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T Troscianko

Publications and source records attributed to T Troscianko.

10 recordsLinked to original sources
PubMed1992

A colour-flicker analysis of visual function in patients with retinal detachment.

Patients with a history of retinal detachment were examined by the following tests: (1) setting of an isoluminant match between yellow and green constituent squares of a checkerboard and (2) measurement of the flicker fusion frequency for a contrast-reversal of this yellow-green pattern. The results suggest that the test may provide useful data for assessing the severity of any damage to a given part of the retina. The fusion frequencies range from over 10 Hz (normal) to about 2 Hz for a severely impaired retina. The data for the relative amounts of red and green light needed to achieve a match rarely show any abnormality; thus, a standard anomaloscope test or pseudoisochromatic plates would not detect these deficiencies.

Adult↗
PubMed1991

The role of colour as a monocular depth cue.

Does colour information play a role in the perception of depth? Its input to stereopsis is weak, and it has been suggested that depth from monocular cues, such as texture gradients, is also abolished at isoluminance (colour contrast with no luminance contrast). We first investigated whether depth from texture gradients disappears at isoluminance. The percept remained unaltered. Further experiments revealed that certain colour gradients (at isoluminance) markedly affected the perceived depth. A gradient in saturation (e.g. red-to-grey) was particularly effective, whereas a red-green hue gradient had no effect on perceived slant. We concluded that colour information can be used by the visual system to encode depth, especially in situations where the visual environments is rich in cues which could be used to signal depth in this way.

Color Perception↗
PubMed1988

Phase discrimination in chromatic compound gratings.

Phase discrimination thresholds were measured for yellow/green isoluminant and non-isoluminant compound gratings in which the amplitude of the two components (f and 3f) was twice the detection threshold. The phase discrimination threshold at isoluminance was worse than in all the other conditions, which gave broadly similar threshold data. It is suggested that this is due to a positional uncertainty in the neural representation of the isoluminant stimuli.

Contrast Sensitivity↗
PubMed1988

Why do isoluminant stimuli appear slower?

There is ample evidence that the perception of movement, both real and apparent, is substantially impaired at isoluminance. Models of movement perception require spatial and temporal information about the stimulus. We ask whether changes at isoluminance result from a spatial or a temporal error or uncertainty. Reaction times to three kinds of stimulus were measured: (a) temporal stimuli, such as the onset of a square in a known location; (b) spatial stimuli, a vernier displacement of two squares; and (c) spatiotemporal stimuli, moving squares either starting or stopping. The results suggest that there is relatively little effect of isoluminance on purely temporal tasks (a). Longer reaction times were, however, obtained for detecting vernier offset (b). The reaction times to moving stimuli (c) were also slower at isoluminance to an extent that implies that perceived velocity at isoluminance is approximately 30% less than that seen at 8% contrast. The slowing of reaction times at isoluminance could be mimicked by adding random positional jitter to a nonisoluminant moving stimulus and also by presenting a low-contrast monochromatic stimulus. A simple explanation of the data is given in terms of a motion-detecting unit coupled to a temporal integrator. It is shown how such a unit can encode perceived velocity. The results of these experiments suggest that the neural coding of isoluminant stimuli is similar to that of low-contrast luminance stimuli and therefore that isoluminance may not be an effective method to find out whether specific visual mechanisms are color-blind.

Adult↗
PubMed1987

Perception of random-dot symmetry and apparent movement at and near isoluminance.

There have been conflicting reports on whether apparent movement in random-dot kinematograms is abolished at isoluminance. The present results suggest that it is, provided that dynamic (uncorrelated) surrounds are used, and the subject has to report the shape of the target rather than the presence of movement in an isolated portion of the target. On the other hand, perception of random-dot symmetry is still possible at isoluminance. The reason for this difference appears to be the need for exact-position information in movement but not symmetry perception. Control experiments suggest that the effects are not due to artefacts such as chromatic aberration in the eye.

Adult↗
PubMed1984

An assessment of two amplitude-compression hearing aid systems, especially in high ambient noise.

A critical test of the suitability of amplitude compression in hearing aid design must look at the performance of such devices with high levels of background noise. A series of tests was carried out, using both normal and hearing-impaired subjects and word-list test material. The results favour some forms of amplitude compression, even under these critical conditions. However, nonlinear compression ('Carrier Clipping') can reduce the signal-to-noise ratio to unity under adverse conditions. Under these circumstances, such compression impairs performance, though in most situations, it is beneficial.

Amplifiers, Electronic↗
PubMed1982

A given visual field location has a wide range of perceptive field sizes.

Increment thresholds were measured at the intersections of a modified Hermann Grid at several retinal locations and at photopic, mesopic and scotopic adaptation levels. On a concentric perceptive field explanation of the illusion, these results suggest that a broad distribution of perceptive field sizes exists at each visual field location. The peak of this distribution lies close to the previously reported perceptive field size at that location. As the adaptation level decreases, the distribution shifts upwards in size. At scotopic levels lateral inhibition only occurs for large stimuli. The size distribution can be used to account for the spatial extent of some contrast phenomena.

Adaptation, Ocular↗