The link between the activity of neurons and our perception of the world remains one of the central questions in visual neuroscience. Pursuit of this issue has been a major theme of my research since I was a post-doctoral research fellow. At that time, I investigated spatial pattern vision in terms of its sensitivity to luminance contrast and the ability to resolve small changes in the spatial configuration of the pattern. In both cases, Mike Hawken and I successfully identified neurons in V1 of the anaesthetized macaque monkey whose responses were statistically reliable enough to account for human psychophysical thresholds. Given the close similarities in the anatomical structure of the visual apparatus of Old World monkeys and humans, this comparison is highly convincing. However, much more direct evidence can be obtained from experiments in which cortical neurons are recorded at the same time as an awake, trained animal is making psychophysical judgments (Parker and Newsome, 1998). This is now a major focus of work in the research group. Recently completed and ongoing projects that use this technique include: the measurement of stereoacuity in V1 neurons (Prince et al, 2000), the response of V5/MT neurons to perceptually reversible figures (Dodd et al. 2001; Parker et al., 2002) and extensions of these paradigms to V2, V3 & V3A.
A different line of research was opened up during a year spent at the MIT Artificial Intelligence Laboratory in order to learn more about the computational approach to vision (supported by a personal research award from the System Development Foundation and hosted by Tomaso Poggio). From this experience, I was appointed to a Lecturership in Physiology at Oxford under the Alvey/IT scheme and initiated a programme of work on binocular stereoscopic vision in biological organisms. The broad aim was to discover whether there were direct correlates in physiological systems of the mechanisms hypothesised on computational grounds. The initial approach used psychophysics with human observers. During this phase, my group investigated the use of binocular stereopsis in human 3-D shape perception, the psychophysical mechanisms underlying binocular correspondence and the statistical pattern efficiency of human stereoscopic vision.  Later we broke away from exclusive use of the traditional random-dot stereogram patterns and investigated human 3-D shape perception with more complex stimuli that included texture, shading, motion and contour cues as well as stereo. 
This line of research spawned two others. In the first, we investigated at the neurophysiological level the fundamental mechanisms underlying stereoscopic depth perception. We successfully established several tests that could distinguish whether a neuron was truly signalling the perception of stereoscopic depth or merely responsive to the stimulus property of binocular disparity. These tests have been applied to V1, with the clear outcome that this cortical area must be a preliminary stage: V1 is primarily responsive to binocular disparity and must be earlier in the processing stream than stages at which depth perception is established (Cumming & Parker, 1997; 1999, 2000). My research group has taken this work forward into V2 and V5/MT, whilst other groups have applied exactly the tests that we devised in other cortical areas: V4, TEo and MST. The second area of work addresses the issue that binocular vision operates within a “visual ecology” in which (a) multiple cues to depth are typically available when inspecting a natural scene and (b) binocular vision can deliver not only depth perception but also assist in breaking camouflage and shape perception. Under a major equipment grant from the Wellcome Trust, my group has recently established a wide-field, virtual reality system, which allows for controlled, dynamic manipulations of multiple cues to depth and 3-D shape with freely-moving human observers. We have therefore moved away from studies with a static human observer inspecting computer display screens. The Getty Research Institute in Los Angeles invited me for two months as a Visiting Scholar to contribute to their theme-year entitled “Frames of Viewing”. This was concerned with the whole range of cognitive, aesthetic and cultural factors that enable humans both to understand and appreciate works of art.
In the UK, our group has established itself with a stable funding structure: (i) our Programme Grant from the Wellcome Trust is in its second 5-year period; (ii) three members of the group (Glennerster, Krug, Bridge) have independent support from the Royal Society, (iii) I was invited by the Director of FMRIB to join the team that has recently applied for the next phase of core support for the FMRIB Centre in the form of a Programme Grant from the MRC and (iv) Dr Wyeth Bair has recently been successful in his application for a Wellcome Trust Senior Fellowship. The work in human MRI builds on research experience that I acquired during a visit to David Heeger’s lab in Stanford in 1999 and, with a further visit by Bridge to Stanford and a successful application for an MRC Project Grant, our group has now established in Oxford the techniques for quantitative, functional MRI of visual cortex. I was recently a co-organizer of a Royal Society Discussion Meeting on the Physiology of Cognitive Processes, which resulted in an edited volume.  I am now Director of the Oxford McDonnell Centre in Cognitive Neuroscience, last academic year I held a Royal Society Leverhulme Senior Research Fellowship and I now hold a Royal Society Wolfson Research Merit Award.

Selected Publications

• Parker Andrew J (2007) Binocular depth perception and the cerebral cortex. Nat Rev Neurosci, 8(5):379-91.

• Glennerster Andrew, Tcheang Lili, Gilson Stuart J, Fitzgibbon Andrew W, and Parker Andrew J (2006) Humans ignore motion and stereo cues in favor of a fictional stable world. Curr Biol, 16(4):428-32.

• Nienborg Hendrikje, Bridge Holly, Parker Andrew J, and Cumming Bruce G (2005) Neuronal computation of disparity in V1 limits temporal resolution for detecting disparity modulation. J Neurosci, 25(44):10207-19.

• Prince S JD, Cumming B G, and Parker A J (2002) Range and mechanism of encoding of horizontal disparity in macaque V1. J Neurophysiol, 87(1):209-21.

• Thomas O M, Cumming B G, and Parker A J (2002) A specialization for relative disparity in V2. Nat Neurosci, 5(5):472-8.

• Dodd J V, Krug K, Cumming B G, and Parker A J (2001) Perceptually bistable three-dimensional figures evoke high choice probabilities in cortical area MT. J Neurosci, 21(13):4809-21.

• Prince S J, Pointon A D, Cumming B G, and Parker A J (2000) The precision of single neuron responses in cortical area V1 during stereoscopic depth judgments. J Neurosci, 20(9):3387-400.

• Neri P, Parker A J, and Blakemore C (1999) Probing the human stereoscopic system with reverse correlation. Nature, 401(6754):695-8.

• Parker A J and Newsome W T (1998) Sense and the single neuron: probing the physiology of perception. Annu Rev Neurosci, 21:227-77.

• Cumming B G and Parker A J (1997) Responses of primary visual cortical neurons to binocular disparity without depth perception. Nature, 389(6648):280-3.