Muscle Vibration-Induced Illusions: Review of Contributing Factors, Taxonomy of Illusions and User’s Guide

in Multisensory Research
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Limb muscle vibration creates an illusory limb movement in the direction corresponding to lengthening of the vibrated muscle. Neck muscle vibration results in illusory motion of visual and auditory stimuli. Attributed to the activation of muscle spindles, these and related effects are of great interest as a tool in research on proprioception, for rehabilitation of sensorimotor function and for multisensory immersive virtual environments. However, these illusions are not easy to elicit in a consistent manner. We review factors that influence them, propose their classification in a scheme that links this area of research to perception theory, and provide practical suggestions to researchers. Local factors that determine the illusory effect of vibration include properties of the vibration stimulus such as its frequency, amplitude and duration, and properties of the vibrated muscle, such as contraction and fatigue. Contextual (gestalt) factors concern the relationship of the vibrated body part to the rest of the body and the environment. Tactile and visual cues play an important role, and so does movement, imagined or real. The best-known vibration illusions concern one’s own body and can be classified as ‘first-order’ due to a direct link between activity in muscle spindles and the percept. More complex illusions involve other sensory modalities and external objects, and provide important clues regarding the hidden role of proprioception, our ‘silent’ sense. Our taxonomy makes explicit this and other distinctions between different illusory effects. We include User’s Guide with tips for anyone wishing to conduct a vibration study.

Muscle Vibration-Induced Illusions: Review of Contributing Factors, Taxonomy of Illusions and User’s Guide

in Multisensory Research

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References

AlbertF.BergenheimM.Ribot-CiscarE.RollJ.-P. (2006). The Ia afferent feedback of a given movement evokes the illusion of the same movement when returned to the subject via muscle tendon vibrationExp. Brain Res. 172163174.

AnsemsG. E.AllenT. J.ProskeU. (2006). Position sense at the human forearm in the horizontal plane during loading and vibration of elbow musclesJ. Physiol. 576445455.

BergenheimM.Ribot-CiscarE.RollJ.-P. (2000). Proprioceptive population coding of two-dimensional limb movements in humans: I. Muscle spindle feedback during spatially oriented movementsExp. Brain Res. 134301310.

BiguerB.DonaldsonI. M. L.HeinA.JeannerodM. (1988). Neck muscle vibration modifies the representation of visual-motion and direction in manBrain 11114051424.

BlanchardC.RollR.RollJ.-P.KavounoudiasA. (2013). Differential contributions of vision, touch and muscle proprioception to the coding of hand movementsPLoS One 8e62475.

BockO.PipereitK.MierauA. (2007). A method to reversibly degrade proprioceptive feedback in research on human motor controlJ. Neurosci. Meth. 160246250.

BrownM. M.EngbergI.MatthewsP. B. (1967). The relative sensitivity to vibration of muscle receptors of the catJ. Physiol. 192773800.

BrunC.GuerrazM. (2015). Anchoring the ‘floating arm’: use of proprioceptive and mirror visual feedback from one arm to control involuntary displacement of the other armNeuroscience 310268278.

BurkeD.HagbarthK. E.LofstedtL.WallinB. G. (1976a). The responses of human muscle spindle endings to vibration of non-contracting musclesJ. Physiol. 261673693.

BurkeD.HagbarthK. E.LofstedtL.WallinB. G. (1976b). The responses of human muscle spindle endings to vibration during isometric contractionJ. Physiol. 261695711.

Calvin-FiguièreS.RomaiguèreP.GilhodesJ.-C.RollJ.-P. (1999). Antagonist motor responses correlate with kinesthetic illusions induced by tendon vibrationExp. Brain Res. 124342350.

Calvin-FiguièreS.RomaiguèreP.RollJ.-P. (2000). Relations between the directions of vibration-induced kinesthetic illusions and the pattern of activation of antagonist musclesBrain Res. 881128138.

ClarkF. J.MatthewsP. B.MuirR. B. (1979). Effect of the amplitude of muscle vibration on the subjectively experienced illusion of movement [proceedings]J. Physiol. 29614P15P.

ConradM. O.ScheidtR. A.SchmitB. D. (2011). Effects of wrist tendon vibration on arm tracking in people poststrokeJ. Neurophysiol. 10614801488.

CordoP.GandeviaS. C.HalesJ. P.BurkeD.LairdG. (1993). Force and displacement-controlled tendon vibration in humansElectroencephalogr. Clin. Neurophysiol. 894553.

