Colour perception of single and mixed monochromatic lights in the blowfly Lucilia cuprina

Colour perception of spectral lights and mixtures of two monochromatic lights of blue and yellow wavelengths was studied in the blowfly Lucilia cuprina by using a generalization test in which the fly had to compare these lights in memory with coloured papers (blue, green, yellow and red) represented in the test array. Flies trained to a monochromatic light in the wavelength range of 429–491 nm responded to blue; those trained to 502–511 nm to green; and those trained to 522–582 nm to yellow. The maximal generalization for blue was found at 429 nm and that for yellow at 543 nm. Flies trained to the mixtures responded neither to blue, green nor yellow, when the blue component was mixed with the yellow component in a ratio of approximately 1 3. It seems that the fly perceives the mixtures as a neutral or an achromatic light. Colour loci of coloured papers, spectral lights and mixtures of two monochromatic lights used formed blue, yellow and neutral clusters in a colour triangle with respect to generalization responses to test colours.     

Learning and discrimination of coloured papers in the walking blowfly,Lucilia cuprina

Summary A new training and testing paradigm for walking sheep blowflies, Lucilia cuprina, is described. A fly is trained by presenting it with a droplet of sugar solution on a patch of coloured paper. After having consumed the sugar droplet, the fly starts a systematic search. While searching, it is confronted with an array of colour marks consisting of four colours displayed on the test cardboard (Fig. 1). Colours used for training and test include blue, green, yellow, orange, red, white and black.Before training, naive flies are tested for their spontaneous colour preferences on the test array. Yellow is visited most frequently, green least frequently (Table 2). Spontaneous colour preferences do not simply depend on subjective brightness (Table 1).The flies trained to one of the colours prefer this colour significantly (Figs. 5 and 9–11). This behaviour reflects true learning rather than sensitisation (Figs. 6–7). The blue and yellow marks are learned easily and discriminated well (Figs. 5, 9, 11). White is also discriminated well, although the response frequencies are lower than to blue and yellow (Fig. 11). Green is discriminated from blue but weakly from yellow and orange (Figs. 5, 9, 10). Red is a stimulus as weak as black (Figs. 8, 9). These features of colour discrimination reflect the spectral loci of colours in the colour triangle (Fig. 14).The coloured papers seem to be discriminated mainly by the hue of colours (Fig. 12), but brightness may also be used to discriminate colour stimuli (Fig. 13).     

Colour choices of naive bumble bees and their implications for colour perception

The innate preferences of inexperienced bumble bees, Bombus terrestris, for floral colour stimuli were studied using artificial flowers. The artificial flowers provided a colour pattern and consisted of a star-shaped corolla and of central colour patches similar to the nectar guide of natural flowers. The innate choice behaviour was assessed in terms of the number of approach flights from some distance towards the artificial flowers and the percentage of approach flights terminating in antennal contact with the floral guide. The colours of the floral guide, the corolla and the background were varied. It was shown that the innate flower colour preference in bumble bees has two components. 1. The frequency of approaches from a distance is correlated with the colour difference between the corolla and the background against which it is presented. If the corolla colour was constant but its background colour varied, the relative attractiveness of the corolla increased with its colour difference to the background. The colour difference assessment underlying this behaviour on a perceptual basis can be attained by means of colour opponent coding, a system well-established in Hymenoptera. 2. The frequency of antennal contacts with the floral guides relative to that of approach flights cannot be accounted for by colour opponent coding alone. Whether the approach flights are interrupted, or whether they end in an antennal contact with the nectar guide is strongly dependent on the direction (sign) of the colour difference, not only its magnitude. The choice behaviour requires a unique perceptual dimension, possibly that of colour saturation or that of hue perception comparable to components of colour perception in humans.     

Spectral responses and chromatic processing in the dragonfly lamina

The dragonfly Hemicordulia tau has five spectral classes of photoreceptor which drive five lamina monopolars, m1-m5. The monopolars encode spectral information. Here, spectral coding by m2, m4 and m5 are described. m2 is the most sensitive to dim light. m4 and m5 are less sensitive than m2, and so we call them photopic cells. The effects of selective adaptation of receptor inputs to m4 and m5 are unusual. For example, in m4 adaptation of the green receptor suppresses the UV input, but green sensitivity is unaffected, while green adaptation of m5 increases its green sensitivity. In m5 the dark adapted spectral tuning resembles the 520 nm receptor, but on adaptation to 430 nm light this narrows markedly. Adaptation either of green or of UV receptor input to m2 and m4 modifies the time course of responses both to green and to UV, implying that changes in the time courses of monopolar responses with adaptation state do not directly reflect receptor responses (Fig. 2). Finally, the antagonistic surround of m2 is UV sensitive, and of m4 green sensitive (Fig. 3).Abbreviations LMC large monopolar cell - LVF long visual fibre - rf receptive field - SVF short visual fibre     

