SNYDER, David William, 1934- the RELATIONSHIP BETWEEN the AREA of VISUAL OCCLUSION and GROUNDSTROKE ACHIEVEMENT of EXPERIENCED TENNIS PLAYERS

This dissertation has been microfilmed exactly as received 69-22,2X2

SNYDER, David William, 1934- THE RELATIONSHIP BETWEEN THE AREA OF VISUAL OCCLUSION AND GROUNDSTROKE ACHIEVEMENT OF EXPERIENCED TENNIS PLAYERS.

The Ohio State University, Ph.D., 1969 Education, physical University Microfilms, Inc., Ann Arbor, Michigan I

THE RELATIONSHIP BETWEEN THE AREA OF VISUAL

OCCLUSION AND GROUNDSTROKE ACHIEVEMENT

OF EXPERIENCED TENNIS PLAYERS

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

By

David William Snyder, B.S., M,Ed.

******

The Ohio State University 1969

Approved by

School of Physical Education f.

I

ACKNOWLEDGMENT

The writer wishes to express his appreciation to Dr. John

Hendrix who first suggested to him the possibility fo a dissertation involving the role of vision in hitting a tennis ball. Dr. Robert

Bartels, the writer's adviser, lent great assistance in the selection and organization of the study. Mr. Larry Tracewell of the Ohio State

Systems Engineering Department designed the special electrical instru­ ments used in this study. Without Mr. Tracewell's assistance the study would not have been possible. The subjects and scoring assistants were

quite generous in offering their services and the writer is grateful

for their contributions. Finally, the writer wishes to express his

gratitude to his wife and family for their continued understanding and

support.

ii VITA

December 14, 1934 * . . Born - Wichita, Kansas

L956 ...... B.S. University of Texas

1956-1957 ...... Physical education teacher and coach, Win­ field, Kansas, Junior-Senior High School

1958 ...... Physical education teacher and coach, San Angelo, Texas, High School

1958-1960 ...... Instructor of Physical Education and Tennis Coach, University of Arizona, Tucson, Ari­ zona

1960 ...... M. Ed., University of Arizona

1960-1964 ...... Assistant Professor of Physical Education and Tennis Coach, University of Arizona, Tucson, Arizona

1964-1965 ...... Teaching Assistant, Physical Education De­ partment, The University of Iowa, Iowa City, Iowa

1965-1967 ...... Associate Professor of Physical Education and Tennis Coach, University of Arizona, Tucson, Arizona

1967-1969 ...... Teaching Assistant, Physical Education De­ partment, The Ohio State University, Columbus, Ohio

PUBLICATIONS

"Sports Skills With A Future." Journal^ of Health, Physical Education, and Recreation, XXX, pp. 34 and 39, December 1959.

FIELDS OF STUDY

Major Field: Physical Education

Minor Field: Teacher Education

iii TABLE OF CONTENTS

Page

ACKNOWLEDGMENT ...... Ii

VITA ...... iii

LIST OF T A B L E S ...... vi

LIST OF FIGURES ...... vii

Chapter

I, INTRODUCTION...... 1

Statement of the P r o b l e m ...... 1 H y p o t h e s i s ...... * ...... 2 Assumptions and Limitations ...... 2 Significance of the Study ...... 3

II, RELATED LITERATURE...... 6

Athletes versus Non-Athletes ...... 7 Skilled versus Less Skilled Performers .... 8 Other Related Research ...... 10

III. METHODS AND PROCEDURES...... 15

Subjects...... 15 Equipment and Apparatus...... 17 Ball Throwing M a c hine ...... 17 Sensing and Triggering Devices ...... 17 O c c l u d e r ...... lB Control B o x ...... 18 Visual Conditions ...... * ...... 19 Broer-Miller Tennis Achievement Test ...... 19 P r o c e d u r e ...... 21 The T e s t ...... 21 Administration...... 22 S c o r i n g ...... 23 Important Controls ...... 23 Weight of the B a l l ...... 23 Court Marki n g s ...... 23 Photocells and Occluders ...... 2k Ball S p e e d ...... 2k Height of the N e t ...... 2h

iv TABLE OF CONTENTS— Continued

Chapter Page

Height of the Restraining R o p e . 24 Subjects' Hitting Area ...... 24 Instructions to Subjects . 25 Tennis Equipment...... 25 Court Location...... 25 Recording, Equipment Operation, and Testing A s s istants ...... 25

IV. ANALYSIS OF THE D A T A ...... 26

Statistical Analysis ...... 26 Summary ...... 30 D i s c u s s i o n...... 31

V. SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS ...... 36

Summary...... 36 Conclusions...... 37 Recommendations ...... 40

APPENDIX

A. SENSING, TRIGGERING, AND OCCLUDING DEVICE ...... 41

B. BROER-MILLER TENNIS ACHIEVEMENT TEST ...... 47

C. INSTRUCTIONS...... 50

D. SCORE S H E E T ...... 52

E. RAW FOREHAND AND BACKHAND SCORES...... 54

F. ANALYSIS OF VARIANCE...... 57

G. DUNCAN MULTIPLE RANGE ...... 59

H. PHOTOGRAPHS OF EXPERIMENTAL EQUIPMENT ...... 62

BIBLIOGRAPHY ...... 71

v I

LIST OP TABLES

Table Page

1. HEIGHT, WEIGHT, AMD AGE OF ALL SUBJECTS AND YEARS OF PARTICIPATION IN TENNIS ...... 16

2. CONDITIONS OF OCCLUSION OR NON-OCCLUSION WITH THE BALL THROWN AT MEDIUM OR FAST SPEEDS UNDER WHICH THE SUBJECTS ATTEMPTED THE GROUNDSTROKES ...... 19

3. THE MEANS AND STANDARD DEVIATIONS OF FOREHAND AND BACKHAND SCORES UNDER ALL EXPERIMENTAL CONDITIONS . . 27

k. ANALYSIS OF VARIANCE OF TEST SCORES OF FOREHAND AND BACKHAND GROUNDSTROKES WITH MEDIUM AND FAST BALL TOSSES ...... 28

5. THE RESULTS OF THE DUNCAN MULTIPLE RANGE TEST OF SCORES ACHIEVED UNDER ALL VISUAL CONDITIONS AND BALL SPEEDS USING FOREHAND AND BACKHAND GROUND­ STROKES ...... 29

6. RESULTS OF THE T-TEST OF THE MEAN SCORE DIFFERENCES OF TEST RESULTS AT THE TWO BALL SPEEDS...... 30

vi LIST OF FIGURES

Figure Page

I. Scoring Areas for Broer-Miller Tennis Achievement T e s t ...... 20

vii CHAPTER I

INTRODUCTION

The physical movements and achievements of those who excel in

athletic contests are often examined to assist in understanding and ex­

plaining why they do excel. Because of the emphasis often given to

"keeping your eyes on the hall until you hit it" by those who instruct

in sports such as tennis and baseball, where a participant attempts to visually track and hit a moving ball, the writer believed that some im­

portant implications might be drawn from an examination of the perform­

ances of experienced tennis players under varied conditions of visual

observation.

Statement of the Problem

The primary concern of this study was to determine to what dis­

tance in front of him the experienced tennis player needed to visually

track the ball prior to making a successful groundstroke. A second

aspect of this study was to determine if a faster ball speed affected

an individual's hitting accomplishment. A final aspect of this study

was to determine at what distance in front of a player were the most

critical points of observation in visually tracking an approaching ball.

In investigating the importance of observing the ball until it

is struck, the writer measured the groundstroking achievements under

conditions that prevented the subjects' tracking the ball when it was a certain distance away. This blockage of vision, ox occlusion, oc­ curred when the ball was either three, six, or nine feet in front of the hitter. Achievement scores under varying conditions of speed, oc­ clusion, and no occlusion were statistically compared.

Hypothesis

In order to study the stated problem, groundstroke achievement was measured using the Broer-Miller Tennis Achievement Test^ with modi­ fications. Possible visual observation of the ball by the subjects was controlled by using a triggering and occluding device built especially for this experiment. The equipment and procedures of the study led to the testing of these hypotheses: 1, A faster traveling ball would re­ sult in lower achievement scored under the tested conditions when com­ pared to scores earned hitting a slower paced ball. 2. Scores would improve when it was possible for the subjects to see the ball longer up until that point when their eyes could no longer track or observe it and/or the swing was committed.

Assumptions and Limitations

It was assumed that the subjects' eyes attempted to follow the ball as long as possible when not occluded.

Since vision is important in maintaining proper balance, it is possible that occluding vision affected the subject's balance and hence his swing in a manner not normally experienced. The subjects did not

^"Marion R. Broer and Donna M. Miller, "Achievement Tests for Beginning and Intermediate Tennis," Res earch Quarterly, XXI (October, 1950), pp. 303-13. complain or demonstrate obvious loss of balance during the testing, however.

The testing situation called for the subjects to hit ground- strokes from a small area behind the baseline. Subjects at times hit the ball from a position several inches in back of the baseline and still remained within the specified .hitting boundary. Several hitters found it rather unnatural to make consecutive groundstrokes without intermittent running between shots. The experimental situation also called for the ball to pass approximately ten feet away from a foreign object not normally found on a tennis court. This, too, was not a com­ pletely realistic condition in tennis.

Possible limitations of the Broer-Miller Tennis Achievement

Test as used in this study will be noted as will the possible influence of the "Hawthorne Effect."

Significance of the Study

Tennis has enjoyed great popularity in both the past and in re­

cent years. A Wall Street Journal article, noting the growth of tennis

and tennis products, estimated that approximately 7,000 new tennis

courts were built in 1968, more than twice the number built in 1965,

This brings the total number of courts in the United States to around

100,000, The United States Lawn Tennis Association estimated that

there were 400 more indoor courts in 1968 than existed in 1963, extend­

ing participation to a year-around affair for more of the estimated 2 four million tennis enthusiasts in the United States.

