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Exposure and Occluded Duration Effects in a Ball-Catching SkillR.H. Sharpa & H.T.A. Whitinga

a Department of Physical Education, University of LeedsPublished online: 13 Aug 2013.

To cite this article: R.H. Sharp & H.T.A. Whiting (1974) Exposure and Occluded Duration Effects in a Ball-Catching Skill, Journal of Motor Behavior, 6:3, 139-147, DOI: 10.1080/00222895.1974.10734990

To link to this article: http://dx.doi.org/10.1080/00222895.1974.10734990

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Journal of Motor Behavior 1974, Vol. 6 No.3, 139-147

EXPOSURE AND OCCLUDED DURATION EFFECTS IN A BALL-CATCHING SKILL

R.H. Sharp and H.T.A. Whiting

Department of Physical Education University of Leeds

Male Ss (N=48) from a university population attempted single­handed catches of lawn tennis balls delivered by a mechanical projection machine. The within- and between-S variables in a split­plot factorial design were the period for which the ball was illumi­nated (VP) and the subsequent period of occlusion (OP). Both variables and their interaction were significant sources of variation. Generally the effect of VP diminished as OP was extended. This was discussed in terms of (1) information processing time and (2) motion prediction. · With respect to the first issue, the most important variable was not VP, but a composite term VP + OP. On the second issue, support was provided for an hypothesis to account for pre­diction error raised in a previous study.

•

Recent studies in the field of human performance have considered the 1formation-processi ng characteristics involved in the performance of certain ball cills (Whiting, 1969; Whiting, Gill, & Stephenson, 1970; Whiting & Sharp, 974). A question that has received particular attention was whether it was ~cessary to view the ball all the time in order to abstract the necessary tformation for success in catching or striking the ball involved. It has generally ~en found that reducing the time for which the performer sees the ball leads to reduction in the probability of catching success (Sharp, 1972; Whiting, Alder­In, & Sanderson, 1973; Whiting et al, 1970). Thus, it had been concluded that 1 achieve optimal performance the ball must be seen over its entire flight path. 1is conclusion is now considered to be unjustified because of the limitations 1plicit in the experimental paradigm used. In particular, both the time for hich the ball could be seen (viewing period-VP) and the subsequent period for 1ich it was occluded (occluded period-OP) were completely confounded.

In an attempt to circumvent this limitation, Whiting and Sharp ( 1974) ed a design in which VP was held constant and OP was varied. In this study tching performance was shown to be curvilinearly related to OP, it being inimal at both extreme periods of occlusion. From this result it was suggested at maximum occlusion caused performance deterioration through motion ~diction errors while minimum occlusion caused performance to deteriorate as result of insufficient information processing time. The previous effect of VP /hiting et al, 1970, 1973) therefore could be explained partly in terms of

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increasing prediction error with greater occlusion, and not solely in terms of insufficient viewing time.

A question that still remained was whether the effect of OP observed in the Whiting and Sharp ( 1974) study was purely a function of the particular VP employed. Varying VP was shown to affect performance in the earlier studies­even though this effect was confounded with OP-and hence it was possible that catching performance was dependent upon the joint effect of VP and OP. The present experiment was designed to investigate this question and to clarify the effect of OP alluded to in the previous paper.

The possibility of OP representing a range effect in the previous paper suggested that a change should be made in the experimental design. Accordingly, the present study considered OP not as a with in-S variable, but a between-S variable (Poulton, 1973a, 1973b; Winer, 1962).

Method Subjects. Males (N=48) from a university population served as Ss (age

range 16 to 36 yr.). For safety reasons those persons who wore glasses were not asked to take part.

Experimental paradigm. The experimental paradigm has been described in detail elsewhere (Whiting & Sharp, 1974). Briefly, S was given the task of catching a lawn-tennis ball that remained in the dark for its entire flight excep1 for a brief period when the room was illuminated. The two independen1 variables were the interval for which the room light was on (VP) and the occluded period (OP) immediately following VP but not including the latenc) period (LP) (see Fig. 1). LP was defined in the previous paper as an interva equivalent to CNS latency plus movement time that represented the perioc immediately prior to ball·hand contact during which any change in the displa\ would have no effect on S's current response. Thus, even though the bal remained continually occluded between light offset and ball-hand contact (ir fact, until approximately 2 sec. after contact) the effective occluded period-th1 variable of interest-was only the interval between light offset and the com mencement of LP. Previous experimentation (Sharp & Whiting, 1974) ha( estimated LP at approximately 200 msec.

Apparatus. A mechanical projection machine was used to deliver whit, lawn-tennis balls 1 to S. It was adjusted so that all projected balls traversed horizontal range of 270 in. before they fell within a centrally positioned circle o 16-in. diameter and center height 60 in. marked on the wall behindS. S stoo1 with his feet 12 in. in front of this wall. Ball velocity remained reliably constan both within and between experimental days (mean horizontal velocity = 29.4: ft/sec).

