A Finger-Mounted, Direct Pointing Device for Mobile Computing John L. Sibert Mehmet Gokturk
The George Washington University Washington D.C. 20052, USA Tel: l-202-994-4953 E-mail:
[email protected] [email protected]
ABSTRACT
PHYSIOLOGICAL
The index (first) finger of the dominant hand seems to be an intuitively natural and efficient means for pointing tasks. This paper presents the design of a device to enable pointing with the index finger as an interaction technique in mobile computers. The device, which uses infrared emission and detection to determine where on a screen the finger is pointing, is inexpensive and can easily be incorporated into a laptop computer.
Pointing with index finger extended is not only an intuitive behavior, it is also a behavior that humans can perform with a high degree of facility. A relatively large proportion of the primary motor cortex is dedicated to controlling the fingers and the neural connection path from the cortex to the finger muscles is relatively direct [4] yielding a high degree of fine motor control.
KEY W 0 R DS : Pointing,
Interaction
devices,
If you take a moment to point at a few objects in the surrounding environment you will note that your intuitive pointing motion is to extend your index finger in the direction of the target object. If you assume your hand is positioned on the keyboard of a laptop and point only with the index finger you will note that the range of motion is more than sufficient to cover the area of a typical laptop screen. This is an additional advantage of pointing with the finger: since you don’t have to take your hand off the keyboard you avoid the problem of alternating device acquisition.
Input
devices, Infrared detection. INTRODUCTION
Pointing with the index finger seems to be a fundamental means of communication among humans. Studies have shown [2] that infants as young as two months will extend the index finger as a means of indicating a desire for attention. By twelve months, infants show facility for both responding to the directional gaze of their mothers by pointing in the direction of the gaze and pointing at an object in order to direct their mothers’ gaze towards it.
To benefit from these physiological advantages, you must be pointing at the target directly with the finger itself, not using one or more fingers indirectly to control a cursor through a device such as a mouse or trackball.
It is interesting that most pointing devices used with computers (mice, styli, trackballs, joysticks etc.) have little or nothing in common with natural pointing. Notable exceptions are [l] which exploited natural pointing with the entire hand arm system and, more recently the FingerMouse [3] which uses video and image processing to determine both the direction the finger is pointing and the configuration of the hand.
DESIGN
97 I3clnfl.4lbertn,
FOR MOBILE
COMPUTING
Mobile computing introduces constraints on input devices that are not present in a workstation environment. Input devices cannot be too large or expensive and they must be contained within the mobile unit (e.g. laptop) or easily attached to it. The input devices most frequently available with laptop computers, trackballs, scratchpads, and isometric joysticks, satisfy these constraints but are used in a relatively difficult indirect control method which most users find less than fully satisfactory. This is why so many users plug a mouse into their laptops whenever possible.
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BASIS
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Copyright 1997 ACM 0-89791~881-9/97/lO..S3.50
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low power consumption and sleep features to make mobile applications more feasible. The total retail cost of the components,. not including the laptop, was under $100, Industrial production quantities would bring the cost down, perhaps by an order of magnitude, and make packaging of the ‘cirbit to PCMCIA size feasible. Another possibility is to en&$+ the circuit during the laptop production stage,
Using the finger directly as described,above should be a more intuitive and efficient control method if it can be made technically feasible. Current approaches to finger pointing as an input technique (e.g. the FingerMouse[3] which should not be confused with the RingMouse, a commercially available device that is not a direct pointing device) depend on video image processing implying tlie need for video cameras and relatively expensive processing algorithms for shape detection etc. This i$ clearly too expensive and cumbersome for mobile computers. Our solution is based on a wearable infrared emitter combined with infrared detectors situated surrounding the computer screen. We have built a prototype of such a device. PROTOTYPE
Dl%IICE
PERFORMANCE
Ou:initial prototype exhibited some sensitivity to ambient light. V?e solved this problem by introducing a 38 KHz oscill$td~ii~nto both the emitter and sensor circuits. Accuracy for precise cursor positioning at high screcq resolutions suffers from the 8 bit resolution of the A/D converter we used. A 12 bit resolution version is available at a slightly higher cost for more accurate results at higher resolutions.
IMPLEMENTATION
The prototype device consists of microcontroller driven A/D converter circiiitryj infrared sigritil detectors, arid an infrared’signal emittbr. The eniitter is attached to a ring worn on the index finger and ii’ designed- to minimize impact dn typing perfotiance. Signtils from &emitter are received by sensors placed,at the’comers of the notebook display, converted into an&g’\;alues and sent to ‘the ’ microcontroller. Figure 1 illustrates’ this laybut.
Inifial’htt&mpts to use our prototype are promising. We arc able td contidl’tbe curtor with no noticeable delay or other perforii&ce,degrada’tion df the laitop. We have been able to I& it dffec’tively for normal GUI interactions such as menu selections. At the time of this writing, we are planning user studies with our prototype: comparing it with a variety of pointing devices. We expect to report the results of these studies in the near future. ACKNOWLEDGMENTS
The,aqthp;s, yo$ like-Jo acknowledge financial support from the School of,Engineering and Applied Science at GWF. L,we $qe also most grateful for the intellectual support and thoughffpl suggestions of our colleagues in the HCI research youp. L ,‘, ,; REFERENCE& iJ
Figure 1: prototype.
’
’
”
1.
Bolt, R., Put-That-There: Voice and Gesture at the Graphics Interface, Proceedings of SIGGRAPH ‘80, Computer Graphics, l!(3), 1980, pp. 262-270 / i ~” I! 2. Btitierworth, G. dnd Grover, L. Joint Visual Attention, + Manila1 ‘Pointing,, and Pr’everbal Cdmmunication in Hliman Infanc):*In Jeannerod M. (ed.) Attention and Perfbrmance XIII. Lawrence Erlbaum ASSOC., cHillsdale, New Jersey, 1990 8 i
Physical laydut &ketch’ of the laptop _ ’ ,, ‘:
The microcontroller preprocesses the’data and sends it to the host computer via a serial line in a, simple asynchronousY format, recognizable by any computer supporting an: RS232 serial i/o port at I 19.2 Kbaud. Device driver software maps the data to the ‘corresponding cursor coordinate values and controls the system cursor. The amplitude of the infrared light received at each of the four sensors, following Lambert’s cosine law, is approximatdy proportional to the cosine of the angle between the direction the emitter is pointing and the direction ihe sensoi’ is pointing. This gives us the proportional distance from each of the four corners of the “pointed at” point. Computation of the point’s Cartesian coordinates is then’ straightforward.
3.
Queck, F. Unencumbered Gestural Interaction. I.E.E.E, MultiMedia, 3(4), Winter 1996, ~~36-47
4.
Rosenzweig,
I,
M.,, Leiman, ‘A. and Breedlove
S,
Biological Psychology. Sinauer Assoc., Sunderland,
Massachusetts, 1996.
We chose an industry standard microcontroller with very
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