^"The Racket Crowd," Wall Street Journal, July 8, 1968, pp. 1 and 19. The recent Lifetime Sports project, among other influences, has encouraged physical educators to improve and perfect their instruction in tennis and other "carry-over” sports being offered in high schools and colleges. New teaching and instructional aids, drills, and teach­ ing progressions have been demonstrated in professional literature and in clinics that have been sponsored across the country.

Those who teach tennis have consistently admonished beginning players to "watch the ball.” Major Walter Wingfield, generally con­ ceded to be the father of lawn tennis due to his role in publishing the first tennis rules, included in his "Useful Hints" the advice, "Hit your ball gently and look well before striking, so as to place it in 3 the corner most remote from your adversary." Tennis champions Tilden,

Vines,^ Budge,^ and Talbert^ are also on record with the same "keep your eye on the ball” advice in their books about playing the game at which they excelled.

^Walter C. Wingfield, The Majors Game, 1873. Photostatically reproduced in Robert Henderson, Materials Relating to the Origin of Lawn Tennis. New York: Typewritten, 1931, as cited by John W. Hen­ drix, "Factors Influencing the Playing Styles of Tennis” (unpublished Ph.D. dissertation, Teachers College, Columbia University, 1955), p. 47.

^William T. Tilden, The Art of Lawn Tennis (New York: George H. Doran Co., 1921), p. 25.

^Ellsworth Vines, How to Play Better Tennis (Drexel Hill, Penn.: Ball Publishing Company, 1937), p. 11.

^Donald J. Budge, Budge on Tennis (Chicago, Philadelphia, Toronto: John C. Winston, 1939), p. 59.

^William F. Talbert and Bruce S. Old, The Game of Singles in Tennis (Philadelphia and New York: J. B. Lippincott Company, 1962), p. 92. The justification for this study is two-fold* One is the at­ tempt to add a piece of information to accumulating knowledge about man's visual perception. Secondly, it may provide some information for physical educators attempting to understand the importance of "watching the ball" in a game such as tennis. 4

CHAPTER II

RELATED LITERATURE

Vision and the ability of human beings to visually follow or track a moving object have received widespread scientific investiga­

tion. Since many sports involve a ball to which the subject must react visually, physical educators are naturally interested in this area of investigation. Despite this involvement and interest in the subject,

they have done very little research dealing with the importance of ob­

serving the ball just prior to hitting it.

Alpern, in describing the sensory processes involved in vision

and eye movements, noted the remarkable effectiveness of six extremely

fast-acting extraocular muscles which move the eye with incredible

speed. He pointed out that the two eyes in man are almost always syn­

chronized. Two eye movements described by Alpern are saccadic and

following movements. Saccadic eye movements are short, sudden changes

of fixation from one object to another. Following or pursuit movements

are the movements that the eye makes during attempts to maintain fixa­

tion on a moving object. "The precision of following movements is ex­

tremely good provided the target moves slower than 25 degrees a second.

Higher target velocities are not adequately followed by the eyes.11^

^Mathew Alpern, Merle Lawrence, and David Wolsk, Sensory Pro­ cesses (Belmont, California: Brooks Cole Publishing Company, 1967), pp. 60-61,

6 Smith and Smith differentiated among three theoretical ap­ proaches to visual tracking and perception. One point of view con­ ceived perception as a feedback process involving the nervous and muscle systems. An explanation of tracking in terms of generalized psychological function and reaction time in perceiving the target was a second approach. A third description viewed tracking behavior in terms 2 of several integrated physical systems.

Although these theories cited furnish background information for the person engaged in visual perception investigation, the studies which have involved athletes and skilled performers in physical tasks seem to be more relevant to the experiment undertaken. These studies of visual perception with athletic implications to be reviewed shall follow this sequence: athletes versus non-athletes; skilled versus

less skilled performers; and other related literature.

Athletes versus Non-Athletes

Three types of visual tests which have been administered to

athletes and non-athletes for comparative purposes are perceptual judg­ ment tests, perceptual speed tests, and span of apprehension tests. 3 4 5 Winograd, Montebello, and Olsen each found that athletes scored 2 Karl U. Smith and William M. Smith, Perception and Motion (Philadelphia and London: W. B. Saunders, 1962), pp. 54-55. 3 Samuel Winograd, "The Relationship of Timing and Vision to Baseball Performance," Research Quarterly, XIII (December, 1942), pp. 481-493. ^Robert A. Montebello, "The Role of Stereoscopic Vision in Some Aspects of Baseball Playing Ability" (unpublished M.S. dissertation, The Ohio State University, 1953), “*Einar A. Olsen, "Relationship Between Psychological Capacities and Success in College Athletics," Research Quarterly, XXVII (March, 1956), pp. 79-89. higher than non-athletes in measures of visual perception. Miller found that athletes make perceptual judgments at a faster speed than non-athletes.^ Olsen studied the span of apprehension by means of a tachistoscope which flashed black dots on a white screen for one-fifth of a second. He reported that both varsity and intermediate athletes had a higher span of apprehension score than non-athletes.^ Thus,' the athletes excelled when compared with non-athletes in the perceptual judgment, perceptual speed, and span of apprehension tests reported.

Skilled versus Less Skilled Performers 8 9 Montebello and Zigrossi, in separate theses, examined the re­ lationship between scores on tests of vision and batting averages of baseball players. In both instances the relationship between superior vision scores and higher batting averages was not significant.

An individual tracking a moving object will attempt to make corrective visual movements in order to catch up and stay with the target. It seems reasonable to assume that with practice and experi­ ence this ability to track the ball may improve. The eye movements of good hitters, as they visually track a fast moving ball, were observed

^Donna M. Miller cited in Bryant J. Cratty, Psychology and Physical Activity (Englewood Cliffs, New Jersey: Prentice-Hall, Inc., 1968), p. 111. 7 Olsen, op. cit. g Montebello, op. cit. 9 Norman A. Zigrossi, "An Analysis of the Relationship Between Visual Performance and the Batting and Slugging Average of College Baseball Players," Abstract in Completed Research in Health, Physical Education, and Recreation, IV (1962), p. 50. as "smoother" than the eye movements of inferior performers in studies

by Hubbard and Seng and by Mott. Oxendine observed that "some per­

sons are able to develop a smooth pursuit movement while others must 12 rely upon jerky (jump-pause, jump-pause) action."

A split-second reaction to observed stimuli is not uncommon in

athletic competition. Visual and kinesthetic cues are used to provide

vital information in perceptive analysis. Lawther summarized the role

■ of visual cues and visual perceptions as he described the skilled ath­

letic performer.

The highly skilled performer keeps his attention directed toward cues for succeeding acts while turning present activity over to the custody of automatism . . . The highly skilled adult integrates movements automatically in terms of cue perception. He looks ahead to discover when and where to perform certain acts. He learns to tie significant cues to appropriate responses. He also is learning many fine discriminatory recognitions. With experience and prompt knowledge of action-results, he gradually refines and abbreviates his cue recognitions. Much of the learn­ ing at the high skill levels in this refinement is perceptual discrimination . . . There is much empirical but little experi­ mental evidence to indicate that the speeding up of cue recogni­ tion is a part of high skill learning in competitive sports . . . The high-level performer catches many cues from a brief peripheral view which, as a beginner, he could only recognize by direct focus and a longer look . . .13

^Alfred W. Hubbard and Charles N. Seng, "Visual Movements of Batters," Research Quarterly, XXV (March, 1954), pp. 42-57.

*^Jane A. Mott, as cited in Cratty, op. cit., p. 110.

12 Joseph B. Oxendine, Psychology of Motor Learning (New York: Appleton-Century-Crofts, 1968), p. 289.

13John D. Lawther, "Motor Learning at the High Skill Levels," Academy Papers, I (Tucson, Arizona: The American Academy of Physical Education, 1967), pp. 39, 40, and 42. Other Related Research

Herrold studied the importance of normal vision with beginning and advanced women tennis players under the seven visual conditions of normal vision, left eye occluded, right eye occluded, and vision dis­ torted using four types of aniseikonia lenses. The purpose of the lenses .was to degrade vision and to disturb the subject's depth percep­ tion. Her subjects wore glasses with one eye occluded during the en­ tire flight of the ball. Herrold's results confirmed the hypothesis that norm. * hi -cjlar vision is a contributing factor in the perform- 14 ance of dynamic movement in tennis skills.

Four depth perception studies as related to tennis have been reported. Graybiel and his associates reported that tennis players had been found to possess better depth perception than football play­ ers. Mail concluded that some aspects of binocular depth perception 16 were positively related to proficiency in learning to play tennis.

Tomlin, on the other hand, using the Howard-Dotman depth perception apparatus and a special adaptation of the same apparatus to measure depth perception of a moving object, found no significant correlations between depth perception scores and results on a tennis wall volley

14 Judith A. Herrold, "An Exploratory Study of the Role of Binocular Vision in Performance of Dynamic Movement in Tennis Skills," (unpublished Ph.D. Dissertation, The Ohio State University, 1967). 15 Ashton Graybiel, Ernst Jokl, and Claude Trapp, "Russian Studies of Vision in Relation to Physical Activity and Sports," Re­ search Quarterly, XXVI (December, 1955), pp. 480-485.

^Patricia D. Mail, "The Influences of Binocular Depth Percep­ tion in Learning of a Motor Skill," Abstract in Completed Research in Health, Physical Education, and Recreation, VIII (1966), p. 90. 11 test,*^ Junior Davis Cup tennis players demonstrated no significant correlation between depth perception and success in tennis when exam- 18 ined by Malmisur.

