour in neonate animals. This mechanism allows the youngs of precocial bird species to learn the characteristics of conspicuous visual stimuli and display affiliative response to them. Although longer exposures to an object produce stronger preferences for it afterwards, this relation is not linear. Sometimes, chicks even prefer to approach novel rather than familiar objects. To date, little is known about how filial preferences develop across time. This study aimed to investigate filial preferences for familiar and novel imprinting objects over time. After hatching, chicks were individually placed in an arena where stimuli were displayed on two opposite screens. Using an automated setup, the duration of exposure and the type of stimuli were manipulated while the time spent at the imprinting stimulus was monitored across 6 days. We showed that prolonged exposure (3 days vs 1 day) to a stimulus produced robust filial imprinting preferences. Interestingly, with a shorter exposure (1 day), animals re-evaluated their filial preferences in functions of their spontaneous preferences and past experiences. Our study suggests that predispositions influence learning when the imprinting memories are not fully consolidated, driving animal preferences toward more predisposed stimuli.

Sensitive periods for social development: Interactions between predisposed and learned mechanisms

We analysed research that makes use of precocial species as animal models to describe the interaction of predisposed mechanisms and environmental factors in early learning, in particular for the development of social cognition. We also highlight the role of sensitive periods in this interaction, focusing on domestic chicks as one of the main animal models for this field. In the first section of the review, we focus on the emergence of early predispositions to attend to social partners. These attentional biases appear before any learning experience about social stimuli. However, non-specific experiences occurring during sensitive periods of the early post-natal life determine the emergence of these predisposed mechanisms for the detection of social partners. Social predispositions have an important role for the development learning-based social cognitive functions, showing the interdependence of predisposed and learned mechanisms in shaping social development. In the second part of the review we concentrate on the reciprocal interactions between filial imprinting and spontaneous (not learned) social predispositions. Reciprocal influences between these two sets of mechanisms ensure that, in the natural environment, filial imprinting will target appropriate social objects. Neural and physiological mechanisms regulating the sensitive periods for the emergence of social predispositions and for filial imprinting learning are also described.

A Neural Network Model With Gap Junction for Topological Detection

Visual information processing in the brain goes from global to local. A large volume of experimental studies has suggested that among global features, the brain perceives the topological information of an image first. Here, we propose a neural network model to elucidate the underlying computational mechanism. The model consists of two parts. The first part is a neural network in which neurons are coupled through gap junctions, mimicking the neural circuit formed by alpha ganglion cells in the retina. Gap junction plays a key role in the model, which, on one hand, facilitates the synchronized firing of a neuron group covering a connected region of an image, and on the other hand, staggers the firing moments of different neuron groups covering disconnected regions of the image. These two properties endow the network with the capacity of detecting the connectivity and closure of images. The second part of the model is a read-out neuron, which reads out the topological information that has been converted into the number of synchronized firings in the retina network. Our model provides a simple yet effective mechanism for the neural system to detect the topological information of images in ultra-speed.

No evidence of spontaneous preference for slowly moving objects in visually naïve chicks

It has been recently reported that young chicks that have received equal exposure to slowly- and fast-rotating objects showed a preference for slowly-rotating objects. This would suggest that visual experience with slowly moving objects is necessary for object recognition in newborns. I attempted to duplicate this finding in newborn chicks using a simple rotating blue cube. No significant preference was found. Using objects similar to the ones used in the previous study (digital embryos), I observed a strong and robust preference for the fast- (not for the slow-) rotating object. To clarify whether the discrepancies with the previous study could be due to the stimuli frame-frequency used (the chicks' visual system is characterized by high temporal resolution), I repeated the experiments by presenting the stimuli with a lower-frame frequency (from 120 fps to 24 fps). However, similar preferences for the fast-rotating objects were found, this time also for the rotating blue cube. These results suggest a preference for fast-rotating objects that is modulated by the shape and, in part, by the frame-frequency. It remains to be established whether the discrepancies between this study and the previous study can be explained by differences related to strains or artefacts due to the use of monitors with a low-refresh rate.

A transient time window for early predispositions in newborn chicks

Neonates of different species are born with a set of predispositions that influence their early orienting responses toward the first stimuli encountered in their life. Human neonates and domestic chicks exhibit several similarities in the predisposition for attending to objects that move with speed changes, face-like stimuli and biological motion. Although early predispositions are connected to physiological development, little is known on the temporal course of early predispositions (whether they are stable or change in time) and on the associated genetic variability. To address these issues, we tested the preference for objects that change in speed vs. linear motion in three chicken breeds (Padovana, Polverara and Robusta maculata) within one day after hatching and three days after hatching. We found that the predisposition to preferentially attend to changes in speed is shared by different breeds on the first day of life and that it disappears by day three. These results indicate the existence of a short and transient time window of early predispositions that does not depend on visual experience.

