REFERENCES

1
Comparison of dynamic touch by hand and foot
A. Hajnal,1 S. Fonseca,1,2 S. J. Harrison,1 P.
Silva,1 J. M. Kinsella-Shaw1,3 and Claudia
Carello1 1Center for the Ecological Study of
Perception and Action, University of
Connecticut 2Federal University of Minas Gerais,
Belo Horizonte, Brazil 3Department of
Physical Therapy, University of
Connecticut Acknowledgments. This research was
supported by grants from the National Science
Foundation (SBR 00-04097), the University of
Connecticut (Co-laboratory of Rehabilitation
Research), and a CAPES Award (BEX 0320-05-06)
from the Brazilian Ministry of Education.
INTRODUCTION
EXPERIMENT 2 PERCEIVING PARTIAL vs. WHOLE LENGTH
BY FOOT AND HAND
When a rod is grasped other than at the end,
both its whole length, WL, and the partial
length, PL, to one side of the grip can be
perceived selectively (e.g., Solomon, Turvey
Burton, 1989). Perception of WL and perception of
PL by hand are constrained by different aspects
of the rods mass distribution. Does the foot
have similar selective perception capabilities?
Most dynamic touch research has focused on the
perceptual capabilities of the upper limbs. One
exception examined a combination of different
tools and tissue contacts (Fig. 1). Perception
was equivalent across conditions and constrained
by moments of the mass distribution (Carello,
Fitzpatrick, Domaniewicz, Chan, Turvey, 1992).
Such a result provides support for Gibsons
(1979) assertion that perception is constrained
by information not sensations. The present
research examines whether the lower limb can
serve as a smart instrument (Runeson, 1977) that
capitalizes on the same information as the upper
limb.

• Participants
• Twenty undergraduate students from the University
  of Connecticut.
• Materials, Design, and Procedure
• 3 lengths (L .6, .8, and 1 m)
• Plastic handle at rods midpoint
• 3 mass conditions no mass, 150 g mass on the
  left or on the right (Fig. 6a)
• For perceived PL (which was always to the left of
  the grip), a single marker was moved to the left.
• For perceived WL, one marker was moved to the
  left and one was moved to the right to indicate
  the felt locations of the two ends of the rod.
• The remaining procedure was the same as
  Experiment 1.
• RESULTS
• Perceived PL. Attention was always to the left
  of the limb. The key expectation, therefore, is
  that Perceived PL should be greatest when the
  mass is on the left. No mass and mass on the
  right should be roughly equivalent.
• ?This pattern was found for both limbs (Fig. 7,
  left). However, this time, limb mattered, with PL
  by hand greater than PL by foot, especially for a
  left mass placement, F(2, 18) 4.68, p lt .02.
• Perceived WL. I1 is the same whether the mass is
  on the left or right for both it is greater than
  I1 with no mass. The key expectation, therefore,
  is that Perceived WL for no mass should be the
  least WL for left mass and right mass should be
  equal.
• ?This pattern was found for both limbs (Fig. 7,
  right). The effect of limb appeared in the Limb x
  Length interaction, F(2, 18) 6.68, p lt .01. PL
  by hand was larger than PL by foot and this
  difference increased with rod length.
• Accuracy and Reliability. Accuracy and
  reliability were superior for PL by hand.
  Accuracy was superior for WL by hand but
  reliability was equivalent for the two limbs
  (Fig. 8).

EXPERIMENT 1 PERCEIVING LENGTH BY FOOT AND HAND

• Participants
• Ten female undergraduate students at the
  University of Connecticut.
• Materials, Design, and Procedure
• 3 lengths (L .6, .8, and 1 m)
• 3 mass conditions 150 g mass attached at .5, .7,
  or .9L (Fig. 2a, b)
• Plastic handle at proximal end
• Hand Handle grasped wielding by movements at
  the wrist
• Foot Handle attached to the shoe wielding by
  movements at the ankle
• Task Move a marker on a pulley system to the
  location that could be reached with the object
  (Fig. 2c, d).
• Trials were blocked by limb limb order was
  counterbalanced. Each object was presented 3
  times yielding a total of 54 trials per
  participant.

PL
RESULTS Perceived length. There was no main
effect of limb, F(2, 18) 1, and no significant
interactions involving limb (Fig. 3).
50
error
25
Figure 3. Mean perceived length judgments by hand
and foot. Main effects of L, F(2, 18) 95.74, p
lt .001, and mass position, F(2, 18) 39.53, p lt
.001, reveal the standard pattern Lengths were
discriminated in similar fashion by hand and by
foot, with a comparable influence of mass position
0
MRS
AD
Figure 8. Accuracy (MRS) and reliability (AD)
for judgments by hand (H) and foot (F). (left)
Perceived PL and (right) Perceived WL.
Mass/L
CONCLUSIONS
Accuracy and Reliability. Two dimensionless Weber
fractions provided measures of accuracy (Mean
Root-Square, MRS) and consistency or reliability
(Absolute Deviation, AD)
Experiments 1 and 2 reveal key properties of the
haptic perceptual system as a smart instrument
(Runeson, 1977). The system capitalizes on
invariants it is determinate insofar as
perception is a single-valued function of
information it is scaled in the appropriate
range of physical stimulation and it is soft,
operating as a temporary assembly of muscle,
tendon and other tissue synergies. As attentional
demands increased, limb differences emerged,
although the basic pattern was unchanged. The
haptic system is assembled from dynamic
properties, not from specific anatomical
components. This suggests a methodological
application for assessing perceptual capabilities
in diabetic and neuropathic patients. Namely, a
healthy limb can provide the control group for
an injured limb.
Hand and foot did not differ on these measures
(Fig. 4). The fact that MRS was greater than AD
indicates that length judgments are
systematically distortedas they should be if the
basis for length judgments is a rods mass
distribution rather than its metric length.
Inertial scaling. Regression analyses revealed a
significant dependence on I1 for both limbs (Fig.
5). The value of r2 ranged from .75 to .97 with a
mean of .89 for hand and from .71 to .92 with a
mean of .83 for foot. This difference was
significant, F(1, 9) 6.39, p lt .04. For the
hand, the slopes ranged from .16 to .55 with a
mean of .37 for the foot, the slopes ranged from
.07 to .67 with a mean of .32. This difference
was not significant, F lt 1.
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(1977). On the possibility of smart perceptual
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Burton, G. (1989). Perceiving extents of rods by
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