Neural mechanisms of colour appearance across the lifespan

健康的老年人在许多对年轻人来说简单的视觉任务中苦苦挣扎。由于多种因素，成年后视力问题会增加，这既与视皮层抑制减少有关，也与神经噪音总体增加有关。也许令人惊讶的是，颜色的出现是一个在一生中保持相对稳定的过程，较低水平的变化被仍然鲜为人知的中央皮质机制所补偿。但是，补偿颜色外观变化的皮质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视野的扩大(有关综述，请参阅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，因此它们的处理为研究使颜色外观在整个生命周期中保持稳定的补偿神经机制提供了一条有希望的途径。在这个项目中，我们的目标是首次使用心理物理和脑电(EEG)方法来表征这些补偿神经机制。该项目结合了Martinovic博士的颜色心理物理实验室的优势，该实验室关注空间色觉的神经基础(例如，Jennings和Martinovic，2014)。与Jentzsch博士在使用个体差异(例如，衰老)作为询问神经功能的一种方法方面的专业知识(例如，Strozyk和Jentzsch，2012)。我们将通过对健康老龄化中的颜色外观进行系统的研究来实现我们的目标。我们将研究不同大小、不同空间频率、不同距离和密度以及不同亮度级别的环境中的彩色元素的外观。我们的目标是通过操纵上述因素来建立饱和和未改变的颜色外观之间的边界条件，然后我们将使用瞬时和稳态视觉诱发电位进行评估。我们预测，在60岁以上的人中，大脑皮质对低水平彩色信号的响应性将会降低，这将对相对较小的斑块以及周围处于其感知范围内的斑块的外观产生重大影响。中央补偿机制可能通过增加信噪比和减少神经噪声来消除在较大刺激大小的感知范围内产生的这种低水平影响。这一发现将有助于理解颜色外观的神经基础随年龄的变化，以及了解代偿皮质机制是如何运作的。它们也将适用于那些旨在通过方便使用的设计来改善老年人生活质量的行业。该项目将在视觉研究和人类神经科学技术方面为学生提供极好的培训前景，例如光度学和使用各种技术和生理颜色空间定义亮度和颜色，使用MatLab呈现刺激和分析数据，设计、进行和分析心理物理和脑电实验，以及与年长参与者合作和评估的经验。所获得的技术和实验技能应该使学生能够在学术界或工业中从事一系列工作。

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.