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. 2025 Mar 20;20(1):39–43. doi: 10.26599/JOTO.2025.9540007

Quantification of vestibular perception during caloric test

Dion J 1,2, Pierre AS 1,2, Cedras AM 1,2, Champoux F 1,3, Saliba I 4,5, Maheu M 1,2,*
PMCID: PMC12510343  PMID: 41069843

Abstract

Background

It has been reported that factors such as age and vestibular pathology (i.e. vestibular migraine) could impact self-motion perception during vestibular stimulation. However, to our knowledge, no objective test has been developed to quantify self-motion perception during clinical vestibular evaluation.

Objective

The main objective of the present study was to quantify vestibular perception during caloric vestibular stimulation using a tachometer.

Methods

Twenty-two participants were divided into three groups: 1) younger healthy adults, 2) older healthy adults and 3) vestibular impaired adults. All participants performed bithermal water caloric irrigation during which slow-phase eye velocity (SPV) was measured using videonystagmography and self-motion velocity perception was assessed using a handheld tachometer (RPM).

Results

The results revealed a significant difference in SPV between vestibular impaired ears and both healthy groups, and a significant difference in self-motion velocity perception between healthy young and vestibular impaired participants.

Conclusions

This study suggest that the SPV similarly to self-motion perception (RPM) can differentiate between vestibular impaired and young healthy participants. Future work is required to assess the influence of self-motion perception in aging.

Keywords: vestibular, caloric test, perception, vertigo, slow-phase eye velocity

1. Introduction

The vestibular system is crucial for everyday life activities such as maintaining balance, stabilizing gaze during head movements (i.e. reading while head is moving) and perceiving self-motion in space (Kingma and van de Berg, 2016). To do so, the vestibular system projects respectively to the vestibulo-spinal, the vestibulo-ocular and vestibular cortical pathways (Cullen, 2016). When a vestibular lesion occurs, it affects the efficacy of these functions resulting in balance difficulties, instability of gaze during head movement and altered perception of self-motion (Curthoys, 2000).

Common clinical vestibular evaluation methods assess the vestibulo-ocular and the vestibulo-spinal pathways. Indeed, the video head impulse test (vHIT), caloric test (videonystagmography) and the ocular vestibular evoked myogenic potential (oVEMP) assess the integrity of the VOR pathway [for a review: (Curthoys et al., 2009, Halmagyi et al., 2017, Shepard and Jacobson, 2016)]. On the other hand, cervical vestibular evoked myogenic potential (cVEMP) and postural tests such as computerized dynamic posturography or modified clinical test sensory integration in balance (mCTSIB) can be used to assess vestibulo-spinal pathway (Black, 2001, et al., 1993, Rosengren et al., 2019). However, to our knowledge, no objective test has been developed to quantify self-motion perception during vestibular evaluation.

Quantifying vestibular perception could offer interesting possibilities to deepen our understanding of the vestibular system. More specifically, dissociation between VOR response and perceptual response has been observed in various populations. First, it has been reported that some elderly patients reported absence of vertigo following caloric irrigation even though the VOR response was within normal limits, suggesting normal function of the horizontal semi-circular canals (Chiarovano et al., 2016, Jacobson et al., 2018, Piker et al., 2020). The lack of perceived self-motion following caloric irrigation has been associated with greater postural instability (Chiarovano, et al., 2016, Piker, et al., 2020). However, these studies investigated elderly patients with symptoms of imbalance (non-vestibular). It remains to date unexplored how normal aging affect perception during caloric irrigation. Secondly, some vestibular pathologies, such as vestibular migraine, have demonstrated enhanced self-motion perception during rotational chair stimulation as compared to controls whereas VOR responses were normal between groups (Wurthmann et al., 2021).

The caloric test is a very common objective vestibular method performed in clinical settings. When the vestibular system is functioning normally, the caloric test induces a nystagmus from which slow phase eye velocity is recorded using videonystagmography informing the clinician on the status of the VOR. Additionally, it induces an illusion of movement (Shepard and Jacobson, 2016). Developing a method to quantify vestibular perception during caloric testing could enable comparison between VOR and vestibulo-cortical responses, providing insights into vestibular perceptual processes. The main objective of this study was to quantify vestibular perception during caloric vestibular stimulation using a tachometer. More specifically, this study aimed at comparing VOR and perceptual response in young healthy adults, older healthy adults and patients with unilateral vestibular hypofunction.

