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Chapter: User Interface Design

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Important Human Characteristics in Design

Perception is our awareness and understanding of the elements and objects of our environment through the physical sensation of our various senses, including sight, sound, smell, and so forth. Perception is influenced, in part, by experience.

Important Human Characteristics in Design

 

Perception

 

Perception is our awareness and understanding of the elements and objects of our environment through the physical sensation of our various senses, including sight, sound, smell, and so forth. Perception is influenced, in part, by experience.

 

Other perceptual characteristics include the following:

 

Proximity. Our eyes and mind see objects as belonging together if they are near each other in space.

 

Similarity. Our eyes and mind see objects as belonging together if they share a common visual property, such as color, size, shape, brightness, or orientation.

 

Matching patterns. We respond similarly to the same shape in different sizes. The letters of the alphabet, for example, possess the same meaning, regardless of physical size.

 

Succinctness. We see an object as having some perfect or simple shape because perfection or simplicity is easier to remember.

 

Closure. Our perception is synthetic; it establishes meaningful wholes. If something does not quite close itself, such as a circle, square, triangle, or word, we see it as closed anyway.

 

Unity. Objects that form closed shapes are perceived as a group. o Continuity. Shortened lines may be automatically extended.

 

Balance. We desire stabilization or equilibrium in our viewing environment. Vertical, horizontal, and right angles are the most visually satisfying and easiest to look at.

 

Expectancies. Perception is also influenced by expectancies; sometimes we perceive not what is there but what we expect to be there. Missing a spelling mistake in proofreading something we write is often an example of a perceptual expectancy error; we see not how a word is spelled, but how we expect to see it spelled.

 

Context. Context, environment, and surroundings also influence individual perception. For example, two drawn lines of the same length may look the same length or different lengths, depending on the angle of adjacent lines or what other people have said about the size of the lines.

 

Signals versus noise. Our sensing mechanisms are bombarded by many stimuli, some of which are important and some of which are not. Important stimuli are called signals; those that are not important or unwanted are called noise.

 

Memory

 

Memory is viewed as consisting of two components, long-term and short-term (or working) memory.

 

Short-term, or working, memory receives information from either the senses or long-term memory, but usually cannot receive both at once, the senses being processed separately. Within short-term memory a limited amount of information processing takes place. Information stored within it is variously thought to last from 10 to 30 seconds, with the lower number being the most reasonable speculation. Knowledge, experience, and familiarity govern the size and complexity of the information that can be remembered.

 

Long-term memory contains the knowledge we possess. Information received in short-term memory is transferred to it and encoded within it, a process we call learning. It is a complex process requiring some effort on our part. The learning process is improved if the information being transferred from short-term memory has structure and is meaningful and familiar. Learning is also improved through repetition. Unlike short-term memory, with its distinct limitations, long-term memory capacity is thought to be unlimited. An important memory consideration, with significant implications for interface design, is the difference in ability to recognize or recall words.

 

Sensory Storage

 

Sensory storage is the buffer where the automatic processing of information collected from our senses takes place. It is an unconscious process, large, attentive to the environment, quick to detect changes, and constantly being replaced by newly gathered stimuli. In a sense, it acts like radar, constantly scanning the environment for things that are important to pass on to higher memory.

 

Repeated and excessive stimulation can fatigue the sensory storage mechanism, making it less attentive and unable to distinguish what is important (called habituation). Avoid unnecessarily stressing it.

 

Design the interface so that all aspects and elements serve a definite purpose. Eliminating interface noise will ensure that important things will be less likely to be missed.

 

 

Visual Acuity

 

The capacity of the eye to resolve details is called visual acuity. It is the phenomenon that results in an object becoming more distinct as we turn our eyes toward it and rapidly losing distinctness as we turn our eyes away—that is, as the visual angle from the point of fixation increases.

 

It has been shown that relative visual acuity is approximately halved at a distance

of 2.5 degrees from the point of eye fixation

 

The eye’s sensitivity increases for those characters closest to the fixation point (the “0”) and decreases for those characters at the extreme edges of the circle (a

 

50/50 chance exists for getting these characters correctly identified). This may be presumed to be a visual “chunk” of a screen

 

Foveal and Peripheral Vision

 

Foveal vision is used to focus directly on something; peripheral vision senses anything in the area surrounding the location we are looking at, but what is there cannot be clearly resolved because of the limitations in visual acuity just described.

 

Foveal and peripheral vision maintain, at the same time, a cooperative and a competitive relationship. Peripheral vision can aid a visual search, but can also be distracting.

 

In its cooperative nature, peripheral vision is thought to provide clues to where the eye should go next in the visual search of a screen.

 

In its competitive nature, peripheral vision can compete with foveal vision for attention. What is sensed in the periphery is passed on to our information-processing system along with what is actively being viewed foveally.

 

Information Processing

 

The information that our senses collect that is deemed important enough to do something about then has to be processed in some meaningful way.

 

There are two levels of information processing going on within us. One level, the highest level, is identified with consciousness and working memory. It is limited, slow, and sequential, and is used for reading and understanding.

 

In addition to this higher level, there exists a lower level of information processing, and the limit of its capacity is unknown. This lower level processes familiar information rapidly, in parallel with the higher level, and without conscious effort.

 

Both levels function simultaneously, the higher level performing reasoning and problem solving, the lower level perceiving the physical form of information sensed.

 

Mental Models

 

A mental model is simply an internal representation of a person’s current understanding of something. Usually a person cannot describe this mental mode and most often is unaware it even exists.

 

Mental models are gradually developed in order to understand something, explain things, make decisions, do something, or interact with another person. Mental models also enable a person to predict the actions necessary to do things if the action has been forgotten or has not yet been encountered.

 

A person already familiar with one computer system will bring to another system a mental model containing specific visual and usage expectations. If the new system complies with already-established models, it will be much easier to learn and use.

 

The key to forming a transferable mental model of a system is design consistency and design standards.

 

 

Movement Control

 

Particularly important in screen design is Fitts’ Law (1954). This law states that:

 

The time to acquire a target is a function of the distance to and size of the target.

This simply means that the bigger the target is, or the closer the target is, the

 

faster it will be reached. The implications in screen design are: o Provide large objects for important functions.

 

Take advantage of the “pinning” actions of the sides, top, bottom, and corners of the screen.

 

Learning

 

Learning, as has been said, is the process of encoding in long-term memory information

 

A design developed to minimize human learning time can greatly accelerate human performance. People prefer to stick with what they know, and they prefer to jump in and get started that is contained in short-term memory.

 

Learning can be enhanced if it:

 

Allows skills acquired in one situation to be used in another somewhat like it. Design consistency accomplishes this.

Provides complete and prompt feedback.

 

Is phased, that is, it requires a person to know only the information needed at that stage of the learning process.

 

Skill

 

The goal of human performance is to perform skillfully. To do so requires linking inputs and responses into a sequence of action. The essence of skill is performance of actions or movements in the correct time sequence with adequate precision.

 

Skills are hierarchical in nature, and many basic skills may be integrated to form increasingly complex ones. Lower-order skills tend to become routine and may drop out of consciousness.

 

Individual Differences

 

In reality, there is no average user. A complicating but very advantageous human characteristic is that we all differ—in looks, feelings, motor abilities, intellectual abilities, learning abilities and speed, and so on.

Individual differences complicate design because the design must permit people with widely varying characteristics to satisfactorily and comfortably learn the task or job, or use the Web site.

 

Multiple versions of a system can easily be created. Design must provide for the needs of all potential users.



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