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Article Excerpt
INTRODUCTION
A successful human-system interaction depends on the human's ability to communicate with the system--to direct it to perform an action, to request a piece of information, and so on. Such communication occurs through use of an input device such as a keyboard, button, knob, mouse, touch screen, or voice activation. The present research focused on variables that could influence input device use. For example, does the optimality of an input device depend on the task being performed? Is performance with a given input device influenced by the age of the user?
Recognition that one input device might be better relative to another device for a particular task is certainly not new. In fact, new input devices often are developed in an attempt to compensate for the limitations of existing devices. However, a systematic analysis of the interactions among task demands, user capabilities, and input device characteristics is lacking.
Input devices may be categorized as direct devices and indirect devices. A direct input device is one for which no translation is required between the activity performed by the person and the action of the device; examples include a touch screen, a light pen, or voice activation. Indirect devices, however, require a translation between the activity of the person and the action of the device. For example, a mouse moves in one dimension on the desktop and the cursor on the screen moves in a different dimension; moreover, depending on the settings of the mouse, a 1-inch movement of the mouse might result in a 3-inch movement of the cursor. Other examples of indirect devices include trackballs, joysticks, and rotary encoders.
The input device categories of direct and indirect have advantages and disadvantages, as summarized in Table 1. Generally, direct devices are best for discrete, pointing, and ballistic types of tasks. Indirect devices yield better performance for precision tasks or repetitive tasks. However, these generalizations are based on studies in which devices were compared for tasks in isolation (for reviews, see Greenstein, 1997; Greenstein & Arnaut, 1987). Whether these studies predict input device superiority and apply to the variety of tasks that must be performed in a complex system are empirical questions.
An additional research question is whether the pattern of advantages and disadvantages for input device categories will generalize across user groups differing in age. As people age, motor behaviors change such that older adults, compared with younger adults, take longer to make similar movements, and their ability to maintain continuous movement declines, coordination is disrupted, and movements are more variable (for a review, see Vercruyssen, 1997). In addition, older adults have more "noise" in their movement control system (Walker, Philbin, & Fisk, 1997), less effective perceptual feedback (Walker et al.), reduced working memory capacity (Zacks, Hasher, & Li, 2000), and declines in spatial ability (Salthouse, 1992). All of these characteristics associated with older age could conceivably influence use of input devices.
Some studies have directly examined older adults' use of input devices. When using a mouse, older adults tend to make more errors and are slower than younger adults (Charness, Kelley, Bosman, & Mottram, 2001; Smith, Sharit, & Czaja, 1999; Walker et al., 1997), even if they are experienced mouse users (Walker, Millians, & Worden, 1996). However, few researchers have compared older adults' performance across different input devices. One notable exception is a recent study by Charness, Holley, Feddon, and Jastrzembski (2004) in which performance using a mouse and a light pen was compared across young, middle-aged, and older adult age groups. They found that using a light pen reduced age-related differences for a menu target acquisition task. They suggested that direct devices might be generally better for older adults because they reduce the need for a translation from the activity of the user to the action of the device. However, additional assessments for a range of tasks are required to determine if the benefits of a direct device are general or specific to certain tasks.
OVERVIEW OF EXPERIMENTS
The purpose of the present research was to assess, comparatively, input device use for younger and older adults. The first experiment contrasted a direct device (a touch screen) and an indirect device (a rotary encoder). Performance for the two devices was assessed within the context of using a system; comparisons were made for a variety of tasks--some predicted to be performed better with the direct device, and others predicted to be performed better with the indirect device. We compared the performance of younger adults and adults over age 50 across tasks to determine if the age of the user interacted with use of each input device.
The second experiment focused solely on touch screen usage. Given the increased prevalence of touch screen interfaces and the potential performance issues found in Experiment 1, we conducted the second study to provide more detailed performance characteristics. We systematically manipulated the size of the target area, the distance of the movement required, the direction of the movement, and the type of movement (tapping or sliding). These comparisons enabled us to assess in more depth the task parameters that influence touch screen performance for younger and older adults.
EXPERIMENT 1: INPUT DEVICE USE IN CONTEXT
This experiment assessed performance differences for a direct versus an indirect input device as a function of the characteristics of the task being performed (i.e., the type of control) and the age of the participant. Rather than assess performance for the different task types in isolation, we assessed performance in the context of interacting with a system. Younger and older adults completed activities on the Entertainment System Simulator using either a direct touch screen device or an indirect rotary encoder device. Performance was assessed on tasks that would be expected either to be better for the direct device (i.e., ballistic, pointing, and discrete tasks) or to be performed better using the indirect device (i.e., precision and repetitive tasks).
EXPERIMENT 1: METHOD
Participants
Forty younger adults (18-28 years) and 40 middle-aged to older adults (51-65; hereafter referred to as older) participated in this experiment. The age range of the older group was chosen to be representative of the "older worker." Younger adults received course credit, and older adults were compensated $10/hr for their participation. Screening requirements were as follows: (a) corrected visual acuity of at least 20/40 (far and near vision); (b) hearing ability sufficient to respond to task-relevant sounds presented via a Visual Basic program; and (c) trimmed fingernails that would not interfere with the touch screen (participants were told prior to coming in to ensure that their fingernails were trimmed).
Upon their arrival, participants were assigned to either the touch screen or the rotary encoder condition. Standard ability tests were administered to evaluate whether the participant groups differed; these data are presented in Table 2, along with the demographic and health data for each group. The only significant difference for the young adults was that simple reaction time (RT) was faster for the rotary encoder group; there were no group differences for the older adults. We tested handedness to ensure that the assignment of left-handed participants was balanced across device conditions. Participants were instructed to use their preferred hand. Overall age differences (p < .05) were as follows: Older adults performed better on the vocabulary test and had more years of education; younger adults performed better on Digit Symbol Substitution, Reverse Digit Span, simple RT, and choice RT. These differences are consistent with those typically reported in the literature (e.g., Rogers, Hertzog, & Fisk, 2000). There were no age differences in self-reported health.
Materials
Input devices. The touch screen was a Data-Lux LMV10 capacitive touch screen, which required a bare finger to be in contact with the screen. The unit was approximately 11.5 inches across and 8 inches high (29.2 x 20.3 cm). The active, touch-sensitive screen was approximately 10.4 inches (26.4 cm) in diagonal. The monitor was securely attached to the desk, so it did not move when touched. The rotary encoder consisted of a black plastic outer casing about 3.25 x 1.5 x 1 inches (8.2 x 3.8 x 2.5 cm). A push button and rotary knob were located on the top face of the box. Participants held the device in one hand and controlled the knob with the other.
Entertainment System Simulator. The interface used in this experiment was a simulation of an entertainment system created using Microsoft Visual Basic 6.0 (see Figure 1 for screen examples). The simulator was sized to fit on the touch screen display, which was 640 pixels wide by 480 pixels tall. All text was sized to be 14 points or larger (equivalent to approximately 4.9 mm). The three primary functions of the Entertainment System Simulator were a compact disc player, an AM/FM radio, and a weather information station. In addition, the system had three subscreens that governed advanced audio controls (e.g., setting treble level), user settings (e.g., date and time), and a message center. The simulator was designed to include a variety of controls that are typically found in human-computer interfaces. (Additional details of the program are available in Rogers et al., 2002.)
[FIGURE 1 OMITTED]
Display configuration. The participant workstation consisted of two monitors. A 17-inch (43.2-cm) video graphics array (VGA) monitor was used to display the...
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