What key phenomena must theories of colour perception account for? Describe and evaluate how theories try to explain the phenomena.

Authors Avatar

        Cognitive Essay semester 2 (4)

What key phenomena must theories of colour perception account for?  Describe and evaluate how theories try to explain the phenomena.

The degree to which we are able to perceive colour is due to our 'ability to distinguish wavelengths of light regardless of their relative intensities' (Abramov, 1997; cited in Hardin and Maffi, 1997). Individuals are thus dependent on purity, intensity, and wavelength, which are all components of physical energy.  These subsequently correspond to psychological attributes; intensity corresponds to brightness, purity to saturation and wavelength to hue (Setrular and Blaker, 1994).  Furthermore, stimuli that can be analysed into all three components are referred to as chromatic (i.e. blue, yellow, green etc) in contrast, stimuli which only has brightness attributed to it is referred to as achromatic (i.e. white/grey/black) (Pinel, 2000).  

The current essay aims to present firstly, an overview of the physiological mechanisms of colour vision illustrating the roles of rods and cones in the retinal anatomy.  Secondly, the occurrence of the key colour phenomena i.e. observations of our perception of colour and their significance will be discussed. Followed by a discussion of the two key theories that either separately, or combined, may account for these colour phenomenon.   These are the Opponent Theory  (Hering, 1878, cited in Eysenk and Keane, 2000) and the Trichromatic Theory or Young-Helmholtz Theory (cited in Reber, 1995).  In addition, the Retinex Theory will be examined briefly.  The essay will conclude by evaluating which model (if any) accounts best for these phenomena of colour perception.

The visual system is involved in converting incidental photons into visual images in the world (Barker, Barasi and Neal, 1999).  Photoreceptors (rods and cones)code electrical signals converted form light that hits the retina. and transmit information to different cortical areas (Barker, et al., 1999).  Rods  reside in all areas of the retina apart from the fovea.  They are responsible for scotopic vision (e.g. vision under low illumination, twilight vision) and movement as they are sensitive to low light levels rather than fine detail (cited in Kaiser and Boynton, 1996).  In contrast, cones are packed into the fovea area.  They are used for photopic vision (high illumination, daylight vision) and fine detail detection, (Kaiser and Boynton, 1996; Eysenck and Keane, 2000).  Cones and rods have distinct functions and contain different photochemicals (Kaiser and Boynton, 1996).  Cones possess one of three different photopigments; with a few of these cones sending information to single retinal ganglion cell (Kaiser and Boynton, 1996;Barker, et al., 1999).

The essay will now discuses several of the phenomena below, firstly looking at mutually exclusive colours.  These are

distinct colours pairs (i.e., red/green, blue/yellow, black/white) that cannot be seen at the same time in the same (Hurvich, 1981).  For example, redy-greens, bluey-yellows, colours are not seen , whereas redy-yellows or bluey-greens are. (Hurvich, 1981).  This is due to the pairs behaving in an opposite or antagonist manor. This may be seen more clearly, when examining successive contrast effects or afterimages (Hurvich, 1981). An afterimage may be produced if the eye fixates on a dot upon a unitary coloured page (e.g. red) for 20 seconds before staring at a blank page.  The page will appear a colour roughly opposite (i.e. the antagonist colour) to that initially fixated e.g. green.  The opponent nature of these mutually exclusive colour pairs is shown in fig.1 (Kaiser and Boynton, 1996; Hurvich, 1981). The two grey lines in the middle of the colour blocks are identical, producing the same reflectance (Kaiser and Boynton, 1996).  If one is fixated on, it will appear the opposite colour to its surround (Yellow block's strip would appear bluish).  Consequently, the other colour block's grey line (red), it will appear greenish when looked at (Hurvich, 1981).  This phenomenon is known as the simultaneous contrast effect.  This effect can be produced in other ways, and enables variations in colour field perception to be checked.

Join now!

Deficiencies of colour may result from congenital or acquired factors e.g. diseases/toxins (Hurvich, 1981).  Some individuals (dichromats) may only be able to see shades of yellow, blue, black, and white (Hardin and Maffi, 1997).  Thus, individuals are unable to discriminate easily between yellow-reds and yellow-greens, as they cannot detect red and green.  Deficiencies in confusions between blues and yellows is less frequent (Hurvich, 1981).  It is suggested that colour blindness may result from alterations in photopigments within individual’s receptors  (Barker, et al., 1999).  The visual field of a normally sighted individual may be divided into 'Zones' (Hurvich, 1981) (fig. 2).  In ...

This is a preview of the whole essay