Ergonomics in Design Lecture 5 PDF

Ergonomics in Design why good people design dumb things! Lecture 5 Dr. Eng. Mohamed ElWakil Cognition Outline During each day, we must process large amounts of information from our environment to accomplish. While the scenario described earlier may seem rather trivial,...

Ergonomics in Design why good people design dumb things! Lecture 5 Dr. Eng. Mohamed ElWakil Cognition Outline During each day, we must process large amounts of information from our environment to accomplish. While the scenario described earlier may seem rather trivial, there are dozens of other cases where difficulties result in injury or death. In this context, we will consider the basic mechanisms by which people perceive, think, and remember, generally known as cognition. As we learn about the various limitations of the human cognitive system, we will consider the implications of, and some solutions for, design problems. ADF 413 - Ergonomics in Design 2 Cognition the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses. ADF 413 - Ergonomics in Design 3 What is cognitive engineering? The study of the human as a component of a complex engineered system with the goal of designing usable systems ADF 413 - Ergonomics in Design 4 Why? Technological innovation is progressing so quickly that we have fallen behind in our ability to manage it. Our world is filled with objects that invite: Human Error —from phones and stoves to hospitals, airplane cockpits and nuclear power plant control rooms. Problems —some potentially catastrophic continuously arise when designs are developed without human nature in mind. ADF 413 - Ergonomics in Design 5 Airbus catastrophic This was an Airbus A320 Crash and 87people died Blaming the accident on pilot error and finding that there was no problem with the engines. ADF 413 - Ergonomics in Design 6 Poor Designs in A320 Programmed landing maneuvers with bug in altitude calculation Warning system alerts only seconds before accident; no time to react Flight path angle and vertical speed indicator have the same display format; confuses pilots. Pilot is either extremely busy or extremely bored. During flight, they get a false sense of security. Error and warning messages during data entry are often indecipherable, so pilots ignore them. ADF 413 - Ergonomics in Design 7 Airbus A320 Cockpit ADF 413 - Ergonomics in Design 8 Why do we need to understand the user? We need to understand cognitive processes and cognitive limitations of users to be able to perform two main functions: 1. Identify and explain the nature and causes of problems users encounter 2. Supply theories, and methods that can lead to the design of better interactive products ADF 413 - Ergonomics in Design 9 Cognitive System ADF 413 - Ergonomics in Design 10 Cognitive Processes 1. Perception and recognition 2. Memory 3. Attention 4. Problem-solving, and decision-making. Perception and recognition How information is acquired from the world and transformed into experiences Design implication Text should be legible Icons should be easy to distinguish and read ADF 413 - Ergonomics in Design 11 Which is easiest to read and why? ADF 413 - Ergonomics in Design 12 Human information processing system 1. perceptual stage in which we bring information in through the senses (sensation – previous lecture) and compare it with knowledge from memory to give it meaning (perception); 2. cognitive stage which is a central processing or thought stage where we compare the new information with current goals and memories, transform the information, make inferences, solve problems, and consider responses; and 3. action stage in which the brain selects a response and then coordinates/sends motor signals for action. ADF 413 - Ergonomics in Design 13 Memory Sensory memory holds a great deal of detailed information but only for a very short period of time (visual sensory memory is about 2-3 seconds). Any information receiving attention is processed further in the perception stage. Perception adds meaning to the information by comparing it with relatively permanent information brought from long-term memory. As an example, if I look out the window, I might see an amorphous area of white and gray surrounded by blue, and the process of perception compares the lines, shadows, and colors to previous knowledge and recognizes the object as a cloud in a blue sky. ADF 413 - Ergonomics in Design 14 Working memory Once meaning is added to sensory information, we either immediately react to the perceptions with a response of some type, or we send the information on to working memory for further processing. Working memory is a term for both the short-term store of whatever information is currently active in central processing, and also for a kind of workbench of consciousness in which we compare, evaluate, and transform cognitive representations. Information in working memory decays quite rapidly unless it is rehearsed to keep it there. This activity is maintained until response selection