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International Review of Sport and Exercise Psychology
ISSN: 1750-984X (Print) 1750-9858 (Online) Journal homepage: https://www.tandfonline.com/loi/rirs20
An early review of stroboscopic visual training:
insights, challenges and accomplishments to guide
future studies
Luke Wilkins & Lawrence Gregory Appelbaum
To cite this article: Luke Wilkins & Lawrence Gregory Appelbaum (2019): An early review of
stroboscopic visual training: insights, challenges and accomplishments to guide future studies,
International Review of Sport and Exercise Psychology, DOI: 10.1080/1750984X.2019.1582081
To link to this article: https://doi.org/10.1080/1750984X.2019.1582081
Published online: 01 Mar 2019.
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An early review of stroboscopic visual training: insights,
challenges and accomplishments to guide future studies
Luke Wilkins
a
and Lawrence Gregory Appelbaum
b,c
a
Institute of Neuroscience, Newcastle University, Newcastle upon Tyne, UK;
b
Department of Psychiatry and
Behavioral Sciences, Duke University, Durham, NC, USA;
c
Duke Sports Vision Center, Duke University, Durham,
NC, USA
ABSTRACT
Stroboscopic visual training (SVT) is a form of training in which an
individual practices a task under intermittent visual conditions
with the intention of enhancing subsequent performance under
normal visual conditions. Training with stroboscopic devices is
theorized to improve important visual, perceptual, and cognitive
skills, which in turn transfers to enhanced sporting performance.
Indeed, while there is an abundance of anecdotal evidence
suggesting benefits of strobe training, empirical evidence is rarer
and less conclusive. This lack of clarity is due, in part, to the
challenging methodological issues faced when conducting
experimental vision training studies in applied contexts. The
present paper is an early review of the research to date with a
focus on the key methodological decisions, such as the training
and testing protocols employed, participant samples and control
groups used, and practical considerations that enable such
training in applied settings. Whilst still at an early stage, the
existing studies point to SVT enhancing some aspects of foveal
visual sensitivity and visual motor control, with notable benefits
for some athletic tasks. Such improvements could have
implications not just in sport, but in domains such as
rehabilitation, education, and motor vehicle safety.
ARTICLE HISTORY
Received 30 March 2018
Accepted 4 February 2019
KEYWORDS
Stroboscopic visual training;
sport; athletes; vision;
eyewear
Introduction
In 2011, Nike released the SPARQ Vapor Strobes: eyewear with liquid-crystal technology in
the lenses to produce a stroboscopic effect. The aim was to provide a sports training tool
which could enhance an athlete’s visual, perceptual, and cognitive skills, and therefore
improve their athletic performance. This type of training has been around for over 20
years –albeit not in the public eye –and was inspired by the experiences of Michael
Jordan, who would often have to cope with performing whilst numerous cameras
flashed from the crowd all around him (Haberstroh, 2016). Though there had been strobo-
scopic research prior to this, it used tethered devices, attached to computers, and tended
to focus on understanding the mechanism of visual integration (see Elliott, 1990,fora
review), with less emphasis on the applied use for activities such as sports. With the
© 2019 Informa UK Limited, trading as Taylor & Francis Group
CONTACT Luke Wilkins lukealexandarwilkins@gmail.com New York Yankees, Player Development Complex, 3102
North Himes Avenue, Tampa 33607, FL, USA
INTERNATIONAL REVIEW OF SPORT AND EXERCISE PSYCHOLOGY
https://doi.org/10.1080/1750984X.2019.1582081
advent of light, portable eyewear that could create a stroboscopic vision, new avenues
became available for applied use in sports, creating a new opportunity for academic
research. In this qualitative review, we will introduce studies that have attempted to
test the efficacy of stroboscopic visual training (SVT) in athletic contexts, by addressing
the theoretical mechanisms, training and testing protocols, and findings that have been
made in this relatively new field.
It is important to note that this review will predominantly focus on studies and papers
that explore the training effects of stroboscopic vision, rather than the acute influence that
stroboscopic vision has on performance. That is, the focus will be on research that exam-
ines the extent to which training under strobe conditions affects performance under
normal visual conditions. Whilst research has been conducted investigating the direct
impact of stroboscopic vision, it lacks the practical application that is important in the
sporting domain; athletes rarely compete with the intermittent vision of the scale experi-
enced during SVT. As a consequence of this, notable stroboscopic research such as that by
Bennett, Ashford, Rioja, and Elliott (2004), Ballester, Huertas, Uji, and Bennett (2017),
Fransen et al. (2017), Lyons, Fontaine, and Elliott (1997), and Rhodes, Mihalik, Franz, and
Wikstrom (2017) will not be discussed in detail. In addition, this review will focus on
studies in which SVT is the sole intervention method, as opposed to work in which SVT
forms part of a larger vision training protocol (such as in the studies by Appelbaum, Lu,
Khanna, & Detwiler, 2016; Clarke, Ellis, Bench, Khoury, & Graman, 2012). Finally, whilst
this paper will predominantly focus on SVT from a sporting perspective, it should be
stated that SVT has the potential to be applied in a wide range of domains, such as in
health care as a rehabilitation tool or in education for children with attention deficits.
