We assessed the ability of an achromatopsic patient to detect and discriminate colour and form concealed in a static or dynamic checkerboard display where the luminance differences among adjacent squares were randomly assigned. There were no conditions under which he could discriminate two very different saturated colours from each other. ...

In the Netherlands veal carcasses are classified according to colour with the aid of a colour scale. The colour scale, existing of five coloured chips, and the results of its application in the classification system were evaluated both theoretically and practically. The result was that theoretically 75% of the samples ...

Monkeys with lesions of visual area V4 have deficits in colour constancy, but are able to discriminate hues and segment the spectrum in a categorical manner. To investigate the nature of the processing mechanisms subserving the spared functions we recorded occipital visual evoked potentials (VEPs) of normal monkeys and monkeys ...

Conventional views of visual perception propose a colour-blind pathway conveying motion information and a motion-blind pathway carrying colour information. Recent studies show that motion perception is not always colour blind, is partially dependent on attention, can show considerable perceptual slowing around isoluminance and is contrast-dependent. If there is a single ...

Additional information is given on the erythrocytic stages of Plasmodium petersi (Poirriez, Baccam, Dei-Cas, Brogan et Landau, 1933), which was found in a Cercocebus albigena monkey from the Central-African Republic. The first colour pictures of P. petersi are presented. In 60% of young trophozoites, the vacuole is divided into two ...

It has been shown in several studies that the selection of letters or numerals from an array can occur efficiently if criteria such as location, colour, shape, or size are used. It is also known that there are at least two components of spatial attention, the transient exogenous and the ...

The albedo hypothesis was tested under apparent transformations of perceived illumination and achromatic colour induced by pseudoscopic inversion of apparent depth. Looking through a pseudoscope made a cone attached to a vertical white screen look like a conical hole in the screen. This in turn caused the shadow which the ...

The aim in this work was to assess the contribution which colour information makes to the perception of motion. Two dependent variables were measured: the reaction time to a sudden cessation of motion (motion-end RT) and the duration of the motion aftereffect (MAE). In each case, a baseline measure of ...

1. An oft-cited view, derived principally from the writings of Gordon L. Walls, is that relatively few mammalian species have a capacity for colour vision. This review has evaluated that proposition in the light of recent research on colour vision and its mechanisms in mammals. 2. To yield colour vision ...

When subjects view an edge in white light, a colour fringe, produced by longitudinal chromatic aberration (LCA) of the eye, is formed at the edge. The colour fringe changes with changes in focus, and serves as a complex colour-coded cue for reflex accommodation. Fincham found that 60% of his subjects ...

The effects of prolonged exposure to intense, short-wavelength light were studied in monkeys through the measurement of increment-threshold spectral sensitivity (ITSS) and threshold-versus-intensity (TVI) functions using a behavioural method. The long-term effect of intense blue-light exposure was to induce a short-wavelength (SW) sensitivity loss which did not depend on the ...

Area V4 has been located in man in the region of the fusiform gyrus on the inferior surface of the occipital lobe. Using multiple dipole source analysis on multichannel EEG recordings of visual evoked potentials to coloured 'Mondrian' stimuli in man, we have confirmed that activity is consistently seen in ...

A stimulus is described that demonstrates the spatial pooling of colour information in the visual system. Chequerboards (or gratings) consisting of alternating squares (or stripes) of complementary colours become achromatic at particular spatial scales; such stimuli have been named 'transchromatic' stimuli. Colour pools are much larger than the receptive fields ...

Reaction time distributions (RTDs) were determined in response to near-threshold increments of long duration. Stimulus parameters were selected to isolate the chromatic and achromatic systems. The RTDs for the achromatic system peak sooner and are more narrow than those obtained for the chromatic system. These results are analyzed in terms ...

Coloured light surrounding a white surface of about equal luminance makes the white surface appear illuminated with an unsaturated light of the complementary colour. In an attempt to discover the neurophysiological basis of such colour induction, we recorded from spectrally opponent cells of the parvocellular layers of the lateral geniculate ...

Our interest is in measuring the threshold for blur, for long borders at well-defined retinal eccentricities between large fields of colour. Our method is to precisely match a centrally fixated sharp-edged disk of one colour against a surround of another, using the minimum distinct border criterion. We then measure the ...

