Naïve chicks do not prefer objects with stable body orientation, though they may prefer behavioural variability

Domestic chicks (Gallus gallus domesticus) have been widely used as a model to study the motion cues that allow visually naïve organisms to detect animate agents shortly after hatching/birth. Our previous work has shown that chicks prefer to approach agents whose main body axis and motion direction are aligned (a feature typical of creatures whose motion is constrained by a bilaterally symmetric body plan). However, it has never been investigated whether chicks are also sensitive to the fact that an agent maintains a stable front–back body orientation in motion (i.e. consistency in which end is leading and which trailing). This is another feature typical of bilateria, which is also associated with the detection of animate agents in humans. The aim of the present study was to fll this gap. Contrary to our initial expectations, after testing 300 chicks across 3 experimental conditions, we found a recurrent preference for the agent which did not maintain a stable front–back body orientation. Since this preference was limited to female chicks, the results are discussed also in relation to sex diferences in the social behaviour of this model. Overall, we show for the frst time that chicks can discriminate agents based on the stability of their front–back orientation. The unexpected direction of the efect could refect a preference for agents’ whose behaviour is less predictable. Chicks may prefer agents with greater behavioural variability, a trait which has been associated with animate agents, or have a tendency to explore agents performing “odd behaviours”

Cerebral and Behavioural Asymmetries in Animal Social Recognition

Evidence is here summarized that animal species belonging to distant taxa show forms of social recognition, a sophisticated cognitive ability adaptive in most social interactions. The paper then proceeds to review evidence of functional lateralization for this cognitive ability. The main focus of this review is evidence obtained in domestic chickens, the animal model employed in the authors' laboratories, but we also discuss comparisons with data from species ranging from fishes, amphib ians and reptiles, to other birds and mammals. A consistent pattern emerges, pointing toward a right hemisphere dominance, in particular for discrimination of social companions and individual (or familiarity-based) recognition, whereas the left hemisphere could be specialized for "category-based" distinctions (e.g., conspecifics versus heterospecifics). This pattern of results is discussed in relation to a more general specialization and processing styles of the two sides of the brain, with the right hemisphere predisposed for developing a detailed, global and contextual representation of objects, and the left hemisphere predisposed for rapid assignment of a stimulus to a category, for processing releaser stimuli and for control of responses

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

Early predispositions to preferentially orient towards 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 these social-orienting mechanisms in ASD. Using embryonic exposure to valproic acid (VPA) we modelled ASD behavioural deficits in domestic chicks. To investigate social predispositions towards 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 six minutes spontaneous choice test for the two stimuli, we compared unlearned 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 towards 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

Abnormal visual attention to simple social stimuli in 4-month-old infants at high risk for Autism

Despite an increasing interest in detecting early signs of Autism Spectrum Disorders (ASD), the pathogenesis of the social impairments characterizing ASD is still largely unknown. Atypical visual attention to social stimuli is a potential early marker of the social and communicative deficits of ASD. Some authors hypothesized that such impairments are present from birth, leading to a decline in the subsequent typical functioning of the learning-mechanisms. Others suggested that these early deficits emerge during the transition from subcortically to cortically mediated mechanisms, happening around 2-3 months of age. The present study aimed to provide additional evidence on the origin of the early visual attention disturbance that seems to characterize infants at high risk (HR) for ASD. Four visual preference tasks were used to investigate social attention in 4-month-old HR, compared to low-risk (LR) infants of the same age. Visual attention differences between HR and LR infants emerged only for stimuli depicting a direct eye-gaze, compared to an adverted eye-gaze. Specifically, HR infants showed a significant visual preference for the direct eye-gaze stimulus compared to LR infants, which may indicate a delayed development of the visual preferences normally observed at birth in typically developing infants. No other differences were found between groups. Results are discussed in the light of the hypotheses on the origins of early social visual attention impairments in infants at risk for ASD

The Evolution of Social Orienting: Evidence from Chicks (Gallus gallus) and Human Newborns

