Paul A S Ward

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Visual detection of a line target differing in orientation from a background of lines may be achieved speedily and effortlessly. Such performance is assumed to occur early in vision and to involve filter mechanisms acting in parallel over the visual field. This study establishes orientational limits on this performance and analytically derives some generic(More)
Monocular accommodation responses to stimuli at vergences from 0 to -4.5 D (i.e. effective object-eye distances from infinity to 22 cm) were measured objectively using artificial pupils of 0.5, 0.75, 1.0 and 3.0 mm diameters and a constant retinal illuminance of 7000 td. The slopes of the response/stimulus curves for the 0.75, 1.0 and 3.0 mm pupils agree(More)
A characteristic of early visual processing is a reduction in the effective number of filter mechanisms acting in parallel over the visual field. In the detection of a line target differing in orientation from a background of lines, performance with brief displays appears to be determined by just two classes of orientation-sensitive filter, with preferred(More)
The steady-state, monocular, accommodation response to sinusoidal grating targets (spatial frequencies 0.67, 2.0, 6.0 and 18 c/deg) at effective distances between 0.2 and 1.0 m was measured with a laser optometer, as a function of the grating modulation. In general, only a rather weak dependence of the response on modulation was observed. The results are(More)
  • P A Ward
  • 1987
Accommodation responses to stimuli of various contrasts at a vergence of -5.0 dioptres were measured with an objective infra-red optometer. Both an edge and sinusoidal gratings were employed. The sinusoidal gratings were 1.67, 5.0 and 15.0 c deg-1. The accommodation responses changed little as object contrast was reduced, until an accommodation response(More)
  • P A Ward
  • 1987
Accommodation responses to sinusoidally modulated vertical gratings, at a vergence of -5.0 D, were measured over a 10 min period. Three spatial frequencies were employed: 1.67, 5.0 and 15 cycles degree-1. The results show that 1.67 and 5.0 cycles degree-1 elicit good accommodation responses which are temporally stable. All five subjects employed were unable(More)
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