Usability First » Psychology

information processing model

jls — Wed, 30 Dec 2009 00:04:13 +0000

in cognitive psychology, the idea of breaking down human behavior into 3 primary systems: perception, cognition, and motor control (action). These systems are similar to the computer’s input, processing, and output. Cognition, in this model, can do hidden mental processing (as opposed to the prevailing behaviorist approach before cognitive psychology came around) and can be measured and studied as an information processing system.

information anxiety

jls — Tue, 29 Dec 2009 23:36:10 +0000

stress caused by the inability to access or understand the information you need, caused by information overload, lack of clear organization to information, insufficient information, excessively difficult presentation of information, etc.

individual differences

jls — Tue, 29 Dec 2009 23:22:58 +0000

people vary in a number of ways that can have an impact on the design of a user interface, and rather than trying to design for “the average user”, it is often better to understand how people vary to design acceptably for a broad audience. Sometimes this may even mean designing separate user interfaces for different user populations, such as when extremely simplified drawing programs are made for young children versus sophisticated versions designed for graphic design professionals.

Some of the main categories of variations that are of interest to designers are:

user experience level – how well users know their subject domain, computing skills, internet skills, …
user preferences – users will choose settings according to their own tastes and work practices
market segment – such as age, gender, education, occupation, hobby, and income level
variation in ability – users often have relevant physical or cognitive limitations; for instance, near-sightedness and color blindness are extremely common, and these can usually be easily addressed when a designer is aware of the issues

Hick’s Law

jls — Tue, 29 Dec 2009 20:38:54 +0000

(1) H = log2(n + 1).
(2) H = Σ pi log2(1/pi + 1).

H = the information-theoretic entropy of a decision.
n = the number of equally probable alternatives.
pi = the probability of alternative i for n alternatives of unequal probability.

The time it takes to make a decision is roughly proportional to H, the entropy of the decision (the log of the number of alternatives), i.e. T = k H, where k ~ 150 msec.

This can be used to make a time estimate for how long people will take to make a decision in using a user interface, such as choosing a menu item, choosing a tool, or selecting an item on a navigation bar. Cognitive modeling approaches such as GOMS apply this to making predictions of human performance.

Hawthorne effect

jls — Tue, 29 Dec 2009 18:35:06 +0000

the tendency for people to improve their performance after any change when they know their performance is being studied — a common potential confound when testing user interface changes for whether they represent an improvement or not.

habituation

jls — Tue, 29 Dec 2009 18:18:29 +0000

developing a habit, a fixed pattern of responses to given situations, which becomes fast and automatic but can lead to user errors when those patterned responses don’t apply, as in modal systems.

gulf of execution

jls — Mon, 28 Dec 2009 18:54:11 +0000

the psychological gap that must be crossed to manipulate a user interface appropriately: goals -> plans -> action specification -> operate interface. In other words, the processes of motor control. The idea here is that representations on the screen should match the psychological goals as well as possible.

gulf of evaluation

jls — Mon, 28 Dec 2009 18:51:45 +0000

the psychological gap that must be crossed to interpret a user interface display: interface -> interpretation -> evaluation. In other words, the process of perception.

GOMS

jls — Mon, 28 Dec 2009 17:32:19 +0000

a family of techniques for modeling and representing the knowledge necessary for a person to perform a task. GOMS is an acronym that stands for Goals, Operators, Methods, and Selection Rules, the components of which are used as the building blocks for a GOMS model.

informed consent

admin — Wed, 23 Dec 2009 23:53:51 +0000

permission from a participant in a user study to participate and to have data collected about them, with that permission hinging on the fact that they have been fully informed of the nature and risks of the study and their rights in participating.

They are typically informed if their information will be confidential (usually it would be) and whether their names or images (as in videotapes) would be shown to others, such as being revealed to their management or shown to developers or in research presentations.

Their rights may include the right to withdraw from the study at any time, for instance if they are feeling distressed by it. They are also told of any compensation they will receive.

inter-observer reliability

admin — Wed, 23 Dec 2009 23:36:41 +0000

or inter-coder reliability; the degree to which 2 observers record the same data (or in some cases, draw the same conclusions) in the same circumstances. Lack of reliability in observations can indicate that observers are missing important details, that they are not categorizing observations in the same way, or that what appeared to be similar circumstances are actually not. Reliability is critical when design decisions are being made based on observations, and critical for allowing researchers to effectively communicate about their findings.

internal validity

admin — Wed, 23 Dec 2009 23:30:36 +0000

the degree to which the design of a study allows you to accurately attribute an observation to a specific cause rather than alternative causes. An undesirable alternative cause for your result is known as a “confound”.

An example is to compare the amount of time it takes in using 2 alternative interface designs. You would like to claim that if one design is faster than another, then the time difference is due solely to differences in the interfaces. An example of a confound is when different groups of people are tested for each design–if one group is more skilled than another, that would be an alternative explanation for the observed time difference.