Visual adaptation and face perception

The appearance of faces can be strongly affected by the characteristics of faces viewed previously. These perceptual after-effects reflect processes of sensory adaptation that are found throughout the visual system, but which have been considered only relatively recently in the context of higher level perceptual judgements. In this review, we explore the consequences of adaptation for human face perception, and the implications of adaptation for understanding the neural-coding schemes underlying the visual representation of faces. The properties of face after-effects suggest that they, in part, reflect response changes at high and possibly face-specific levels of visual processing. Yet, the form of the after-effects and the norm-based codes that they point to show many parallels with the adaptations and functional organization that are thought to underlie the encoding of perceptual attributes like colour. The nature and basis for human colour vision have been studied extensively, and we draw on ideas and principles that have been developed to account for norms and normalization in colour vision to consider potential similarities and differences in the representation and adaptation of faces.     

Biological significance of distinguishing between similar colours in spectrally variable illumination: bumblebees (<Emphasis Type="Italic">Bombus terrestris</Emphasis>) as a case study

Individual bumblebees were trained to choose between rewarded target flowers and non-rewarded distractor flowers in a controlled illumination laboratory. Bees learnt to discriminate similar colours, but with smaller colour distances the frequency of errors increased. This indicates that pollen transfer might occur between flowers with similar colours, even if these colours are distinguishable. The effect of similar colours on reducing foraging accuracy of bees is evident for colour distances high above discrimination threshold, which explains previous field observations showing that bees do not exhibit complete flower constancy unless flower colour between species is distinct. Bees tested in spectrally different illumination conditions experienced a significant decrease in their ability to discriminate between similar colours. The extent to which this happens differs in different areas of colour space, which is consistent with a von Kries-type model of colour constancy. We find that it would be beneficial for plant species to have highly distinctive colour signals to overcome limitations on the bees performance in reliably judging differences between similar colours. An exception to this finding was flowers that varied in shape, in which case bees used this cue to compensate for inaccuracies of colour vision.     

Simultaneous and successive colour discrimination in the honeybee (Apis mellifera)

The colour discrimination of individual free-flying honeybees (Apis mellifera) was tested with simultaneous and successive viewing conditions for a variety of broadband reflectance stimuli. For simultaneous viewing bees used form vision to discriminate patterned target stimuli from homogeneous coloured distractor stimuli, and for successive discrimination bees were required to discriminate between homogeneously coloured stimuli. Bees were significantly better at a simultaneous discrimination task, and we suggest this is explained by the inefficiency with which the bees brain can code and retrieve colour information from memory when viewing stimuli successively. Using simultaneous viewing conditions bees discriminated between the test stimuli at a level equivalent to 1 just-noticeable-difference for human colour vision. Discrimination of colours by bees with simultaneous viewing conditions exceeded previous estimates of what is possible considering models of photoreceptor noise measured in bees, which suggests spatial and/or temporal summation of colour signals for fine discrimination tasks. The results show that when behavioural experiments are used to collect data about the mechanisms facilitating colour discrimination in animals, it is important to consider the effects of the stimulus viewing conditions on results.     

Patterns of chromatic information processing in the lobula of the honeybee, Apis mellifera L

The honeybee, Apis mellifera L., is one of the living creatures that has its colour vision proven through behavioural tests. Previous studies of honeybee colour vision has emphasized the relationship between the spectral sensitivities of photoreceptors and colour discrimination behaviour. The current understanding of the neural mechanisms of bee colour vision is, however, rather limited. The present study surveyed the patterns of chromatic information processing of visual neurons in the lobula of the honeybee, using intracellular recording stimulated by three light-emitting diodes, whose emission spectra approximately match the spectral sensitivity peaks of the honeybee. The recorded visual neurons can be divided into two groups: non-colour opponent cells and colour opponent cells. The non-colour opponent cells comprise six types of broad-band neurons and four response types of narrow-band neurons. The former might detect brightness of the environment or function as chromatic input channels, and the latter might supply specific chromatic input. Amongst the colour opponent cells, the principal neural mechanism of colour vision, eight response types were recorded. The receptive fields of these neurons were not centre surround as observed in primates. Some recorded neurons with tonic post-stimulus responses were observed, however, suggesting temporal defined spectral opponency may be part of the colour-coding mechanisms.     

Visual pigments, oil droplets, ocular media and cone photoreceptor distribution in two species of passerine bird: the blue tit (Parus caeruleus L.) and the blackbird (Turdus merula L.)

