Insight into Goal-Directed Movements: Beyond Fitts’ Law

Abstract

Abstract. Various methods and measures have been developed to assess the quality of input devices and interaction techniques. One approach to investigating the performance of input devices and interaction techniques is to focus on the quality of the produced movements. The current paper proposes a new method of analyzing goal-directed movements by dividing them into meaningful phases. In addition to the proposed analysis method a selection of measures is suggested to assess different aspects of rapidly aimed movements. In order to evaluate the added value of the proposed analysis method an experiment has been conducted to compare two input devices (mouse versus stylus with tablet) with respect to their performance on a multi-directional pointing task. The results show that the analysis into several phases reveals clear differences in the movement strategy.

Insights from Dividing 3D Goal-Directed Movements into Meaningful Phases

“…This was confirmed in a study investigating 2D goal-directed movements carried out with a mouse and a stylus with a tablet. 10 This study demonstrated that the five phases' duration and other measures applied to the ballistic and correction phases can indeed provide more information about the movement strategies people use when interacting through different input devices.…”

“…From this assumption and our study of many velocity profiles, we concluded that we could robustly distinguish five phases: latency, initiation, ballistic, correction, and verification (see Figure 1). 10 The latency phase starts when the task is set and ends when the actual movement starts. The initiation phase consists of small movements made before the ballistic phase.…”

Assessing Goal-Directed Three-Dimensional Movements in a Virtual Reality Block Design Task

“…This contention is supported by [1], who described Fitts' Law as a gross measure (one outcome per test), not providing detail on the movement during a trial. For this reason, other research [9] had identified a need to develop additional measures that account for variations in goal-directed movements as a function of time.…”

“…While there has been extensive research describing target acquisition movements, the tasks selected for these studies have primarily been repeated trials of artificial point-to-point target acquisition tasks [9,19]. Alternatively, existing psychomotor tasks, including the Purdue Pegboard Test [20], the Minnesota Manual Dexterity Test [21] and the Block Design (BD) test [22] feature a target acquisition component, but also have been validated for use in applied settings such as physical therapy, occupational therapy, vocational evaluation and employment screening [21].…”

“…Objective studies of human movement generally follow two general approaches [9]. One approach is to evaluate overall movement characteristics through general measures such as total task time or difficulty.…”