Psychology

Reference Article
Article Seeing in Colour. Optics and Laser Technology (2010), doi 10. 1016j.optlastec.2010.02.006.
Authors Beau Lotto, Richard Clarke, David Corney and Dale Purves.
The Reference Cited in the Textbook
The Reference cited in the Textbook.

The article written by Lotto, Clarke, Corney and Purves (2010), is the reference cited in the textbook. The subject matter being discussed is why understanding perception as well as biology of color is challenging for humans. The text book seeks to address this subject by developing a framework that will clearly explain color perception. The text book seeks to explain this by exploring color vision and its biological advantages, the mechanisms underlying color perception, trichromacy, the psychological explanations of contextual impact of color and any new approaches to understanding color effects in humans.

Chosen Article
Article Color Vision The Wonder of Hue. Current Biology, 18 (16) R700-R702.
Authors Jay Neitz and Maureen Neitz
Summary of Introduction Section of the Paper, the Subject Matter and the Relevant Background

This paper seeks to explain how the brain works in terms of color vision. Just like in the reference material which emphasizes that understanding the perception of color is a hard task as what is seen always is not always what is there, the article by Neitz and Neitz (2008), also stresses that for one to understand the biology of the brain, they have to think outside the usual tradition of natural science. According to these authors, this biology has to be connected something that is intangible or to a personal experience. This article seeks to explore the area of color visionexperience by using what psychologists have verified from neurons that guarantee to help make this link.

This study is based on observation and on literature review. It uses observation of how children differentiate between different colors noting the uniqueness of the colors and builds on it to explain the biology behind color vision. This study is purely developed from literature and compiles different findings to explain the nature of different colors to various neurons in the brain.  This study uses Albert Einsteins observation that progress in the way we understand nature originate from an instinctive grasp of essentials of complex facts which leads scientist to postulate basic laws which are hypothetical from which they use to draw conclusions. Since this formula has been found to be useful in shedding light on the cosmos, the authors argue that it could be fruitful in comprehending the workings of the brain which are quite complex. It is on this formula that the study or rather the article is founded on. The authors acknowledge that neurosurgeons are yet to agree on the hypothetical laws that should be adopted.  Mller s law of specific nerve energies  is one of the grand postulates that have guided efforts to fathom the brain. According to this law, each sensory nerve ending type, whether stimulated mechanically, electrically or any other way, results to its own sensation particular sensation. In addition, sensation type is not determined by any special character of the various nerves but rather by the part of the brain where their fibers terminate.

The proposal that an individual neuron located somewhere in the brain results to a specific sensation relates the firing of a neuron to perceptual experience. This paper therefore seeks to explore the mechanisms that determine the relationship between the perception of color, the physical stimulus and the wave composition of light by reviewing literature n prior studies.

Summary of the Methodology used in the Paper
Unlike other typical papers, this paper does not clearly indicate the methodology that was used to achieve the research objective. However, from the article, one can deduce that as an explanatory study, the researchers critically analyzed and reviewed literature on prior studies on similar topics so as to address the research problem. The authors therefore collected data using secondary sources. Though this method has been criticized by many authors who argue that the researcher is not able to identify the errors that were committed hence provide for them to increase validity and reliability, it still is a good method as it saves on time and financial resources which are very critical in research work. Besides, this method is the best to use considering the comprehensive nature of this study. As long as the authors conduct a critical analysis and review as many articles as is possible before making the conclusion, use of secondary sources and analysis methods such as content analysis that was used in this article are quite reliable.

The researchers use a model in which they start by explaining the biology behind color vision. According to the authors, there are a set of receptors whose function is to transform light absorption into signals that are electrical for each point that is discriminable in the retinal image. The characteristicsfeatures of each of the tiny parts are extracted as these signals are transmitted to higher regionscenters to form the basis of percepts.  The way the brain represents a small segment in a visual scene should be comparable to a pixel in a video display though not necessarily perfect. The color as well as brightness of light for each pixel are represented as 3 numbers that denote the intensities of each of the colors red, blue and green. In the visual brain, the features of each small subdivision of a specific scene are experienced as some blend of essential color sensations. That is the unique hues of red, blue, green, yellow as well as white and black. This explains why more than four crayons added to the page of coloring book whether white or black will satisfactorily represent the world to children.

The authors then go on to review literature on similar topics. They use Stoughton and Conways discovery of the posterior inferior temporal cortex, a brain region where the there is clustering of turning chromatic sensitivities of neurons around the unique hues as a historical perspective of the topic under study. The researchers use this discovery to address the question of how three types of cone photoreceptor eventually relate to black, white and the four unique hues green, yellow, red and blue as the six fundamental color percepts.

