International Journal Elsevier
of Psychophysiology,
81
9 (1990) 81-84
PSYCHO 00264
The effect of low-frequency whole-body vibration under different visual conditions on auditory evoked potentials Helmut
Seidel, Uwe Schuster,
Departments
Gerhard
Menzel, Peter Ullsperger
and Ralph Bliithner
of Occupational Hygiene and Occupational Physiology, Central Institute for Occupational Medicine of the GDR, Berlin (G. D. R.) (Accepted 20 March 1989)
Key words: Whole-body vibration; Auditory evoked potential; Vision; Sensory interaction
Auditory evoked brain potentials (AEP) were recorded from 9 healthy males during sinusoidal whole-body vibration (WBV) in the longitudinal (*a,) direction with 0.6 Hz, 1.85 ms-*rms (Fl), 1.01 Hz, 4.27 ms-*rms (F2) and without WBV (F3) under 3 visual conditions - homogeneous bright visual field (B), normal vision (N), and complete darkness (D). The sequences of the different experimental conditions were arranged according to a 9 X 9 Latin Square design. A subtraction technique was used to eliminate vibration-synchronous activity from the EEG. The Nl and NlP2 amplitudes decreased during Fl and F2, compared to F3. The latencies of Nl and P2 increased during Fl and F2. The effects of Fl and F2 did not differ. The visual conditions exhibited no systematic effect on the AEP. The results suggest (1) Fl and F2 to be equivalent exposure conditions and (2) the dominance of vestibular-auditory interactions, compared with visual-auditory ones.
INTRODUCTION Up to now, the evaluation of very low-frequency whole-body vibration (WBV) has given rise to controversy (Allen and Sussmann, 1975; Griffin, 1986; Yonekawa and Miwa, 1972). Its effects have been much less investigated than responses to higher frequencies. WBV below 1 Hz is known to be a potential cause of motion sickness (O’Hanlon and McCauley, 1974). A better knowledge of human response to WBV is essential for a better understanding of motion sickness and its related symptoms. Sensory mismatch between the ongoing sensory experience and long-term memory (Kohl, 1983) has been considered an important mechanism responsible for the development of motion sickness.
Correspondence: H. Seidel, Zentralinstitut fur Arbeitsmedizin der DDR, Noldnerstr. 40/42, 1134 Berlin, G.D.R. 0167-8760/90/$03.50
Auditory evoked brain potentials (AEP) proved to be informative measures for studying the human response to WBV (Ullsperger and Seidel, 1980; Ullsperger et al., 1986). The amplitude of AEP diminished with decreasing frequencies of WBV between 8 and 1 Hz (Ullsperger et al., 1986). With decreasing frequency and constant acceleration of WBV, sensory afferent patterns change due to a decrease of somatosensory input and simultaneous increase of visual input resulting from increasing displacements, whereas vestibular afferences are supposed to remain constant. The question has remained open to which extent sensory interactions between the visual input and other afferences contribute to the changes of central nervous information processes during WBV (Ullsperger et al., 1986). The present study aimed at (1) comparing the effects of WBV-exposures with 0.6 and 1 Hz; (2) examining the consequences of different visual inputs on these effects.
0 1990 Elsevier Science Publishers B.V. (Biomedical Division)
82
MATERIALS Nine years
AND
healthy
participated
METHODS
males
aged
between
in the experiment.
23 and Except
31 for
one subject, they had no previous experience with WBV. Vertical sinusoidal WBV in the Z-axis was generated by an electronically controlled electrohydraulic vibrator. The subjects were exposed to WBV with 0.6 Hz and 1.85 msK2 rms (Fl), 1.01 Hz and 4.27 msK2 rms (F2) and control conditions without WBV (F3 = 0 Hz), each under 3
a computer, the peak amplitudes of the AEP’s were measured against a baseline calculated across a prestimulus part of 200 ms from which the vibration-synchronous (component windows:
activity was eliminated too Nl 50-200 ms, P2 150-250
ms). During the exposure, subjects were asked to keep their sitting posture as constant as possible and not to pay attention to the auditory stimuli. All data were tested by multifactorial analyses of variance (ANOVA) and r-tests for paired sam-
different visual inputs: homogeneous t ight visual field without the possibility of the perception of motion (B), normal vision (N), and complete dark-
ples.
ness (D). The visual conditions were realized by means of dust-protection spectacles and ad-
RESULTS
ditional illumination (B only). The spectacles fitted close to the head and restricted the peripheral
Fig. 1 shows the AEP grand mean waveforms for the conditions tested, averaged across all sub-
visual field. During B and D, the glasses of the spectacles were covered with white or black paper,
jects and experiments. The gross AEP waveform remained unchanged under all conditions tested.