To date, there are seven sports-specific peer-reviewed articles addressing SVT, though
there also exists some work that has been presented at conferences (Jones, Carnegie, &
Ellison, 2016) or produced as graduate projects (Holliday, 2013; Janssen, Burger, &
Mann, 2016). This review will explore this early stage of SVT work by first briefly introdu-
cing the theoretical premise underpinning its use and the devices that are available to
create this experience. Next, each of the seven studies will be briefly reviewed. Following
this, we will highlight the training protocols, testing protocols, and experimental design
considerations that shape this literature. Finally, we will consider the future directions of
SVT research and provide some concluding remarks. It is our intention that this early
review will help guide practitioners in their use of SVT, whilst aiding researchers in addres-
sing areas of need in this potentially fruitful area of sports science.
Theoretical mechanisms
Though research on this nascent approach has yet to arrive at strong conclusions regard-
ing the mechanisms of action driving SVT, the underlying premise is twofold. Namely, that
when experiencing a rapid and repeated interruption of visual input, an individual is
forced to (1) utilise the limited visual samples they receive more efficiently, and/or (2)
utilise other facilities, such as kinaesthetic awareness and auditory cues, more effectively.
In both instances, the individual is engaging in potentially advantageous strategies that
they otherwise wouldn’t were they to experience full vision.
These two theoretical mechanisms underpin other potential benefits of SVT, such as the
forced practice of extrapolating speeds and trajectories when aiming to intercept a
2L. WILKINS AND L. G. APPELBAUM
moving object. Other positive outcomes of SVT may relate to the need to maintain higher
attentional vigilance or to change the focus of attention in a manner that promotes the
visual-motor engagement being practiced. With regards to the latter point, it is logical
that interrupting the visual scene of an individual would result in an increase in attention
to external aspects of the primary task at hand, due reductions in the sensory input avail-
able and increased difficulty. For instance, a baseball hitter may increase their attentional
resources to the ball (an external object), and reduce their attentional resources to their
swing mechanics or body position (internal foci). Considerable research has found external
attention to be superior to internal attention in skilled performance and learning, particu-
larly for intermediate and elite athletes (Wulf, 2013). Finally, it is possible that SVT may
create conditions where temporal integration of information is more efficient, leading
to a perceptual advantage once normal vision is restored. Considerable past research
has addressed the temporal dependencies of visual integration including during optic
flow (Burr & Santoro, 2001), the detection and tracking of moving objects (Irani, Rousso,
& Peleg, 1992), and across saccadic eye movements (Melcher & Morrone, 2003), each of
which are utilized in sporting contexts and may be affected by the intermittent conditions
induced during SVT. It has been suggested that the imposed overload of effort on the
visual system caused by SVT is such that tasks feel easier (or moving objects feel
bigger/slower) once the glasses are removed (Smith & Mitroff,2012), akin to jogging
with ankle weights or swimming in a drag suit. This increased effort may also serve to func-
tion as a pseudo-psychological warm-up, with the glasses ensuring that typically basic
skills are honed with focus and without complacency.
Stroboscopic eyewear
Whilst the premise underpinning stroboscopic effects is similar across different eyewear
products, the specific details of each piece of eyewear do vary from company to
company. The now discontinued Nike SPARQ Vapor Strobe glasses consist of liquid
crystal lenses that alternate between transparent and semi-transparent states when an
electrical current is either passed through the lens or withheld, respectively. This
eyewear has a duty cycle consisting of a fixed 100 ms ‘open’state, in which the lenses
are fully transparent, and a ‘closed’state that ranges from 67 to 900 ms, at eight set incre-
ments. In the closed state, the Nike glasses are semi-transparent and have been shown to
allow for luminance of 128 lux under ambient room lighting (Ballester et al., 2017), con-
ditions almost equivalent to that of a ‘very dark overcast day’(Schlyter, 2015). Furthermore,
through a button on the temple of the eyewear, it is possible to alternate between binocu-
lar viewing with strobing in both lenses, and monocular viewing with one or the other lens
held in the opaque state.
Following the discontinuation of the Nike eyewear, Senaptec LLC began manufactur-
ing eyewear that utilized the same basic form factor, but improved upon the design of
the lenses to create a semi-transparent state that blocked nearly all light. In addition,
Senaptec introduced a digital application that allowed for remote control of their
eyewear through Bluetooth connectivity. More recently, the company has introduced
the ‘Senpatec Quad Strobe’eyewear with segmented lenses, allowing each quadrant
to be controlled separately so that specific parts of the visual field could be manipulated
individually.
INTERNATIONAL REVIEW OF SPORT AND EXERCISE PSYCHOLOGY 3
In addition to the Senaptec eyewear, three additional companies produce commercial
products intended for applied activities such as sports. Vima produces both the Rev Sport
and the Rev Tactical, each of which comes with 11 levels and digital control through a
Bluetooth connected application. MJ Impulse and Vision up Store have also produced
lightweight battery powered strobe eyewear that has gained use in both sports and
research (e.g. Hülsdünker et al., 2018). Whilst the ‘closed’state in all of these products con-
sists of semi-transparent lenses, the degree of opacity differs to some extent within each
set of glasses.
