The paper challenges the notion that any Fitts' Law model can be applied generally to human-computer interaction, and proposes instead that applying Fitts' Law requires knowledge of the users' sequence of movements, direction of movement, and typical movement amplitudes as well as target sizes. Two experiments examined a text selection task with sequences of controlled movements (point-click and point-drag). For the point-click sequence, a Fitt's Law model that used the diagonal across the text object in the direction of pointing (rather than the horizontal extent of the text object) as the target size provided the best fit for the pointing time data, whereas for the point-drag sequence, a Fitts' Law model that used the vertical size of the text object as the target size gave the best fit. Dragging times were fitted well by Fitts' Law models that used either the vertical or horizontal size of the terminal character in the text object. Additional results of note were that pointing in the point-click sequence was consistently faster than in the point-drag sequence, and that pointing in either sequence was consistently faster than dragging. The discussion centres around the need to define task characteristics before applying Fitts' Law to an interface design or analysis, analyses of pointing and of dragging, and implications for interface design.

Two experiments examined selecting text using a movement sequence of pointing and dragging. Experiment 1 showed that, in the Point-Drag sequence, the pointing time was related to the pointing distance but not to the width of the text to be selected; in contrast, pointing time was related to both the pointing distance and the width of the text in the Point-Click sequence. Experiment 2 demonstrated that both the pointing and dragging times for the Point-Drag sequence were sensitive to the height of the text that was selected. The discussion of the results centers around the application of Fitts' Law to pointing and dragging in a point-drag sequence, proposing that the target for pointing is the leftmost edge of the text to be selected, and the target for dragging is the rightmost edge of the text.

Three models of human interactions with computer-displayed statistical graphics were developed and tested in an experiment which examined users' speed and accuracy on identification and comparison questions using 17 graph types. The results indicated that response time and accuracy were influenced by the perceptual and informational complexity of the graph, as well as the relation between the figure and axes, (Model 1); by the physical elements of the graph — points, lines, and areas (Model 2); and by the data-ink ratio and data density (Model 3). The discussion focuses on the development of a single integrated model of interactions with graphics.

No abstract available.

NASA Space Station missions will include crewmembers who are highly experienced in the use of the Space Station computer system, as well as others who are novices. Previous research into novice-expert differences has strongly implied that user interface changes that aid novices tend to impair experts and vice versa. This experiment investigated the impact reformatting alphanumeric information on current Space Shuttle computer displays had on the speed and accuracy of experts and nonexperts in two different search tasks. Large improvements in speed and accuracy were found for nonexperts on the reformatted displays. Experts had fewer errors but no response time difference on the reformatted displays. Differences in expert and nonexpert search strategies and implications for the design of computer displays are discussed.