2. Methodology

2.1. Participants

A total of twenty-two participants were recruited divided into three groups (healthy young adults (n=6), healthy older adults (n=6), vestibular impaired adults (n=10)). Participants in the vestibular impairment group had previously received a diagnosis of Meniere’s disease (n=3), vestibular migraine (n=2), both Meniere’s disease and vestibular migraine (n=3), or had an unknown etiology (n=2). Participants were tested during interictal phases. Table 1 describes the groups’ characteristics. None of the participants from both healthy groups reported complaints of postural instability or vestibular problems. The vestibular impaired group (VI) were adults that reported complaints of postural instability and had a significant caloric vestibular asymmetry (>20%).

Table 1. Participants characteristics (VI: vestibular impairment).

Groups Number of
participants		 Age
(mean [min-max])		 Sex(F|M) Ears tested
Young 6 24.2[23−26] 5|1 10(4 Right |6 Left)
Old 6 70.7[67−76] 6|0 10(4 Right |6 Left)
VI 10 47.5[33−58] 4|6 10(4 Right |6 Left)
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2.2. Protocol

2.2.1. Pre-experimental procedures

To ensure normal function of the middle ear (i.e. avoid presence of retro tympanic fluid, ear drum perforation), otoscopy and tympanometry was performed on all participants prior to perform caloric test. Participants with abnormal tympanometry results were excluded. Additionally, vestibular function was screened using the video head impulse test (vHIT; ICS Impulse, Otometrics, Denmark) according to the usual protocol (Maheu et al., 2022). A gain between 0.8 and 1.2 with absence of significant catch-up saccades was considered normal (Halmagyi, et al., 2017). Participants from both healthy groups were excluded if vHIT results were abnormal. We performed bithermal and binaural caloric irrigation in both ears in each group to ensure the caloric asymmetry criteria was respected. The order of irrigation (ear and temperature) was randomized. Additionally, participants within both healthy groups were excluded if SPV following irrigation was lower than 12°/s or if an asymmetry in SPV was greater than 20% (Shepard and Jacobson, 2016). However, for analysis only the affected ears (weaker SPV) from the vestibular impaired group (4 right ears; 6 left ears) was selected to measure the influence of vestibular loss on VOR and perception. Therefore, to avoid a possible ear effect, we randomly selected and analyzed 4 right ears and 6 left ears in both healthy groups (younger and older). A total of 10 ears per group was analyzed and compared.

2.2.2. Experimental procedures

Participants performed the vestibular caloric test using open loop warm and cold water irrigation (Aquastim, Interacoustics) as previously performed in our laboratory (Cedras et al., 2021). The temperature of irrigation was 44 °C for warm and 30 °C for cold irrigations, each lasting 30 seconds with a total volume of 250 ml (Shepard and Jacobson, 2016). Participants were laying on their back at an angle of 30 degrees relative to horizontal, placing the lateral canals in line with gravity (Jacobson et al., 2021). The nystagmus slow-phase velocity was measured using videonystagmography (VNG; VNS 3X, Synapsys, Ulmer) goggles at a sampling rate of 50 Hz. Additionally, during the irrigation, participants were required to turn a handwheel of a tachometer (SHIMPO, DT-2100, PC Software) to match the velocity of the perceived induced vertigo (Figure 1). During the irrigation and until induced nystagmus resolves, VOR and self-motion perception were continuously measured. Participants were indicated to stop turning the handwheel when they no longer perceived rotation. The tachometer sampled the rotation per minute (RPM) at a sampling rate of 10 Hz. Raw slow phase eye velocity and rotation per minute were exported and analyzed in Matlab (R2020a).

Figure 1.

Figure 1

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Photograph of the tachometer (SHIMPO, DT-2100) used to measure perceived velocity during caloric irrigation.