Finally, while not typically used in sporting settings, the PLATO Visual Occlusion Spec-
tacles (Milgram, 1987) were employed in much of the early work testing intermittent vision
by Digby Elliott and colleagues. The ‘closed’state of the lenses in these spectacles are
translucent such that light is permissible, but due to the scattering of light all local con-
trasts are destroyed and no vision of objects or movement is perceptible. The duty
cycle is customisable and limited only by the transition time between open and closed
states (approximately 7 ms), whilst users can also implement non-periodic series of
cycles; thus, the spectacles allow for the greatest amount of variation in the stroboscopic
conditions induced. As these spectacles are large, fragile and require the individual to wear
either a wallet-sized battery pack or remain tethered to an external power supply their use
in sporting contexts (particularly excessively active or contact sports) has been limited.
Primary research literature
As noted, there are currently seven published peer-reviewed articles testing the efficacy of
SVT. In the following section, we briefly describe the primary application and findings from
these studies in order to provide an overview of the nascent literature. This is not intended
to be an exhaustive account of all the studies, but rather background information for sub-
sequent sections that detail the methodological considerations used in each study.
The first published SVT study using the Nike glasses was carried out by Appelbaum,
Schroeder, Cain, and Mitroff(2011). University students and athletes were assigned to
either an SVT group or a control group that wore altered versions of the eyewear that
remained transparent, with measures of motion coherence (experiment 1), divided atten-
tion (experiment 2), and multiple-object tracking (experiment 3) compared before and
after the intervention period. The authors found that, compared to the control group,
SVT led to (1) significantly improved detection of centrally presented, but not peripherally
presented, motion coherence, and (2) significantly improved divided attention in terms of
central field processing, but not peripheral field processing. SVT did not, however, lead to
improvements in multiple-object tracking.
Using a similar design and population, Appelbaum, Cain, Schroeder, Darling, and Mitroff
(2012) carried out two experiments to examine the effect of SVT on short-term visual
memory. In the first, they found that SVT led to significantly greater improvement in
memory compared to a control group. In the second, with a new group of individuals,
the study found that these improvements in memory were retained 24 h following
training.
The effect of SVT on anticipation (as assessed by a Bassin Anticipation Timer –a 4-m
long track of light-emitting diodes and response button used to test coincidence antici-
pation) was examined by Smith and Mitroff(2012). Here, participants completed 5–7
4L. WILKINS AND L. G. APPELBAUM
min of training which consisted of practice with the anticipation timer, either whilst
wearing the Nike Strobe eyewear (experimental group) or whilst not wearing any
eyewear (control). The study included an immediate post-test, 10-min retention test,
and 10-day retention test. It was found that the experimental group had (1) significantly
better anticipation in the post-test, but not in either retention condition, (2) significantly
greater bias towards reporting early responses in the post-test and the 10-min retention,
but not in the 10-day retention (though significant pre-training differences make infer-
ences about any real changes difficult), and (3) significantly more consistent anticipation
errors in the post-test and the 10-min retention, but not the 10-day retention.
Mitroff, Friesen, Bennett, Yoo, and Reichow (2013) conducted a pilot study with elite ice-
hockey players. Despite a small sample size (six participants in the experimental group and
five in the control group), and the lack of intervention blinding, it was found that the
players who undertook SVT significantly improved their precision in either an on-ice shoot-
ing task (forwards) or an on-ice passing task (defensemen), whilst the control group of
players showed no such improvement.
The fifth solely-SVT study published was by Wilkins and Gray (2015). Here, university
students were assigned to either an experimental group undertaking variable SVT (i.e.
the frequency of the strobe varied during training) or a pseudo-control group undertaking
constant SVT (i.e. the frequency of the strobe remained at the lowest/easiest setting during
training). No significant group differences emerged following the 5-week training inter-
vention in either motion sensitivity, processing speed, divided attention, or tennis ball-
catching performance. However, for both groups, it was found that motion sensitivity
did improve in the post-test, whilst there were significant correlations between changes
in catching performance and both changes in motion sensitivity and changes in proces-
sing speed.
A case-study approach was taken by Wilkins, Nelson, and Tweddle (2017) to explore
the outcomes of SVT with three elite youth soccer goalkeepers. In this study, the
players underwent seven weeks of SVT and conducted a number of visual-perceptual
tests pre- and post-training, as well as engaging in semi-structured interviews post-
training. This study highlighted three themes with regards to SVT: (1) the belief that
it improved their visual and perceptual skills, (2) the belief that it improved their
on-field goalkeeping performance, and (3) the opinion that SVT was both effortful
and enjoyable.
Finally, Hülsdünker et al. (2018) recently conducted the first SVT study utilising neuro-
physiological measures (electroencephalography indicative of cortical visual processing)
alongside a sport-specific performance task. Here, five elite badminton players who under-
went a four-week SVT intervention were compared against a control group of five, age and
ability matched, players completing the same training intervention, but without the strob-
ing eyewear. Post-test performance in the badminton task (when controlled for pre-test
scores) were significantly higher for the SVT group compared to the control group,
though there were no group differences for the neurophysiological measure (N2
latency). A significant negative relationship between change in N2 latency and change
in badminton performance was reported, however, this was based on all 10 participants
(both SVT and controls) and any interpretation of the mechanisms-of-action are not
specific to the strobe training. Nevertheless, the research provides promising evidence
for the benefits of SVT in applied contexts.
