Sachi Mizobuchi

Tapping vs. circling selections on pen-based devices: evidence for different performance-shaping factors

Tapping-based selection methods for handheld devices may need to be supplemented with other approaches as increasingly complex tasks are carried out using those devices. Circling selection methods (such as the Lasso) allow users to select objects on a touch screen by circling with a pen. An experimental comparison of the selection time and accuracy between a circling method and a traditional tapping style of selection was carried out. The experiment used a two dimensional grid (varying in terms of the sizes and the distances of the targets). Analysis of variance showed that tapping selection time differed significantly depending on the size and spacing of the targets. In contrast, circling selection times differed significantly for different levels of target cohesiveness and shape complexity. The results are discussed in terms of implications for design of new pen-based selection methods for handheld devices, and also in terms of evaluation methodology for input selection methods.

The effect of stereoscopic viewing in a word-search task with a layered background

— The benefits of stereoscopic viewing were explored in searching in words superimposed over a background. In the first experiment, eight participants searched for text in a normal 2-D display, a 3-D display using a parallax barrier, and a darkened 2-D display of equivalent brightness to the 3-D display. Word-search performance was significantly faster for the bright 2-D display vs. the 3-D display, but when brightness was controlled, performance on the 3-D display was better relative to the 2-D (dim) display. In a second experiment, the effect of floating text vs. sinking background disparity was assessed across four background conditions. Twenty participants saw only the floating-text (FT) condition and 20 participants saw only the sinking-background (SB) condition. Performance of the SB group was significantly better than that of FT group, and the advantage of SB disparity was greater with the more-complex backgrounds. Thus, when a parallax-barrier 3-D display is used to view text or other figural information overlaid on a background, it is proposed that the layer of primary interest (foreground) should be displayed with zero disparity (on the physical display surface) with the secondary layer (background) appearing to be sunk beneath that surface.

Central executive functions likely mediate the impact of device operation when driving

We measured multitasking performance across a range of device interfaces and investigated the relationship between task performance and three measures of cognitive capacity (assessing the executive processes of shifting, inhibition, and updating, respectively). In the first experiment, higher levels of ability on the three executive processes of shifting, updating and inhibition were associated with improved multitasking performance. However, the impact of cognitive demands was reduced when touch input and combined visual and audio output was used in the device interaction task. When a simulated driving task was added in the second experiment, the impact of cognitive demands increased, and the use of combined audio and video output no longer reduced the impact of Central Executive (CE) function ability on performance. While inhibition, updating, and shifting all seemed to be involved when carrying out the device operation during simulated driving, the effects of shifting and updating ability were greater than the effect of inhibition. Detailed analysis of the data indicated that the impact of cognitive demand when using a device in a dual task setting was restricted to people with low levels of shifting, updating, and inhibition ability. It is suggested that future research on the impact of in-vehicle technology focus on drivers with low levels of ability on or more of a range of cognitive factors, including the CE functions of shifting, updating, and inhibition. Based on the present results it seems likely that less cognitively able drivers will be put at most risk by inappropriate or poorly designed device tasks and interfaces.

Combining Speed and Accuracy into a Global Measure of Performance

Response time and accuracy are two of the most frequently collected dependent measures. Tradeoffs between speed and accuracy are often observed, both between people, and between experimental conditions. In this paper we consider how speed, and accuracy, can be combined into a single, overall measure of performance. We consider two different approaches that adjust accuracy scores based on observed speed of responding and we examine how well those measures work with different data sets. We then present a third approach that combines standardized speed and accuracy scores. We show how this latter approach can represent the data fairly well regardless of which (if any) speed-accuracy tradeoff occurs in the data. We also show how this measure can be further generalized by applying differential weightings to the standardized scores of speed, and accuracy, respectively. We conclude by discussing the value of the measure for use in analyzing human performance data where continuous indicators of accuracy or error can be collected or constructed relatively easily. Our goal in developing the global measure of performance is not to accurately model the speed-accuracy relationship, but rather to create a measure that is more sensitive to experimental differences and causal relationships than either speed or accuracy alone.

Looking or Listening? Impacts of Secondary Task Timing and Difficulty on Tracking Performance and Modality Selection

We conducted an experiment with 22 participants to investigate the effect of presentation style of a secondary task on a 1-D tracking task that simulated gap control in driving. Participants operated the tracking task with a foot pedal while performing a secondary task (counting vowels in a list of multiple letters) under conditions involving different modalities (audio/ visual), presentation styles (simultaneous/ sequential), task complexity (the number of distractors), and time dependency (list length). Our results showed that audio conditions with a longer and/or more complex secondary task did not improve primary (tracking) task performance, even though eye gaze dwelling time on the primary monitor in these cases tended to be substantially longer than the corresponding times in visual conditions. For a more complex version of the secondary task (longer list lengths) visual presentation of the task all at once (simultaneously) led to better performance then sequential presentation (whether visual or auditory). When given a choice people also tended to prefer simultaneous visual presentation of the secondary task. We discuss the effect of presentation modality of the secondary task in terms of its implications for user interface design in vehicles.

Sensitivity of a Voluntary Interruption of Occlusion Measure to Cognitive Distraction During a Pedal Tracking Task

We conducted an experiment with 16 participants to investigate the effect of cognitive distraction on performance of a 1-D tracking task that simulated gap control in driving. Participants operated the tracking task with a foot pedal while performing a secondary task (an auditorily presented N-back task) under eight conditions involving all possible (2x2x2) combinations of degree of secondary task difficulty (1-back vs. 2-back), pedal tracking difficulty (hard vs. easy amounts of lag) and presence vs. absence of visual occlusion. In conditions involving occlusion participants could press a button to get rid of the occlusion for a short period of time, i.e., they used Voluntary Interruption of Occlusion (VIO). Our results showed that use of VIO is associated with updating ability and that it trades off against pedal tracking performance. We also found evidence that cognitive distraction due to the impact of updating requirements in the secondary N-Back task affects performance on the primary, pedal tracking, task.