Biological Processing Systems & Coin-operated Commercial Laundromat Dryers
Human Factors in Information Design, Bentley University
HF700: Human Factors Foundations
William Gribbons
October 05, 2020
Human perception developed to aid survival in varying environments. Human senses are vehicles of human perception, categorized as visual, auditory, kinesthetic, or tactile. With sensory perception, humans rapidly extract and process environmental information at the interaction of the sensory system and the high-order cognitive processes to ultimately conduct an appropriate response (Marr, 2010) (Milner & Goodale, 1996). However, regardless of sensory type, perception must be contextualized within given parameters and environment. Gibson (2015) describes the environment, “as the surfaces that separate substances from the medium in which the animals live... And if there is information in light for the perception of surfaces, is there information for the perception of what they afford?” This paper will primarily focus on visual perception as human vision typically offers greatest sensitivity and bandwidth, and respective design implications and recommendations in the form of a product review.
Sensory Perception and Signal Detection
Human perception can be conveyed through the information processing model, which models how humans may interpret and process signals of their environment through detection/ discrimination, encoding, retention, and recall. Signals can be “represented as a function of one or more variables” and “may be defined as an observable change in a quantifiable entity” (Chakravorty, 2018). Humans are neurologically engineered to detect differences in signals in their environments rather than changes in absolute measurements. Signal detection refers to the detection of degree of change of a sensory signal within an environment, while signal discrimination refers to the ability to differentiate a change of a sensory signal within an environment.
While signal perception of the senses varies in physiological processes, each is guided by the interpretation of similar principles: frequency and pressure. The biological benchmark of signals, the Just-Noticeable-Difference (JND), marks the absolute threshold and minimum change required for a noticeable, detectable difference in a signal at least half of the time (Gollan & Ferscha, 2016). Each of these principles can be understood in terms of Visual Attention Allocation: salience, effort, expectancy, and value/ bandwidth. Top-down information sampling includes expectancy and value/ bandwidth—the first is the probability that a signal may occur and answers the question: ‘Is the person expecting a change in signal?’ while the latter is the importance of the given signal and answers: ‘How important is the change in signal?’ (Gollan & Ferscha, 2016). Top-down information sampling suggests an individual brings expectations and experience to interpreting a signal. However, bottom-up information sampling focuses on the parameters of information access, including salience and effort (Gollan & Ferscha, 2016). Salience is the attractiveness of a signal, affected by contrast from its environment, and answers: ‘Was the signal strong enough to be noticed?’ Onset typically indicates when a signal begins and this is the point at which the signal is the most salient (Sewell & Smith, 2012). Effort represents the only inhibitor to a signal, either physical or mental, and answers: ‘Was the person capable of noticing the change in signal?’ Designers are responsible for optimizing interactions via signals that can be effectively detected, and in some cases discriminated against, in size, feel, color, and shape, etc. To measure the success of a signal, pressure, or amplitude, and frequency require critical consideration. A strong signal supports the task and environment and receives prioritization in the brain's processing center. Signals that are too strong or lack variation may foster fatigue and inattentive behavior. Counter, signals that are too weak may be missed. Signals vary in strength and, further, some signal detection varies across humans. (Smith & Atchison, 1995). This human variability can be further exacerbated by age and disability (Lockhart & Shi, 2010). Environmental and contextual factors such as distance, precipitation, smog, and smoke may affect perception (Peli, 1999).
Human Eye and Visual Perception
Of available sensory perception, the human eye offers visual perception as the most sensitive to signal detection and discrimination. The eye is optimized to receive information from its surroundings, and physiology of the eye informs and operates in tandem with visual perception, a nearly instantaneous interaction between both eyes and the brain via a complex network of neurons, receptors, and specialized cells. Eyes can detect a type of signal, an image, that is “an example of a two-dimensional signal, with the horizontal and vertical coordinates of the image representing the two dimensions” (Haykin, 2003). As diagrammed in Figure 01: Anatomy of the Human Eye Diagram, an image enters the human eye as light from the anterior chamber, traveling through the convex clear barrier of the cornea, the aqueous humor, and then through the pupil, a hole that may vary 2-8 mm as defined by the iris (Spring, Fellers, & Davidson). The iris, a circular diaphragm, restricts the amount of light that enters the eye depending on surrounding environmental light conditions. Next, light reaches a biconvex lens, which sends an inverted image to the posterior chamber of the eye to focus and translate it into an image and subsequent signal (Spring, Fellers, & Davidson).