INTERNATIONAL REVIEW OF SPORT AND EXERCISE PSYCHOLOGY 5
Training protocols
A major strength of SVT compared to many visual, perceptual, and cognitive training tools
used by athletes is that it allows for training to take place in natural contexts. Athletes can
practice their regular sports-specific drills within their sports-specific domain whilst
wearing the stroboscopic eyewear, rather than performing tasks outside of the sports
field/court/pitch. It is widely acknowledged that the benefits of practice are dependent
upon the similarity between the practiced-context and the later performed-context
(Henry, 1968), with a strong push in recent years to adopt high levels of task representa-
tiveness (Krause, Farrow, Reid, Buszard, & Pinder, 2018). Because SVT can be adapted to the
natural contexts of a training regime, it offers the opportunity to maximize near-transfer
learning. At the same time, this variability means that training protocols do not follow a
regulated format, which leads to variability between and within interventions. Specifically,
this variability manifests itself in three forms: (1) the length of the training (both per
session and across the whole intervention), (2) the exact activities performed by the indi-
viduals, and (3) the frequency of the strobe rate experienced by the individuals.
In terms of training length, SVT not only varies between studies, but within-studies as
well. For instance, in Appelbaum et al. (2011) participants completed between 2 and 10
SVT sessions of between 15 and 30 min, with the resultant total training between 54
and 300 total minutes. Table 1 highlights the between-study variance, with interventions
lasting as little as 5–7 min (Smith & Mitroff,2012), or as long as 635 min (Wilkins et al.,
2017).
With the release of the SPARQ Vapor Strobes, Nike produced a series of videos which
recommended an assortment of training drills with which to use the eyewear. These
videos mostly comprised variations on simple ball catching tasks, such as a ‘wall catch’,
‘power ball drop’, and ‘turn and catch’, but also included some agility and strength
based drills (Athletic Republic, 2011a). These are practiced on the easiest (fastest) strobe
frequency rate, before being made progressively harder (strobe frequency rate slows) at
a certain time- or performance-based intervals (i.e. every 5 min or every 5 successful
catches). Much of the existing literature adopts this ‘levelling up’approach while utilizing
adaptations of these drills within sport-specific activities. While training protocols gener-
ally start on the fastest/easiest level and get progressively harder, the reporting of the
precise details are understandably vague within current literature. Specifically, none of
the studies listed in Table 1 specify the exact duration with which participants trained
on each strobe level, making inference on this dimension challenging at this point.
More generally, while levelling up is understandable and appealing due to its simplicity,
it may not prove best practice for SVT. It is certainly possible that the effects of SVT
may be greater (or indeed reduced) if participants remain on just one strobe frequency.
Wilkins and Gray (2015) discuss this possibility and suggest that it may be that the
‘mere interruption of visual input, regardless of whether it is constant or variable …is
sufficient to produce advantageous training effects’(p. 75).
Much of the variance seen in SVT protocols is due to the logistical constraints imposed
by using athlete populations (e.g. limited time, impracticable matching control partici-
pants, and changeable training schedules). Yet these issues do not take away from the
fact that the lack of clearly identified structure makes understanding of optimal interven-
tions challenging. The work by Appelbaum et al. (2011,2012) usefully included ‘cohort’–
6L. WILKINS AND L. G. APPELBAUM
the athletic sample by which the training protocol typically varied –as a factor in their ana-
lyses and found no significant differences in the effect of SVT. Whilst this may indicate that
the differing protocols all had the same effect, it remains possible that length of training,
activities performed, frequency of strobe rate, or something else entirely may all contrib-
ute to an as-yet undetermined optimal SVT intervention.
Testing protocols –timing
Testing protocols entails both assessments that are designed to measure constructs that
might change due to SVT, as well as temporal structure that dictates the timing of pre- and
post-tests relative to training activities. Across the seven studies reviewed here, five post-
tests occurred immediately after the final training session, ensuring minimal interference
of learning that may lessen any potential effects. Indeed, in both studies by Wilkins and
Gray (2015), Wilkins et al. (2017), the experimental procedure was specifically designed
such that a shortened training session could be undertaken prior to the post-tests.
While immediate post-tests provide the best opportunity to observe SVT effects, it is
also of fundamental interest to assess whether training effects persist for any period of
Table 1. Synopsis of training protocols used in the seven solely-stroboscopic training studies published
in the literature.
Length of training Activities performed Frequency of strobe rate
Appelbaum
et al. (2011)
54–300 min (2–10 ×
20–30 min
sessions)
Dependent upon cohort. Recommended
training drills from Nike. Specifically, the
‘forward-facing and turn-and-catch drills’.
‘Typical soccer activities, such as passing
and dribbling drills’.‘Warm-up and agility
drills’.
Ranged from 1 to 6 Hz, though
‘participants primarily
experienced levels 2–4
(5–3 Hz)’
Appelbaum
et al. (2012)
54–315 min (2–7×
15–45 min
sessions)
Dependent upon cohort. Recommended
training drills from Nike. Specifically, the
‘forward-facing and turn-and-catch drills’.
‘Typical Ultimate Frisbee activities
involving passing and throwing drills in
both stationary and running situations’.
‘Warm-up and agility drills’.
Ranged from 1 to 6 Hz, though
‘participants primarily
experienced levels 2–4
(5–3 Hz)’
Smith and
Mitroff(2012)
5–7 min (1 × 5–7
min session)
5 blocks of 10 trials, whereby a trial
consisted of participants practicing their
anticipation using a 200-light Bassin
Anticipation Timer. Note: this was the
same as the pre- and post-test task.
