Minini Loredana, Jeffery Kathryn J
Institute of Behavioural Neuroscience, Department of Psychology, University College London, London WC1H 0AP, United Kingdom.
Learn Mem. 2006 May-Jun;13(3):287-97. doi: 10.1101/lm.84406. Epub 2006 May 16.
Visual discrimination tasks are increasingly used to explore the neurobiology of vision in rodents, but it remains unclear how the animals solve these tasks: Do they process shapes holistically, or by using low-level features such as luminance and angle acuity? In the present study we found that when discriminating triangles from squares, rats did not use shape but instead relied on local luminance differences in the lower hemifield. A second experiment prevented this strategy by using stimuli-squares and rectangles-that varied in size and location, and for which the only constant predictor of reward was aspect ratio (ratio of height to width: a simple descriptor of "shape"). Rats eventually learned to use aspect ratio but only when no other discriminand was available, and performance remained very poor even at asymptote. These results suggest that although rats can process both dimensions simultaneously, they do not naturally solve shape discrimination tasks this way. This may reflect either a failure to visually process global shape information or a failure to discover shape as the discriminative stimulus in a simultaneous discrimination. Either way, our results suggest that simultaneous shape discrimination is not a good task for studies of visual perception in rodents.
视觉辨别任务越来越多地被用于探究啮齿动物的视觉神经生物学，但目前尚不清楚动物是如何完成这些任务的：它们是整体处理形状，还是利用诸如亮度和视角敏锐度等低层次特征呢？在本研究中，我们发现，当大鼠区分三角形和正方形时，它们并非利用形状，而是依赖于下半视野中的局部亮度差异。第二个实验通过使用大小和位置不同的刺激物——正方形和长方形——来阻止这种策略，对于这些刺激物，唯一恒定的奖励预测因素是长宽比（高度与宽度的比率：一种简单的“形状”描述符）。大鼠最终学会了使用长宽比，但只有在没有其他辨别因素可用时才会如此，而且即使在渐近线时，表现仍然很差。这些结果表明，虽然大鼠可以同时处理这两个维度，但它们并非自然地以这种方式解决形状辨别任务。这可能反映出在视觉上处理全局形状信息失败，或者在同时辨别中未能将形状作为辨别刺激物发现。不管怎样，我们的结果表明，同时形状辨别对于啮齿动物视觉感知研究而言并非一个好任务。
