Universal Principles of Design: Interference Effects, Inverted Pyramid, Iteration and Law of Prägnanz
Excerpted from Universal Principles of Design, Revised and Updated (Rockport Publishers)
By William Lidwell, Kritina Holden and Jill Butler
A phenomenon in which mental processing is made slower and less accurate by competing mental processes.
Interference effects occur when two or more perceptual or cognitive processes are in conflict. Human perception and cognition involve many different mental systems that parse and process information independently of one another. The outputs of these systems are communicated to working memory, where they are interpreted. When the outputs are congruent, the process of interpretation occurs quickly and performance is optimal. When outputs are incongruent, interference occurs and additional processing is needed to resolve the conflict. The additional time required to resolve such conflicts has a negative impact on performance. A few examples of interference effects include: 1
Stroop Interference—an irrelevant aspect of a stimulus triggers a mental process that interferes with processes involving a relevant aspect of the stimulus. For example, the time it takes to name the color of words is greater when the meaning and color of the words conflict.
Garner Interference—an irrelevant variation of a stimulus triggers a mental process that interferes with processes involving a relevant aspect of the stimulus. For example, the time it takes to name shapes is greater when they are presented next to shapes that change with each presentation.
Proactive Interference—existing memories interfere with learning. For example, in learning a new language, errors are often made when people try to apply the grammar of their native language to the new language.
Retroactive Interference—learning interferes with existing memories. For example, learning a new phone number can interfere with phone numbers already in memory.
Prevent interference by avoiding designs that create conflicting mental processes. Interference effects of perception (i.e., Stroop and Garner) generally result from conflicting coding combinations (e.g., a red go button, or green stop button) or from an interaction between closely positioned elements that visually interact with one another (e.g., two icons group or blend because of their shape and proximity). Minimize interference effects of learning (i.e., proactive and retroactive) by mixing the presentation modes of instruction (e.g., lecture, video, computer, activities), employing advance organizers, and incorporating periods of rest every thirty to forty-five minutes.
1 The seminal works on interference effects include “Studies of Interference in Serial Verbal Reactions” by James R. Stroop, Journal of Experimental Psychology, 1935, vol. 28, p. 643–662; “Stimulus Configuration in Selective Attention Tasks” by James R. Pomerantz and Wendell R. Garner, Perception & Psychophysics, 1973, vol. 14, p. 565–569; and “Characteristics of Word Encoding” by Delos D. Wickens, in Coding Processes in Human Memory edited by A. W. Melton and E. Martin, V. H. Winston, 1972, p. 191–215.
A method of information presentation in which information is presented in descending order of importance.
The inverted pyramid refers to a method of information presentation in which critical information is presented first, and then additional elaborative information is presented in descending order of importance. In the pyramid metaphor, the broad base of the pyramid represents the least important information, while the tip of the pyramid represents the most important information. For example, in traditional scientific writing, a historical foundation (tip of the pyramid) is presented first, followed by arguments and evidence, and then a conclusion (base of the pyramid). To invert the pyramid is to present the important information first, and the background information last. The inverted pyramid has been a standard in journalism for over one hundred years, and has found wide use in instructional design, technical writing, and Internet publishing.1
The inverted pyramid consists of a lead (critical information) and a body (elaborative information). The lead is a terse summary of the “what,” “where,” “when,” “who,” “why,” and “how” of the information. The body consists of subsequent paragraphs or chunks of information that elaborate facts and details in descending order of importance. It is increasingly common in Internet publishing to present only the lead, and make the body available upon request (e.g., with a “more…” link).
The inverted pyramid offers a number of benefits over traditional methods of information presentation: it conveys the key aspects of the information quickly; it establishes a context in which to interpret subsequent facts; initial chunks of information are more likely to be remembered than later chunks of information; it permits efficient searching and scanning of information; and information can be easily edited for length, knowing that the least important information will always be at the end. The efficiency of the inverted pyramid is also its limiting factor. While it provides a succinct, information-dense method of information presentation, the inverted pyramid does not allow the flexibility of building suspense or creating a surprise ending, so is often perceived as uninteresting and boring.
Use the inverted pyramid when presentation efficiency is important. Develop leads that present a concise overview of the information, followed by short chunks of information of decreasing importance. If interestingness is important and has been compromised, include multiple media, interesting layouts, and interactivity to complement the information and actively engage audiences. When it is not possible to use the inverted pyramid method (e.g., in standard scientific writing), consider a compromise solution based on the principle by providing an executive summary at the beginning to present the key findings.
1 The development of the inverted pyramid is attributed to Edwin Stanton, Abraham Lincoln’s Secretary of War (1865). See, for example, Just the Facts: How “Objectivity” Came to Define American Journalism by David T. Z. Mindich, New York University Press, 2000.
