"I can see it in your eyes: What the Xenopus laevis eye can teach us about motion perception"
The maintenance of visual acuity during active and passive locomotion is ensured by gaze stabilizing reflexes that aim at minimizing retinal image slip. For the optokinetic reflex (OKR), large-field visual motion patterns form the essential stimuli that activate eye movements that follow the motion of the visual surround. Since properties of the visual world are known to influence cognitive motion perception, estimation of visual image velocity and thus the performance of brainstem mediated visuo-motor behaviors might also depend on various characteristics of the image scene. Employing semi-intact preparations of mid-larval stages of Xenopus laevis tadpoles, we studied the influence of contrast polarity, intensity, contour shape and motion stimulus patterns on the performance of the OKR and multi-unit optic nerve discharge during motion of a large-field visual scene. At high contrast intensities, the OKR amplitude was significantly larger for visual scenes with a positive contrast compared to those with a negative contrast. This effect persisted for luminance-matched pairs of stimuli, and was independent of contour shape. The relative biases of OKR performance as well as the independence of the responses from contour shape was closely mirrored by the discharge of the optic nerve in response to the respective stimuli. However, the multi-unit activity of the latter in response to a single moving vertical edge with a height of 2.5 mm was strongly influenced by the light intensity in the vertical neighborhood. This suggests that the underlying mechanism of OKR biases related to contrast polarity directly derives from visual motion processing properties of retinal circuits.
Gravot CM, Knorr AG, Glasauer S, Straka H (2017) It’s not all black and white: Visual scene parameters influence optokinetic reflex performance in Xenopus laevis tadpoles. J. Exp. Biol. 220: 4213-4224. Subject of an Editorial letter in J. Exp. Biol.
Knorr AG, Gravot CM, Gordy C, Glasauer S, Straka H (2018) I spy with my little eye: a simple behavioral assay to test color sensitivity on digital displays. Biol. Open 7: bio035725.