Christine Sutter

BendDesk: dragging across the curve

We present BendDesk, a hybrid interactive desk system that combines a horizontal and a vertical interactive surface via a curve. The system provides seamless touch input across its entire area. We explain scalable algorithms that provide graphical output and multi-touch input on a curved surface. In three tasks we investigate the performance of dragging gestures across the curve, as well as the virtual aiming at targets. Our main findings are: 1) Dragging across a curve is significantly slower than on flat surfaces. 2) The smaller the entrance angle when dragging across the curve, the longer the average trajectory and the higher the variance of trajectories across users. 3) The curved shape of the system impairs virtual aiming at targets.

Notebook input devices put to the age test: the usability of trackpoint and touchpad for middle-aged adults.

In two experiments, the usability of input devices integrated into computer notebooks was under study. The most common input devices, touchpad (experiment 1) and trackpoint (experiment 2) were examined. So far, the evaluation of mobile input devices has been restricted to younger users. However, due to ongoing demographic change, the main target group of mobile devices will be older users. Therefore, the present study focused on ageing effects. A total of 14 middle-aged (40–65 years) and 20 younger (20–32 years) users were compared regarding speed and accuracy of cursor control in a point-click and a point-drag-drop task. Moreover, the effects of training were addressed by examining the performance increase over time. In total, 640 trials per task and input device were executed. The results show that ageing is a central factor to be considered in input device design. Middle-aged users were significantly slower than younger users when executing the different tasks. Over time, a significant training effect was observed for both devices and both age groups, although the benefit of training was greater for the middle-aged group. Generally, the touchpad performance was higher than the trackpoint performance in both age groups, but the age-related performance decrements were less distinct when using the touchpad.

Considerations on efficient touch interfaces: how display size influences the performance in an applied pointing task

The limited screen space in small technical devices imposes considerable usability challenges. On the one hand objects displayed on small screens should be big enough to be hit successfully, but also small enough to house several objects on the screen at the same time. However, findings up to now show that single pointing is more effective in a large display compared to a smaller display. In the present experiment this was also confirmed for an applied multidirectional serial pointing task. Especially in more difficult tasks, results point at a shift of the speed-accuracy tradeoff. In large displays a fast and comparably accurate execution is chosen in contrast to a very inaccurate and time-consuming style in small displays. From an ergonomic point of view the outcomes recommend an optimized balance of task difficulty and display size in small screen devices.

Sensumotor transformation of input devices and the impact on practice and task difficulty

In the present study, the usability of two laptop input devices, touchpad and trackpoint, is evaluated. The focus is set on the impact of sensumotor transformation of input devices on practice and task difficulty. Thirty novices and 14 experts operated either touchpad or trackpoint over a period of 1600 trials of a point-click task. As hypothesized, novices and experts operated the touchpad by 15% faster compared to the trackpoint. For novices, performance rose distinctly and levelled off after 960 trials. This consolidation occurred earlier than reported in literature (1400–1600 trials) and, contrary to the assumption, learning was similar for touchpad and trackpoint. The impact of task difficulty dropped remarkably by practice, which points at a more general than specific task learning. In conclusion, ergonomic guidelines can be derived for the user-specific optimization of the usage of touchpad and trackpoint. Actual and potential applications of this research include the user-specific optimization of laptop input devices. Within the theoretical framework of psychomotor models, a profound knowledge of user behaviour in human – computer interaction is provided. Ergonomic guidelines can be derived for the efficient usage of laptop input devices and an optimized hardware and software design.

Interacting with notebook input devices: an analysis of motor performance and users' expertise.

In the present study the usability of two different types of notebook input devices was examined. The independent variables were input device (touchpad vs. minijoystick) and user expertise (expert vs. novice state). There were 30 participants, of whom 15 were touchpad experts and the other 15 were mini-joystick experts. The experimental tasks were a point-click task (Experiment 1) and a point-drag-drop task (Experiment 2). Dependent variables were the time and accuracy of cursor control. To assess carryover effects, we had the participants complete both experiments, using not only the input device for which they were experts but also the device for which they were novices. Results showed the touchpad performance to be clearly superior to mini-joystick performance. Overall, experts showed better performance than did novices. The significant interaction of input device and expertise showed that the use of an unknown device is difficult, but only for touchpad experts, who were remarkably slower and less accurate when using a mini-joystick. Actual and potential applications of this research include an evaluation of current notebook input devices. The outcomes allow ergonomic guidelines to be derived for optimized usage and design of the mini-joystick and touchpad devices.

Action control while seeing mirror images of one's own movements: Effects of perspective on spatial compatibility

It is examined whether and how the perspective of seeing ones own movements exerted an influence on action control. Such change in the perspective challenges an information processor, as she or he has to handle successfully the discrepancies between the tactile/proprioceptive feedback and the visual feedback on a projection screen. In the experiments participants responded to visual stimuli, but saw their responses either from the top or with an x-axis reflection, a y-axis reflection, or a reflection about both axes. The results showed that a change in perspective did not impair performance as long as the left–right relations corresponded with the body space (e.g., with visual feedback reflected about the x-axis). By contrast, performance was drastically reduced when visual feedback was reflected about the y-axis or about both axes, so that performed left-side (right-side) movements were seen as right-side (left-side) movements. It is concluded that an actor preferably relies on the information of the visual system, but refers to the tactile/proprioceptive information when it facilitates the task demands.

