Evidence for brightness constancy in the mongolian gerbil

Abstract

Event Abstract Back to Event Evidence for brightness constancy in the mongolian gerbil Josephine Henke1, Christian Garbers1, Christian Leibold1, 2, Thomas Wachtler1, 2 and Kay Thurley1, 2* 1 Ludwig-Maximilians-University, Munich, Department Biology II, Germany 2 Bernstein Center for Computational Neuroscience Munich, Germany The mongolian gerbil (Meriones unguiculatus) retina is composed of a combination of two cone photoreceptors that are maximally sensitive at a wavelength of 360 nm and 493 nm, respectively, and one rod photoreceptor with a maximal sensitivity at 501 nm [1]. It is the only known mammal that has a rod receptor with a peak sensitivity at longer wavelength than all the cone receptors. Gerbils therefore exhibit photopic vision with a peak sensitivity at shorter wavelength than that of the scotopic mechanism [2]. Since gerbils can be trained to visual discrimination tasks, their visual capabilities can be analysed in behavioral experiments [1,2]. However, so far little is known about visual processing in these animals. In our behavioral experiments we used a virtual reality (VR) setup with a spherical treadmill that is surrounded by a 360° toroidal screen onto which the virtual environment is projected. This design permits a fixation of the animal such that it can freely rotate around its vertical body axis. The VR setup offers a highly controlled environment for sensory testing. Visual stimuli were presented as a two-alternative choice task using a virtual y-maze in which the animal had to run to the end of the chosen arm to receive a reward. First we trained gerbils to discriminate between bright and dark walls at the ends of the maze arms. In a second set of experiments, we trained the gerbils on the brightness of a central spot relative to its local background. One group of animals had to choose the side with the relative brighter spot and the other group the side with the relative darker spot. Despite differences in the absolute luminance of the stimuli the animals chose the ones with the correct relative brightness. These results are an indication of brightness constancy in the mongolian gerbil.