Towards a cognitive definition of colour vision
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- Biological & Chemical Sciences, Queen Mary, University of London
- Queen Mary University of London
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This manuscript is a preprint. A published version is available at:
10.1016/j.optlastec.2008.12.015 (Peer Reviewed) Published as "Is colour cognitive?" in Optics & Laser Technology.- Document Type:
- Manuscript
- Date:
- Received 04 April 2008 12:35 UTC; Posted 07 April 2008
- Subjects:
- Ecology, Neuroscience
- Abstract:
In recent years, colour vision abilities have been rather generously awarded to vari-ous invertebrates and even bacteria. This uncertainty of when to diagnose colour vi-sion stems in part from confusing what colour vision can do with what it is. What col-our vision can do is discriminate wavelength independent of intensity. However, if we take this as a definition of what colour vision is, then we might indeed be obliged to conclude that some plants and bacteria have colour vision. Moreover, there is a simi-lar confusion of what are necessary and what are sufficient mechanisms and behav-ioural abilities for colour vision. To humans, seeing in colour means seeing an image in which objects/lights have chromatic attributes – in contrast to the sensation that we have when viewing monochrome movies, or our experience in dim light when only rod vision is possible. The necessary basic equipment for this is to have at least two types of photoreceptors that differ in spectral sensitivity, and at least one type of spectrally opponent cell to compare the signals from the photoreceptors. Clearly, however, a necessary additional prerequisite for colour vision is to have vision, which entails the identification of shapes, sizes and locations of objects in the world. Thus if an animal has colour vision, it should see an image in which distinct objects/lights have colour attributes. This distinguishes colour vision from what has historically been called wavelength-specific behaviour: a type of behaviour triggered by fixed configurations of spectral receptor signals; however, we discuss difficulties in diagnosing wavelength specific behaviour as an indicator of the absence of colour vision.
Discussion
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7 votes
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5 comments
This article successfully avoids the pitfalls of two entrenched ways of thinking about colour vision. The first of these is the ‘detectionist’ model, where colour vision is seen simply as the response to some physical quantity such as wavelength or SSR. This may be appropriate for ‘wavelength specific behaviours’, where a particular stimulus is rigidly correlated with a fixed response, but the complexity of the relation between physical stimulus and conscious colour perception, as demonstrated e.g. by simultaneous contrast effects, means that detection is the wrong way to think about colour perception.
Another trap is to to acknowledge that colour vision involves a complex elaboration of the physical stimulus, but to see this processing as happening separately from spatial vision, and just as the ‘colouring in’ of an achromatic image pre-assembled by a spatial vision. The problem here is that since this colouring-in can’t be said to be the representation of any particular physical property, one is tempted to conclude that colour is an illusory projection onto the world, which has no information bearing function.
I think that colour can only be understood if its interactions with other visual processing are taken seriously (see Shevell and Kingdom 2007 Ann. Rev. Psych. for review of these) – for only then can it be appreciated how colour can be part of a valid representation of an object, even though it fails to represent any particular physical property. Cognitive colour vision, where colour is abstracted and used for the identification and memorisation of objects, is likely the result of a plethora of colour-spatial vision interactions.
I feel like the caveat stated near the end of the manuscript is one that must be emphasized; that is the notion of false negatives arising following the evaluation of behavioral criteria for animal color vision. The authors state that the experiment must discriminate between lack of color vision and a lack of “understanding” the task. This must be disentangled. For example, if John Stroop had conducted the behavioral tests to determine the existence of color vision in humans, based on the data, we could conclude that humans do not have color vision…
Stroop, John Ridley (1935) Studies of interference in serial verbal reactions. Journal of Experimental Psychology 18:643-622.
