title: Neurons Responsive to Global Visual Motion Have Unique Tuning Properties in Hummingbirds.
abstract: Neurons in animal visual systems that respond to global optic flow exhibit selectivity for motion direction and/or velocity. The avian lentiformis mesencephali (LM), known in mammals as the nucleus of the optic tract (NOT), is a key nucleus for global motion processing [1-4]. In all animals tested, it has been found that the majority of LM and NOT neurons are tuned to temporo-nasal (back-to-front) motion [4-11]. Moreover, the monocular gain of the optokinetic response is higher in this direction, compared to naso-temporal (front-to-back) motion [12, 13]. Hummingbirds are sensitive to small visual perturbations while hovering, and they drift to compensate for optic flow in all directions [14]. Interestingly, the LM, but not other visual nuclei, is hypertrophied in hummingbirds relative to other birds [15], which suggests enhanced perception of global visual motion. Using extracellular recording techniques, we found that there is a uniform distribution of preferred directions in the LM in Anna's hummingbirds, whereas zebra finch and pigeon LM populations, as in other tetrapods, show a strong bias toward temporo-nasal motion. Furthermore, LM and NOT neurons are generally classified as tuned to "fast" or "slow" motion [10, 16, 17], and we predicted that most neurons would be tuned to slow visual motion as an adaptation for slow hovering. However, we found the opposite result: most hummingbird LM neurons are tuned to fast pattern velocities, compared to zebra finches and pigeons. Collectively, these results suggest a role in rapid responses during hovering, as well as in velocity control and collision avoidance during forward flight of hummingbirds.
authors.affiliation: Department of Zoology, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
authors.forename: Andrea H
authors.initials: AH
authors.lastname: Gaede
authors.affiliation: Department of Zoology, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Goller
authors.affiliation: Department of Zoology, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
authors.forename: Jessica P M
authors.initials: JP
authors.lastname: Lam
authors.affiliation: Neuroscience and Mental Health Institute and Department of Psychology, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Wylie
authors.affiliation: Department of Zoology, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada. Electronic address: doug@zoology.ubc.ca.
authors.forename: Douglas L
authors.initials: DL
authors.lastname: Altshuler
mesh_terms: D000818:Animals; D005426:Flight, Animal / Q000502:physiology*; D009039:Motion Perception; D009474:Neurons / Q000166:cytology / Q000502:physiology*; D010775:Photic Stimulation; D020308:Songbirds / Q000502:physiology*; D014795:Visual Pathways
keywords: avian vision; hummingbird; optic flow; pigeon; visual motion processing; zebra finch