Converging evidence from different species indicates that some newborn vertebrates, including humans, have visual predispositions to attend to the head region of animate creatures. It has been claimed that newborn preferences for faces are domain-relevant and similar in different species. One of the most common criticisms of the work supporting domain-relevant face biases in human newborns is that in most studies they already have several hours of visual experience when tested. This issue can be addressed by testing newly hatched face-na\uefve chicks (Gallus gallus) whose preferences can be assessed prior to any other visual experience with faces

Early predispositions for social stimuli: the case of face perception

Converging evidence from several different species has led to the proposal that some newborn vertebrates, including humans and domestic chicks, have visual predispositions to attend to the head region of conspecifics (or of animals of other species that share similar characteristics) (Johnson and Horn 1988; Morton and Johnson, 1991; Sugita 2008). More specifically it has been claimed that these newborn preferences are (i) domain-relevant to the extent that other naturally occurring stimuli do not draw attention in the same way, (ii) are not based on rapid early learning, but are present from birth/hatching, and (iii) may be mediated by phylogenetically ancient brain routes common to many vertebrates. One of the most common criticisms of the work supporting domain-relevant face biases in human newborns is that the majority of the studies conducted (with some notable exceptions) regard newborns of more than a few hours old. Thus, it remains possible that very rapid early learning contributes to the specificity of some of the effects observed (Nelson, 2001). This criticisms of the data from human newborns can be addressed by testing newly hatched visually-deprived chicks whose preference for visual stimuli can be assessed prior to any other visual experience with faces, a procedure obviously not viable with human newborns for ethical reasons. The main aim of present study is thus to investigate from a new perspective and employing an animal model (the domestic chick) a long-debated issue: the specificity vs. non-specificity of the perceptual factors involved in face preferences. One central issue in cognitive science is how brain processes knowledge of specific domains, as for example the visual information regarding faces. Some existing evidences seem to indicate that faces are processed by anatomically and/or functionally dedicated domain-specific brain circuits, in humans and possibly also in animals. This idea seems also to be consistent with the striking processing abilities that human beings have demonstrated in face perception. It seems plausible that, because of the relevance of faces for social life, natural selection led to the evolution of innate face-specific devices that are available prior to any postnatal experience. In fact, a number of studies have demonstrated that, even from a few hours or minutes after birth, a schematic pattern representing an upright face elicits greater visual attention in human newborns than do similar stimuli presenting the same internal face-features in scrambled positions or arranged upside-down (see Morton and Johnson, 1991 for a review). According to Morton & Johnson (1991) this evidence would indicate that human newborns respond to the unique structural configuration of the face (i.e. to facedness) due to a face-detecting mechanism (CONSPEC) that contains a configural representation of the structure of the face’s inner features (three darker areas in an upside-down triangular configuration). Similarly, domestic chicks have been shown to posses an unlearned representation for the appearance of a social object. Such a representation would guide the imprinting process ensuring that chicks would imprint on an animate object instead of on an inanimate feature of the environment. In particular, this unlearned representation of the appearance of a social object would include a very broad structural description of the features contained in the head region of a vertebrate creature (e.g. Johnson & Horn, 1988). It has thus been hypothesised that the same mechanism described to explain face preferences in newborn babies (CONSPEC) would underlie also spontaneous preferences of visually naïve chicks (Morton and Johnson, 1991). However, in the human developmental literature it has often been debated whether newborns’ preference for faces would not be simply the secondary effect of some more general and not domain-specific visual preference displayed by newborn vertebrates. This kind of domain-general preference would direct the organism’s attention toward any stimulus presenting a certain physical attribute, regardless of whether this stimulus is a face or a non-face object (Acerra, Burnod and de Schonen, 2002; Kleiner, 1987; Macchi Cassia et al., 2008; Simion et al., 2002; Turati et al., 2002). In my thesis I will thus assess the role of three perceptual properties (that are considered influential in the developmental literature) in determining face preferences in visually naïve domestic chicks. The role of the vertical asymmetry of inner elements Recently, in the developmental literature, it has been argued that newborn infants’ preferences for faces could be a secondary effect determined by non-specific biases due to constraints imposed by the immature visual system of the child. In particular, Turati et al. (2002) provided evidence that the preference for face-like stimuli could