We conduct research with the aim of understanding human

visual perception. What is it that allows us to see the world
as we do? Our research techniques 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:




    visual crowding




A particular 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.


Selected publications:

  1. Greenwood, J. A., Szinte, M., Sayim, B., & Cavanagh, P. (2017). Variations in crowding, saccadic precision, and spatial localization reveal the shared topology of spatial vision. Proceedings of the National Academy of Sciences, 114(17), E3573-E3582. [Download]

  2. Greenwood, JA, Sayim, B, & Cavanagh, P. (2014). Crowding is reduced by onset transients in the target object (but not in the flankers). Journal of Vision, 14(6):2, 1-21. [Download]

  3. Anderson, EJ, Dakin, SC, Schwarzkopf, DS, Rees, G, & Greenwood, JA. (2012). The neural correlates of crowding-induced changes in appearance. Current Biology, 22(13), 1199-1206. [Download]

  4. Greenwood, JA, Bex, PJ, & Dakin, SC. (2012). Crowding follows the binding of relative position and orientation.
    Journal of Vision, 12(3):18, 1-20. [Download]

  5. Greenwood, JA, Bex, PJ, & Dakin, SC. (2010). Crowding changes appearance. Current Biology, 20(6), 496-501. [Download]

  6. Greenwood, JA, Bex, PJ, & Dakin, SC. (2009). Positional averaging explains crowding with letter-like stimuli. Proceedings of the National Academy of Sciences of the United States of America, 106(31), 13130-13135. [Download]



  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. 


Selected publications:

  1. Bossi, M., Tailor, V. K., Anderson, E. J., Bex, P. J., Greenwood, J. A., Dahlmann-Noor, A., & Dakin, S. C. (2017). Binocular therapy for childhood amblyopia improves vision without breaking interocular suppression. Investigative Ophthalmology & Visual Science, 58(7), 3031-3043. [Download]

  2. Tailor, V, Bossi, M, Greenwood, JA & Dahlmann-Noor, A (2016). Childhood amblyopia: Current management and new trends. British Medical Bulletin, 119(1): 75-86. [Download]

  3. Tailor, V, Bossi, M, Bunce, C, Greenwood, JA, & Dahlmann-Noor, A. (2015). Binocular versus standard occlusion or blurring treatment for unilateral amblyopia in children aged three to eight years. Cochrane Database of Systematic Reviews, 11, CD011347. [Download]

  4. Greenwood, JA, Tailor, VK, Simmers, AJ, Sloper, JJ, Bex, PJ, & Dakin, SC. (2012). Visual acuity, crowding and stereo-vision are linked in children with and without amblyopia. Investigative Ophthalmology & Visual Science, 53(12), 7655-7665. [Download]




  motion perception



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 here 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 our motion perception can be multi-valued at a given point in space - as you can see in the gif image here. 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.

Selected publications:

  1. Dakin, SC, Greenwood, JA, Carlson, TA & Bex, PJ. (2011). Crowding is tuned for perceived (not physical) location. Journal of Vision, 11(9):2, 1-13. [Download]

  2. Greenwood, JA & Edwards, M. (2009). The detection of multiple global directions: Capacity limits with spatially segregated and transparent-motion signals. Journal of Vision, 9(1), 1-15. [Download]

  3. Greenwood, JA & Edwards, M. (2007). An oblique effect for transparent-motion detection caused by variation in global-motion direction-tuning bandwidths. Vision Research, 47(11), 1411-1423. [Download]

  4. Greenwood, JA & Edwards, M.  (2006). Pushing the limits of transparent-motion detection with binocular disparity.
    Vision Research, 46(16), 2615-2624. [Download]




  spatial vision





A major focus of our recent research has been to investigate the way we p
erceive the spatial properties of objects. How do we determine the shape and location of an object, or the properties that distinguish one region of texture from another? One recent focus here is position coding - are the processes that determine the perceived position of an object the same as those that determine our perception of its motion? We have also examined individual differences in the perception of object sizes and their relationship with idiosyncrasies in visual regions of the brain, as well as the processes by which we judge the number and density of elements within a given region of space.


Selected publications:

  1. Moutsiana, C, de Haas, B, Papageorgiou, A, van Dijk, JA, Balraj, A, Greenwood, JA, & Schwarzkopf, DS (2016). Cortical idiosyncrasies predict the perception of object size. Nature Communications, 7, 12110. [Download]

  2. Tibber, MS, Greenwood, JA, & Dakin, SC. (2012). Number and density discrimination rely on a common metric: Similar psychophysical effects of size, contrast and divided attention. Journal of Vision, 12(6):8, 1-19. [Download]

  3. Dakin, SC, Tibber, MS, Greenwood, JA, Kingdom, FAA, & Morgan, MJ. (2011). A common visual metric for approximate number and density. Proceedings of the National Academy of Sciences of the United States of America, 108(49), 19552-19557. [Download]




  face recognition





We are also interested in the way we recognise faces.
Many findings suggest that faces are processed in a unique ‘holistic’ fashion within the visual system, unlike other objects. The classic finding in this regard is that the recognition of faces 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 at 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.


Selected publications:

  1. Kalpadakis-Smith, AV, Goffaux, V, & Greenwood, JA (submitted). Crowding is not holistic: Visual similarity determines the effect of clutter on faces. Pre-print online at PsyArXiv. [Web link]

  2. Goffaux, V & Greenwood, JA (2016). The orientation selectivity of face identification. Scientific Reports, 6, 34204.
    [Download]


 

research