Another area of study in athletics has been peripheral vision, called "field of vision" by some researchers. It refers to one's abil­ ity to see to the side while looking ahead. Oxendine stated that most individuals are able to see about 90 degrees to each side while looking straight ahead. He also wrote that peripheral vision cannot be appre­ ciably improved by practice, but one might become alert and make greater 19 use of his innate field of vision. Graybiel and associates, who re­ viewed some Russian research, reported that performance deteriorated significantly in certain track and field events when peripheral vision

■t j . 2 ° was excluded.

Size, speed, and angle of object approach as they are visually perceived have all been studied. Reynolds found that a small moving object resulted in duration estimates somewhat shorter than those for 21 an object twice as large which traveled at the same speed. Cratty

17 Frances A, Tomlin, "A Study of the Relationship Between Depth Perception of Moving Objects and Sports Skill," Abstract in Completed Research in Health, Physical Education, and Recreation, IX (1967), pp. 89-90. 18 Michael C, Malmisur, "Selected Physical Characteristics of Junior Davis Cup Players and Their Relation to Success in Tennis" (unpublished Ph.D. dissertation, The Ohio State University, 1966). 19 Oxendine, op. cit. 20 Graybiel, op. cit. 21 Horace N, Reynolds, "Temporal Estimation in the Perception of Occluded Motion," Dissertation Abstracts, XXVIII (July, 1967), p. 367B. 12 wrote, "The more rapidly an object is seen to get larger when approach- 22 ing, the faster it is perceived as traveling." Tracking errors in­ creased when target motion increased from an average speed, according 23 to Brown. Mott found that the angle at which a ball approaches an individual affects the accuracy with which he is able to perceive its 24 speed and the point he may intercept it.

Sherman and Mooney conducted a series of visual training ex­ periments with the 1948 Ohio State varsity football and basketball teams. One phase of the testing involved the use of a visor which was worn by a passer. The football player began with the visor in a down position. Just prior to the receivers' signal to run, the passer was told he would soon be signaled to pass to a receiver wearing a particu­ lar colored jersey. Three receivers wearing different colored jerseys then ran specified pass patterns downfield. At the moment the receiv­ ers reached a proper distance, the signal was given to "flash the flap." At that signal the visor was lifted manually by an assistant using a string attached to the visor. The visor was then allowed to drop almost immediately and the passer, without vision, then passed to the receiver wearing the assigned jersey. Limitations of this study include the manually operated equipment and evaluation of experimental success which was attempted by comparing the 1948 teams' won-loss

22 Cratty, op. cit. 23 Robert H. Brown, "Visual Sensitivity to Differences in Velocity," Psychological Bulletin, LVIII (March, 1961), pp. 89-101. 24 Mott, as cited in Cratty, op. cit., p. 110. 13 records and game passing statistics with those compiled by the 1947

teams which had been without this particular visual training program.

Sherman and Mooney, nevertheless, concluded on the basis of these com- 25 parisons that the "Flash Training" was successful.

Studies by Hubbard and Seng and by Slater-Hammel are also most pertinent in their relationships and implications for the study being reported. Hubbard and Seng analyzed, primarily through cinematography,

the visual tracking movements of the eyes of twenty-nine major league baseball players during batting practice. They reported that tracking movements of the batters' eyes stopped while the ball was still eight

to fifteen feet from the plate. Hubbard and Seng concluded that .either

further tracking would provide no useful information after the swing of

the bat had begun or that pursuit movements of the eyes break down due

to the high velocity with which the pitched ball approached the hitter,^

Slater-Hammel measured the time lapse of an eye blink to be be­

tween .04 to .09 seconds. In a baseball situation he estimated that the

pitched ball would cover the distance of approximately nine feet during 27 an average blink blackout of a batter.

25 Hoyt Sherman and Ross Mooney, Report on the Visual Training of the Varsity Football Team and Varsity Basketball Team. Research Program on Seeing-and-Doing, The Ohio State University, March 1, 1949, 26 Hubbard and Seng, op. cit. 27 A. T. Slater-Hammel, "Blackout Intervals During Eye Blinks," Research Quarterly, XXIV (October, 1953), pp. 362-387. I

14

In summary, athletes scored higher than non-athletes in meas­ ures of visual perception, perceptual speed, and apprehension. It has been suggested that the highly skilled athlete has an improved ability to use cues and responds appropriately. The relationship between depth perception and achievement in tennis has not been definitely estab­ lished. Superior baseball hitters have been reported as having

"smoother" eye movements. High visual scores did not correlate sig­ nificantly with higher batting averages in baseball. The baseball studies by Hubbard and Seng and by Slater-Hammel indicate that a hitter does not normally see a ball the entire time until its contact with his bat. One could speculate that induced occlusion that blocks the indi­ vidual's view of the ball would have little negative effect once the ball gets to the point where the eyes "break down" in their attempt to continue tracking or observe the ball and/or at the point where the swing of the bat or racket is too committed for any last instant changes.

Little has been done experimentally to illustrate that a tennis player needs to see or track the ball until he strikes it with his racket. The above-mentioned studies by Hubbard and Seng, Slater-Hammel, and a previous quote by Alpern lead the writer to believe that in fact it is often impossible for him to do so, A primary reason for the breakdown of the eyes is not the speed of the ball alone, but the change of the angle as the ball nears and passes to the side of the hitter. Obviously the hitter cannot consider one without the other, but the importance of angular movement of the ball to the side of the body is an extremely important factor as the eyes gather movement in­ formation. \

CHAPTER* III

METHODS AND PROCEDURES

Data for this study was gathered in November of 1968 on the

Ohio State University campus. The tennis court used was located inside

the French Fieldhouse. The court's playing surface was a type of as­ phalt finish known as Laykold. The color was green. The court was in good repair, the background was good, and the conditions were appropri­ ate for championship performance. Green tarpaulins were used to cover windows or doors to prevent a glare from the sun. The overhead light­

ing was adequate.

Subjects

Eleven experienced male tennis players were tested. The number

of years which the subjects had played tennis ranged from five to

twenty-two. They had all competed and excelled on high school and/or

college tennis teams and are still actively competing in tennis tourna­

ments. Two have held national rankings.

All subjects normally played tennis without glasses.

All but one subject had played regularly on the indoor court

where the testing occurred. Six had played or practiced on the court

over 100 times previous to the testing.

Table I includes the subjects' heights, weights, ages, and

years of playing tennis,

15 TABLE 1

HEIGHT, WEIGHT, AND AGE OF ALL SUBJECTS AND YEARS OF PARTICIPATION IN TENNIS

Number of Years Player Height8 Weight*3 Age Playing Tennis

B.H. 185.37 77.27 22 7

J.C. 169.54 65.91 26 9

D.B. 192.98 76.36 18 8

B.C. 180.27 72.73 20 6

P.W. 182.85 75.00 26 14

R.B. 187.88 83.64 19 5'

R.B. 185.37 75.00 28 18

R.B. 180.27 79.55 17 5

C.M. 180.27 79.55 23 13

D.S. 169.54 77.27 33 22

J.P. 170.15 59.09 22 15

M = 28.13 M = 74.67 M = 23+ M = 11+ SD = 1.0 SD = 7.5 SD = 4.9 SD = 5.7

£ Height in centimeters, 1 inch = 2.54 centimeters

Weight in kilograms, 1 kilogram = 2 . 2 pounds r'

L'quipment and Apparatus

.-3a 1J, Throwing Machine. Two Bell-Boy machines were uti:i .:a in

the testing to throw tennis balls to the hitters. For ide;l ; C ■,._auion

purposes one was marked "medium speed" and the other r i'.t . .;peed," The

"medium speed" machine had a slightly higher throvi ;-.y trajectory and

ordinarily the ball it threw landed within a tU'iameter approxi­ mately five feet), the center of which was j J tuna sud one-hall feet in

r*roat of the baseline and the hitter, Th: Vi'tl which was thrown from

tiie "medium speed" machine was travclir ;, ; proximo' uly f out teen miles pep: hour when it was hit. The ‘f,..; eueed" machine threw o ball which traveled approximately sixteen m ’-i-s par hour as ic -wa-s being hit. It ordinarily landed within ;> c ^ ' 'o the same size as that cited for the "medium speed" throw, the cent/1 o' which was eleven feet in

front of the baseline and the waiting hitter. The locations from which

the machines operated were marked on the court and were identical, The

front of the machines from which the ball departed was five feet in

front of tha baseline across the net from the hitter.

Each machine had a ball rack which held over forty balls. The machine released a ball every five seconds.

Sensing and Triggering Devices.*- The sensing and triggering devices used in this study included a bank of eighteen photoelectric

cells mounted one ' three-O" rter inches apart in an aluminum pole.

These ii&ht-censiti yhotoel ■ trie cells were illuminated by a large

24-volt sealed beam bulb. lIk v.oelectt : - cells change their resistance

^See Append in V 18 proportionally to the amount of light striking their sensitive surface, and therefore a shadow cast by a passing tennis ball on any one of the cells caused an electric reaction that resulted in a de-energization of a magnetic coil mounted on a pair of outfielder glasses. At this time the lenses, being spring-loaded, were freed and swung down.

Occluder. The occluders were a pair of glasses commonly worn by outfielders in baseball. The uniqueness of the glasses as used in baseball is that they have swinging lenses which can be set in an "up position" allowing normal vision or they can be tapped from above, causing them to swing down and serve as sunglasses. For the experiment a slight spring adjustment was made. Also, a coil was mounted above the rims for the purpose of magnetically holding the lenses up (a piece of metal was soldered to the top of the lenses) until a circuit was broken, at which time the spring-loaded lenses swung down. The lenses were painted black so that vision forward was occluded once they had dropped.