CordoP. J.GurfinkelV. S.BrumagneS.Flores-VieiraC. (2005). Effect of slow, small movement on the vibration-evoked kinesthetic illusionExp. Brain Res. 167324334.

CordoP.LutsepH.CordoL.WrightW. G.CacciatoreT.SkossR. (2009). Assisted movement with enhanced sensation (AMES): coupling motor and sensory to remediate motor deficits in chronic stroke patientsNeurorehabil. Neural Repair 236777.

CraskeB. (1977). Perception of impossible limb positions induced by tendon vibrationScience 1967173.

DiZioP.LacknerJ. R.ChampneyR. K. (2014). Proprioceptive adaptation and aftereffects in: Handbook of Virtual Environments: Design Implementation and ApplicationsHaleK. S.StanneyK. M. (Eds) pp.  835856. CRC PressBoca Raton, FL, USA.

EhrssonH. H.KitoT.SadatoN.PassinghamR. E.NaitoE. (2005). Neural substrate of body size: illusory feeling of shrinking of the waistPLoS Biol. 318.

FrimaN.RomeS. M.GrünewaldR. A. (2003). The effect of fatigue on abnormal vibration induced illusion of movement in idiopathic focal dystoniaJ. Neurol. Neurosurg. Psychiat. 7411541156.

FuentesC. T.GomiH.HaggardP. (2012). Temporal features of human tendon vibration illusionsEur. J. Neurosci. 3637093717.

GallagherS. (2005). The terms of embodiment in: How the Body Shapes the MindGallagherS. (Ed.) pp.  1739. Oxford University PressOxford, UK.

GandeviaS. C. (1996). Kinesthesia: roles for afferent signals and motor commands in: Handbook of Physiology Sect. 12 Exercise: Regulation and Integration of Multiple SystemsShepherdJ. T.RowellL. B. (Eds) pp.  128172. Oxford University PressNew York, NY, USA.

GayA.ParratteS.SalazardB.GuinardD.PhamT.LegreR.RollJ. P. (2007). Proprioceptive feedback enhancement induced by vibratory stimulation in complex regional pain syndrome type I: an open comparative pilot study in 11 patientsJoint Bone Spine 74461466.

GilhodesJ. C.RollJ. P.Tardy-GervetM. F. (1986). Perceptual and motor effects of agonist-antagonist muscle vibration in manExp. Brain Res. 61395402.

GoodwinG. M.McCloskeyD. I.MatthewsP. B. (1972a). The contribution of muscle afferents to kinaesthesia shown by vibration induced illusions of movement and by the effects of paralysing joint afferentsBrain 95705748.

GoodwinG. M.McCloskeyD. I.MatthewsB. C. M. (1972b). Proprioceptive illusions induced by muscle vibration: contribution by muscle spindles to perception? Science 17513821384.

GooeyK.BradfieldO.TalbotJ.MorganD. L.ProskeU. (2000). Effects of body orientation, load and vibration on sensing position and movement at the human elbow jointExp. Brain Res. 133340348.

GraybielA.HuppD. I. (1946). The oculogyral illusion, a form of apparent motion which may be observed following stimulation of the semicircular canalsJ. Aviat. Med. 43327.

GregoryJ. E.MorganD. L.ProskeU. (1988). Responses of muscle spindles depend on their history of activation and movementProg. Brain Res. 748590.

GregoryJ. E.MorganD. L.ProskeU. (2004). Responses of muscle spindles following a series of eccentric contractionsExp. Brain Res. 157234240.

HagbarthK.EklundG. (1966). Motor effects of vibratory muscle stimuli in man in: Nobel Symposium I Muscular Afferents and Motor ControlGranitR. (Ed.) pp.  177186. Almqvist and WiksellStockholm, Sweden.

HaguraN.TakeiT.HiroseS.AramakiY.MatsumuraM.SadatoN.NaitoE. (2007). Activity in the posterior parietal cortex mediates visual dominance over kinesthesiaJ. Neurosci. 2770477053.

HolcombeA. O.Seizova-CajicT. (2008). Illusory motion reversals from unambiguous motion with visual, proprioceptive, and tactile stimuliVision Res. 4817431757.

HowardI. P. (1997). Interactions within and between the spatial sensesJ. Vestib. Res. 7311346.

InglisJ. T.FrankJ. S. (1990). The effect of agonist/antagonist muscle vibration on human position senseExp. Brain Res. 81573580.

InglisJ. T.FrankJ. S.InglisB. (1991). The effect of muscle vibration on human position sense during movements controlled by lengthening muscle contractionExp. Brain Res. 84631634.

