Does colour constancy exist?

For a stable visual world, the colours of objects should appear the same under different lights. This property of colour constancy has been assumed to be fundamental to vision, and many experimental attempts have been made to quantify it. I contend here, however, that the usual methods of measurement are either too coarse or concentrate not on colour constancy itself, but on other, complementary aspects of scene perception. Whether colour constancy exists other than in nominal terms remains unclear.     

One blue colour channel or two?

Contrary to the general belief that the yellow-blue mechanism has lower spatial resolution than the red-green mechanism, it has been recently claimed that both mechanisms have similar spatial sensitivity (McKeefry et al, 2001 Vision Research 41 245-255). Studying high-spatial-frequency tritanopia (a colour illusion based on spatio-chromatic interactions in human vision), we found strong evidence for the existence of two blue mechanisms-with low and high spatial-frequency resolution. If confirmed, this may resolve the apparent paradox concerning spatial resolution of the yellow-blue mechanism.     

“Filling-in” colour in natural scenes

Our subjective experience of the world as being in full colour across the entire visual field is at odds with the highly fovea-biased distribution of cones in the retina. It is unclear how this percept of “pan-field colour” comes about. We use novel stimuli—“colour chimeras”—to demonstrate a related visual phenomenon in which observers perceive rich colour throughout images with large achromatic regions. This percept appears to critically depend on natural scene statistics. By separately manipulating chromatic and structural content in such images, we demonstrate that both the spatial distribution of colour and the presence of recognizable scene structure contribute to the experience of pan-field colour in these stimuli. Our results suggest that this percept is unlikely to be due to a low-level colour spreading process. Instead, we suggest that mechanisms dependent on natural scenes’ chromatic and luminance statistics provide the basis for the phenomenon.     

Are there nontrivial constraints on colour categorization?

In this target article the following hypotheses are discussed: (1) Colour is autonomous: a perceptuolinguistic and behavioural universal. (2) It is completely described by three independent attributes: hue, brightness, and saturation: (3) Phenomenologically and psychophysically there are four unique hues: red, green, blue, and yellow; (4) The unique hues are underpinned by two opponent psychophysical and/or neuronal channels: red/green, blue/yellow. The relevant literature is reviewed. We conclude: (i) Psychophysics and neurophysiology fail to set nontrivial constraints on colour categorization. (ii) Linguistic evidence provides no grounds for the universality of basic colour categories. (iii) Neither the opponent hues red/green, blue/yellow nor hue, brightness, and saturation are intrinsic to a universal concept of colour. (iv) Colour is not autonomous.     

Does low perceptual load enable capture by colour singletons?

There is considerable debate as to whether colour singletons can capture attention in a stimulus-driven manner. In this study, we explore one potential capture enabling condition—low perceptual load. To test this hypothesis, we manipulated perceptual load in a flanker task in which flanking letters sometimes were colour singletons. If low load enhances capture by colour singletons, then colour singletons should produce an especially large increase in overall reaction times and in flanker–target compatibility effects. Neither of these predictions was confirmed in any of the four experiments reported here, although we did replicate the classic load effects from previous studies. These experiments indicate that although perceptual load does strongly modulate overall performance, it does not facilitate capture by colour singletons. This finding contrasts sharply with findings from other types of salient stimuli (abrupt onsets and moving objects). Implications for theories of attentional capture will be discussed.     

Looking at anything that is green when hearing “frog”: How object surface colour and stored object colour knowledge influence language-mediated overt attention

Three eye-tracking experiments investigated the influence of stored colour knowledge, perceived surface colour, and conceptual category of visual objects on language-mediated overt attention. Participants heard spoken target words whose concepts are associated with a diagnostic colour (e.g., “spinach”; spinach is typically green) while their eye movements were monitored to (a) objects associated with a diagnostic colour but presented in black and white (e.g., a black-and-white line drawing of a frog), (b) objects associated with a diagnostic colour but presented in an appropriate but atypical colour (e.g., a colour photograph of a yellow frog), and (c) objects not associated with a diagnostic colour but presented in the diagnostic colour of the target concept (e.g., a green blouse; blouses are not typically green). We observed that colour-mediated shifts in overt attention are primarily due to the perceived surface attributes of the visual objects rather than stored knowledge about the typical colour of the object. In addition our data reveal that conceptual category information is the primary determinant of overt attention if both conceptual category and surface colour competitors are copresent in the visual environment.     