4Hz
Mitroffet al.
(2013)
160+ minutes (16 ×
minimum 10 min
sessions)
‘a range of natural activities in which the
professional hockey players engage, such
as on-ice skills (eg, skating, passing) and
off-ice skills (eg, balance and
conditioning drills).’
Ranged from 1 to 6 Hz
Wilkins and
Gray (2015)
165 min (8 × 20 min
sessions, 1 × 5 min
session)
Recommended training drills from Nike.
Specifically, the ‘wall catch’, the ‘front
catch’, the ‘turn and catch’, and the
‘power ball drop’(all using a tennis ball).
Ranged from 1 to 6 Hz
Wilkins et al.
(2017)
635 min (14 × 45
min sessions, 1 ×
5 min session)
‘simple catching-based drills using a tennis
ball …and goalkeeper-specific drills
using a football’.
Ranged from 1 to 6 Hz
Hülsdünker
et al. (2018)
108–300 min (12–
20 × 12–15 min
sessions)
‘badminton-specific training protocols …
integrated into regular training …
midcourt longline drives, two forms of
midcourt cross drives as well as net
drives …defend long drives as well as
different forms of cross drive’.
Ranged from 5 to 6 hz and
50–70% duty cycle
INTERNATIONAL REVIEW OF SPORT AND EXERCISE PSYCHOLOGY 7
time following training. As such, retention-test data has been collected in a number of
studies. These included delays of 10 min (Jones et al., 2016; Smith & Mitroff,2012), 24 h
(Appelbaum et al., 2012), 10 days (Smith & Mitroff,2012), two weeks (Holliday, 2013),
and four weeks (Wilkins et al., 2017). Complicating matters slightly is that, in some
instances, what was termed by the researchers as a ‘post-test’session did not occur
immediately after training, and therefore may be better classified as retention tests. For
example, Mitroffet al. (2013) conducted post-tests 24 h after their last training session.
Interestingly, in the only qualitative data to date regarding athlete perceptions of SVT, a
key theme identified by researchers was that participants found the training intervention
‘effortful’(Wilkins et al., 2017). This opens questions about the interpretation of post-tests
which occur immediately after an SVT session and might be underweighting potential
effects of athlete fatigue. Further research should investigate this point.
Testing protocols –assessed measures
Gray (2017) highlights the need for research designs in sports training to include both
an assessment of far transfer (i.e. performance in the sport) and an assessment of the
mechanisms which are intended to positively impact this transfer. For SVT research, it
would be beneficial for studies to include measures of visual/perceptual/cognitive
skills and measures of the sporting performance captured by specific motor skills.
Within the seven published studies considered here, four report only visual/perceptual
assessments, one reports only sporting performance, and just two report assessments
for both markers of visual/perceptual skill and motor performance (see Table 2). It
should be noted that assessment of motor skills in the form of ball-catching (Appelbaum
et al., 2011) and free-throw shooting (Appelbaum et al., 2012) were obtained in the
Table 2. List of dependent variables measures in the seven solely stroboscopic training studies
published in the literature.
Visual/perceptual/cognitive measures Motor/other performance measures
Appelbaum et al.
(2011)
Motion coherence (central field, peripheral field)
Divided attention
Multiple object tracking
Appelbaum et al.
(2012)
Short-term visual memory
Smith and Mitroff
(2012)
Anticipation
Mitroffet al.
(2013)
Ice hockey shooting
Ice hockey passing
Wilkins and Gray
(2015)
Motion-in-depth sensitivity
Processing speed
Divided attention
Tennis ball catching (% success, % positional
errors, % timing errors)
Wilkins et al.
(2017)
Processing speed
Divided attention
Selective attention
Sustained attention
Anticipation
Visual response speed
Hand-eye coordination
Response inhibition (accuracy, speed)
Visual-spatial working memory
Hülsdünker et al.
(2018)
N2 visual evoked potential to motion stimuli
(used as an indicator of visual processing)
Badminton-specific smash-defence task (%
successful hits, % frame hits, % missed balls)
8L. WILKINS AND L. G. APPELBAUM
studies by Appelbaum and colleagues, though they were not reported due to ceiling
effects within the data.
Across the extant literature, studies have generally found good evidence supporting
a positive effect of SVT on a variety of visual, perceptual, and cognitive skills. In par-
ticular, findings point towards a beneficial effect of SVT on fast, foveal vision. That
is, visual and perceptual skills which are reliant on interpreting visual information in
the central field and/or with transient stimuli can be improved by undergoing a
period of SVT. By contrast, SVT does not appear to enhance skills that are based on
more sustained visual stimuli or stimuli appearing in the peripheral field. For instance,
SVT has been shown to improve centrally presented motion coherence and central
field processing (Appelbaum et al., 2011), visual memory of rapidly presented stimuli
(Appelbaum et al., 2012), anticipation of the sequence of rapidly illuminated lights
(Smith & Mitroff,2012), and motion sensitivity of fast-flowing 3-D stimuli (Wilkins &
Gray, 2015). Conversely, SVT has been found to have no effect on peripherally pre-
sented motion coherence, peripheral field processing, multiple object tracking (Appel-
baum et al., 2011), or divided attention (Wilkins & Gray, 2015). It should be noted,
however, that processing speed (a fast, foveal skill) was not improved in Wilkins and
Gray’s(2015) work, whilst the anticipation task in Smith and Mitroff’s(2012) study
may have involved peripheral field detection depending upon the strategy employed
by participants.
