a preliminary investigation into a consistency in the ... · a preliminary investigation - into a...
TRANSCRIPT
A PRELIMINARY INVESTIGATION - INTO A CONSISTENCY I N THE -
ACCELLRATIONS OF OBJECTS LIFTEn FY WRIST FLEXION - --a - - -
William Lee Roberts
B.A., Reed College, 1969
A THESIS SUBMITTED I N PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF ARTS
i n t h e Department
o f
Psychology
WILLIAM LEE ROBERTS 1974
SIMON FRASER UNIVERSITY
J u l y 1974
A l l r i g h t s reserved . This t h e s i s may n o t be
reproduced i n whole o r i n p a r t , by photocopy
o r o t h e r means, without permission o f t h e au thor .
APPROVAL
Name : William Lee Roberts
Degree : Master o f Arts
T i t l e of Thesis : A Preliminary Investigation i n t o a
Consistency i n the Accelerations o f Objects
Lifted by Wrist Flexion
Examining Committee:
Chairman : A. L. Diamond
C . M . Davis Senior Supervisor
A . R. Blackman
Assistant Professor Simon Fraser University Burnaby , B . C .
Date Approved: , ?q /$/q '7.c/ CI
PARTIAL COPYRIGHT LICENSE
,
I hereby g r a n t t o Simon F r a s e r U n i v e r s i t y t h e r i g h t t o lend
my t h e s i s o r d i s s e r t a t i o n ( t h e t i t l e of which i s shown below) t o u s e r s
of t h e Simon F r a s e r U n i v e r s i t y L i b r a r y , and t o make p a r t i a l o r s i n g l e
c o p i e s o n l y f o r s u c h u s e r s o r i n r e s p o n s e t o a r e q u e s t from t h e l i b r a r y
of any o t h e r u n i v e r s i t y , o r o t h e r e d u c a t i o n a l i n s t i t u t i o n , on i t s 'own
b e h a l f o r f o r one of i ts u s e r s . I f u r t h e r a g r e e t h a t pe rmiss ion f o r
m u l t i p l e copying of t h i s ' t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d
b y me o r t h e Dean of Graduate S t u d i e s . It is unders tood t h a t copying
o r p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l n o t b e a l lowed
w i t h o u t my w r i t t e n pe rmiss ion .
T i t l e o f ~ h e s i s / ~ i s s e r t a t i o n :
A Preliminary In-test igation i n t o a Cmsis tencv i n t h e A c c m t i o n s
of Objects Lif teu by Wrist Flexion.
Author :
( s i g n a t u r e )
W, L. Roberts
(name )
25 July 1974
( d a t e )
I
Abstract
In examining fi lms of l i f t i n g movements made
during a study of the size-weight i l l u s i o n (Davis & Roberts,
1973), a consistency was noted i n the values obtained f o r
the maximum accelerat ions of t he objects l i f t e d . This
consistency, while a t f i r s t surpr is ing, seemed more
reasonable upon re f lec t ion , and t h i s study was designed
t o confirm i ts existence.
Twenty-four - Ss were filmed l i f t i n g four objects
which d i f fe red i n s i z e , shape, substance, color , and weight.
The f i lm was analysed frame by frame, and the da ta col lected
were subjected t o a two-way ana lys i s of variance. The r e s u l t s
indicated t h a t the - Ss, while d i f f e r ing from one another,
were consis tent i n t he maximum accelerat ions they applied t o
the three heaviest of the four objects. The accelerations of
t he l i g h t e s t object d i f fered s ign i f i can t ly from the accelera-
t i ons of t he other three , but it seems l i ke ly t h a t t h i s was
an aberrat ion due t o t he experimental task i t s e l f .
iii
L....
What a piece of work is a man! . . . i n f o m and moving how express and admirable!
i n action how l i k e an angel!
Hamlet, 11, ii, 317
I
Table o f Contents
Approval
Abstract
Introduction
Method
Results
Discussion
Figure 1
Figure 2
. Figure 3
Table 1
Table 2
Table 3
Appendix 1
References
i i
iii
1
6
10
16
8
11
15
12
I l l u s i o n s t y p i c a l l y a r i s e when t h e t a c i t
assumptions underlying t h e processing o f pe rcep tua l in fo r -
mation are v io la ted . A s such, t h e i r s tudy is a p o t e n t i a l l y
informative and f r u i t f u l approach t o our understanding o f
perceptual-motor systems, providing, a s Leucippus a s s e r t e d
of t h e senses themselves, "a glimpse of t h e obscure".