Representation or context as a cognitive strategy in colour constancy?

If an identification task with colour constancy as its objective is carried out under drastically changing illumination, do people rely mainly on colour information or do they rely on other sources of information? This question suggested two hypotheses for testing: (i) context hypothesis: people rely mainly on colour information (spectral reflectance or illumination chromaticity) to achieve colour constancy; (ii) representation hypothesis: people rely mainly on all other clues associated with colour to achieve colour constancy, including form information (any shape elements) and space information (spatial coordinates or spatial correlation). Experiment 1 showed that form information was readily associated with colour information to produce implicit representation. This gave the best colour-constancy performance (95.72%) and the fastest processing speed, so it probably used a top-down process. However, it was also prone to error owing to assumptions. Space information was not readily associated with colour information so colour-constancy performance was halved (48.73%) and processing time doubled. When the subject was deprived of both information sources and only given colour information, this resulted in the longest reaction times and the worst colour-constancy performance (41.38%). These results clearly support the representation hypothesis rather than the context hypothesis. When all three clues were available at the same time, the order of preference was: symbol, location, then colour. Experiment 2 showed that when form information was the main clue, colour-constancy performance was conceptually driven and processed more quickly; this supports the representation hypothesis. However, when form information was not used, colour constancy was data-driven, processed more slowly, and achieved an inferior identification rate overall; this supports the context hypothesis.     

Do we only dream in colour? A comparison of reported dream colour in younger and older adults with different experiences of black and white media

This study aimed to find out whether differences in the reported colour of dreams can be attributed to the influence of black and white media or to methodological issues. Two age groups, with different media experience, were compared on questionnaire and diary measures of dream colour. Analysis revealed that people who had access to black and white media before colour media experienced more greyscale dreams than people with no such exposure, and there were no differences between diary and questionnaire measures of dream colour. Moreover, there were inter-group differences in the recall quality of colour and black and white dreams that point to the possibility that true greyscale dreams occur only in people with black and white media experience.     

Incidental memory for colour word associates processed in colour naming and reading aloud tasks: is a blue ocean more memorable than a yellow one?

ABSTRACT

Congruency effects for colour word associates (e.g., ocean) have been reported in Stroop colour naming tasks. However, incidental memory for such words after word reading and colour naming tasks has not been examined. In the current study, participants incidentally recalled colour word associates (e.g., ocean) and neutral words (e.g., lawyer) immediately after naming their font colour (Experiment 1a) or reading them aloud (Experiment 1b). In both tasks, recall was better for congruent colour word associates (e.g., ocean appearing in blue) than incongruent colour word associates (e.g., ocean appearing in green) or neutral items (lawyer appearing in blue).

This outcome is consistent with the idea that co-activation of a semantic colour code and a lexical representation strengthens the episodic memory representation and makes it more accessible.     

Colours sometimes count: Awareness and bidirectionality in grapheme–colour synaesthesia

Three experiments were conducted with 10 grapheme–colour synaesthetes and 10 matched controls to investigate (a) whether awareness of the inducer grapheme is necessary for synaesthetic colour induction and (b) whether grapheme–colour synaesthesia may be bidirectional in the sense that not only do graphemes induce colours, but that colours influence the processing of graphemes. Using attentional blink and Stroop paradigms with digit targets, we found that some synaesthetes did report “seeing” synaesthetic colours even when they were not able to report the inducing digit. Moreover, congruency effects (effects of matching the colour of digit presentation with the synaesthetic colour associated with that digit) suggested that grapheme–colour synaesthesia can be bidirectional, at least for some synaesthetes.     

