Neural mechanisms of colour appearance across the lifespan

健康的老年人很难完成许多对年轻人来说很简单的视觉任务。由于多种因素，视觉问题在成人衰老过程中会增加，这些因素与视觉皮层抑制作用的降低和神经噪声的总体增加有关。也许令人惊讶的是，颜色外观是一个在整个生命过程中保持相对稳定的过程，低水平的变化由仍然知之甚少的中央皮层机制补偿。但是，大脑皮层补偿颜色外观变化的机制只对相对较大的刺激有效；小刺激的外观仍然受到影响，因为衰老会导致感知场大小的扩大（回顾，见Werner， Delahunt, Hardy, 2004）。由于图像的空间属性是颜色外观的核心决定因素，因此它们的操作为研究代偿神经机制提供了一条有希望的途径，从而使颜色外观在整个生命周期中保持稳定。在这个项目中，我们的目标是首次使用心理物理和脑电图（EEG）方法的结合来表征这些代偿性神经机制。该项目结合了Martinovic博士的色彩心理物理实验室的优势，该实验室关注空间色彩视觉的神经基础（例如，Jennings和Martinovic， 2014），以及Jentzsch博士在使用个体差异（例如衰老）作为询问神经功能的方式方面的专业知识（例如，Strozyk和Jentzsch， 2012）。我们将通过对健康衰老中的颜色外观进行系统的调查来实现我们的目标。我们将研究不同尺寸、不同空间频率、不同接近度和密度以及不同亮度水平的环绕的彩色元素的外观。我们的目标是通过操纵上述列出的因素来建立去饱和和未改变颜色外观之间的边界条件，然后我们将使用瞬态和稳态视觉诱发电位对其进行评估。我们预测，60岁以上的人大脑皮层对低水平色度信号的反应会减少，这将对相对较小的斑块以及周围的斑块的外观产生重大影响。中枢代偿机制可能通过增加信噪比和减少神经噪声来消除这种源自较大刺激大小的感知领域的低水平影响。这些发现对于理解颜色外观的神经基础随着年龄的增长而发生的变化，以及理解代偿皮层机制是如何运作的，都是相关的。它们也将与旨在通过用户友好的设计提高老年人生活质量的行业相关。该项目将为学生在视觉研究和人类神经科学技术方面提供良好的培训前景，例如光度学和使用各种技术和生理色彩空间的亮度和颜色定义，使用Matlab来呈现刺激和分析数据，设计，进行和分析心理物理和脑电图实验，以及与老年人一起工作和评估老年人的经验。获得的技术和实验技能应使学生能够在学术界或工业界从事一系列工作。

Healthy older adults struggle with many visual tasks that appear simple to younger adults. Visual problems increase during adult aging due to multiple factors, related both to reduced inhibition in the visual cortex and to overall increases in neural noise. Perhaps surprisingly, colour appearance is one process which remains relatively stable across life, with lower-level changes compensated for by central cortical mechanisms which remain little understood. But cortical mechanisms that compensate for changes in colour appearance are only effective for relatively large stimuli; appearance of small stimuli is still affected, since aging leads to enlarged perceptive field sizes (for a review, see Werner, Delahunt, Hardy, 2004). As spatial attributes of the image are a core determinant of colour appearance, their manipulation thus provides a promising route for the study of compensatory neural mechanisms that enable stability of colour appearance throughout the lifespan.In this project, we aim to characterise these compensatory neural mechanisms for the first time, using a combination of psychophysical and electroencephalographic (EEG) methods.The project combines the strengths of Dr Martinovic's colour psychophysics lab, which concerns itself with the neural underpinnings of spatiochromatic vision (e.g., Jennings and Martinovic, 2014), with Dr Jentzsch's expertise in the use of individual differences (e.g. aging) as a way of interrogating neural function (e.g., Strozyk and Jentzsch, 2012). We will achieve our aim by conducting a systematic investigation of colour appearance in healthy aging. We will investigate appearance of chromatic elements of different sizes, different spatial frequencies, with surrounds of different proximity and density, and of different luminance levels. We will aim to establish boundary conditions between desaturated and unaltered colour appearance by manipulating the above listed factors, which we will then assess using both transient and steady-state visual evoked potentials. We predict that the cortical responsiveness to low-level chromatic signals will be reduced in over-60 year olds, and that this will have a major impact on the appearance of relatively small patches as well as patches with surrounds falling within their perceptive fields. The central compensatory mechanism may eliminate such low-level influences that originate within perceptive fields for larger stimulus sizes, possibly through an increase in signal-to-noise ratio and reduction in neural noise. The findings will be relevant both for understanding changes in the neural underpinnings of colour appearance with aging, and for understanding of how compensatory cortical mechanisms operate. They will also be relevant for industries which aim to improve the quality of life of the elderly through user-friendly design. The project will offer excellent training prospects for the student in techniques of both vision research and human neuroscience, e.g. photometry and definitions of brightness and colour using various technical and physiological colour spaces, the use of Matlab to present stimuli and analyse data, designing, conducting and analysing psychophysical and EEG experiments, as well as the experience of working with and assessing older participants. The gained technical and experimental skills should enable the student for a range of jobs in academia or industry.