The i l l u s i o n s a r i s i n g when t h e usua l r e l a t i o n s h i p s o f s i z e ,
ma te r i a l , and weight a r e a l t e r e d (Charpentier , 1891; Seashore,
1898; Usnadze, 1931) can provide i n s i g h t i n t o some of t h e
f a c t o r s which g ive r i s e t o our sensa t ions of weight and t h e
formation of judgments o f r e l a t i v e weight, a s w e l l as pro-
v id ing a c l e a r e r p i c t u r e of how we c o n t r o l ' t h e con t rac t ion
of our muscles.
The theory t h a t t h e size-weight i l l u s i o n
( and, by extens ion, a l l j udgrnents of heaviness ) are pr in-
c i p a l l y caused by pe r iphera l events , i . e . , by t h e l i f t it-
self and t h e subsequent sensory feedback, is both p l a u s i b l e
and venerable. I t was f i r s t proposed by Muller (Martin &
Muller, 18991, who hypothesized t h a t t h e s u b j e c t , a n t i c i p a t i n g
t h a t t h e l a r g e r ob jec t would be t h e heavier , app l i ed t o o
much fo rce i n l i f t i n g it; and t h i s excess fo rce , by causing
t h e ob jec t t o be l i f t e d quickly, r e s u l t e d i n a sensa t ion /
of l i g h t n e s s .
This hypothesis was p a r t i a l l y confirmed by
Claparede (1901) who, by d i r e c t l y measuring t h e ascension
o f both weights, found t h a t t h e l a r g e r was indeed l i f t e d
more quickly and with a s h o r t e r la tency. Loomis (1907)
d i r e c t l y measured t h e e n t i r e l i f t , and found t h a t even
when t h e l i f t was considered a s a whole, t h e l a r g e r weight
was s t i l l t y p i c a l l y l i f t e d with g r e a t e r f o r c e than t h e smaller .
But t h e s e two s t u d i e s , although well-conceived and ingeniously
executed, f e l l i n t o an i l l -deserved obscur i ty , and references
t o them i n t h e l a t e r l i t e r a t u r e a r e sparse .
And s o psychology d r i f t e d i n t o e r r o r . People
spoke of d e n s i t i e s and c e n t r a l mechanisms (e.g., Koseleff , 1958;
Helson, 1959), and while some dismissed t h e pe r iphera l theory
a s somehow not s a t i s f a c t o r y (Nyssen 4 Bourdon, 1956), o t h e r s
even denied t h a t t h e l i f t a f f e c t e d judgment a t a l l (Fourche,
quoted i n Whipple, 1921). However, ~ a v i s & Roberts (197 3)
demonstrated t h a t not only were t h e two o b j e c t s l i f t e d d i f -
f e r e n t l y , and t h e l a r g e r , f a s t e r , but t h a t by changing t h e
speed of t h e lift, t h e judgment of weight could be a l t e r e d ,
and t h e size-weight i l l u s i o n , one o f t h e g r o s s e s t and most
tenacious o f a l l t h e perceptual i l l u s i o n s , reversed (Davis,
personal communication).
I n examining t h e phys ica l c h a r a c t e r i s t i c s
o f t h e l i f ts , w e found extremely marked ind iv idua l d i f f e rences
i n he igh t , du ra t ion , and mean veloci ty . However, maximum
a c c e l e r a t i o n s demonstrated no t only a (comparatively) modest
v a ~ i a b i l i t y , b u t no s t a t i s t i c a l l y r e l i a b l e ind iv idua l d i f -
ferences: i.e., i n terms of maximum acce le ra t ion , everyone
l i f t e d t h e same o b j e c t s i n nea r ly t h e same way.
This consistency, which seemed a t first glance
s o remarkable, became, upon r e f l e c t i o n , more expl icable .
I t i s an everyday observation t h a t not only people but o t h e r
animals as we l l , a r e q u i t e s k i l l e d a t es t ima t ing t h e amount
o f muscular e f f o r t needed t o perform any c e r t a i n ac t ion:
w e move around and up and down with a modicum of grace, and
we a r e seldom surpr i sed by t h e weight o f t h i n g s when we pick
them up. This is t r u e not only o f t h e a d u l t s of any spec ies ,
but a l s o o f t h e young, who develop t h i s s k i l l about t h e time
they begin t o move about t h e i r environment (Held & Bauer, 19.67).