Control Box. The control box contained much of the wiring, printed circuit boards, SCR’s, and other important electrical equipment involved in the entire system. On the control box was a reset button which was used in the process of electrically resetting the glasses to the "up position" and to prepare the system for the next trial. If the reset button was depressed when the ball passed through the beam, the glasses remained up. The non-occluded attempts were controlled in this manner by the equipment operator. 19

Visual Conditions

There were a total of eight visual conditions for each of the forehand and backhand series of shots. These visual conditions are presented in Table 2.

TABLE 2

CONDITIONS OF OCCLUSION OR NON-OCCLUSION WITH THE BALL THROWN AT MEDIUM OR FAST SPEEDS UNDER WHICH THE SUBJECTS ATTEMPTED THE GROUNDSTROKES

Medium Speed Fast Speed

No occlusion No occlusion

Occlusion when the ball reached Occlusion when the ball reached a point three feet in front of a point three feet in front of the baseline the baseline

Occlusion when the ball reached Occlusion when the ball reached a point six feet in front of a point six feet in front of the baseline the baseline

Occlusion when the ball reached Occlusion when the ball reached a point nine feet in front of a point nine feet in front of the baseline the baseline

2 Broer-Miller Tennis Achievement Test

The Broer-Miller Tennis Achievement Test was selected because it places a premium on low, long drives in measuring the groundstroking achievement of subjects. A student dropped and groundstroked fourteen forehand shots and fourteen backhand shots in the original Broer-Miller

2 See Appendix B, 20

Test. The ball was to be hit under a rope stretched across the court four feet above the net for a full point total. Balls passing over the rope scored one-half the value of the area in which they landed. The scores and scoring areas were those indicated in Figure 1.

Hitting Areas points 2

I—

Figure 1. Scoring Areas for Broer-Miller Tennis Achieve­ ment Test.

Broer and Miller reported a reliability of .80 i .043 and a validity of ,85 for intermediate players using this system.

A modification used in this study was the use of a Ball-Boy machine, which projected the ball toward the experienced players.

McDonald compared scores using the Broer-Miller scoring system with the drop method and with the Ball-Boy machine delivering the balls. He re­

ported that, based upon three judges' ratings of ability to drive a

tennis ball,1 the test, when the Ball-Boy machine was utilized, was more

valid for intermediate players. McDonald noted that the two methods 21 3 seemed equally reliable. In a pilot study the investigator found the

Broer-Miller Test as used in this investigation to be a discriminating achievement test between players judged as advanced and intermediate.

Limitations of the Broer-Miller Test using the Ball-Boy machine

Were that the seven-foot restraining rope was at times in the line of flight.of the machine’s throw and that the rope made it difficult to achieve the maximum score of eight when the player returned a high bouncing ball.

Procedure

The Test. The tennis court was marked off with masking tape and the restraining rope was positioned as specified by the Broer-

Miller Tennis Achievement Test. Points were marked off with chalk in the hitting areas to aid the assistants in calling out the score of each hit. The point values for forehand and backhand drives were eight,

Six, four, two, and zero. A higher score indicated that a better groundstroke was hit. A subject could score a "zero” by hitting the ball into the net or wide to the left or to the right of the singles court. If a ball was stroked over the rope stretched above the net, one-half of the point value was recorded. If the machine threw a ball

that hit the restraining rope or that required lateral movement over

3 KayeMcDonald, "A Comparison of the Broer-Miller Forehand Drive Test and a Modified Form of the Broer-Miller Forehand Drive Test in Which a Ball-Boy is Employed to Deliver the Ball,” Abstract In Com­ pleted Research in Health. Physical Education, and Recreation, II (1961), p. 38. I

22 approximately twenty-four inches by the subject, the subject was in­ structed to let the ball pass and wait for the next accurate throw.

The test as used in this experiment consisted of hitting forty- two balls under each of the conditions of occlusion and ball speeds for the forehand and backhand. Fourteen of the forty-two were selected 4 randomly to be occluded. Non-occlifsion scores were also selected ran­ domly for purposes of comparison.

' Administration. Previous to each testing period the assistants were instructed concerning their responsibilities and duties.

The pole with the photocells and the apparatus holding the floodlight involved in the triggering system were placed at either three, six, or nine foot spots marked on the court in front of the baseline and to the side of the hitter. The visual conditions, ball speeds, and forehand or backhand groundstroke hitting rotations were chosen randomly and varied from subject to subject.

Previous to testing, each subject 1) read the instruction 5 sheet, 2) warmed up by hitting groundstrokes for ten minutes, 3) put on the occluders and hit ten balls thrown from the Ball-Boy machine with no occlusion involved, 4) stationed himself in the hitting area along

the baseline and, wearing the occluders, was given five practice hits

in the upcoming testing situation where the glasses dropped at either

the three, six, or nine foot occlusion spot. Then each subject hit forty-two groundstrokes while his scores were recorded,

4 Herbert Arkin and Raymond R. Colton, Tables for Statisticians (New York: Barnes and Noble, Inc., 1963), pp. 158-159. 5 See Appendix C. 23

When one phase of the testing was completed, the photoelectric

cells and floodlight were moved to a new location, five practice throws

again were given with the glasses dropping, and then again the actual

testing began and the scores were recorded. This was repeated until a

total of 504 hits made under all conditions of speed, occlusion, and

non-occlusion were recorded. The testing time was approximately one

hour and forty-five minutes for each subject.

Scoring. The equipment operator recorded an "8," "6," "4,"

n2," or "0" on each groundstroke after the assistants had noted where

the ball landed and called out the appropriate score. A form was de­

signed especially for this test.^ After the 504 hits under all condi­

tions and speeds were recorded, the subject filled out information at

the top of the recording form giving information on his tennis back­ ground .

Important Controls

Weight of the Ball. Sixty Wilson Championship tennis balls from newly-opened pressurized cans were used in the study. The weight of the balls was between 54 and 57 grams from the beginning of the

testing until the final subject had completed the test. Measurement was made on an Arthur H. Thomas scale-Seko chain-weight 356-M. The sixty tennis balls received equal use. The testing was completed in a

ten-day period to insure the freshness of the tennis balls.

Court Markings. Previous to the testing sessions, the court was marked with masking tape as specified by the Broer-Miller Tennis

^See Appendix D. 24

Achievement Test. Chalk was used to write in the points to be awarded in each scoring area. Chalk was also used to indicate the target areas in which the balls from the "medium" and "fast" Ball-Boy machines should land. The hitting areas and machine sites were also marked off.

Points three, six, and nine feet in front of the baseline where the photocells and floodlight were to be stationed were marked with mask­ ing tape.

Photocells and Occluders. The time from the activation of the photocells by the ball until the painted lenses reached the down posi­ tion was a constant 60 milliseconds. This was confirmed by repeated trials using a 564 Tektronix Storage Oscilloscope, which assured -the investigator of highly reliable equipment.

Ball Speed. Approximate ball speed was determined by recording the sound of the ball bounce and subsequent sound of the groundstroke when hit at the baseline. This time delay was measured on a Tektronix

548A Oscilloscope and Hughes Memo-corder Model 106 Storage Unit, and

the miles per hour were determined with a knowledge of the distance

the ball had traveled during that length of time.

Height of the Net. The net was three feet high at the center.

Height of the Restraining Rope. The restraining rope was seven feet from the ground.

Subjects' Hitting Area. Subjects hit the ball after its first bounce from within a three and one-half by four foot area adjacent to and in back of the baseline. 25

Instructions to Subjects. Subjects were instructed not to at­ tempt to hit balls which were inaccurately thrown or which hit the re­ straining rope. They were also instructed to continue on and do their best when the toss was accurate regardless of any occlusion or lack of it.

Tennis Equipment. Subjects dressed in appropriate tennis r clothing and used their own rackets.

Court Location. All subjects were tested on the same indoor

Laykold court surface.

Recording, Equipment Operation, and Testing Assistants. The writer recorded scores and operated the equipment during all but one testing. Ohio State students enrolled in intermediate tennis classes assisted by calling out the scores of each groundstroke and picking up and replacing tennis balls in the Ball-Boy's ball rack. The assistants were instructed to watch the ball in its flight and to call out only one-half the score normally given when a ball passed over instead of under the restraining rope. CHAPTER IV

ANALYSIS OF THE DATA

Data were gathered and analyzed on eleven subjects hitting forehand and backhand groundstrokes under conditions of visual occlu­ sion at three, six, and nine feet, and without occlusion. Each sub­ ject hit forty-two forehand groundstrokes under each of the visual conditions against a fast ball toss, forty-two against a medium ball toss under each visual condition, and then duplicated this while hit­ ting backhand groundstrokes. This made a grand total of 504 hit? which were scored per subject and 5,544 hits for eleven subjects.

Statistical Analysis '

The analysis of variance test was used to determine if signifi­ cant differences existed among the four conditions (occlusion at nine feet, six feet, and three feet and no occlusion) of each groundstroke at each speed. When the analysis of variance yielded a significant difference, the Duncan Multiple Range was used to analyze differences between particular conditions within each speed grouping. Finally, a t-test was used to determine if significant differences existed between mean results recorded using the two different ball speeds.

Table 3 indicates the mean scores and standard deviation on the

Broer-Miller Tennis Achievement Test scores under the conditions of oc­ clusion, non-occlusion, and differing ball speeds while using forehand and backhand groundstrokes.

