Of Cognitive Fallacies, Streaks and the "Hot Hand" in Volleyball

Human Frailty

For many years psychologists have studied the human tendency to see patterns where none exist.  We look for patterns in random data and we see patterns in random events.  In studies of probability guessing where colors are randomly presented, but weighted to appear with different probabilities, humans guess the next color by trying to guess the pattern and rats just go with the color that appears most often in the series, and with that, humans allow themselves to be outperformed by rats.[1]

We don't do so well analyzing situations involving chance.  We do even worse when we feel uncertain or out of control.  Randomness fools us because we don't recognize it.  We like to make sense of the world by seeing patterns and assigning to every event a distinct and definite cause.  So our thinking leads us to misinterpret all kinds of events around us and to make decisions that sometimes are less than optimal and other times are flat out wrong.[2]

The world is full of "patterns of randomness" - streaks - that are routinely misinterpreted and then relied upon as if they portended a trend.  In our oceans of data we struggle to interpret correctly and sometimes see meaning where none exists.  Indeed, that's why most readers will see (or suspect) a pattern in this random sequence:      

OXXXOXXXOXXOOOXOOXXOO[3]

We see patterns everywhere, but perhaps in no context do we do so more fervently than in sports.  So let's look at our bias toward patterns as it manifests itself in the popular belief in the "hot hand."
 
The "Hot Hand"

The "hot hand" in sports has been debated for years.  Is a basketball player more likely to continue shooting well after making his first four shots?  Will a volleyball player more likely get a kill after putting away the last three balls?  Athletes, coaches and fans nearly universally accept that players running a streak of success are more likely to continue succeeding on subsequent attempts until they "cool off."

But is this really true?  Is there any such thing as a "hot hand" in sports or are we just seeing random streaks of success within a much larger performance range and body of work?  Is each hit, goal and kill independent of the one before (as in flipping a coin) or does the streak of success drive further success? 

Fallacy or Not?

In the seminal study of the hot hand in sports, psychologist Thomas Gilovich and his colleagues looked at streak shooting in basketball.[4]  Extensive shot analysis revealed no evidence that a player's chance of hitting a shot was greater following a hit than following a miss.  Indeed, Gilovich found that for nearly 90 percent of players studied, the probability of making a shot was actually slightly lower following a make than following a miss.  Accordingly, it was concluded that belief in the "hot hand" was merely "an erroneous perception of a positive correlation between successive shots" - in other words, a cognitive fallacy.

Research since then has by and large reached a similar conclusion, leading some experts to summarily state that empirical evidence of the existence of the hot hand in sports is "considerably limited."[5]

Though the hot hand may be a myth, research has spawned analysis of some interesting questions on the periphery.  Researchers have questioned what impact opponent's defensive changes have on detection of the "hot hand."  Others have examined whether belief in the hot hand, even if fallacious, can beneficially drive in-game allocation decisions and result in the optimal player getting the ball[6].

"Hot Hand" Revisited - Attacking Streaks in Volleyball

In the last six months a group of German researchers re-visited the hot hand phenomenon to determine whether it exists in the sport of volleyball and whether belief in it drives players' and coaches' decisions to distribute the ball to particular players.  The research is published in the Journal of Experimental Psychology: Applied[7].

Defining the Hot Hand

When we speak of the "hot hand" we mean more than just a performance streak.  Streaks in sports occur all of the time and have been shown in a variety of settings.  We all know that baseball players can get three or four hits in a row and volleyball players can get three or four straight kills.  A belief in the hot hand, however, refers to a belief that the streak portends a greater likelihood of success on each successive attempt.  Thus researchers in the present study defined a hot hand as a "higher probability  . . . to score again after two or more [kills] compared with two or three [hitting errors]."

What they found was rather interesting:  the hot hand exists in volleyball; athletes and coaches overwhelmingly believe in it; and both rely on it to make allocation decisions in the game.

Summary of Results

To determine whether athletes believe in the hot hand in volleyball the authors asked 94 sports science students with athletic experience at the German Sport University Cologne to respond to a questionnaire on the subject.  Eighty-six of the ninety-four athletes (91%) reported believing in the hot hand in volleyball.   In other samples taken, 90% of 21 other athletes reported and 92% of coaches also reported believing in the hot hand.

The authors next sought to determine whether that belief was founded. To determine whether a hot hand does in fact exist the researchers analyzed game performances of 26 male volleyball players from the top volleyball league in Germany.  They found that half of the players experienced a hot hand phenomenon and half did not.

