A distant large display can have the same display FOV as a close small display, even though it may incur different viewing experiences. If possible, it is desirable to choose the most economical display, not necessarily the biggest or the one with the highest resolu- tion, with respect to the requirement of the task and the typical user characteristics.
On the other hand, the rods are distributed mainly in the periphery of the retina and are responsible for motion detection and less detailed peripheral vision. While details may not be sensed, the rods contrib- ute to our awareness of the surrounding environment. Differently from that of human perception, most displays have uniform resolution. Figure 3. Is it really worth the cost?
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Consequently, it can be argued that it is more economical to use a smaller high-resolution display placed at a close distance. Contrast in brightness is measured in terms of the difference or ratio of the amounts of light ener- gies between two or more objects. The recommended ratio of the foreground to background brightness contrast is at least Color contrast is defined in terms of differences or ratios in the dimensions of hue and saturation.
Before all these low-level-part features are finally Energy Hue dominant wavelength Energy of dominant wavelength Saturation Energy of white light Brightness total light energy Wavelength Figure 3. From Hemer, M. Pre-attentive features are compos- ite, primitive, and intermediate visual elements that are automatically recognized before entering our consciousness, typically within 10 ms after entering the sensory system .
Human-Computer Interaction Fundamentals by Andrew Sears
These features may rely on the relative differences in color, size, shape, orientation, depth, texture, motion, etc. At a more conscious level, humans may universally recognize certain high-level complex geometric shapes and properties as a whole and understand the underlying concepts. From Ware, C. The actual form of sound feedback can be roughly divided into three types: a simple beep- like sounds, b short symbolic sound bytes known as earcons e.
As we did for the visual modal- ity, we will first go over some important parameters of the human aural capacity and the corresponding aural display parameters. The dominant frequency compo- nents determine various characteristics of sounds such as the pitch e. Humans can hear sound waves with frequency values between about 20 and 20, Hz . 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 Hz and com- posed of at least four prominent harmonic frequency components fre- quencies that are integer multiples of one another , each within the range of — Hz . Aural feedback is more commonly used in intermittent alarms. However, overly loud i.
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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. First, sound is effectively omnidirectional.
However, as already mentioned, it can also be a nuisance as a task interrupter e. Making use of contrast is possible with sound as well. For instance, auditory feed- back would require a 15—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. In general, only one aural aspect can be interpreted at a time. Humans do possess an ability to tune in to a particular part of the sound e. 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 com- mands has become very robust lately. In most cases, it still requires speaker-specific training or a relatively quiet background. As such, many voice input systems operate in an explicit mode or state. The need to switch to the voice-command mode is still quite a nuisance to the ordinary user. Thus, voice input is much more effective in situations where, for example, hands are totally occupied or where modes are not necessary because there is very little background noise or because there is no mixture of conversation with the voice commands.
Machine understanding of long sentences and natural-language- based commands is still very computationally difficult and demanding. With the spread of smart-media client devices that might be computationally light yet equipped with a sleuth of sensors, such a cloud-based natural-language interaction combined with intelligence will revolutionize the way we interact with computers in the near future.
To be precise, the term Figure 3. The smart- media client devices would send the captured sentence in voice or text , and a correct and intel- ligent response is given back in real time. Thus haptic refers to both the sensation of force feedback as well as touch tactile. For convenience, we will use the term haptic to refer to the modal- ity for sensing force and kinesthetic feedback through our joints and muscles even though any force feedback practically requires contact through the skin and the term tactile for sensing different types of touch e.
The fingertip is one of the most sensitive areas and is frequently used for HCI purpose. Vibration fre- quency of about Hz is said to be the optimal for comfort- able perception . For a fingertip, this amounts to about 0. As mentioned previously, there are many types of tactile stimula- tion, such as texture, pressure, vibration, and even temperature. For the purposes of HCI, the following parameters are deemed important, and the same goes for the display system providing the tactile-based feedback.
Physical tactile sensation is felt by a combination of skin cells and nerves tuned for particular types of stimulation, e.
From Proprioception, Intl. While there are many research prototypes and commercial tactile display devices, the most practical one is the vibration motor, mostly applied in a single actuator configuration. Most vibration motors do not offer separate controllability for amplitude and frequency. In addi- tion, most vibrators are not in direct contact with the stimulation tar- get e. Thus additional care is needed to set the right parameter values for the best effects under the circumstances. Another way to realize vibratory tactile display is to use thin and light piezoelectric materials that exhibit vibration responses according to the amounts of electric potential supplied.
Due to their flat form factor, such materials can be embedded, for instance, into flat touch screens. Along with tactile feed- 3. Right: tactile array with multiple actuators. The activation force for the joints is between 0. Note that haptic devices are both input and output devices at the same time. We briefly discuss this issue of haptic input in the next section in the context of human body ergonomics. 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 deliv- ered in the direction relative to the game controller. Such a device is not appropriate for fast-occurring interaction e. More-complicated haptic devices are in the form of a robotic kine- matic chain, either fixed on the ground or worn on the body.
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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. Using a similar control structure, body-worn devices transfer force with its mechanism directly attached to the body.
Important haptic display parameters are a the degrees of freedom the number of directions in which force or torque be can displayed , b the force range should be at least greater than 0. Stability is in fact a by-product of the proper sampling period, which refers to the time taken to sense the current amount of force at the interaction point and then determine whether the target value has been reached and reinforce it a process that repeats until a target equilibrium force is reached at the interaction point. The ideal sampling period is about Hz, and when the sampling period falls under a certain value, the robotic mechanism exhibits instability e.
The dilemma is that provid- ing a high sampling rate requires a heavy computation load, not only in updating the output force, but also in physical simulation e. They tend to be heavy, clunky, dangerous, and take up a large volume. The cost is very high, often with only a small operating range, force range, or limited degrees of freedom. In many cases, simpler devices, such as one-directional latches or vibra- tors, are used in combination with visual and aural feedback to enrich the user experience.
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 . Here are some represen- tative examples. For instance, the ring of a phone call can be simulta- neously aural and tactile to strengthen the pick-up probability. For multimodal interfaces to be effective, each feedback must be properly synchronized and consistent in its representation.
The representation must be coordinated between the two: In the previous example, if there is one highlighting, then there should also be one corresponding beep. When inconsistent, the interpretation of the feedback can be confus- ing, or only the dominant modality will be recognized.
Human-Computer Interaction Fundamentals
In this section, we briefly look at ergonomics aspects. To be precise, ergonomics is a discipline focused on making products and interfaces comfortable and efficient. Thus, broadly speaking, it encom- passes mental and perceptual issues, although in this book, we restrict the term to mean ways to design interfaces or interaction devices for comfort and high performance according to the physical mechanics of the human body. For HCI, we focus on the human motor capabilities that are used to make input interaction. Thus, to reiterate, ID represents an abstract notion of difficulty of the task, while MT is an actual prediction value for a particular task.
From MacKenzie, I. Berard et al. In addition to discrete-event input methods e. Obviously, humans will exhibit different motor-control perfor- mances with different devices, as already demonstrated with the two types of device mentioned previously e. The mouse and 3-D stylus, for instance, belong to what is called the isomet- ric devices, where the movement of the device directly translates to the movement in the display or virtual space.
Nonisometric devices are those that control the movement in the display in principle with some- thing else such as force, thus possibly with no movement input at all.