26 TABLE 3

THE MEANS AND STANDARD DEVIATIONS OF FOREHAND AND BACKHAND SCORES* UNDER ALL EXPERIMENTAL CONDITIONS

Medium Speed Fast Speed Medium Speed Fast Speed

Forehand Backhand

No occlusion M=9 2.27 SD=10.7 M=85 SD=12.19 M=87.18 SD= 8.86 M=86.27 SD= 7.56

3' occlusion M=81.55 SD=11.59 M=87 SD=13.05 M=82.91 SENll.58 M=77.73 SD= 9.31

6' occlusion M=84.91 SIN 13,48 M=79.18 SD=13.8 M=84.18 SD=10,86 M=68.73 SEN11.08

9* occlusion M=59.73 SD=15.38 M=49.82 SD=15.78 M=64.18 SD=12.95 M=52.73 SEN 8.03

* Scores for II subjects. 28

Table 4 depicts the F-scores between the non-occluded and the three occluded conditions in each the forehand medium speed, forehand fast speed, backhand medium speed, and backhand fast speed groups of scores.

TABLE 4

ANALYSIS OF VARIANCE OF TEST SCORES OF FOREHAND AND BACKHAND GROUNDSTROKES WITH MEDIUM AND FAST BALL TOSSES

Groundstroke - Speed F-score

Forehand - medium speed 12.92s

Forehand - fast speed 17.32a

Backhand - medium speed 9.63a

Backhand - fast speed 27.33s

aP<.01 = 4.31

The results of the Duncan Multiple Range test, shown in Table

5, identify the location of significant and non-significant differences found between scores within each grouping.

The scores at the same condition using two ball speeds were

compared and Table 6 indicates at which conditions significant differ­

ences exist. I

29

TABLE 5

THE RESULTS OF THE DUNCAN MULTIPLE RANGE TEST OF SCORES ACHIEVED UNDER ALL VISUAL CONDITIONS AND BALL SPEEDS USING FOREHAND AND BACKHAND GROUNDSTROKES

Conditions Scores Conditions Scores

Forehand - Medium Speed Forehand - Fast Speed

3* - 9 ’ 21.82a 6* - 9' 29.36a

3' - 6' 3.36 N.O. - 6' 5.82

N.O.b - 6’ 7.36 N.O. - 3' 2.00

6* - 9* 25.IB8 N.O. - 9’ 13.30a

3' - N.O. 10.72 3' - 6' 7.82

N.O. - 9' 32.008 3' - 9' 37.I8a

Backhand - Medium Speed Backhand - Fast Speed

3' - 9' 18.73a 6* - 9' 16.00a

3* - 6' 1.25 3' - 6' 9.00a

N.O. - 6' 3.00 N.O. - 31 8.50a

6' - 9* 20.00a 3' - 9' 25.00a

N.O. - 3’ 4.20 N.O. - 6' 17.54a

N.O. - 9' 23.008 N.O. - 9 ’ 33.74a

a Significant

No occlusion I

30

TABLE 6

RESULTS OF THE T-TEST OF THE MEAN SCORE DIFFERENCES OF TEST RESULTS AT THE TWO BALL SPEEDS

Condition t

Forehand - no occlusion 1.92

Forehand - occlusion at 3* 1.38

Forehand - occlusion at 6’ 1.43

Forehand - occlusion at V 3.268

Backhand - no occlusion ;38

Backhand occlusion at 3 1 2.85b

Backhand - occlusion at 6' 5.708

Backhand occlusion at 9* 3.62a

8 P<.01

b P < .05

Summary

The analysis of variance indicated that a significant differ­ ence existed between some of the conditions in each of four primary groupings. The Duncan Multiple Range test indicated that significant differences existed between test scores achieved under conditions of: no occlusion and occlusion at nine-feet; occlusion at three feet and at nine feet; and occlusion at six feet and at nine feet while hitting the forehand groundstrokes with the ball thrown at the fast and medium speeds. These differences also existed while hitting the backhand groundstrokes with the ball thrown at the medium speed. A significant 31 difference was found between all conditions of occlusion and non­ occlusion while hitting the backhand groundstroke with the ball thrown at the fast speed. The t-test results indicated a significant differ­ ence between mean scores achieved at two different ball speeds on the forehand groundstroke with occlusion at nine feet (.01), the backhand groundstroke with occlusion at three feet (.05), the backhand ground­ stroke with occlusion at six feet (.01), and the backhand groundstroke with occlusion at nine feet (.01). In these instances the medium speed scores were superior.

Discussion

One primary concern of this study was to analyze to what dis­ tance ahead or in front of him the tennis player needed to see the ball in order to hit it successfully. The fact that a person can hit the ball at all with his vision blocked the last nine feet of its flight indicates the importance of careful observation well before this nine- foot distance. This would be even more important in a game situation where a person is running than it was during the testing situation used in this study that involved the steady, almost identical ball toss of the machine. Certainly observation of the oncoming ball when it is be­ tween nine and six feet away is important since scores were found to be significantly improved at the six-foot condition. Scores at the back­ hand, fast speed grouping improved significantly under each condition that allowed more observation time. While achievement without occlu­ sion and with occlusion at three feet did not ordinarily improve sig­ nificantly from scores earned at six-foot occlusion, one should not 32

interpret this as proof that a player should not try to keep visually

tracking the ball until it is hit. Even a slight, non-significant im­ provement in scores with increased vision indicates that continued ball

observation could influence the results of a match between two evenly matched opponents.

Although having his vision blocked is a disadvantage to a

player, the condition of occlusion in the experimental study could have

aided a subject in avoiding the common error of looking up while hit­

ting the ball in order to observe his opponent or to anticipate the

destination of his shot. Since a player in the study soon learned that

he could not observe anything when the dark lenses dropped, he was less

tempted to even try to look up. In addition to this slight advantage

which the experimental situation might have had, the creditable scores

achieved under the conditions of occlusion lead to mention of the pos­

sible presence of a "Hawthorne effect."*' If it were present, It

would have aided the occluded scores rather than those made without

occlusion because of the uniqueness of the occlusion which was more

experimental in nature.

Although this study seems to uphold the recommendation to

"watch the ball," there are times when players lose sight of the ball

and still manage to hit it accurately. The conditions of occlusion in

this study could be compared to the conditions present when a hitter

is momentarily blinded by the sun or blinks his eyes. Slater-Hammel

*"Dale L. Hanson, "Influence of the Hawthorne Effect upon Physi­ cal Education Research," Research Quarterly. XXXVIII (December, 1967), pp. 723-724. studied baseball players at bat and pointed out that a pitched baseball would travel approximately nine feet during a batter's blink. Tennis players, too, experience times when they momentarily lose sight of the ball, and still they are often able to hit a reasonably satisfactory groundstroke. While the experienced tennis players tested in this study had never before worn occluders when hitting groundstrokes, un­ doubtedly they have all hit groundstrokes with a less than perfect ob­

servation of the ball. Better tennis players probably possess some

innate ability to visually perceive rather successfully and this

ability has been further developed through practice and overlearning.

The results indicated that there was a point at which the eyes break down or where the.swing is too committed for any last instant in­

formation to be helpful. The fact that scores did not ordinarily im­

prove significantly once the ball passed the six-foot point is proof

that the break-off point for the eyes or swing change in this study was 2 probably in the vicinity of that distance. Hubbard and Seng found

that major league hitters' eyes ordinarily stopped tracking the pitched

ball when it was somewhere between eight and fifteen feet away. A ball

delivered from the Ball-Boy machine was traveling considerably slower

than a pitched baseball, which would allow the tennis player to con­

tinue tracking or usi#g information gathered visually at a closer

range (i.e., 6' to 9'). That the tennis players' scores under condi­

tions of non-occlusion were not ordinarily significantly higher than

those made with vision blocked six or three feet away supports Hubbard

2 Hubbard and Seng, op. cit. 34

and Seng's findings that either the eyes break down when the ball nears

the player or that visual information gathered cannot be used once his

swing is committed. - —

The effect of medium and faster ball toss speeds on hitting ac­

complishment was a stated concern of this dissertation. In seven out of

eight hitting conditions the mean scores were higher when a medium-paced ball toss was used. These scores were significantly higher, indicating greater accomplishment, with the forehand at nine feet occlusion and

the backhand with occlusion at three feet, six feet, and nine feet.

In analyzing these findings, one must consider not only the

ball speed but also the angular velocity of the ball as it is observed

by the hitter. The slower-paced ball throw allowed the waiting hitter more time before he had to begin the process of shifting his body weight and swinging his arm. Since the angular velocity increases or

decreases in direct proportion to the increased or decreased speed of

the ball, the slower-paced ball tosses allowed longer visual observa­

tion before the angular velocity became so great that the eyes could

no longer track or observe the ball.

When the ball was at a distance of fifty or sixty feet from the

hitter, the angular velocity was not likely to pose any real problem

since the ball at that point appeared to be coming straight toward him.

However, once the approaching ball bounced and moved on to the side of

the hitter, the angular velocity became increasingly greater. Even with

the relatively slow-paced throws by the Ball-Boy machines, the degrees

per second the ball traveled through the hitter's field of vision Just

prior to hitting it surpassed his visual tracking capability. 35

Thus, it seems obvious that a tennis player must rely on information gathered early in the ball's flight. First of all, the momentum and body torque required for a successful stroke demands early preparation and commitment when the ball is several feet in front of the hitter.

Secondly, as has been noted, the angular velocity of the ball nearing and passing to the side of the hitter increases so greatly that visual information-gathering at this point becomes an extremely difficult, if not impossible, task.

In general, the backhand groundstroke scores were affected negatively to a greater extent by occlusion and faster speed than were the forehand scores. This deserves a possible explanation. This writer is of the opinion that for most players the backhand ground­ stroke requires relatively better footwork and mechanics to execute successfully. In contrast, many players find they can often hit an accurate forehand groundstroke with less perfect footwork, balance, and ball observation than is necessary when hitting the backhand ground­ stroke. If one accepts this opinion, any deviation from the normal ob­ servation time could be expected to influence and cause more of a deterioration in backhand scores than in forehand scores.

