Mapping number to space in the two hemispheres of the avian brain

Pre-verbal infants and non-human animals associate small numbers with the left space and large numbers with the right space. Birds and primates, trained to identify a given position in a sagittal series of identical positions, whenever required to respond on a left/right oriented series, referred the given position starting from the left end. Here, we extended this evidence by selectively investigating the role of either cerebral hemisphere, using the temporary monocular occlusion technique. In birds, lacking the corpus callosum, visual input is fed mainly to the contralateral hemisphere. We trained 4-day-old chicks to identify the 4th element in a sagittal series of 10 identical elements. At test, the series was identical but left/right oriented. Test was conducted in right monocular, left monocular or binocular condition of vision. Right monocular chicks pecked at the 4th right element; left monocular and binocular chicks pecked at the 4th left element. Data on monocular chicks demonstrate that both hemispheres deal with an ordinal (sequential) task. Data on binocular chicks indicate that the left bias is linked to a right hemisphere dominance, that allocates the attention toward the left hemispace. This constitutes a first step towards understanding the neural basis of number space mapping.

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.

Numerical discrimination by frogs (Bombina orientalis)

Evidence has been reported for quantity discrimination in mammals and birds and, to a lesser extent, fish and amphibians. For the latter species, however, whether quantity discrimination would reflect sensitivity to number or to the continuous physical variables that covary with number is unclear. Here we reported a series of experiments with frogs (Bombina orientalis) tested in free-choice experiments for their preferences for different amounts of preys (Tenebrio molitor larvae) with systematic controls for variables such as surface area, volume, weight, and movement. Frogs showed quantity discrimination in the range of both small (1 vs. 2, 2 vs. 3, but not 3 vs. 4) and large numerousness (3 vs. 6, 4 vs. 8, but not 4 vs. 6), with clear evidence of being able to discriminate numerousness even when continuous physical variables were controlled for in the case of small numerousness (i.e., 1 vs. 2), whereas in the case of large numerousness it remains unclear whether the number or surface areas were dominant. We suggested that task demands are likely to be responsible for the activation of different systems for small and large numerousness and for their relative susceptibility to quantitative stimulus variables.

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 previous studies 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, Experiment 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 Experiment 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.

Spatial reversal learning is impaired by age in pet dogs

Aged dogs spontaneously develop progressive decline in both cognitive and behavioral function, in addition to neuropathological changes, that collectively parallel several aspects of human aging and Alzheimer's disease progression and likely contribute to the development of canine cognitive dysfunction syndrome. In the current study, ethologically relevant spatial learning, retention, and reversal learning tasks were conducted, with the goal of expanding canine neuropsychological testing to pet dogs. Initially, dogs (N = 44, aged 7.8 ± 2.8 years, mean ± SD) had to learn which of two alternative routes successfully led out of a T-maze. Two weeks later, long-term memory retention was assessed, immediately followed by a reversal learning task in which the previously correct route out of the maze was reversed compared with the initial learning and memory retention tasks. No effects of age were evident on the learning or retention tasks. However, older (≥ 8 years) dogs were significantly impaired on the reversal learning task compared with younger ones (< 8 years). Moreover, trial response latency was significantly increased in aged dogs across both the initial and reversal learning tasks but not on the retention task, which suggests that processing speed was impaired by increasing age during the acquisition of novel spatial information but not during performance of previously learned responses. Overall, the current study provides a framework for assessing cognitive function in pet dogs, which should improve understanding of the effects of aging on cognition in the dog population.

