Jc. Stevens et Mq. Patterson, DIMENSIONS OF SPATIAL ACUITY IN THE TOUCH SENSE - CHANGES OVER THE LIFE-SPAN, Somatosensory & motor research, 12(1), 1995, pp. 29-47
Spatial acuity of the touch sense and its variation in aging came unde
r psychophysical scrutiny at the fingertip and control body sites. Acu
ity is viewed as encompassing the discrimination of four features of s
imple stimulus configurations: (1) discontinuity (gaps in lines or dis
ks), (2) locus on the skin, (3) length (or area), and (4) orientation
(e.g., along or across the finger). Each of these dimensions of acuity
serves uniquely in tactile perception, as illustrated in the structur
e of braille. For their measurement, psychophysical tests were develop
ed and refined. These were aimed at freedom from bias, rapid estimatio
n of acuity thresholds in hundreds of subjects, and eventual applicabi
lity to the whole body surface. Some 14 versions of the tests were adm
inistered in three experiments, yielding 1478 individual thresholds. E
xperiment I (15 young and 15 elderly subjects) and Experiment II (131
subjects, ages 18 to 87 years) shed light on the nature of discriminat
ion of discontinuity and orientation. These mainly concern pitfalls of
measurement and influence of exact stimulus configuration. Experiment
III (1 15 subjects, ages 8 to 86 years) examined refined versions of
tests for all four dimensions of acuity. Four principal findings emerg
ed: (1) At all ages, thresholds for the four dimensions of acuity diff
er from one another in size-in order from smallest to largest: length,
locus, orientation, and discontinuity. Exact sizes differ for transve
rse and longitudinal stimulus alignment. (2) All four acuity dimension
s deteriorate with age, to a first approximation manifesting a constan
t increase in threshold of approximately 1% per annum between ages 20
and 80 years. That similar rates of deterioration characterize all fou
r dimensions in the fingertip suggests a common mechanism, possibly th
inning of the same mediating receptor network. (3) Acuity at more cent
ral sites (forearm, lip) deteriorates more slowly than at the fingerti
p. (4) Individual differences in acuity abound, even after the effects
of aging are discounted.