IzumizakiM.TsugeM.AkaiL.ProskeU.HommaI. (2010). The illusion of changed position and movement from vibrating one arm is altered by vision or movement of the other armJ. Physiol. 58827892800.

JonesL. A. (1988). Motor illusions: what do they reveal about proprioception? Psychol. Bull. 1037286.

KitoT.HashimotoT.YonedaT.KatamotoS.NaitoE. (2006). Sensory processing during kinesthetic aftereffect following illusory hand movement elicited by tendon vibrationBrain Res. 11147584.

LacknerJ. R. (1988). Some proprioceptive influences on the perceptual representation of body shape and orientationBrain 111(Pt 2)281297.

LacknerJ. R.LevineM. S. (1979). Changes in apparent body orientation and sensory localization induced by vibration of postural muscles: vibratory myesthetic illusionsAviat. Space Environ. Med. 50346354.

LacknerJ. R.TaubliebA. B. (1984). Influence of vision on vibration-induced illusions of limb movementExp. Neurol. 8597106.

LeonardisD.FrisoliA.BarsottiM.CarrozzinoM.BergamascoM. (2014). Multisensory feedback can enhance embodiment within an enriched virtual walking scenarioPresence Camb. 23253266.

LewaldJ.KarnathH. O.EhrensteinW. H. (1999). Neck-proprioceptive influence on auditory lateralizationExp. Brain Res. 125389396.

LindauerM. S.BaustR. F. (1974). Comparisons between 25 reversible and ambiguous figures on measures of latency, duration, and fluctuationBehav. Res. Methods Instrum. Comput. 619.

LongoM. R.KammersM. P.GomiH.TsakirisM.HaggardP. (2009). Contraction of body representation induced by proprioceptive conflictCurr. Biol. 19727728.

ManningH. L.BasnerR.RinglerJ.RandC.FenclV.WeinbergerS. E.WeissJ. W.SchwartzsteinR. M. (1991). Effect of chest wall vibration on breathlessness in normal subjectsJ. Appl. Physiol. 71175181.

MatthewsP. B. (1966). The reflex excitation of the soleus muscle of the decerebrate cat caused by vibration applied to its tendonJ. Physiol. 184450472.

MatthewsP. B. (1988). Proprioceptors and their contribution to somatosensory mapping: complex messages require complex processingCan. J. Physiol. Pharmacol. 66430438.

McCloskeyD. I. (1973). Differences between the senses of movement and position shown by the effects of loading and vibration of muscles in manBrain Res. 61119131.

McCloskeyD. I. (1978). Kinesthetic sensibilityPhysiol. Rev. 58763820.

McCloskeyD. I. (1981). Corollary discharges: motor commands and perception in: Handbook of Physiology Vol. 2 The Nervous System Motor ControlBrooksV. B. (Ed.) pp.  14151447. American Physiological SocietyBethesda, MD, USA.

NaitoE. (2004). Sensing limb movements in the motor cortex: how humans sense limb movementNeuroscientist 107382.

NaitoE.EhrssonH. H. (2001). Kinesthetic illusion of wrist movement activates motor-related areasNeuroreport 1238053809.

NaitoE.EhrssonH. H.GeyerS.ZillesK.RolandP. E. (1999). Illusory arm movements activate cortical motor areas: a positron emission tomography studyJ. Neurosci. 1961346144.

NaitoE.RolandP. E.EhrssonH. H. (2002). I feel my hand moving: a new role of the primary motor cortex in somatic perception of limb movementNeuron 36979988.

NaitoE.RolandP. E.GrefkesC.ChoiH. J.EickhoffS.GeyerS.ZillesK.EhrssonH. H. (2005). Dominance of the right hemisphere and role of area 2 in human kinesthesiaJ. Neurophysiol. 9310201034.

PorroC. A.FrancescatoM. P.CettoloV.DiamondM. E.BaraldiP.ZuianiC.BazzocchiM.Di PramperoP. E. (1996). Primary motor and sensory cortex activation during motor performance and motor imagery: a functional magnetic resonance imaging studyJ. Neurosci. 1676887698.

Precision Microdrives Ltd. (2016). AB-004: Understanding ERM Vibration Motor Characteristics [Online]. Available: https://www.precisionmicrodrives.com/application-notes/ab-004-understanding-erm-vibration-motor-characteristics. Accessed June 28 2016.

