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1.  Spontaneous discrimination of possible and impossible objects by newly hatched chicks 
Biology Letters  2011;7(5):654-657.
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.
doi:10.1098/rsbl.2011.0051
PMCID: PMC3169041  PMID: 21429912
impossible objects; early predispositions; object perception; domestic chick
2.  Chicks, like children, spontaneously reorient by three-dimensional environmental geometry, not by image matching 
Biology Letters  2012;8(4):492-494.
Spatial reorientation by layout geometry occurs in numerous species, but its underlying mechanisms are debated. While some argue that navigating animals' sense of place is based on geometric computations over three-dimensional representations, others claim it depends on panoramic image-matching processes. Because children reorient by subtle three-dimensional perturbations of the terrain and not by salient two-dimensional brightness contours on surfaces or freestanding columns, children's sense of place cannot be explained by image matching. To test image-matching theories in a different species, the present experiment investigates the reorientation performance of domestic chicks (Gallus gallus) in environments similar to those used with children. Chicks, like children, spontaneously reoriented by geometric relationships of subtle three-dimensional terrains, and not by salient two-dimensional brightness contours on surfaces or columns. These findings add to the evidence for homologous navigation systems in humans and other vertebrates, and they cast doubt on image-matching theories of reorientation in these species.
doi:10.1098/rsbl.2012.0067
PMCID: PMC3391460  PMID: 22417791
navigation; reorientation; geometry; image matching
3.  Re-orienting in space: do animals use global or local geometry strategies? 
Biology Letters  2010;7(3):372-375.
Here we compare whether birds encode surface geometry using principal axes, medial axes or local geometry. Birds were trained to locate hidden food in two geometrically identical corners of a rectangular arena and subsequently tested in an L-shaped arena. The chicks showed a primary local geometry strategy, and a secondary medial axes strategy, whereas the pigeons showed a medial axes strategy. Neither species showed behaviour supportive of the use of principal axes. This is, to our knowledge, the first study to directly examine these three current theories of geometric encoding.
doi:10.1098/rsbl.2010.1024
PMCID: PMC3097861  PMID: 21159689
orientation; geometric encoding; domestic chick; racing pigeon
4.  Is it only humans that count from left to right? 
Biology Letters  2010;6(3):290-292.
We report that adult nutcrackers (Nucifraga columbiana) and newborn domestic chicks (Gallus gallus) show a leftward bias when required to locate an object in a series of identical ones on the basis of its ordinal position. Birds were trained to peck at either the fourth or sixth element in a series of 16 identical and aligned positions. These were placed in front of the bird, sagittally with respect to its starting position. When, at test, the series was rotated by 90┬░ lying frontoparallel to the bird's starting position, both species showed a bias for identifying selectively the correct position from the left but not from the right end. The similarity with the well-known phenomenon of the left-to-right spatially oriented number line in humans is considered.
doi:10.1098/rsbl.2009.0960
PMCID: PMC2880063  PMID: 20071393
avian brain; mental number line; domestic chick; Clark's nutcracker

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