Neural mechanisms of long-range spatial vision: an investigation of perceptive, integrative and association fields across the lifespan

Incoming light is processed by retinal receptors. Light reflected from objects that are nearby each other will fall onto adjacent retinal locations, and will be fed to correspondingly located neurons in the visual cortex. In the visual cortex, units of different complexity will process this information further, ultimately giving rise to our everyday visual experience. The area of space on the retina to which a visual cortex unit responds is called a visual field. The concept of visual fields has played a crucial role in the study of visual perception since the pioneering studies of Hubel and Wiesel in the 1960s. Visual fields determine which information will be bound together and which will be individuated. Away from the centre of the retina, visual fields increase in size, but this size is flexible and, somewhat surprisingly, depends on the strength of the received signals (colour or brightness) as well as the presence or absence of nearby objects, which activate neighbouring neural units. There are also visual fields of different complexity: while neurons in the primary visual cortex simply integrate the amount of brightness or colour contrast that fall within their scope, neurons beyond it integrate or individuate more complex attributes of objects, e.g. orientation, to identify the object's shape. Therefore, visual fields determine information processing across space, especially processing of relatively long-range spatial information, which will be at some distance from each other once we move away from the centre of the retina.

The aim of this project is to build a unitary framework that would encompass neural processing within visual fields of different complexity across the lifespan. Despite years of research, such a unitary framework is still lacking: while we know a lot about "low-level" processing of colour and luminance supported by neurons in the primary visual cortex, the intermediate stages of visual processing are more difficult to probe and distinct aspects of such "mid-level" vision are often studied separately. The uniqueness of our approach is that we will probe visual fields of different complexity, covering both "low" and "mid-level" vision, using the same paradigm. This paradigm is simple yet powerful: it relies on the same stimulus, consisting of multiple oriented elements (black and white gratings known as Gabor patches) that can form different letters, to probe visual fields of different complexity by simply changing the task that the participants are performing: a) detecting the presence or absence of a target element, b) judging its properties, or c) judging the identity of the whole letter. We will establish how visual fields process stimuli defined by brightness, colour, or both, thus integrating all types of contrast visible to the human eye. Finally, we will conduct our experiments on a large sample that consists of participants that are between 20 and 80 years of age. Our experiments will combine behavioural and neuroscientific techniques, using new, state-of-the-art electroencephalographic (EEG) techniques to ascertain which neural mechanisms underlie age-related changes in visual processing. We will determine the degree to which age-related deficits are driven by an increase in neural noise, and relate it to more basic changes in contrast sensitivity. Such analyses of age-related differences will offer an exciting window into the neural mechanisms that sustain information processing in human vision. In this way, this project will not only provide a basis for theoretical developments in visual perception, but will also considerably affect our understanding of the aging of sensory mechanisms. Such information can be used to improve the quality of life for the elderly.

Human vision contains several kinds of visual fields, which organise different types of information. Receptive fields take in basic signals on brightness and colour from the environment, while integrative and association fields constrain more advanced, feature-based processes crucial for perceptual organisation of visual scenes. Similarities and differences between neural processes that occur within different kinds of visual fields have posed an important research question for many years, but despite that we still lack a robust unitary framework that assesses neural processing within all three types of visual fields. Using an established paradigm developed by the investigators, which can probe different visual fields with the same stimulus, this project intends to combine behavioural and neuroscientific techniques to systematically examine processes occurring within receptive, integrative and association fields. We will determine their common processing constraints using stimuli defined by both luminance and colour contrast. We will also trace age-related changes in their function using a large cohort of participants between 20 and 80 years old. The participants will be without neurological or visual deficits, allowing for a thorough insight into healthy aging. We will use powerful, new single-trial EEG methods that are able to quantify both the strength and the variability of neural activity. In this way, we will be able to assess the neural mechanisms that underpin processing of visual information within visual fields of different complexity. By contrasting the strength and variability of neural activity, we will determine the degree to which the neural inhibition model or the information degradation hypothesis can account for the age-related changes in the visual system.

We have identified the following beneficiaries:
Academic community: Primarily of interest to visual and cognitive neuroscientists, the outputs of this project will also appeal more broadly to the fields of psychology, computer science and optometry. Academic work will be presented at a variety of specialist and general neuroscience and vision science conferences, to ensure impact in all these fields. We will explore potential avenues for ophthalmic impact, e.g. in the early diagnosis of visual impairment, as our large dataset will provide normative data on healthy aging of visual mechanisms. Some of the proposed work will complement and feed into an active interdisciplinary project on spatio-chromatic appearance modelling (Wuerger & Martinovic, funded by EPSRC), whose aim is to specify models that are consistent and constrained by biological vision including chromatic processing at different spatial scales. We will further engage with academics from complementary disciplines as part of the workshops on real and virtual environment design, which we intend to organise at the end of the project. There will also be a positive impact on the UK research skill-base as the PDRA and the graduate RA will both obtain a high-level, multi-method research training and interdisciplinary experience. UK is a leader in fundamental research in the fields of cognitive and visual neurosciences and this hard-earned reputation will be reinforced by the projected academic impact of the proposed work.

The public: We will engage the public through science events and through the project's website, which will be regularly updated by the PI and PDRA, populated with Youtube videos and other accessible content. Public engagement activities will be facilitated by the University of Aberdeen's Public Engagement with Research unit and Press and Events Teams. The PI has considerable experience in public engagement and is a member of the STEM network. PDRA will be trained in public engagement by the PI and encouraged to join the STEM network.
Design industries: Even though we propose a fundamental neuroscience project, there are potential applications that may be of high value to the UK at large. In familiar environments humans often reach for objects without looking at them directly, e.g. when grasping a bar of soap in a shower from a small holder cluttered with a facial wash, shampoo, and conditioner. However, failures to perceive due to insufficient object individuation can lead to failures in correct action; bending to reach for a dropped item may lead to falls. Failures to detect information on websites due to reduced visibility caused by clutter are also higher in older adults and can lead to frustration and disengagement with technology. We intend to actively seek applications for our work in the domains of real and artificial environmental design.

Through the North of Scotland Knowledge Transfer Partnership (KTP) centre, we have obtained contact with local experts, including those involved in designing bathrooms in residences for the elderly. The KTP centre will further help to invite relevant stakeholders to our impact workshops, which we will hold to ensure the application of our results. To get a better impression of the challenges posed by visual changes occurring in the healthy ageing population (e.g. reduced ability to see in low lighting, glare sensitivity) we will organise yearly focus groups, recruiting older adults from the School of Psychology participant panel. In essence, these focus groups are also another, more detailed way of engaging with the public. We will also contact organisations representing partially sighted individuals to canvas their views and needs on improving ease-of-access both in terms of interior design and display technologies. Ultimately, the outcome of our work could lead to improvements to "Good Practice in Design for Dementia and Sight Loss", which is a set of guidelines for the use of colour in design.