Colour layering and colour constancy

Loosely put, colour constancy for example occurs when you experience a partly shadowed wall to be uniformly coloured, or experience your favourite shirt to be the same colour both with and without sunglasses on. Controversy ensues when one seeks to interpret ‘experience’ in these contexts, for evidence of a constant colour may be indicative a constant colour in the objective world, a judgement that a constant colour would be present were things thus and so, et cetera. My primary aim is to articulate a viable conception of Present Constancy, of what occurs when a constant colour is present in experience, despite the additional presence of some experienced colour variation (e.g., correlating to a change in illumination). My proposed conception involves experienced colour layering – experiencing one opaque colour through another transparent one – and in particular requires one of those experienced layers to remain constant while the other changes. The aim is not to propose this layering conception of colour constancy as the correct interpretation of all constancy cases, but rather to develop the conception enough to demonstrate how it could and plausibly should be applied to various cases, and the virtues it has over rivals. Its virtues include a seamless application to constancy cases involving variations in filters (e.g., sunglasses) and illuminants; its ability to accommodate experiences of partial colours and error-free interpretations of difficult cases; and its broad theoretical-neutrality, allowing it to be incorporated into numerous perceptual epistemologies and ontologies. If layered constancy is prevalent, as I suspect it is, then our experiential access to colours is critically nuanced: we have been plunged into a world of colour without being told that we will rarely, if ever, look to a location and experience just one of them

Infant colour perception

We have learnt a lot about the development and maturation of colour vision in infants, but know comparatively little about the development and structure of colour perception once trichromacy has been established. This thesis aims to characterize infant colour perception in the first year of life over several areas which have previously been well documented in adults; colour categorisation, colour preference, perception of illusions, and infant sensitivity to natural scene statistics. Paper 1 (Skelton, Catchpole, Abbott, Bosten, and Franklin, 2017) systematically mapped infant colour categories revealing that infant colour categories are related to the retinogeniculate pathways of colour vision. Paper 1 also illustrates and quantifies the correspondence between infant colour categories and commonalities found across the worlds’ colour lexicon. Paper 2 shows that infants look for longer at the colours which adults prefer, and provides evidence for an influence of low-level mechanisms on infant response to colour and adult preference. Paper 3 (under review) reopens the question perception of the Munker-White illusion in infants aged 4 to 8 months, through the replication of a previous study and the use of an alternative method, with discussion of the reasons for studying illusions in infancy. Finally, paper 4 provides the first substantive evidence that infants aged 4 months are sensitive to natural scene statistics, as evidenced though the presence of a blue-yellow discrimination bias commonly associated with the distribution of chromaticities found in natural scenes. Paper 4 also has critical implications for the use of psychophysical methods in infants and adults. The findings inform our understanding of infant colour perception and general perceptual processes by outlining some of the structure around which infants’ colour perception is built. The early structure of infants’ perception of colour is shown to often have commonalities with adult colour perception

The components of colour vision

Colour perception is formed of many different components, such as colour discrimination, colour constancy, colour term naming, and the dimensions of colour (hue, chroma and lightness). It is a ‘toolbox’ of processes, not one cohesive function. Some of the components of colour vision develop into adult-like function over childhood, but they do not necessarily mature at the same speed. The studies in this thesis investigate adult, child and infant colour perception and cognition. Paper 1 finds a relationship between colour constancy and colour term naming in three- to four-year-old children. This relationship has wider implications for the co-development of language and perception. Paper 2 (Rogers, Knoblauch & Franklin, 2016) uses the technique of Maximum Likelihood Conjoint Measurement (MLCM) in adult participants to investigate the interaction between lightness and chroma in perception. Paper 3 combines MLCM analysis with preferential looking methods to compare interaction of lightness and chroma in infant and adult participants. This study paves the way for the use of MLCM and eye-tracking for studying other dimensions in development such as face perception, language, surface and shape. Paper 4 investigates why discrimination is poorest along the blue-yellow direction of cone opponent space (also known as the daylight locus). We tested the theory that this is adaptive for colour constancy by comparing illumination discrimination to surface discrimination in adult participants. We found equally poor discrimination for blue-yellow in both conditions, suggesting colour constancy is not the only explanatory factor. Together, these papers add to our understanding of the key components of colour vision over the life span and how perception of colour depends on various contextual and individual factors. Furthermore, this thesis develops novel applications of experimental techniques, and paves the way for these methods to be used to study other cognitive and developmental domains

