Our analysis of the state-of-the-art on HCI studies of tactile interaction for older adults, presented in section II.3, demonstrates that tactile interaction has already been extensively designed and evaluated for older adults, but when comparing this group to younger users, older adults usually make more errors and take longer times to execute the gestures of interaction (M. K. Chung et al., 2010; Findlater et al., 2013; Hourcade and Berkel, 2006). Indeed, human aging is related to changes in perceptual, psychomotor, cognitive and physical systems. Moreover, older adults have different psychological, social and cultural characteristics. It is though difficult to understand which factors related to the aging can be affecting interaction performances of older adults.
Contrary to traditional input devices used in desktop settings, where the users’
arms are resting on the desk, the users’ arms are usually floating when interacting with touchscreens. Consequently, the execution of the gestures of interaction on touchscreen requires fine dexterity of the user (Jin et al., 2007; Nicolau and Jorge, 2012;
Wacharamanotham, 2011). The effects of aging on the movements the users executes during interaction with touchscreen devices need to be further studied in order to provide information to design tactile interactive systems and interaction techniques better adapted to the older users’ motor skills.
In this section, we discuss our Research Question 4 concerning the evaluation of the effects of aging on movements of the users and their possible relationship with time of movement and accuracy of tactile interaction. First, due to the high implication of the users’ arms and hands when using touchscreen devices, we describe main considerations about the differences in the movements of the upper limbs of older adults and adults.
Then, we review the literature to establish the state-of-the-art on studies about the movements and postures of the users during interaction with touchscreens.
Age effects on the movements of users’ upper limbs II.4.1.
To accomplish the gestures of interaction, movements of the user must be planned and executed with accuracy, which requires a good functioning and coordination of the central nervous system (CNS) and musculoskeletal system. According to Roy et al.
(1996), the cognitive processing of movements of the user’s body can be analyzed inside an information processing framework: “information from the environment that serves as input to the perceptual-motor system is processed through a number of stages resulting in an observable motor response” (Roy et al., 1996).
Previous studies on the movements of the arms of older adults have demonstrated the effects of lower muscle strength and decline on sensorimotor systems related to the aging on the trajectories of the arms (Cooke et al., 1989; Darling et al., 1989). Moreover, the age-related changes in proprioceptive acuity of the upper-limbs resulted on impaired detection of wrists’ joint motions for older adults, negatively affecting goal-oriented arm movements (Wright et al., 2011). Indeed, the effects of age on the movements are related to the insufficient neural, perceptual or physiological information implying sensorimotor constraints to the movements of the arms (Roy et al., 1996) and these movement constraints limit the way in which movements are organized and controlled (Marteniuk et al., 1987).
According to Walker et al. (1997), there is a consistent documentation on age-related differences in movements of upper limbs of older adults and adults based on the analysis of ballistic movements (Walker et al., 1997). The aging effects on the execution of movements have been evaluated through time of movement (i.e., the overall timing for executing one movement) and kinematics of the movement (i.e., control processes of motor performances such as trajectories, articular angles, speed) (Roy et al., 1996). The analysis of the trajectories and speed of the movements of the arms of older adults and adults demonstrated that older subjects executed longer movement times, characterized by asymmetrical acceleration and deceleration curves (Cooke et al., 1989; Darling et al., 1989). This asymmetry is due to a longer deceleration phase, usually related to sub-corrective movements (Darling et al., 1989). Effectively, the same characteristics of movements have been observed on the trajectories of the cursor on the screen during the evaluation of age effects on pointing tasks with a computer mouse (Walker et al., 1997).
Lepicard and Vigouroux (2012) demonstrated movements of older adults during tactile interaction are slower and characterized by irregular speed compared to younger adults (Lepicard and Vigouroux, 2012).
The analysis of the movements of the upper-limbs can be defined through the evaluation of the effects of movement constraints (Marteniuk et al., 1987; Roy et al., 1996), and their consequences on the strategies employed by the users to execute the gestures of interaction. Movement constraints are variables limiting the way in which movements are organized and controlled (Marteniuk et al., 1987). According to Roy et al.