Some people declare that they possess a personal visual representation of numbers: some automatically "see" the numbers they are confronted with in a precise location in a structured mental space, others "associate" specific colours with given numbers. Such visuo-spatial representations of numbers were first described by Galton in 1880 but ...

Colour constancy is traditionally defined as the invariance of perceived surface colours under changes in the spectral composition of the illuminant. Existing quantitative studies show that, by this definition, human subjects show poor colour constancy. A different and complementary aspect of colour constancy is considered which is concerned with the ...

In this paper, a small dual-wavelength light-emitting diode (LED) based detector for FIA process analysers is designed. The detector's optical parts include a flow cell, a dual-wavelength LED and a photodiode. Neither mirrors nor lenses are used. The optical paths for the different light beams are almost the same, distinguishing ...

Behavioural tests were carried out with 9 hymenopteran insect species, which ranked certain sets of coloured stimuli according to their subjective similarity to a previously memorized stimulus. Kendall's tau co-efficient is employed for the analysis of correlation between these similarity rankings and the colour distance rankings predicted by various models ...

To investigate the effects of colour upon motion detection, the short-range motion displacement limit (Dmax) was determined using two-frame kinematograms in which the two classes of square comprising the pattern differed both in luminance and in colour. In the second motion frame, the squares retained either the same luminance and ...

We report experiments which compare the ability of subjects to employ colour vs luminance contrast as a basis for discriminating the degree of collinearity of random element string pairs. The purpose of the study was to determine the extent to which spatial integration mechanisms could utilize colour contrast. In order ...

Two effects which can modify the appearance of a colour seen in a context compared to isolation are chromatic induction and colour constancy. These effects transform colour in ways which depend on the visual system rather than physical characteristics of light and surfaces. They need not reflect different processes within ...

In the circumscribed, long-standing, clinically absolute visual field defects of three patients with vascular lesions that involved the optic radiation and visual cortex, forced-choice discrimination between coloured stimuli was tested. Paired stimuli were matched for luminous efficiency on the basis of previous measurements of increment-threshold spectral sensitivity made in the ...

A new method of measuring normal hue discrimination ellipses and dichromatic zones using a high resolution colour monitor is described. The test involves the detection of chromatic bars on a grey background (x = 0.305, y = 0.323) having a luminance of 34 cd m-2. Elements of the background matrix ...

Colour constancy is traditionally interpreted as the stable appearance of the colour of a surface despite changes in the spectral composition of the illumination. When colour constancy has been assessed quantitatively, however, by observers making matches between surfaces illuminated by different sources, its completeness has been found to be poor. ...

It has been demonstrated widely that at isoluminance moving chromatic stimuli are seen to be stationary or moving more slowly than their luminance counterparts. We have examined the effect on perceived velocity of adding luminance contrast to an isoluminant chromatic stimulus. We show that moving luminance contrast 'captures' colour so ...

Colours of objects tend to be constant regardless of the colour of the illuminant, therefore, regardless of the quanta catch of the retinal cones. Various mechanisms for this including context recognition, adaptation of retinal sensitivities and independent processing by receptor types have been proposed. These present experiments test the hypothesis ...

Depth perception is known to be impaired for chromatic equiluminant patterns. To investigate this phenomenon I have compared the effects of binocularly presented stimuli in the form of stripes, which contain only luminance information with similarly presented stimuli which contain only chromatic information. Observations of the reported percepts for the ...

Two experiments investigated Michotte's launch event, in which successive motion of two objects appears to evoke an immediate perception that the first motion caused the second, as in a collision. Launching was embedded in event sequences where a third event (a colour change of the second object) was established as ...

Recently it has been claimed by Livingstone and Hubel that, of three anatomically and functionally distinct visual channels (the magnocellular, parvocellular interblob, and blob channels), only the magnocellular channel is involved in the processing of stereoscopic depth. Since the magnocellular system shows little overt colour opponency, the reported loss of ...

The first step in this work of reconstruction of a theory of insect vision was to demonstrate that visual behaviour relies on scanning by self-motion and apparently involves measurement of angular velocities of contrasts moving across the eye. The next step was to demonstrate that parallax is also significant as ...

This study presents two distinct effects produced by manipulation of the background illumination on the directional sensitivity to colour- and orientation-carried motion. The two motion percepts were produced with two of a class of stimuli extensively used by the first and last authors in apparent-motion studies. The stimuli were designed ...

