Orsola Salva

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.

Here, we review evidence of unlearned predispositions to orient toward visual and auditory cues asso- ciated with the presence of animate creatures. We concentrate on studies on chicks of galliform species, whose behavioural preferences for social partners are analyzed in a comparative perspective with respect to the human developmental literature. The emerging nature of chicks’ social predispositions is discussed in relation to the underlying physiological mechanisms and to the role of genetic and environmental factors in their development. In the second part of the review, we summarize evidence on the neural substrate of the animacy detectors, again focusing on our animal model of election, the domestic chick. On the basis of a substantial amount of indirect evidence, subpallial structures, among which the optic tectum (homologous to the mammalian superior colliculus), seem to comprise the most probable candi- dates. We also discuss some preliminary evidence of different brain activity, measured by IEG expression, in chicks exposed to predisposed or a non-predisposed stimulus.

An extensive literature has been accumulating, in recent years, on face-processing in sheep and on the relevance of faces for social interaction in this species. In spite of this, spontaneous preferences for face or non-face stimuli in lambs have not been reported. In this study we tested the spontaneous preference of 8-day- old lambs (N = 9) for three pairs of stimuli. In each pair, one stimulus was a face-like display, whereas the other presented the same inner features displaced in unnatural positions. One pair of stimuli was obtained from photographic images of ewes’ faces, the other two pairs were schematic face-like stimuli. Lambs could differentiate the two stimuli obtained by photos of conspecifics, looking longer
at the non-face stimulus (p < 0.05). We interpret this as a novelty preference, proving that few day-old lambs have already encoded the structural properties that define a face and recognize violations of those general properties.

The tendency of fish to perceive the Ebbing- haus illusion was investigated. Redtail splitfins (Xenotoca eiseni, family Goodeidae) were trained to discriminate between two disks of different sizes. Then, fish were pre- sented with two disks of the same size surrounded by disks of large or small size (inducers) arranged to produce the impression (to a human observer) of two disks of different sizes (in the Ebbinghaus illusion, a central disk surrounded by small inducers appears bigger than an identical one surrounded by large inducers). Fish chose the stimulus that, on the basis of a perception of the Ebbinghaus illusion, appeared deceptively larger or smaller, consistent with the condition of training. These results demonstrate that redtail splitfins tend to perceive this particular illusion. The results are discussed with reference to other related illusions that have been recently observed to be experienced by fish (such as the Navon effect), and with regard to their possible evolutionary implications.

Fish are a complex taxonomic group, whose diversity and distance from other vertebrates well suits the comparative investigation of brain and behavior: in fish species we observe substantial differences with respect to the telencephalic organization of other vertebrates and an astonishing variety in the development and complexity of pallial structures. We will concentrate on the contribution of research on fish behavioral biology for the understanding of the evolution of the visual system. We shall review evidence concerning perceptual effects that reflect fundamental principles of the visual system functioning, highlighting the similarities and differences between distant fish groups and with other vertebrates. We will focus on perceptual effects reflecting some of the main tasks that the visual system must attain. In particular, we will deal with subjective contours and optical illusions, invariance effects, second order motion and biological motion and, finally, perceptual binding of object properties in a unified higher level representation.

It is currently being debated whether human newborns’ preference for faces is due to an unlearned, domain-specific and configural representation of the appearance of a face, or to general mechanisms, such as an up-down bias (favouring top-heavy stimuli, which have more elements in their upper part). Here we show that 2-day-old domestic chicks, visually naïve for the arrangement of inner facial features, spontaneously prefer face-like, schematic, stimuli. This preference is maintained when the up-down bias is controlled for (Experiment1) or when put in direct conflict with facedness (Experiment 4). In contrast, we found no evidence for the presence of an up-down bias in chicks (Experiment 2). Moreover, our results indicate that the eye region of stimuli is crucial in determining the expression of spontaneous preferences for faces (Experiments 3 and 4).