2.3. Analysis

The slow phase eye velocity (SPV) and tachometer (RPM) were retrieved to analyze respectively VOR and perceptual responses. SPV peak was determined as the maximum value of SPV. To determine the peak velocity of tachometer, as seen in Figure 2A, first a Gaussian curve was fitted across RPM data. The time value corresponding to the peak of the gaussian fit was retrieved. Using this time coordinate, the mean across 21 samples was calculated (10 samples before; one sample at time value; 10 samples after) allowing to reduce the influence of artifacts such as unexpected high peak RPM due to unvoluntary rotation of the tachometer wheel. For example, Figure 2B, demonstrate the results of a participant that did not perceive motion, but accidently touched the handwheel. Averaging across a larger number of samples allowed to correct for such artifacts, without significantly affecting those who perceived movements.

Figure 2.

Figure 2

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Representation of a tachometer response in two different participants with vestibular impairment. A) The individual circles represent samples of tachometer handwheel rotation (RPM) across time (time samples). First, a Gaussian curve was fitted through the data (sample points) to determine the region where perception was maximal. Second, the mean of samples (individual circles) around the peak of the Gaussian was computed (star). The vertical dash lines represent the region of where the RPM data were averaged (10 samples before and 10 samples after the peak). This had the advantage to protect from artifacts as seen in figure B. The participant in panel B reported no perceived motion, but accidently touched the handwheel. Averaging allowed to correct for that artifact.

For each temperature, a one-way ANOVAs was performed to compare the VOR responses (SPV peak velocity) and the perceived velocity (RPM) between groups. Post-hoc t-test analysis were bootstrapped using bias-corrected accelerated method with 1000 replicates (Efron, 1987). Statistical analyses were conducted using JASP (version 0.18.3).

3. Results

For cold caloric irrigation, a significant group difference was observed for SPV [F(2, 27)=18.68; p<0.001; η2=0.62] and for RPM [F(2, 27)=3.70; p=0.038; η2=0.214]. Figure 3A illustrates the results from the post-hoc analysis. Post-hoc analysis revealed significant SPV differences between vestibular impaired and younger adults [p<0.001] and vestibular impaired and older adults [p<0.001], but not between younger and older adults [p=1.00]. Post-hoc analysis revealed significant RPM differences only between vestibular impaired and younger adults [p=0.036], but not between vestibular impaired and older adults [p=0.304] and not between younger and older adults [p=0.986].

Figure 3.

Figure 3

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Comparisons between groups for the VOR response (SPV) and the perceptual response (Tachometer) for cold (in A) and warm (in B) conditions. (*=p < 0.05; **=p < 0.01; ***=p < 0.001). (VI: vestibular impairment)

For warm caloric irrigation, a significant group difference was observed for SPV [F(2, 27)=18.68; p<0.001; η2=0.603] and for RPM [F(2, 27)=3.70; p=0.024; η2=0.188]. Figure 3B illustrates the results from the post-hoc analysis. Post-hoc analysis revealed significant SPV differences between vestibular impaired and younger adults [p<0.001] and vestibular impaired and older adults [p<0.001], but not between younger and older adults [p=0.595]. Post-hoc analysis revealed significant RPM differences only between vestibular impaired and younger adults [p=0.045] but not between vestibular impaired and older adults [p=1.00] and not between younger and older adults [p=0.059].

4. Discussion

In the present study, vestibular-impaired participants had a weaker VOR response compared to healthy participants. This suggests that VOR response (SPV) can distinguish between vestibular-impaired and healthy ears, independent of the age group. This is in accordance with previous literature supporting no influence of age on caloric response (Mallinson and Longridge, 2004, Peterka et al., 1990). These authors investigated age related changes in slow-phase eye velocity following caloric irrigations and both revealed no significant influence of age on SPV. The absence of age-related changes in slow phase eye velocity in caloric testing contrasts with the structural changes observed in the central vestibular system with aging such as neuronal loss [for reviews: (Ishiyama, 2009, Iwasaki and Yamasoba, 2015). Therefore, structural alterations in the vestibular pathways could lead to potential reduction in VOR. However, future studies are required to better understand the mechanism responsible for maintaining VOR response in the elderly.