Biases and regularities of grapheme–colour associations in Japanese nonsynaesthetic population

Associations between graphemes and colours in a nonsynaesthetic Japanese population were investigated. Participants chose the most suitable colour from 11 basic colour terms for each of 40 graphemes from the four categories of graphemes used in the Japanese language (kana characters, English alphabet letters, and Arabic and kanji numerals). This test was repeated after a three-week interval. In their responses, which were not as temporally consistent as those of grapheme–colour synaesthetes, participants showed biases and regularities that were comparable to those of synaesthetes reported in past studies. Although it has been believed that only synaesthetes, and not nonsynaesthetes, tended to associate graphemes with colours based on grapheme frequency, Berlin and Kay's colour typology, and colour word frequency, participants in this study tended in part to associate graphemes with colours based on the above factors. Moreover, participants that were nonsynaesthetes tended to associate different graphemes that shared sounds and/or meanings (e.g., Arabic and kanji numerals representing the same number) with the same colours, which was analogous to the findings in Japanese synaesthetes. These results support the view that grapheme–colour synaesthesia might have its origins in cross-modal association processes that are shared with the general population.     

An exploratory study of linguistic–colour associations across languages in multilingual synaesthetes

In one of the most common forms of synaesthesia, linguistic–colour synaesthesia, colour is induced by stimuli such as numbers, letters, days of the week, and months of the year. It is not clear, however, whether linguistic–colour synaesthesia is determined more by higher level semantic information—that is, word meaning—or by lower level grapheme or phoneme structure. To explore this issue, we tested whether colour is consistently induced by grapheme or phoneme form or word meaning in bilingual and trilingual linguistic–colour synaesthetes. We reasoned that if the induced colour was related to word meaning, rather than to the acoustic or visual properties of the words, then the induced colours would remain consistent across languages. We found that colours were not consistently related to word meaning across languages. Instead, induced colours were more related to form properties of the word across languages, particularly visual structure. However, the type of inducing stimulus influenced specific colour associations. For example, colours to months of the year were more consistent across languages than were colours to numbers or days of the week. Furthermore, the effect of inducing stimuli was also associated with the age of acquisition of additional languages. Our findings are discussed with reference to a critical period in language acquisition on synaesthesia.     

Which kind of attention is captured by cues with the relative target colour?

Most theories of visual search maintain that attention is selectively tuned to the attributes of the search target (e.g., orange). Conversely, according to the relational account, attention is biased to the relative feature of the target (e.g., redder). However, previous studies that supported the relational account mainly measured mean response times. Hence, the results might not reflect early, perceptual mechanisms (e.g., signal enhancement) but later, decision-based mechanisms (channel selection). The current study tested the relational account against feature-specific theories in a spatial cueing task, in which the targets were backward-masked, and target identification accuracy was measured. The first experiment corroborated earlier results, demonstrating that relational effects are due to signal enhancement. In the second experiment, we chose highly discriminable colours along the blue–red continuum, and obtained results that were more consistent with broad feature-specific rather than relational tuning. The implications of these findings for current theories of attention are discussed.     

Does segregation by colour/luminance facilitate the detection of structure-from-motion in noise?

The aim in the experiments was to examine whether the detection of structure-from-motion (SFM) in noise was facilitated when target and noise were segregated by colour and/or luminance polarity. The SFM target was a rotating 'V-shape' structure simulated with limited-lifetime Gaussian micropatterns and embedded in random-motion noise. Threshold levels of V-shape slant were measured for stimuli in which target and noise were segregated or unsegregated by colour/luminance, and under two conditions, with and without static form cues to the SFM target. The presence or absence of static form cues to the SFM target was manipulated by varying the relative numbers of micropatterns in target and noise. In the absence of static form cues, segregation of target and noise by colour and/or luminance polarity did not facilitate target detection, even when subjects knew which micropatterns belonged to the target. On the other hand, when static form cues were present, segregation improved performance. These results imply that SFM processing is 'form-cue invariant' except when the target form is immediately identifiable in the static view of the stimulus. The significance of the results for understanding the role of colour vision in breaking camouflage and in 'grouping' is discussed.     

