The Biological Processing System Discussion and Design Review February 17, 2015
Introduction Signal detection is the ability to detect a pattern or stimulus present in a given environment, and the subsequent cognitive process of perception, and action that occurs in response. There are several modalities of signal detection that leverage the five senses; sight, smell, hearing, taste, and touch. These modalities are often used in combination with one another in order to cognitively process and react to a stimuli. The strength of the signal determines the pace at which it reaches the brain. The stronger the signal, the more swiftly it is detected and processed. (Gribbons, 2013)The following writing will focus on the visual modality of signal detection, namely the visual sensory system. The visual system is the strongest modality of signal detection, with the capacity to relay more information than all four remaining senses combined. (Gribbons, 2013) This writing evaluate the visual sensory system and the physiological process that occurs in response to a stimuli. Elements that affect the perception of stimuli will then be discussed, and applied to an example design case with elderly users as an area of focus. The Visual Sensory System The visual sensory system has been an integral part of human interaction with the environment and a determinant of survival since the beginning of human life. The process begins when a stimulus emerges in the environment. This stimulus, or signal could be anything from an object, to a surface, to a widget on a computer screen. The visual sensory process begins by detecting electromagnetic energy that is being emitted, absorbed, or reflected by this stimuli. (Purves, Cabeza, & Hutteul, 2013)This electromagnetic energy, also referred to as light, is the sole element of a stimulus that is received and processed by the visual sensory system. The human visual system can process electromagnetic wavelengths between the range of 400 to 700 nanometers, which accounts for a small portion of the electromagnetic spectrum. (Purves, Cabeza, & Hutteul, 2013)Once the stimulus has initially been detected, a physiological receptor system is enacted, and the process leading to perception begins. Visual Physiological Response to Stimuli Once a stimuli enters the range of vision, its electromagnetic rays traverse the cornea, the outer most protective layer of the eyeball (Fletcher, 2013)This fibrous layer remains static, however absorbs a portion of the light rays that pass through (Fletcher, 2013). The rays then travel through the pupil, which adjusts in accordance to the luminance of the environment, narrowing in bright light, and expanding in dim light, in order to receive a clear image of the stimuli. (Ritter, 1998) After the optimal size of the pupil has been obtained, the light moves through the lens, which adapts its shape depending on the proximity of the stimuli. When the stimuli is up close, light rays converge as they enter the eye. (Purves, Cabeza, & Hutteul, 2013)This causes the ciliary muscles to tighten, contouring the lens into a round shape in order to bring the image into focus. When the stimuli is farther away, the light rays enter the eye as straight, concurrent
beams. In order to effectively receive these rays, the ciliary muscles shift the lens to create a flattened shape. Once the light has passed through the lens, the focused image is reflected onto the retina, where visual reception occurs. (Purves, Cabeza, & Hutteul, 2013) The retina is the area of the eye which holds the visual receptor cells that transform electromagnetic waves into neural impulses to be sent to the brain. There are two types of visual receptor cells, also known as photoreceptors,that exist in the retina: rods, and cones. Rods function as a part of the scotopic, or dark adapted visual process. (Purves, Cabeza, & Hutteul, 2013)The rods are enacted in levels of low light, and in low luminance environments, making them integral part of night vision. This is attributed to their ability to process wide bandwidths of light due to a pigment they contain, Rhodopsin. The presence of rhodopsin in their structural makeup also results in color insensitivity and poor acuity. This is especially true for colors with long wavelengths, namely red, which tends to appear black in low luminance. Rods govern the peripheral retina and are chiefly responsible for detecting stimuli in peripheral vision. (Purves, Cabeza, & Hutteul, 2013)The rod’s counterpart, cones, function best in high luminance environments as a part of the photopic visual process, also known as day vision. (Purves, Cabeza, & Hutteul, 2013) In contrast to rods, cones process a limited bandwidth of light, classifying them as chromatic, and making them highly sensitive to color, able to provide high visual