Weiffen Michael, Mauck Björn, Dehnhardt Guido, Hanke Frederike D
Department of General Zoology & Neurobiology, University of Bochum, ND 6/33, D-44780 Bochum, Germany.
Department of General Zoology & Neurobiology, University of Bochum, ND 6/33, D-44780 Bochum, Germany ; Institute for Biosciences, Sensory and Cognitive Ecology, University of Rostock, Albert-Einstein-Str. 3, 18059 Rostock, Germany.
Springerplus. 2014 Nov 25;3:688. doi: 10.1186/2193-1801-3-688. eCollection 2014.
Motion vision is one of the fundamental properties of the visual system and is involved in numerous tasks. Previous work has shown that harbor seals are able to perceive visual motion. Tying in with this experimental finding, we assessed the sensitivity of harbor seals to visual motion using random dot displays. In these random dot displays, either all or a percentage of the dots plotted in the display area move into one direction which is referred to as percent coherence. Using random dot displays allows determining motion sensitivity free from form or position cues. Moreover, when reducing the lifetime of the dots, the experimental subjects need to rely on the global motion over the display area instead of on local motion events, such as the streaks of single dots. For marine mammals, the interpretation of global motion stimuli seems important in the context of locomotion, orientation and foraging. The first experiment required the seal to detect coherent motion directed upwards in one out of two stimulus displays and psychophysical motion coherence detection thresholds were obtained ranging from 5% to 35% coherence. At the beginning of the second experiment, which was conducted to reduce the differential flickering of the motion stimulus as secondary cue, the seal was directly able to transfer from coherent motion detection to a discrimination of coherent motion direction, leftward versus rightward. The seal performed well even when the duration of the local motion event was extremely short in the last experiment, in which noise was programmed as random position noise. Its coherence threshold was determined at 23% coherence in this experiment. This motion sensitivity compares well to the performance of most species tested so far excluding monkeys, humans and cats. To conclude, harbor seals possess an effective global motion processing system. For seals, the interpretation of global and coherent motion might e. g. play a role in the interpretation of optic flow information or when breaking the camouflage of cryptic prey items.
运动视觉是视觉系统的基本特性之一，涉及众多任务。先前的研究表明，斑海豹能够感知视觉运动。结合这一实验发现，我们使用随机点显示来评估斑海豹对视觉运动的敏感度。在这些随机点显示中，显示区域内绘制的所有点或一定比例的点会朝一个方向移动，这被称为相干百分比。使用随机点显示可以在不受形状或位置线索影响的情况下确定运动敏感度。此外，当缩短点的持续时间时，实验对象需要依靠显示区域上的全局运动，而不是局部运动事件，比如单个点的条纹。对于海洋哺乳动物来说，在运动、定向和觅食的背景下，对全局运动刺激的解读似乎很重要。第一个实验要求海豹在两个刺激显示中检测向上的相干运动，得到的心理物理学运动相干检测阈值在5%到35%相干之间。在第二个实验开始时，为了减少作为次要线索的运动刺激的差异闪烁，海豹能够直接从相干运动检测转换为相干运动方向的辨别，即向左还是向右。在最后一个实验中，即使局部运动事件的持续时间极短，海豹的表现依然良好，在这个实验中，噪声被编程为随机位置噪声。在这个实验中，其相干阈值被确定为23%相干。这种运动敏感度与目前测试的大多数物种（不包括猴子、人类和猫）的表现相当。总之，斑海豹拥有一个有效的全局运动处理系统。对于海豹来说，对全局和相干运动的解读可能例如在光流信息的解读中或在识破隐蔽猎物的伪装时发挥作用。
