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Page | 28 HUMAN FACTORS OF HCI THEORIES Topic:
1. Human Information Processing
a. Task Modeling and Human Problem Solving Model
b. Human Reaction and Predictions of Cognitive Performance
2. Sensation and Perception of Information
a. Visual
b. Aural
c. Tactile and Haptic
d. Multimodal Interaction
3. Human Body and Ergonomics
a. Fitts Law
b. Motor Control
Objectives:
• Explain the importance of Human Factors of HCI theories.
• Classify Users needs according to Human Factor Knowledge
of HCI to design user Interface for HCI
• Identify what human factors involve to design an
effective user interface for HC
Content
1. Human Information Processing Any effort to design an effective interface for human–computer interaction (HCI) requires two basic elements: an understanding of a) computer factors (software/hardware) and b) human behaviour. To practice user-centered design by following these principles and guidelines, the interface requirements must often be investigated, solicited, derived, and understood directly from the target users through focus interviews and surveys. However, it is also possible to obtain a fairly good understanding of the target user from knowledge of human factors. As the main underlying theory for HCI, human factors can largely be divided into: a) Cognitive science , which explains the human’s capability and model of conscious processing of high-level information and
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Page | 29 b) Ergonomics , which elucidates how raw external stimulation signals are accepted by our five senses, are processed up to the pre-attentive level, and are later acted upon in the outer world through the motor organs. Human-factors knowledge will particularly help us design HCI in the following ways. i. Task/interaction modelling : Formulate the steps for how humans might interact to solve and carry out a given task/problem and derive the interaction model. A careful HCI designer would not neglect to obtain this model by direct observation of the users themselves, but the designer’s knowledge in cognitive science will help greatly in developing the model. ii. Prediction, assessment, and evaluation of interactive behavior : Understand and predict how humans might react mentally to various information-presentation and input- solicitation methods as a basis for interface selection. Also, evaluate interaction models and interface implementations and explain or predict their performance and usability. a. Task Modeling and Human Problem-Solving Model Cognitive science has investigated the ways in which humans solve problems, and such a model can help HCI designers analyse the task and base the interaction model or interface structure around this innate problem-solving process. Thus for a smaller problem of “fixing the font,” the action could be a “menu item selection” applied to a “highlighted text.” There are several “human problem-solving” models that are put forth by a number of researchers, but most of them can be collectively summarized as depicted in Figure 3.1.
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Page | 31 commanding the motor system (e.g., to click the mouse left button). Figure 3.2 shows an example of a hierarchical task plan (equivalent to hierarchical goal structure) illustrating how the simple task of changing the font of a text could be solved, i.e., what kinds of basic tasks would be needed. Note that in a general hierarchical task model, certain subtasks need to be applied in series, and some may need to be applied concurrently. One can readily appreciate from the simple example in Figure 3.2 how an interactive task model can be hierarchically refined and can serve as a basis for the interface structure. Note that, based on this model, we could “select” interfaces to realize each subtask in the bottom of the hierarchy, which illustrates the crux of the HCI design process. The interaction model must represent as much as possible what the user has in mind, especially what the user expects must be done (the mental model) in order to accomplish the overall task. This way, the user will be “in tune” with the resulting interactive application. The interface selection should be done based on ergonomics, user preference, and other requirements or constraints. Finally, the subtask structure can lend itself to the menu structure, and the actions and objects to which the actions apply can serve as the basis for an object-class diagram (for an object-oriented interactive software implementation).
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Page | 32 b. Human Reaction and Prediction of Cognitive Performance We can also, to some degree, predict how humans will react and perform in response to a particular human interface design. We can consider two aspects of human performance: one that is cognitive and the other ergonomic. Norman and Draper spoke of the “gulf of execution/evaluation,” which explains how users can be left bewildered (and not perform very well) when an interactive system does not offer certain actions or does not result in a state as expected by the user (Figure 3.3). Such a phenomenon would be a result of an interface based on an ill-modeled interaction. A user, when solving a problem or using an interactive system to do so, will first form a mental model that is mostly equivalent to the hierarchical “action” plan for the task. The mismatch between the user’s mental model and the task model employed by the interactive system creates the “gulf.” On the other hand, when the task model and interface structure of the interactive system maps well to the expected mental model of the user, the task performance will be very fluid. Memory capacity also influences the interactive performance greatly. As shown in Figure 3.1, there are largely two types of memory in the human cognitive system: the short term and the long term. The short-term memory is also sometimes known as the working memory, in the sense that it contains (changing) memory elements meaningful for the task at hand (or chunks). Humans are known to remember about eight chunks of memory lasting only a very short amount of time. This means that an interface cannot rely on the human’s short- term memory beyond this capacity for fast operation. Imagine an interface with a large number of options or menu items. The user would have to rescan the available options a number of times to make the final selection. In an online purchasing system, the user might not be able to remember all of the relevant information such as items purchased, delivery options, credit card chosen, billing address, usage of discount cards, etc. (Figure 3.4). Thus such information will have to be presented to the user from time to time to refresh one’s memory and ensure that no errors are made.