Blue or red? The effects of colour on the emotions of Chinese people

Two experiments were performed to examine the effects of red and blue on the emotional pleasure of Chinese people. Experiment 1 explored the effects of the ‘physical’ colours red and blue on emotion, and the results showed that red induced positive and negative emotion, while blue only induced positive emotion. Experiment 2 further explored the effects of the ‘verbal’ colours red and blue on emotion, and the results showed that red induced only positive emotion, while blue induced neither positive nor negative emotion. The findings indicate that the influence of colour on emotion is rooted in both natural and social associations. For Chinese, the associations between blue and positive emotion, and red and negative emotion, were natural associations; however, the associations between red and positive emotion were social associations. Moreover, physical colour and verbal colour stimuli induced emotions by activating different mechanisms: physical colour induced emotions via both natural and social associations, whereas verbal colour induced emotions via social associations.     

Interlinguistic conflict: Word–word Stroop with first and second language colour words

The congruency (or Stroop) effect is a standard observation of slower and less accurate colour identification to incongruent trials (e.g. “red” in green) relative to congruent trials (e.g. “red” in red). This effect has been observed in a word–word variant of the task, when both the distracter (e.g. “red”) and target (e.g. “green”) are colour words. The Stroop task has also been used to study the congruency effect between two languages in bilinguals. The typical finding is that the congruency effect for L1 words is larger than that for L2 words. For the first time, the present report aims to extend this finding to a word–word variant of the bilingual Stroop task. In two experiments, French monolinguals performed a bilingual word–word Stroop task in which target word language, language match, and congruency between the distracter and target were manipulated. The critical manipulation across two experiments concerned the target language. In Experiment 1, target language was manipulated between groups, with either French (L1) or English (L2) target colour words. In Experiment 2, target words from both languages were intermixed. In both experiments, the congruency effect was larger when the distracter and target were from the same language (language match) than when they were from different languages (language mismatch). Our findings suggested that this congruency effect mostly depends on the language match between the distracter and target, rather than on a target language. It also did not seem to matter whether the language-mismatching distracter was or was not a potential response alternative. Semantic activation of languages in bilinguals and its implications on target identification are discussed.

     

Can orange colour facilitate the processing of happiness? An exploration study on happiness metaphor

Colour is a ubiquitous perceptual stimulus, and theoretical models of colour and psychological functioning posit that colour plays a key role in influencing the behaviour and mental function of a person. One investigation and two experiments investigated the colour metaphor representation of happiness concepts and the mapping mode of the colour metaphor of happiness concepts. A questionnaire was conducted to explore the relationship between colour preference and happiness. Study 2 shows that the identification of happiness words was facilitated more when words were viewed on an orange background than when viewed on a blue background. Study 3 further verifies the links of the connection between colour and happiness at the sentence level, and the orange-happiness facilitation effect was replicated. These results document a novel influence of colour on emotion recognition processes, where an orange background may facilitate the processing of the concept of happiness and provide support for conceptual metaphor theory and colour-in-context theory.     

Grapheme–colour synaesthesia yields an ordinary rather than extraordinary memory advantage: Evidence from a group study

In synaesthesia, the input of one sensory modality automatically triggers an additional experience, not normally triggered by the input of that modality. Therefore, compared to non-synaesthetes, additional experiences exist and these may be used as retrieval cues when memory is tested. Previous case studies have suggested that synaesthesia may yield even extraordinary memory abilities. However, group studies found either a task-specific memory advantage or no performance advantage at all. The aim of the present study was to test whether grapheme–colour synaesthesia gives rise to a general memory benefit using a standardised memory test (Wechsler Memory Scale). The synaesthetes showed a performance advantage in episodic memory tests, but not in short-term memory tests. However, performance was still within the ordinary range. The results support the hypothesis that synaesthesia provides for a richer world of experience and as a consequence additional retrieval cues may be available and beneficial but not to the point of extraordinary memory ability.