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Gijs Bloemsaat
11-12-2002, 07:36 PM
Dear BIOMCH-Ls,

Maybe because I posted my question on 'Veterans-day' , until now I have
received only one reaction. I will give it a second try with extra
information added.


I have a question concerning the friction of a pen on a digitizer tablet
(Calcomp 9000). In an experiment where subjects had to make a precise
single fast movement
from one point to the other, axial pen pressure and velocity were measured.
A secondary, cognitive load, condition was included. Motor preparation and
motor performance of 2 groups
were investigated.

We measured the development of mean axial pen pressure during 3 phases:
holding the pen still on the tablet (P1) - reaction (P2) - actual movement (P3)
The first number between the parenthesis is the condition without cognitive
load, the 2nd number is the condition with load

GRP1: P1(117;131) / P2(129;149) / P3(142;158)
GRP2: P1(118;113) / P2(139;134) / P3(183;199)


Both groups reacted in 'P3' on the cognitive load with a +- 15 gram raise.
However,
GRP1 raised pen pressure from 142 to 158 grams, GRP2 from 183 to 199
gram.
Both groups performed the task at comparable speed. RTs were higher in GRP2


My question: Is the force increase needed to move the pen along the
trajectory equal for both groups? My hunch is (but that is not scientific)
that GRP2 will need disproportionate more force input -1- because of
the tablets' elastic properties, the tablet will spring back and the pen
point is pressed more into the tablet, thus more friction and -2- the
springing back curve and friction curve are not linear.
Do I need to consider more mechanisms to shed more light on the issue?

I will, of course, post a summary of responses.


Thanks,


Gijs Bloemsaat




__________________________________________________ _________
Gijs Bloemsaat
Nijmegen Institute for Cognition and Information
University of Nijmegen - Dept. of Experimental Psychology
Room B.01.02
P.O. Box 9104, 6500 HE Nijmegen, The Netherlands
Voice +31 (0)24 3612758 Fax +31 (0)24 3616066
E-mail bloemsaat@nici.kun.nl
__________________________________________________ __________

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