The spectral absorption characteristics of the retinal photoreceptors of the blue tit (Parus caeruleus) and blackbird (Turdus merula) were investigated using microspectrophotometry. The retinae of both species contained rods, double cones and four spectrally distinct types of single cone. Whilst the visual pigments and cone oil droplets in the other receptor types are very similar in both species, the wavelength of maximum sensitivity (λ_max) of long-wavelength-sensitive single and double cone visual pigment occurs at a shorter wavelength (557 nm) in the blackbird than in the blue tit (563 nm). Oil droplets located in the long-wavelength-sensitivesingle cones of both species cut off wavelengths below 570–573 nm, theoretically shifting cone peak spectral sensitivity some 40 nm towards the long-wavelength end of the spectrum. This raises the possibility that the precise λ_max of the long-wavelength-sensitive visual pigment is optimised for the visual function of the double cones. The distribution of cone photoreceptors across the retina, determined using conventional light and fluorescence microscopy, also varies between the two species and may reflect differences in their visual ecology. Accepted: 8 January 2000     

Visual detection of paradoxical motion in flies

Summary From psychophysics it is known that humans easily perceive motion in Fourier-stimuli in which dots are displaced coherently into one direction. Furthermore, motion can be extracted from Drift-balanced stimuli in which the dots on average have no distinct direction of motion, or even in paradox -motion stimuli where the dots are displaced opposite to the perceived direction of motion. Whereas Fourier-motion can be explained by very basic motion detectors and nonlinear preprocessing of the input can account for the detection of Drift-balanced motion, a hierarchical model with two layers of motion detectors was proposed to explain the perception of -motion. The well described visual system of the fly allows to investigate whether these complex motion stimuli can be detected in a comparatively simple brain.The detection of such motion stimuli was analyzed for various random-dot cinematograms with extracellular recordings from the motion-sensitive Hl-neuron in the third visual ganglion of the blowfly Calliphora erythrocephala. The results were compared to computer-simulations of a hierarchical model of motion detector networks.For Fourier- and Drift-balanced motion stimuli, the Hl-neuron responds directionally selective to the moving object, whereas for -motion stimuli, the preferred direction is given by the dot displacement. Assuming nonlinear preprocessing of the detector input, such as a half-wave rectification, elementary motion detectors of the correlation type can account for these results.Abbreviations EMD elementary motion detector     

The influence of the development rates of immature stages of Eristalis arbustorum (Diptera; Syrphidae) on adult abdominal colour pattern

Abstract. The abdominal colour pattern of Eristalis arbustorum (L.) shows seasonal variation, with animals emerging in spring being darker than those emerging during summer. One of the most important environmental cues influencing the abdominal colour pattern is developmental temperature. An experiment was carried out to establish which period during the immature stages was important in determining final adult colour pattern. The results indicate a good relationship between the length of the pupal period and both the extent of the paler markings on the abdomen and the grey score of these markings. The length of the larval period did not have any effect on adult colour pattern.     

Optical releasers of the innate proboscis extension in the hoverfly Eristalis tenax L. (Syrphidae,Diptera)

Freshly emerged, inexperienced imagos of the hoverfly Eristalis tenax L. extend their proboscis towards small, yellow colour stimuli, such as anther parts and artificial floral guides. The releasing of this behaviour, which is adapted to pollen feeding, was investigated in behavioural tests using white, UV-reflecting artificial flowers with four small screens illuminated with test stimuli serving as artificial floral guides. The releasing of the innate proboscis extension was tested using monochromatic test lights. Within an intensity range from approx. 5·10¹¹ to approx. 10¹⁴ quanta · cm^-2· s^-1, the flies extended their proboscis only towards green and yellow test lights (approx. 520–600 nm). The inhibition of the innate proboscis extension was tested using mixed light stimuli composed of a yellow monochromatic reference light (560 nm, 10¹³ quanta·cm^-2-1) and of a monochromatic test light. When the reference light was mixed with ultraviolet or blue test lights, the releasing of the innate proboscis extension was strongly inhibited, whereas admixing green/yellow light slightly promoted it; admixing red light had no effect. The results indicate that the releasing of the innate proboscis extension is mediated by the photoreceptor type R8y. Other receptor types which could cause the inhibition of the proboscis reaction are discussed.     

Avian colour perception predicts behavioural responses to experimental brood parasitism in chaffinches

Hosts of cuckoos have evolved defences allowing them to discriminate and reject parasite eggs. Mechanisms of discrimination are mostly visually mediated, and have been studied using approaches that do not account for what the receiver (i.e. host) actually can discriminate. Here, for the first time we apply a perceptual model of colour discrimination to study behavioural responses to natural variation in parasite egg appearance in chaffinches Fringilla coelebs. Discrimination of parasite eggs gradually increased with increasing differences in chromatic contrasts as perceived by birds between parasite and host eggs. These results confirm that colour differences of the eggs as perceived by birds are important integral parts of a matching signal used by chaffinch hosts.     

