Hand, Steve

Powell, Wendy

Simmonds, M.

Stevens, Brett

English

Portsmouth University Research Portal (Pure)

Sounding Better: Fast Audio Cues Increase 
Walk Speed in Treadmill-Mediated Virtual 
Rehabilitation Environments 
Wendy POWELLa,1
a
 School of Creative Technologies, University of Portsmouth, UK 
, Brett STEVENSa, Steve HANDa and Maureen SIMMONDS b 
b
 School of Physical & Occupational Therapy, McGill University, CANADA 
Abstract. Music or sound effects are often used to enhance Virtual Environments, 
but it is not known how this audio may influence gait speed. This study 
investigated the influence of audio cue tempo on treadmill walking with and 
without visual flow. The walking speeds of 11 individuals were recorded during 
exposure to a range of audio cue rates. There was a significant effect of audio 
tempo without visual flow, with a 16% increase in walk speed with faster audio 
cue tempo. Audio with visual flow resulted in a smaller but still significant 
increase in walk speed (8%).  The results suggest that the inclusion of faster rate 
audio cues may be of benefit in improving walk speed in virtual rehabilitation.   
Keywords. Virtual reality, audio cues, gait speed, treadmill walking 
Introduction 
Music and sound effects are often added to Virtual Environments (VEs) in an attempt 
to enhance engagement or enjoyment.  However, Virtual Reality (VR) is being used 
increasingly for motor rehabilitation, and it is not yet known whether audio input may 
not only enhance engagement but also influence the speed or quality of movement of 
individuals moving in VEs. Treadmill-mediated VR has the potential to be used for 
locomotor rehabilitation [e.g.1-4], but indiscriminate use of audio without 
understanding its effect on the desired outcomes could confound treatment goals.  If 
audio is to be included in VR rehabilitation environments, it is important to understand 
whether, and how, it affects gait, and thus how audio cues  can be utilised to facilitate 
the achievement of therapeutic goals. 
There is evidence that music can influence cadence (step tempo) and effort in 
exercise [5, 6] and also that increased audio beat frequency can increase walk speed [7-
9] and decrease gait variability [10,11]. However, music can also influence mood 
(affect) during exercise [6], and this altered affect can modulate gait kinematics [12].  
Furthermore, the type of music also has a differential effect on gait kinematics [5, 6, 
13].  Nevertheless, although it has been observed that walking with music is a rich 
multidisciplinary topic [8], it is also clear from a wide range of studies that there is an 
underlying effect of audio tempo on gait, whether delivered as music or as a simple 
metronome-type beat.  Indeed a number of researchers suggest that the body has an 
                                                         
1 Corresponding Author 
intrinsic ability to synchronise to an external rhythmic cue [13-15], and this may have 
the potential to enhance walking rehabilitation.  
However, to date there is little research into the effect of audio cues in Virtual 
Reality. Moreover, it has previously been noted that self-speed estimation is altered 
when walking in VR [4, 16, 17], and it is not known whether this visuo-motor 
modulation may interact with the effect of audio cues on walking speed. Thus it cannot 
be assumed that the results of previous 'real-world' studies can be generalised for 
application in Virtual rehabilitation. This paper reports a preliminary study 
investigating the influence of gait-referenced audio cue tempo on treadmill walking in 
Virtual Environments. 
1. Method 
Eleven healthy adults (4 male, 7 female, aged 23-54) participated in the study. All 
participants were familiarized with the self-paced motorized treadmill placed in front of 
a large (5mx3m) display screen.  A virtual walkway lined with pillars was back-
projected on the screen (Figure 1). During the test conditions the image of the walkway 
was either static on the screen (no visual flow) or linked to the treadmill via a virtual 
camera (VR condition - visual flow present).  The VR condition was matched to the 
treadmill speed, such that each 1m walked on the treadmill advanced the participant 1m 
in the Virtual Environment. 
 
 
Figure 1: Walking in treadmill-mediated VR 
 
Previous work had demonstrated that baseline cadence (step frequency) differs between 
treadmill and over-ground walking [18], therefore a 3-min baseline walk test was 
conducted on the treadmill, during which average speed (m/s) and cadence (steps/s) 
were recorded. Participants then walked for 3 minutes in each of the test conditions 
(Table 1) in pre-randomised and counterbalanced order.   
 
Table 1: The combination of audio cue rate and visual flow used in the  experimental conditions 
Audio Cue rate as % of 
baseline cadence 
none 
(baseline) 75% 100% 125% none 75% 100% 125% 
 
Visual flow  linked to 
treadmill motion absent (no VR) present (VR) 
 
 
2. Results 
Table 2: Mean speed (m/s) and cadence (steps/s) for audio condition in the presence and absence of visual 
flow 
Audio Cue rate as % of  
baseline cadence 
Visual flow absent (no VR) Visual flow present (VR) 
Speed (m/s) Cadence (steps/s) Speed (m/s) Cadence (steps/s) 
no audio 1.12 1.76 1.16 1.77 
75% 1.24 1.78 1.07 1.70 
100% 1.20 1.77 1.13 1.75 
125% 1.30 1.87 1.26 1.86 
 
A two-way ANOVA (audio x visual) for gait velocity showed a significant main effect 
of audio cue tempo (F3,30 = 4.69 p < 0.05). Participants walked fastest in the 125% 
audio-only condition, with a 16% increase in gait speed compared to baseline (p<0.01), 
and an 8% increase compared to matched audio cue tempo. There was no significant 
difference between the other conditions (Figure 2).  
 
