D Birtles
University College London
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Publication
Featured researches published by D Birtles.
Journal of Vision | 2010
Oliver Braddick; D Birtles; Susanna Mills; Julien Warshafsky; John Wattam-Bell; Janette Atkinson
Coherence thresholds for concentric patterns of contour segments or dot trajectories have revealed differential development and vulnerability of extrastriate form and motion pathways respectively (Braddick et al, Neuropsychologia, 2003). Here we explore the properties of visual evoked potentials (VEPs) specific to form and motion coherence. Coherent contour or motion arrays alternate with incoherent arrays at 0.5-4 Hz. A 2nd harmonic VEP signal (F2) may arise from local changes occuring at each transition, but a first harmonic (F1) must reflect differential responses to coherence and incoherence, indicating global processing. F1 amplitude is approximately linear with coherence for both form and motion, confirming that F1 measures global processing. F2 is independent of coherence for form, and nearly so for motion, implying that it reflects local changes. Occipital F1 amplitudes for motion: form coherence are approximately 2:1. However, this does not reflect underlying sensitivity: psychophysical form and motion coherence thresholds are similar, and extrapolation of the linear region of F1 amplitude vs coherence reaches zero close to threshold coherence in each case. F1 amplitude for both displays increases gradually from 0.5-4 Hz. However, this is opposite to psychophysical coherence sensitivity, which falls over the same range. We conclude: (a) coherence-dependent VEPs provide measures of global form and motion processing, practical for infants and non-verbal (e.g. autistic) children; (b) this response is elicited efficiently at relatively high presentation rates; (c) the level tapped by the VEP does not provide the limiting factor on temporal integration in global perceptual processing.
Current Biology | 2010
John Wattam-Bell; D Birtles; Pär Nyström; Claes von Hofsten; Kerstin Rosander; S Anker; Janette Atkinson; Oliver Braddick
Investigative Ophthalmology & Visual Science | 2003
Janette Atkinson; Oliver Braddick; S Anker; D Birtles; A Barnett; David Edwards; Frances Cowan; Mary A. Rutherford; Eugenio Mercuri; A Mason
Journal of Vision | 2004
Janette Atkinson; John Wattam-Bell; Oliver Braddick; D Birtles; Anna Barnett; Dorothy Cowie
Perception | 2007
John Wattam-Bell; Pär Nyström; Oliver Braddick; D Birtles; Janette Atkinson; Kerstin Rosander; C von Hofsten
In: PERCEPTION. (pp. 3 - 3). PION LTD (2006) | 2006
J Braddick; D Birtles; J Warshafsky; F Akthar; John Wattam-Bell; Janette Atkinson
Journal of Vision | 2011
Janette Atkinson; D Birtles; S Anker; John Wattam-Bell; Mary A. Rutherford; Frances Cowan; David Edwards; Michela Groppo; Oliver Braddick
Investigative Ophthalmology & Visual Science | 2011
Jin Lee; Morag Andrew; D Birtles; John Wattam-Bell; Janette Atkinson; Oliver Braddick
Perception | 2014
D Birtles; Janette Atkinson; S Anker; John Wattam-Bell; Mary A. Rutherford; Frances Cowan; D Edwards; M Groppo; Oliver Braddick
Journal of Vision | 2011
Jin Lee; D Birtles; John Wattam-Bell; Janette Atkinson; Oliver Braddick