Numerical abstraction in young domestic chicks (Gallus gallus)

In a variety of circumstances animals can represent numerical values per se, although it is unclear how salient numbers are relative to non-numerical properties. The question is then: are numbers intrinsically distinguished or are they processed as a last resort only when no other properties differentiate stimuli? The last resort hypothesis is supported by findings pertaining to animal studies characterized by extensive training procedures. Animals may, nevertheless, spontaneously and routinely discriminate numerical attributes in their natural habitat, but data available on spontaneous numerical competence usually emerge from studies not disentangling numerical from quantitative cues. In the study being outlined here, we tested animals' discrimination of a large number of elements utilizing a paradigm that did not require any training procedures. During rearing, newborn chicks were presented with two stimuli, each characterized by a different number of heterogeneous (for colour, size and shape) elements and food was found in proximity of one of the two stimuli. At testing 3 day-old chicks were presented with stimuli depicting novel elements (for colour, size and shape) representing either the numerosity associated or not associated with food. The chicks approached the number associated with food in the 5vs.10 and 10vs.20 comparisons both when quantitative cues were unavailable (stimuli were of random sizes) or being controlled. The findings emerging from the study support the hypothesis that numbers are salient information promptly processed even by very young animals.

The cradle of causal reasoning: newborns' preference for physical causality

Perception of mechanical (i.e. physical) causality, in terms of a cause-effect relationship between two motion events, appears to be a powerful mechanism in our daily experience. In spite of a growing interest in the earliest causal representations, the role of experience in the origin of this sensitivity is still a matter of dispute. Here, we asked the question about the innate origin of causal perception, never tested before at birth. Three experiments were carried out to investigate sensitivity at birth to some visual spatiotemporal cues present in a launching event. Newborn babies, only a few hours old, showed that they significantly preferred a physical causality event (i.e. Michotte's Launching effect) when matched to a delay event (i.e. a delayed launching; Experiment 1) or to a non-causal event completely identical to the causal one except for the order of the displacements of the two objects involved which was swapped temporally (Experiment 3). This preference for the launching event, moreover, also depended on the continuity of the trajectory between the objects involved in the event (Experiment 2). These results support the hypothesis that the human system possesses an early available, possibly innate basic mechanism to compute causality, such a mechanism being sensitive to the additive effect of certain well-defined spatiotemporal cues present in the causal event independently of any prior visual experience.

Structural imbalance promotes behavior analogous to aesthetic preference in domestic chicks

Background

Visual images may be judged ‘aesthetic’ when their positioning appears imbalanced. An apparent imbalance may signify an as yet incomplete action or event requiring more detailed processing. As such it may refer to phylogenetically ancient stimulus-response mechanisms such as those mediating attentional deployment.

Methodology/Principal Findings

We studied preferences for structural balance or imbalance in week-old domestic chicks (Gallus gallus), using a conditioning procedure to reinforce pecking at either “aligned” (balanced) or “misaligned” (imbalanced) training stimuli. A testing phase with novel balanced and imbalanced stimuli established whether chicks would retain their conditioned behavior or revert to chance responding. Whereas those trained on aligned stimuli were equally likely to choose aligned or misaligned stimuli, chicks trained on misaligned stimuli maintained the trained preference.

Conclusions/Significance

Our results are consistent with the idea that the coding of structural imbalance is primary and even overrides classical conditioning. Generalized to the humans, these results suggest aesthetic judgments based upon structural imbalance may be based on evolutionarily ancient mechanisms, which are shared by different vertebrate species.

Symmetry perception by poultry chicks and its implications for three-dimensional object recognition

Bilateral symmetry is visually salient to diverse animals including birds, but whereas experimental studies typically use bilaterally symmetrical two-dimensional patterns that are viewed approximately fronto-parallel; in nature, animals observe three-dimensional objects from all angles. Many animals and plant structures have a plane of bilateral symmetry. Here, we first (experiment I) give evidence that young poultry chicks readily generalize bilateral symmetry as a feature of two-dimensional patterns in fronto-parallel view. We then test the ability of chicks to recognize symmetry in images that would be produced by the transformed view produced by a 40° horizontal combined with a 20° vertical rotation of a pattern on a spherical surface. Experiment II gives evidence that chicks trained to distinguish symmetrical from asymmetrical patterns treat rotated views of symmetrical 'objects' as symmetrical. Experiment III gives evidence that chicks trained to discriminate rotated views of symmetrical 'objects' from asymmetrical patterns generalize to novel symmetrical objects either in fronto-parallel or rotated view. These findings emphasize the importance of bilateral symmetry for three-dimensional object recognition and raise questions about the underlying mechanisms of symmetry perception.