A “control variable” is a potential confound that has been controlled for so that it can reasonably be ruled out as a possible explanation. For instance, to avoid the above confound, subjects can be a control variable by assigning them randomly to each test condition.

gestalt principles

jls — Wed, 23 Dec 2009 23:24:18 +0000

principles of perception that address the interpretation of arrangements and relationships of objects; the whole is greater than the sum of the parts. Some of the common principles are:

good continuation – objects along a common path form a unit
proximity – objects that are close together are related
common fate – objects that move in the same direction and speed are a unit
similarity – objects with similar properties (color, shape, etc.) are related

fundamental attribution error

jls — Wed, 23 Dec 2009 22:41:05 +0000

the tendency for people to blame themselves rather than external factors for problems they have. In computer terms, the tendency to blame the user rather than the technology or its design when users have trouble with computers.

kinesthetic feedback

admin — Wed, 23 Dec 2009 22:39:45 +0000

knowledge people have about the position and movement of their bodies based on nerves in their joints and muscles (also known as proprioception). Such feedback may play a role in hand-eye coordination, the use of input devices, and reaction to output devices that cause the body to move.

KLM

admin — Wed, 23 Dec 2009 22:37:02 +0000

Keystroke Level Model. A simple GOMS technique dealing mainly with observable events and organized as a single stream of sequential operators. KLM is easy to learn and can provide fast, but crude, task execution times.

learned helplessness

admin — Wed, 23 Dec 2009 22:19:18 +0000

when a person has repeated experiences of failure at a task or skill and learns to assume that they aren’t capable, when in fact they may simply need to be taught from a different point of view or to break the problem down into smaller, achievable subcomponents. In user interface design, this problem is encountered when someone is overwhelmed by complex interfaces, and a simplified interface or improved training procedure is called for.

Likert scale

admin — Wed, 23 Dec 2009 22:08:35 +0000

a type of survey question where respondents are asked to rate the level at which they agree or disagree with a given statement. For example:

I find this software easy to use.
strongly disagree 1 2 3 4 5 6 7 strongly agree

A Likert scale is used to measure attitudes, preferences, and subjective reactions. In software evaluation, we can often objectively measure efficiency and effectiveness with performance metrics such as time taken or errors made. Likert scales and other attitudinal scales help get at the emotional and preferential responses people have to the design. Is it attractive, fun, professional, easy?

locus of attention

admin — Wed, 23 Dec 2009 21:50:41 +0000

or focus of attention; the single source or location of sensory input that a person attends to at a given time, such as the point in space that they’re looking at and able to devote mental resources to interpreting. In some cases, expertise can reduce the need for attentional resources, leading to the effect of being able to attend to multiple sources.

mental map

admin — Wed, 23 Dec 2009 20:53:49 +0000

(website navigation) a representation in a person’s mind of the structure of a website, which is likely to be incomplete and simplified. A mental map helps people simplify the job of remembering what they’ve seen to the problem of remembering an overall structure rather than every page and link. When a mental map is a fairly accurate representation of the actual site structure, a person can use it to quickly navigate without a lot of mental effort. However, where the mental map doesn’t match the actual site structure, navigation can be slower than optimal and people can make incorrect inferences about what is and is not included on the site.

mental model

admin — Wed, 23 Dec 2009 20:52:34 +0000

Humans establish mental models of how things work, or how they would behave in a particular situation. For example, having been a student at a university for a while, a student can establish a “mental model” of attending a university. That is, he goes to classes, talks to his classmates about how to accomplish certain assignments, he knows how to interact with his professors, etc. Suppose now a virtual university is being offered to students for online courses, and a website is to be constructed for the virtual university. This website should understand and respect the “mental models” of targeted students in order to avoid confusion for the students to find their way around the virtual university.

Meyer’s Law

admin — Wed, 23 Dec 2009 19:20:18 +0000

T = A + B * SQRT(D/W)

T = time to move to a target
D = distance to target
W = width of target
A ~ -13 msec
B ~ 108 msec

Meyer’s Law is a refinement of Fitts’ Law for predicting the time it takes for rapid aimed movements, such as hitting a button on the screen by moving a mouse to it. (A and B are constants which may vary with the input device.)

Meyer’s Law is derived from a stochastic optimized-submovement model. This model says that movements consist of a primary submovement and a possible corrective secondary submovement toward a target.

Meyer’s Law can be used to make predictions of how much time it will take for a user to accomplish a task involving selection of targets on the screen (such as icons, menus, or hypertext links).

Meyer, D.E. et al (1988). Optimality in human motor performance: ideal control of rapid aimed movements. Psychological Review, 95:3, 340-370.

MHP

admin — Wed, 23 Dec 2009 19:18:17 +0000

Model Human Processor. A simple cognitive architecture used as the basis of the GOMS family of user modeling techniques. This representation of human cognition consists of separate components for cognitive, motor, and perceptual processors (and associated buffers), as well as for long and short-term memory.

mistake

admin — Wed, 23 Dec 2009 19:08:24 +0000

an error of reasoning or inappropriate subgoals, such as making a bad choice or failing to think through the full implications of an action.

mode error

admin — Wed, 23 Dec 2009 18:56:30 +0000

a type of slip where a user performs an action appropriate to one situation in another situation, common in software with multiple modes. Examples include drawing software, where a user tries to use one drawing tool as if it were another (e.g. brushing with the Fill tool), or text editors with both a command mode and an insert mode, where a user accidentally types commands and ends up inserting text.