This may be a matter of hours, a s i n precocial animals,
o r of months, a s i n man. Graceful movement is s o much con-
sidered a mormal a t t r i b u t e of animals t h a t its lack i n ea r ly
infancy is taken a s prima f a c i e evidence of brain damage -- (cf . Windle, 1963, 1969; Pasamanick, Knoblock, & Lil ienfeld ,
1956; Apgar, Girdany, McIntosh, h Taylor, 1955; Jenkins G
West, 1958).
Moreover, it seemed t h a t being well-co-ordi-
nated (of which reaching and l i f t i n g a r e f ace t s ) is very
probably an innate a b i l i t y : i ts un iversa l i ty both within and
between species, the consistency of its development among
individuals, and the obviousness of the evolutionary pressures
favoring i t s se lec t ion , a l l argue s t rongly f o r it. Clearly,
too, it is an a b i l i t y t h a t seems t o be organized i n t o an
h ie ra rch ica l system (cf. Bowlby, 1972). Walking, f o r instance,
is organized on a sp ina l l eve l , but is a l so influenced by
events i n t he brain: by perceptual inputs , f o r example, and
by plans (c f . Miller , Galanter, & Pribam, 1960). There a r e
some obvious feed-back elements i n t h i s system ( the j o in t
receptors , tendon organs, and muscle spindles , f o r instance),
whose sensory input of posi t ion o r e f f o r t modifies on-going
muscular activities. These modifications can be considered
as goal-corrected (in Bowlbyts sense): the movement of the
hand, arm, and body in reaching, for instance, is corrected
with reference to the goal of arriving at and grasping. some
object; in walking, to the normal gait (the Platonic Form)
as well as to the intended destination (the Aristotelian
telos): by sub-plans and plans, in Miller, Galanter, and - Pribam's terminology.
The initial muscular effort exerted at the
beginning of any action (and the over-all co-ordination of
the entire action) is affected not only by our past experiences
(and implicitly by our genetic make-up, which influences how
easily or hardly we profit from our experiences) but also
by cues from the environment. When these cues are misleading,
the initial muscular force applied may be inappropriate, i.e.,
either too little or too much for the action in question, and.
this inappropriate effort will be reflected objectively in
abnormal lifts or clumsiness of movement and subjectively in
erroneous sensations of weight or effort.
Thus this consistency of acceleration which
we had noticed in studying the size-weight illusion seemed
t o be an i n d i c a t i o n of a widely-functioning neuro-muscular
system which al lows us t o move normally i n t h e world and whose
misfunctions account f o r some of t h e common i l l u s i o n s of
weight which w e experience. A s such, it seemed worthwhile
t o look a t t h i s consistency more c l o s e l y , t o s e e whether, indeed,
t h e r e were no s t a t i s t i c a l l y r e l i a b l e d i f f e r e n c e s between
ind iv idua l s o r between ob jec t s o f a familiar nature.
Method
Procedure. These hypotheses were t e s t e d by
f i lming ind iv idua l s l i f t i n g o b j e c t s of d i f f e r e n t shapes,
substances, weights, and colors . (These are, apparently,
important pe rcep tua l parameters: c f . Huang, 1945; Seashore, 1899;
Wolfe, 1898; Darube, 1964. Factors which a f f e c t t h e perception of
weight a l s o presumeably a f f e c t t h e way i n which t h e o b j e c t s a r e
l i f t e d physica l ly . ) The f i lm, which was sho t a t twenty-four
frames p e r second, was analysed frame by frame t o determine t h e
maximum acce le ra t ions . Two of t h e o b j e c t s were hal f -p in t and
quar t cans, pa in ted white, which had previous ly been used i n t h e
s e r i e s of experiments on t h e size-weight i l l u s i o n (Davis & Roberts,
1973). The smal l can weighed 486 grams, c l o s e t o i t s previous
weight o f 500 grams,
and t h e l a r g e can weighed 705 grams, which a p i l o t s tudy
had ind ica ted t o be s u f f i c i e n t t o prevent t h e size-weight
i l l u s i o n from occurring (c f . Nyssen & Bourdon, 1954).
The t h i r d and f o u r t h o b j e c t s were wooden blocks, each 8.9
cm. i n c r o s s s e c t i o n , one equal i n he ight t o t h e small can,
t h e o the r , t o t h e l a r g e can, and weighing 288 and 486 grams
respec t ive ly . A l l f ou r ob jec t s had w i r e handles a t tached s o
t h a t they could be l i f t e d from t h e same height by w r i s t
f l e x i o n alone. I n t h i s manner, t h e Ss d id not have t o r a i s e - o r lower t h e i r hands t o grasp t h e d i f f e r e n t ob jec t s . The
Ss a l s o wore p l e x i g l a s s guides on t h e i r f i n g e r s ; t h e s e guides - had s l o t s i n t o which t h e wire handles f i t t e d . This s tandardized
t h e r e l a t i v e l e v e r lengths through which t h e o b j e c t s were
l i f t e d , a f a c t o r t h a t demonstrably a f f e c t s t h e percept ion of
weight, al though i n no simple manner (Davis, 1973, 1974).