As noted above, since SVT has the overall goal of enhancing sporting performance, it is
beneficial for studies to include measures of physical skill that are inherent to sporting per-
formance. Of the seven studies discussed, three include such measures.
Wilkins and Gray had participants complete a tennis ball catching task under normal
visual conditions, before and after five weeks of SVT. Importantly, in the study, two SVT
groups were compared: a variable strobe rate group (akin to traditional levelling up)
and a constant strobe rate group (easiest level; proposed to act as a pseudo-control).
Various visual measures were also recorded. With regards to the effects of SVT, no
group differences were elicited though motion-in-depth sensitivity increased post-training
for both groups. The authors suggest that the stroboscopic eyewear used in the study
(PLATO occlusion spectacles as opposed to the Nike or Senaptec glasses used in much
of the other SVT work) could explain the lack of findings. It should also be noted that
unlike in the work of Mitroffet al. (2013) and Hülsdünker et al. (2018)–where positive
effects of SVT on motor performance were found –the participants here were not of an
elite sporting level.
The pilot work by Mitroffet al. (2013)had NHL ice-hockey players perform pre- and
post-tests of passing (for defensemen) and shooting (for forwards) in between which an
experimental group underwent 16 days of SVT. Despite the small sample size (six in the
SVT group and five in the control group), a significant and substantial positive effect of
SVT on performance was found. When comparing pre-to-post measures of hockey puck
placement, it was observed that the SVT group significantly improved precision by 18%
whilst the control group did not change. Although the performance measures nicely
reflected the contextual demands of the athletes (i.e. has good far transfer), this study is
limited due to the relatively small sample size and the possibility that placebo, or
Hawthorne, effects may have contributed to some extent. These results should rightly
be considered a pilot study warranting follow up research.
INTERNATIONAL REVIEW OF SPORT AND EXERCISE PSYCHOLOGY 9
The badminton task devised by Hülsdünker et al. (2018) required players to defend a
ball played by the coach to the opposite side of the back of the court, with the player
beginning 2 m from the net. Like the work by Mitroffet al. (2013), the test accurately rep-
resented the true sporting demands of these athletes, but the small sample size and poss-
ible placebo effect are justifiable caveats. The scoring system devised could also have
allowed for greater sensitivity, with trial performance rated purely on whether the ball
was successfully hit, hit with the frame of the racket, or missed.
Finally, as mentioned previously, there has been one paper which collected qualitative
data regarding SVT. Thematic analysis of the semi-structured interviews from Wilkins et al.
(2017) revealed three consistent themes; (1) players believed that their visual and percep-
tual skills (particularly ‘focus’,‘reactions’, and ‘judgement’) improved due to SVT, (2) players
believed that their on-field goalkeeping performance improved due to SVT, and (3) players
found the SVT both effortful and enjoyable. This last theme is an interesting one, and sup-
ports data collected in the study by Wilkins and Gray (2015) indicating participants’beliefs
regarding their perceived improvement in focus, reactions, and judgement. Of course, it
should be noted that it is possible, or perhaps even likely, that the subjective data col-
lected in these studies is prone to biases such as the placebo effect and experimenter
effect.
Collectively, it can be inferred from the testing protocols and assessed measures
described above that SVT is broadly thought to influence specific aspects of the spatio-
temporal dynamics of vision. While the preliminary conclusion of this review is that the
main effect of SVT is to improve fast foveal vision, more research, utilizing pre-registered
and sufficiently powered samples will be needed to draw stronger conclusions.
Control groups and participant samples
Perhaps the greatest challenge in SVT research relates to the identification of appropriate
control groups. In traditional controlled designs (e.g. drug trials), it is possible to create a
placebo intervention to balance the experience, and importantly motivation, of the partici-
pants. In the case of stroboscopic vision, it is not possible to introduce a placebo, nor is it
possible to blind one to the experience of the intervention, so motivational effects may
exist. The most common solutions among stroboscopic research studies have been to
either (1) have control group participants wear the eyewear, but have the lenses remain
transparent throughout, or (2) have the control group participants not wear the
eyewear at all (Table 1, right). In the first case, participants are typically instructed to
press the buttons on the side of the glasses in the same manner as the experimental
groups, in an attempt to balance the procedure. While it is not possible to validate the
efficacy of this approach, consistent patterns of task-level effects provide anecdotal evi-
dence that training effects were not due to motivation, which would have been equivalent
across tasks for individuals in either group. Another approach taken by Wilkins and Gray
(2015), involved the use of contrasts across different stroboscopic conditions. This was
done to combat the potential for differing motivation, enjoyment, and effort levels
between SVT and control group participants (subjective data collected post-training indi-
cated no group differences in these metrics). In their study, the fastest strobe setting acted
as a pseudo-control, based on previous research showing that catching performance
under such conditions did not significantly differ from normal visual conditions (Bennett
10 L. WILKINS AND L. G. APPELBAUM
et al., 2004). Thus, rather than compare an intermittent vision SVT group with a continuous
vision control group, they compared a variable strobe rate group and a constant strobe
rate group.
