Movement perception
Animals move around to find food, shelter, and potential mates, and to avoid being eaten. So they also need to sense visual movement, whether to navigate their way through the world safely or to detect other mobile animals such as approaching friends or foes. Specialised neurons in the visual system of the brain detect movement in the images received by the eyes. The outputs of these neurons are used by the brain to infer the character and cause of the movement. My research investigates how this complex neural process supports our perception of visual movement, using experiments on human observers as well as computer simulations.
The Peripheral Drift or Rotating Snakes illusion has been the focus of my most recent research, in collaboration with Prof. Patrick Cavanagh of York University, Toronto. We have been testing whether this well-known illusion of movement is caused by reflexive changes in pupil diameter that are triggered by blinks and eye movements.
Demonstrations of this and many other motion illusions that I and others have used to study human motion perception can be found on the Motion Demos section of the web site.
Perception of visual art
Artworks are among the most complex and diverse of human achievements. They can be studied from many different perspectives, including their cultural context, the personal and social history of the artist, the techniques and materials used to create the artwork, and so on. The perspective I use as a vision scientist is based on experimental psychology and neuroscience. Visual art is a product of the brain. It depends in particular on the immense mass of neurons the make up the visual system of the brain (the parts of the brain that respond to light entering the eye). Activity in these neurons mediates all of our conscious visual experiences, including those we have when making and viewing art.
The visual system is arguably the most studied neural system in the brain. This scientific knowledge can be applied to help us to understand and appreciate certain aspects of visual art, with the aim of supplementing rather than supplanting the insights of other, more traditional disciplinary perspectives.
In recent research work I have asked whether scientific knowledge about the statistical properties of images can improve our understanding of visual art. The images of the world around us that are captured by eyes and cameras may seem hugely diverse (mountains and seas, tiny insects and huge mammals, modern cities, and so on), but in a statistical sense they are surprisingly predictable. Early digital cameras had a spatial resolution of only 512x512 picture-elements or pixels, each of which could take on one of 256 lightness levels. Even such rudimentary devices had the capacity to capture an almost infinite variety of possible images. The number of unique images available is equal to 256 raised to the power of (512x512), more than the number of atoms in the universe. However, the real-world images that are actually captured by an eye or camera are far from a random selection of these possible images. They constitute a very selective sub-set of the possible images, because natural scenes have certain very consistent properties. For example, the lightness values of neighbouring pixels in real scenes do not vary independently, but are often quite alike because they arise from nearby points on natural surfaces and objects. The visual system can exploit this natural consistency to optimise the way that it processes images. The visual character of artworks should in turn be constrained by the processing strategies built into the visual system of artists and viewers.
The fundamental research question: 'What can we learn about visual art by studying the visual system of the brain, and vice-versa?'
Further details of this research, including the computer algorithms I have used to analyse images, can be found in my publications and in my project pages at the Open Science Framework.
Funding
Leverhulme Emeritus Fellowship (2024-2026)
The Moving Pupil of the Eye and Visual Illusions of Motion
£12,401
ESRC Research Grant (2013-2016)
The Influence Of The Human Form On Visual Judgements Of Movement
£286,945
Wellcome Trust Research Grant (2008-2011)
Computational and psychophysical studies of polarity effects in human visual motion processing
£126,654
EPSRC Network Grant (2004-2005)
Network: Art and Science of Motion Perception
£15,259.
Wellcome Trust Research Grant (2000-2003)
Integrating models of motion analysis in the human visual system.
£116,520
EPSRC Research Grant (1997-2000)
The use of image blur as a depth cue in human vision.
£137,017
EPSRC Research Grant (1993-1996)
Psychophysical studies of interactions between first-order and second-order motion stimuli.
£98,565
MRC Project Grant (1991-1993)
Temporal properties of low-level motion processes in human vision.
£46,155
SERC Research Grant (1990-1993)
Perceptual studies of high level motion processing in the human visual system.
£58,477
SERC Research Grant (1988-1991)
Psychophysical studies of the aperture problem in motion processing.
£47,707
MRC Project Grant (1985-1988)
Spatial and temporal primitives involved in early processing of visual motion.
£12,756