Results
To explain the wave composition of light, the researchers use the experiment conducted by Thomas Young who demonstrates that representation of a wavelength of light which is continuous variable requires a set of receptors that code the virtual amount of light in spectral bands that are discrete. Since the visual system is required to analyze each point of an image for its wavelength, its biology is limited to a number of detectors with varying spectral sensitivities. This is because it is impossible for each point to be conceived as containing an infinite number of particles. It is therefore necessary to limit assume that the number limited for each filament of the nerve which is sensitive may comprise of three portions (one for each of the principle colors). The proposed receptors have been linked to human perceptions by Herman Helmholtz who argued that Youngs postulation is a law of specific sense of energies which tries to explain the sensations of green, red, and violet. This statement resulted to a search for a theory of color perception that can be comprehended in terms of efforts to fit the properties of neurons to peoples perceptions of color.

Other literature however shows that the three postulated receptors by Helmholtz and Young do not match up with the number of the unique hues people experience. The authors use a diagram to demonstrate the perception of an equal energy spectrum in the event the hue perception is directly attributed to three photoreceptors. According to Herring, one of the reviewed authors, the colors are in fact four and not three as earlier suggested by Helmholtz and Young. These colors are blue, red and green plus yellow- which the trichromatic does not seem to explain. According to this author, the four colors have a simplicity that other colors lack and though colors may be explained as shades of one or two of these four colors which are psychologically simple, such as green , blue, or blue-green, colors can never be explaineddescribed as simultaneously being yellow and blue or as red and green.

This argument is resolved in modern literature by a two-stage color processing model proposed by Hurvich and Jameson. In this model, the first stage produces outputs from the three types of cone which undergo the second stage in where they are combined using neural circuitry that compares the cones quantal catches to create circuits for hue percept that exist as pairs that are opponent to each other. That is blue-yellow and red-green.  In the second processing, the opponent character explains the yielding of a percept of white which is absence of hue that is caused by mixtures of all visible wavelengths of light. It also explains Herings observation that no color is seen as reddish-green or as bluish-yellow.

According to the authors, advances in electrophysiology since the 1950s have made recording of chromatic response properties of neurons possible. The fact that recordings from neurons that are spectrally opponent in the lateral geniculate nucleus of the thalamus seemed to confirm the features of the two-stage color processing model proposed by Hurvich and Jameson excited biologists. Although the classes of blue (B) - yellow (Y) lateral geniculate nucleus appeared to be two Y-B and B-Y, which would be expected to match up with blue and yellow, and the two lateral geniculate nucleus of red G-R and R-G as required for4 green and red respectively, the illustrated spectral signatures of the neurons illustrated by this model do not correspond with the way humans perceive color. These discrepancies have been noted but ignored by most textbooks which try to explain the human color perception.

The authors found that there is great precision in the characterization of absorption of the three cone pigments over the last couple of years. As a result, it is now possible to describe explicitly the difference between perpetual, opponent hue mechanisms and the textbook lateral geniculate nucleus cells in terms of the contribution of the specific cones to each. Here, there is substantial difference between the two. The text book lateral geniculate nucleus of red-green opponent cells lack short wavelength sensitive cone input and the middle wavelength sensitive cones oppose the signals of the long wavelength sensitive cones. On the contrary humans red-green perceptions are based on circuitry where signals from short wavelength sensitive as well as long wavelength sensitive cones account for red perception in that the redness sensation at the spectrums long-wave-length end is mediated by long wavelength sensitive cones while the redness at the violet end of the spectrum are mediated by short wavelength sensitive cones. Signals from the middle wavelength sensitive cones which account for greenness oppose both the short wavelength sensitive and long wavelength sensitive inputs.

Likewise, blue-yellow lateral geniculate nucleus cells that are best characterized have input from short wavelength sensitive cones which is against the sum of long wavelength sensitive and middle wavelength sensitive cones.  However, unique hues spectral location requires blue-yellow color vision to have a basis on short wavelength sensitive and middle wavelength sensitive cones minus the long wavelength sensitive circuitry where middle wavelength sensitive cones mostly produce blueness of wavelength that is above 460nm while the short wavelength sensitive cones produce blueness of wavelength that is below 460nm. From the results it is clear that most typical lateral geniculate nucleus cells predict an absence of redness in the spectrums short wavelength end and an absence of blueness in the long wavelength part of the spectrum (above 460nm), and the unique hues will be located in locations that are different from those observed by humans. The phenomenological color experience does not therefore match with the properties of lateral geniculate nucleus neurons.

