Abstract
Visual perception of the world around us is an essential part of life for almost all species. Past and current literature tells us that visual information is processed in a hierarchical fashion throughout the mammalian visual stream, and yet despite evidence to suggest that the avian visual system is as least as efficient, if not more so, than the mammalian visual system, how birds solve category and object representation in the absence of a cortex is still unknown. The aim of the current experiment was to determine whether birds also display category representation, with a focus on avian and human facial representation in three visual forebrain structures: entopallium (ENTO), mesopallium ventrolaterale (MVL) and the visual wulst (VW). We performed electrophysiological recordings from 14 pigeons during a passive visual looking task that presented birds with five categories of stimuli: human, human scrambled, pigeon, pigeon scrambled and sine gratings. We recorded from a total of 140 cells in ENTO, 121 in MVL and 96 in VW. We found no neurons that fired selectively to pigeon or human faces in either ENTO, MVL or VW. The MVL region did, however, display the highest proportion of category-preference and category-selective cells, suggesting that the region of the brain that may be responsible for categorisation and category-learning could lie within higher-order visual areas, compared to earlier visual areas such as ENTO and VW. The current failure to find face-selective cells (or face-patches) also highlights the need to consider alternative computational mechanisms that might underly visual recognition in non-mammalian species. The use of novel experimental techniques such a fMRI, eye-tracking and comprehensive receptive field mapping will be key in uncovering whether birds exhibit single-cells (or patches) selective for categories or objects, parallel to those found within the mammalian extra-striate cortex.