Finally, the significant improvement of scores which has been noted when occlusion of vision occurred at six feet rather than at nine feet indicates that the eyes are apparently still tracking the ball or at least relaying valuable movement information during that portion of

the ball's flight. Observation of the ball when it is between six and nine feet away from the hitter is very critical for best hitting ac­ complishment. I

CHAPTER V

SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS

The purpose of this study was to examine the necessity for con­ tinued observation of an approaching tennis ball for superior ground- stroking accomplishment. Primary concerns were to determine to what distance in front of him an experienced tennis player needed to see or track the ball in making a successful groundstroke, to determine if faster ball speed affected hitting accomplishment, and to determine to what distances in the direction of the oncoming ball were the most crit­ ical points of observation in visually tracking an approaching ball.

Summary

In reviewing the literature, the writer found no evidence of comparable research. Original sensing, triggering, and occluding equipment was designed and constructed to control the visual varia­ bles. A shadow cast by the tennis ball on a photocell caused an elec­ trical reaction which de-energized a magnetic coil mounted on baseball glasses, and the opaque glasses, being spring-loaded, swung down and occluded the subjects' vision.

Using this equipment, the writer has experimentally analyzed experienced tennis players' groundstroking achievement under different visual conditions and at two different ball speeds. These conditions involved occluding the eyes, thus halting their vision, with the ap­ proaching ball at distances of three, six, and nine feet in front of the baseline. An alternate form of the Broer-Miller Tennis Achievement

36 37

Test, which involved hitting 504 groundstrokes into target areas, was administered to determine the effects of these conditions of occlusion and non-occlusion on groundstroke hitting achievement. The subjects hit from behind one baseline into target areas across the net. Ball-

Boy machines throwing at two different ball speeds were used. The faster ball traveled at an approximate speed of sixteen miles per hour as it was being groundstroked, and the slower ball was traveling ap­ proximately fourteen miles per hour when it was being hit. A record was kept of groundstroke scores achieved under the conditions of occlu­ sion and non-occlusion at two ball speeds and statistical comparison was made of randomly selected scores using the analysis of variance test, the Duncan Multiple Range test, and the t-test.

Eleven experienced male tennis players living in Columbus,

Ohio, served as subjects. These players ranged in age from seventeen to thirty-three years. All were tournament players with five or more years of tennis playing experience. Their achievement was measured on a single indoor court during the fall of 1968. Testing time was ap­ proximately one hour and fifty-five minutes per subject.

Conclusions

In answer to the stated concerns or problems, three important conclusions are drawn from the results of this study under the previ­ ously stated conditions. First of all, achievement did not ordinarily improve significantly with more observation possible once the ball was within six feet of the hitter. One notable exception was that scores earned hitting the backhand with the faster-paced ball improved 38 significantly under each condition when more observation was possible.

Generally speaking, scores did improve slightly when continued vision was permitted up until the ball was hit, thus supporting the advice that one should keep his eye on the ball for best results.

Secondly, groundstroking achievement in hitting tennis balls traveling at a faster speed was not ordinarily as high as hitting ■ against a medium-paced ball. These differences were not always sta­ tistically significant, however. The backhand was more affected by increased ball speed than was the forehand groundstroke. More time for preparation and observation with the slow ball toss and the mechanical m difficulty involved in hitting a backhand groundstroke have been of­ fered as explanations for these findings.

Thirdly, the experienced tennis players visually tracking a tennis ball received valuable information, when the ball was between six and nine feet away from them, which they used to improve their groundstroking achievement. The results indicated that the subjects found it difficult to continue observing and/or using visual information once the oncoming ball was approximately six feet away from them.

The great increase in angular velocity as the ball neared and passed to the side of the hitter has been noted. In this study the angular velocity of the thrown tennis ball greatly exceeded that cited as within the range for human tracking. The duration and usefulness of information gathered through peripheral vision once the visual tracking stopped is questionable. 39

To summarize statistically, on both the forehand and backhand groundstrokes at both medium and faster paced ball speeds, scores and achievement were significantly higher:

1) when vision was occluded at six feet than when it was oc­ cluded at nine feet,

• 2) when vision was occluded at three feet than when it was occluded at nine feet, and

3) without occlusion than when vision was occluded at nine feet.

On the backhand, fast speed, it was also found that:

1) scores achieved when vision was occluded at three feet were significantly higher than those achieved when vision was occluded at six feet, and

2) scores achieved under the condition of no occlusion were significantly higher than scores achieved when vision was occluded at three feet.

The writer accepted the hypothesis that the longer a person could visually track or observe the ball, the higher his achievement score would be. However, once the ball reached the point at which the eyes could not continue following or observing it or the groundstroke was committed, the hitter's scores did not ordinarily improve to a

level that was statistically significant with continued vision.

A second hypothesis was that faster ball speeds would have a negative effect on groundstroking achievement. In seven out of eight

testing conditions, medium speed scores were higher than faster ball speed scores with the difference being significant on:

1) forehand groundstroke, occlusion at nine feet;

2) backhand groundstroke, occlusion at three feet;

3) backhand groundstroke, occlusion at six feet; and

4) backhand groundstroke, occlusion at nine feet.

Recommenda tions

The following are recommendations for further study of the re­ lationship of vision to performance in physical activity:

1. This study should be repeated with subjects of different experience and skill levels.

2. The attempt should be made to more accurately define that point at which a player's swing is committed or he can no longer vis­ ually follow the ball by using more occlusion points and narrowing the distance between them.

3. The triggering and occluding device should be used experi­ mentally as a training aid.

4. Eye movement in normal tracking has been studied through the use of eye marking cameras and hopefully adjustments can be made so this equipment can be used experimentally in athletic situations,

5. It is possible that less skilled tennis players do not ordinarily watch the ball as long as highly skilled players. The re­

lationship between performance and ball observation deserves further analysis,

6. The angular velocity of a tennis ball traveling at differ­ ent speeds deserves more careful analysis. 1

APPENDIX A

SENSING, TRIGGERING, AND OCCLUDING DEVICE

41 42

To determine the effects of deprivation of information in hit­ ting a tennis ball, two components were designed and built,^ The first component was a pair of baseball outfielder glasses equipped with an electromagnetically-controlled opaque shutter that could be made to swing down and occlude vision when worn by the subject, A second com­ ponent was a sensing and triggering .device which was activated by the passage of the tennis ball between the device and a light source. This device, in turn, released the opaque lenses.

Basically, the triggering system consisted of eighteen photo­ cells connected in an OR configuration and illuminated by a single high intensity light source.

The lenses on the glasses were held up by an energized electro­ magnetic coil. When a shadow cast by the ball broke the light source, the output of the gate circuit triggered an SCR in parallel with the magnetic coil, thus de-energizing the magnetic coil and causing the spring-loaded lenses to drop. The Ball-Boy machine threw the ball to pass approximately ten feet away from the pole in which the photocells were mounted. This assured a clear shadow on at least one of the photocells spaced one and three-quarters inches apart.

Lights on the control box indicated which photocell had been i triggered and hence the height of the ball as it passed in front of the photocells.

*The following description of the equipment was made by Mr, Larry Tracewell with minor alteration. Mr. Tracewell designed the system being described. 43

A reset button was used to return the glasses to the "up” posi­ tion and to prepare the system for the next trial. If the reset button was depressed when the hall passed through the beam, the glasses re­ mained up.

Some restriction on the use of the system included the fact that the intensity of the light source and its position relative to the photocells were critical. The correct intensity and position were de­ termined readily by trial and error. It was also necessary that the surface of the photocells be positioned so that they were within a few degrees of being perpendicular to the beam of light.

Because zener diodes(which are noted on the schematic) were deleted from the circuit, it was important to insure that the control box be kept "off” except when the photocells were illuminated. The control box itself was also reset as soon as possible in order to pre­ vent damage to SCR #19. Both of these last two problems could be elim­ inated with the addition of the zener diodes.

It wasfound necessary to use a large 24-volt sealed beam bulb as a luminaire for the system. This bulb has an expected life of about

30 hours at 24 volts.

When the velocity of the tennis ball was increased, it was nec­ essary to increase the sensitivity of the photocells. This was done by using the sensitivity control on the side of the metal control box.

The control was numbered from one to ten with the lower number indi­ cating higher sensitivity. Increasing the sensitivity of the photo­ cells makes the problem of the placement of the light source with respect to the photocells more critical. I

kk

Number ^ type of photocells was used. If the decrease in decay time that is achieved by increasing the intensity of the light source

Is not great enough, then number 7 type of photocells can be used to further decrease the decay time.

The response time of the system (i.e., the time from the pas­ sage of an object in front of the photocells until the glasses were completely down) was determined using a Tektronix 56^ Storage Oscillo­ scope. This response time was found to be 60 milliseconds.

The unique characteristics and capabilities of the SCR and the photocells and their roles in the overall theory of the circuit's oper­ ation are as follows:

The SCR is a semiconductor, a rectifier, a sensitive amplifier, and a static latching switch capable of operating in microseconds. As a latching switch the SCR is an "on-off" switch. The SCR can be turned

"on" by a momentary application of control current to the gate. A pulse as short as a fraction of a microsecond will do so. In short, the SCR latches into conduction providing an inherent memory.

Photocells are basically light-sensitive resistors that change their resistance proportionally to the amount of light striking their sensitive surface. Two types of cells are available: the cadmium sul­ phide cell and the cadmium selenide cell. Although the former was used in this apparatus, the latter is a faster-acting, highly sensitive photoconductor that has a better response to the infrared region.

There were three power supplies. The first supply was an adjust­ able supply (from 0 to 2UV DC). This supply was used for the SCR gate supply. The second supply was a 2l*V DC supply used for producing the 45 primary source for SCR’s one to eighteen and illuminated each indica­ tor lamp.