Given that the hot hand appeared to exist for some players but not everyone, the authors examined how setters use their belief in the hot hand to distribute the ball.  Setters in an experiment were sensitive to both a hot hand belief and overall hitting percentages, but the "hot hand" belief was the stronger cue in actual set distribution.

Significantly, the researchers found that setters more often distributed the ball to players experiencing streaks of success and this lead to better performance than when setting the ball to the player with the higher average hitting percentage.  The authors cautioned, however, that a distribution strategy that ignores hitting percentage would be less than optimal where the differences in hitting percentage between the "hot" and the "non-hot" player compensate for the advantage of setting the streak. 

The German authors are not the first to posit that optimal play may result from setting the player with the perceived "hot hand."  A study published in 2001 by a psychologist at the University of Michigan showed that distributing the ball to the player perceived to be "hot" in basketball positively impacts the team regardless whether the hot hand phenomenon actually exists.

The studies' author demonstrated that basketball players with higher shooting percentages experience more streaks of made shots, so when streak shooting produces a perception of "hotness," distributing the ball to the "hot hand" actually results in the best shooting player getting the ball more often[8].

Why Do We Care?

So what does all this mean?  As a volleyball coach I really don't know whether the "hot hand" phenomenon exists in volleyball or not.  I do know that collectively I've played in, watched and coached thousands of volleyball games and sometimes players hit hot streaks and sometimes players hit cold streaks.  What to do with that information - I'm still learning.

But uncertainty should not shroud the more fundamental point of research on the subject - that people, coaches included, tend erroneously to detect patterns in random data and often make poorer judgments because of it.  Recognition of this fact - of the frailty of our own thinking - should inform and improve the process by which we all make decisions.

As coaches we make thousands of decisions every season.  We make personnel decisions, we decide tactics, strategies, and systems of play.  We choose whether, how and when to give feedback.  We decide whether to run practice, how long it will be, and what its design will consist of.  We even decide who will be on our teams and whether and how often they will play.  Our thinking and our choices permeate our programs and touch the lives of many, many people.  With research continuously showing our impact on the lives of other people we should care deeply about how we make decisions and at least be aware of our own frailties.  We owe it to our players and the profession to constantly search for ways to improve.

NOTES

[1]  Mlodinow, L., (2009).  The drunkard's walk: How randomness rules our lives.  New York: Vintage Books.

[2]  For two excellent books on how we make decisions when faced with uncertainty I recommend Leonard Mlodinow's The Drunkard's Walk: How Randomness Rules Our Lives and Thomas Gilovich's How We know What Isn't So: The Fallacy of Human Reasoning in Everyday Life.

[3]  Gilovich, T. (1991).  How we know what isn’t so: The fallibility of human reason in everyday life.
New York: The Free Press.

[4]  Gilovich, T., Vallone, R., Tversky, A. (1985).  The hot hand in basketball: On the misperception of random sequences. Cognitive Psychology 17: 295–314.

[5]  Bar-eli, M., Avugos, S., Raab, M., (2006). Twenty years of hot hand research: Review and critique.  Psychology of Sport and Exercise 7(6): 525-553. 

[6]  Burns, B. D. (2001). The hot hand in basketball: Fallacy or adaptive thinking? In J. D. Moore, & K. Stenning (Eds.), Proceedings of the Twenty-third Annual Meeting of the Cognitive Science Society (pp. 152-157). Hillsdale, NJ; Lawrence Erlbaum; Raab, M., Gula, B., Gigerenzer, G. (2012).  The hot hand exists in volleyball and is used for allocation decisions.  Journal of Experimental Psychology: Applied 18(1): 81-94.

[7]  Raab, M., Gula, B., Gigerenzer, G. (2012).  The hot hand exists in volleyball and is used for allocation decisions.  Journal of Experimental Psychology: Applied 18(1): 81-94 (available here).

[8] Burns, B. D. (2001). The hot hand in basketball: Fallacy or adaptive thinking? In J. D. Moore, & K. Stenning (Eds.), Proceedings of the Twenty-third Annual Meeting of the Cognitive Science Society (pp. 152-157). Hillsdale, NJ.

Visual Search Pattern Analysis Reveals Differences in How Experts and Novices See the Serve in Volleyball

In the sport of volleyball, service reception is best accomplished by athletes capable of identifying and interpreting relevant visual cues from the server and the ball and predicting where the ball will be served to and where it will arrive.  Indeed the essential key to passing, like playing defense, is the ability to anticipate the future both efficiently and correctly. 