and execution processes occur. ADF 413 - Ergonomics in Design 15 Model of human information processing ADF 413 - Ergonomics in Design 16 Perceptual recognition Perceptual recognition is a cognitive process that compares incoming stimulus information with stored knowledge to categorize the information. Thus, a set of sensory elements are transformed into a mental code. These codes then become the concepts and images with which we work in central processing. Perception is a many-to-one mapping; as it gives meaning to sensory input, it efficiently reduces many simple information "bits" into fewer representations. For human factors design, there are at least two important characteristics of this process: (1) perception by feature analysis and (2) simultaneous top-down and bottom- up processing. ADF 413 - Ergonomics in Design 17 Feature analysis Complex stimuli can be broken down into component parts or features. Feature analysis involves recognizing the features that make up a pattern and then evaluating their combination. It is essentially a three-stage process: we break the stimulus pattern into component features, match the features to stored patterns in long-term memory, decide which stored pattern is the best match. The best match determines the object perception. This appears to occur for both text and object perception. ADF 413 - Ergonomics in Design 18 Text Perception Feature analysis is relatively straightforward for text perception. The visual stimulus for the letter A can be broken down into the features of /, \, and -. The top angle would count as a feature as well. We compare the features with stored knowledge specifying the features for a capital A. If the features match the memory features for A more closely than for any other letter, we recognize the letter as a capital A. ADF 413 - Ergonomics in Design 19 Text Perception However, subjects reported that the stimuli did not disappear immediately but rather faded in a piecemeal fashion, as shown in the series on the right side of Figure. It can be seen that as the image faded, the remaining stimuli corresponded to features that were still being processed automatically and recognized as meaningful letters or numbers. ADF 413 - Ergonomics in Design 20 Text Perception Features are combined into letters, letters into words, and words into sentences. There are occasions where this process is bypassed as words that we see extremely frequently begin to be processed holistically as a single word. Thus, if we see the word the enough times, we begin to process it automatically as a global shape rather than as a set of features. This transformation from feature analysis into more global processing is called unitization. In some environments, unitization is a distinct perceptual advantage because the features can be very degraded and the general shape of the word still recognized. ADF 413 - Ergonomics in Design 21 Implications - Feature compatibility Accuracy and speed of recognition will be greatest when the features in the display are in a format compatible with the features and units in memory. For example, the features for printed words stored in memory preserve diagonal lines, angles differing from 90 degrees, and curves. Text that is displayed on grids or with only horizontal and vertical lines will be less well perceived. This is especially critical when the display must be read in a short time frame or under degraded conditions, such as a long distance or poor lighting. ADF 413 - Ergonomics in Design 22 Implications – Upper and lowercase For isolated words, printed capital letters are recognized more easily than lower case letters. HOWEVER, IN SENTENCES, A MIXTURE OF UPPERCASE AND LOWERCASE PRINT IS MOST EASILY PERCEIVED. ADF 413 - Ergonomics in Design 23 Implications – text display Useprint for text display. Print is more easily recognized and read than cursive writing. ADF 413 - Ergonomics in Design 24 Implications – Minimize abbreviations In general, full words rather than abbreviations should be used for displays. When abbreviations must be used, it is best to employ a consistent rule, where the same transformation is always made to determine the abbreviation. Finally, the best abbreviation rule is truncation, in which only the first few letters of the word are used, such as "reinf" for reinforcement. ADF 413 - Ergonomics in Design 25 Implications – Space Space between words or character strings. Gaps between words or even arbitrary strings of letters or digits are important for accurate perception If random alphanumeric strings are being displayed, the most effective number of characters to "chunk" together between gaps is three to four. An example would be two small groups of letters or numbers on a vehicle license plate rather than six or seven items all clustered together. ADF 413 - Ergonomics in Design 26 Object Perception Feature analysis may be useful in explaining relatively simple patterns such as letters, but what about more complex objects such as buildings, cars, or