The participant sample tested in a given study is another important area to consider
within SVT research. It has been suggested that SVT may have greater efficacy for elite
athletes compared to intermediate or novice athletes, given that the visual abilities of
the latter are less likely to be limiting factors to their performance (Wilkins et al.,
2017). Conversely, it could also be argued that the benefits may be larger for novice ath-
letes given that they have more room for improvement. Of the seven solely-SVT studies
published to date, four contained data from participants classified as university students,
three contained data from participants classified as university athletes, and three con-
tained data from elite-level athletes; thus, the early literature has managed to explore
a range of sporting abilities. Despite this, no studies have yet to empirically test for
differences in strobe effects as a function of athlete experience. Furthermore, all the
studies referred to in the previous paragraph demonstrate significant findings (to
varying extents), so identifying whether SVT is more or less effective for particular indi-
viduals is challenging.
Within the athlete populations studied, the sports played have also varied considerably.
Soccer, given its popularity, has been studied on a number of occasions, whilst predomi-
nantly-American sports have received the majority of interest. One of the difficulties in
conducting research with athletes, as opposed to the general public, is in the recruitment
of large enough samples. The three published papers using only elite-level sportsmen con-
sisted of a total of 11 (Mitroffet al., 2013), six (Wilkins et al., 2017) and 10 (Hülsdünker, et al
2018) participants. Such small sample sizes make reliable statistical analyses difficult, yet
are often an inescapable fact in elite sport settings. It should be noted that the participant
sample used in the work by Appelbaum and colleagues (2011,2012) did contain a reason-
ably large number of Division 1 varsity athletes (67 total), though the data was eventually
collapsed across all cohorts, including non-athlete students, as no cohort difference was
observed for any of the statistical tests. Sufficient recruitment of student populations,
such as those in Appelbaum et al. (2011), Appelbaum et al. (2012) and Smith and
Mitroff(2012) may be easier, but they bring with them issues of generalizability if the
intention of a strobe intervention is to improve elite athletes.
Applications of SVT
Visual training has become a popular tool in the arsenal of sports teams and coaches in
recent years. The fact that SVT allows athletes to train in-situ is a significant advantage
over many traditional programmes, and is in line with optimal approaches according to
representative learning designs and the recently devised Modified Perceptual Training Fra-
mework (Hadlow, Panchuk, Mann, Portus, & Abernethy, 2018). It also makes SVT a more
appealing prospect from the logistical perspective of coaches and athletes. Anecdotal
reports indicate that SVT has been used by elite athletes in a wide range of sports, includ-
ing American football (Athletic Republic, 2011b), baseball (Berardino, 2016), basketball
(Haberstroh, 2016), ice hockey (Jackson, 2013), rugby (Carayannis, 2016), and soccer
(Kent, 2014). Given the positive reception towards the training, it is likely that such prac-
tices will continue and increase in use.
INTERNATIONAL REVIEW OF SPORT AND EXERCISE PSYCHOLOGY 11
From a coaching perspective, SVT has the logistical benefit of being easy to admin-
ister, and can allow athletes a degree of autonomy over their training. Studies such as
the one by Mitroffet al. (2013) have demonstrated that significant improvements can be
found even when the SVT is not regulated or recorded. Alongside the data showing that
SVT is both highly enjoyable and highly motivating (Wilkins & Gray, 2015), it is reason-
able to suggest that coaches could implement the practice with minimal guidance or
monitoring.
Coaches do, however, need to be aware of the safety limitations with SVT. First of all,
athletes with epilepsy or a history of seizures should not use the eyewear. Though the
strobe eyewear operates at a frequency below the photo-epileptic seizure sensitivity
threshold, and the prevalence of this disorder is less than 1% (World Health Organisation,
2017), it is recommended that athletes are carefully monitored to mitigate possible risks.
Secondly, disrupting an athlete’s vision whilst they are undertaking physical activity –par-
ticularly if that involves intercepting moving objects –brings with it potential physical
hazards. Having athletes perform tasks slightly below full speed, or with softer equipment
(e.g. tennis balls instead of cricket balls, or slightly deflated footballs), may reduce contex-
tual matching, but would provide less risk of injury.
Another potential application of stroboscopic training is that of rehabilitation and
health care. In a recent review, Grooms, Appelbaum, and Onate (2015) discuss the possi-
bility of incorporating SVT into the athletic rehabilitation process for neuromuscular inju-
ries, in particular, ruptures of the anterior cruciate ligament. They argue that such injuries
cause athletes to experience a reduction in somatosensory input that is compensated for
by an over-reliance on visual feedback. This adaptation may become detrimental when
returning to the sport as the complex and challenging athletic environment has the poten-
tial to overload the now more-utilised visual system. Consequently, resources for neuro-
muscular control are reduced and the risk of re-injury (or new injury) increases. Training
with stroboscopic glasses during the rehabilitation process reduces the visual input an
individual receives and therefore, in theory, reduces over-reliance from occurring.
Instead, the central nervous system is forced to use more proprioceptive inputs, which
should lead to a smoother and safer transition when returning to the challenging athletic
environment. Such a theory has begun to receive empirical support from recent clinical
studies testing this approach during lower-extremity injury rehabilitation (Kim, Kim, &
Grooms, 2017; Rhodes et al., 2017).
