Summary The colour of the hair of 65 subjects was measured using a Minolta Chromameter model CR200. Readings were taken by holding the unit against the back of the subject's head, and recorded using the L*a*b* system of colour co-ordinates. All subjects had hair in which yellow and red (rather ...

It has long been recognised that chromatic aberration can introduce luminance artifacts into nominally isoluminant colour stimuli. In this study the effects of chromatic aberration (along with those of defocus and stimulus spatial frequency) on the chromaticity of the retinal image are considered. Such optical effects have important methodological and ...

Visual search for an element defined by the conjunction of its colour and orientation has previously been shown to be a serial processing task since reaction times increase linearly with the number of distractor elements used in the display. Evidence is presented that there are parallel processing constituents to this ...

The predominant colour of the Anatolian Shepherd dog varies from a dark fawn to light red, with a variable black muzzle and face (mask). Evidence is presented that the colour is due to the dominant yellow allele (Ay) of the agouti locus. Two other frequent colours are white spotting, due ...

Visual objects that differ from the surroundings for some simple feature, e.g. colour or line orientation, or for some shape parameters ("textons", Julez, 1986) are believed to be detected in parallel from different locations in the visual field without requiring a serial search process. Tachistoscopic presentations of textures were used ...

An experiment is described which investigates the spatial determinants of the apparent difference in hue between the central grey patches of chromatic 'H' pattern pairs, an effect similar to that first demonstrated by Wright (1969, The Measurement of Colour, Hilger, London) in coloured gratings. The hue difference is shown to ...

Frequency-dependent predation may maintain or prevent colour pattern polymorphisms in prey, and can be caused by a variety of biological phenomena, including perceptual processes (search images), optimal foraging and learning. Most species are preyed upon by more than one predator species, which are likely to differ in foraging styles, perceptual ...

A computer program was used to generate "populations" of dimorphic "prey" on the screen of a colour monitor. Different subjects were presented with the prey at seven different frequencies and were asked to use a light pen to remove each prey they detected. They all received the same two types ...

We hypothesized that in the decodification of connotative aspects of visual chromatic stimuli the periphery of the body plays an important role. In particular we hypothesized that the decodification process of so called "warm" and "cold" colours is related to a real modification of the temperature of the body which ...

We report measurements on discrimination of orientation and magnification made for elements differentiated in colour and/or luminance from their background. By performing measurements at a series of background luminances and for fixed luminance of the elements, we show that with colour contrast, discrimination for both spatial parameters is unimpaired when ...

In recent years, analysis of the second order statistics of ultrasound speckle has led to accurate prediction and measurements of the average speckle size in the transducer focal zone. In this paper, that work has been extended to the average speckle size as determined by the normalized autocovariance in the ...

A mechanistic model is presented that describes the temporal behaviour of a red-green colour opponent channel such as has been investigated for the macaque monkey. The model incorporates luminance- and chromaticity-adaptation mechanisms. Receptive field properties such as retardation and attenuation of the surround signals with respect to the center signals ...

The iridophores of the Neon tetra Paracheirodon innesi consist of alternating layers of guanine and cytoplasm. In the dark-adapted state the reflected light from constructive interference is in the ultraviolet or blue. When exposed to light the cytoplasm layers increase in thickness and as a result the reflections shift to ...

An achromatic surface in a complex scene has both an apparent reflectance attribute (lightness) and an overall intensitive attribute (brightness). We studied changes of these two attributes as a function of changes in illumination level and pattern complexity. Subjects observed simultaneously two arrays of simulated achromatic surfaces with identical reflectance ...

A skin reflectance spectrophotometer was constructed for determination of colour changes in dermatological disorders. Objective quantification of human skin colour in vivo can be achieved with this apparatus. The spectrophotometer is of simple construction, and it has improved reproducibility compared to previously described instruments. Reproducibility is better than 1.7%, measured ...

Objective changes in colour vision have not been demonstrated previously in patients on long-term amiodarone therapy, although the occurrence of blurring of vision and seeing coloured haloes around lights has been widely reported. In a masked study, colour vision was assessed in 15 patients who had been treated with amiodarone ...

An experimental examination was made of some paradigms designed to isolate the opponent-colour system at increment threshold. The effectiveness of a uniform white conditioning field spatially coincident with a 1.05-deg uniform test field was assessed by measuring intensity thresholds for simple detection and for colour discrimination. Values were obtained both ...