The results demonstrated that self-motion perception velocity could distinguish between young healthy ears and vestibular impaired ears. Indeed, similarly to what was observed with SPV, self-motion velocity perception was reduced in vestibular impaired ears. This is consistent with the fact that less peripheral stimulation (due to lesion) would lead to a lesser self-motion velocity perception. The present results contrast, however, with previous literature as no significant differences were observed between younger and older adults regarding self-motion velocity perception. Indeed, previous studies revealed that great proportions of older adults had an absence of motion perception following caloric irrigation (Jacobson, et al., 2018, Piker, et al., 2020). It is possible that the difference between our study and previous literature stems from the inclusions criteria. Indeed, Jacobson et al. (Jacobson, et al., 2018) and Piker al. (Piker, et al., 2020) selected participants with complaints of dizziness (non-vestibular origin) as opposed to healthy participants in our study. The significant absence of self-motion perception in these studies likely reflects central abnormalities, as the SPV remained within normal limits, yet the perception of self-motion was absent. Indeed, a lack of self-motion perception or elevated perception thresholds have previously been observed in patients with acute traumatic brain injury (Calzolari et al., 2020) and in those with small vessel disease (Kaski et al., 2019). Therefore, monitoring self-motion during caloric irrigation may provide a more comprehensive assessment beyond traditional VOR responses, aiding in the identification of central vestibular deficits. Indeed, absence of self-motion perception or elevated perception thresholds have previously been found in acute traumatic brain injury patients (Calzolari et al., 2020) and in patients with small vessels disease (Kaski et al., 2019).

The present study support for the first time the feasibility to simultaneously record slow phase eye velocity and self-motion velocity during caloric irrigation offering a new methodology, which can easily be transferred in clinical settings, to assess vestibular function beyond the traditional vestibulo-ocular reflex. As some pathologies seem to modulate vestibular perception, this method opens interesting opportunities to assess this in clinical settings. However, the use of the tachometer presents several limitations that needs to be considered in future studies. First, the tachometer limits the direction of motion in a rotation axis, which increase the difficulty for some participants to accurately match the velocity of perceived self-motion. Indeed, following caloric irrigation, participants do not always report a sensation of rotation (Mijovic et al., 2017). In the present study, two participants reported non-rotatory type of self-motion following caloric irrigation (pulled to one side and rocking sensation). This may have influenced the ability to accurately represent velocity of motion using tachometer. Future studies should aim at developing a method that allows recording velocity in different directions. Secondly, the caloric vestibular stimulation stimulates the vestibular system at very low frequencies (>0.003 Hz) (Shepard and Jacobson, 2016). Such stimulation is thought to be non-physiologic and therefore caution is required before using caloric stimulation as a pure vestibular perception test. However, as it is the most commonly available method in clinical settings, it is worth assessing the perceived vestibular motion to investigate possible dissociations between VOR and cortical pathways. Thirdly, in the present study, we did not include a practice session to minimize discomfort associated with caloric stimulation. However, we acknowledge that a practice trial could be very informative in assessing the participant’s ability to adequately complete the task. We suggest that future studies incorporate a practice session with other forms of stimulation, such as visual rotating stripes or rotational chair tests. Finally, as it was not part of the objective, we did not measure postural control abilities in these participants. This limits our ability to compare the influence of self-motion perception and postural control similarly to other previous studies (Chiarovano et al., 2016; Jacobson et al., 2018; Piker et al., 2020).

5. Conclusion

The present study demonstrates the feasibility to objectively monitor self-motion perception following caloric stimulation. The results suggest that VOR response (SPV) similarly to self-motion perception (RPM) can differentiate between vestibular impaired and healthy ears.

Acknowledgments

Conflict of interest statement

None of the authors have potential conflicts of interest to be disclosed.

Author contributions

Designed research : Maxime Maheu; Performed research : All authors; Analyzed data: All authors Wrote paper: All authors

Funding Statement

This work was supported bsy NSERC (RGPIN-2022-04402) and by the Fonds de Recherche en Santé du Québec (FRQS-329974) both awarded to Dr Maheu.

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