people? There is evidence that the same type of feature analysis can account for object recognition. Everyday objects are recognized on the basis of combinations of subobjects. These subobjects are simple geometric shapes called geons. ADF 413 - Ergonomics in Design 27 Object Perception Figure shows six of Biederman's proposed thirty geons. Geons are made up of defining features just like letters, and object recognition proceeds much like word recognition. We recognize an object by three steps: 1. Break the object up into its component geons, 2. Categorize each geon on the basis of feature match, 3. Identify the object on the basis of the component geons and their configuration. ADF 413 - Ergonomics in Design 28 Object Perception An important feature of this type of object recognition is that only edges of the geons are critical for object recognition. Other characteristics such as color, pattern, or texture are not used. Of course, when discriminating between objects having the same geon, such as between an orange and a basketball, these characteristics would become important. Color and detail will only be necessary if the subobject shapes are similar for two or more objects, and the objects therefore cannot be discriminated on the basis of component shape. ADF 413 - Ergonomics in Design 29 Top-Down and Bottom-Up Processing Up until now, object recognition has been described as being bottom-up or data driven. The entire process is guided by sensory features. However, one sensory pattern may be recognized as different objects under different environmental conditions. For example, a round object may be recognized as a basketball in one situation and as a beachball in another. The context surrounding an object provides information that is used in the recognition process. ADF 413 - Ergonomics in Design 30 Top-Down Processing The process of using context to recognize information is termed top-down processing or conceptually driven processing because high-level concepts and information is used to process "low-level" perceptual features. ADF 413 - Ergonomics in Design 31 Processing The process of using context to recognize information is termed top-down processing or conceptually driven processing because high-level concepts and information is used to process "low-level" perceptual features. The use of top-down processing occurs simultaneously and automatically along with bottom-up processing. It occurs with text, visual stimuli such as drawings, icons, or photographs, and with auditory stimuli. ADF 413 - Ergonomics in Design 32 The principle of redundancy When we read a word, there is a great deal of redundant information because, in context, we do not need to read all of the letters in a word to recognize it. I cxn rxplxce xvexy txirx lextex of x sextexce xitx an x, anx yox stxll xan xanxge xo rxad ADF 413 - Ergonomics in Design 33 Top-Down and Bottom-Up Processing While the printed word endures in front of us, the voice image is fleeting. Therefore top-down processing is even more critical for speech recognition than reading; the verbal context around critical spoken words greatly facilitates their recognition. For example, pilots listened to synthesized speech warnings presented against background noise. The warnings were either the critical words only, such as "fuel low;' or the warnings in a sentence context, such as "Your fuel is low.” Recognition for the warnings was much more accurate in the sentence context condition. ADF 413 - Ergonomics in Design 34 Top-Down and Bottom-Up Processing Top-down and bottom-up processing often trade off against one another. When the stimulus quality is high, bottom-up processing will predominate. As stimulus quality degrades, increases in context and redundancy will be necessary so that more top-down processing can keep recognition levels high. The relative effects of top-down and bottom-up processing are important for design of text displays, icons.. etc. ADF 413 - Ergonomics in Design 35 Guidelines 1. Optimize bottom-up processing for text and objects by optimizing critical factors such as size, contrast, etc.. 2. Optimize top-down processing for text and objects by methods such as: Using actual words rather than random text strings, using more rather than fewer words. Restrict the total overall message vocabulary; if there are fewer possible words to be recognized, top-down processing becomes more efficient. Provide as much context information as possible to aid in recognition and comprehension of information. ADF 413 - Ergonomics in Design 36 Guidelines 3. Evaluate tradeoffs. Given a limited space for displaying text or objects, evaluate total environment for degraded viewing conditions and availability of context effects to determine the appropriate trade-off between bottom-up and top-down processing. 