A process of repeating a set of operations until a specific result is achieved.
Ordered complexity does not occur without iteration. In nature, iteration allows complex structures to form by progressively building on simpler structures. In design, iteration allows complex structures to be created by progressively exploring, testing, and tuning the design. The emergence of ordered complexity results from an accumulation of knowledge and experience that is then applied to the design. For example, a quality software user interface is developed through a series of design iterations. Each version is reviewed and tested, and the design is then iterated based on the feedback. The interface typically progresses from low fidelity to high fidelity as more is learned about the interface and how it will be used. Iteration occurs in all development cycles in two basic forms: design iteration and development iteration.1
Design iteration is the expected iteration that occurs when exploring, testing, and refining design concepts. Each cycle in the design process narrows the wide range of possibilities until the design conforms to the design requirements. Prototypes of increasing fidelity are used throughout the process to test concepts and identify unknown variables. Members of the target audience should be actively involved in various stages of iterations to support testing and verify design requirements. Whether tests are deemed a success or failure is irrelevant in design iteration, since both success and failure provide important information about what does and does not work. In fact, there is often more value in failure, as valuable lessons are learned about the failure points of a design. The outcome of design iteration is a detailed and well-tested specification that can be developed into a final product.2
Development iteration is the unexpected iteration that occurs when building a product. Unlike design iteration, development iteration is rework—i.e., unnecessary waste in the development cycle. Development iteration is costly and undesirable, and generally the result of either inadequate or incorrect design specifications, or poor planning and management in the development process. The unknowns associated with a design should ideally be eliminated during the design stage.
Plan for and employ design iteration. Establish clear criteria defining the degree to which design requirements must be satisfied for the design to be considered complete. One of the most effective methods of reducing development iteration is to ensure that all development members have a clear, high-level vision of the final product. This is often accomplished through well-written specifications accompanied by high-fidelity models and prototypes.
1 A seminal contemporary work on iteration in design is The Evolution of Useful Things by Henry Petroski, Vintage Books, 1994. See also Product Design and Development by Karl T. Ulrich and Steven D. Eppinger, McGraw-Hill Higher Education, 2nd ed., 1999. See also “Positive vs. Negative Iteration in Design” by Glenn Ballard, Proceedings of the Eighth Annual Conference of the International Group for Lean Construction, 2000.
2 A common problem with design iteration is the absence of a defined endpoint—i.e., each iteration refines the design, but also reveals additional opportunities for refinement, resulting in a design process that never ends. To avoid this, establish clear criteria defining the degree to which design requirements must be satisfied for the design to be considered complete.
Law of Prägnanz
A tendency to interpret ambiguous images as simple and complete, versus complex and incomplete.1
The Law of Prägnanz is one of several principles referred to as Gestalt principles of perception. It asserts that when people are presented with a set of ambiguous elements (elements that can be interpreted in different ways), they interpret the elements in the simplest way. Here, “simplest” refers to arrangements having fewer rather than more elements, having symmetrical rather than asymmetrical compositions, and generally observing the other Gestalt principles of perception.2
For example, a set of shapes that touches at their edges could be interpreted as either adjacent or overlapping. When the shapes are complex, the simplest interpretation is that they are adjacent like pieces in a puzzle. When the shapes are simple, the simplest interpretation is that they overlap one another. The law applies similarly to the way in which images are recalled from memory. For example, people recall the positions of countries on maps as more aligned and symmetrical than they actually are.
The tendency to perceive and recall images as simply as possible indicates that cognitive resources are being applied to translate or encode images into simpler forms. This suggests that fewer cognitive resources may be needed if images are simpler at the outset. Research supports this idea and confirms that people are better able to visually process and remember simple figures than complex figures.3
Therefore, minimize the number of elements in a design. Note that symmetrical compositions are perceived as simpler and more stable than asymmetrical compositions, but symmetrical compositions are also perceived to be less interesting. Favor symmetrical compositions when efficiency of use is the priority, and asymmetrical compositions when interestingness is the priority. Consider all of the Gestalt principles of perception (closure, common fate, figure-ground relationship, good continuation, proximity, similarity, and uniform connectedness).
1 Also known as the law of good configuration, law of simplicity, law of pregnance, law of precision, and law of good figure.
2 The seminal work on the Law of Prägnanz is Principles of Gestalt Psychology by Kurt Koffka, Harcourt Brace, 1935.
3 See, for example, “The Status of Minimum Principle in the Theoretical Analysis of Visual Perception” by Gary Hatfield and William Epstein, Psychological Bulletin, 1985, vol. 97, p. 155–186.
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Excerpted from Universal Principles of Design, Revised and Updated by William Lidwell, Kritina Holden and Jill Butler. Copyright © 2010. Used with permission of Rockport Publishers.