Colour Calibration of a Head Mounted Display for Colour Vision Research Using Virtual Reality

Virtual reality (VR) technology ofers vision researchers the opportunity to conduct immersive studies in simulated real-world scenes. However, an accurate colour calibration of the VR head mounted display (HMD), both in terms of luminance and chromaticity, is required to precisely control the presented stimuli. Such a calibration presents signifcant new challenges, for example, due to the large feld of view of the HMD, or the software implementation used for scene rendering, which might alter the colour appearance of objects. Here, we propose a framework for calibrating an HMD using an imaging colorimeter, the I29 (Radiant Vision Systems, Redmond, WA, USA). We examine two scenarios, both with and without using a rendering software for visualisation. In addition, we present a colour constancy experiment design for VR through a gaming engine software, Unreal Engine 4. The colours of the objects of study are chosen according to the previously defned calibration. Results show a high-colour constancy performance among participants, in agreement with recent studies performed on real-world scenarios. Our studies show that our methodology allows us to control and measure the colours presented in the HMD, efectively enabling the use of VR technology for colour vision research

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Optimising Light Source Spectrum to Reduce the Energy Absorbed by Objects

Light is used to illuminate objects in the built environment. Humans can only observe light reflected from an object. Light absorbed by an object turns into heat and does not contribute to visibility. Since the spectral output of the new lighting technologies can be tuned, it is possible to imagine a lighting system that detects the colours of objects and emits customised light to minimise the absorbed energy. Previous optimisation studies investigated the use of narrowband LEDs to maximise the efficiency and colour quality of a light source. While these studies aimed to tune a white light source for general use, the lighting system proposed here minimises the energy consumed by lighting by detecting colours of objects and emitting customised light onto each coloured part of the object. This thesis investigates the feasibility of absorption-minimising light source spectra and their impact on the colour appearance of objects and energy consumption. Two computational studies were undertaken to form the theoretical basis of the absorption-minimising light source spectra. Computational simulations show that the theoretical single-peak spectra can lower the energy consumption up to around 38 % to 62 %, and double-peak test spectra can result in energy savings up to 71 %, without causing colour shifts. In these studies, standard reference illuminants, theoretical test spectra and coloured test samples were used. These studies are followed by the empirical evidence collected from two psychophysical experiments. Data from the experiments show that observers find the colour appearance of objects equally natural and attractive under spectrally optimised spectra and reference white light sources. An increased colour difference, to a certain extent, is found acceptable, which allows even higher energy savings. However, the translucent nature of some objects may negatively affect the results

A framework for predicting the non-visual effects of daylight – Part II: The simulation model

This paper describes a climate-based simulation framework devised to investigate the potential for the non-visual effects of daylight in buildings. It is part 2 of a study where the first paper focused on the formulation of the photobiological underpinnings of a threshold-based model configured for lighting simulation from the perspective of the human nonvisual system (e.g. circadian response). This threshold-based model employs a static dose-response curve and instantaneous exposure of daylight at the eye to estimate the magnitude of the non-visual effect as a first step towards a simulation framework that would establish a link between light exposure at the eye in an architectural context and expected effects on the non-visual system. In addition to being highly sensitive to the timing and duration of light exposure, the non-visual systems fundamentally differs from the visual system in its action spectrum. The photosensitive retinal ganglion cells that communicate light exposure to the brain is known to be shifted to the blue with respect to the photopic sensitivity curve. Thus the spectral character of daylight also becomes a sensitive factor in the magnitude of the predicted non-visual effect. This is accounted for in the model by approximating `yellow' sunlight, `grey' skylight and `blue' skylight to three distinct CIE illuminant types, and then tracking their `circadian-lux' weighted contributions in the summation of daylight received at the eye. A means to `condense' nonvisual effects into a synthesised graphical format for the year, split by periods of the day, is described in terms of how such a format could inform design decisions. The sensitivity of the simulation model's predictions to prevailing climate and building orientation is demonstrated by comparing results from eight European locations

