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DOI: 10.1145/1993060.1993063

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ACM Transactions on Computer-Human Interaction 18, 3 (2011) 13:1--13:32

Effects of Motor Scale, Visual Scale and Quantization on Small Target Acquisition Difficulty

Olivier Chapuis 1, 2, Pierre Dragicevic 3

(2011-07)

Targets of only a few pixels are notoriously difficult to acquire. Despite many attempts at facilitating pointing, the reasons for this difficulty are poorly understood. We confirm a strong departure from Fitts' Law for small target acquisition using a mouse and investigate three potential sources of problems: motor accuracy, legibility, and quantization. We find that quantization is not a problem, but both motor and visual sizes are limiting factors. This suggests that small targets should be magnified in both motor and visual space to facilitate pointing. Since performance degrades exponentially as targets get very small, we further advocate the exploration of uniform, target-agnostic magnification strategies. We also confirm Welford's 1969 proposal that motor inaccuracy can be modeled by subtracting a ''tremor constant'' from target size. We argue for the adoption of this model, rather than Fitts' law, when reflecting on small target acquisition.

1:	IN-SITU (INRIA Saclay - Ile de France)
	INRIA – CNRS : UMR8623 – Université Paris XI - Paris Sud
2:	Laboratoire de Recherche en Informatique (LRI)
	CNRS : UMR8623 – Université Paris XI - Paris Sud
3:	AVIZ (INRIA Saclay - Ile de France)
	INRIA

Subject

:

Computer Science/Human-Computer Interaction

Keyword(s): Fitts' Law – small targets – quantization – C-D gain – pointing techniques – target-agnostic

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From: Olivier Chapuis <>

Submitted on: Tuesday, 9 August 2011 08:33:00

Updated on: Tuesday, 9 August 2011 14:48:40