The o b j e c t s were presented i n counter-balanced o rde r by t h e
E, who set them on a smal l revolving t a b l e i n f r o n t o f t h e - sea ted - S. Figure 1 shows t h e experimental arrangement.
The beginning o f t h e l i f t was ind ica ted t o
t h e S by a warning l i g h t followed two seconds l a t e r by a - l i f t l i g h t ; t h e s e l i g h t s were placed d i r e c t l y i n f r o n t of
t h e S a t a d i s t ance of one metre. The camera (an e l e c t r i c a l l y -
Figure 1: A r m , hand, and arm-rest; t a b l e and four objec ts .
This arrangement minimized t h e mechanical d i f f e rences i n
t h e l i f t s . Note t h e p l e x i g l a s s guides on - S.
driven 16mm Bolex with a r e f l e x l e n s ) began f i lming when t h e
warning l i g h t came on; it was placed a t t h e S 1 s r i g h t , - perpendicular t o t h e plane of t h e l i f t , a t a d i s t ance of two
metres. After each l i f t , each S gave an es t imate of t h e - absolute weight of t h e ob jec t i n grams ( t h i s was merely a
precautionary measure, t o insure t h a t t h e Ss at tended t o t h e - t a sk of l i f t i n g ) . This was repeated u n t i l each S had l i f t e d - each ob jec t twice. Only t h e second s e t of four l i f t s was
analysed, t h e f i r s t set c o n s t i t u t i n g a p r a c t i c e t r i a l . This
seemed an advisable procedure, s i n c e t h e purpose of t h e
experiment was t o study l i f t i n g movements i n f a m i l i a r s i tua t ions - -
and although it was intended t h a t t h e ob jec t s and t h e s i t u a t i o n
should be a s s t ra ight forward a s poss ib le , a labora tory is an
unnatural p lace , and white cans and wooden blocks with wire
handles, r a r e objects . Moreover, a p r a c t i c e t r i a l seemed
appropr ia te s ince , i n our non-laboratory l i v e s , we t y p i c a l l y
have count less p r a c t i c e t r i a l s preceding every a c t i o n we
undertake.
After processing, t h e f i l m was projec ted , t h e
d i s t ance between the screen and p r o j e c t o r being adjus ted
u n t i l t h e image was l i f e - s i ze . The height of t h e ob jec t
above t h e t a b l e was then d i r e c t l y measured f o r every
frame. The fuzziness of t h e image prevented t h i s measurement
from being more accura te than + one-fourth mi l l imeter . - Subjects. Twenty-four u n i v e r s i t y s tuden t s ,
aged between 18 and 30 years , were Ss. F i f t een were female.
They were t o l d t h a t t h e purpose o f t h e experiment was t o
ga in information on how es t imat ions o f weight were formed.
The experimental requirements were explained, and any
ques t ions were answered.
Resul ts
The frequency d i s t r i b u t i o n of t h e maximum
a c c e l e r a t i o n values f o r each ob jec t l i f t e d is shown i n
Figure 2. I t is r e a d i l y apparent t h a t t h e d i s t r i b u t i o n s
f o r t h e t h r e e l a r g e s t ob jec t s a r e very s i m i l a r , and t h a t
they r e f l e c t a genera l ly slower r a t e o f l i f t than t h a t
f o r t h e smal l e s t ob jec t ( t h e smal l block). The mean and
modal maximum acce le ra t ion values f o r each o b j e c t a r e given
i n Table 1.
large can
small can
large block
small block
Figure 2. Frequency distributions of maximum acceleration
values for the four objects.
Table 1: The mode, mean, and standard
deviation of the maximum acceleration
values for each object lifted.
mode - small can 4.8 cm/sec2
large can 4.8
large block 4.8
small block 8.4
mean 7
standard deviation
A two-way a n a l y s i s o f var iance (24 Ss x - 4 o b j e c t s ) was appl ied t o t h e maximum acce le ra t ion data.