The contribution of colour opponent mechanisms to detection thresholds is investigated at different spatial frequencies by presenting monochromatic, sinusoidal gratings on a uniform white background. Colour opponent mechanisms, characterised by a triple peaked spectral sensitivity function, determine threshold at low spatial frequencies (below 1 c/deg) and their contribution flattens the ...

Colour vision is spatially organized. A light stimulus has to strike spectrally different photoreceptors, covering the center and surround of the receptive field of a colour opponent retinal ganglion cell. Otherwise, no colour opponent processing of signals will occur. Vice versa, spatial summation provided by a large field may compensate ...

Simultaneous and successive methods of comparison of stimuli are studied by comparing experimental results of colour discrimination experiments. In this way, colour differential thresholds for two normal observers and four different stimuli were measured by the two methods. In most cases, the capacity to discriminate colour decreased when the successive ...

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 ...

The Australian sheep blowflies Lucilia cuprina were trained by presenting droplets of sugar solution on a light spot of blue (460 nm wavelength) or green (520 nm wavelength). During the test, the searching behaviour was elicited by sugar stimulation. Then, the flies were allowed to walk in the arena where ...

The temporal resolution of colour vision was measured in freely-flying honeybees by testing the performance of trained bees in discriminating between two stimuli, one of which presented a steady, homogeneous mixture of two colours, while the other offered a heterochromatic flicker between the two colours at various temporal frequencies. Pairwise ...

Freely flying bees were rewarded with sugar solution on a variety of black-and-white shapes as well as on coloured gratings in various training situations. In subsequent dual-choice tests, the bees' discrimination between the various shapes was measured. In addition, the bees were video-filmed while flying in front of the shapes. ...

The spectrophotometric method of colour measurement was applied to an investigation of the colour stability of dimethacrylate based composite resins exposed to thermal and photochemical aging. A good correlation was observed between visual perception of colour change and the spectrophotometric colour difference [delta E (FMC-2)] of unexposed and aged specimens, ...

This paper is about the visual requirements for reading with normal vision. It is the first in a series devoted to the psychophysics of reading with normal and low vision. We have measured reading rates for text scanned across the face of a TV monitor while varying parameters that are ...

Very little is known about the effects of visual impairment on reading. We used psychophysical methods to study reading by 16 low-vision observers. Reading rates were measured for text scanned across the face of a TV monitor while varying parameters that are likely to be important in low vision: angular ...

In response to an energy flux density, E(lambda), the output of a linear detector of radiation with spectral response R(lambda) can be calculated by integrating the product R(lambda) E(lambda) over the spectral range for which R (lambda) and E (lambda) are both non-zero. This method is also applied when the ...

Two fields of random dots that were identical except for a slight shift in a central square region were presented in rapid alternation. This produced a vivid impression of a square moving back and forth above the background. When the kinematogram is presented in equiluminous red/green, the motion of the ...

The smallest, continuous target displacement which is sufficient to cause a sensation of movement was measured under conditions of chromatic adaptation. The experiments were carried out for test target and background field wavelengths which selectively isolate the activity of the colour mechanisms of the human eye. The results show that, ...

Colour constancy is commonly considered to be the product both of high-order (cognitive) and of lower-order (retinal) mechanisms. A study is reported of colour appearance in situations where the spectral radiance of an object changes significantly with viewing distance. Subjects were instructed to match the colour appearance of a number ...

A critical survey is made of neurophysiological and psychophysiological investigations of colour vision. A neuronal model of colour-spatial vision is suggested. The model allows a unified explanation of the whole range of psychophysiological phenomena: the mixing of colours of high-frequency image components, the McCollough type colour after-effects, the simultaneous and ...

Red-coloured flicker is claimed to be more epileptogenic than white or that of other colours matched for subjective intensity. A feature of the colour opponent system is that the response of luminosity-sensitive cortical units to stimulation of ganglion cells of a particular spectral sensitivity is reduced when cells of other ...

The squirrel monkey (Saimiri sciureus) exhibits a polymorphism of colour vision: some animals are dichromatic, some trichromatic, and within each of these classes there are subtypes that resemble the protan and deutan variants of human colour vision. For each of ten individual monkeys we have obtained (i) behavioural measurements of ...

