Egocentric Localization: Normal and Abnormal Normal and Abnormal Aspects

37 Pages·2010·1.47 MB·English

by  Paul Alan Harris

““EEgocenttriic LLocalliizattiion:
NNoorrmmaall aanndd AAbbnnoorrmmaall
Aspects”
Kenneth J. Ciuffreda,
O.D., Ph. D.
Diana P. Ludlam,
B.S., C.O.V.T.
Naveen K. Yadav,,
B.Sc.((Opptom.)),, M.Sc.
“Langguagge should not
”
obscure the concept
((KKJJCC))
Discuss 3 areas:
1. Definitions and basic conceppts
22. FFour criittiicall llabborattory experiimentts
3. Clinical assessment of egocentric
llooccaalliizzaattiioonn ((EELL)) iinn AABBII ppaattiieennttss
DDeeffiinniittiioonnss aanndd bbaassiicc
conceppts
SSppaattiiaall SSeennssee
“The means by which an organism
establishes a stable, constant
relationship with its surroundings”
((RReeaaddiinngg,, 11998833))
Sppatial Sense:
• Orientation –
The information needed to
know where we are with respect to our
environment (e.g., equilibrium
mechanisms).
• Localization –
The information needed to
know where objects are with respect to the
individual.
oculocentric
eeggoocceennttrriicc
OOccuulloocceennttrriicc
• eye – based
• fovea is the center of the coordinate center
• objects are referenced with respect to the
fovea
• monocularly-based
EEggoocceennttrriicc
• body – based
• center of the trunk along the body midline is the
center of the coordinate syystem in normals
• objects are referenced with respect to the body
• bbiinocullarlly-bbasedd
• subjective straight-ahead is within -/+ 2 degs of
obbjjecttiive zero iin normalls, so iitt iis very accuratte
To sppecifyy ppreciselyy an objject’s eggocentric
localization, you need 3 parameters:
11. MMeerriiddiiaann
2. Eccentricity
3. Absolute distance
 iitt iis a PPOOLLAARR – bbasedd coorddiinatte systtem.
((e.gg.,, “the objject is over there upp and to the
right about 20 feet away”)
In Acquired Brain Injury (ABI) patients, especially
CVA,, eggocentric localization ((EL)) can sometimes
be disturbed by the brain injury, especially if the
right posterior parietal cortex region is damaged.
objective is not equal to the subjective sense of
ssttrraaiigghhtt aahheeaadd ddiirreeccttiioonn.
tthheeyy hhaavvee “aabbnnoorrmmaall eeggoocceennttrriicc llooccaalliizzaattiioonn” ((AAEELL))
(aka VMSS), mainly laterally-biased into the
‘seeing’ hemi-field.
 produces “cue conflict” leading to visuomotor
probbllems ((““outt off synchh wiitthh tthheiir enviironmentt””))