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Page | 34
2. Sensation and Perception of Information Humans are known to have at least five senses. Among them, those that would be relevant to HCI (at least for now) are the modalities of visual, aural, haptic (force feedback), and tactile sensation. Taking external stimulation or raw sensory information (sometimes computer generated) and then processing it for perception is the first part in any human–computer interaction. Naturally, the information must be supplied in a fashion that is amenable to human consumption, that is, within the bounds of a human’s perceptual capabilities. Another aspect of sensation and perception is attention, that is, how to make the user selectively (consciously or otherwise) tune in to a particular part of the information or stimulation. Highly attentive information can be used for alerts, reminders, highlighting of prioritized/structured information, guidance, etc. Note that attention must occur and be modulated within awareness of the larger task(s). While we might tune in to certain important information, we often still need to have an
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Page | 35 understanding, albeit approximate, of the other activities or concurrent tasks, such as in multitasking or parallel processing of information. Just as cognitive science was useful in interaction and task modeling, this knowledge is essential in sound interface selection and design. a) Visual - Visual modality is by far the most important information medium. Over 40% of the human brain is said to be involved with the processing of visual information. In this section, we review some of the important properties of the human visual system and their implications for interface design. Visual and Display Parameters ✓ Field of view (FOV): This is the angle subtended by the visible area by the human user in the horizontal or vertical direction. The shaded area in Figure 3. illustrates the horizontal field of view. The human FOV is nearly 180° in both the horizontal and vertical directions. ✓ Viewing distance: This the perpendicular distance to the surface of the display. Viewing distance (dotted line in Figure 3.6) may change with user movements. However, one might be able to define a nominal and typical viewing distance for a given task or operating environment. ✓ Display field of view: This is the angle subtended by the display area from a particular viewing distance. Note that for the same fixed display area, the display FOV will be different at different viewing distances. ✓ Pixel : A display system is typically composed of an array of small rectangular areas called pixels. ✓ Display resolution : This is the number of pixels in the horizontal and vertical directions for a fixed area. ✓ Visual acuity : In effect, this is the resolution perceivable by the human eye from a fixed distance. This is also synonymous with the power of sight, which is different for different people and age groups.
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Page | 37 c. Color, Brightness, and Contrast - Other important properties and attributes of visual quality are brightness, color, and contrast. ✓ Brightness : The amount of light energy emitted by the object (or as perceived by the human). ✓ Color : Human response to different wavelengths of light, namely for those corresponding to red, green, blue, and their mixtures. A color can be specified by the composure of the amounts contributed by the three fundamental colors and also by hue (particular wavelength), saturation (relative difference in the major wavelength and the rest in the light), and brightness value (total amount of the light energy) (Figure 3.10). ✓ Contrast : Relative difference in brightness or color between two visual objects. Contrast in brightness is measured in
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Page | 38 terms of the difference or ratio of the amounts of light energies between two or more objects. The recommended ratio of the foreground to background brightness contrast is at least 3:1. Color contrast is defined in terms of differences or ratios in the dimensions of hue and saturation(Figure 3.11). d. Pre-Attentive Features and High-Level Diagrammatic Semantics - Detail, color, brightness, and contrast are all very-low-level raw visual properties. Before all these low-level-part features are finally consolidated for conscious recognition (of a larger object) through the visual information processing pipeline, pre- attentive features might be used to attract our attention. Pre- attentive features are composite, primitive, and intermediate visual elements that are automatically recognized before entering our consciousness, typically within 10 ms after entering the sensory system [12]. These features may rely on the relative differences in color, size, shape, orientation, depth, texture, motion, etc. Figure 3.12 shows several examples and how they can be used collectively to form and design effective graphic icons. At a more conscious level, humans may universally recognize certain high-level complex geometric shapes and properties as a whole and