The r e s u l t s , shown i n Table 2, revealed s i g n i f i c a n t
e f f e c t s f o r both s u b j e c t s and ob jec t s . However, when t h e d a t a
f o r t h e smal l e s t ob jec t a r e omit ted, t h e s i g n i f i c a n t
o b j e c t effect disappears, confirming t h e consistency of
l i f t i n g previous ly noted.
Four o t h e r l i f t c h a r a c t e r i s t i c s were a l s o
computed, and t h e d a t a subjec ted t o similar analyses.
S i g n i f i c a n t e f f e c t s o f ob jec t s were found f o r mean and
maximum v e l o c i t y , but again t h e s e disappear when t h e da ta f o r
t h e smal l block a r e omitted ( s e e Table 2). No s i g n i f i c a n t
e f f e c t s o f o b j e c t s were found f o r measures o f maximum
height o r maximum decelera t ion . F ina l ly , t h e only measure
which f a i l e d t o y i e l d a s i g n i f i c a n t v a r i a t i o n due t o - S
d i f f e r e n c e s was maximum dece le ra t ion f o r t h e t h r e e l a r g e s t
ob jec t s .
The consistency o f l i f t i n g behavior is s t r i k i n g l y
demonstrated i n Figure 3 , which shows almost i d e n t i c a l maximum
Table Two:
Results of the analysis of variance
Maximum
subjects
Height
. objects
Mean
subjects
Velocity
objects
Maximum
subjects
Velocity
objects
Maximum
subjects
Acceleration
objects
Maximum
subjects
Deceleration
objects
Four Objects
F= 27.62,
df=
23/69, 6.001
F=
.15,
df=
3/69, p).
50
Three Heaviest Objects
-
smal l can t h r e e heav ies t o b j e c t s (pooled )
Figure 3. Frequency d i s t r i b u t i o n s of t h e pooled maximum a c c e l e r a t i o n
va lues f o r t h e t h r e e heav ies t o b j e c t s and f o r t h e smal l can i n
Davis & Roberts (1973).
accelerat ion d i s t r ibu t ions of the pooled data f o r the
th ree l a rges t objects i n the present experiment and of the
values obtained by Davis & Roberts (1973) f o r t h e i r small
can. (This, incidental ly , confirms Muller's i n t u i t i o n
t h a t it i s the la rger can i n t h e size-weight i l l u s i o n t h a t
is l i f t e d abnormally, and thus is the source of the i l lus ion . )
The data from both Davis & Roberts (1973)
study and the present experiment c l ea r ly support t he
hypothesis t h a t people l i f t d i f f e r en t objects s imi la r ly
and consistently. Provided, t h a t is, t h a t they weigh enough.
Discussion
It appears t h a t while the muscular e f f o r t
needed f o r an act ion can be i n i t i a l l y s e t with precision
and consistency over a wide range of a c t i v i t i e s , it can ' t
be s e t exactly; and these minor perturbations i n force
cause a g rea te r va r i ab i l i t y i n the accelerat ion of l i g h t e r
objects. For the l e s s mass an object has, the more ea s i l y
i ts accelerat ion can be a l te red . (And conversely, of course,
the heavier the object , the l e s s its accelerat ion w i l l
be a f fec ted by minor v a r i a t i o n s i n t h e f o r c e appl ied t o it.
It is probably no t acc iden ta l t h a t o f t h e four ob jec t s , t h e
heavies t was t h e most cons i s t en t ly l i f t e d , while t h e l i g h t e s t
e l i c i t e d t h e g r e a t e s t variance.)
From Newton's Second Law; F= ma, w e know t h a t
it takes a f o r c e of 2300 dynes t o a c c e l e r a t e 486 grams t o 4.8
cm/sec2, t h e modal maximum a c c e l e r a t i o n of t h e smal l can, l a r g e
block, and l a r g e can. It t akes 2900 dynes t o a c c e l e r a t e them
t o t h e i r mean maximum acce le ra t ion . The smal l wooden block, on
t h e o t h e r hand, needs a force of 2450 dynes t o reach i ts modal
maximum acce le ra t ion of 8.4 cm/sec2, and 2200 dynes t o reach i t s
mean maximum acce le ra t ion . I t seems a s though t h e l i g h t e s t weight
was being l i f t e d with about t h e same e f f o r t a s was appl ied t o t h e
o t h e r weights: a proper s t r a t e g y , i f one is t r y i n g t o determine
r e l a t i v e weights, and a p e r f e c t l y poss ib le one ( c f . Payne & Davis,
1941); and one, moreover, t h a t was i n t h e s e circumstances very
l i k e l y , s i n c e t h e - Ss were given t h e t a s k o f es t imat ing t h e weights
of t h e objec ts .