Behavioural evidence for colour vision in stomatopod crustaceans

If an organism can be taught to respond in a particular way to a wavelength of light, irrespective of that light's intensity, then it must be able to perceive the colour of the stimulus. No marine invertebrate has yet been shown to have colour vision. Stomatopod crustaceans (mantis shrimps) are colourful animals and their eyes have many adaptations which indicate that they are capable of such spectral analysis. We adopted an associative learning paradigm to attempt to demonstrate colour vision. Stomatopods readily learnt to choose some colours from arrays of greys, even when the correct choice colours were darker than the ones they had been trained to. Possible mechanisms underlying colour vision in these animals, and their ecological significance are discussed. A simple model is presented which may help interpret the complex-stomatopod colour vision system and explain some of the learning anomalies.Abbreviations ND neutral density - OD optical density - R8 Retinular cell 8 - R1–7 Retinular cells 1–7 - R1D Distally placed R1–7 retinular cells in mid-band row 1 - e.g. R1P Proximally placed R1–7 retinular cells in mid-band row 1 - D/P Estimate of chromatic signal ratio     

Opponent colour coding is a universal strategy to evaluate the photoreceptor inputs in Hymenoptera

Summary 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 coefficient is employed for the analysis of correlation between these similarity rankings and the colour distance rankings predicted by various models of neural colour computation. The models are based on the measured spectral sensitivities of photoreceptor colour types and use a variety of simple colour coding systems to derive hypothetical colour distances. The correlation between the predictions of the models and the behavioural results serves as a measure for the likelihood of existence of a colour coding system. In all species, the similarity rankings can be best explained by assuming that colour is coded on a perceptual level by two colour opponent mechanisms. Brightness differences are ignored, indicating that an intensity-coding sub-system is not used in colour discrimination by the insects investigated. The weighting factors of the colour opponent mechanisms differ between species in detail, but not in the principles involved. It is thus possible to employ a standard measure of perceptual colour distance (colour hexagon distance) to predict the capacities of colour discrimination adequately in all the tested insects.     

Vocal-auditory functions of the chimpanzee: consonant perception

The perception of consonants which were followed by the vowel [a] was studied in chimpanzees and humans, using a reaction time task in which reaction times for discrimination of syllables were taken as an index of similarity between consonants. Consonants used were 20 natural French consonants and six natural and synthetic Japanese stop consonants. Cluster and MDSCAL analyses of reaction times for discrimination of the French consonants suggested that the manner of articulation is the major determinant of the structure of the perception of consonants by the chimpanzees. Discrimination of stop consonants suggested that the major grouping in the chimpanzees was by voicing. The place of articulation from the lips to the velum was reproduced only in the perception of the synthetic unvoiced stop consonants in the two dimensional MDSCAL space. The phoneme-boundary effect (categorical perception) for the voicing and place-of-articulation features was also examined by a chimpanzee using synthetic [ga]-[ka] and [ba]-[da] continua, respectively. The chimpanzee showed enhanced discriminability at or near the phonetic boundaries between the velar voiced and unvoiced and also between the voiced bilabial and alveolar stops. These results suggest that the basic mechanism for the identification of consonants in chimpanzees is similar to that in humans, although chimpanzees are less accurate than humans in discrimination of consonants.     

Odour and colour information in the foraging choice behaviour of the honeybee

1. Honeybees Apis mellifera ligustica were trained to work on a patch with artificial rewarding and non-rewarding flowers, coupled to an air extractor. The perceptual colour distance between the rewarding and the non-rewarding flowers was varied and the flower choice and the repellent scent-marking behaviour of the bees were recorded. 2. The discrimination between rewarding and non-rewarding flowers depended on their colour distance, improving with a greater colour difference. This task was guided thus visually and was not affected by activating the air extractor. 3. The scent-marking activity was only observable when the colour information of both groups of flowers was the same or very similar. This thus represents the first reported case of a modulation of an olfactory activity through the visual input provided by colour distances. When the air extractor was activated, rejections associated with the scent-marking behaviour disappeared, thus confirming the olfactory nature of this behaviour. 4. Honeybees are thus capable of using one or more sensory cues to enhance their foraging efficiency, according to the environmental situation. This great plasticity allows them to attain an enhanced efficiency while foraging. 5. We successfully applied the model of colour choice behaviour of the honeybee. Since the original theory was developed for Apis mellifera carnica, this work also constitutes the first attempt to describe the behaviour of the honeybee race, Apis mellifera ligustica, using the postulated model, and reaffirms thus its generality.