The interval from ball projection to light onset and VP were preset by two-channel interval timer capable of 1-msec. precision. By presetting this unit i was possible to fix the levels of VP and OP required for a particular trial. Bot the interval timer and a timer could be started by the signals from two photoce

1 Standardized lawn tennis balls were supplied by the International Sports C1 Ltd, Barnsley, whose support is kindly acknowledged.

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Ball Catching Skill

units assembled on the projection machine chassis and located immediately in front of the point of ball projection. The timer was used to measure flight time and was stopped upon receiving an impulse via a voice-key from a mini·

• microphone. This was attached to the third phalangeal dorsal area of the middle finger of S's catching hand.

Ball Projection

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Fig. 1. Schematic illustration of the experimental paradigm.

11-Hand Contact

Ball illumination was provided by a centrally positioned 80-watt fluo­rescent tube, modified to operate on de to allow rapid rise and decay; direct

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glare was avoided by a suitably located screen. Two fixation lamps (6-v., amber colored) were positioned on either side of the slit in a screen through which the balls were projected. Depending upon his preferred hand (right/left) S stood with his right/left foot 16 in. to the left/right of the vertical projection plane and observed the same fixation lamp throughout. Each lamp was located such that when S fixated on it the ball would be seen above and below this direction of gaze a similar amount of time across all experimental conditions. To afford a least confusing display, all apparatus and E were hidden by the screen through which the balls passed, and the entire room was painted matt black.

Experimental design. A split-plot factorial design was employed (Kirk, 1968). OP was the between-S variable with levels of 0, 80, 160 and 240 msec., and VP was the within-S variable with levels of 20, 40, 80, 120 and 160 msec. Ss were randomly allocated to levels of OP and then received VP conditions randomized in sets of five with 18 such sets comprizing the total of 90 ~xperimental trials. Each S received a different random ordering of sets. The Jerformance index used was the number of balls caught divided by 18. A caught Jail was considered to be one which was held upon first contact. Ss were also 1sked to assess their timing accuracy when having missed a ball; however, these iata proved to be too unreliable for serious consideration. Flight times were ecorded to afford a comparison between actual and expected values of OP, as here was the possibility that a catcher adopting an "early"/"late" strategy night reduce/extend OP to the extent that he would be operating at an adjacent ~vel. Observation of these figures showed that this did not occur.

Procedure. Upon entering the laboratory S was read the instructions nd his preferred hand was ascertained. His task was to attempt clean catches nd to follow his attempt by informing E whether the ball was "caught,"

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"early," or "late." If he was unsure on either of the last two categories he was told to make no comment. A filament lamp was turned on between trials, and its offset was a warning to S that ball projection was imminent. At this momentS raised his hand into the approximate acquisition area and directed his gaze to the amber fixation lamp. Some 3 to 4 sec. later a ball was projected, remaining in the dark for its entire flight except for the duration of VP. Following S's attempted catch and verbal response, the filament lamp came on again2 and S rested his arm for a few sec. before the start of the next trial. Trials were spaced every 9 sec., and S received two 1-min. rest intervals spaced equally within the experimental trials.

Preceding the experimental session S received 10 trials under contin­uous illumination, then observed the lighting sequence for each VP condition followed by two practice trials under each condition. No S reported any unfavorable reaction to the lighting sequence.

Results Percentage scores for both VP and OP are shown in Fig. 2. In order to

normalize the raw data, a square-root transformation was applied (Bartlett, 1947; Kirk, 1968). The transformed scores were subjected to an ANOVA which showed OP (F=6.70). VP (F=21.17) and their interaction (F=3.26).tobe significant sources of variation (p < .01 ). Following this result, analysis of simple main effects showed OP to be significant at all levels of VP, p < .01, and VP to be significant at all levels of OP, p < .01, except at 240 msec.

At the expense of increasing the probability of making Type II errors, a relatively powerful a posteriori test was used to examine pairwise comparisons within simple effects. This was considered justified because of the small number of Ss used and substantial between-S consistency. Newman-Keuls procedure was adopted (Winer, 1962) and the results of this analysis are listed in Table 1.

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TABLE I

Results of tests on pairwise comparisons using Ncwman-Keuls procedure

VP Simple Effects

OP VP 40 80 120 160

20 0 00 00 00

0 40 00 00 00 80 0 0

120 20 00 00 00 eo

80 40 80

120 20 • 0 0

160 40 0 • 80

120 20

240 40 80

120

OP Simple Effects

VP

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160 0

40 80 160

0 80 80

160 0

120 80 160

0 160 80

160

o p < .OS

• 0 p < .01

OP ao 160 240 00 0

I

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• •• •• • •• •• 0

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Ball Catching Skill •

50

40

"" 0

10

0 80 160 240

OCCLUDED PERIOD (msec.)

