The neural mechanisms of duration on contrast perception in natural vision

物体的可见性是由其与背景的对比度决定的。但对比感知中还有一个关键因素，人们对它的理解还不太清楚：物体的持续时间。眼球运动、物体在世界中的运动以及随时间变化的照明（例如人工照明中的闪烁）都可以改变物体将光子照射到视网膜感光器上的时间量。心理学实验表明，当一个物体被呈现60- 90毫秒时，明显的对比度，即物体相对于其背景的显著性最高，如果物体被呈现的时间太短或太长，则会降低。 巴罗神经学研究所的斯蒂芬·麦克尼克博士和他的同事们将通过记录视觉皮层单个神经元的电活动来研究这些时间效应背后的神经生理过程。这个项目将提供经验数据，导致这些时间效应如何发生的机械帐户。理解确定对象呈现的最佳持续时间的神经机制可以允许发现人工照明中的最佳闪烁率。可能的是，与当今闪烁照明中所使用的不同的照明中的时间动态可以支持最佳感知并且同时节省功率。 也就是说，如果视觉照明针对人类感知进行优化，则可以在照明设备中使用更少的电流来实现与当前“未优化的”人工照明动态中相同量的表观对比度。为了研究与最佳刺激持续时间相关的神经机制，研究人员将记录初级视觉皮层（V1区）中的ON与OFF神经元，这些神经元分别响应于光的增量和减量而增加和降低其放电率。他们将测试这两种类型的神经元之间的相互作用将解释与不同刺激持续时间相关的感知对比度的变化的假设。 为了确保研究结果适用于真实的世界场景，如办公室和家庭的照明，研究人员不仅使用精心控制的视觉刺激（目标1），而且使用来自自然场景的视觉刺激（目标2）。最后，研究人员将确定更高水平的认知功能，特别是注意力，如何调节单个ON和OFF神经元以及ON和OFF神经元群体之间的相互作用（目标3）。对比度感知是所有视觉的基础，无论是正常的还是患病的。然而，大量的科学文献主要集中在整个视觉空间的对比度，很少有人知道对比度感知如何随刺激持续时间而变化。 目前的项目填补了这一主要的知识空白，考虑到对比度感知的时间方面，并提出了新的作用，以及研究的ON和OFF神经元。

The visibility of an object is determined by its contrast against the background. But there is another critical factor in contrast perception that is less well understood: the object's duration. Eye movements, motion of the object in the world, and lighting that changes over time, such as flicker in artificial lighting, all act to vary the amount of time that the object shines photons onto the photoreceptors of the retina. Psychological experiments showed that the apparent contrast, the salience of the object against its background, is highest when an object is presented for ~60-~90 milliseconds and reduced if the object is presented for too short or too long a duration. Dr. Stephen Macknik and his colleagues at the Barrow Neurological Institute will investigate the neural physiological processes underlying these temporal effects by recording electrical activity of single neurons from the visual cortex. This project will provide the empirical data leading to a mechanistic account of how these temporal effects occur. Understanding the neural mechanisms that determine optimal duration of object presentation may allow the discovery of the optimal flickering rate in the artificial lighting. It is possible that temporal dynamics in lighting that is different from what is used in today's flickering lighting can support optimal perception and at the same time save power. That is, if visual lighting is optimized to human perception, less electrical current could be used in lighting devices to achieve the same amount of apparent contrast as in current "unoptimized" artificial lighting dynamics. To investigate the neural mechanisms associated with optimal stimulus durations, the investigators will record from the ON versus OFF neurons in the primary visual cortex (area V1) that increase and decrease their firing rates in response to light increments and decrements respectively. They will test the hypothesis that the interplay between these two types of neurons will explain the variations in perceived contrast associated with different stimulus durations. To ensure that the findings are applicable to real world scenarios such as lighting in the office and home, the investigators will use not only carefully controlled visual stimuli (Objective 1) but also visual stimuli from natural scenes (Objective 2). Finally, the investigators will determine how higher level cognitive functions, specifically attention, modulates the interactions between both single ON and OFF neurons and populations of ON and OFF neurons (Objective 3). Contrast perception is fundamental to all vision, normal or diseased. Yet the large body of scientific literature has mainly focused on contrast across visual space and little is known about how contrast perception vary with stimulus duration. The current project fills this major knowledge gap by taking the temporal aspect of contrast perception into consideration and suggesting new roles for the well studied ON and OFF neurons.