Precision Microdrives Ltd. (2016). AB-029: Vibration Motors — Voltage vs Frequency vs Amplitude [Online]. Available: https://www.precisionmicrodrives.com/application-notes/ab-029-vibration-motors-voltage-vs-frequency-vs-amplitude. Accessed June 28 2016.

Precision Microdrives Ltd. (2016). VAB-02: How Do Vibration Motors Work? [Online]. Available: https://www.precisionmicrodrives.com/application-notes/vab-02-how-do-vibration-motors-work. Accessed June 28 2016.

ProskeU.GandeviaS. C. (2012). The proprioceptive senses: their roles in signaling body shape, body position and movement, and muscle forcePhysiol. Rev. 9216511697.

ProskeU.MorganD. L.GregoryJ. E. (1993). Thixotropy in skeletal muscle and in muscle spindles: a reviewProg. Neurobiol. 41705721.

ProskeU.TsayA.AllenT. (2014). Muscle thixotropy as a tool in the study of proprioceptionExp. Brain Res. 23233973412.

RabinE.GordonA. M. (2004). Influence of fingertip contact on illusory arm movementsJ. Appl. Physiol. 9615551560.

RabinE.GordonA. M. (2006). Prior experience and current goals affect muscle-spindle and tactile integrationExp. Brain Res. 169407416.

RamachandranV. S.AltschulerE. L. (2009). The use of visual feedback, in particular mirror visual feedback, in restoring brain functionBrain 13216931710.

RedonC.HayL.RigalR.RollJ. P. (1994). Contribution of the propriomuscular channel to movement coding in children: a study involving the use of vibration-induced kinaesthetic illusionHum. Mov. Sci. 1395108.

ReguemeS. C.BarthèlemyJ.GauthierG. M.NicolC. (2007). Changes in illusory ankle movements induced by tendon vibrations during the delayed recovery phase of stretch-shortening cycle fatigue: an indirect study of muscle spindle sensitivity modificationsBrain Res. 1185129135.

RinderknechtM. D. (2012). Device for a novel hand and wrist rehabilitation strategy for stroke patients based on illusory movements induced by tendon vibration in: 16th IEEE Mediterranean Electrotechnical Conference (MELECON) Medina Tunisia pp.  926931. DOI:10.1109/MELCON.2012.6196579.

RollJ. P.VedelJ. P. (1982). Kinaesthetic role of muscle afferents in man, studied by tendon vibration and microneurographyExp. Brain Res. 47177190.

RollJ. P.VedelJ. P.RibotE. (1989). Alteration of proprioceptive messages induced by tendon vibration in man — a microneurographic studyExp. Brain Res. 76213222.

RollJ. P.RollR.VelayJ.-L. (1991). Proprioception as a link between body space and extra-personal space in: Brain and SpacePaillardJ. (Ed.) pp.  112132. Oxford University PressNew York, NY, USA.

RollJ.-P.AlbertF.ThyrionC.Ribot-CiscarE.BergenheimM.MatteiB. (2009). Inducing any virtual two-dimensional movement in humans by applying muscle tendon vibrationJ. Neurophysiol. 101816823.

RothM.DecetyJ.RaybaudiM.MassarelliR.Delon-MartinC.SegebarthC.MorandS.GemignaniA.DécorpsM.JeannerodM. (1996). Possible involvement of primary motor cortex in mentally simulated movement: a functional magnetic resonance imaging studyNeuroreport 712801284.

SchofieldJ. S.DawsonM. R.CareyJ. P.HebertJ. S. (2015). Characterizing the effects of amplitude, frequency and limb position on vibration induced movement illusions: implications in sensory-motor rehabilitationTechnol. Health Care 23129141.

Seizova-CajicT.AzziR. (2010). A visual distracter task during adaptation reduces the proprioceptive movement aftereffectExp. Brain Res. 203213219.

Seizova-CajicT.AzziR. (2011). Conflict with vision diminishes proprioceptive adaptation to muscle vibrationExp. Brain Res. 211169175.

Seizova-CajicT.SachtlerW. L. B. (2007). Adaptation of a bimodal integration stage: visual input needed during neck muscle vibration to elicit a motion aftereffectExp. Brain Res. 181117129.

Seizova-CajicT.SachtlerW. L. B.CurthoysI. S. (2006). Eye movements cannot explain vibration-induced visual motion and motion aftereffectExp. Brain Res. 173141152.

Seizova-CajicT.SmithJ. L.TaylorJ. L.GandeviaS. C. (2007). Proprioceptive movement illusions due to prolonged stimulation: reversals and aftereffectsPLoS One 2e1037. DOI:10.1371/journal.pone.0001037.