be determined by an “up-down bias” (Simion et al., 2002) that directs the babies’ attention toward any configuration presenting more elements in its upper part (a “top-heavy configuration”, as opposed to a “bottom-heavy configuration”, presenting more elements in its lower part). Thus, we decided to investigate whether visually naive domestic chicks spontaneously prefer schematic faces or other top-heavy stimuli and whether such a preference is determined by an up-down bias, as suggested by some literature on newborn babies (Turati et al., 2002). Eggs were incubated and hatched in the darkness and after hatching, for about 24 h, chicks were placed in an uniform white cage whose walls and floor were made of opaque white paper. The only stimulus available to chicks during this rearing period was an artificial orange cardboard imprinting object that presented an identical outline with respect to stimuli that will be employed at test (the outline of a schematic face and neck), but no inner feature. Thus, the imprinting object could not provide chicks with any bias for one of the test stimuli or with any information regarding faces’ inner features. During the second day of life chicks underwent a spontaneous preference test, in which each chick had to choose between one of two stimuli that were simultaneously presented at the two opposite ends of a longitudinal runway. The runway was divided into three virtual sectors. At the beginning of the test each chick was placed in the central sector of the apparatus. In order to approach one of the two stimuli the chick had to leave the central sector of the apparatus and enter one of the two lateral sectors adjacent to the stimuli. Thus, entrance and residence of the chick in one of the side compartments indicated a preference for the adjacent object. The test lasted for 6 minutes. Stimuli employed at test were identical to the imprinting object in size, shape and colour, but presented three inner features (three black squares) that were absent in the imprinting object. The two stimuli in each test-pair differed from one another only in the configuration created by the three black squares (in line with standard stimuli used in the developmental literature). Changing the disposition of the three inner elements it was thus possible to test chicks preferences for face-like vs. non-face like objects controlling also for the role of the up-down bias. Each chick was tested only once and was thus exposed to only one pair of stimuli. With this procedure we demonstrated that chicks prefer to approach a schematic face-like configuration similar to those used in newborn studies with respect to another equally top-heavy, but non-face-like, stimulus (Exp. 1). In line with this result, in a second experiment chicks did not show any evidence of a preference for a top-heavy stimulus over a bottom-heavy stimulus, if none of them represents a face (Exp. 2). Moreover, chicks preferred to stay near a bottom-heavy and face-like stimulus over a top-heavy non-face-like one (Exp. 4). Thus, results obtained in this first cycle of experiments demonstrated that domestic chicks, that are visually naïve with respect to faces’ inner structure, show a spontaneous preference for schematic face-like stimuli that resemble the representation of a face as theorised by Morton and Johnson (1991). Moreover, the vertical asymmetry of inner elements (i.e. the up-down bias, Simion et al., 2002; Turati et al., 2002) does not seem to have a crucial role in the expression of this preference in the animal species that we tested. The role of the spatial frequencies composing stimuli During the past decades another alternative interpretation, based on the so called linear system model (LSM, e.g. Kleiner, 1987), has been proposed to explain face preferences in newborn babies, as opposed to the CONSPEC model proposed by Morton and Johnson (1991). According to this interpretation (confirmed also by the results of a recent neural network model by Acerra, Burnod and de Schonen, 2002) faces would elicit preferential attention in newborn babies simply because they happen to be composed of the range of spatial frequencies more visible to newborns. In previous studies existing in the literature, stimuli were controlled for properties such as vertical symmetry or for the presence of structure (Morton and Johnson, 1991; Farroni et al., 2005; Rosa Salva, Regolin and Vallortigara, 2009). The research conducted in similar studies already generated a good amount of evidence for the role of the above mentioned properties. We thus decided to concentrate our efforts on the role of another potentially relevant perceptual property, namely, spatial frequency composing stimuli. The use of stimuli that exactly match spatial frequencies between face-stimuli and control-stimuli, comparing faces to frequency matched visual noise, is already a common standard in works investigating neural correlates of face perception (Csibra et al., 2004; Blasi et al., 2007). However, to the best of our knowledge, this approach has not yet been systematically applied to the investigation of behavioural preferences in newborn babies and domestic chicks. We thus decided to fill this gap between behavioural and neuroimaging studies. In a recent study (Rosa Salva et al., submitted) we were able to demonstrate that newborn babies show a preference for looking at faces with respect to visual noise stimuli that were matched in terms of their component spatial frequencies. In Expt. 5 of my thesis we thus decided to run a comparative study in order to be able to directly compare data