With respect to the SCR #1 circuit, if the photocell was illum­ inated, its resistance was low (around 2,000 ohms with 100 foot candles).

The R^ on the schematic is a fixed value (47,000 ohms) so most of #1 supply voltage was dropped across this resistor. The SCR #1 was not conducting but was an open circuit.

When a shadow was cast by the ball, the photocell resistance went up to around .5 megohms, dropping most of supply #1 across the cell. SCR #1 required .8 volts at the gate to latch into conduction.

This momentary higher voltage drop across the photocell turned SCR #1 on. The lamp then turned on. This resulted in a voltage drop across

R 20 of one volt. However, this was enough gate voltage to fire SCR

#19 which was in parallel with the magnetic coil. When SCR #i9 was conducting, its resistance was very low (near 0 ohms), effectively

shorting out the electromagnetic coil. Resistor R 19 limits the cur­ rent which flows through SCR #19. Reset was accomplished by interrupt­

ing supply number two and supply number three voltage, enabling the

SCR15 to become unlatched.

In short, a shadow cast by the ball on any one of the photo­

cells caused an SCR circuit to latch on. Regardless of the number of

SCR circuits latched on, SCR #19 was triggered, which de-energized the magnetic coil, and the opaque glasses, being spring-loaded, swung down. in o ^ 2 m w co r* a n ■«£ in & > > •? m v9 1 a. m n 8 ^ 0 00

O U 111 u 2 £ go : ® "> pj ^ - ~ r \ — Q^iJ •— ■ ' ^ M ___ 4 ^ hi C i < (0 U £^.i— od tit fa}, pi -Jh-». £ «7 — tr>

X IT' --- r v

i't___

+i

t \. APPENDIX B

BROER-MILLER TENNIS ACHIEVEMENT TEST

47 4B

Description of the Test^

The test was designed to measure students' ability to place forehand and backhand drives into the backcourt area. It consisted of hitting a given number of balls so that they would pass between the top of the net and a .restraining rope placed above the net, and of at­ tempting to place these balls into the back 9 feet of the court. The ball was put into play by the student bouncing the ball to herself.

A. Equipment

1. One regulation court.

2. One regulation net with a rope stretched 4 feet above the top of the net. Note: The most effective drives are those that are hit with a good deal of force into the backcourt. This restraining rope is a device to measure, to a degree, the force of the drive. A ball passing between the net and this restraining rope and landing in the backcourt area must have been hit with more force than a ball going high (over the rope) and landing in the same area. Driver constructed a tennis test which made use of the restraining rope placed 7 feet above the top of the net. However, dur­ ing experimentation it was observed that a restraining rope placed that high did not discriminate between players of varying ability; i.e., it was possible for a player to hit balls slowly and with little force 7 feet high and have them hit in the backcourt and therefore score as high as a player who hit fast low drives.

3. One racket and 15-20 balls in good condition.

4. Score sheets for each player and pencils.

5. Special court markings.

a. Two chalk lines drawn across the court 10 feet inside the service line and 9 feet outside the service line and parallel to it,

b. Two chalk lines drawn across the court 5 feet and 10 feet, respectively, outside the baseline and parallel to it.

c. Chalked numbers in the center of each area to indi­ cate its scoring value.

^Broer-Miller Achievement Test, op. cit., pp. 309-11. I

49

B. Test

1. The player taking the test stands behind the baseline, bounces the ball to herself, hits the balls and attempts to place them in the back 9 feet of the opposite court,

2. Each player is allowed fourteen trials on the forehand and fourteen trials on the backhand,

3. In order to score the values as shown on the figure, balls must go between the top of the net and the rope and lahd in the designated area or on lines bounding the area (balls landing on a line receive the highest score for that area).

4. Balls which go over the rope score one-half of the value of that area in which they land.

5. If the player misses the ball in attempting to strike it, it is considered a trial.

6. Let balls are taken over.

C. Scoring

1. The number of each trial is marked on the score card dia­ gram in the relative position as the ball landed on the court.

2. Each ball hit is scored 2-4-6-8-6-4-2, depending upon the area in which it lands. Note: Each ball going over the rope is scored one-half of the value of the area in which it lands (this may be indicated by circling the ball number on the scoring diagram).

3. The total score equals the sum of fourteen balls on the forehand and fourteen balls on the backhand. 1

APPENDIX C

INSTRUCTIONS

50 51 This adaptation of the Broer-Miller Tennis Achievement Test measures one's ability to hit low, long forehand and backhand ground- strokes into the singles court across the net. The diagram below il­ lustrates the points given for hits landing in each portion of the court--note drives going beyond the baseline also receive points.

The ball should be hit underneath the rope stretched across the top- of the net for full point value. If your groundstroke travels over the rope you are given only one-half the value of the area in which it lands. Balls hit wide of the singles court or into the net receive no points. Naturally the object is to score as many points as possible.

At times the lenses on the glasses you will be wearing will swing down. You should go ahead and hit the best groundstroke possible on each ball tossed to you whether the lenses swing down or not. You reset the lenses by lifting them up to their original position before your next shot.

You are to stay behind the baseline and hit each ball after the first bounce. If the ball toss hits the rope coming over or if the ma­ chine throws the ball too far away forcing you to move beyond the indi­ cated forehand and backhand hitting areas, just make no effort to swing at the ball--wait and hit the next ball to be thrown from the machine.

i— + - 5' 15' 9* 9' 10' I 11' distance Hitting i Areas points 2 ]4 6 8 1 6 4 [ 2

\

i 1 __ I

APPENDIX D

SCORE SHEET

52 53

SCORE SHEET Name______Date Number of years you have played tennis . Most outstanding tennis playing accomplishment ______. Approximate number of times you have played tenths on the French Fieldhouse tennis court . Preferred ground­ stroke______under 25; 25-50; 50-100; over 100. Have you played or practiced on the Fieldhouse court in the last week?______(Yes or No). O " occlusion Q - no occlusion Forehand or Backhand (circle) it No. M S' F M 6' F M 3' F M 9i f M 6t F M 3' F 1 o 0 o □ □ 22 2 o o 23 o □ o o o 3 □ o , o 24 o o * 4 □ o □ o 25 o o □ o 5 o □ o 0 26 □ o o o o 6 0 0 27 7 0 0 0 28 o 8 0 □ 0 0 29 □ □ o 9 0 o 30 0 10 0 0 31 o □ o 0 11 o o o 32 o □ 0 12 o 33 o o o * 13 34 o 14 o □ □ o 35 o 0 o 15 o □ o 36 o □ o o □

16 o o 37 0 o 0 17 o o o 38 0 o o 18 □ □ 0 o 0 39 □ 19 0 0 40 □ □ o □ □ 20 o 41 □ □ o o 21 42 o APPENDIX E

RAW FOREHAND AND BACKHAND SCORES

54 55

TABLE 7

NON-OCCLUDED AND OCCLUDED FOREHAND SCORES AT MEDIUM AND FAST SPEEDS

Medium Speed Fast Speed Medium Speed Fast Speed

Forehand Non-occlusion Forehand Occlusion at Six Feet

92 94 88 76 78 86 90 80 96 68 100 87 95 90 100 78 98 94 96 77 92 64 62 94 100 100 88 62 68 80 62 74 104 92 91 69 102 95 82 104 90 72 75 50 1015 935 934 871 M = 92,27 M = 85 M = 84.91 M = 79.18

Forehand Occlusion at Three Feet Forehand Occlusion at Nine Feet

88 90 68 50 80 82 81 65 86 92 62 71 86 90 50 41 80 85 45 37 76 78 52 56 93 100 62 62 52 82 52 30 96 102 44 36 82 100 92 70 78 56 49 30 897 957 657 548

M » 81.55 M = 87 M = 59.73 M = 49.82 I 56

TABLE 8

NON-OCCLUDED AND OCCLUDED BACKHAND SCORES AT MEDIUM AND FAST SPEEDS

Medium Speed Fast Speed Medium Speed Fast Speed

Backhand Non-occlusion Backhand Occlusion at Six Feet

76 90 62 78 91 88 87 69 78 88 84 75 84 94 84 78 86 76 79 54 94 70 91 70 100 88 93 76 74 84 88 46 84 92 68 58 96 95 98 78 96 84 92 74 959 949 926 756

M = 87.18 M = 86.27 M = 84.18 M = 68.73

Backhand Occlusion at Three Feet Backhand Occlusion at Nine Feet

72 69 82 62 72 66 72 47 104 94 63 58 78 73 48 51 71 74 46 51 92 92 68 38 92 86 81 58 76 70 50 47 98 80 64 46 81 74 76 57 76 77 56 65 912 855 706 580

M = 82.91 M = 77.73 M = 64.18 M = 52.73 X

APPENDIX F

ANALYSIS OF VARIANCE

57 I

58

Forehand - Medium Speed

D.F. Sum of Squares Mean Squares F

3 6462.43 2154.14 12.92a 40 6669.99 166.75

Forehand - Fast Speed

D.F. Sum of Squares Mean Squares F

3 9848.98 3282.99 17.32a 40 7583.27 189.58

Backhand - Medium Speed

D.F. Sum of Squares Mean Squares F •

3 3598.61 ■ 1199.54 9.63a 40 4983.82 124.60

Backhand - Fast Speed

D.F. Sum of Squares Mean Squares F

3 6787.45 2262.48 27.33a 40 3310.73 82.77

a P<.01 = 4.31 I

APPENDIX G

DUNCAN MULTIPLE RANGE

59 Forehand - Medium Speed

Means 9' 3' 6* N.O.

