Compare and contrast theories of perception

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Compare and contrast theories of perception

Yellowish-green light, for example, stimulates both L and M cones equally strongly, but only stimulates S-cones weakly.

Red light, on the other hand, stimulates L cones much more than M cones, and S cones hardly at all; blue-green light stimulates M cones more than L cones, and S cones a bit more strongly, and is also the peak stimulant for rod cells; and blue light stimulates S cones more strongly than red or green light, but L and M cones more weakly.

The brain combines the information from each type of receptor to give rise to different perceptions of different wavelengths of light.

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The opsins photopigments present in the L and M cones are encoded on the X chromosome ; defective encoding of these leads to the two most common forms of color blindness.

The OPN1LW gene, which codes for the opsin present in the L cones, is highly polymorphic a recent study by Verrelli and Tishkoff found 85 variants in a sample of men. X chromosome inactivation means that while only one opsin Compare and contrast theories of perception expressed in each cone cell, both types occur overall, and some women may therefore show a degree of tetrachromatic color vision.

Color in the human brain[ edit ] Visual pathways in the human brain. The ventral stream purple is important in color recognition.

Compare and Contrast Gibson’s and Gregory’s theories of perception | Free Essays -

The dorsal stream green is also shown. They originate from a common source in the visual cortex. Color processing begins at a very early level in the visual system even within the retina through initial color opponent mechanisms. Both Helmholtz's trichromatic theory, and Hering's opponent process theory are therefore correct, but trichromacy arises at the level of the receptors, and opponent processes arise at the level of retinal ganglion cells and beyond.

In Hering's theory opponent mechanisms refer to the opposing color effect of red—green, blue—yellow, and light—dark.

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However, in the visual system, it is the activity of the different receptor types that are opposed. Some midget retinal ganglion cells oppose L and M cone activity, which corresponds loosely to red—green opponency, but actually runs along an axis from blue-green to magenta.

Small bistratified retinal ganglion cells oppose input from the S cones to input from the L and M cones. This is often thought to correspond to blue—yellow opponency, but actually runs along a color axis from yellow-green to violet.

Visual information is then sent to the brain from retinal ganglion cells via the optic nerve to the optic chiasma: After the optic chiasma the visual tracts are referred to as the optic tractswhich enter the thalamus to synapse at the lateral geniculate nucleus LGN.

The lateral geniculate nucleus is divided into laminae zonesof which there are three types: M- and P-cells receive relatively balanced input from both L- and M-cones throughout most of the retina, although this seems to not be the case at the fovea, with midget cells synapsing in the P-laminae.

The koniocellular laminae receive axons from the small bistratified ganglion cells.


Within V1 there is a distinct band striation. This is also referred to as "striate cortex", with other cortical visual regions referred to collectively as "extrastriate cortex". It is at this stage that color processing becomes much more complicated.

In V1 the simple three-color segregation begins to break down. Many cells in V1 respond to some parts of the spectrum better than others, but this "color tuning" is often different depending on the adaptation state of the visual system.

A given cell that might respond best to long wavelength light if the light is relatively bright might then become responsive to all wavelengths if the stimulus is relatively dim. Because the color tuning of these cells is not stable, some believe that a different, relatively small, population of neurons in V1 is responsible for color vision.

These specialized "color cells" often have receptive fields that can compute local cone ratios. Such "double-opponent" cells were initially described in the goldfish retina by Nigel Daw; [13] [14] their existence in primates was suggested by David H.

Hubel and Torsten Wiesel and subsequently proven by Bevil Conway. Modeling studies have shown that double-opponent cells are ideal candidates for the neural machinery of color constancy explained by Edwin H. Land in his retinex theory.

The human eye can distinguish about 10 million different colors. The cells in V2 that are most strongly color tuned are clustered in the "thin stripes" that, like the blobs in V1, stain for the enzyme cytochrome oxidase separating the thin stripes are interstripes and thick stripes, which seem to be concerned with other visual information like motion and high-resolution form.

Neurons in V2 then synapse onto cells in the extended V4. This area includes not only V4, but two other areas in the posterior inferior temporal cortex, anterior to area V3, the dorsal posterior inferior temporal cortex, and posterior TEO.

Subjectivity of color perception[ edit ] See also: Linguistic relativity and the color naming debate Nothing categorically distinguishes the visible spectrum of electromagnetic radiation from invisible portions of the broader spectrum.

In this sense, color is not a property of electromagnetic radiation, but a feature of visual perception by an observer. Furthermore, there is an arbitrary mapping between wavelengths of light in the visual spectrum and human experiences of color.

Although most people are assumed to have the same mapping, the philosopher John Locke recognized that alternatives are possible, and described one such hypothetical case with the " inverted spectrum " thought experiment. Synesthesia or ideasthesia provides some atypical but illuminating examples of subjective color experience triggered by input that is not even light, such as sounds or shapes.An experiment is a procedure carried out to support, refute, or validate a plombier-nemours.comments provide insight into cause-and-effect by demonstrating what outcome occurs when a particular factor is manipulated.

Experiments vary greatly in goal and scale, but always rely on repeatable procedure and logical analysis of the results. 1. The Ordinary Conception of Perceptual Experience. In this section we spell out the ordinary conception of perceptual experience.

There are two central aspects to . This book provides a superb critique of the philosophies of logical positivism and empiricism, which, arising from the solid logical structure exemplified by Whitehead's and Russell's "Principia Mathematica" attempted to put the philosophy of science on a firm footing in the sense of absolute knowledge and truth.

Compare and Contrast Gibson’s and Gregory’s theories of perception Gibson’s and Gregory’s theories of perception both suggest that eye-retina is important for perception. The both believe that without eye-retina, a person will not be able to see.

A listing of psychological research being conducted online.

Compare and contrast theories of perception

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