Finally, it should be noted that SVT has the potential to be a useful tool in any domain
which benefits from improved visual and perceptual skills. Notably, recent research by
Zavlin and colleagues (2019) has demonstrated improvements in surgical training task
performance of medical students following SVT, demonstrating efficacy in domains
outside of sports. Though there is not currently empirical evidence to support their
claims, it is worth noting that manufacturers, such as Vima, advertise their Rev Tactical
strobe glasses as being ‘built for athletes, professional shooters, military, law enforcement,
and first responders’(www.vima.com). Driving safety may be a particularly fruitful avenue
given that the visual skills shown to be enhanced by SVT, such as motion-in-depth-sensi-
tivity, have also been associated with improved driving performance (Wilkins, Gray, Gaska,
& Winterbottom, 2013). Indeed, early work has already investigated whether SVT can
improve time-to-collision judgements (Braly & DeLucia, 2017). Thus, research exploring
the effects of SVT on performance in these various areas may be is desirable.
12 L. WILKINS AND L. G. APPELBAUM
Future of SVT
SVT has rapidly emerged as a viable visual training approach that is easy to use and has
gained traction in sport and other domains. Based on this growth and the larger
growth of digital sports vision training tools (reviewed in Appelbaum & Erickson, 2016)
it is important to consider how future use, and future research, with this tool can be opti-
mized. As the growth of SVT continues, it is essential that research guides the parameters
and protocols employed. As identified previously, the current literature varies in a multi-
tude of factors including intervention duration, training drills performed, and strobe fre-
quency used. Future research can build on the currently reviewed studies to provide a
more systematic exploration of the optimal SVT strategy. Moreover, as this field continues
to grow, and more empirical studies emerge, it will be possible to conduct meta-analyses
that aggregate empirical findings that speak to the magnitude of effect sizes, moderators
that influence effects and publication biases that may present or absent within the litera-
ture at-large.
A number of open questions remain. For example, while numerous studies have found
immediate improvements following SVT, it is unclear how long these effects last. Systema-
tic studies of retention may inform this gap. As noted earlier, SVT presents a unique chal-
lenge for blinding and for creating placebo-controlled reference groups. Future studies
may wish to explore dose–response relationships (both over time and over level) as a
way to infer more information, given these challenges. Comparisons of SVT with other
digital visual and perceptual training programmes –like Dynavision, Neurotracker, Neuro-
Trainer, or EyeGym –would be particularly useful from an applied perspective, as they
would provide coaches with direct evidence for the most effective types of visual/percep-
tual training for their athletes. In addition, future studies may wish to explicitly test how
skill level (e.g. expert versus novice) interacts with strobe training effects.
In light of the challenges highlighted in this review, it is important that future SVT
studies make efforts to ensure the following:
1. Inclusion of assessments that measure of both visual/perceptual performance and
sport-specific motor performance.
2. Training and testing protocols that are (1) systematic, repeatable, and based on best
evidence, and (2) specific to the nature of the sport in question.
3. Inclusion of appropriate reference conditions such as adequate control group with
equal motivation, or dose–response designs.
4. Blinding of investigators during the statistical analysis of data.
5. Hypotheses are pre-registered prior to data collection (e.g. Appelbaum et al 2018).
Conclusions
The purpose of this paper has been to review the emerging scientific literature that has
tested stroboscopic visual training in athletic contexts. The goals of this review have
been to frame out the methodological considerations that have been used, their pros
and cons, and to make recommendations where the nascent field can be strengthened.
The goal of SVT as an athletic training tool is to transfer to performance under normal
visual conditions. This is an important point to consider given findings demonstrating
INTERNATIONAL REVIEW OF SPORT AND EXERCISE PSYCHOLOGY 13
that fundamental visual abilities correlate with on-field performance in domains such as
baseball (Burris et al., 2018; Klemish et al 2018). Moreover, the growth of studies which
explore the direct effect of stroboscopic vision on performance present a plausible
approach to enhance these fundamental abilities and improve sporting outcomes. In
light of this, the promising findings of early SVT research, and the abundance of positive
anecdotal reports, it would appear that SVT will remain a training tool for athletes and
sports teams for the foreseeable future.
Despite the limited amount of studies, there are a number of key themes which have
emerged. First, it does appear that SVT can enhance visual and perceptual skills. Specifi-
cally, skills relating to fast, foveal vision –as opposed to more sustained and peripheral
vision –have been shown to improve following SVT. Impressively, two studies have
demonstrated that training effects translate to sporting performance in both professional
hockey (Mitroffet al., 2013) and elite handball (Hülsdünker et al., 2018).
Secondly, there is considerable variation in how SVT research is carried out, and this
limits our ability to draw firm conclusions on the topic. There is as yet no consensus as
to the optimal training protocol, which will determine the effectiveness of SVT interven-
tions. With additional research that is more systematic in its design, evidence for SVT
may be able to back up the theoretically-driven approach and the considerable anecdotal
support that exists. The implications of this could extend far beyond sport and into impor-
tant areas such as motor vehicle safety, rehabilitation, military combat, and many more.
Acknowledgments
The authors would like to thank Susan Hilbig and Sicong Liu for their helpful comments on this
manuscript.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
Neither of the authors declares any financial interests or benefits that have arisen from the direct
applications of this research. Funding was provided for author L.G.A by Army Research Office
grant award number W911NF-15-1-0390.
ORCID
Luke Wilkins http://orcid.org/0000-0001-6735-1903
Lawrence Gregory Appelbaum http://orcid.org/0000-0002-3184-6725
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