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A conceptual framework for the use of Fitts’ Law to
detect Intentional Misrepresentation of Skills and/or
Abilities (IM) in Paralympic athletics
Rebecca L Deuble, Mark J Connick, Emma M Beckman, Bruce Abernethy, Sean M Tweedy
The University of Queensland, School of Human Movement Studies, QLD 4072, Australia
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“In athletics there's always been a willingness to cheat if it looks like you're not cheating. I think that's just a quirk of human nature” Kareem Abdul-
Jabbar
Introduction
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Introduction – Classification
and IM in Paralympic Sport
• Purpose of classification in Paralympic sport is to minimise the impact of impairment on the outcome of competition
• Paralympic Athletics and focused on 5 impairment
types
- Impaired Strength
- Impaired Range of Movement
- Ataxia
- Hypertonia
- Athetosis
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Introduction - subjective vs.
objective tests of Impairment
• Currently use subjective tests rely on clinical judgement
• Measure of impaired coordination: Finger to Nose Test
• IPC mandated development of evidence-based methods of classification
• Objective tests are required which are valid and reliable, so we can look at the relationship between impairment and performance
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Objective Test of Impaired
Coordination
• Upper Limb Reciprocal Tapping Task
• Objective – measures movement time
• Maximal speed = a valid classification system
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Overview of Problem: Intentional
Misrepresentation of Skills and/or
Abilities (IM)
“Form of cheating in which athletes attempt to exaggerate impairment severity by not fully cooperating on impairment tests” (IPC, 2007)
• Severe punishments are available but not enforced
• Currently no objective tests of impairment to facilitate detection
Research Aim: To develop and evaluate objective methods which can distinguish maximal test results from submaximal
• Closely linked with developed tests of impairment
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Fitts’ Law
• Describes established log-linear relationship between movement time and index of difficulty: ID = log2 (2A/W)
Where A = amplitude and W = target width (Fitts, 1954)
Amplitude
Target width
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Fitts’ Law Relationship
Under maximal effort conditions – “as fast and as accurately as possible” )
Fitts Original Study (1954) – Results from Reciprocal Tapping Task (n = 16)
R² = 0.9897
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 1 2 3 4 5 6 7 8
Mo
vem
en
t ti
me (
s)
Index of difficulty (ID)
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Fitts Law Literature –
Submaximal Effort Maruff and Velakoulis (2000)
Individuals who feigned an arm injury during visually guided pointing task were unable to conform to Fitts law.
(*p < 0.01)
Note: individuals in this study were completely naive to purpose of study and had not completed task previously
Feigning an injury
(n =10)
Controls (n =10)
Linear Regression 0.10 0.67**
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Equivalent IDs with
different configurations
Amplitude = 606mmWidth = 100mm ID = 3.6
Amplitude = 304mm Width = 50mm ID = 3.6
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Fitts’ Law Relationship
Under maximal effort conditions – “as fast and as accurately as possible” )
Fitts Original Study (1954) – Results from Reciprocal Tapping Task (n= 16)
R² = 0.9897
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 1 2 3 4 5 6 7 8
Mo
vem
en
t ti
me (
s)
Index of difficulty (ID)
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Fitts’ Law literature –
Submaximal Effort Young et al. 2009
Significant differences in movement times for four different configurations of same ID (equivalent difficulty) were achieved by healthy individuals moving at submaximal speeds (n = 12)
R² = 0.5044
R² = 0.9367
0
0.5
1
1.5
2
2.5
0 1 2 3 4 5 6 7
Mo
vem
en
t ti
me (
s)
Index of difficulty (ID)
NaturalMovement
Fastmovement
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Experiment 1: Using Fitts’ law to Detect
Intentional Misrepresentation of Skills and/or
Abilities in a Reciprocal Tapping Task
The primary aim of this study is to: 1) Determine whether participants can intentionally move at submaximal speeds and produce a relationship between movement time and ID which conforms to Fitts’ law- Strength of association- Difference in movement times for IDs that are the same difficulty but
differently configured
Participants: 30 non-disabled participants aged between 18-35
Methods: Reciprocal tapping task performed with dominant hand across 7 IDs (4 of the 7 were identical in difficulty but configured differently)
• Task performed on 3 separate occasions
• Maximal and Cheating Conditions
• Monetary reward: $100, $50, $25 awarded to three participants who are best able to conform to Fitts’ law while moving at slower speeds
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Results – cheating example
R² = 0.0089
0
0.1
0.2
0.3
0.4
0.5
0.6
0 1 2 3 4 5
Mo
vem
en
t ti
me (
s)
Index of difficulty (ID)
Cheating attempt example
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Preliminary Results
** *
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Visit 1 Visit 2 Visit 3
Lin
eari
ty (
R2
valu
e)
Visit number
maximal effort
cheating
Figure 1: Average R2 (+ SD) achieved for both maximal and cheating
efforts (n = 10) for each of the three visits. (* indicates p <0.05)
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Potential criteria for
identifying IM
R² = 0.0089
0
0.1
0.2
0.3
0.4
0.5
0.6
0 1 2 3 4 5
Mo
vem
en
t ti
me (
s)
Index of difficulty (ID)
Cheating attempt example
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Preliminary Results
* *
0.000
0.050
0.100
0.150
0.200
0.250
0.300
0.350
Visit 1 Visit 2 Visit 3
Dif
fere
nce in
mo
vem
en
t ti
mes (
s)
Visit number
maximal effort
cheating
Figure 2: Mean Differences (+ SD) between the fastest and the
slowest movement times for IDs 3.6 (a, b, c, d), for both maximal
and cheating efforts. (n= 10) (* p<0.05)
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Future Analysis
• Results from preliminary group level analysis highlight Fitts’ law’s potential to differentiate between maximal and cheating efforts
• Receiver Operating Characteristic (ROC) curve analysis will confirm sensitivity and specificity of method – individual analysis (if want to differentiate at individual level)
• Stability of measure over time
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Thanks you!
Questions and comments?
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References
Fitts PM. The information capacity of the human motor system in controlling the amplitude of movement. J Exp Psychol 1954 Jun; 47 (6): 381-91
International Paralympic Committee. International Paralympic Committee Classification Code and International Standards. Bonn International Paralympic Committee 2007
Maruff P, Velakoulis D. The voluntary control of motor imagery. Imagined movements in individuals with feigned motor impairment and conversion disorder. Neuropsychologia 2000; 38 (9): 1251-60
Tweedy SM, Vanlandewijck YC. International Paralympic Committee position stand--background and scientific principles of classification in Paralympic sport. Br J Sports Med 2011 Apr; 45 (4): 259-69
Young SJ, Pratt J, Chau T. Target-Directed Movements at a Comfortable Pace: Movement Duration and Fitts's Law. Journal of Motor Behavior 2009 Jul; 41 (4): 339-46