Interpretations of the Results by the Authors
This paper acknowledges that it is a challenge to understand color vision as far as its biology is concerned. The article attributes this to the inability to solve the lacking correspondence between phenomenological color experience and the properties of lateral geniculate nucleus which are the only cells that have been offered as candidates for arbitrating hue experience. As a result, some vision scientists are questioning the possibility or whether it is sensible to reconcile neurophysiology and phenomenology domains. According to the article, the discovery of cells that have spectral signatures that match humans hue perception presents a possibility to eventually solving the transformation of cone signals into color vision by the circuit. Previously, difficulty in finding a hypothetical logical solution has been the main challenge to resolving the inconsistency between hue perception and the characteristics of color opponent cells. According to the authors, the simplest idea is to extend the two-stage model where more processing stages can be added to the cortex so as to further that are wrong into ones that correspond to perception. The authors however note that this idea, however well the version is explained or thought out is not adequate in explaining the biology of color vision and raises more questions than it actually answers. Presently, it is not clear how and why cone signals would be recombined by the cortex.

In contrast to the above multistage idea, another alternative has been offered in which it is argued that parvicellular lateral geniculate nucleus spectral opponent cells that are most frequently recorded are not a substrate for color vision. According to the proponent of this hypothesis, most of the spectrally opponent neurons are highly responsive to wavelength and to spatial contrast. It is therefore possible that only a small subset of opponent lateral geniculate nucleus cells, ones which all along have the appropriate spectral signatures mediate hue perceptions. This suggestion has turned out to be prophetic as new findings imply that there are populations of cells whose cone inputs match the required circuitry for human hue perception. The authors argue that it could be possible that the human brain utilizes the majority of the lateral geniculate nucleus cells for spatial vision by obtaining their robust responses to luminance contrast and having the spectral responses filtered out. Signals from population cells that are much smaller but with the proper spectral signatures at the lateral geniculate nucleus level could be used for color. The authors conclude that the two discoveries of neurons that possess the appropriate spectral properties to arbitrate phenomenological color experience, one population in the lateral geniculate nucleus and the other in the posterior inferior temporal cortex is welcoming news. These discoveries could signify two levels of a color processing pathway that starts in the retina and terminates in hue perception.

How this Article relates to the Reference Material.
Lotto, Clarke, Corney and Purves (2010), argue that understanding the perception of color is quite difficult as what humans see is not what is always there. Neitz and Neitz (2008) also explain that comprehending the brain requires thinking that is beyond the main tradition of natural science and that its biology has to be related to something that is not tangible. Both papers seek to provide frameworks that clearly explain why humans see what they see.  The article by Neitz and Neitz (2008), acknowledges that it is a challenge to understand color vision as far as its biology is concerned and attributes this to the inability to solve the lacking correspondence between phenomenological color experience and the properties of lateral geniculate nucleus which are the only cells that have been offered as candidates for arbitrating hue experience. In so doing, this paper supports what is in the text book and is referenced as (Lotto, Clarke, Corney and Purves (2010)) discusses.

In discussing the mechanisms that underlie color perception, I feel that the text book should have used  more of information from the reference particularly as far as Youngs postulation which is a  law of specific sense of energies that tries to explain the sensations of green, red, and violet is concerned. The article covers this part more comprehensively and explains how the referred to Youngs postulations as a law of specific energies, a statement that has increased the quest for a theory for a theory of color perception that can be comprehended in terms of efforts to fit the properties of neurons to peoples perceptions of color. The fact that the article used literature which shows that the three postulated receptors by Helmholtz and Young do not match up with the number of the unique hues people experience also matches with the discussions of the reference on trichromacy. Einsteins postulations should also be added to Newtons concept to make the conceptional framework of the textbook more comprehensive.

The psychological explanations of the effects of color are not as comprehensively covered in the article as they are in the reference but what is there is quality material that could be added to the text book. The fact this article compares the psychological perception of color and what actually happens increases its quality. The authors have adequately addressed and compared phenomenological color experience with the psychological contextual effects of color in terms of the properties of lateral geniculate nucleus cells. This article basically explains why understanding the concept and biology of color perception in humans is challenging and tries to provide an easier framework that explains the concept of color vision. The findings also give the identified suggestions of models that could make this explanation and understanding much easier. This article should be given more weight in the text book because of its various contributions to the topic under discussion. The author should use particularly in explaining why comprehending perception of color remains challenging.