Components are a section or subsection of a designed space. They take up a significant portion of the screen, and may be as large as the viewport (or, depending on your point of view, larger).

Components are concerned with displaying large amounts of information, or allowing the user to interact with the system is some significant, primary manner. Combining them, with the small, reusable, interactive or display Widgets (see that section) gives an unlimited number of options for design.

Understanding How Visual Information is Perceived

Our visual perception model is complex. Our human mind is like a leaky bucket. It holds plenty of information, but can easily let information slip away and spill out. If we can understand how our mind works, and its limits, we can create visual information displays that limit our information loss and mental load during decision making processes. Basically, information processing involves these major processes.

This chapter will provide you brief information on Sensation and Perceptual Processing and how understanding them can provide you a framework to designing better visual displays.

Sensation: Getting Information Into Our Heads

Sensation is a process referring to the capture and transformation of information required for the process of perception to begin (Bailey 1996). Each of our sensors (eyes, ears, nose, skin, mouth) collects information, or stimuli, uniquely but all will transform the stimulus energy into a form the brain can process.

All of these senses respond selectively to certain types of stimuli. There are four types of stimuli our bodies can sense:

Each of these stimuli can be collected through different senses. Electromagnetic stimuli can be collected through vision. Mechanical stimuli can be collected by hearing, touch, pain, vestibular, and kinesthetic. Thermal by cold and warmth. Chemical by taste and smell (Ellingstad, 1972).

Our sensory processing has limits. For example, we can only see wavelengths between 400 and 700 nanometers. Our thermal sensors respond only to infrared wavelengths. Our skin temperature is about 91.4 degrees F and stimuli at this temperature do not cause a noticeable thermal sensation. However, below 60 degrees F, the skin will transmit a cold feeling and above 105 degrees, the skin will transmit a hot feeling.

Our sense of touch (pressure) is experienced when an object contacts our skin. The skin within certain locations, can identify where the object is, its size and shape, and its movement. (**talk in detail about this in chapter of Navigation and Gesturing?**) For more information on sensory limits, refer to Chapter 3: Sensing and Responding (Bailey, 1996).

This chapter details patterns on Displaying information. Therefore, it is beneficial to discuss in greater detail the sense of vision, how it works, and it’s limits.

The human eye. Many people use the analogy that our eye works similar to a camera. Both eye and camera have a lens, an aperture (pupil), and film (retina). However, the similarity stops there. Because the image that is shown on the back of our retina does not resemble our perception of it.

How Does the Eye Work?

The eye is an organ responsible for vision. It first collects, filters, and focuses light. Our eyes can only experience a narrow band of radiation in the electromagnetic spectrum.

The narrow range is approximately 400 nanometers (where we can perceive the violet color) to about 700 nanometers (where red is perceived). The focused beam of light is then projected onto the back part of our retina where it contacts photoreceptors, known as rods and cones. These receptors are light sensitive. The cones are used for seeing when there is bright light and are color sensitive. The rods are sensitive to dim lighting and are not color sensitive. These receptors convert light into electro-chemical signals which travel along the optic nerve to the brain for processing.

The eye is sensitive to stimuli in many ways at any moment, including the size of stimulus, its brightness and contrast, and the part of the retina that is stimulated.

As a designer, it’s important to understand how these stimuli can affect and influence our design decisions.******* The size of the stimulus is measured with visual angle. This is the angle formed at the eye by the viewed object. The visual angle can be calculated using the following formula: Visual Angle (minutes of arc) = (3438)(length of the object perpendicular to the line of sight)/distance from the front of the eye to the object. Visual angle is typically measured in degrees of arc where one degree=60’(minutes of arc), and 1 minute of arc=60”(seconds of arc).

With an understanding of visual angle, we can determine the appropriate size of visual elements including character size viewed at specific distances. According to Human Factors Society (1988), the following visual angles are recommended for reading tasks: When reading speed is important, the minimum visual angle should not be less than 16 minutes of arc and not greater than 24 minutes of arc. When reading speed is not important, the visual angle can be as small as 10 minutes of arc. Characters should never be less than 10 minutes of arc or greater than 45 minutes of arc. So, let’s assume I’m designing a text that is to be read quickly on a mobile device with a viewing distance of 30 centimeters(11.8 inches). The equation would look like this: Length= 16 minutes of arc(30)/3438. The smallest acceptable character height would then = .14cm. or about 10 points. Now, other factors that need to be addressed when designing character size on mobile is 1: The distance changes all of the time, and 2: Glare and wobble affects legibility. This will be further addressed in another chapter*******