CS252. User Interface Design

Lecture Outline for Jan. 28
Mental Models


1.     Human Channel Capacities (Constraints on "User Resources")
     Example of seminal paper in human-computer interaction: George Miller, "The Magical
          Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information,"
          The Psychological Review, Vol 63, No. 2, 1956, pp. 81-97.


     Tests of sensory perception capabilities typically structured as stimulus/response





Miller explored human limitations on perceiving/identifying various types of stimuli Channel capacity: Example of how he determined limit Pollack [1952] asked listeners to identify tones and assign numbers to them tones actually covered different frequencies from 100 to 8000 cycles/sec Pollack's results
What Miller said about it: Intuition says that we get better with practice "We cannot pick more than 6 different pitches that the listener will never confuse" "Or, stated slightly differently, no matter how many alternative tones we ask him to judge, the best we can expect him to do is to assign them to about 6 different classes without error." Miller also presents data on: loudness of sounds, saltiness of tastes, visual perception of position of points on a line, sizes of squares, curvature of lines, color brightness, many other sensory stimuli Overall results: "There seems to be some limitation built into us either by learning or by the design of our nervous sytems, a limit that keeps our channel capacities in this general range." 2. Multi-dimensional Sensory Stimuli Miller next looks at multi-dimensional stimuli Miller then compared effects of perception with those of recall from "immediate memory" Second barrier limits our short-term memory (now working memory) to 5-7 "items" So how do we recognize hundreds of people / voices / songs? We recode stimuli, to increase how much info we can process with 5-7 items Guidelines based on Miller's study? (1) increase the number of dimensions along which stimuli can vary (change both sound pitch and loudness, rather than just one; we'll see examples with color) (2) arrange tasks so we make a sequence of several judgements in a row 3. Mental models Cognitive psychology makes heavy use of term mental model Exercise [from Preece, Ch. 6]: Simple example of "running" a mental model Key factor: appropriateness Example of central heating [from Preece, Ch. 6] In general: Mental models are derived from experiences in the real world, but go beyond what we have experienced If model is sufficiently accurate, If model is inappropriate, Most of Jordan's "ten principles of usability" are related to helping the user build an accurate mental model consistency compatibility feedback error prevention and recovery user control visual clarity prioritization of functionality and information appropriate transfer of technology explicitness 4. The Role of Affordances In discussing explicitness, Jordan refers to affordances Let's look at examples from Norman [1988], who originally defined the concept Basic concept: Examples from software: [Preece 1994]