SibuyaM.YamadaM.KanamaruA.TanakaK.SuzukiH.NoguchiE.AltoseM. D.HommaI. (1994). Effect of chest wall vibration on dyspnea in patients with chronic respiratory diseaseAm. J. Respir. Crit. Care Med. 14912351240.

SimonsD. J.ChabrisC. F. (1999). Gorillas in our midst: sustained inattentional blindness for dynamic eventsPerception 2810591074.

SittigA. C.Denier van der GonJ. J.GielenC. C. (1985). Separate control of arm position and velocity demonstrated by vibration of muscle tendon in manExp. Brain Res. 60445453.

SittigA. C.Denier van der GonJ. J.GielenC. C. (1987). The contribution of afferent information on position and velocity to the control of slow and fast human forearm movementsExp. Brain Res. 673340.

TaylorJ. L. (2013). Kinesthetic inputs in: Neuroscience in the 21st CenturyPfaffD. W. (Ed.) pp.  931964. SpringerNew York, NY, USA.

TaylorJ. L.McCloskeyD. I. (1991). Illusions of head and visual target displacement induced by vibration of neck musclesBrain 114(Pt 2)755759.

ThiemeH.MehrholzJ.PohlM.BehrensJ.DohleC. (2012). Mirror therapy for improving motor function after strokeCochrane Database Syst. Rev. 3CD008449. DOI:10.1002/14651858.CD008449.pub2.

ThyrionC.RollJ.-P. (2009). Perceptual integration of illusory and imagined kinesthetic imagesJ. Neurosci. 2984838492.

TidoniE.FuscoG.LeonardisD.FrisoliA.BergamascoM.AgliotiS. A. (2015). Illusory movements induced by tendon vibration in right- and left-handed peopleExp. Brain Res. 233375383.

TsugeM.IzumizakiM.KigawaK.AtsumiT.HommaI. (2012). Interaction between vibration-evoked proprioceptive illusions and mirror-evoked visual illusions in an arm-matching taskExp. Brain Res. 223541551.

VallboA. B. (1970). Discharge patterns in human muscle spindle afferents during isometric voluntary contractionsActa Physiol. Scand. 80552566.

VelayJ. L.RollJ. P.RollR.LennerstrandG. (1994). Eye proprioception and visual localization in humans: influence of ocular dominance and visual contextVision Res. 3421692176.

VolpeD.GiantinM. G.FasanoA. (2014). A wearable proprioceptive stabilizer (Equistasi®) for rehabilitation of postural instability in Parkinson’s disease: a phase II randomized double-blind, double-dummy, controlled studyPLoS One 9e112065. DOI:10.1371/journal.pone.0112065.

YaoH.-Y.HaywardV. (2010). Design and analysis of a recoil-type vibrotactile transducerJ. Acoust. Soc. Am. 128619627.

Figures

  • View in gallery

    An easy way to demonstrate and experience vibration-induced movement illusion (similar to the method used by Goodwin et al., 1972a). The demonstrator actively supports volunteer’s right arm by holding it at the wrist to ensure the arm is stationary. A hand-held vibrator purchased in a department store (vibration frequency approx. 90 Hz) is firmly pressed into the biceps tendon of the blindfolded volunteer. The volunteer uses her other arm to indicate the extent of illusory movement and displacement of the vibrated arm, which usually begin a few seconds following the onset of vibration. Here the volunteer indicates an illusory forearm extension of approximately 30 deg.

  • View in gallery

    Vibration of right dorsal neck results in the false sensory input that indicates contralateral head movement (consistent with the lengthening of right dorsal neck muscles). If during such stimulation the observer fixates a small stationary object in an otherwise dark visual field, the object will appear to move to the left, consistent with the misleading signal regarding head movement. Consistent with the oft-silent contribution of proprioceptive messages to sensory processing, the head movement itself may not be consciously perceived even if the visual motion is (Taylor and McCloskey, 1991; see Section 4.2 for details).

  • View in gallery

    Muscle spindle and vibration-induced sensations. Muscle spindles are elongated sensory organelles embedded in the muscle and lying in parallel with muscle fibres (see image). Muscle spindles have sensory endings that respond to stretch. Primary endings respond most to dynamic stretch and are served by Ia afferent nerve fibres. Secondary endings respond most to static stretch and are served by type II afferent fibres. Thus natural muscle stretch during limb movement results in the stretch of the muscle spindle and activation of sensory neurons.