Figure 01: Anatomy of the Human Eye Diagram
The posterior chamber, filled with vitreous humor, is lined by the retina, a layer of photoreceptor cells called rod and cones at the interior and back of the eye as seen in Figure 02: Cone and Rod Cell Distribution in the Retina Graph (Spring, Fellers, & Davidson). Here, the inverted image is detected for processing of visual perception. While rods are a greater proportion of the photoreceptor cells and more sensitive to low light levels, cones are more concentrated in the center back of the eye and are more sensitive to color, offering higher visual acuity under normal light conditions—these differences point to familiar characteristics of visual perception and properties of light as wavelengths as seen in Figure 03: Absorption Spectra of Human Visual Pigments Graph (Spring, Fellers, & Davidson). The image is then translated from these photoreceptor cells through connected fibers of the optic nerve bundle as a series of signal transmissions to the brain.
Figure 02: Cone and Rod Cell Distribution in the Retina Graph
Figure 03: Absorption Spectra of Human Visual Pigments Graph
Peripheral vision, vision occurring outside of the point of visual fixation and known as scotopic vision, is formed by blue sensitive cones and 120 million light sensitive rods located at the periphery of the optical axis of each eye (Ingram, Sampath, & Fain, 2016). These light sensitive rod cells are primarily responsible for detecting more significant contextual changes, especially at the periphery of our vision, including contour, motion, and night vision. Contour, enhanced by the neurological structure of the eye, compounds visual contrast as photoreceptor cells detect change along a boundary of an object and proceed to turn off when representing background or less poignant context (Ratliff, 1971)(Loffler, 2008). Detection of edges, or contours of stimuli in an environment, can also indicate texture and surface, providing an augmented perception of surroundings (Fish & Scrivener, 1990). In conjunction with the aperture of the iris, which adjusts for more light to reach the retina in low ambient lighting, light sensitive rod cells enable humans to detect change at night or in dark environments. Finally, peripheral vision equips humans with motion vision in most of the visual field, which qualifies a critical survival adaptation to process threats outside the scope of primary gaze.
The macula, the central portion of the eye with significant visual acuity, is home of the fovea, aligned with the optical axis of each eye, and a small indentation called the foveola, which offers the highest concentration of green and red sensitive cones and therefore highest visual acuity and temporal resolution. This direct foveal vision under well-lit conditions, photopic vision, is composed of approximately six million cone cells, which primarily function to detect: color, contrast, and size, which may impact sensory fatigue (Arshavsky, 2012). Color, compiles with arbitrary standards of the visual light spectrum and can be measured as wavelengths. Color is composed of luminance, saturation, and hue. Luminance is the strongest factor in color and is the intensity of a light source, measured as energy at a source, while brightness is the human experience of the light source, which is often less intense due to refraction. Saturation indicates the purity of the light wavelength and higher saturated colors are described as “garish” or “vivid.” However, when saturation is too high, or “overpowering,” in an image that requires a prolonged viewing period, we see the gradual stages of fatigue. Fatigue can occur at any frequency or amplitude type and resides on a continuum, which begins with fostering inattentive behavior and leads to high levels of mindlessness, a dangerous situation where signals may be missed. There may also be confusion in depth perception and fatigue in after image and sensory memory (Jackson, MacDonald, & Freeman, 1994). Finally, color includes hue, which refers to chroma or typical “names'' of colors. Hues of the visible light spectrum range from “red” at ~700 nm to “violet” at ~400 nm. And the region of the light spectrum that offers the greatest sensitivity to detection in humans is centralized at yellow-green at ~535 nm, meaning that signals of yellow-green color occur at peak signal perception for humans. Some of the differing properties based on perception of the eye of these wavelengths include: red—good visibility in high ambient lighting and poor visibility in low symbol luminance; green, yellow, and orange—good visibility at a broad range of intermediate luminances; and blue—good visibility in low symbol luminance and poorest overall visual acuity. Next, visual acuity indicates size and shape of an image or stimuli within its environment, influenced by: visual competition of stimuli and variation in visual acuity (Anstis, 1998); appropriate contrast in hue, saturation, perceived brightness; relative viewing conditions and distance which may refract light and perception of the image; and overall vision quality, which deteriorates over time (Foley & Legge, 1981). Finally, contrast is the perceptual difference of signals within an environment. The design goal of contrast is to achieve a just noticeable-difference or optimum contrast, which is significantly affected by the intersection of: size, luminance, saturation, hue, overall color palette, and sound and touch in terms of amplitude and frequency.
