Graeme Phillipson MRes

Graeme Phillipson


Publications:
2010
  Algorithms for automatic neuron tracing in noisy 3D image stacks
Knowles-Barley, S, Phillipson, G, Teriakidis, A, Sterratt, D, Larkworthy, T, O'Leary, T, Down, MP, Hennig, M, Withers, JPJ & Hull, M 2010, 'Algorithms for automatic neuron tracing in noisy 3D image stacks' Neuroscience Day 2010, Edinubrgh, United Kingdom, 29/03/10 - 29/03/10, .
General Information
Organisations: Institute for Adaptive and Neural Computation .
Authors: Knowles-Barley, Seymour, Phillipson, Graeme, Teriakidis, Adrianna, Sterratt, David, Larkworthy, Thomas, O'Leary, Timothy, Down, Matthew P., Hennig, Matthias, Withers, James P. J. & Hull, Michael.
Publication Date: 2010
Publication Information
Category: Poster
Original Language: English
  GPU Computing for 3D Data Annotation
Knowles-Barley, S, Teriakidis, A, Phillipson, G, Sterratt, D & Willshaw, D 2010, 'GPU Computing for 3D Data Annotation'.
A quick, flexible, accurate and automatic volumetric image processing software package will enable biomedical researchers to analyse orders of magnitude more data. In particular this could have a huge impact on the advancement of the field of neuroscience and our understanding of the brain. For certain operations Graphics Processing Unit (GPU) processing is many times faster than performing the same operations on a standard computer Central Processing Unit (CPU).
General Information
Organisations: Institute for Adaptive and Neural Computation .
Authors: Knowles-Barley, Seymour, Teriakidis, Adrianna, Phillipson, Graeme, Sterratt, David & Willshaw, David.
Publication Date: 2010
Publication Information
Category: Poster
Original Language: English
  A specialization for vertical disparity discontinuities
Serrano-Pedraza, I, Phillipson, G & Read, J 2010, 'A specialization for vertical disparity discontinuities' Journal of Vision.
Because our eyes are set apart horizontally in our head, most disparities between the retinal images are horizontal. However, vertical disparities also occur, and can influence depth perception. The classic example is Ogle's induced effect (K. N. Ogle, 1938), in which applying a uniform vertical magnification to one eye's image produces the illusion that the surface has been rotated around a vertical axis. This is thought to be because uniform vertical magnifications can be produced in natural viewing when the eyes are in eccentric gaze (J. E. Mayhew, 1982; J. E. Mayhew H. C. Longuet-Higgins, 1982). Thus, vertical magnification is taken by the visual system as indicating that the viewed surface is slanted away from the line of sight. Here, we demonstrate that the induced effect becomes stronger when the sign of the magnification alternates across the visual field. That is, as one moves horizontally across the screen, the left eye's image is alternately stretched and squashed vertically relative to the right eye's image, producing the illusion of a surface folded into triangular corrugations (H. Kaneko I. P. Howard, 1997). For most subjects, slant judgments in this folded surface have lower thresholds and greater reliability than the classic induced effect, where magnification is applied uniformly across the whole visual field. This is remarkable, given that the disparity pattern of the classic induced effect can be produced by real surfaces with the eyes in eccentric gaze, whereas it is not clear that stripes of alternating vertical disparity could be produced by any physically realizable situation. The analogous improvement for alternating horizontal magnification is attributed to neuronal mechanisms which detect the jumps in horizontal disparity that occur at object boundaries. Our results suggest that a similar, previously unreported system may exist for vertical disparity. Jumps in vertical disparity do occur at object boundaries, and we suggest that our surprising results may reflect the activation of neuronal mechanisms designed to detect these.
General Information
Organisations: Neuroinformatics DTC.
Authors: Serrano-Pedraza, Ignacio, Phillipson, Graeme & Read, Jenny.
Publication Date: 2010
Publication Information
Category: Article
Journal: Journal of Vision
ISSN: 1534-7362
Original Language: English
  Stereo correspondence is optimized for large viewing distances
Phillipson, GP & Read, JCA 2010, 'Stereo correspondence is optimized for large viewing distances' European Journal of Neuroscience, vol 32, no. 11, pp. 1959-1969. DOI: 10.1111/ejn.2010.32.issue-11
Stereo ‘3D’ vision depends on correctly matching up the differing images of objects seen by our two eyes. But vertical disparity between the retinal images changes with binocular eye posture, reflecting for example the different convergence angles required for different viewing distances. Thus, stereo correspondence must either dynamically adapt to take account of changes in viewing distance, or be hard-wired to perform best at one particular viewing distance. Here, using psychophysical experiments, we show for the first time that human stereo correspondence does not adapt to changes in physical viewing distance. We examine performance on a stereo correspondence task at a short viewing distance (30 cm) and show that performance is improved when we simulate the disparity pattern for viewing infinity, even though these disparities are impossible at the physical viewing distance. We estimate the vertical extent of the retinally fixed ‘search zones’ as < 0.6° at 14° eccentricity, suggesting that most V1 neurons must be tuned to near-zero vertical disparity. We also show that performance on our stereo task at 14° eccentricity is affected by the pattern of vertical disparity beyond 20° eccentricity, even though this is irrelevant to the task. Performance is best when vertical disparities within and beyond 20° eccentricity both indicate the same convergence angle (even if not the physical angle), than when the pattern of vertical disparity across the visual field is globally inconsistent with any single convergence angle. This novel effect of the periphery may indicate cooperative interactions between disparity-selective neurons activated by the same eye postures.
General Information
Organisations: Neuroinformatics DTC.
Authors: Phillipson, Graeme P. & Read, Jenny C. A..
Pages: 1959-1969
Publication Date: 1 Dec 2010
Publication Information
Category: Article
Journal: European Journal of Neuroscience
Volume: 32
Issue number: 11
ISSN: 0953-816X
Original Language: English
DOIs: 10.1111/ejn.2010.32.issue-11
2009
  Latitude and longitude vertical disparities
Read, JCA, Phillipson, GP & Glennerster, A 2009, 'Latitude and longitude vertical disparities' Journal of Vision, vol 9, no. 13, pp. 11-11. DOI: 10.1167/9.13.11
The literature on vertical disparity is complicated by the fact that several different definitions of the term “vertical disparity” are in common use, often without a clear statement about which is intended or a widespread appreciation of the properties of the different definitions. Here, we examine two definitions of retinal vertical disparity: elevation-latitude and elevation-longitude disparities. Near the fixation point, these definitions become equivalent, but in general, they have quite different dependences on object distance and binocular eye posture, which have not previously been spelt out. We present analytical approximations for each type of vertical disparity, valid for more general conditions than previous derivations in the literature: we do not restrict ourselves to objects near the fixation point or near the plane of regard, and we allow for non-zero torsion, cyclovergence, and vertical misalignments of the eyes. We use these expressions to derive estimates of the latitude and longitude vertical disparities expected at each point in the visual field, averaged over all natural viewing. Finally, we present analytical expressions showing how binocular eye position—gaze direction, convergence, torsion, cyclovergence, and vertical misalignment—can be derived from the vertical disparity field and its derivatives at the fovea.
General Information
Organisations: Neuroinformatics DTC.
Authors: Read, J. C. A., Phillipson, G. P. & Glennerster, A..
Pages: 11-11
Publication Date: 1 Dec 2009
Publication Information
Category: Article
Journal: Journal of Vision
Volume: 9
Issue number: 13
ISSN: 1534-7362
Original Language: English
DOIs: 10.1167/9.13.11