Part of this process of anticipation involves athletes’ visual search patterns -- their eye movements -- while performing a volleyball skill.  Recent research has shed some light on this process, which helps explain one of the significant performance differences between experienced and inexperienced volleyball players.

In a study published in the International Journal of Applied Sports Sciences, researchers examined the visual search patterns of expert and novice volleyball players receiving serve and found that the two groups not only focused on different cues during the act of serving but also began tracking the ball at distinctly different times.[1]

Experts focused more on the server’s arm and shoulder area than novices did[2] and experts began tracking the flight of the serve significantly earlier than their novice counterparts.[3]  These findings suggest an important evidence-based approach to coaching reading in service reception.

It was also revealed that experts were capable of predicting the arrival point of the serve, resulting in their eyes coming off the ball immediately prior to contact, [4] while novices were unable to predict the target point and instead tried to maintain tracking all the way to contact with their platform (see Fig 1 – reproduced from original work).  This conclusion may dispel a volleyball coaching myth that passers should strive to track the ball directly into the platform.

Fig. 1

Figure 1. Frames from the mobile eye tracker video, showing the receiver’s view between expert (E) and novice (N) during the flight phase, and the direction foveal gaze as he watches it.

(1 = serve impact; 2 = 2frame after impact; 3 = 4frame after impact; 4 = ball flight peak point; 5 = 0.18sec before serve reception; 6 = 2frame before serve reception).

NOTES

[1] Lee, S. (2010).  Does Your Eye Keep on the Ball?:  The Strategy of Eye Movement For Volleyball Defensive Players During Spike Serve Reception.  Int’l J. Applied Sports Sciences, 22(1) 128-137.

[2] Location variables were the server’s shoulder, arm, head, and impact point of the hand with the ball.  Experts fixated in the server’s shoulder and arm area for 66.20% of total locations.  Novices fixated on the same areas only 7.46% of total locations.

[3] Experts began tracking the ball within a mean of 0.14 seconds after the server's contact with the ball.  Novices had a mean tracking onset of 0.21 seconds – a rate nearly 33% slower than the expert.

[4] For experts, the time between the last eye fixation on the ball and actual reception was less than 0.18 seconds.

How to Build Confidence in Your Volleyball Athletes

Confidence is king.  That's right, KING.  I've never heard anyone say confidence is queen.  That got me thinking about confidence in female athletes and in particular, how we can get better at building self-confidence in girl's and women's volleyball.

Being in a gym on a daily basis I am amazed how often successful, skilled, hard-working, well-educated, healthy, young women in the sport of volleyball lack self-confidence.  We coaches need to get better at building confidence in our players.  It's not that we don't try, but sometimes the methods most familiar and comfortable to us are woefully inadequate to the task.

How many times have we heard coaches implore their players to play with confidence?  It's well-intentioned but completely ineffective advice.  Telling someone to be confident is like advising the hungry to feel full.  Building confidence is also not a matter of being a cheerleader or puffing up players with constant praise and pats on the back.  Intelligent young woman are too smart for that.  Besides, the best available research on the subject indicates it's counterproductive.[1]  

So how do we begin moving our players toward a more confident state of mind?  It takes a consistent, creative, daily effort that begins with including in our practices successful moments for the players and by delivering effective feedback.


Put Athletes in Successful Situations

We all know that practice is about training our weaknesses, and that can be very stressful, but sometimes we just have to put our athletes in successful situations and let them do what they do best.  Success builds confidence.

For example, allow your blockers to block some balls.  Blocker don't always get a lot of positive reinforcement.  Sure, we know that blockers can do their job effectively without actually blocking the ball but there's nothing like the feeling of actually blocking a ball to build a little confidence and provide some motivation as well.  This can be done in a coverage drill, a blocking drill or both.  Be creative and let your blockers block some balls.

There are hundreds of other examples  It's up to you.

Teaching is Not Always Correcting

Let your positive feedback substantially outweigh your corrective feedback.  Too many female players cringe when they hear a coach say their name because they assume we're going to correct something they did "wrong."  If a player's first reaction when you say her name is quickly to explain herself or, worse yet, apologize then you need to build her confidence by recognizing all the correct things she does; and be specific with the behavior being complimented.  There's volumes of research on percentages and ratios for giving positive and corrective feedback.  The takeaway?  We need to develop young women who aren't surprised when we stop the action to give credit rather than correction.