    A vibrating object pressed firmly into the muscle causes rapid repetitive muscle stretches to which muscle spindles respond very well. Both types of sensory endings respond to vibration, but they are most sensitive to different frequencies. Dissociation between illusory movement and illusory displacement (Section 4.1) is attributed to their different response properties.

    The process is complicated by the fact that muscle spindle sensory endings need to remain taut at different muscle lengths in order to stretch when the muscle stretches. This is achieved through the activity of intrafusal muscle fibres on which the sensory endings are located. Because these tiny muscle fibres within the spindle capsule only contract at their ends, their activation stretches their central portions where the sensory endings lie. When the muscle contracts (due to the commands sent through the alpha motor system), so do the intrafusal fibres (due to the activity of the gamma motor system, see image), keeping the spindle endings taut although the muscle has shortened — a process known as alpha–gamma co-activation (Vallbo, 1970). Information about commands sent to muscles is also available to the brain (known as efference copy or corollary discharge) and may itself contribute to the movement sensation. Thus rather than being a simple consequence of muscle stretch, sensory input and the sensation will vary depending on the overall muscle length, movement preceding it or any concurrent movement, fatigue and other factors (see Section 2). A number of physiological studies provided detailed description of response to vibration in primary afferents (Burke et al., 1976a, b; Cordo et al., 1993; Roll et al., 1989). Central response to muscle vibration involves a network of areas, including both sensory and motor cortices (Naito et al., 2005).

  • Mechanical properties of vibrators. Sourcing of vibrators that can be used for purposes described in this manuscript is varied — from pneumatic drills, physiotherapy massagers and sex toys to custom-made devices. Mechanical properties of vibrators need to match their intended use in muscle vibration studies, and basic understanding of those properties is therefore desirable. We present some of the relevant information below, relying on sources that describe vibrators use in haptic research and applications (see Precision Microdrives Ltd., 2016: “AB-004: Understanding ERM vibration motor characteristics”, 1238; “AB-029: Vibration motors  — voltage vs frequency vs amplitude”, 1238; “VAB-02: How do vibration motors work?”, 1238; Yao and Hayward, 2010). A typical vibrator used for our purposes is larger than vibrators used in haptics but the same general principles of operations apply.

    Vibrators are devices that create fast and repetitive displacement of mass. Vibration frequency (in Herz) is a number of cycles of repetitive motion per second, and is the vibration property most commonly reported in the literature on vibration illusions. Vibration also needs to have sufficient amplitude of displacement with which a normal force is applied to the muscle tendon or belly in order to stretch muscle spindle. The force increases with the mass of vibrator’s moving part, so a very small vibrator will not do for a large muscle. The force actually delivered will also vary with leanness, i.e., bulkiness of the muscle (force delivered is rarely specified, let alone controlled; for one exception, see Cordo et al., 1993). Below we describe two basic vibrator types based on the direction of displacement of mass, i.e., direction in which they exert force.

    1. Eccentric rotating mass (ERM) vibration motor (also known as ‘rumble motor’) has an off-centre spinning load, the rotation of which results in a centrifugal force and motor displacement, i.e., vibration. The speed of rotation, i.e., vibration frequency is positively related to acceleration and the two parameters cannot be independently controlled. For any given vibrator, increasing the input voltage (DC current) increases both frequency and acceleration. Amplitude of displacement decreases with increasing frequency, other factors being constant (see Fig. 1a, Naito et al., 1999). Numerous vibration studies (including Goodwin et al., 1972a) used ERM vibrators and thus necessarily confounded changes in frequency with changes in amplitude of displacement. When applied to the muscle, orientation of the shaft around which the mass rotates should be parallel to it. That way a part of the centrifugal force will act as a normal force on the muscle.

    2. Linear vibration motors have a mass displaced by a force created by magnetic fields and electrical currents. Some of those vibrators operate at a single resonant frequency (linear resonant actuators, LRA) but their amplitude of displacement can be manipulated. In other types, frequency and amplitude can vary independently of each other, which has clear advantages in terms of stimulus control in vibration studies.

    Note: Terminology may confuse: in technical papers, ‘amplitude’ often means rate of acceleration and is measured in G or ms−2, but in the literature on vibration illusions, ‘amplitude’ usually refers to the extent of peak-to-peak vibrator displacement measured in µm or mm (e.g., Goodwin et al., 1972a; Naito et al., 1999; Schofield et al., 2015). We refer to the former as acceleration, and to the latter, as amplitude of displacement.

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