A technique is described for the recording of multichannel cerebral evoked potential data and their conversion to colour-coded displays of scalp electrical activity at up to 40 instants in time. Such mapping gives a more readily assimilated picture of the evolution of the potential changes over the scalp than the ...

J.E. Purkynĕ (1787-1869) was one of the leading physiologists in the first half of the 19th century, became the founder of the "exact subjectivism", and remained during his entire life a very careful observer in psychophysical experiments. He made moreover many important discoveries in anatomy, neuroanatomy, embryology and pharmacology. Despite ...

Succeeding in lighting industrial, office and other work environments is dependent on many factors. Good result is not guaranteed if only one of these factors is taken into account. It is essential to choose appropriate light sources and use them correctly for different tasks. Although the amount of light and ...

The reaction of wavelength-selective (WL), wavelength-opponent (WLO) and colour-coded (CO) cells in monkey visual cortex to changes in the wavelength composition of the light reflected from the area in their receptive fields was studied, using multicoloured displays. Wavelength-selective and wavelength-opponent cells were found to be very sensitive to changes in ...

A 31-year-old Japanese male with unilateral bouts of transient visual loss lasting for variable periods of time has been observed. In spite of the prolonged duration of some of these attacks (the longest attack lasted 7 1/2 hours), the patient sustained a relatively small amount of functional damage to the ...

Following adaptation to a moving coloured stimulus pattern the contrast threshold for detecting a similar moving pattern is raised. Threshold elevation is greatest when the adaptation and test patterns have the same direction of motion and the same colour. Unlike most other colour-contingent aftereffects, colour-specificity is preserved under dichoptic viewing ...

Equations have been derived that improve the quantification of sensory equidistant colour and lightness differences. This has been achieved by a physiological approach involving non-linear responses of cone mechanisms and two subsequent stages of linear opponent transformation to describe the Munsell System (Seim and Valberg, 1980). Using the formulation for ...

Contrast detection thresholds for spatiotemporal colour modulation were determined at several retinal locations. Colour discrimination is studied for red-green modulation of a yellow field and for yellow-blue modulation of a white field. For constant target size colour vision deteriorates if the stimulus is moved away from the fovea, but if ...

Light measurements were made at seven sites in the Amazon river system near Manaus. It was found that very little light penetrates into the white water of the Solimões because of the large amount of suspended material it contains. In lakes off the Solimões the suspended material settles out, and ...

The breast can be examined by transillumination with white light. The tissues transmit more light in te red and infrared part of the spectrum than in the blue. Images of the breast are normally recorded on colour infrared film. An alternative to photography is the use of a television camera ...

Cell responses to complex visual patterns such as compositions of broad-band (non-monochromatic) colour areas are presented. Patterns were scanned over the receptive field, and cell response at each point was recorded. "Response patterns" were constructed which display the cell transform of the stimulus pattern. Parvocellular layer (PCL) cells in the ...

This paper deals with a single male subject, M., who has a well-defined visual defect of a kind not previously described. The defect is associated with a potent inhibitory response to long-wavelength stimuli, which spreads for up to 12 deg from the area of stimulation, suppressing M.'s detection of other ...

Reflectance readings with the EEL Reflectance Spectrophotometer, used in many studies of human skin colour, depend on the spatial orientation of the applicator head of the instrument. Variations of over 15% of the calibration value have been observed. The present paper shows that this orientation dependence is due to the ...

Normal and abnormal fundi were photographed at various magnifications in one and the same fundus camera, with and without 'red-free' filters and various types of black-and-white and colour films. Colour diapositive films were copied on various black-and-white negative films, with and without filters. The final negatives were evaluated under magnification ...

Some 5,000 schoolboys of the Khoikhoi, Negro, "Coloured," and Malay populations were screened with the Ishihara plates, and those with defective red-green vision were diagnosed with an anomaloscope. The findings are presented in terms of the six protan and deutan mutant alleles, a few large population-samples (e.g., Nama and Zulu) ...

A "mechanical oscilloscope" is described in which a lightbeam (Z-axis) is projected via a single front aluminized moving mirror. The mirror is mounted in a suspension frame allowing the simultaneous rotation about two mutually perpendicular axes. The linear displacements of two loudspeaker-coils are transformed mechanically into mirror rotations and an ...