acuity. Cones are responsible for processing stimuli located in the central vision due to their positon in the fovea. (Purves, Cabeza, & Hutteul, 2013) Elements that Affect Visual Perception Based on the physiological process of visual sensory system, one can identify three main variables that have the most impact on the perception of a stimuli; contrast, brightness, and hue. Through manipulation of these factors, an influencer can help determine how a stimuli is received. In the following paragraphs each of these elements will be evaluated in terms of their role in perception. Contrast: Contrast can be defined as the degree of perceived difference in appearance between a subject and its background. (Guo, 2008 )It is the element that enables humans to identify edges and shapes. It is also first characteristic that reaches the brain when a person is exposed to stimuli, making it one of the strongest elements of a signal. (Peli, 1990) When manipulating contrast, one must always keep in mind that in order for the subject to be distinguishable, it must maintain the minimum amount of contrast that can be detected, also known as the contrast threshold. (De Sa, 2004) When contrast between visual elements is low, visibility is low. Contrast polarity is also an important concept in the realm of contrast. Polarity is positive when the background of a given stimuli is light, with the subject being darker. Negative Polarity occurs when the background is darker than the stimuli. Positive polarity is clearer, and easier to read. Spatial frequency is another variable that impacts the perception of contrast. This is the number of dark to light sequences within the space that is occupied by the stimulus. (De Sa, 2004)In general, high spatial frequency requires high contrast, medium spatial frequency
requires very low contrast, and low spatial frequency requires medium contrast in order for a gradient to be identified by the subject. (De Sa, 2004) The brightness of the environment is also crucial in relation to high spatial frequency, which requires a high level of illumination for visibility. (Bex & Makous, 2002) Brightness: Brightness can be defined as the intensity of light either given off, or reflected by an object. It determines the visibility of the stimuli to the human, and has the second strongest impact on the perception of stimuli following contrast. (Wickens, Lee, Liu, & Becker, 2004) Brightness can be separated into two iterations: luminance and illuminance. Luminance is the measure of electromagnetic energy emitted by a stimuli while illuminance is the measure of light in an environment. (Wickens, Lee, Liu, & Becker, 2004) Illumination is affected directly by the distance from a light source, the closer to the light source, the stronger the brightness. (Eagleman & Jacobson, 2004 )Brightness can be manipulated in order increase or decrease the visibility of a stimuli. Color sensitivity and visual acuity are also highly affected by the luminance of the surrounding environment, “Two people can perceive the colour of an object very differently, depending on how they are viewing it. For instance, if you go into a room that is illuminated blue, the cone receptors on your retina compensate within 10 to 15 seconds, making the blue appear less intense. If a second person enters the blue room, it takes time for their retina to adjust so they will, at least for a short time, have a different colour experience from you. Alternatively, if the lighting is suddenly changed from blue to white, everything in the room takes on an orange hue until your eyes readjust.” (Spinney, 2006) Hue: The hue of a stimuli refers to the wavelength of electromagnetic rays that comprise color. As mentioned earlier, cones located in the fovea are responsible for color vision. (Purves, Cabeza, & Hutteul, 2013)There are three types of cones each containing a pigment called cone opsins. This specializes in capturing wavelengths of different sizes. (Purves, Cabeza, & Hutteul, 2013)Short wavelengths are perceived as blue-violet, medium are recognized as green or yellow, while longer wavelengths are perceived as red. The trichromatic theory of color maintains that hue is determined by three colors; red, blue and green. It also states that all colors are derived from a combination of these three primary hues. (Purves, Cabeza, & Hutteul, 2013) Wavelengths of pure color that display the most intense hue are referred to as saturated color. Saturated colors should be used in order to identify elements of high priority (Lidwell, Holden, & Butler, 2010)Colors can also be diluted by white and gray tones, which are referred to as “achromatic” colors. Bright achromatic colors are commonly perceived as friendly and professional, while darker desaturated colors are perceived as serious and professional. (Lidwell, Holden, & Butler, 2010)Colors with longer wavelengths tend to come to the foreground of vision, while colors with shorter wavelengths merge into the background (Lidwell, Holden, & Butler, 2010) In terms of color combination, there several approaches to ensure an aesthetically pleasing mix. These color combinations include: analogous, triadic, complementary and quadratic. Each is named for the combination of colors designated by their