Fig. 2. Percentage number of balls caught as a function of viewing and occluded period.

50

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'" 20

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0 80 ' 160 240

0 80 160

OCCLUDED PERIOD (msec.)

320 Whiting & Sharp, 1973

240 Current study

Fig. 3. Catching success as a function of occluded period.

2 Modification to the fluorescent lamp required its heater unit to be on con­tinuously. This in turn caused the lamp to fluoresce slightly when it was normally "off." To guard against S adapting to this level of illumination and consequently to avoid the possibility of him seeing the ball before or after the actual viewing period, the room light was always switched on between trials .

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Discussion A secondary aim of the study was to consider OP as a between-S

variable. Its effect could then be compared with that when it was a within-S variable (Whiting & Sharp, 1974). Fig. 3 illustrates the comparable mean scores for OP and indicates quite clearly the independence of the effect of OP on design type. The hypothesis that the effect of OP is purely a range effect can thus be discounted. The slightly better performance exhibited at all levels of OP in the current study may be considered due to sampling variability and/or a lower ball velocity making the task a little easier than before. A third factor may also have some bearing and this is discussed later.

The results illustrated the dependence of ball-catching success on the interactive effect of VP and OP. Generally, the effect of VP was most clearly marked at the shorter occlusion periods and assumed less importance as OP was extended. This is seen in Fig. 2 and is illustrated further by the pattern of significant comparisons shown in Table 1.

When OP was zero, increments in VP were followed by significant improvements in catching success until VP was 120 msec. Presumably, increasing VP within this range provided S with more time to see the ball and hence with more time to both acquire relevant flight information and to translate his perception of such information into an appropriate spatia-temporal catching response. Unfortunately it is not possible to differentiate these processes at present but it is notable that an increase in VP of as little as 20 msec. can facilitate the entire process. At this stage then it would appear that Sis limited by the amount of time he has to process flight information. This can be circumvented by increasing VP and also by increasing OP. This latter finding is illustrated in Fig. 2 where it can be seen that increasing OP by 80 msec. led to proportionate increases in performance for every level of VP.

An unexpected feature of these results was the apparent ceiling effect which was reflected in the non-significant difference between VPs of 120, and 160 msec. at OP=O msec., and between VPs of 40, 80, 120, and 160 msec. at OP=80 msec. This may represent a real ceiling effect caused by a general suppression in performance due to the unusual lighting conditions operating. Another explanation is that there is a non-linear relation between catching success and VP such that the effect of VP is less for greater durations than smaller ones. This cannot be considered viable however, because the interaction between VP and OP suggests that catching performance should really be ex­plained in terms of both these variables. Thus it was considered that a more meaningful relation would involve the total time available for processing, i.e., VP+OP. This is illustrated in Fig. 4 for all levels of VP at OP=O and 80 msec., and it can be seen that there was a systematic, negatively accelerating relation between catching performance and the total time available for processing flight information. This relationship was quantified by a curve-fitting analysis (Lewis, 1960) which showed a parabolic function to account for 93% of the perfor­mance variance. Furthermore, this curve predicted almost 100% success when the ball could be seen for its entire flight.

It appears then that it is not the time the ball is seen per se that is important when processing flight information (although there will be a lower threshold duration), but rather it is the interval VP+OP, i.e., the total time

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W 40 50 50 W 1W 140 160 180 200 220 MO

VIE\\'Ii\C PERIOD + OCCLUDED PERIOD (mseq

.

Ball Catching Skill

Fig. 4. Relation between catching performance and total processing time, i.e., viewing period +occluded period. ·

available, that is important. Furthermore, the evidence suggested that it does not matter how VP and OP each contribute to the total time; the conditions OP=80, VP=40 msec. and OP=O, VP=120 msec. both resulted in the same performance, as did the conditions OP=80, VP=80 msec. and OP=O, VP= 160 msec. This latter issue is interesting in that it reflects a similar finding observed in both the perception of static letter displays (Haber· & Nathanson, 1969) and visual persistence judgments (Efron, 1973).

The point should be raised here concerning the variable dark period between projection and light onset (see Fig. 1). It could be argued that catching success increases with total time not as a result of additional processing time but because of a concomitant decrease in the prior dark period. As these parameters covary it was not possible to isolate their individual effects statistically, although a comparison with the data from Whiting and Sharp (1974) suggested that the dark period, at least in these studies, had little effect. This stemmed from the use of different ball velocities in both experiments which meant that the prior dark

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period was different for comparable treatments (same values of VP and OP). In the current experiment this interval was approximately 125 msec. longer than in the previous study, and, as Fig. 3 illustrates, the similarity in results suggested that it has no effect. It is also notable that when commenting on the tasks' difficulty, Ss always indicated that it was based on the extent of the subsequent dark period (OP) rather than the prior dark period. Current work is investigating this particular issue especially in connection with the performer's capacity to anticipate the ball's first visual appearance.