Design Implications
Tendencies of the visual perception outline pragmatic design implications: guide attention and navigation with appropriate hierarchical contrast; exercise caution in large areas of bright colors, highly saturated colors, or repetitive patterns; consider fatigue in prolonged viewing conditions and accessibility limitations such as detailed blue images for aging eyes; and restrict user control of color (Mouroulis). Sensory perception informs humans of their environments. Human responses are informed by these perceived parameters. However, designers can significantly alter these interactions to stimulate automatic and predictable responses, leaving us with considerable design implications.
Product Review and Design Walkthrough
Figure 04: Product Image Context 01, Context 02
The product under review is the coin-operated commercial laundromat dryer Huebsch Stack Dryer 30LB Capacity, pictured in context in Figure 04: Product Image Context 01, Context 02 and described in the product manual (Alliance Laundry Systems, 2015).
Usually found in public laundromats, this dryer functions in the prototypical American standard process of laundry to dry fabric materials via heat, forced air, and stimulation of a rotating barrel. To operate, a user must place the clothes in the machine—first opening the door of the machine; inserting damp materials into the drying barrel; and then pressing the door closed. Next, a user must select settings in the interface—inserting quarters appropriately; selecting the desired settings for barrel temperature by pressing one of four buttons until a given light indicates successful selection; and finally beginning a cycle by pressing the “start” button. Upon completion of the cycle, a user must see the blinking “0” timestamp and proceed to remove their materials from the barrel or choose to repeat the process. While this product exhibits examples of all types of sensory signals: visual, auditory, kinesthetic, or tactile, this design review will focus on analysis and recommendations for visual senses.
The environment and relative visual stimulus of a typical commercial dryer varies greatly, as do cities across North America (Vartabedian, 2017). Some factors that influence visual perception include ambient lighting conditions: natural sunlight, affected by weather or environment; and properties of type of lighting such as LED, incandescent, or halogen. There is the additional immediate visual stimuli of adjacent machines in use and actions of surrounding customers. The user profile exhibits the following characteristics: 60% women, mostly low income renters, and lower literacy/English not a first language (Martin Ray Laundry Systems). Laundromats are busy environments with distinct, task-oriented individuals; therefore it is critical that the signals of this product effectively elicit appropriate human response. In particular, we must consider aging populations limitations in regard to this product as it applies to a significant subset of the user profile. In vision, aging typically indicates reduced overall acuity with reduced perception of contrast and blue light, and diminished peripheral range and temporal sensitivity. These compounded factors reduce overall visual sensitivity. While consequences of failing to select a temperature or begin a drying cycle may seem banal, enhanced design could reduce errors, thus, eliminating unnecessary user frustration, and increase efficiency and customer satisfaction.
The visual signals required to successfully operate a machine can be found in the primary interface of the machine as pictured in Figure 05: Product Image Detail 01, Detail 02.
Figure 05: Product Image Detail 01
Figure 05: Product Image Detail 01
First, the screen that indicates the amount of money or time remaining in a digital clock format offers an effective signal to most users. This digital screen uses high contrast in its numerical display with rectangular bright green-yellow lettering of high luminance and saturation, approximately one inch in cap height and ⅛ in letter weight, on a black background. Eyes are highly sensitive to this color and contrast, ensuring detection across variations of ambient light. This panel also serves to indicate time remaining for in the dryer cycle and upon reaching no minutes remaining will indicate the end of the cycle with a blinking “0” icon. This design employs the strength of signal onset, as the variations from blank black screen to the appearance of a highly visible “0” clearly indicate to a user that the machine has entered a new stage in the process and user action may be required. While the eye may fatigue if viewing this interface for an extended period of time due to such high contrast, the time spent in interacting with this display is unlikely to result in significant undesired consequences. However, to improve this signal, a designer could replace the reflective surface with a more matte finish to reduce issues of glare and reflectivity. The next interface that a user addresses is the panel of settings for temperature and the “start” button. To select temperature, a user must read dark grey button tags labeled with small light grey letters, approximately ¼ inch in cap height. While again we see this highly effective signal of a bright green-yellow light to indicate selection, the icons of temperature only offer a moderately effective signal, as text size inhibits legibility. Further, in this panel the start button fails as a detectable signal, as its button is a blue-green hue with low saturation. Given the grey colored background, it is not easy for a user to discriminate between the green start button and one of the grey temperature buttons. Additionally, this design overlooks any visual limitations such as a colorblindness and aging. To improve this design signal, the designer should offer users higher contrast between buttons based on functionality and increased text size.
Overall, given the varying contextual factors of this product demand strong signals that may be detected in various environments. However, understanding the process of visual perception enables a designer to strengthen these signals to enhance user experience with the product.
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