location on the color wheel. The number of colors used should be limited to five, as to not fatigue the eye of the user. Example Design Case: Boomergrandparents.com Boomergrandparents.com is a website dedicated to the sharing of experience and advice on the baby boomer lifestyle in the digital age. The target user is a person age fifty five and up, with grandchildren, and the behavior of utilizing the internet as a vehicle for information gathering, leisure time activities and experience sharing. There several physiological changes that occur during the aging process that directly impact the visual sensory system that should be considered when evaluating the design of this website. Physiological Changes that impact the Visual Sensory System for the elderly: Many components of the visual sensory system are impaired for the elderly. As humans age, the lens of the eye becomes less supple, and the ability for the ciliary muscles to shape the lens to accommodate light rays declines. This presents extreme difficulty in focusing the eye in an optimal matter, and significantly decreases the amount of light that arrives to the retina. One study showed that the retina of a 60 year-old retina receives only 30% of the light that reaches a 20 year-old's retina (Long, 1998 ). The implication of this change results in a decreased perception of color and contrast, as well as a less focused picture of the stimuli communicated to the retina. Over time the tissue at the center of the lens thickens, making the lens more opaque. (Leopold, 1965 )This tissue yellows due to exposure to UV rays, which results in lowered sensitivity to the color blue. (Pollack & Atkeson, 1978) The diameter of the pupil decreases, limiting the ability to accommodate environments with less illuminance. (Botwinik, 1973) This causes a decreased ability to see in the dark. The abilities of peripheral vision are also compromised over time, and reduced significantly in elderly populations. (Cerella, 1985 ) Boomergrandparents.com Design Issues: There are several areas of Boomergrandparents.com that could be iterated in order to augment the limitations of its elderly user population. Below several of the most critical design flaws have been evaluated based on the physiological limitations of the user.
Menu Bar: The blue background of the menu bar would be difficult for elderly users to detect due to the yellowing of the lens that occurs with age. This would also result in a lack of contrast sensitivity, with the blue background blending in with the white lettering. The color arrangement of orange and blue represents a complementary color combination. In some cases, this is an encouraged design choice, however considering the user’s difficulty in identifying blue, a different combination would improve the visibility within this user group’s perception. Often, a
combination of highly saturated colors like the blue and orange presented here can fatigue the eye due to interference with one another. One recommendation could be to use more desaturated colors to guard against fatigue. Also, avoiding blue would be a wise choice in the context of the elderly demographic. One option for the design of the menu bar would be to keep a white background with black lettering for maximum contrast and thus readability. Peripheral Information:
In this example, the information placed on the margin could be considered a serious design mistake considering the elderly user. As a person ages, their aptitude for peripheral vision decreases. This makes information located on the side of the screen less obvious, and more difficult for the user to detect. The green boxes with white font also present a contrast issue that could make the writing hard to discern. In the “About Me & BG� the presence of blue font is prevalent. As described above, this color is difficult for elderly users to read. This section also presents a contrast issue with the thin blue font against a light grey/white gradient background. This could be difficult for users to read to due to a lack of difference of color from the font to the background. The image is also small, and slightly distorted which presents more difficulty on top of a preexisting lack of visual acuity. One design improvement could be to increase the contrast by using a darker font in a more visually accessible color such as black, and to enlarge the image or replace it with a larger, higher quality image that still communicates the intended point. Heading:
