Target Expansion Lens: It is Not the More Visual Feedback the Better!

International audienceTo enhance pointing tasks, target expansion techniques allocate larger activation areas to targets. We distinguish two basic elements of a target expansion technique: the expansion algorithm and the visual aid on the effective expanded targets. We present a systematic analysis of the relevance of the visual aid provided by (1) existing target expansion techniques and (2) Expansion Lens. The latter is a new continuous technique for acquiring targets. Expansion Lens namely, uses a round area centered on the cursor: the lens. The users can see in the lens the target expanded area boundaries that the lens is hovering over. Expansion Lens serves as a magic lens revealing the underlying expansion algorithm. The design rationale of Expansion Lens is based on a systematic analysis of the relevance of the visual aid according to the three goal-oriented phases of a pointing task namely the starting, transfer and validation phases. Expansion Lens optimizes (1) the transfer phase by providing a simple-shaped visual aid centered on the cursor, and (2) the validation phase regarding error rates, by displaying the target expanded area boundaries. The results of our controlled experiment comparing Expansion Lens with four existing target expansion techniques show that Expansion Lens highlights a good trade-off for performance by being the less-error prone technique and the second fastest technique. The experimental data for each phase of the pointing task also confirm our design approach based on the relevance of the visual aid according to the phase of the pointing task