59.73 81.55 84.91 92.27

59.73 - 81.55 S5 21.82 11.13 Significant (31 to 9’) 2/ 84.91 - 81.55 VS 3.36 11.13 Not Significant 92.27 - 84.91 m 7.36 11.13 Not Significant

84.91 - 59.73 a 25.18 11.71 Significant (6' to 9') 3/ 92.27 - 81.55 = 10.72 11.71 Not Significant

4/ 92.27 - 59.73 a 32.54 12.06 Significant (01 to 9')

Forehand - Fast Speed

Means 9 1 6' N.O.

49.82 79.18 85 B7

79.18 - 49.82 29.36 11.87 Significant (6' to 9') 2/ 85 - 79.82 ' 5.82 11.87 Not Significant 87 - 85 2 11.87 Not Significant

85 - 49.82 35.18 12.49 Significant (N.O. to 9') 3/ 87 - 79.18 7.82 12.49 Not Significant

4/ 87 - 49.82 = 37.18 12.87 Significant (3* to 9') I

61

Backhand - Medium Speed

Means 9' 3' 6' N.O.

64.18 82.91 84.18 87.18

82.91 - 64.18 ss 18.73 9.64 Significant (3' to 9') 2/ 84.18 - 82.91 s 1.25 9.64 Not Significant 87.18 - 84.18 & 3.0 9.64 Not Significant

. 84.18 - 64.18 o 20 10.14 Significant (6' to 9') 3/ 87.18 - 82.91 = 4.27 10.14 Not Significant

4/ 87.18 - 64.18 ss 23 10.47 Significant (N.O. to 9')

Backhand - Fast Speed

Means 9' 6' 31 N.O.

52.73 68.73 77.73 86.27

68.73 - 52.73 SS 16 7,84 Significant (61 to 9') 2/ 77.73 - 68.73 = 9 7.84 Significant (61 to 3') 86.27 - 77.73 = 8.5 7.84 Significant (31 to N.O.)

3/ 77.73 - 52.73 S 3 25 8.25 Significant (91 to 3') 86.27 - 68.73 17.54 8.25 Significant (6* to N.O.)

4/ 86.27 - 52.73 = 33.54 8.49 Significant (9* to N.O.) APPENDIX H

PHOTOGRAPHS OF EXPERIMENTAL EQUIPMENT

62 I

PLATE I

FLOODLIGHT AND PHOTOCELLS USED IN THE EXPERIMENT

63 P H OTOj FLOOD CELLS I LIGHT I

PLATE II

CONTROL BOX AND BASEBALL GLASSES USED AS OCCLUDERS

65

PLATE III

OCCLUDERS AS WORN BY A SUBJECT

67 68 PLATE IV

EXPERIMENTAL SITE AND EQUIPMENT IN OPERATION

69

I

BIBLIOGRAPHY

Alpern, Mathew, Lawrence, Merle, and Wolsk, David. Sensory Proceases. Belmont, California: Brooks/Cole Publishing Company, 1967.

Arkin, Herbert, and Colton, Raymond R. Table for Statisticians. New York: Barnes and Noble, Inc., 1963.

Barsch, Ray H. Achieving Perceptual Motor Efficiency. Seattle, Wash.: Special Child Publications, 1967.

Bartley, S. Howard. The Human Organism As a Person. Philadelphia, New York, London: Chilton Book Company, 1967.

Boring, Edwin G. Sensation and Perception in the History of Experi­ mental Psychology. New York, London: D. Appleton-Century Company, 1942.

Broer, Marion R., and Miller, Donna N. "Achievement Tests for Begin­ ning and Intermediate Tennis," Research Quarterly. XXI (October, 1950), 303-13.

Brown, Robert H. "Visual Sensitivity to Differences in Velocity." Psychological Bulletin. LVIII (March, 1961), 89-101.

Budge, Donald J. Budge on Tennis. New York: Prentice-Hall, Inc., 1939.

Cratty, Bryant J. Movement Behavior and Motor Learning. Philadelphia: Lea and Febiger, 1967.

______. Psychological and Physical Activity. Englewood Cliffs, New Jersey: Prentice-Hall, Inc., 1968,

Freund, John E., Livermore, Paul E., and Miller, Irwin. Manual of Ex­ perimental Statistics. Englewood Cliffs, New Jersey: Prentice- Hall, Inc., 1960.

Gelhard, Frank A, The Human Senses. New York, London: John Wiley and Sons, Inc., 1953.

Gibson, James J. The Senses Considered As Perceptual Systems. Boston: Houghton-Mifflin Company, 1966.

Graybiel, Ashton, Jokl, Ernst, and Trapp, Claude. "Research Studies of Vision in Relation to Physical Activity and Sports." Research Quarterly, XXVI (December, 1955), 480-485.

71 I

72

Gregory, R. L. Eye and Brain. New York, Toronto: McGraw-Hill Book Company, 1966.

Hanson, Dale L. "Influence of the Hawthorne Effect Upon Physical Edu­ cation Research." Research Quarterly. XXXVIII (December, 1967), 723-724.

Herrold, Judith A. "An Exploratory Study of the Role of Binocular Vision in Performance of Dynamic Movement in Tennis Skills." (Unpublished Ph.D. Dissertation, The Ohio State University, 1967.

Hubbard, Alfred W. "Rebuttal to Above Comments on 'Visual Movements of Batters.1" Research Quarterly. XXVI (October, 1955), 366-368.

Hubbard, Alfred W., and Seng, Charles N. "Visual Movements of Batters." Research Quarterly. XXV (March, 1954), 42-57.

Lawther, John D. "Motor Learning at the High Skill Levels," in The Academy Papers, ed. by Donna Mae Miller and Elwood C. Davis (Tucson, Ariz., 1968).

Mail, Patricia D. "The Influence of Binocular Depth Perception in Learning of a Motor Skill," Completed Research in Health. Physi­ cal Education, and Recreation. VIII (1966), 90.

Malina, Robert M,, and Rarick, Lawrence G. "A Device for Assessing the Role of Information Feedback in Speed and Accuracy of Throwing Performance." The Research Quarterly, XXXIX (March, 1968), pp. 220-223.

Malmisur, Michael C. "Selected Physical Characteristics of Junior Davis Cup Playets and Their Relation to Success in Tennis," Un­ published Ph.D. dissertation, The Ohio State University, 1966.

McDonald, Kaye. "A Comparison of the Broer-Miller Forehand Drive Test and a Modified Form of the Broer-Miller Forehand Drive Test in Which a Ball-Boy is Employed to Deliver the Ball." Completed Research in Health, Physical Education, and Recreation. II (1961), 38.

Montebello, Robert A, "The Role of Stereoscopic Vision in Some Aspects of Baseball Playing Ability." Unpublished M.S. dissertation, The Ohio State University, 1953.

Ogle, Kenneth N. Researches in Binocular Vision. Philadelphia and London: W. B. Saunders Company, 1950.

Olsen, Einar A. "Relationship Between Psychological Capacities and Success in College Athletics." Research Quarterly. XXVII (March, 1956), 79-89. 73

Oxendine, Joseph B. Psycho logy of Motor Learning. New York: Appleton- Crofts, 1968.

Perry, Fred J. Perry on Tennis. Philadelphia, Chicago: The John C. Winston Company, 1937.

Reynolds, Horace N. "Temporal Estimation in the Perception of Occluded Motion." Dissertation Abstracts. XXVIII (July, 1957), 367-B.

Sherman, Hoyt, and Mooney, Ross. Report on the Visual Training of Varsity Football Team and the -Varsity Basketball Team. Research on Seeing-and-Doing, The Ohio State University, March 1, 1949.

Singer, Robert N. Motor Learning and Human Performance. New York: The Macmillan Company, 1968.

Slater-Hammel, Arthur T. "Blackout Intervals During Eye Blinks." Re­ search Quarterly. XXIV (October, 1953), 362-367.

______. "Comments on the Article by Alfred W. Hubbard and Charles N. Seng, 'Visual Movements of Batters.' Research Quarterly, 25: 42-57 (March 1954)," Research Quarterly, XXVI (October, 1955), 365-366.

Smith, Karl U., and Smith, William M. Perception and Motion. Phila­ delphia and London: W. B. Saunders, 1962.

Solley, Charles M., and Murphy, Gardner. Development of the Perceptual World. New York: Basic Books, Inc., 1960.

Stallings, Loretta M. "The Role of Visual-Spatial Abilities in the Performance of Certain Motor Skills," Research Quarterly, XXXIX (October, 1968), 708-713.

Talbert, William F., and Old, Bruce S. The Game of Singles in Tennis. Philadelphia: J. B. Lippincott Company, 1962.

Tilden, William T. The Art of Lawn Tennis. New York: George H. Doran Co., 1921.

Tomlin, Frances A. "A Study of the Relationship Between Depth Percep­ tion of Moving Objects and Sports Skill." Completed Research in Health, Physical Education, and Recreation, IX (1967), 89-90.

Vines, Ellsworth. How To Play Better Tennis. Drexel Hill, Pa.: Bell Publishing Co., 1938.

Wall Street Journal. "The Racket Crowd," July 8, 1968. 74

Wingfield, Walter C. The Majors Game in Materials Relating to the Origin of Law Tennis, ed, by Robert Henderson as cited by John W, Hendrix. "Factors Influencing the Playing Styles of Tennis." Unpublished Ph.D. dissertation, Teachers College, Columbia Uni­ versity, 1955.

Winograd, Samuel. "The Relationship of Timing and Vision to Baseball Performance." Research Quarterly, XIII (December, 1942), 481- 493.

Yarbus, Alfred L, Eye Movements and Vision. New York: Plenum Press, 1967.

Zigrossi, Norman A. "An Analysis of the Relationship Between Visual Performance and the Batting" and Slugging Average of College Baseball Players." Abstract in Completed Research in Health, Physical Education, and Recreation, IV (1962). 50.