My research examines human visual perception, primarily using techniques from behavioural psychophysics and computational modelling, as well as eye tracking and functional magnetic resonance imaging (fMRI). During my Ph.D., I examined the integrative processes required to perceive multiple directions of motion simultaneously. More recently, my research has focussed on peripheral vision and ‘crowding’ in both the ‘normal’ visual system and in children with amblyopia. Along the way I have also examined visual adaptation, saccadic eye movements, the perception of depth, position, and numerosity, as well as change-detection and attention.
A particular research focus is visual crowding, the deleterious effect of clutter on object recognition. Particularly in the peripheral visual field, objects can be highly visible when presented in isolation and extremely difficult to identify when surrounded by clutter, even when they are scaled to be just as visible (in isolation) as in the fovea. This effect, known as crowding, is of both applied and basic interest. From a clinical perspective, crowding limits the visual function of many patients with low vision, while elevated crowding is associated with common visual disorders such as strabismic amblyopia. It is also of basic theoretical interest because it is crowding, and not acuity or contrast sensitivity, that imposes the principle restriction on visual function in the peripheral visual field. My work examines the mechanisms underlying crowding, using simple stimuli to develop computational models that can be generalized to understand crowding with more complex letter-like stimuli and natural scenes.
Meet the researcher
Dr. John Greenwood’s research on focuses on peripheral vision, or vision outside of the centre of gaze which constitutes 95% of your visual field. The brain devotes less resources to the periphery and as a result uses a number of “short-cuts” to help process information. One of these is called visual crowding and John illustrates the phenomena in the video with several examples. In some visual disorders such as lazy eye and particular types of dyslexia, crowding appears to be even more pronounced so understanding this issue is not only important for normal vision but also for developing appropriate methods for ameliorating it in some patients.
On the web
- Dissociable effects of visual crowding on the perception of color and motion. Proc Natl Acad Sci U S A DOI: 10.1073/pnas.1909011117
- Population receptive field estimates for motion-defined stimuli NeuroImage, 199, 245-260 DOI: 10.1016/j.neuroimage.2019.05.068
- Crowding for faces is determined by visual (not holistic) similarity: Evidence from judgements of eye position. Scientific Reports, 8 (12566), 1-14 DOI: 10.1038/s41598-018-30900-0
- View all publications by John Greenwood