the relationship between spectral stimuli and sensations of colour
DESCRIPTION
David A. Quebradas A.TRANSCRIPT
The Relationship Between Spectral Stimuli and Sensations of
Colour: Taking the Right Shirt.
Everyday, when we wake up, the light reach our retinas given us one part of material what
we need to see what we see. Even though what se see is not always what is outside of our
minds. Even if our vision cannot grasp the properties of physical world, we can get the shirt
what we want. If we are focus on our target we will not make a mistake. Then, if we agree
with this idea that what wee see is not what it is because the visual system cannot access the
physical world by means of retinal light patterns per se (Purves, 2000, 2011, 2014), how is
possible getting the thing what we want or a least what we need? How Vision works? Well,
It was a big question. I cannot solve this question and I don not want to do it. The purpose
of this short assay is just to take a little problem about the relationship between spectral
stimuli and sensations of colour. Specifically, why we see colours that are not there and
keep being successful into an unknowable world?
What we know about colours what we see? Colour experience is composed by three
perceptual qualities. One of these is hue, which is the perception of color per se (i.e. Pure
colors as Red, Blue, Green and Yellow). Another one is saturation, which is the degree to
which hue differs from the neutral gray. The last one, color brightness, perceived intensity
of colours (Purves, Lotto & Polger, 2000; Purves, 2009).
Now, we need to state that any color percepts “should accord with the way
reflectances and illuminants interact in generating the distributions of wavelengths that fall
on the eye.” (Lotto & Purves, 2002, p. 614). Despite the colours we perceive are not a direct
outcome of the spectral composition of light returned by an object, spectral stimuli
necessarily conflate the contribution of the consequence of the reflectance of a surface, the
spectrum of the illuminant and the transmittance of the intervening medium (Ibid).
Thus, up to the present moment, we have 1) three perceptual qualities and 2) a
definition about spectral stimuli. Going ahead with these, we can deal with one of the most
interesting problems about color vision, Color Contrast. How two spectrally identical
colours can be perceived as different colours? Understanding how a perceived color can
look different from another one, which has the same spectrum colour, we might understand
that different contexts (different chromatic surrounds) can induce changes in the perception
of the hue, saturation and brightness of a spectral stimuli (Fig.1). In the same way, these
changes are in each instance “complementary to the way spectral returns from surfaces
change under different chromatic illuminants”(Ibid, p. 618).
Fig. 1. “Two identical target stimuli are physically different surfaces,
then they will appear different” -color contrast- (Lotto & Purves, 2002)
Hence, we can perceive different colours coming from the same spectra as well as same
spectra under different illumination can be perceived like two opposite colors. Alike we see
in the figure 2. where the blue tiles on the in the left cube are physically identical to the
yellow tiles on the right cube, both kind of tiles coming from a gray patches.
Fig. 2 . “The effects on color perception when the same or differently reflective surfaces are
presented in scenes that are consistent with illumination by spectrally different light sources.” (Lotto &
Purves, 2002)
Despite these sorts of tricks, it’s the way what see. But how have we been
successful into this world if we have never ever taken a real picture of the world and we
will not do it? It’s seem to be a outcome from phylogenetic (evolution) and ontogenetic
(development and learning processes) history interaction, which allow us to get a set of
patterns of neural activity triggered by past experiences of what generated the same or
similar stimuli previously (Purves, 2001, Lotto, 2010). Thereby, we always get the
right shirt not because we have solved the inverse problem (or our vision could access
physical reality), but “because the perceptual values assigned by the frequency of
occurrence of visual stimuli accord with the reproductive success of the species and
individual” (Purves, 2014, p .4753).
In conclusion, if we attend 1) the following rules:
“1. When a target is presented on a saturated background whose perceived hue is similar to the hue the target would elicit if on a neutral background, the apparent color of the target decreases in saturation and brightness, with little change in hue2. When a target is presented on a background whose perceived hue is opposite that of the target on a neutral background, the apparent color of the target increases in saturation and brightness, with little change in hue.3. When a target is presented on a background whose perceived hue is neither the same as nor complementary to that of the target on a neutral background, the apparent hue of the target moves away from the apparent hue of the surround , with little change in saturation and brightness.4. These contextual effects on hue, saturation and brightness are all diminished by increasing the apparent saturation of the chromatic surround.” (Lotto & purves, 2002)
And 2) the role of the physical world is just to provide empirical feedback regarding which perceptions and behaviors have been related reproductive success, we can understand why we see colours that are not there and we will keep being successful into an unknowable world.
References
Lotto R.B. & Purves D. (2002). The empirical basis of color perception. Consciousness and
Cognition 11: 609-629.
Lotto, R.B., Clarke, R., Corney, D. and Purves, D. (2011). Seeing in colour. Optics and
Laser Technology, 43(2), 261-269.
Purves D, Lotto RB and Polger T (2000). Color vision and the four-color-map problem. J
Cog Neurosci 12: 233-237.
Purves D, Lotto RB, Williams SM, Nundy S, and Yang Z (2001). Why we see things the
way we do: Evidence for a wholly empirical stategy of vision. Philos Trans R Soc Lond B,
356: 285-297.
Purves D., Wojtach W.T. and Lotto RB (2011) Understanding vision in wholly empirical
terms. Proc Natl Acad Sci, 108 (3): 15588-15595.
Purves, D., Monsona, B.B., Sundararajana, J. and Wojtachc W.T. (2014). How biological
vision succeeds in the physical world Proc. Natl. Acad. Sci. USA April 1, 111 (13) 4750-
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