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Page | 40 where 0 dB corresponds to the lowest level of audible sound and about 130 dB is the highest. It is instructive to know the decibel levels of different sounds as a guideline in setting the nominal volume for the sound feedback (Table 3.3). ✓ Sound - can be viewed as containing or being composed of a number of sinusoidal waves with different frequencies and corresponding amplitudes. The dominant frequency components determine various characteristics of sounds such as the pitch (e.g., low or high key), timbre (e.g., which instrument), and even directionality (where is the sound coming from?). Humans can hear sound waves with frequency values between about 20 and 20,000 Hz [13]. ✓ Phase - refers to the time differences among sound waves that emanate from the same source. Phase differences occur, for example, because our left and right ears may have slightly different distances to the sound source and, as such, phase differences are also known to contribute to the perception of spatialized sound such as stereo. When using aural feedback, it is important for the designer to set these fundamental parameters properly. A general recommendation is that the sound signal should be between 50 and 5000 Hz and composed of at least four prominent harmonic frequency components (frequencies that are integer multiples of one another), each within the range of 1000 – 4000 Hz [14]. Aural feedback is more commonly used in intermittent alarms. However, overly loud (i.e., needlessly high amplitude) alarms are
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Page | 41 known to rather startle the user and lower the usability. Instead, other techniques can be used to attract attention and convey urgency by such aural feedback techniques as repetition, variations in frequency and volume, and gradual and aural contrast to the background ambient sound (e.g., in amplitude and frequency). b) Other Characteristics of Sound as Interaction Feedback We further point out a few differences of aural feedback from the visual. First, sound is effectively omnidirectional. For this reason, sound is most often used to attract and direct a user’s attention. However, as already mentioned, it can also be a nuisance as a task interrupter (e.g., a momentary loss of context) by the startle effect. Making use of contrast is possible with sound as well. For instance, auditory feedback would require a 15– 30 - dB difference from the ambient noise to be heard effectively. Differentiated frequency components can be used to convey certain information. Continuous sound is somewhat more subject to becoming habituated (e.g., elevator background music) than stimulation with other modalities. In general, only one aural aspect can be interpreted at a time. That is, it is difficult to make out the aural content when the sound is jumbled/masked with multiple sources. Humans do possess an ability to tune in to a particular part of the sound (e.g., string section in a symphony); however, this requires much concentration and effort. c) Aural Modality as Input Method So far, the aural modality has been explained only in the context of passive feedback. As for using it actively as a means for input to interactive systems, two major methods are: (a) keyword recognition and (b) natural language understanding. Isolated-word-recognition technology (for enacting simple commands) has become very robust lately. In most cases, it still requires speaker-specific training or a relatively quiet background. Another related difficulty with voice input is the “segmentation” problem, i.e., how to segment out, from a stream of continuous voice input or background noise, the portion that corresponds to the actual command.
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Page | 43 frequency of about 250 Hz is said to be the optimal for comfortable perception. ✓ Pressure threshold: The lightest amount of pressure humans can sense is said to be about 1000 N/m2. For a fingertip, this amounts to about 0.02 N for the fingertip area. The maximum threshold is difficult to measure, because when the force/torque gets large enough, the kinesthetic senses start to operate, and this threshold will greatly depend on the physical condition of the user (e.g., strong vs. weak user). f) Haptic and Haptic Display Parameters Along with tactile feedback, haptic feedback adds a more apparent physical dimension to interaction. Force feedback and movement is felt by the cells and nerves in our muscles and joints. For instance, the muscle spindle/ tendon takes the inertial load, and Pacinian/Ruffini/Golgi receptors sense the joint movements, pressure, and torque. The activation force for the joints is between 0.5 to 2.5 mN. The simplest form of a haptic device is a simple electromagnetic latch that is often used in game controllers. It generates a sudden inertial movement and slowly repositions itself for repeated usage. Normally, the user holds on to the device, and inertial forces are delivered in the direction relative to the game controller. Such a device is not appropriate for fast-occurring interaction (e.g., successive gun shots) or for displaying a continuously sustained force (e.g., leaning against a wall). More-complicated haptic devices are in the form of a robotic kinematic chain, either fixed on the ground or worn on the body. As a kinematic chain, such devices offer higher degrees of freedom and finer force control (Figure 3.17). For the grounded device, the user interacts with the tip of the robotic chain through which a force feedback is delivered. The sensors in the joints of the device make it possible to track the tip (interaction point) within the three- dimensional (3-D) operating space.