Summation of large numerousness by newborn chicks

Newly hatched domestic chicks, reared with identical objects, when presented with sets of 3 vs. 2 objects disappearing one-by-one behind separate screens, spontaneously inspected the screen occluding the larger set; even when the continuous variables (area or perimeter) were controlled for (Rugani et al., 2009). Here, using a similar paradigm, we investigated the ability of chicks to perform addition on larger sets of objects. Chicks imprinted on five identical objects, were presented at test with 6 vs. 9 objects which disappeared one-by-one (Exp. 1). In Exp. 2, the same overall number of objects (15) was used, but employing an increased ratio, i.e., 5 vs. 10. In both experiments, when continuous variables were not made equal, chicks spontaneously inspected the screen occluding the larger set. However, when the size of the objects was adjusted so as to make the total surface area or perimeter equal for the two sets, chicks did not exhibit any preference. Lack of choice in the control conditions could be due to a combination of preferences; to rejoin the larger numerousness as well as the bigger objects (Rugani et al., 2010a). In Exp. 3, chicks were familiarized, during imprinting, with objects of various dimensions, in an attempt to reduce or suppress their tendency to approach objects larger than the familiar ones. Again chicks failed to choose at test between 5 vs. 10 objects when continuous variables were made equal. Results showed that chicks, after a one-by-one presentation of a large number of objects, rejoined the larger set. In order to choose the larger set, chicks estimated the objects in the two sets and then compared the outcomes. However, differently to what has been described for small numerousness, chicks succeeded only if non-numerical cues as well as numerical cues were available. This study suggests that continuous variables are computed by chicks for sets of objects that are not present at the same time and that are no longer visible at the time of choice.

The evolution of social orienting: evidence from chicks (Gallus gallus) and human newborns

BACKGROUND

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-naïve chicks (Gallus gallus) whose preferences can be assessed prior to any other visual experience with faces.

METHODS

In the present study, for the first time, we test the prediction that both newly hatched chicks and human newborns will demonstrate similar preferences for face stimuli over spatial frequency matched structured noise. Chicks and babies were tested using identical stimuli for the two species. Chicks underwent a spontaneous preference task, in which they have to approach one of two stimuli simultaneously presented at the ends of a runway. Human newborns participated in a preferential looking task.

RESULTS AND SIGNIFICANCE

We observed a significant preference for orienting toward the face stimulus in both species. Further, human newborns spent more time looking at the face stimulus, and chicks preferentially approached and stood near the face-stimulus. These results confirm the view that widely diverging vertebrates possess similar domain-relevant biases toward faces shortly after hatching or birth and provide a behavioural basis for a comparison with neuroimaging studies using similar stimuli.

Spontaneous discrimination of possible and impossible objects by newly hatched chicks

Four-month-old infants can integrate local cues provided by two-dimensional pictures and interpret global inconsistencies in structural information to discriminate between possible and impossible objects. This leaves unanswered the issue of the relative contribution of maturation of biologically predisposed mechanisms and of experience with real objects, to the development of this capability. Here we show that, after exposure to objects in which junctions providing cues to global structure were occluded, day-old chicks selectively approach the two-dimensional image that depicted the possible rather than the impossible version of a three-dimensional object, after restoration of the junctions. Even more impressively, completely naive newly hatched chicks showed spontaneous preferences towards approaching two-dimensional depictions of structurally possible rather than impossible objects. These findings suggest that the vertebrate brain can be biologically predisposed towards approaching a two-dimensional image representing a view of a structurally possible three-dimensional object.