4. Usability Testing. When performing usability testing, we often evaluate the recognition (and comprehension) of icons. Given that real-world recognition involves top-down processing, designers should not do usability testing for icons in a laboratory without the surrounding environmental and/or task context. ADF 413 - Ergonomics in Design 37 Transfer to working memory Only a very limited amount of information can be brought from the sensory register to working memory. This can be thought of as the first major bottleneck in the information processing system, one that is often overlooked in system design. The sensory register only holds visual information for about 1 second, and auditory information for 3-5 seconds. ADF 413 - Ergonomics in Design 38 Transfer to working memory During that time, attention may be focused on a subset of the information and brought into working memory for further processing. This attentional process is called selective attention and refers to the process of focusing on some pieces of information but not others. An analogy is that of a spotlight, which can be moved around a field and narrowed in on certain objects or information. ADF 413 - Ergonomics in Design 39 What can you hear? ADF 413 - Ergonomics in Design 40 What can you hear? In the auditory domain, if you are in a room with five conversations going on around you, you are able to focus attention on one message and bring it into working memory for processing. You will only be dimly aware of the other messages including certain basic physical characteristics such as gender. These other messages are not processed at a detailed level (unless you switch attention back and forth). Thus, we say that people can only attend to one auditory channel at a time. The spotlight of selective attention can also be directed inwardly to purely mental activity, such as rehearsal and problem solving. ADF 413 - Ergonomics in Design 41 Guidelines First, designers must be careful not to present a large quantity of information and expect people to be able to process it in a short time. ADF 413 - Ergonomics in Design 42 Guidelines Designers should realize that for displays with numerous components, only a small amount of information will be attended to at a time. This means that the information most critical to task performance must be provided in a way that will catch the person's attention. ADF 413 - Ergonomics in Design 43 Where is my car? ADF 413 - Ergonomics in Design 44 The problem with the classic ‘7(+/-)2’ George Miller’s theory of how much information people can remember People’s immediate memory capacity is very limited Many designers have been led to believe that this is useful finding for interaction design ADF 413 - Ergonomics in Design 45 Memory Involves encoding and recalling knowledge and acting appropriately We don’t remember everything – (memory involves filtering and processing) We recognize things much better than being able to recall things The rise of the GUI over command-based interfaces Better at remembering images than words The use of icons rather than names ADF 413 - Ergonomics in Design 46 Memory ADF 413 - Ergonomics in Design 47 Memory Correct recall (percent) 1 item 3 items 5 items >working memory Retention interval ADF 413 - Ergonomics in Design 48 How to Make a Good Usable Design In Cognitive Engineering, the objective is to design products that are: 1. Efficient and safe to use 2. Easy to learn and remember 3. Motivating and pleasing “Norman’s Principles” ADF 413 - Ergonomics in Design 49 Norman’s Principles Visibility Feedback Constraints Mapping Consistency Affordance ADF 413 - Ergonomics in Design 50 Visibility Make what has to be done obvious Make relevant parts visible How fast are we going? ADF 413 - Ergonomics in Design 51 Feedback Sending back information about what has been done Includes (sound, highlighting, animation) ADF 413 - Ergonomics in Design 52 Constraints Restricting the possible actions that can be performed Three main types: Physical Cultural Logical ADF 413 - Ergonomics in Design 53 Mapping Controls and displays should exploit natural mapping Natural mapping takes advantage of physical analogies and cultural standards Physical: Steering wheel Cultural: red means stop, green means go ADF 413 - Ergonomics in Design 54 Good mapping? ADF 413 - Ergonomics in Design 55 How do I make a call? ADF 413 - Ergonomics in Design 56 Consistency Design interfaces to have similar operations and use similar elements for similar tasks ADF 413 - Ergonomics in Design 57 Affordance Refers to an attribute of an object that allows people to know how to use it ADF 413 - Ergonomics in Design 58 Affordance The affordances of an object determine, naturally, how it can be used Button affords pushing Handle affords grasping Chair affords sitting Knob affords turning Just by looking at the object, a user should know how to use it Example: The doors with handles to push, mop sink ADF 413 - Ergonomics in Design 59 Good affordance The best way to create an affordance is to echo the shape of the human hand in "negative space". Look closely at the (excellent) Kodak DC-290 digital camera, shown here front and back ADF 413 - Ergonomics in Design 60