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Page | 44 g) Multimodal Interaction Conventional interfaces have been mostly visually oriented. However, for various reasons, multimodal interfaces are gaining popularity with the ubiquity of multimedia devices. By employing more than one modality, interfaces can become more effective in a number of ways, depending on how they are configured [22]. Here are some representative examples. ✓ Complementary : Different modalities can assume different roles and act in a complementary fashion to achieve specific interaction objectives. For example, an aural feedback can signify the arrival of a phone call while the visual displays the caller’s name. ✓ Redundant : Different modality input methods or feedback can be used to ensure a reliable achievement of the interaction objective. For instance, the ring of a phone call can be simultaneously aural and tactile to strengthen the pick-up probability. ✓ Alternative : Providing users with alternative ways to interact gives people more choices. For instance, a phone call can be made either by touching a button or by speaking the callee’s name, thereby promoting convenience and usability. For multimodal interfaces to be effective, each feedback must be properly synchronized and consistent in its representation. For instance, to signify a button touch, the visual highlighting and beep sound effect must occur within a short time (e.g., less than 200 ms) to be recognized as one consistent event.
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Page | 46 Self-Assessment Question: Quiz 1 - 2. What are the two(1) basic elements to design and effective user interfaces for human computer interaction(HCI)
- It is a HCI human factors that explains the human capability and model of conscious processing of high level information - (Cognitive science)
- It is a HCI human factors that explain how raw external stimulation signals are accepted by our five senses are processed up to the pre-attentive level, and are later acted upon in the outer world through the motor organs.
- It is the most important information medium which 40 per cent of human brains is said to be involved with.
- It is a visual and display parameter that is angle subtended by the visible area by the human user in the horizontal or vertical directions.
- It is a visual and display parameter that is angle subtended by the display is form a particular viewing distance.
- It is a visual and display parameters that is composed of an array of small rectangular areas.
- It is the number of pixels in the horizontal and vertical directions for a fixed area. 10 - 12. This are the 3 properties and attributes of visual quality. Essay
- Discuss what user cantered design in Human Computer Interaction.
- Discuss the important parts of Human Problem Solving / Information-Processing.
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Page | 47 Summary In this chapter, we have reviewed the essence of human factors, including sensation, perception, information processing, and Fitts’s law, as the foremost underlying theory for the design of interfaces for human–computer interaction. By the very principle of “Know thy user,” it is clear that the HCI designer must have a basic understanding of these areas so that any interface will suit the user’s most basic mental, perceptual, and ergonomic capabilities. We can also readily see that many of the HCI principles discussed previously in this book naturally derive from these underlying theories. References: ✓ Norman, Donald A., and Stephen W. Draper. 1986. User centered system design: New perspectives on human-computer interaction. Boca Raton, FL: CRC Press. ✓ Miller, George A. 1956. The magical number seven, plus or minus two: Some limits on our capacity for processing information. Psychological Review 63 (2): 81. ✓ Marois, Rene, and Jason Ivanoff. 2005. Capacity limits of information processing in the brain. Trends in cognitive sciences 9 (6): 296 – 305. ✓ Anderson, J. R., D. Bothell, M. D. Byrne, S. Douglass, C. Lebiere, and Y. Oin. 2004. An integrated theory of the mind. Psychological Review 111 (4): 1036 – 60. ✓ Polk, T. A., and C. M. Seifert. 2002. Cognitive modeling. Cambridge, MA: MIT Press. ✓ Salvucci, D. D., and N. A. Taatgen. 2008. Threaded cognition: An integrated theory of concurrent multitasking. Psychological Review 130 (1): 101 – 30. ✓ Card, Stuart K., Thomas P. Moran, and Allen Newell. 1986. The model human processor: An engineering model of human performance. In Handbook of human perception. Vol. 2, Cognitive processes and performance, ed. K. R. Boff, L. Kauffman, and J. P. Thomas, 1 – 35. New York: John Wiley and Sons. ✓ Schulz, Trenton. 2008. Using the keystroke-level model to evaluate mobile phones. In Public systems in the future: Possibilities, challenges, and pitfalls, Proceedings of the 31st Information Systems Research Seminar (IRIS31). Åre, Sweden.
