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Jonathan T Erichsen, Christopher M Dillingham, John A Barnes, Turgut Meydan, Tomasz Kutrowski, Noor Aldoumani; Saccadic and optocollic head movements in homing pigeon (Columba livia). Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2909.
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© ARVO (1962-2015); The Authors (2016-present)
Quantitative measurement of the dynamical properties of visuomotor movements provides useful information about the interrelationship between the sensory capabilities of the visual system and the control of motor responses in people and other animals. The purposes of this study in pigeon were: 1) to define the main sequence of saccadic head movements, and 2) characterise the nature and thresholds of the reflexive optocollic response to an OKN stimulus.
To investigate saccadic head movements, 17 birds were placed in a Perspex box with a transparent lid, and the angular position of their heads was recorded with a high-speed video camera (500fps). Both spontaneous movements and those in response to a non-localisable auditory stimulus were measured. A second group of birds (n=9) were gently restrained and placed in the centre of an arena comprising 6 LCD monitors on which could be displayed a vertical square wave (0.16 cycles/°) OKN stimulus moving at different velocities. Head position was recorded with a digital camera (60fps). In both experiments, horizontal head angle was determined frame by frame with purpose-designed software using LabView.<br /> <br /> The OKN stimuli were presented either: a) using stepped increases (2, 4, 6, 8 or 10°/s) of velocity from 2 to 60°/s with each step lasting 10 or 20s, or b) at randomly chosen velocities (1-100°/s) that lasted 60s.
The slope of the approximately linear relationship between the peak velocity and amplitude of the pigeons’ head movements was considerably higher for movements in response to an auditory stimulus. Similar to humans, the duration of head movements over a range of 7° to 70° is relatively constant and shorter in response to sound (110ms vs 150ms). In response to the stepped OKN stimulus, slow phases of the pigeons’ head responses had a gain close to 1 up to a velocity of 50-60°/s, above which the gain decreased to below 0.5. In contrast, random presentation resulted in a drop in gain above 30°/s. Responses were only recruited above a velocity threshold of 5°/s. At higher velocities, attaining a gain of 1 took progressively longer.
Saccadic head movements in pigeons reveal a main sequence similar to that of head movements in humans. Ramping up the speed of the OKN stimulus at least doubles the velocity at which the bird achieves a gain of 1, suggesting only a limited range of visual velocities are capable of recruiting the optocollic response.
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