Perceptual Constancy

We perceive objects and events in a way that makes it possible to act, react, think, believe, etc. in reliable and predictable ways. To explain this perceptual stability, as well as its behavioral consequences, theorists invoke a set of capacities known as perceptual constancies. Thanks to constancies, perceivers latch onto what’s unchanging in the world even though sensory stimulation is in continuous flux. In this dissertation, I present and defend a new view of both perceptual constancy and perceptual objectivity, i.e. the capacity of perception to present the world as mind-independent. According to the traditional view, perceptual constancy is the capacity of perceptual systems to recover perceiver-independent properties of distal objects from a largely ambiguous proximal stimulus, ‘discounting’ contextual, perceiver-dependent information. I argue that the traditional view should be rejected because it is, on the one hand, too ‘visuo-centric’, and, on the other hand, unable to fully explain the roles that constancy plays in our lives. These roles include guiding action and enabling the stable conscious experiences that ground our perceptual judgments. The view I favor, which I call “Relational Invariance view”, holds that constancy is the capacity to track invariant relations within the perceptual scene or between some element in the scene and the perceiver. These invariant relations are specified by patterns of variation in the proximal stimulus over time, and perceivers can sometime directly control this variation through movement. This view explains the role that, intuitively, perceptual constancy plays in guiding motor action and in a wide variety of perceptual recognition tasks, where recovering perceiver-independent properties seems unnecessary. The Relational Invariance view is then tied to a new view of perceptual objectivity, whose core insight is that the ‘job’ of perception in enabling the experience of a mind-independent world is not to ‘abstract away’ from any sort of perspectival or contextual influence, but rather to ‘embrace’ these influences as intrinsic to the very idea of what it means to perceive the world for creatures like us

Color constancy in philosophy and science

Color constancy is the phenomenon in which the visual system reliably ensures that objects that are the same color continue to look the same color despite, what one might call, interference. It is frequently appealed to in philosophy to support a myriad of theories about the nature of color and the metaphysics of experience. The dissertation investigates color constancy, particularly the empirical work on it, and reconsiders how it has been employed philosophically. The dissertation begins by analyzing a landmark empirical study of color constancy and explains the ways in which this work has figured in a number of philosophical theories. Then, it is argued that there is another, more neglected type of color constancy, and that this second type of color constancy cannot be easily assimilated by the above philosophical theories. This second type of color constancy is then applied to a puzzle about how things look when they are under varying illumination. This puzzle has motivated certain theories of color and color-like properties. The dissertation argues that such motivation is undercut once the puzzle is seen to dissolve in light of the second category of color constancy. Finally, the dissertation turns from the issue of what color constancy is to the issue of how it is accomplished, i.e. the mechanisms by which the visual system produces color-constant experiences. It is argued, from an empirical basis, that an appeal to color constancy in the grounding of perceptual representations falters because of error about these mechanisms.Philosoph

Color-appearance modeling for cross-media image reproduction

Five color-appearance transforms were tested under a variety of conditions to determine which is best for producing CRT reproductions of original printed images. The transforms included: von Kries chromatic adaptation, CIELAB color space, RLAB color appearance model, Hunt\u27s color appearance model, and Nayatani\u27s color appearance model. It was found that RLAB produced the best matches for changes in white point, luminance level, and background changes, but did not accurately predict the effect of surround. The ability of CIELAB color space was equal to that of RLAB in many cases, and performed better for changes in surround. Expert observers generated CRT images in one viewing condition that they perceived to match an original image viewed in another condition. This technique produced images that were equal to or better than the best color appearance model tested and is a useful technique to generate color appearance data for developing new models and testing existing models