Limits and Localisation of Speed Perception: an investigation of the processing of object speed by the human visual system.

生物体估计周围环境中运动物体速度的能力，为它获得有关外部世界性质的信息提供了一种重要手段。对速度的分析很重要，因为它为生物体跟踪、捕捉甚至避免周围的移动物体提供了基础，这些任务使得对速度的感知对生物体的生存至关重要。这项研究旨在提高我们对人类大脑和视觉系统如何完成速度分析等基本任务的基本了解。直到最近，人们才开始了解如何以及在大脑的哪些部位分析移动物体的速度。然而，尽管洞察力不断增长，但我们的知识仍存在许多差距。有两个基本的问题尚未被探索：1）不同类型的运动提示如何用于速度感知？外部世界中的对象的移动可以通过许多不同种类的运动线索的变化来表示，例如颜色、纹理和光或亮度水平的变化，仅举几例。我们希望研究由各种信息定义的运动是如何被视觉系统处理的，以及在刺激速度的整体分析中，这些线索在多大程度上被结合在一起。在行为实验中，我们将测量人类受试者检测成对移动刺激之间速度差异的能力。特别是，我们将研究如何影响这些速度的判断时，刺激是由不同的运动线索，以及如何判断可以受到影响的存在下，额外的移动刺激，这可能是一个类似或不同的性质，这些刺激被直接比较。在这些条件下，表现如何受到影响，将使我们能够衡量在何种程度上各种刺激属性被视觉系统用于刺激速度的分析。2)在人脑中，对速度的分析是在哪里进行的？最近对猴子的实验已经确定了它们大脑中含有对移动物体速度敏感的神经元的区域。相比之下，对于人类大脑的等效区域是否在刺激速度的分析中扮演类似的角色，我们知之甚少。我们希望确定人脑的哪些区域在分析物体速度时很重要。为了解决第二个问题，类似的行为实验将与一种称为经颅磁刺激（TMS）的技术结合使用。这项技术允许我们在不伤害人类受试者的情况下，用磁场暂时扰乱大脑小区域的运作。基本上，如果某些区域对于刺激速度的分析至关重要，那么我们可以预期，当受试者被要求对视觉呈现的刺激的速度做出判断时，对这些区域的干扰将导致表现的大幅下降。通过刺激人脑的不同区域，我们可以评估它们对刺激速度感知的相对贡献。将视觉表现的行为测量与TMS相结合，将能够得出关于正常人类视觉系统中支持速度感知的神经过程的组织，时间和位置的确切结论。

The ability of an organism to estimate the speed of moving objects in the surrounding environment provides an important means by which it can obtain information about the nature of the outside world. The analysis of speed is important because it provides the basis for enabling organisms to track, catch or even avoid moving objects around it, tasks which make the perception of speed vital to an organism's maintained survival. This research aims to improve our basic understanding about how the human brain and visual system accomplish something as fundamental as the analysis of the speed. It has only been relatively recently that a picture has started to emerge as to exactly how, and in which parts of the brain, the speed of moving objects is analysed. Yet despite growing insight there remain many gaps in our knowledge. Two fundamental questions that have been largely unexplored are: 1) How are different kinds of motion cue used in the perception of speed? Movement of objects in the outside world can be signalled by changes in many different kinds of motion cues, such as changes in colour, texture and light or luminance levels, to name but a few. We wish to examine how motion that is defined by various kinds of information is handled by the visual system and to what extent these cues are combined in the overall analysis of stimulus speed. In behavioural experiments we will measure the ability of human subjects to detect differences in speed between pairs of moving stimuli. In particular, we will examine how these speed judgements can be affected when the stimuli are defined by differing motion cues and how judgements can be affected by the presence of additional moving stimuli which may be of a similar or dissimilar nature to those stimuli being directly compared. How performance is affected under these conditions will allow us to gauge to what extent various stimulus attributes are used by the visual system in the analysis of stimulus speed. 2) Where in the human brain does the analysis of speed take place? Recent experiments on monkeys have identified areas of their brains that contain neurons which are sensitive to the speed of moving objects. By comparison, relatively little is known about whether equivalent regions of the human brain perform a similar role in the analysis of stimulus speed. We want to identify which regions of the human brain are important in the analysis of object speed. To address this second question, similar behavioural experiments will be used in conjunction with a technique known as transcranial magnetic stimulation (TMS). This technique allows us, without harming human subjects, to momentarily disrupt the operation of small regions of the brain with magnetic fields. Basically, if certain areas are crucial for the analysis of stimulus speed, then we would expect that disruption to those areas would lead to major reductions in performance when subjects are asked to make judgements about the speed of visually presented stimuli. By stimulating different areas of the human brain we can assess their relative contributions to the perception of stimulus speed. The combination of behavioural measures of visual performance with TMS will enable firm conclusions to be drawn about the organisation, timing and location of the neural processes that underpin the perception of speed in the normal human visual system.