Combined predisposed preferences for colour and biological motion make robust development of social attachment through imprinting

To study how predisposed preferences shape the formation of social attachment through imprinting, newly hatched domestic chicks (Gallus gallus domesticus) were simultaneously exposed to two animations composed of comparable light points in different colours (red and yellow), one for a walking motion and another for a linear motion. When a walking animation in red was combined with a linear one in yellow, chicks formed a learned preference for the former that represented biological motion (BM). When the motion-colour association was swapped, chicks failed to form a preference for a walking in yellow, indicating a bias to a specific association of motion and colour. Accordingly, experiments using realistic walking chicken videos revealed a preference for a red video over a yellow one, when the whole body or the head was coloured. On the other hand, when the BM preference had been pre-induced using an artefact moving rigidly (non-BM), a clear preference for a yellow walking animation emerged after training by the swapped association. Even if the first-seen moving object was a nonbiological artefact such as the toy, the visual experience would induce a predisposed BM preference, making chicks selectively memorize the object with natural features. Imprinting causes a rapid inflow of thyroid hormone in the telencephalon leading to the induction of the BM preference, which would make the robust formation of social attachment selectively to the BM-associated object such as the mother hen.

Unlearned visual preferences for the head region in domestic chicks

Unlearned tendencies to approach animate creatures are of great adaptive value, especially for nidifugous social birds that need to react to the presence of potential social companions shortly after hatching. Domestic chicks’ preferences for taxidermized hens provided the first evidence of social predispositions. However, the nature of the stimuli eliciting this predisposition is not completely understood. Here we explore the unlearned preferences of visually naïve domestic chicks for taxidermized animals. Visually naive chicks were tested for their approach preferences between a target stimulus (an intact stuffed animal whose head region was clearly visible) and a control stimulus. After confirming the predisposition for the intact stuffed fowl hen (Exp. 1), we found an analogous preference for a taxidermized, young domestic chick over a severely scrambled version of the same stimulus, whose body structure was completely disrupted, extending to same-age individuals the results that had been obtained with taxidermized hens (Exp. 2). We also directly tested preferences for specimens whose head region is visible compared to ones whose head region was occluded. To clarify whether chicks are sensitive to species-specific information, we employed specimens of female mallard ducks and of a mammalian predator, the polecat. Chicks showed a preference for the duck stimulus whose wings have been covered over a similar stimulus whose head region has been covered, providing direct evidence that the visibility of the head region of taxidermized models drive chicks’ behaviour in this test, and that the attraction for the head region indeed extends to females of other bird species (Exp. 3). However, no similar preference was obtained with the polecat stimuli (Exp. 4). We thus confirmed the presence of unlearned visual preferences for the head region in newly-hatched chicks, though other factors can limit the species-generality of the phenomenon.

Ducklings imprint on chromatic heterogeneity

Avian filial imprinting is a rapid form of learning occurring just after hatching in precocial bird species. The acquired imprint on either or both parents goes on to affect the young bird's survival and social behaviour later in life (Bateson in Biol Rev 41:177-217, 1966). The imprinting mechanism is specialized but flexible, and causes the hatchling to develop high-fidelity recognition and attraction to any moving stimulus of suitable size seen during a predefined sensitive period. It has been observed (Martinho and Kacelnik in Science 353:286-288, 2016; Versace et al. in Anim Cogn 20:521-529, 2017) that in addition to visual and acoustic sensory inputs, imprinting may incorporate informational rules or abstract concepts. Here we report a study of mallard ducklings (Anas platyrhynchos domesticus) undergoing imprinting on the chromatic heterogeneity of stimuli, with a focus on how this may be transferred to novel objects. Ducklings were exposed to a series of chromatically heterogeneous or homogeneous stimuli and tested for preference between two novel stimuli, one heterogeneous and the other homogeneous. Exposure to heterogeneity significantly enhanced preference for novel heterogeneous stimuli, relative to ducklings exposed to homogeneous stimuli or unexposed controls. These findings support the view that imprinting does not rely solely on exemplars, or snapshot-like representations of visual input, but that instead young precocial animals form complex multidimensional representations of the target object, involving abstract properties, either at the time of learning, or later, through generalization from the learnt exemplars.