Intra- and intermodal integration of discrepant visual and proprioceptive action effects

Integration of discrepant visual and proprioceptive action effects puts high demands on the human information processing system. The present study aimed to examine the integration mechanisms for the motor (Exp. 1) and visual modality (Exp. 2). According to theories of common coding, we assumed that visual as well as proprioceptive information is represented within the same cognitive domain and is therefore likely to affect each other (multisensory cross talk). Thus, apart from the often-confirmed visual dominance in multisensory integration, we asked about intra- and intermodal recall of either proprioceptive or visual information and whether there were any differences between the motor and visual modality. In a replication paradigm, we perturbed the relation between hand movements and cursor movements. The task required the (intra- vs. intermodal) replication of an initially performed (seen) hand (cursor) movement in a subsequent motor (visual) replication phase. First, mechanisms of integration were found to be dependent on the output modality. Visual action effects interfered the motor modality, but proprioceptive action effects did not have any effects on the visual modality. Second, however, intermodal integration was more susceptible to interference, and this was found to be independent from the output modality. Third, for the motor modality, the locus of perturbation (perturbation of cursor amplitude or perturbation of hand amplitude) was irrelevant, but for the visual modality, perturbation of hand amplitudes reduced the cross talk. Tool use is one field of application of these kinds of results, since the optimized integration of conflicting action effects is a precondition for using tools successfully.

Age Effects on Controlling Tools with Sensorimotor Transformations

Controlling tools in technical environments bears a lot of challenges for the human information processing system, as locations of tool manipulation and effect appearance are spatially separated, and distal action effects are often not generated in a 1:1 manner. In this study we investigated the susceptibility of older adults to distal action effects. Younger and older participants performed a Fitts’ task on a digitizer tablet without seeing their hand and the tablet directly. Visual feedback was presented on a display in that way, that cursor amplitude and visual target size varied while the pre-determined hand amplitude remained constant. In accordance with distal action effects being predominant in controlling tool actions we found an increase in hand movement times and perceptual errors as a function of visual task characteristics. Middle-aged adults more intensely relied on visual feedback than younger adults. Age-related differences in speed-accuracy trade-off are not likely to account for this finding. However, it is well known that proprioceptive acuity declines with age. This might be one reason for middle-aged adults to stronger rely on the visual information instead of the proprioceptive information. Consequently, design and application of tools for elderly should account for this.

Understanding flicking on curved surfaces

Flicking is a common interaction technique to move objects across large interactive surfaces, but little is known about its suitability for use on non-planar, curved surfaces. Flicking consists of two stages: First, visually determining the direction in which to flick the object, then planning and executing the corresponding gesture. Errors in both stages could influence flicking accuracy. We investigated flicking interactions on curved interactive surface to evaluate which type of error influences accuracy. Therefore, we carried out three user studies to analyze how each stage of flicking on a curved surface is influenced. Our main findings are: 1) Flicking gestures are more accurate if horizontal and vertical surface are joined by a continuous curve than if they are separated by an edge or gap. 2) Flicking gestures on curved surfaces are mostly influenced by the motor execution stage of the gesture rather than the visual perception stage. 3) Flicking accuracy decreases as the starting point of the gesture is moved closer to the curve. 4) We conclude with a first mathematical model to estimate the error users will make when flicking across a curve.

Mirrored visual feedback limits distal effect anticipation

Modern tools in technological environments are often characterized by a spatial separation of hand actions (operating a remote control) and their intended action effects (displayed movements of an unmanned vehicle, a robot, or an avatar on a screen). Often non-corresponding proximal and distal movement effects put high demands on the human information processing system. The present study aimed to investigate how modern technological environments influence processes of planning and controlling actions. Participants performed ipsi- or contralateral movements in response to colored stimuli, while the stimulus location had to be ignored. They did not see the stimuli and hands directly, but received visual feedback (with retained or reversed spatial relations) on a projection screen in front of them. Visual feedback retaining spatial relations led to the usual Simon effect. However, visual feedback reversing spatial relations inverted the Simon effect in ipsilateral responses, and eliminated it in contralateral responses (Exp. 1). Impairing the proximal movement-effect loop so that proprioceptive/tactile information from the moving hand was no longer a reliable source for planning and controlling actions attenuated compatibility effects (Exp. 2). Moreover, distal action effects predominated action control even for opposing body-related effects. It seemed that action control of transformed movements depended on the reliability of proprioceptive/tactile and visual information. When the amount of feature overlap between proprioception and vision was low and proprioceptive (visual) information was no longer reliable, then distal (proximal) action effects stepped forward and became crucial in controlling transformed actions.