Playing with confidence is something that is instilled over time by successful, creative coaching, not something players will do if we "remind" them.  Let's stop telling and start teaching.    


NOTES

[1]  See Carol Dweck, Mindset: The New Psychology of Success (Random House 2006); see also Po Bronson, How Not To Talk To Your Kids: The Inverse Power of Praise, New York Magazine, Feb. 19, 2007 available online at http://nymag.com/news/features/27840/    

Can Exercising After Practice Improve Retention of Volleyball Skills?

If you're like most coaches you may have wondered at one time or another why your athletes perform one way in practice but differently in competition.  The answer may be found in your practice design.  To best train players for competition, coaches must create practice environments that promote long term retention and transfer.  What does this mean?  It means skills learned in practice must be retained beyond the training session and must be taught in such a way that the motor programs developed in practice transfer to competition.

Retention and Transfer of Motor Skills

To help coaches do this, motor learning science has identified several prominent features of effective practice design.  Practices should train whole skills, under randomized conditions, with effective feedback, in a game-like environment that re-creates the moods and emotions of competition.  Coaches who follow these "laws of learning" enable their athletes to develop in practice the "relatively permanent improvements in the execution of skilled motor behaviors."[1] that are essential to improved performance in competition. 

Does Exercise Promote Retention of New Skills?

Want more good news?  New research out of the University of Copenhagen now suggests another potential element for promoting long term retention and learning.  Researchers in the Department of Neuroscience and Pharmacology examined the impact of exercise both on the rate of acquisition and retention of new skills and found that participants who exercised after practice retained more of what they learned when later tested for proficiency.[2]

Study Methods

Participants were asked to engage in 15 minutes of intense cycling either before or after practicing an accuracy tracking task.  The task required right-handed men to use a joy stick to trace a white line over a red squiggling line appearing on a monitor in front of them.  Researchers wanted to explore whether the exercise or its timing in relation to practice effected the acquisition or retention of the practiced skill.  Acquisition was measured during practice and retention was measured 1 hour, 24 hours and 7 days after practice.

Study Results

Regardless of timing, the cycling exercise did not significantly effect the rate of motor skill acquisition or short term (1 day) retention.  However, both exercise groups showed significant retention when measured 24 hours and 7 days after practice; and compared to participants who exercised before practice, participants who exercised after practice showed even greater retention when measured 7 days after practice.

According to researchers, these findings "indicate that one bout of intense exercise performed immediately before or after practicing a motor task is sufficient to improve the long-term retention of a motor skill.  The positive effects of acute exercise on motor memory are maximized when exercise is performed immediately after practice, during the early stages of memory consolidation."

Application to Volleyball Coaches

So what does cycling and tracking a red line have to do with coaching volleyball players?  Maybe nothing - human understanding of motor learning continues to develop.  In the meantime, this research may suggest to coaches that a short intense bout of exercise inserted at the end of their practices may enhance the long-term learning of what is taught in practice.

NOTES

[1] Bain, S., McGown, C., Motor Learning Principles and the Superiority of Whole Training in Volleyball.  Available here.
[2]  The study, A Single Bout of Exercise Improves Motor Memory, is available here.

Video Feedback and Expert Modeling Can Promote Skill Development

Feedback is a critical element of skill acquisition.  When we think of feedback we usually think of a coach giving an athlete information about her performance or perhaps the athlete receiving information directly from her own eyes, such as seeing the ball hit the floor after an attack.  Whether extrinsic or intrinsic, feedback provides athletes with information that can guide future performances.  Feedback can help athletes link cause and effect (e.g., hitting the right side of the ball causes it to move left) and provide motivation to continue training as well.  Without effective feedback, practice loses much of its purpose.

An increasingly popular form of feedback is video replay.  Video replay gives athletes a unique perspective on their performance unavailable through other means - the ability to see themselves in action (and at different speeds).  According to research, video replay combined with expert video modeling can promote skill acquisition and retention.  This research may support the use by coaches of video replay systems (such is TiVO) in the practice gym to assist athletes' skill development. 

In a study conducted at the University of South Florida a researcher examined the effects of combining expert video modeling and video feedback on the development of athletic skills used in gymnastics routines. "Video feedback" involves showing a recorded video clip of an athlete performing a particular skill (or part of it) to that athlete while "video modeling" shows the athlete a video of an expert performing the skill.

