Open your big mouth online, and someone is bound to draft you to write a column. That's what happened to me a few months ago when someone on an electronic discussion list about usability threw out the question "Is there really a way to apply psychology to HCI design?" and I felt compelled to respond with a page and a half of examples. So here I am, once more asked to describe the relevance of knowledge from my chosen field.
Is psychology just a set of esoteric theories and models that don't translate to the real world? Or are there data and a firm knowledge base that can inform design directly?
Psychology, by definition, is the study of behavior. It allows us to understand why humans behave the way they dowhich, in turn, enables us to guide and influence behavior. For more than 100 years, psychologists in numerous subspecialties, including physiological, environmental, and developmental psychology, as well as cognition, perception, and learning and memory have conducted research, generating a wealth of data and elaborating many general principles that govern behavior under various conditions. When you apply psychology to design, you make use of these principles and data.
As I was mulling over the ways in which knowledge from psychology can be applied, a tailor-made classic example fell right into my lap. Very recently someone asked a group of usability specialists why so many people feel the need to double-click when a single click is all that's needed for many actions. Lots of explanations were bandied about, but the right explanation was crystal clear, I think only to psychologists. Like rats in a Skinner box pressing a bar, people double-click because that behavior is rewarded (i.e., positively reinforced) far more often than a single click is. Yes, folks, in the parlance of behavioral psychologists, it's a simple case of operant conditioning under a variable ratio reinforcement schedule! As one of these "double-clickers" myself, and a "mouse-impaired" person, I "learned" early on that single clicks often didn't "do" anythingmaybe because the intended action required a double-click, or because the pointer wasn't precisely on my target when I clicked. But swift and forceful double-clicking almost never failed, even in cases when a single click was all that was required. I developed a habit. And no amount of chastisement from my husband, who knows very well the rules that govern double-clicking and single clicking, could make me break the habit. Why? Because, as psychologists know, it's very difficult to extinguish a behavior that's been learned on a variable ratio reinforcement schedule!! So, my friends, as designers you're responsible for creating this population of aberrant double-clickers, and you've done a stellar job!
But, you say, why doesn't everyone double-click all the time? Again, the answer is fairly simple, from a psychological perspective. If you look closely at your population of double-clickers, you are apt to find that they can't articulate the rules governing clicking, and they are trial-and-error learners with respect to their computers (says something about me, doesn't it?). They are random searchers, if you will, for cause-and-effect relationships and are prone to develop superstitious behaviorsmuch more so than the person who learns in a systematic course-driven or manual-driven way. Much like habits developed on variable ratio reinforcement schedules, superstitious behaviors are difficult to extinguish.
Psychology doesn't bring us just a snapshot of human behavior, either. It also attempts to describe how behavior, capabilities, and limitations change over the life span. The world is not full of 25-year-old software developers, even though much of our software (oddly!?) looks like it is. Most of the U.S. population is significantly older, with capabilities and limitations far different from those of these youngsters in several ways. Shouldn't these differences be considered during the design of applications intended for the entire population? Case in point: My 79-year-old father-in-law received an electronic greeting card and wanted to send one in return, but told me via e-mail that he was so confounded by the Web site that he'd given up. He just got his first computer (as a wedding presentwhich suggests he's a pretty spry guybut he's a novice when it comes to using the Web). Upon visiting the greeting card site myself, I discovered an absolute circuslights flashing, no organization, no navigational cues, sentences in different colors, animated charactersoverwhelming. It looked like confetti strewn across the screen. As much as the bells and whistles of this site may be entertaining for younger, skilled users, they are barriers to older, less-skilled users who can be more easily distracted by irrelevant information and are more in need of explicit aids and cues for navigation. "Dad," I said in my reply, "ignore everything at the Web site except what I tell you. Step 1......" Twenty minutes later, he sent me a card.
Sometimes psychology doesn't get credit for its contributions, perhaps because we've been using its principles so long that we forgot where they came from. This is particularly true for learning, memory, and information processing. The differences between a good user manual and a poor one, for example, probably depend on the writer's knowledge of these principles. When do you write paragraphs versus a list of steps? How many steps should be in a procedure and how should the elements of those steps be visually grouped on a page? How do considerations of memory load affect decisions to display instead of hiding something on a computer screen? What sort of information can a user process in parallel versus serially? Psychologists have asked and answered these and many other questions, and for years we have been using design guidelines and principles based on these investigations.
Although psychologists' understanding of visual perception continues to evolve, current knowledge in this area guides our layout of information on screens and helps to determine our use of color and texture, to name just a few user interface characteristics. Understanding the differences among the senses helps us to make valid design choices as we move from visually based applications to applications employing other modalities. No doubt many of you recall some of the horrendous interactive voice response (IVR) applications that emerged when designers who didn't appreciate the differences between vision and audition attempted to transplant a screen-based application onto the telephone. The unfortunate results included overly long menus, severe memory loads placed on callers, and general confusion because auditory way finding is different from visual way finding. Those who understand auditory perception would not have made these kinds of design errors.