The theme colors of the website are orange, green and blue. This is exemplified in the header of the site depicted above. The color with the longest wavelength in this combination is orange,
which will stand out most prominently to the user, then green which maintains a medium a wavelength, followed by blue. As discussed in several points throughout this writing, blue is a difficult color for this specific user group to detect. With the orange wavelength coming to the foreground of vision, the word “boomer” will be the first recognized by the viewer. The website title is also listed in the logo box in white writing. The white writing with a black background is an example of negative polarity, as referred to in the contrast section. It is more difficult for users to read text that is depicted in negative polarity. The green writing against the dark grey background presents an easy to read text, with little fatigue due to a good balance of contrast from the words to the background. There is also a photograph surrounded by a border with the three theme colors. Color should be used to draw attention to the most important areas of the site, rendering this border unnecessary. One recommendation would be to remove the borders on both the logo, and the photo and reserve color for areas of the site that the designer would like to lead the user to. Also, using a more aesthetic color combination such as; analogous, triadic, complementary or triadic would create a more visually appealing experience. (Lidwell, Holden, & Butler, 2010) Trending Box: The “Trending Now” box appears on the side margin in the right hand side of the page. The blue background with the white lettering presents a contrast issue that could cause a lack of distinction between the background and the letters. A red arrow also appears on the left side of the box. This combination of red and blue causes a vibration along the edge and is barely visible to user. The location of the box also presents an issue. As referenced previously, due to declining abilities in peripheral vision information placed on the side of the page is often overlooked by the elderly user. The font size is also small and would result in eye strain for elderly users that lack visual acuity. An amendment to these issues could be the change the colors of the background and the lettering to increase the contrast and thus the visibility. Also the location could be moved to a more focal area on the page, and the font could be increased to help improve visibility.
References (n.d.). Bex, P., & Makous, W. (2002). Spatial Frequency, phase, and the contrast of natural images . Journal of the Optical Society of America , 1096-1106. Botwinik, J. (1973). Aging and Behavior: A Comprehensive Integration of Research Findings. New York : Springer. Cerella, J. (1985 ). Age Related Decline in Extra Foveal Perception . Journal of Gerontology , 727736. De Sa, V. (2004). Contrast and Spatial Frequency . Retrieved from www.cogsci.ucsd.edu: http://www.cogsci.ucsd.edu/~desa/101a/midterm2reviewsheet.pdf Eagleman, D., & Jacobson, J. (2004 ). Percieved Luminance . Nature , 854-856. Fletcher, T. (2013, January). Lecture 16:The Visual System. Retrieved from http://vanat.cvm.umn.edu/: http://vanat.cvm.umn.edu/NeuroLectPDFs/LectVisualSys.pdf Gribbons, W. (2013, February ). Sensory Perception Week Three and Four Powerpoint . Guo, P. (2008 , January ). User Interface Design and Implementation . Retrieved from courses.csail.mit: http://courses.csail.mit.edu/6.831/archive/2008/lectures/L15-graphicdesign/L15-graphic-design.pdf Leopold, I. (1965 ). The Eye in Clinical Features of the Older Patient . JT Freeman . Lidwell, W., Holden, K., & Butler, J. (2010). Universal Principles of Design . Beverly : Rockport Publishers . Long, N. (1998 ). Exploring the Ways we approach the elderly consumer . Journal of Market Research , 73-91. Peli, E. (1990, March 26). Contrast in Complex Images . Retrieved from http://citeseerx.ist.psu.edu/: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.146.5582&rep=rep1&type= pdf Pollack, R., & Atkeson, B. (1978). A Life Span Approach to Perceptual Development . New York Academic Press. Purves, D., Cabeza, R., & Hutteul, S. (2013). Principles of Cognitive Nueroscience , Second Edition. In D. Purves, R. Cabeza, & S. Hutteul, Principles of Cognitive Nueroscience , Second Edition (p. Chapter 3). Sinaur Associates .
Ritter, F. (1998). Basic Psychology for Human Factors . Retrieved from frankritter.com: http://www.frankritter.com/ithf/notes/lecture4/lecture4b.html Spinney, L. (2006). How the Light Takes You. New Scientist , 50-62 . Wickens, C., Lee, J., Liu, L., & Becker, S. G. (2004). An Introduction of Human Factors Engineering . New Jersey: Prentice Hall.