Participants were four 7-10 year old competitive gymnasts.  Each gymnast performed a specific skill and then viewed a video of an expert gymnast performing the same skill. The gymnast then viewed a replay of her own performance followed by a slow motion with freeze frame comparison of her performance with that of the expert model.  Lastly, the gymnast viewed the expert video clip again, followed by her own performance of the skill.

The results showed that the gymnasts’ skills increased following exposure to video feedback and modeling when combined with normal practice sessions.  It was also noted that "improvements were largely maintained during follow-up assessments," indicating successful skill retention as well.

Link to Study:  http://scholarcommons.usf.edu/cgi/viewcontent.cgi?article=1145&context=etd

Title: Expert video modeling with video feedback to enhance gymnastics skills.

Research Shows Younger Children Unable to Understand Negative Feedback

Research published in the Journal of Neuroscience says that 8-9 year old children learn radically different from 11-13 year olds and adults.[1]  The difference relates to how children of different ages process negative and positive feedback.

According to researchers, 8-9 year old children respond disproportionally inaccurately to negative feedback whereas the opposite is true in 12 year olds.  As negative feedback generally signals a need to adjust current behavior, the younger children have a more difficult time interpreting it.  The ability to make the interpretive leap necessary to respond accurately to negative feedback appears to develop as children become closer to the age of 11.

This information can have significant consequences for volleyball coaches teaching children under twelve.

The research, Evaluating the Negative or Valuing the Positive?  Neural Mechanisms Supporting Feedback-Based Learning Across Development is available at the Journal of Neuroscience website here.

NOTES

[1]  von Duijvenvoorde, A., Zanolie, K., Rombouts, S., Raijmakers, M., Crone, E. (2008).  Evaluating the Negative or Valuing the Positive?  Neural Mechanisms Supporting Feedback-Based Learning Across Development.  The Journal of Neuroscience 28(38) : 9495-9503.  

Reading Revisited: The Challenge of Reading Left-Handers in Volleyball

Last year I wrote about teaching the skill of "reading" in volleyball and posited that we coaches need to spend a lot more practice time teaching this skill to our players by (a) creating practice environments that afford the players game-like reading opportunities; and (b) teaching players what cues to look for and what they mean by giving effective feedback.  Here's an update.

Reading Can Be Taught

Whether we call it the "premier skill" in the game (Hugh McCutcheon) or the "most important skill" (John Kessel), it is by now settled that the skill of reading is in fact trainable and not some mystical innate talent.[1]  When we see volleyball players who always seem to be in the right place, it is because they have advanced cognitive perceptual skills developed from proper training.  A player's ability to forecast the future of the game by seeing, interpreting and responding to the visual cues presented by it is borne of deliberate practice with effective feedback in a game-like training environment. 

So why are we re-visting this great subject of reading in volleyball?  Well, the last six months has produced some very interesting research on the subject that can improve our knowledge of the game and help all of us to coach better.

The Lefty Advantage in Sports

In the last decade and a half research has shown that left handed athletes present considerable difficulties for their opponents in interactive sports.[2]  Lefties are overrepresented in many sports (as compared to their presence in the general population) and their left handedness appears to give them an advantage over their opponents.[3]  The "advantage" seems to be their opponents' greater difficulty in predicting the left-hander's behavior.  For example, soccer goalkeepers have been shown to have a more difficult time predicting ball direction for left-footed opponents,[4] and tennis athletes (regardless of their own handedness) have shown themselves to be better at predicting the direction stroke of right handed as opposed to left-handed opponents.[5]  Researchers have supposed that one explanation for this phenomenon is that players have less experience with left-handed opponents and therefore lack familiarity with their techniques and strategies, leaving opponents to act (react) the same as when faced with a right-hander.[6]  The hypothesis is referred to as the "negative perceptual frequency effect."

Reading Left -Handers in Volleyball

So this takes us to the sport of volleyball.  In a game where the premier skill of the players is accurately predicting the action of opponents, do lefties still maintain an advantage by being less "readable" than their right-handed counterparts?  A study recently published in the journal of Attention, Perception & Psychophysics says "yes."[7] 

To test the negative perceptual frequency effect in the sport of volleyball, researchers invited 18 expert and 18 novice volleyball athletes to predict the shot direction of left- and right-handed attacks.  Participants predicted the outcome of attacks using a video-based occlusion model.  To control the amount of advance visual information (and identify its importance to reading) footage of the attacks was occluded at three different time points: (a) 4 frames prior to hand contact with the ball, (b) 2 frames prior to hand contact, and (c) moment of contact.  Consistent with earlier research, participants performed more poorly predicting the shot direction of left handers, i.e., the lefties were more difficult to read.  Moreover, "the left-right bias" was most distinct when participants were required to make reads based on pre-contact cues (before contact with the ball).  According to the authors, "[t]he study’s findings corroborate the assumption that skilled visual perception is attuned to more frequently encountered actions."

