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皮层中颞叶内侧区(MSTd)的追踪速度补偿

Pursuit speed compensation in cortical area MSTd.

作者信息

Shenoy Krishna V, Crowell James A, Andersen Richard A

机构信息

Division of Biology, California Institute of Technology, Pasadena, California 91125, USA.

出版信息

J Neurophysiol. 2002 Nov;88(5):2630-47. doi: 10.1152/jn.00002.2001.

Abstract

When we move forward the visual images on our retinas expand. Humans rely on the focus, or center, of this expansion to estimate their direction of self-motion or heading and, as long as the eyes are still, the retinal focus corresponds to the heading. However, smooth pursuit eye movements add visual motion to the expanding retinal image and displace the focus of expansion. In spite of this, humans accurately judge their heading during pursuit eye movements even though the retinal focus no longer corresponds to the heading. Recent studies in macaque suggest that correction for pursuit may occur in the dorsal aspect of the medial superior temporal area (MSTd); neurons in this area are tuned to the retinal position of the focus and they modify their tuning to partially compensate for the focus shift caused by pursuit. However, the question remains whether these neurons shift focus tuning more at faster pursuit speeds, to compensate for the larger focus shifts created by faster pursuit. To investigate this question, we recorded from 40 MSTd neurons while monkeys made pursuit eye movements at a range of speeds across simulated self- or object motion displays. We found that most MSTd neurons modify their focus tuning more at faster pursuit speeds, consistent with the idea that they encode heading and other motion parameters regardless of pursuit speed. Across the population, the median rate of compensation increase with pursuit speed was 51% as great as required for perfect compensation. We recorded from the same neurons in a simulated pursuit condition, in which gaze was fixed but the entire display counter-rotated to produce the same retinal image as during real pursuit. This condition yielded the result that retinal cues contribute to pursuit compensation; the rate of compensation increase was 30% of that required for accurate encoding of heading. The difference between these two conditions was significant (P < 0.05), indicating that extraretinal cues also contribute significantly. We found a systematic antialignment between preferred pursuit and preferred visual motion directions. Neurons may use this antialignment to combine retinal and extraretinal compensatory cues. These results indicate that many MSTd neurons compensate for pursuit velocity, pursuit direction as previously reported and pursuit speed, and further implicate MSTd as a critical stage in the computation of egomotion.

摘要

当我们向前移动时,视网膜上的视觉图像会扩大。人类依靠这种扩张的焦点或中心来估计自身运动或前进的方向,并且只要眼睛保持静止,视网膜焦点就与前进方向相对应。然而,平稳跟踪眼球运动给不断扩大的视网膜图像增加了视觉运动,并使扩张焦点发生位移。尽管如此,人类在跟踪眼球运动过程中仍能准确判断自己的前进方向,即使视网膜焦点不再与前进方向相对应。最近对猕猴的研究表明,对跟踪的校正可能发生在内侧颞上区(MSTd)的背侧;该区域的神经元会根据焦点的视网膜位置进行调整,并且它们会修改其调谐以部分补偿由跟踪引起的焦点偏移。然而,问题仍然存在,即这些神经元在更快的跟踪速度下是否会更大程度地改变焦点调谐,以补偿更快跟踪所产生的更大焦点偏移。为了研究这个问题,我们在猴子对一系列模拟自我或物体运动显示以不同速度进行跟踪眼球运动时,记录了40个MSTd神经元的活动。我们发现,大多数MSTd神经元在更快的跟踪速度下会更大程度地改变其焦点调谐,这与它们无论跟踪速度如何都能编码前进方向和其他运动参数的观点一致。在整个群体中,补偿增加率随跟踪速度的中位数为完美补偿所需值的51%。我们在模拟跟踪条件下记录了相同神经元的活动,在该条件下注视固定,但整个显示反向旋转以产生与实际跟踪期间相同的视网膜图像。这种条件产生的结果是,视网膜线索有助于跟踪补偿;补偿增加率为准确编码前进方向所需值的30%。这两种条件之间的差异具有显著性(P < 0.05),表明视网膜外线索也有显著贡献。我们发现,偏好的跟踪方向和偏好的视觉运动方向之间存在系统性的反对齐。神经元可能利用这种反对齐来结合视网膜和视网膜外的补偿线索。这些结果表明,许多MSTd神经元会补偿跟踪速度、如先前报道的跟踪方向以及跟踪速度,进一步表明MSTd是自我运动计算中的一个关键阶段。

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