 
Figure 2:  Modulating effect of audio cues on walk speed 
 
 
Figure 3: Modulating effect of audio cue tempo on cadence 
 
There was however a significant interaction between the audio cues and visual flow 
(F3,30 = 3.45 p <0.05).  In both the fast and slow cue conditions, participants walked 
significantly slower in VR than with audio alone. However, the participants walked 
faster (8%) in the 125% VR condition, compared to baseline. 
For cadence there was a significant effect for audio cues (F3,30 = 2.89  p = 0.05), 
with a 6% increase in cadence in the 125% audio condition compared to baseline and 
matched audio conditions. There was no significant difference between the other 
conditions (Figure 3).  There was no significant effect of visual flow on gait cadence. 
3. Discussion 
This study demonstrated a clear effect of audio cue frequency on treadmill walk speed, 
with audio cues above baseline step frequency being associated with a significant 
increase in walk speed.  This is consistent with the findings of previous studies [7-9].  
Although there is a natural tendency for humans to synchronise movements to external 
audio rhythms [9, 13], the increased walk speed is achieved by a combination of 
increased cadence and increased stride length. This supports the observations of Durgin 
et al. [19], who note that step length/cadence is maintained at a relatively constant ratio 
across varying walk speeds.   
This study extends previous work, by evaluating the effect of audio cues when the 
treadmill was linked interactively to a virtual environment.  In the presence of visual 
flow there was still a significant effect of audio cue frequency on walk speed, although 
there was difference in the effect in the fast and slow audio conditions. It has 
previously been observed that perception of self-motion is altered in treadmill-
mediated VR [e.g. 16, 17], leading to visuo-motor recalibration [20], and this may 
influence the magnitude of the effect of the audio cues.  However, one would expect 
this to be consistent across all audio conditions,  but it was observed that the VR only 
changed the effect of audio cues in the conditions where the cues were in conflict with 
the preferred cadence. This suggests that a different mechanism of action needs to be 
considered.   
Auditory and visual stimuli both require attention, which can be considered to be a 
finite shared resource [21].  In the presence of audio cues alone, there is sufficient 
attention to respond to the cues, but by adding the visual cues the attention is divided 
between two cues [9].  Audio cues which are in conflict with the preferred cadence may 
disrupt the automatic synchronicity of walking, necessitating more conscious attention. 
The suppression of the effect of audio on walk speed by the addition of visual flow 
may therefore be attributable to a reduction of attention to the audio cues in the 
presence of a competing attentional load.  It is notable that there is a marked difference 
in the effect of the slow audio cues between the two conditions.  In the audio-only 
condition, the slow audio was associated with an increase in walk speed.  Previous 
studies have noted the ability to 'double' a tempo [8], and this would be consistent with 
the speed increase seen with this cue frequency.  However, in the VR condition the 
slow audio frequency was associated with a decrease in walk speed, which may be 
attributable to a decreased ability to double tempo with additional attentional demands.  
 
4. Conclusion  
This  study demonstrated that the frequency of audio cues in treadmill-mediated VR 
can significantly influence walk speed. This supports and extends previous studies 
which have indicated that rhythmic audio cues may have a facilitating effect on the 
descending motor pathways, giving rise to an increased walk speed with increased 
tempo. The results suggest that the inclusion of faster rate audio cues may be of benefit 
in improving walk speed in virtual rehabilitation., and further studies are underway to 
evaluate this effect in clinical populations. 
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A treadmill and motion coupled virtual reality system for gait training post-stroke.

Calibration of locomotion resulting from visual motion in a treadmill-based virtual environment.

Editorial: Virtual reality: A healthy perspective.

Effect of emotion on the kinematics of gait. in American Society of Biomechanics.

Effects of external rhythmical cueing on gait in patients with Parkinson's disease: a systematic review.

Evaluation of the effect of training using auditory stimulation on rhythmic movement

Gait Coordination After Stroke: Benefits of Acoustically Paced Treadmill Walking.

Influence of tempo and subjective rating of music in step frequency of running.

Locomotor rehabilitation in a complex virtual environment,

Pain Demands Attention: A Cognitive-Affective Model of the Interruptive Function of Pain.

Perception of visual speed while moving.

Psychophysical and ergogenic effects of synchronous music during treadmill walking.

Resonance in the Perception of Musical Pulse.

Sensorimotor synchronization: A review of the tapping literature.

Software Gearing in a Virtual Environment: The Effect on Perception of Optic Flow.

Step frequency and perceived self-motion.

The perception of absolute speed during self-motion.

The psychophysical effects of music in sport and exercise: a review.

Treadmill Interface for Virtual Reality vs. Overground Walking: A Comparison of Gait

Walking on music.

Sounding better: fast audio cues increase walk speed in treadmill-mediated virtual rehabilitation environments

Name not available

Sounding better: fast audio cues increase walk speed in treadmill-mediated virtual rehabilitation environments

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