The comment above – that there is a risk of “false negative diagnoses” in animal colour vision tests – is a very important one. Indeed in all research on animal perception or cognition, a negative result could mean that the animal is incapable of solving the task (due to sensory or cognitive constraints) – OR, it could mean that we have not trained or tested the animal in a way that generates the performance we might have expected for a positive result. In some cases, an animal’s inaccuracy might in fact be a strategy – if for example, we haven’t controlled for speed accuracy tradeoffs, an animal might adopt a fast-and-inaccurate approach to any given task, if solving the problem accurately would involve high temporal costs. If an animal fails to distinguish the numbers 11 and 12, for example, is this because it is incapable of counting? Or is the animal choosing a clever strategy, because counting the dots on two boxes (and ascertaining the difference) takes longer than opening both boxes without paying attention to the number of dots (even if one of the boxes contains no food)? Returning to colour vision, the issue of negative results is one that extends beyond the question of whether an animal sees colour. For example, we might use colour discrimination with progressively smaller colour differences as an indicator of just-noticable difference, below which colour discrimination is no longer possible. But absence of behavioural colour discrimination does not necessarily mean absence of perceived colour difference – the animal might simply not “get” that we’re interested in probing its limits, and might happily generalise to similar (but distinguishable) targets. The same problem occurs with the dimensionality of colour vision – bees, for example – sometimes tend to ignore brightness in colour discrimination tasks – but is this because they don’t see them, or because they don’t attach relevance to these differences? These are problems we have to live with – our only access to perception is behaviour, since physiological work can only provide circumstantial evidence for the equipment necessary for a perceptual ability, but no conclusive proof. Negative physiological results, conversely, allow more decisive conclusions: if an animal possesses only a single spectral receptor type, it can not possibly have colour vision. Negative behavioural results never conclusively prove the absence of an ability – so all we can do is to refine training and testing procedures to sharpen our picture of an animal’s perception of the world.
References:
Dyer, AG. & Chittka, L. (2004) Bumblebees (Bombus terrestris) sacrifice foraging speed to learn difficult colour discrimination tasks. Journal of Comparative Physiology A, 190: 759-763.
Dyer, AG; Neumeyer, C (2005) Simultaneous and successive colour discrimination in the honeybee (Apis mellifera). . Journal of Comparative Physiology A, 191: 547-557.
Is true that a cognitive definition of colour vision is a complex task as Skorupsli and Chitka suggested. I very sympathique with the meaning of colour vision introduce by several authors including Merleau Ponty, Francisco Varela, Evan Thompson, Kevin O´Regan, Alva Noe.
Colours are internalized as cognitive percept after a history of behavioural sensory-motor interaction with particulars objects embedded in an ecological context. In that sense the chromatic properties of objects will be enacted through a series of visuo-motor interactions resulting in that either a single (or combination of) wavelength will produce an experiential-cognitive content of the perceiving “object”. Then a “blue” object will correspond to the experiential –context dependent– properties associated to that particular objects under different background illumination and behavioural actions. Therefore colour to be cognitive need to be enacted through behavioural actions. In that sense it’s no clear to me if invertebrate and some vertebrates as well will be able to enjoy a cognitive experience of colours.
Adrian
1) Ponty M. Phénoménologie de la perception, París: Gallimard, 1945.
2) Noe A., O’Regan JK “A sensorimotor account of vision and visual consciousness.” Behavioral and Brain Sciences 24 (5), 2001: 883-917.
3) Thompson E, Palacios AG, Varela FJ (1992). Ways of coloring: comparative color vision as a case study for cognitive science. Behavioral Brain Science 15, 1-75. - (Login to share with a colleague)
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Skorupski, Peter and Chittka, Lars. Towards a cognitive definition of colour vision. Available from Nature Precedings <http://hdl.handle.net/10101/npre.2008.1766.1> (2008)
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Published version:
10.1016/j.optlastec.2008.12.015 (Peer Reviewed) Published as "Is colour cognitive?" in Optics & Laser Technology. -
Other versions of this document in Nature Precedings
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Adrian Dyer on 07 May 2008 04:38 UTC
A fresh insight into how we can understand the evolution of colour vision. The manuscript nicely links some of the complexities surrounding how colour and spatial vision interplay, and helps to define (or perhaps redefine) some of the boundaries for how we attribute colour vision. One point that came to mind in reading the different sections relating to colour/spatial vision and how receptors undergo a process of adaptation is the evidence from retinal stabilization studies where if the image is kept still on a retina then the image will disappear in a relatively short period (perhaps as short as 80 ms; Proc Nat Acad Sci v93 p 8001; Nature Reviews Neuroscience v5 p229). Thus, how colour visual information is sensed in relation to different complex spatial and temporal parameters potentially allows us to better understand what it means to perceive colour; the manuscript opens some interesting windows on recent (and past) studies, and how future studies might approach the field of colour cognition.