obtained in newborn babies and visually naïve domestic chicks, tested with comparable procedures and identical stimuli. The experimental procedures were the same as those described in the previous session, with the exception that no imprinting stimulus was provided to the chicks. Stimuli consisted in a colour photographic image of a human face and in a frequency matched noise stimulus. Domestic chicks displayed a clear preference for the face-like stimulus. The strength of this preference was comparable to that displayed by newborn human babies. The results of the present research demonstrated that analogue effects can be obtained in both visually deprived domestic chicks and human newborn babies, in that both species show a preference for images of faces. Moreover, such a preference is, in both species, independent from component spatial frequencies. Thus, the present study extends the existing analogy between results obtained in newborn babies and domestic chicks (Johnson and Horn, 1988; Morton and Johnson, 1991; Rosa Salva, Regolin and Vallortigara, 2009), confirming the validity of use of the domestic chick as an animal experimental model to investigate issues connected with the developmental literature. Finally, results obtained showed that the preference for faces observed in domestic chicks is not species-specific (in fact chicks’ preferences could be elicited by a human face). This confirms previous evidence suggesting the presence of a very broad template for the detection of faces in this species (Johnson and Horn, 1988). Effects originated by contrast reversal In recent years it has been demonstrated that contrast reversal eliminates the preference of newborn babies for schematic faces. The normal preference for faces can however be made to remerge by adding a pupil-like dot within the schematic face features (Farroni et al., 2005). These results have been interpreted as due to the fact that the mechanisms underling face preference have been selected to identify faces under natural (top-down) illumination. Such mechanisms are thus sensitive to the light-shadow pattern generated on faces by such conditions (the eye and mouth regions are recessed on a face and therefore appear to be darker than other parts of the face). As a consequence, infants should show no preference for face-like patterns where the elements within the face are lighter than the background, because those elements would indicate protrusions rather than recesses for their visual system (Farroni et al., 2005). We decided to investigate the effect of contrast reversal on the preference for schematic face-like configurations displayed by chicks. The experimental procedure was the same as that described for experiments 1-4. Stimuli employed were obtained from those used in Expt. 1 (where a preference for the face-like stimulus was observed), and consisted in two top-heavy configurations, of which only one represented a face. Stimuli employed in Expt. 6 were identical to those used in Expt. 1, with the relevant exception that they presented a reversed contrast (they were made of lighter inner features on a darker face background). No preference for one of the two stimuli was observed. In Expt. 7, after Farroni et al. (2005), we introduced a pupil-like dot within the lighter inner features of both stimuli. This was done in order to try to restore the initial preference for the face-like stimulus observed in Expt. 1 using stimuli with “normal” contrast polarity. On the contrary, if anything, a preference for the non-face-like stimulus was observed in the present experiment. We interpreted this result as due to the fact that chicks are innately scared of stimuli resembling a pair of eyes. This is especially true for stimuli having a darker pupil within a lighter iris, because such stimuli look predator-like to them (Gagliardi, Gallup and Boren, 1976). Chicks, would thus avoid the face-like stimulus because its two upper features would resemble a pair of predators’ eyes. We tested this hypothesis in Expt. 8, by increasing the pupil-to-iris ratio of our stimuli in order to reach the ratio that is most effective in determining a fear reaction in chicks. With this manipulation results obtained in the previous experiment were confirmed and extended, showing again a preference for the non-face-like stimulus. Moreover, in Expt. 9, we investigated brain lateralization using the same stimuli as in Expt. 8, but testing chicks in monocular vision condition (in chicks this is an effective way for limiting visual processing to the hemisphere contralateral to the eye in use). We hypothesised that the fear reaction elicited by the face-like stimulus should be more pronounced in chicks using their right hemisphere (specialized for fear reactions to the eye-gaze of predators, Rosa Salva, Regolin and Vallortigara, 2007). Some of the results obtained in Expt. 9 were in favour of this hypothesis. As a final control (Expt. 10) we presented chicks with a pair of stimuli that had the normal direction of contrast polarity for a face (i.e. presented darker inner features on a lighter background), but had also an eye-like appearance of their inner features. No preference whatsoever was observed, this was possibly interpreted as a consequence of the simultaneous presence of two opposite tendencies: a social preference for the face-like configuration, now emerged again thanks to the normal direction of contrast polarity, and a fear reaction elicited by its eye-like features. Finally, in Expt. 11 we tested monocular chicks using identical stimuli to those of Expt. 10, in order to