Nordström Karin, Barnett Paul D, O'Carroll David C
School of Molecular and Biomedical Science, The University of Adelaide, Adelaide, Australia.
PLoS Biol. 2006 Mar;4(3):e54. doi: 10.1371/journal.pbio.0040054. Epub 2006 Feb 7.
Detection of targets that move within visual clutter is a common task for animals searching for prey or conspecifics, a task made even more difficult when a moving pursuer needs to analyze targets against the motion of background texture (clutter). Despite the limited optical acuity of the compound eye of insects, this challenging task seems to have been solved by their tiny visual system. Here we describe neurons found in the male hoverfly, Eristalis tenax, that respond selectively to small moving targets. Although many of these target neurons are inhibited by the motion of a background pattern, others respond to target motion within the receptive field under a surprisingly large range of background motion stimuli. Some neurons respond whether or not there is a speed differential between target and background. Analysis of responses to very small targets (smaller than the size of the visual field of single photoreceptors) or those targets with reduced contrast shows that these neurons have extraordinarily high contrast sensitivity. Our data suggest that rejection of background motion may result from extreme selectivity for small targets contrasting against local patches of the background, combined with this high sensitivity, such that background patterns rarely contain features that satisfactorily drive the neuron.
在视觉杂波中检测移动目标是动物寻找猎物或同类时的常见任务，当移动的追捕者需要根据背景纹理（杂波）的运动来分析目标时，这项任务就变得更加困难。尽管昆虫复眼的视敏度有限，但这项具有挑战性的任务似乎已被它们微小的视觉系统解决。在这里，我们描述了在雄性食蚜蝇（Eristalis tenax）中发现的神经元，它们对小的移动目标有选择性反应。尽管许多这些目标神经元会被背景图案的运动所抑制，但其他神经元在令人惊讶的大范围背景运动刺激下，对感受野内的目标运动有反应。一些神经元无论目标与背景之间是否存在速度差异都会做出反应。对非常小的目标（小于单个光感受器视野大小）或对比度降低的目标的反应分析表明，这些神经元具有极高的对比度敏感性。我们的数据表明，对背景运动的抑制可能源于对与背景局部斑块形成对比的小目标的极端选择性，再加上这种高敏感性，使得背景图案很少包含能令人满意地驱动神经元的特征。
