Sneaking a peek: pigeons use peripheral vision (not mirrors) to find hidden food.

A small number of species are capable of recognizing themselves in the mirror when tested with the mark-and-mirror test. This ability is often seen as evidence of self-recognition and possibly even self-awareness. Strangely, a number of species, for example monkeys, pigs and dogs, are unable to pass the mark test but can locate rewarding objects by using the reflective properties of a mirror. Thus, these species seem to understand how a visual reflection functions but cannot apply it to their own image. We tested this discrepancy in pigeons-a species that does not spontaneously pass the mark test. Indeed, we discovered that pigeons can successfully find a hidden food reward using only the reflection, suggesting that pigeons can also use and potentially understand the reflective properties of mirrors, even in the absence of self-recognition. However, tested under monocular conditions, the pigeons approached and attempted to walk through the mirror rather than approach the physical food, displaying similar behavior to patients with mirror agnosia. These findings clearly show that pigeons do not use the reflection of mirrors to locate reward, but actually see the food peripherally with their near-panoramic vision. A re-evaluation of our current understanding of mirror-mediated behavior might be necessary-especially taking more fully into account species differences in visual field. This study suggests that use of reflections in a mirrored surface as a tool may be less widespread than currently thought.

Evidence for interhemispheric conflict during meta-control in pigeons.

In birds each hemisphere receives visual input from the contralateral eye. Since birds have no corpus callosum, avian brains are often seen as 'natural split brains'. How do birds cope with situations, when both hemispheres are brought into conflict? If under such conditions one hemisphere completely determines the response, this is called meta-control. This phenomenon has recently been demonstrated in pigeons. The aim of the current study is to test, if meta-control results from an interhemispheric conflict that would require interhemispheric interaction, possibly via the commissura anterior. To this end, we trained pigeons in a forced-choice color discrimination task under monocular condition such that each hemisphere was trained with a different pair of colors. Subsequently, pigeons were binocularly tested with conflicting and non-conflicting stimulus patterns. Conflicting stimuli indeed produced a delayed reaction time as expected when two divergent decisions create a conflict. In addition, we sometimes observed a pecking pattern that seemed to represent the average of two discrepant and hemisphere-specific movements. Thus, pigeons possibly undergo interhemispheric conflict during meta-control even without a corpus callosum. However, also when having decided to peck a certain color, the planned movement trajectory of the other hemisphere sometimes compromises the final pecking movement.

Pigeons identify individual humans but show no sign of recognizing them in photographs.

Photographs, especially of humans, are widely used as stimuli in behavioural research with pigeons. Despite their abundant use, it is not clear to what extent pigeons perceive photographs as representing three-dimensional objects. To address this question, we trained 16 pigeons to identify individual, real-life humans. This discrimination depended primarily on visual cues from the heads of the persons. Subsequently, the pigeons were shown photographs of these individuals to test for transfer to a two-dimensional representation. Successful identification of a three-dimensional person did not facilitate learning of the corresponding photographs. These results demonstrate limitations of cross-recognition of complex objects and their photographs in pigeons.