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Colouring the Mind: the Impact of Visual Environment on Colour Perception

Periodic Reporting for period 3 - COLOURMIND (Colouring the Mind: the Impact of Visual Environment on Colour Perception)

Reporting period: 2021-07-01 to 2022-12-31

To perceive scenes and the people and objects within them, the human mind must accommodate the dynamic and variable nature of the world, with variation in lighting, multiple viewpoints, and a plethora of contexts and environments. The human mind copes with these demands by constructing a perception of the world that draws on experience. However, the relative contribution and interaction of experience and ‘innate’ biological processes has been the focus of much multidisciplinary argument. In addition, there is extensive debate on which aspects of perception are modulated by experience, the nature and neural mechanisms of the processes involved, and the contribution of experience to human perceptual development. Colour perception is an excellent testing ground for these debates since it is a well characterised and fundamental feature of human vision.

The COLOURMIND project aims to understand how perception draws on experience by investigating the impact of the visual environment on the perception of colour. The COLOURMIND project aims to tackle three main questions: What aspects of colour perception are affected by the visual environment, such that people from different environments perceive colour differently?; What processes enable colour perception to calibrate to visual experience and what is their nature and scope?; Does colour perception ‘tune-in’ to the visual input experienced during infancy with long lasting implications for mature perception? COLOURMIND is adopting a diverse range of methods to address these questions. One set of studies is quantifying variation in chromatic scene statistics and illumination across radically different environments (e.g. jungle, urban, arctic) and seasons and is investigating whether this variation relates to differences in the colour perception of people immersed in those environments. A second set of studies aims to elucidate the nature and scope of calibrative processes in colour perception. ‘Altered-Reality’ is being used to create immersive environments with manipulated chromatic scene statistics and experiments are investigating how observers’ colour perception calibrates to these manipulations. Innovative neuroimaging methods are also being used to identify how the visual cortex represents chromatic scene statistics. Finally, COLOURMIND is conducting experiments with infants to address the impact of the chromatic environment on the early development of colour perception. The methodological innovation, data and theory that result will lead to advances in understanding how the human mind perceives colour, the role of experience in perceptual development and the calibration and optimisation of the visual system to the environment.
Research is underway on all three of the main COLOURMIND questions. First, fieldwork in Ecuadorian rainforest and urban environments in Ecuador and the UK has commenced. A database of calibrated images of these environments generated from head cameras worn by participants during daily life has been created. The project team have created an image analysis toolbox and have used this to identify variation in the chromatic and spatial scene statistics of the environments sampled. Two experiments have identified that people from the different environments differ systematically in their sensitivity and aesthetic response to hues. Second, work is underway to elucidate the nature and scope of calibrative processes in colour perception. Psychophysical experiments have found that observers are able to adapt to the colour variance of ensembles of different colours and that this variance adaptation generalises to non-colour features of the ensembles as well. Another experiment finds shifts in colour appearance after observers watch a film with altered chromatic scene statistics, suggesting that colour appearance adapts and calibrates to the immediate experienced environment. Neuroimaging analyses of a high resolution fMRI data set of people viewing natural scenes are revealing areas of the brain related to chromatic scene statistics. Finally, a number of experiments investigating the role of experience and chromatic scene statistics in infant colour perception have been completed and are providing insight into how colour vision optimises to the environment during development. The most notable developmental finding so far is that infants’ sensitivity to different hues is aligned with variation in daylight and chromatic scene statistics at just 4 months.
The findings of COLOURMIND so far are making progress beyond the state of the art on several fronts. First, the initial findings from the cross-environmental fieldwork are providing some of the first clear evidence that colour perception is not universal, and that effects presumed to be universal such as tuning of hue sensitivity to the blue-yellow axis in fact vary substantially across observers from different environments. This challenges traditional frameworks of colour perception, emphasises the role of experience and points to the need for colour science to test more diverse samples to understand how humans see colour. Second, the developmental findings so far, particularly the finding that infant hue sensitivity is aligned with the natural daylight axis, provides the clearest evidence so far that the early visual system is tuned to the environment. This raises exciting questions about how that early tuning takes place, its time course and the impact on perception across the lifespan. Third, innovative analysis of a high resolution neuroimaging data set of observers viewing natural scenes has revealed not just one but two distinct colour selective streams in the ventral visual pathway.

The methodological innovation of COLOURMIND also provides progress. Considerable effort has gone into calibrating ipad models to enable online and remote testing of colour perception with accurate colour rendering. This opens up many possibilities for doing precise colour science outside of the psychophysics lab in the field, and online, the latter being particularly important during the pandemic. This has also enabled the team to do colour science with infants remotely over zoom, without needing parents and babies to come into the lab for face to face testing. This method of ‘baby zoom’ testing enables more geographically diverse infant samples to be recruited and makes it considerably easier for parents to take part in science. COLOURMIND is also making notable methodological advances in a number of other ways, the project has: devised protocols for capturing observer’s lived ‘visual diet’ with head cams and body worn spectral sensors; provided new psychophysical tasks for measuring infant sensitivity to visual stimuli; and provided new methods of chromatic image analysis and manipulation.
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