Biomedical subjects

R W Ditchburn

Publications and source records attributed to R W Ditchburn.

14 recordsLinked to original sources

PubMed1987

What is psychophysically perfect image stabilization? Do perfectly stabilized images always disappear?: comment.

This Communication calls attention to an earlier paper [L. E. Arend and G. T. Timberlake, J. Opt. Soc. Am. A 3, 235 (1986)] in which direct measurements have shown that retinal-image movements less than 1 arc min are required for perfect stabilization. It also cites papers that show that stabilized images of targets that contain no sharp structure in the foveal region disappear completely and permanently. Other targets disappear and reappear as a whole or as fragments intermittently.

Humans↗

PubMed1986

Effect of imposed retinal image movements on colour vision at a heterochromatic boundary in a stabilized retinal image.

A stabilized image, including a straight-line boundary between two areas of different colour was displayed. Movements normal to itself were imposed on this boundary while other boundaries remained stabilized. Broad band filters giving red, yellow, green and blue were used in various pairs. Step movements, pulse movements and oscillatory movements (including sinusoidal, triangular and square wave forms) were applied in turn. Threshold movements to give perception of hue were measured for steps and pulses and signal/photon-noise ratios were calculated for a red/blue boundary. The ratio was found to be constant at a value of about 20 when the retinal illuminance (ER) varied between 5 td and 60 td. When ER was increased (up to 2000 td) the ratio increased rapidly. None of the colour appearances produced by moving the boundary exactly matched the corresponding appearances in an unstabilized image, though the nearest matches were obtained with oscillatory movements of frequency 2 Hz and displacement greater than 5'.

Color Perception↗

PubMed1985

Effect of imposed step-movements and pulse-movements of the retinal image on perception of hue with coloured targets.

There is strong experimental evidence that colour discrimination depends upon signals originating at colour boundaries. Controlled movements were imposed on a boundary between an illuminated coloured area and a dark area in a previously stabilized image. Red, yellow, green and blue fields were used. Step-movements of amplitude M min arc and pulse-movements of amplitude M min arc and pulse width tau s were studied. The movement M50 to produce 50% positive responses for perception of hue was measured as a function of retinal illuminance, boundary length and speed for step-movements and pulse-width (tau) for pulse movements. Signal/photon-noise ratios were calculated.

Color Perception↗

PubMed1985

Effect on perception of hue of imposed oscillatory movements of a stabilized retinal image.

A stabilized image of a coloured square seen against a black background was produced. After the image had faded, oscillatory movements were applied in a direction parallel to a diagonal so that all boundaries had an equal component of motion normal to themselves. Movements of different frequency, amplitude and wave-form were studied. Most of the experiments were carried out at fairly high retinal illuminance (80-500 td). The objective was to find the amplitude and frequency required for perception of hue and saturation. It was found that these movements had (i) a minimum amplitude of about 5' (10' peak-to-peak), (ii) a minimum velocity of 15'(-1) and (iii) a frequency range from about 1 Hz to about 4 Hz. The movements required are larger than those required for perception of the shape of the target and also larger than the normal movements which remain when a subject fixates a well-defined mark. Also the movements associated with the perception of hue and saturation are restricted to a narrower frequency range. These features probably imply that it is necessary to excite numbers of cones covering a minimum area to give perception of hue and saturation.

Color Perception↗

PubMed1983

Information concerning colour derived from a single boundary.

Two experiments are described in which visual information is derived from a single moving boundary in the retinal image, all other boundaries being stabilized so that they contribute no visual information. In this situation the subject perceives the same colours on the two sides of the boundary as would be perceived in normal vision when, owing to eye-movements, all boundaries in the retinal image are moving relative to the retina. Thus complete information leading to perception of hue and saturation as well as brightness, and not merely differences of hue etc. on the two sides, can be derived from a single boundary.

Color Perception↗

PubMed1980