A COMPARATIVE STUDY ON OBJECT INVARIANCE IN PIGEONS AND JACKDAWS

Object invariance is the ability to form robust visual object representations in the face of unstable viewing conditions. While object invariance has been extensively investigated in mammals, little is known about how birds solve this formidable computational challenge. Considering the largely independent evolution of mammalian and avian brains, a clade-level comparison of object recognition performance and its associated neuronal adaptations can shed new light on the foundations of high-level vision. In this study we aimed to quantify object invariance performance in pigeons and jackdaws using a two-alternative forced-choice task that requires subjects to recognize two artificial objects under a range of identity-preserving transformations (i.e., rotations in two orthogonal axes, size transformations, and changes of lighting condition). We found significant resemblances between the behavioral signatures of pigeons and jackdaws such that presentations of novel object views resulted in lower recognition performance relative to a trained configuration. Compared to pigeons, however, jackdaws recovered more efficiently from this initial deficit and were able to recognize the objects invariantly by the end of the experiment. While their high late performance is, in principle, primate-like, published research shows that primates needed substantially less training to excel in the task. These results suggest that, although many animals have an ability to recognize objects, their brains have evolved different strategies to process visual input, and these differences seem to be clade-dependent to some extent.