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

,

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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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