Table of Contents
Introductory remarks
Talking
Visual Perception and Bottom Up Processing
Contrast and Contour with Color
Size and motion
Case Study in Design
Advice on Design
In summary
Citing sources
Starting off,
Visual perception refers to the way we perceive the world through the light entering our eyes. Since the dawn of time, humans have had to learn to distinguish between signals and noise in order to be able to adapt to changing environments. Because humans can distinguish between the targeted signals and background noise, these signals are crucial to cognition. This review examines theories, concepts, and analyses the key aspects of signal processing. These concepts have profound implications when applied to user experience. It can be used to distinguish between an effective and usable interface. Examining the Boston Citgo sign is a great example of how user experience can be impacted by a solid understanding of visual perception.
DiscussionVisual perception and bottom-up processing Humans are able take in signals from their environment and make the appropriate actions to protect themselves. Although our nervous system is highly skilled at recognizing signals and interpreting them, they aren’t always easy to understand. Signals are usually ambiguous. Knowing the strength will enable you to discriminate between noise and signals. Bottom-up Processing. Because of its many connections to an optic nerve and other sensitive receptors, the human eyes are sensitive to signals. The cornea allows light to enter the eye, where it is focused onto the photoreceptors. The retina is composed of rods and cones. For high resolution and color vision, the fovea is “densely packed” with cones. The rods are located near the periphery and help in processing light and moving in different environments. One glance can be enough to process many signals in one go. The human eye is capable of detecting contrast, color and contour in one glance. This will all be explained in the sections below.
Contrast and color contrast are key factors in determining signal strength. Contrast describes the difference between a stimulus and the stimuli surrounding it. It perceives changes between the background, foreground, and background. The brain perceives the stimulus as a change in the background and foreground, just like our brains do with signals. To produce the best signal, it is important to strike a balance between maximum and threshold contrasts in design. Designing on the edge of only noticeable differences (JND), or over-designing, is not a good idea. Visual perceptions vary greatly depending on the viewers and viewing conditions.
Contour and Luminance. Contrast is most affected by Luminance. Luminance is the measurement of perceived brightness. In practice, brightness and luminance are different terms. Because there are more light-processing devices in the retina than ever before, humans are therefore more sensitive for luminance. This luminance sensitivities allows people to adapt to various light conditions and detect changes easily.
Humans have developed the ability to detect changes in the environment throughout evolution through contour enhancements or variances on luminance levels. Edges are formed when the object’s brightness changes rapidly. This creates a high contrast between the stimulus background and it. Once an object is identified as having an edge, its luminance changes rapidly, and the nerves in the eyes exaggerate it. This allows the visual cortex of the brain to process it. This allows humans to identify objects in the environment and give them meaning or value based upon their appearance.
Hue and saturation. Hues allow us to distinguish between different spectral colors on the visible spectrum. The intensity of a hue’s dominant wavelength at saturation, also known as purity, is called the hue’s saturation. If a hue’s purest form is found, it will be the most saturated. Accordingly, this has a huge impact on the signal’s intensity as well as contrast. An unsaturated color would have more “contributions from other wavelengths” than a saturated hue and therefore a lower contrast. It is best to avoid using too saturated colors in designs. While humans tend to enjoy more saturated hues, there are some drawbacks to using them.
Motion and sizeMotion. As it has a major impact on contrast and depth as well as luminance sensitivities, detecting motion is an important function of visual perception. The nerve endings at the retina’s peripheral are responsible for processing and calculating motion. Motion “reflects changes in one’s visual environment” and can have an effect on how behavioral responses and actions are formed. Motion is a design concept. Overuse can lead to over-stimulation. Humans cannot block out motion. Designers must strategically and intentionally use motion and movement to communicate meaning.