investigate brain lateralization. In this final experiment, an opposite tendency was observed for chicks using their right hemisphere with respect to what observed in Expt. 9. In fact, chicks using their right hemisphere tended to prefer again the face-like configuration. This is not completely unexpected if two things are taken in consideration. First of all, the right hemisphere is not only dominant for fear reactions to eye gaze, but also for recognition of social partners (e.g. Daisley et al., 2009, for a review). Moreover, the face stimulus used in the present experiment was conspicuously “more social” than that used in Expt. 9, because it presented the normal direction of contrast polarity for a face. This probably caused the right hemisphere to be driven by the social nature of the stimulus rather than by its aversive predator-eye-like inner features. Results of this last cycle of experiments show that, in line with the evidence available in developmental literature, contrast reversal is effective in suppressing chicks’ preferences for schematic faces. However, adding a pupil-like eye dot on inner face features had an opposite effect in chicks with respect to newborn babies. In fact, in chicks this manipulation elicited a preference for the non-face-like stimulus, possibly due to an anti-predator fear reaction. Overall, my results are consistent with the presence in chicks of an unlearned mechanism for the detection of faces based on a very broad template representing the structure of a face (i.e. CONSPEC, Morton and Johnson, 1991). Moreover, contrary to evidence obtained in newborn babies (Turati et al., 2002), it seems that chicks’ preferences for faces are not influenced by the vertical asymmetry of inner elements. On the other hand, both chicks and human babies (Rosa Salva et al., submitted) seem to prefer faces regardless of their component spatial frequencies. Similarly, contrast reversal effectively abolishes the preference for faces in both human newborns (Farroni et al., 2005) and domestic chicks.Sulla base di evidenze sperimentali ottenute in diverse specie animali è stato teorizzato che i piccoli di alcuni vertebrati possano avere predisposizioni precoci o innate per prestare attenzione alla regione della testa e del volto dei conspecifici (o di altri animali che ne condividano la struttura generale) (Johnson e Horn 1988; Morton e Johnson, 1991; Sugita 2008). In particolare è stato teorizzato che tali predisposizioni siano (i) di natura dominio-specifica in quanto altri stimoli presenti in ambiente naturale non attraggono l’attenzione con la stessa efficacia dei volti, (ii) non siano basate su fenomeni di apprendimento precoce, ma piuttosto siano presenti sin dal momento della nascita/schiusa, e (iii) siano mediate da sistemi neurali filogeneticamente antichi comuni a diverse specie di vertebrati. Una delle principali critiche ai lavori che hanno dimostrato la presenza di preferenze dominio-specifiche per i volti nei neonati della specie umana è legata al fatto che, per lo più, tali lavori abbiano testato neonati di alcune ore di vita. Per tale ragione non è mai stato possibile escludere il fatto che le preferenze per i volti riscontrate nei neonati fossero dovute in realtà ad effetti di apprendimento legati all’esperienza avuta dai neonati stessi con i volti (Nelson, 2001). Tale critica può essere tuttavia aggirata da studi che impieghino pulcini di pollo domestico, deprivati di esperienza visiva riguardo ai volti, come modello animale per investigare la presenza di preferenze spontanee per i volti. Lo scopo del mio lavoro di tesi è perciò quello di investigare da una nuova prospettiva ed usando un modello animale (il pulcino domestico) un problema a lungo dibattuto in letteratura: ovvero la specificità o non specificità dei fattori percettivi coinvolti nelle preferenze per i volti. Un tema centrale nelle scienze cognitive è rappresentato dalle modalità con le quali il cervello elabora la conoscenza relativa a degli specifici domini, come ad esempio l’informazione visiva riguardante i volti. Alcune evidenze presenti in letteratura sembrano indicare che i volti siano processati da circuiti cerebrali specificamente dedicati sia nell’uomo, che probabilmente negli animali. Questa idea è anche coerente con le incredibili capacità di elaborazione che la nostra specie dimostra per le informazioni relative ai volti. Sembra perciò plausibile che, a casa della rilevanza dei volti per la vita sociale, la selezione naturale abbia portato all’evoluzione di meccanismi specifici deputati all’elaborazione dei volti e disponibili in modo non appreso. Infatti, numerosi studi hanno dimostrato che neonati umani di poche ore o minuti di vita preferiscono guardare uno stimolo schematico rappresentante un volto rispetto ad uno stimolo simile in cui i medesimi elementi interni componenti il volto sono presentati in posizioni scrambled o capovolte (Morton e Johnson, 1991). Secondo il modello proposto da Morton e Johnson (1991), questi risultati indicherebbero che i neonati umani preferiscono osservare qualsiasi stimolo che presenti la peculiare struttura di un volto, grazie ad un meccanismo innato per la detezione dei volti (CONSPEC), il quale conterrebbe una rappresentazione della struttura di un volto e della disposizione spaziale delle sue componenti interne. Tale rappresentazione potrebbe semplicemente comprendere la presenza di tre aree più scure su fondo chiaro poste in corrispondenza dei vertici di un invisibile triangolo rovesciato, ovvero in posizioni corrispondenti ad occhi e bocca di un volto. In linea con il modello p