Perhaps more than anything else, psychology has provided us with some rich models that can guide the ways in which we approach the design process and increase our creativity. For example, all designersno matter what they designwould benefit from reading J.J. Gibson's books, An Ecological Approach to Visual Perception  and The Senses Considered as Perceptual Systems . An understanding of his concept of affordances alone is probably worth the effort to dig up these classic texts. For Gibson, affordances are invariant combinations of variables in the optical array that naturally invite, or even demand, particular goal-directed behaviors. A chair, a park bench, and a tree stump, because of a particular set of elements each possess, all afford "sittability," for example. Perception of "sittability" and, in turn, sitting behavior follow directly and naturally, without much need for decision making or other processing of the information. Gibson laid out a decidedly different way of thinking about perception and, implicitly, design that has endured among psychologists.
Unfortunately, not every psychologist encounters J.J. Gibson's work. (When I was in graduate school, at least, there were "Gibsonians" and "non-Gibsonians" when it came to the study of perception, and the two barely acknowledged each other.) Those who did study Gibson, however, were also treated to something else that was importantthe concept of systems and a systems approach to studying behavior. Too often, we forget that our Web site or our software user interface is just a small part of a much larger system that goes beyond the computer in which the software resides; it extends to the immediate environment, the organization in which it's used, and even the world at large.
Understanding this "bigger picture" has huge implications for the overall design of applicationstheir "look and feel," marketing, consumer acceptance, and so on. All of these topics are to be found somewhere in the halls of psychology departments: industrial/organizational psychology, environmental psychology, and motivation, for example. Much has been made of the fact that user interface designers and usability specialists don't seem to get the respect they deserve within the world of software design. Perhaps one of the reasons is that many of them focus too heavily on immediate concerns related to the screens in front of them and the most obvious users, without a real understanding of how their work fits within a larger system. I think it's no accident that many of the most successful managers of user interface design and usability groups within the industry come from the ranks of psychology, as opposed to some other specialty. They bring to an organization a far richer skill set and greater knowledge of the big picture than do many of their colleagues from other fields.
And finally, there are biological psychology and physiological psychology, which, thanks to recent monumental strides in imaging technology and computing speed, are providing us with new discoveries, concepts, and data at a breakneck pace. This autumn I have the pleasure of teaching a graduate survey course in biological psychology. Every time I revisit this subspecialty, I'm inspired by the extent to which more and more of the principles we derive from behavioral studies are supported with biological, physiological, and genetic data. Certainly, understanding of the structure and functioning of the nervous system of both humans and animals has contributed to evolutionary, if not revolutionary, designs in computer science, especially, but in design, generally, as well. And the more you understand the beauty and elegance of the biological, physiological, and neurochemical processes that regulate behavior, the more you can buy into Gibson's idea that, fundamentally, we were meant to perceive the world in the way we do. Much of the initial part of my course deals with the structure and functioning of our sensory and perceptual systems. For years scientists have specialized in studying one particular sense, most often vision. An area that we've studied lessbut that has tremendous implications for the design of, say, multimedia applicationsis sensory interaction. Did you know that a cat often will not react to a bird unless it both sees and hears the bird?  Neither the visual nor the auditory stimulus alone is sufficient. Did you know that there are nerve cells that respond only to simultaneous input from more than one sensory modality? Who even considers such things as they decide whether to present something visually, auditorially, or multimodally in an application? At least some psychologists do.
User interface design is more than just an art. Psychology provides a wealth of scientific knowledge that speaks directly to design and also addresses design indirectly as part of the larger picture of a dynamic system. Although I admit I don't know the rules that govern double-clicking and single-clicking in a software package (woe is me!), I know why people do it, what it would take to make them stop doing it, and what design solution could have prevented the problem in the first place. That's part of what psychology brings to the table. Today it's harder than ever to be an eclectic, because (1) the volume of knowledge has expanded to such a great extent, (2) academia hates eclectics, and (3) businesses are often too myopically focused to appreciate interdisciplinary kinds of approaches. Nevertheless, user interface designers and usability specialists who haven't delved into psychology would be surprised at how much it enriches the design experience. That MBA you were considering? Let it wait!
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Daryle Gardner-Bonneau, Ph.D., is the principal of Bonneau and Associates. During her 25 years in the human factors field, she has been a university professor in psychology and industrial and systems engineering departments, a senior scientist with an aerospace government contractor, a director of a medical school research program, and a user interface consultant to industry, specializing in medical and telecommunications applications, particularly those employing speech technology interfaces.
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