Embryonic Exposure to Valproic Acid Affects Social Predispositions for Dynamic Cues of Animate Motion in Newly-Hatched Chicks

Early predispositions to preferentially orient toward cues associated with social partners have been documented in several vertebrate species including human neonates and domestic chicks. Human newborns at high familiar risk of Autism Spectrum Disorder (ASD) show differences in their attention toward these predisposed stimuli, suggesting potential impairments in the social-orienting mechanisms in ASD. Using embryonic exposure to valproic acid (VPA) we modeled ASD behavioral deficits in domestic chicks. To investigate social predispositions toward animate motion in domestic chicks, we focused on self-propulsion, using two video-animations representing a simple red circle moving at constant speed (speed-constant) or one that was changing its speed (accelerating and decelerating; speed-change). Using a spontaneous choice test for the two stimuli, we compared spontaneous preferences for stimuli that autonomously change speed between VPA- and vehicle-injected chicks. We found that the preference for speed changes was abolished in VPA-injected chicks compared to vehicle-injected controls. These results add to previous findings indicating similar impairments for static social stimuli and suggest a specific effect of VPA on the development of mechanisms that enhance orienting toward animate stimuli. These findings strengthen the hypothesis of an early impairment of predispositions in the early development of ASD. Hence, early predispositions are a potentially useful tool to detect early ASD symptoms in human neonates and to investigate the molecular and neurobiological mechanisms underlying the onset of this neurodevelopmental disorder.

Visually-naïve chicks prefer agents that move as if constrained by a bilateral body-plan

From the first hours of life, the prompt detection of animate agents allows identification of biologically relevant entities. The motion of most animate agents is constrained by their bilaterally-symmetrical body-plan, and consequently tends to be aligned with the main body-axis. Thus parallelism between the main axis of a moving object and its motion trajectory can signal the presence of animate agents. Here we demonstrated that visually-naïve newborn chicks (Gallus gallus domesticus) are attracted to objects displaying such parallelism, and thus show preference for the same type of motion patterns that elicit perception of animacy in humans. This is the first demonstration of a newborn non-human animal's social preference for a visual cue related to the constraints imposed on behaviour by bilaterian morphology. Chicks also showed preference for rotational movements - a potential manifestation of self-propulsion. Results are discussed in relation to the mechanisms of animacy and agency detection in newborn organisms.

Embryonic Exposure to Valproic Acid Impairs Social Predispositions of Newly-Hatched Chicks

Biological predispositions to attend to visual cues, such as those associated with face-like stimuli or with biological motion, guide social behavior from the first moments of life and have been documented in human neonates, infant monkeys and domestic chicks. Impairments of social predispositions have been recently reported in neonates at high familial risk of Autism Spectrum Disorder (ASD). Using embryonic exposure to valproic acid (VPA), an anticonvulsant associated to increased risk of developing ASD, we modeled ASD behavioral deficits in domestic chicks. We then assessed their spontaneous social predispositions by comparing approach responses to a stimulus containing a face configuration, a stuffed hen, vs. a scrambled version of it. We found that this social predisposition was abolished in VPA-treated chicks, whereas experience-dependent mechanisms associated with filial imprinting were not affected. Our results suggest a specific effect of VPA on the development of biologically-predisposed social orienting mechanisms, opening new perspectives to investigate the neurobiological mechanisms involved in early ASD symptoms.

Newborn chicks show inherited variability in early social predispositions for hen-like stimuli

Predispositions of newborn vertebrates to preferentially attend to living beings and learn about them are pervasive. Their disturbance (e.g. in neonates at risk for autism), may compromise the proper development of a social brain. The genetic bases of such predispositions are unknown. We use the well-known visual preferences of newly-hatched chicks (Gallus gallus) for the head/neck region of the hen to investigate the presence of segregating variation in the predispositions to approach a stuffed hen vs. a scrambled version of it. We compared the spontaneous preferences of three breeds maintained genetically isolated for at least eighteen years while identically raised. Visually-naïve chicks of all breeds (Padovana, Polverara and Robusta maculata) showed the same initial preference for the predisposed stimulus, suggesting that the direction of the initial preference might be genetically fixed. A few minutes later though, striking differences emerged between breeds, which could indicate different strategies of dealing with affiliative objects: while the Polverara breed maintained a constant preference across the entire test, the Padovana and Robusta breeds progressively explored the alternative stimulus more. We hence documented the presence of inherited genetic variability in the expression of early social predispositions in interaction with environmental stimuli.