(1996), the evaluation of the age effects on the movements of older adults is defined by three kinds of constraints: sensorimotor, physical and high level constraints. Sensorimotor constraints refer to the temporal and spatial limitations of the central nervous system to
compensate age-related decreases on neural, perceptual or physiological information, necessaries to effectuate the movement. These constraints are though centered in the characteristics of the performers: the users. Physical constraints refer to the biomechanical limitations of the performer (e.g. the ways a hand can be postured), the properties of the objects and the relationship between the objects and the environment (e.g. shape, location, distance). Finally, high levels constraints are informational, related to the knowledge the performers have about the context, as their previous experiences, motivational, related to their intentions for the movement they are executing, and functional, depending on the goals of the task being executed (Mackenzie and Iberall, 1994; Roy et al., 1996). Based on previous experience, for example, performers determine the forces, speeds and strategies for placing or throwing, lifting or transporting.
The constraints framework is suitable for analyzing how the effects of aging on cognitive processing and motor responses affect the movements of older users during interaction, and consequently their interaction performances. Indeed, aging leads to changes on psychomotor and physiological systems that hinder the execution of movements with accuracy (e.g., reduce of proprioception sensibility, decrease of muscle strength, reduce of bone density, etc.).
The sensorimotor constraints define the movements of the users during the execution of the movements of interaction. For example, longer movement times and increased deceleration phases have been observed for trajectories of the arms of older adults (Cooke et al., 1989; Darling et al., 1989) as well on trajectories of cursor during mouse tasks (Ketcham et al., 2002; Walker et al., 1997) and tactile interaction (Lepicard and Vigouroux, 2012). Other studies have also demonstrated the effects of users’
different motor skills on their interaction performances when interacting with touchscreen (Caprani et al., 2012; Irwin and Sesto, 2012; Jin et al., 2007). Users with motor disabilities made more errors of interaction and used more pressure than non-disabled users (Irwin and Sesto, 2012). Besides, older users with low dexterity skills (according to results of pre-experiment tests) take longer times and make more errors that older users with normal or high dexterity (Jin et al., 2007; Nicolau and Jorge, 2012).
Concerning the physical constraints, Geronimi and Gorce (2009) have demonstrated that the properties of the objects and obstacles influenced particularly the movements of older adults, with increased time of movement, range of motion and variability among users (Geronimi and Gorce, 2007). In regard to interaction with touchscreen devices, the properties of the devices (e.g., screen size, orientation), the
parameters of tactile interactive systems (e.g., targets sizes) and the input modalities (e.g., pen, finger, multi-touch interaction) can be considered as physical constraints to the movements of the users. As discussed in section II.3.1.2 (p.51) and II.3.1.4 (p.59), the different situations of use of tactile interaction affect interaction performances. Indeed, the situations of use influence planning and execution of movements of the user during interaction.
Moreover, the high level constraints for the execution of movements of interaction would refer to the experience of the user using interactive technologies, executing the gesture of interaction or using the interactive system. The results presented and discussed by Darling et al. (1989) demonstrate that practice reduced the variability of movement trajectories of older subjects; this result showed that the ability of learning and improving performances in motor task is not affected by aging (Darling et al., 1989). Concerning tactile interaction, it has also been demonstrated that older users get better times and stabilization after executing several trials (about 20) of tapping tasks (Vetter et al., 2011).
A week period for experiencing and executing gestures of interaction on touchscreen helped older users to enhance their interaction performances (Kobayashi et al., 2011).
In the next section, we review of the literature on studies about the movements of the users during interaction with touchscreen. Through the analysis of the characteristics of the populations studied, the situations of use of touchscreen evaluated on the studies reviewed and the tasks that were executed, we try to identify which sensorimotor, physical and high level constraints could influence the movements of the users during interaction with touchscreen devices.