The ability to differentiate between colours varies from individual to individual. This variation is attributed to factors such as the presence of colour blindness. Colour is used to encode information in information visualizations. An example of such an encoding is categorization using colour (e.g., green for land, blue for water).<p> As a result of the variation in colour differentiation ability among individuals, many people experience difficulties when using colour-encoded information visualizations. These difficulties result from the inability to adequately differentiate between two colours, resulting in confusion, errors, frustration, and dissatisfaction.<p> If a user-specific model of colour differentiation was available, these difficulties could be predicted and corrected. Prediction and correction of these difficulties would reduce the amount of confusion, errors, frustration, and dissatisfaction experienced by users. This thesis presents a model of colour differentiation that is tuned to the abilities of a particular user. To construct this model, a series of judgement tasks are performed by the user. The data from these judgement tasks is used to calibrate a general colour differentiation model to the user. This calibrated model is used to construct a predictor. This predictor can then be used to make predictions about the user's ability to differentiate between two colours.<p> Two participant-based studies were used to evaluate this solution. The first study evaluated the basic approach used to model colour differentiation. The second study evaluated the accuracy of the predictor by comparing its performance to the performance of human participants. It was found that the predictor was as accurate as the human participants 86.3% of the time. Using such a predictor, the colour differentiation abilities of particular users can be accurately modeled.

The ability to differentiate between colours varies from individual to individual. This variation is attributed to factors such as the presence of colour blindness. Colour is used to encode information in information visualizations. An example of such an encoding is categorization using colour (e.g., green for land, blue for water).<p> As a result of the variation in colour differentiation ability among individuals, many people experience difficulties when using colour-encoded information visualizations. These difficulties result from the inability to adequately differentiate between two colours, resulting in confusion, errors, frustration, and dissatisfaction.<p> If a user-specific model of colour differentiation was available, these difficulties could be predicted and corrected. Prediction and correction of these difficulties would reduce the amount of confusion, errors, frustration, and dissatisfaction experienced by users. This thesis presents a model of colour differentiation that is tuned to the abilities of a particular user. To construct this model, a series of judgement tasks are performed by the user. The data from these judgement tasks is used to calibrate a general colour differentiation model to the user. This calibrated model is used to construct a predictor. This predictor can then be used to make predictions about the user's ability to differentiate between two colours.<p> Two participant-based studies were used to evaluate this solution. The first study evaluated the basic approach used to model colour differentiation. The second study evaluated the accuracy of the predictor by comparing its performance to the performance of human participants. It was found that the predictor was as accurate as the human participants 86.3% of the time. Using such a predictor, the colour differentiation abilities of particular users can be accurately modeled.

In this thesis, I investigated how human vision processes colour and luminance information to enable perception of our environment. I first tested how colour can alter the perception of depth from shading. A luminance variation can be interpreted as either variation of reflectance (patterning) or variation of shape. The process of shape-from-shading interprets luminance variation as changes in the shape of the object (e.g. the shading on an object might elicit the perception of curvature). The addition of colour variation is known to modify this shape-from-shading processing. In the experiments presented here I tested how luminance driven percepts can be modified by colour. My first series of experiments confirmed that depth is modulated by colour. I explored a larger number of participants than previously tested. Contrary to previous studies, a wide repertoire of behaviour was found; participants experienced variously more depth, or less depth, or no difference. I hypothesised that the colour modulation effect might be due to a low-level contrast modulation of luminance by colour, rather than a higher-level depth effect. In a second series of experiments, I therefore tested how the perceived contrast of a luminance target can be affected by the presence of an orthogonal mask. I found that colour had a range of effects on the perception of luminance, again dependant on the participants. Luminance also had a similar wide range of effects on the perceived contrast of luminance targets. This showed that, at supra-threshold levels, a luminance target's contrast can be modulated by a component of another orientation (colour or luminance defined). The effects of luminance and colour were not following a particular rule. In a third series of experiments, I explored this interaction at detection levels of contrast. I showed cross-interaction between luminance target and mask but no effects of a colour mask.