The evolution of visual pigment spectral sensitivities is probably influenced by the reflectance spectra of surfaces in the animal's environment. These reflectances, we conjecture, fall into three main classes: i. Most inorganic and many organic surfaces, including tree bark, dead leaves and animal melanin pigmentation, whose reflectance increases gradually as ...

Achromatic constancy refers to the invariance of either lightness or brightness despite changes in illumination intensity. Previous results disagree as to the extent to which constancy occurs with fixed luminance ratio conditions. This may reflect a lack of distinction between lightness and brightness. We measured both lightness and brightness constancy ...

We have measured the chromatic threshold sensitivity to stimuli with spectral composition determined by a periodic function of energy over wavelength. This approach is analogous to frequency studies of spatial vision for the study of colour. A device was constructed permitting the synthesis of illuminants over the entire visible range ...

Synopsis The evaluation of sun-product efficacy, with laboratory solar simulators or in actual sun, implicates clinical and subjective assessment of the various skin responses in terms of wavelengths constitutive of solar light. These photobiological responses vary according to skin types and particularly to basic skin melanic content, i.e. with skin ...

Patients with scotomas or blind-spots in their visual field resulting from damage to the visual pathways often report that the pattern from the rest of the visual field 'fills in' to occupy the scotoma. Here we describe a novel technique for generating an artificial perceptual scotoma which enabled us to ...

Three members of a family with dominantly inherited juvenile optic atrophy with tritan type of colour vision deficiency all showed dysfunction of the rod mechanism tested with green light after 30 min of dark adaptation. Two subjects had typical optic atrophy, centrocaecal scotoma and lower than normal visual acuity. In ...

When spectral light increases in luminance, the hues change. Normally, long-wavelength light becomes increasingly yellow, and short-wavelength light turns blue or blue-green. This is known as the Bezold-Brücke hue shift. Less notice has been paid to the change in relative chromatic content (saturation or chromatic strength) that accompanies these shifts ...

After a 2 h period of dark adaptation the iridescent cornea of the sand goby, Pomatoschistus minutus, responds to illumination by increasing the amplitude of iridescent reflexions and shifting the wavelength of maximum reflexion towards longer wavelengths. This characteristic response is found to occur in both the intact eye and ...

Discussion is focused on the relationship between the new media and the human visual system. First, the process of information transmission in the human visual system is shown as a hierarchically structured model. Second, examples of the human interface in the development of a Japanese teletext system are shown, such ...

This report summarizes the behavioural effects of a right occipital stroke in the author. An upper left quandrantanopia resolved over the first 50 poststroke days to leave a scotoma that included the left upper quadrant of the fovea and extended upwards about 6 degrees and lateral about 15 degrees. There ...

Recent research on aging of chromatic and spatial vision processes is reviewed. Changes in these visual processes with advancing age are largely continuous. Age-related declines in visual performance may be explained in terms of reductions in the illuminance of the visual stimulus due to changes in the ocular media and ...

So far, no epidemiological studies have dealt with the relationship between dark and light pigmented Caucasians and the risk of developing age-related macular degeneration (AMD). Based upon hospital referred eye patients, dark ocular pigmentation has previously been suggested as a protective factor. The present study reviews macular degeneration, defined as ...

The colour-opponent and broad-band channels of the primate visual system originate in the retina and remain segregated through several neural stations in the visual system. Until now inferences about their function in vision have been based primarily on studies examining single-cell receptive field properties which have shown that the colour-opponent ...

When a disc with two dots stuck on it a few centimetres apart is set in slow rotatory motion, the two dots appear displaced in depth and rigidly connected to form the two extremities of a rod. The rod appears as a diaphanous transparent object, slightly tinted to the same ...

We have measured response times for the detection of a single target presented against a set of reference elements which are characterised by combinations of four different stimulus parameters; colour, contrast polarity, magnification and orientation. The aim of the experiments was to determine the response characteristics of visual mechanisms which ...

Edwin Land's Mondrian demonstrations (Land 1977, 1983, 1986a) are striking examples that the perceived colours of objects are largely independent of the chromaticity of the light incident upon them. Attempts to implement this independence in artificial vision systems have renewed interest in colour constancy and contrast, and the explanation of ...

The spectral transmittance characteristics of each of thirty-two solid tint hydrogel contact lenses available in the United Kingdom were investigated using a dual beam spectrophotometer. Good agreement was found with the small number of spectral functions that had previously been published. Lenses with similar colour appearances were seen to differ ...