The systematic relation between performance and total time breaks down for occluded periods greater than 80 msec. This is seen quite clearly in Fig. 2 where, regardless of VP, for increases in OP above 80 msec., performance decreased. It thus seems that the additional processing time gained by incre­menting OP beyond 80 msec was outweighed by other factors that were detrimental to performance. The simplest explanation is that those factors are concerned with motion prediction error (Whiting & Sharp, 1974). It is well known that motion prediction errors increase with prediction extent, (e.g., Foot, 1969). and so while increasing OP may provide additional processing time it also increases prediction extent which, as it becomes larger, outweighs the advantage gained by the concomitant increase in processing time. The general curvilinear trend observed in Fig. 2 may thus represent the relative extent to which the two factors-information processing time and prediction extent-each affect perfor· mance as OP is varied. This thesis was supported by S observations that as OP was increased the difficulty in catching the ball changed from one of insufficient time to deal with the task to one of increasing uncertainty of the ball's trajectory.

It is important to note that the interaction between VP and OP was still evident during the "prediction" phase, i.e., when OP was greater than 80 msec. Studies of motion prediction have often shown prediction extent to be the prime parameter governing performance (Alderson, 1973; Weiner, 1962). This effect was also evident in the current data when OP was maximal at 240 msec., although not so when OP was 160 msec. At this latter le.vel it was beneficial for S to have observed the ball for a longer period prior to the period of occlusion. This finding supported an hypothesis alluded to previously (Whiting & Sharp, 1974). It was suggested then that S's inability to predict over longer intervals was due to his uncertainty about the ball's flight path. From an information­theory standpoint this hypothesis predicts that if S's uncertainty is reduced he will make fewer errors. If it is assumed that increasing VP provides S with more time to acquire flight information-an assumption implied previously-which in turn provided him with a more informative representation of the ball's trajec· tory, then prediction over the occluded period should be easier for longer viewing periods. As this was found when OP was 160 msec. the thesis was supported. Presumably the reason why VP had no effect when OP was maximal is because the uncertainty associated with predicting over such a long interval was not reduced significantly by the information value of the greater VP. Perhaps extending VP further than 160 msec. would have aided this process.

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Ball Catching Skill

References Alderson, G.J. K. The perception and prediction of I inear motion. Paper pre­

sented at the meeting of the British Psychological Society, Liverpool, April, 1973.

Bartlett, M.S. The use of transformations. Biometrics, 1947, 3, 39-52. Efron, R. An invariant characteristic of perceptual systems in the time domain.

In S. Kornblum (Ed.). Attention and performance IV. London: Academic Press, 1973.

Foot, H.C. Visual prediction of the point of coincidence of two moving targets. Ergonomics, 1969, 12, 723-733.

Haber,R.N., & Nathanson, L.S. Processing of sequentially presented letters. Perception and Psychophysics 1969, 5, 359-361.

Kirk, R.E. Experimental design: Procedures for the behavioral sciences. Bel­mont, California: Brooks/Cole, 1968.

Lewis D. Quantitative methods in psychology. New York: McGraw-Hill, 1960. Poulton, E.C. Bias in ergonomic experiments. Applied Ergonomics, 1973, 4,

17-18. (a) •

Poulton, E.C. Unwanted range effects from using within-subject experimental designs. Psychological Bulletin, 1973, 80, 113-121. (b)

Sharp, R.H. Keep the eye on the ball! Paper presented at the 6th annual meeting of the British Society of Sports Psychology, Leeds, September, 1972.

Sharp, R.H., & Whiting, H.T.A. Prediction extent due to reaction and movement time in a single-handed catching task. Unpublished paper, Department of Physical Education, Leeds University, 1974.

Weiner, E.L. Motion prediction as a function of target speed and duration of presentation. Journal of Applied Psychology, 1962, 46, 420-424.

Whiting, H.T.A. Acquiring ball skill. London: Bell, 1969. Whiting, H.T.A., Alderson, G.J.K., & Sanderson, F.H. Critical time intervals for

viewing and individual differences in performance of a ball-catching task. International Journal of Sports Psychology, 1973, 4, 155-164.

Nhiting, H.T.A., Gill, E.B., & Stephenson, J.M. Critical time intervals for taking. in flight information in a ball-catching task. Ergonomics, 1970, 13, 265-272.

Nhiting, H.T.A., & Sharp, R.H. Visual occlusion factors in a discrete ball­catching task. Journal of Motor Behavior, 1974, 6, 11-16.

Niner, B.J. Statistical principles in experimental design. New York: McGraw­Hill, 1962.

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