I argue that conscious visual experience consists in a direct and noninferential grasp of the way one’s current perceptual contact with the environment poises one to pursue various intentional plans, goals and projects. I show that such a view of visual consciousness is supported by current work in cognitive neuroscience, affords a compelling account of colour perception, and suggests a way to bridge the ‘explanatory gap’ between consciousness and the language of the natural sciences. In chapter 1, I examine the reasoning that leads to the appearance of an explanatory gap between the phenomenal and the physical in more detail, and set out the constraints on a solution that our discussion of the problem has imposed. I then sketch the two rival takes on the relationship between perception and action mentioned above – adjudicating between these two theories (and finding in favour of the action-space view) is the task of the next two chapters, and is a recurring theme throughout. Chapter 2 moves on to discuss some recent work in the neuropsychology of vision and what it might suggest about the functional role of conscious vision, and the first half of chapter 3 considers two puzzle cases concerning colour perception. Each of these discussions turns out to constitute a source of support for the actionspace view that visual perception consists in a grasp of the practical consequences of sensation, and the second half of chapter 3 sets out this view and responds to an initial range of questions and objections it might face. Chapter 4 illustrates our view via a discussion of colour perception, and chapter 5 discusses the type of grasp of practical consequences that is necessary for perceptual sensitivity to issue in conscious experience. By chapter 6, we are in a position to see how the action-space approach can help close the explanatory gap for phenomenal consciousness, and our final chapter sets out how I think this should be done. I conclude with a brief discussion of further questions and prospects for the action-space approach.

This thesis develops and explores a constitutive approach to colour vision, which serves as an alternative to the standard experiential view of colour vision operating in the philosophy of colour. The approach seeks to describe the nature or essence of colour vision qua psychological kind. I argue that it is constitutive of colour vision that an organism possesses the ability to achieve colour constancy. An important feature of my account is that colour constancy is characterised as the ability to discriminate differences in surface reflectance properties across changes in illumination conditions. This differs from the standard ‘appearance invariance view’, which characterises colour constancy by appealing to the phenomenology of apparent colour. I consider an important objection to the appearance invariance view posed by the argument from illumination, which might also seem to carry over to the reflectance discrimination view. The objection is based on the claim that in standard cases of colour constancy the phenomenology of apparent colour is partly illumination-dependent. I argue that the reflectance discrimination view is perfectly able to accommodate this point. As a case study in applying the constitutive approach to illuminate the distinctive nature of colour vision, I argue that a vivid feature of our ordinary experience of colour known as categorical perception should be dissociated from our colour vision abilities. Although colour ontology often is not at the forefront of discussion, these constitutive theses support the ontological view of colour known as reflectance physicalism. I critique the argument from colour similarity, which many take to pose the greatest threat to reflectance physicalism. The thrust of the argument is that colours phenomenally appear to stand in similarity relations that do not correlate with the similarities that are evident among reflectance properties. This argument lacks much force, however, as it fails to acknowledge the extreme context sensitivity of similarity and the presentation sensitivity of our knowledge of similarities.

No / We present a numerical analysis of rendered pairs of rooms, in which the spectral power distribution of the illuminant in one room matched the surface reflectance function in the other room, and vice versa. We ask whether distinction between the rooms is possible and on what cues this discrimination is based. Using accurately rendered three-dimensional (3D) scenes, we found that room pairs can be distinguished based on indirect illumination, as suggested by A. L. Gilchrist and A. Jacobsen (1984). In a simulated color constancy scenario, we show that indirect illumination plays a pivotal role as areas of indirect illumination undergo a smaller appearance change than areas of direct illumination. Our study confirms that indirect illumination can play a critical role in surface color recovery and shows how computer rendering programs, which model the light¿object interaction according to the laws of physics, are valuable tools that can be used to analyze and explore what image information is available to the visual system from 3D scenes.

Yes / There has been an intense discussion among the public about the colour of a dress, shown in a picture posted originally on Tumblr (http://swiked. tumblr.com/post/112073818575/ guys-please-help-me-is-this-dress white-and; accessed on 10:56 am GMT on Tue 24 Mar 2015). Some people argue that they see a white dress with golden lace, while others describe the dress as blue with black lace. Here we show that the question “what colour is the dress?” has more than two answers. / The full text was made available at the end of the publisher's embargo, 14th May 2016

