He Qing-Zhi

Numerosity perception is an evolutionarily conserved ability observed across diverse taxa, from insects and fish to birds and primates. Unlike traditional visual categories, numerosity possesses an intrinsic metric structure, making it well suited for quantitatively investigating how categorical representations emerge along the visual hierarchy. While numerical representations are well characterized in high-level associative areas of non-human primates and avian species, neuronal processing of numerosity in upstream regions remains largely unexplored. To address this gap, we recorded single-unit activity in the pigeon entopallium during a delayed match-to-numerosity task. We found a subset of neurons that encoded numerosity independently of the non-numerical feature controlled in the corresponding recording session, exhibiting quasi-monotonic increasing (QMI) or decreasing (QMD) response profiles. Compared with QMI neurons, QMD neurons exhibited a markedly later coding window and stronger category discriminability. Moreover, in both neuronal populations, the normalized response functions and category discriminability were better described by compressed numerosity scales than by a linear scale, with the logarithmic scale showing a modest overall advantage. These findings help refine current theoretical frameworks for how numerosity information is extracted and represented along the avian visual processing hierarchy, providing a comparative basis for cross-species research.

Understanding how birds perceive and recognize objects remains a fundamental question in neuroscience. The entopallium, a key node in the avian tectofugal pathway, is involved in complex visual processing, yet its functional organization remains incompletely understood. Here, we systematically mapped entopallium neuronal responses in pigeons using controlled visual stimuli varying in color, shape, and motion. Entopallium neurons exhibited strong hue selectivity invariant to luminance, pronounced orientation tuning to shape stimuli, and robust direction selectivity to motion. Spatial analyses revealed distinct functional segregation, with color-selective neurons localized anteroventrally, shape-selective neurons dorsally, and motionselective neurons posteriorly. Despite this segregation, a subset of neurons exhibited joint tuning across stimulus dimensions, suggesting an integrated yet modular organizational scheme. Notably, entopallium neurons exhibited a moderate level of feature integration, sharing key characteristics with early to intermediate stages of mammalian visual processing. Together, these findings establish the entopallium as a central hub for multidimensional visual processing in birds and provide new insights into the convergent evolution of sophisticated visual systems across vertebrates.