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Ilya Khaytin, Xiangmin Xu, Christine E. Collins, Peter M. Kaskan, Daniel W. Shima, Jon H. Kaas, Vivien A. Casagrande; The Organization of the Middle Temporal Visual Area (MT) in Bush Babies and Owl Monkeys Revealed by Optical Imaging. Journal of Vision 2004;4(8):279. doi: 10.1167/4.8.279.
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Area MT has been studied in a variety of primates since its discovery in the early 1970s (Allman & Kaas, 1971). Aspects of the organization of MT remain controversial, including whether properties such as orientation and direction are mapped the same way in MT across species and whether a global retinotopic map can be demonstrated in MT. We used optical imaging to obtain functional maps of MT in bush babies (Otolemur garnetti) and owl monkeys (Aotus trivirgatus). Stimuli were moving full field gratings, random dot stimuli, or retinotopically restricted rectangular or circular windows containing moving gratings. With the full field stimuli, results confirmed that MT in both bush babies and owl monkeys contain a continuous map of orientation. Orientation domain sizes were larger than those seen in area V1, but, like V1, were organized into pinwheels, where the orientation preference map had discontinuity, and linear zones, where orientation preference changed gradually over the area. Maps produced with restricted stimuli showed that retinotopic organization was preserved on both local and global scales. In owl monkeys the cortical magnification factor (CMF) was greater than for bush babies for the central 0–2.5°. In fact, centrally, owl monkeys had a CMF which was more similar to that of macaque monkeys than bush babies. The latter difference may reflect a greater emphasis on central vision in simian compared to prosimian primates. Taken together with previous findings, our results demonstrate remarkable similarities among species, suggesting that the basic organizational features of MT are preserved across primates. (Supported by EY01778 (VAC), S10RR13947 (VAC) and core grants EY08126, HD15052, T32GM07347)
Julia A. Mavity-Hudson, Ronald S. Hamrick, Maria H. Couppis, Meghan E. Jennings
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