The field of telehealth has developed rapidly in recent years. It provides medical support particularly to those who are living in remote areas and in emergency cases. Although developments in both technology and practice have been rapid, there are still many gaps in our knowledge with regard to the effective application of telehealth. This study investigated human colour perception in telehealth, specifically the colour red as one of the key symptoms when diagnosing different pathologies. The quality of medical images is safety critical when transmitting the symptoms of pathologies in telehealth, as distorted or degraded colours may result in errors. The study focused on the use of digital images in teleconsultation, particularly on images showing cellulitis (bacterial skin infection) and conjunctivitis (red eye) as case studies, as both of these pathologies involve the colour red in their diagnosis. The study proposed and tested the use of an image quality scale, which represented the level of image resolution; a red colour scale, which represented the intensity of redness in an image; and a confidence scale, which represented the levels of confidence that telehealth users had when judging the colour red. The research involved a series of experiments using hypothetico-deductive and formal hypothesis testing with two groups of participants, medical doctors and non-medical participants. The experiments were conducted in collaboration with the local National Health Service (NHS) Accident and Emergency (A&E) department at Aberdeen Royal Infirmary (ARI). Medical experts in ophthalmology and dermatology were also involved in selecting and verifying the relevant images. The study found that doctors and non-doctors were consistent in the majority of the experiments. The accuracy of the participants was demonstrably higher when using a colour scale with pictures, more so for the non-doctor group than the doctor group. It also found that the level of accuracy for both doctors and nondoctors was higher when using red colour scale of three divisions than when using a scale of five divisions. This result was supported by previous studies, which used telehealth for diagnosing extreme cases. The study also found that when the image quality was poor the participants had higher error rates and less consistency in their answers. The study found poor correlation between accuracy, confidence and time for both participant groups. The study found that most participants in both doctor and non-doctor groups had high confidence most of the time, whether the accuracy was high or low. It was also found that medical background or clinical experience had no effect on the accuracy level across the experiment sets. In some cases, doctors with no or little experience had higher accuracy than those with greater experience. This result may have significant implications for the feasibility of involving non-doctors in the management of telehealth systems, especially in tasks not requiring medical skills, such as colour classification. This has the potential to provide a considerable saving in resources and costs for healthcare providers. An auto-evaluation system was introduced, and proposed for further study, in order to improve the current telehealth diagnostic protocol and to avoid or prevent errors by making red colour classification more objective and accurate.

Colour is a basic aspect of perception and the perception of colour varies from individual to individual. This indicates that the perception of colours mean different semantics in various contexts to different individuals. Therefore, these differences in perception forms to behave in different attitudes towards colours among individuals and it is likely to achieve different attitudinal responses to colours from individuals. Relying on the effects of colours on individuals, the initial interest of this thesis is to explore the attitudinal approaches of individuals to colours. This thesis is first and foremost exploratory in nature. This thesis intended as a first step towards exploring the ways in which the individuals think of, construe and give meaning to colours in their own words. The subjective approach proposed in terms of this thesis is based on the underlying philosophy behind Personal Construct Theory (PCT). In order to elicit the individuals&rsquo / ways of construing and giving meaning to colours in their own words, an experiment was conducted with the utilisation of the Repertory Grid Technique (RGT). Sixty undergraduate students of Middle East Technical University (METU) Faculty of Architecture were voluntarily participated in the experiment. As a stimuli, eleven basic colours which were black, grey, white, yellow, orange, red, pink, purple, brown, blue and green were utilised. For the second step, this thesis intended investigating the structure and interrelations between the elicited attitudes of individuals and eleven basic colours. As a result of the experiment, 60 repertory grids were elicited and were analysed by using the qualitative and quantitative applications of content analysis. The resulted data afterwards were analysed by using multivariate statistical analysis methods. The overall results of this research can support certain information for further scientific investigations on colour perception and colour psychology. Additionally, the results of this research can help and guide designers to attain objective understandings about the individuals&rsquo / attitudes to colours. This can contribute to designers as a practical worthwhile during colour design and colour planning in their products and services.

Colour is a basic aspect of perception and the perception of colour varies from individual to individual. This indicates that the perception of colours mean different semantics in various contexts to different individuals. Therefore, these differences in perception forms to behave in different attitudes towards colours among individuals and it is likely to achieve different attitudinal responses to colours from individuals. Relying on the effects of colours on individuals, the initial interest of this thesis is to explore the attitudinal approaches of individuals to colours. This thesis is first and foremost exploratory in nature. This thesis intended as a first step towards exploring the ways in which the individuals think of, construe and give meaning to colours in their own words. The subjective approach proposed in terms of this thesis is based on the underlying philosophy behind Personal Construct Theory (PCT). In order to elicit the individuals&rsquo / ways of construing and giving meaning to colours in their own words, an experiment was conducted with the utilisation of the Repertory Grid Technique (RGT). Sixty undergraduate students of Middle East Technical University (METU) Faculty of Architecture were voluntarily participated in the experiment. As a stimuli, eleven basic colours which were black, grey, white, yellow, orange, red, pink, purple, brown, blue and green were utilised. For the second step, this thesis intended investigating the structure and interrelations between the elicited attitudes of individuals and eleven basic colours. As a result of the experiment, 60 repertory grids were elicited and were analysed by using the qualitative and quantitative applications of content analysis. The resulted data afterwards were analysed by using multivariate statistical analysis methods. The overall results of this research can support certain information for further scientific investigations on colour perception and colour psychology. Additionally, the results of this research can help and guide designers to attain objective understandings about the individuals&rsquo / attitudes to colours. This can contribute to designers as a practical worthwhile during colour design and colour planning in their products and services.