Neutralizing the Left-Hander's Volleyball Advantage

So what can we coaches do with this information?  We must train in reality.  As long as left handed volleyball players continue to play the game we must expose our athletes to more left handed attacks.  We must make familiar what is unfamiliar.  If you have lefties on the team, give them a few extra swings and play defense against their attack.  Let the left handed players hit even if they're not your "hitters."  The training will be good for your defensive players and every player on the team, particularly at the junior level, should have a basic proficiency in attacking anyway.

Coach eye sequencing for your defenders and design drills that allow you to coach them while they perform in a pass-set-hit environment.  Do your defenders use the same eye sequence for lefties and righties?  Watch and coach them.  Ask your players what they see when facing the left-handed attack.  Is it the same as for righties?  Engage your athletes in a dialogue and help guide their discovery; you might find that your players are not focusing on the right kinematic cues against the lefties.  It wouldn't be the first time.  An early study from 1983 that examined the visual search behavior of German volleyball players found that participants incorrectly focused on the right arm and shoulder of attackers even when they were left handed.[8]

The available evidence suggests that the key to neutralizing the "left-handers advantage" is to design practices that promote exposure to lefty tactics and techniques.  This makes intuitive sense and is supported by the most recent research on the subject.[9]  Researchers successfully reversed the negative perception frequency effect in a study published in February by exposing participants to a perceptual training program that improved their reading skills against left-handers.  Apparently anything can be learned with the right kind and amount of practice.

One of our many tasks as coaches is to identify and improve weaknesses in our players and teams.  As the skill of reading plays a critical role in achieving success in volleyball, we have a heightened responsibility to guide our players' development in this area.  Coaches who creatively help athletes become better readers against all attackers are being good for and good to their players and also helping to raise the level of the game in all gyms.

NOTES:

[1]  See Farrow, D. (2008). Reading the play in team sports: yes it’s trainable. Australian Institute of Sport Coaching Magazine; Abernethy, B., Wood, J.M., and Parks, S. (1999). Can the anticipatory skills of experts be learned by novices? Research Quarterly for Exercise and Sport, 70, 313-318.

[2]  Grouis, G., Koidou, I., Tsorbatzoudis, H., and Alexandris, K., (2002).  Handedness in sport.  Journal of Human Movement Studies, 43, 347-361.

[3] Lefties Have Element of Surprise in Sport, Discovery News (Apr. 26, 2012) (available at http://news.discovery.com/adventure/left-handed-athletes-sports-120426.html) (last visited September 26, 2012).

[4] McMorris, T., & Colenso, S. (1996). Anticipation of professional soccer goalkeepers when facing right- and left-footed penalty kicks. Perceptual and Motor Skills, 82, 931–934.

[5] Hagemann, N. (2009).  The advantage of being left-handed in interactive sports. Attention, Perception, & Psychophysics, 71, 1641–1648.

[6] See, e.g., Loffing, Hagemann, N., & Strauss, B. (2010).  Automated processes in tennis: Do left-handed players benefit from the tactical preferences of their opponents?  Journal of Sports Sciences, 28, 435-443.

[7] Loffing, F., Schorer, J., Hagemann, N., Baker, J., (2012).  On the advantage of being left-handed in volleyball: further evidence of the specificity of skilled visual perception.  Attention, Perception, & Psychophysics, 74, 446-453.

[8] Neumaier, A. (1983). Beobachtungsstrategien und Antizipation beider Abwehr von Volleyballangriffen. [Observational strategies and anticipation during the defence of attacks in volleyball.].  Leistungssport, 13, 5–10 (cited in Loffing, F., Schorer, J., Hagemann, N., Baker, J., (2012).  On the advantage of being left-handed in volleyball: further evidence of the specificity of skilled visual perception.  Attention, Perception, & Psychophysics, 74, 446-453).

[9] Loffing, F., Schorer, J., Hagemann, N., Baker, J., (2012).  Human handedness in interactive situations: Negative perceptual frequency effects can be reversed!  Attention, Perception, & Psychophysics, 74, 446-453 (participants underwent a perceptual training program to improve their reading skills against left-handers).