Our research aims to understand human visual perception. What is it that allows us to see the world as we do? Research techniques that we use include behavioural psychophysics, computational modelling, eye tracking and functional magnetic resonance imaging (fMRI).
The lab name derives from our research focus on peripheral
(‘eccentric’) vision. The visual system takes a lot of
interesting shortcuts in the periphery that we think can reveal much about visual perception in general. Here’s a selection of some of our current areas of research:
One focus of our research is ‘crowding’ - the deleterious effect of clutter on object recognition. In our visual field, objects are typically easy to see when we look directly at them and difficult to see in the periphery (the ‘edges’ of our vision). This difference is not simply to do with resolution – even when a target object is large enough to be seen in isolation in peripheral vision, the placement of other objects nearby can render the target ‘jumbled’ and impossible to recognise. This is known as ‘visual crowding’. You can see an example below. Fix your gaze on the cross in the centre – the letter ‘E’ should be visible in the left hand side of your peripheral vision. In contrast, you should find it considerably more difficult to identify the central letter of the three on the right, despite all letters being exactly the same size. This is due to crowding. It is crowding and not simple resolution that limits our object recognition over more than 95% of the visual field.
Our interest in crowding stems firstly from this fundamental limitation and much of our research is aimed at understanding its underlying basis. We are also interested in crowding because of its elevation in central/foveal vision during development, and in clinical conditions such as amblyopia (see below) and potentially also in cases of congenital nystagmus and posterior cortical atrophy.
amblyopia & development
Although crowding does not greatly affect the centre of gaze (where you’re looking) in ‘normal’ vision, it becomes elevated the case of strabismic amblyopia, often known as ‘lazy eye’. Amblyopia is the most common cause of visual impairment in children and affects ~3% of the population. It is defined by impaired resolution in one eye that occurs despite optical correction. In addition, the central vision of the amblyopic eye is also strongly affected by crowding – one of our research areas is to examine whether the mechanisms underlying amblyopic crowding are the same as those that produce crowding in our peripheral vision. We are also interested in the development of new treatment programs for amblyopia, specifically those aimed at the development of binocular vision (unlike traditional ‘patching’ approaches).
Recent research suggests that the central vision of children younger than 12 is affected by crowding in much the same way as in cases of amblyopia. That is, where adults can recognise closely spaced objects when gazing directly at them, the same is not true for children. This places a significant restriction on the vision of children and processes such as their ability to learn to read. As with amblyopia, we are investigating whether the same mechanisms could give rise to crowding in all these cases.
How do we see the direction of a moving object? Our visual system is constantly bombarded with motion - both from objects in the visual field and from our own movement through the environment. Determining the dominant motion signal in a given region is a major problem in these circumstances. One focus of our research has been transparent motion - the perception of multiple overlapping planes of motion in the same place at the same time. This poses a problem for many models of motion perception because it demonstrates that motion perception can be multi-valued at a given point in space - as you can see in the gif on the right. We have investigated the maximum number of motion signals that can be seen simultaneously, in order to provide a constraint on these operations, as well as considering the mechanisms that would allow this to be processed within the visual system.
We are also interested in illusions of motion perception and how these processes interact with spatial vision - for instance, we have investigated the De Valois illusion (where moving objects appear to be positioned ahead of their actual positions in space) and its interaction with the magnitude of visual crowding.
How is it that we see the shape and location of objects in our visual field? One key aspect of this process is the retinotopic organisation of visual areas in our brain - neurons adjacent to one another on the cortical surface respond to adjacent regions of space. We have recently examined the heritability of these retinotopic maps in early visual areas, following on from earlier work in which we examined individual differences in the perception of object size and the relationship between these idiosyncrasies and the structure of retinotopic maps in visual cortex. We are also interested in the perception of object position and the processes by which we judge the number and density of elements within a given region of space.
A great deal of research suggests that faces are processed in a unique ‘holistic’ fashion within the visual system, distinct from other objects. The classic finding in this regard is face recognition is disproportionately impaired with upside-down images, compared with the recognition of other objects. We are currently investigating how this ‘special’ processing arises and how it relates to other visual processes.
One aspect of this continues our research focus on visual crowding (as above) - although some studies have suggested that the crowding of faces may operate in a distinct ‘holistic’ fashion, our findings indicate that the disruption to face recognition in clutter follows the same principles as other visual dimensions (like orientation or colour). We have also examined the orientation selectivity of face recognition - the top face on the right has been filtered so that only the orientations near to horizontal remain, while the face below contains only near-vertical orientations. The clearer identity within the top face suggests that horizontal information carries the greatest amount of information relevant for face recognition. We have recently investigated the way that this sensitivity to orientation differs for upright and inverted faces.
Infantile nystagmus (sometimes referred to as congenital nystagmus) is a visual disorder characterised by involuntary eye movements, with associated deficits in visual acuity. Given reports that elevations in crowding may also arise in these instances, we have been examining the properties of crowding in congenital nystagmus in order to test whether the origin of these effects lies in the same mechanism as crowding in amblyopia and the typical visual periphery (as above).