This s t r a t e g y should, of course, a l s o a f f e c t t h e
l i f ts of t h e heavies t ob jec t , a s we l l as t h e l i g h t e s t . I f an
(approximately) equal i n i t i a l fo rce was appl ied t o a l l t h e
o b j e c t s , t h e heavies t ought t o reach i t s maximum acce le ra t ions
a t a s l i g h t l y l a t e r time t h a t t h e o the r s . And indeed t h e r e i s
a marked (al though not s t a t i s t i c a l l y s i g n i f i c a n t ) t r end i n t h i s
d i r e c t i o n (X2= 6.23, d f= 3, p= . lo) . See Table 3.
Table Three:
Distribution of maximum accelerations by
time.
Small Can
Large Can
Small Block
Large Block
First
. one-eighth
second
Second
one-eighth
second
percentage of
total lifts in
first quarter-second
84.4%
of all maximu. accelerations occurred in the first quarter-second of the lift.
That t h e r e a r e l i m i t s t o t h e accuracy
with which w e s e t t h e i n i t i a l e f f o r t needed f o r any a c t i v i t y
is not only c l e a r - a p r i o r i , but is a l s o suggested by t h e
exis tence o f thresholds and j.n.d.s i n t h e es t imat ion of
absolute weight (because these es t imat ions depend i n p a r t
on t h e physica l c h a r a c t e r i s t i c s of t h e l i f t , which depend,
i n t u r n , on t h e muscular tens ion j u s t p r i o r t o t h e l i f t )
and by t h e curious f a c t t h a t f o r weights of less than t h r e e
grams, t h e size-weight i l l u s i o n is reversed (Howard, 1954)--
a remarkable f inding, given t h e t e n a c i t y of t h e i l l u s i o n
a t g r e a t e r weights, and suggest ive i n i ts impl ica t ions f o r
t h e nature of the l i f t s themselves.
O f course, these d a t a po in t t o a l e v e l of
breakdown a t weights f a r l e s s than 288 grams: which may
wel l b e . s o , s i n c e t h e experimental t a s k imposed on t h e sub jec t s
i n t h i s experiment may have had an important e f f e c t on how
t h e l i g h t e s t weight was l i f t e d . But i n genera l , from a simple
considera t ion of t h e physics of t h e s i t u a t i o n , one would
expect more v a r i a b i l i t y i n t h e acce le ra t ions of l i g h t e r
weights, and l e s s i n t h e acce le ra t ion of heavier. These
parameters, whatever they a r e , can i n p r i n c i p l e be e a s i l y
established by further observation and the methodology de-
scribed in this paper.
While the hypothesized consistency between
Ss has had to be rejected in the face of the reliable indi- - vidual differences reported, the similarity of the distribu-
tions of the maximum accelerations of the four heaviest
weights (the three from this experiment plus the small can
Gom Davis & Roberts, 19731, their relative compactness,
and the concentration of values at the modes, constitute,
in my opinion, a sufficient experimental confirmation of
the hypothesized consistency with which objects of varying
sorts are lifted. And this consistency, it seems to me,
is merely a reflection of the greater co-ordination that
characterizes the movements of all animals.
Appendix 1. Some r e f l e x i o n s on Table 2.
Any experiment involving l i f t i n g is profoundly
and s u b t l y influenced by t h e mechanics of t h e l i f t , i.e., by
t h e experimental s i t u a t i o n i t s e l f . For ins tance , i n t h e
a n a l y s i s of t h e maximum heights , t h e main e f f e c t f o r ob jec t s
was extremely i n s i g n i f i c a n t . This was probably due s o l e l y
t o t h e physica l set-up of t h e l i f t : each - S tended t o l i f t
each ob jec t through t h e e n t i r e range allowed: t h e s h o r t a r c
formed by t h e f l e x i o n of t h e wrist. It is, the re fo re , impos-
s i b l e t o say whether differences. would emerge i f - Ss were
given more phys ica l freedom of movement.
Likewise, t h e abso lu te values o f t h e v e l o c i t i e s ,
a c c e l e r a t i o n s , and dece le ra t ions would no doubt vary depending
on whether t h e o b j e c t s were l i f t e d by w r i s t f l ex ion , elbow
f l ex ion , o r by some l a r g e r movement involving t h e t o r s o o r t h e
l egs . However, t h e consistency of those values would,
presumably, p e r s i s t .
I
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