Lateralized mechanisms for encoding of object. Behavioral evidence from an animal model: the domestic chick (Gallus gallus)

In our previous research we reported a leftward-asymmetry in domestic chicks required to identify a target element, on the basis of its ordinal position, in a series of identical elements. Here we re-coded behavioral data collected in a previous study from chicks tested in a task involving a different kind of numerical ability, to study lateralization in dealing with an arithmetic task. Chicks were reared with a set of identical objects representing artificial social companions. On day 4, chicks underwent a free-choice test in which two sets, each composed of a different number of identical objects (5 vs.10 or 6 vs. 9, Exp. 1), were hidden behind two opaque screens placed in front of the chick, one on the left and one on the right side. Objects disappeared, one by one, behind either screen, so that, for example, one screen occluded 5 objects and the other 10 objects. The left-right position of the larger set was counterbalanced between trials. Results show that chicks, in the attempt to rejoin the set with the higher number of social companions, performed better when this was located to the right. However, when the number of elements in the two sets was identical (2 vs.2, in Exp.2) and they differed only in the coloration of the objects, this bias was not observed, suggesting a predisposition to map the numerical magnitude from left to right. Future studies should be devoted to the direct investigation of this phenomenon, possibly employing an identical number of mono-chromatic imprinting stimuli in both conditions involving a numerical discrimination and conditions not involving any numerosity difference

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

Brain asymmetry modulates perception of biological motion in newborn chicks (Gallus gallus)

Few light-points on the joints of a moving animal give the impression of biological motion (BM). Day-old chicks prefer BM to non-BM, suggesting a conserved predisposition to attend to moving animals. In humans and other mammals a network of regions, primarily in the right hemisphere, provides the neural substrate for BM perception. However, this has not been investigated in avians. In birds the information from each eye is mainly feeding to the contralateral hemisphere. To study brain asymmetry, we recorded the eye spontaneously used by chicks to inspect a BM stimulus. We also investigated the effect of lateralization following light exposure of the embryos. In Experiment 1, highly-lateralized chicks aligned with the apparent direction of motion only when they were exposed to a BM-stimulus moving rightward first, monitoring it with the left-eye-system. In Experiment 2 weakly-lateralized chicks did not show any behavioral asymmetry. Moreover, they counter aligned with the apparent direction of motion. Brain lateralization affects chicks behavior while processing and approaching a BM stimulus. Highly-lateralized chicks aligned their body with the apparent direction of the BM, a behavior akin to a following response, monitoring the stimulus preferentially with their left eye. This suggests a right hemisphere dominance in BM processing. Weakly-lateralized chicks counter-aligned with the apparent direction of the BM, facing it during interaction, and monitored it equally with both eyes. Environmental factors (light stimulation) seem to affect the development of lateralization, and consequently social behavior