Size. Signal processing requires that the stimulus size be considered along with its luminance, contour and shape. The signal’s size has a direct correlation with its stimulus size. The signal strength increases with increasing stimulus size. Other influences and complicating factors such as distance and viewing angle can also have an impact on size. The relationship between size and viewing distance is inverted. As distance increases, perceived size becomes smaller. The opposite is true for size and viewing angles. As the stimulus grows in size, so does its viewing angle.
Design Case Despite each concept being described in separate sections above, each one of the concepts relating to signal processors is interrelated. Analyzing a real-world case of design, we will examine Boston’s Citgo sign as seen at night. This will allow us to see if the design conforms to or goes against bottom-up visual perception.
Brightness and Contours. The driver will be able to see the sign’s boundaries by looking at the sharp horizontal and/or vertical edges. These stark contrasts in luminance along its edges make the sign stand out against the dark background. A red triangle, with its sharp edges and shape, has a strong contrast to its white background. The human brain is wired to sense contoured edges so the retina will amplify the edges along both the sides and the triangle. This enhances the perceived contrast.
The LED lights inside the sign emit intense luminance at night. This is sending a strong signal through the visual cortex. The Citgo sign is visible from the driver’s view when they travel west on Storrow Drive. This can make it dangerous for their safety. Even in bad weather, the bright lights can blind or blur the vision temporarily, making it easier to get into accidents. It is not surprising that drivers could be distracted by the Citgo sign when driving, as they are most sensitive to changes in luminance.
Hue and saturation. The Citgo LED sign features high saturation and strong luminance. Citgo’s logo features the most intense colors, which are the dominant wavelengths of visible light. Saturation should be used sparingly in interface design. Too many colors can cause fatigue and eye strain. Red has good visibility because of the many red-sensitive fovea cones. However, visibility is poor under low lighting conditions. The retina is more sensitive than red to blue but has fewer blue receptors. When low illumination levels are low, the human eyes tend to shift towards blue which gives the illusion of a higher luminance. While both blue and red hues can be found at the visible spectrum, it is not a good design choice to place them close together, especially when they are full saturated. Red hues tend toward the forefront of stimuli, while the blues fade to the background. The close proximity of the lights to the eyes creates a quivering effect similar to motion at the periphery. Citgo already employs motion through different flashing patterns with high contrast, but the added distraction caused by saturated hues is only going to make it more distracting.
Size. Because the sign, which measures sixty feet tall, can be seen from most parts of Boston, it is easily visible from the skyline above all the buildings. It is visible from the westbound traffic on Storrow Drive because of its size. At night, the sign’s stark contrast with the sky and buildings around it makes it stand out more than the rest. The sign’s strong contrast makes it visible from any distance. This high contrast can be dangerous especially while driving. Rapid eye movements and rapid onset can cause fatigue in the sensory system. LEDs that have higher levels of saturation and luminance tend to have a quicker onset time than other light sources.
Recommendations for designThe Citgo sign’s strong contrast can create dangerous driving conditions for drivers, particularly at night. The sensory system will become fatigued if there are too many strong signals. Interface designers must find the optimal contrast in order to achieve visual perception. Split complement theory may be used to reduce Citgo’s blue and red colors. Alternately, you can reduce the intensity by mixing darker colors with the red and blue. Aside from reducing luminance at night, this will also decrease the strength of signal to passersby. This can reduce brightness perception and lessen the glare created by bright lights. You can control the contrast by making these changes. This will give you a predictable and controlled result.
Conclusion: Vision is the way humans perceive and process their environment. It involves how light enters our eyes. Designers will be better able to understand signals and noise. This knowledge will help them to influence the behavior and psychology of signal processing. Designers want predictable outcomes. This is possible by applying psychological and perceptual concepts related to signal strength, contrast and other factors. Each factor has a unique role in determining contrast and signal strength. But it’s important to know how all these concepts impact visual perception, design, and overall perception. The combination of all these factors can have a negative effect on the eye, as demonstrated by the iconic Citgo sign in Boston. A designer will become more efficient if they are able to understand the role of each factor. Designers can make design more appealing and less burdensome by understanding each factor.
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