respectively. N means the normal visual surrounding of the laboratory with an illumination of about
The results of the ANOVA and comparisons of mean values of the AEP amplitudes and the peak
600 lux. Each
latencies
run lasted
5 min. The sequence
the experimental runs was arranged 9 x 9 Latin square (9 experimental
of
according to a conditions, 9
subjects). Auditory stimuli (1 kHz, 50 ms, 86 dB, interstimulus interval 7 s) were presented via headphones to both ears. The background noise amounted to 50 dB. The EEG signal was recorded from the vertex with a right mastoid reference, preamplified near the electrodes and amplified in
are presented
in Table
I. Amplitudes,
as
well as peak latencies were influenced by the factor ‘Frequency of WBV’. The factor ‘Visual condition’ had no significant effect. During WBV exposures with Fl and F2, the amplitudes P2 and Nl-P2 decreased; increased.
the
latencies
of Nl
and
P2
the frequency band from 0.1 Hz to 15 Hz (resulting time delay caused by analog filters: 30 ms) and online averaged (sampling interval 2 ms) for epochs
of 600 ms, including
prestimulus
parts
of
200 ms. Possible changes of the DC-level due to WBV could not be detected because of the low cutoff frequency. After excluding artifacts on the basis of excessive amplitudes, the vibration-synchronous activity was automatically eliminated by a subtraction technique similar to that described earlier (Ullsperger and Seidel, 1980; Ullsperger et al., 1986). This subtraction method was also performed in runs without WBV in order to have a signal-to-noise ratio comparable to that during WBV. Thirty treated EEG-epochs were averaged to obtain the evoked potential for each run. Using
Fig. 1. Grand mean waveforms of auditory evoked potentials (AEPs) averaged across all 9 subjects. AEPs obtained during whole-body vibration (WBV) with frequencies 0.6 Hz (Fl), 1.01 Hz (F2) and control without WBV (F3) under visual conditions of a homogeneous bright visual field (bright). normal vision (normal), and complete darkness (dark).
83 TABLE
tudes was pronounced during the visual conditions N and D. The changes of latencies were independent of the visual condition. Effects of Fl and F2 did not differ.
I
F-ratios calculated by multi-factorial analysis of variance for the AEP amplitudes NI, P2, NI - P2 and their peak latencies Significant differences between mean values are indicated by the exposure conditions Fl (WBV 0.6 Hz), F2 (1.01 Hz), and F3 (0 Hz, control).
DISCUSSION
Source
Subject
Visual condition
Amplitudes Nl 2.23
Frequency
Significant differences
1.91
0.56
_
7.89 * 6.43 *
0.88 2.56
5.79 * 3.64 *
FliF3F2F3 Fl>F3F2>F3
P2 Nl-P2
Ullsperger et al. (1986) previously discussed 4 mechanisms by which WBV possibly affects AEP: (1) direct mechanical action on the inner ear, (2) changes of peripheral gating mechanisms, (3) sensory interactions, and (4) changes in central nervous activation. The internal mechanisms of multisensory integration are poorly understood at present (Meredith and Stein, 1986; Schaefer, 1985). In the case of vestibulo-auditory interactions, Ovsjanik et al. (1987) found the changes of medium latent acoustic potentials to depend on individual characteristics too. Therefore, the possibility that identical changes of AEP indicate different underlying processes cannot be excluded. With re-
* Significant F-ratios.
Table II presents the mean values of amplitudes and latencies for the 9 experimental conditions tested. The WBV-induced decrease of ampli-
TABLE II Mean values and standard deviations (in parentheses) of AEP-amplitudes with Fl = 0.6 Hz, F2 = 1.01 Hz and F3 = 0 Hz (control)
Nl, P2, NI-P2 and peak latencies during whole-body vibration
B: bright homogeneous visual field; N: normal visual field; D: darkness. Amplitude (pV) B Nl
P2
Nl-P2
Latency (ms) N
D
B
N
D
Fl
12.1
9.2
10.5
152
147
140
F2
(5.5) 12.3
(2.4) 9.6
(3.3) 11.0
(16) 141
(16) 142
(16) 140
F3
(4.5) 10.5
(2.9) 10.2
(4.0) 12.0
(17) 131
(19) 132
(20) 130
(2.2)
(4.8)
(8.5)
(13)
(13)
(16)
7.3
8.0
234
234
228
F2
9.3 (4.7) 9.6
(4.3) 6.9
(5.9) 7.6
(18) 226
(23) 228
(19) 214
F3
(6.5) 11.0
(4.1) 11.8
(3.5) 11.2
(23) 214
(27) 214
(30) 212
(4.2)
(5.6)
(2.5)
(21)
(18)
(21)
Fl
21.4
16.5
18.5
F2
(8.4) 21.9
(4.0) 16.5
(5.8) 18.6
F3
(9.5) 21.5
(5.2) 22.0
(2.6) 23.2
(5.1)
(9.6)
(4.2)
Fl
84
gard to the exposure conditions in the present experiment, mechanisms (3) and (4) seem to be of greatest significance. The equal effects of Fl and F2 indicate agreement with the frequency weighting proposed by Allen and Sussman (1975) and biological effects. WBV with both frequencies tested systematically acted on the AEP, whereas visual conditions did not. Considering mechanism 3, this is a surprising result, since vision is the most important human sense. It might hint at close links between the auditory and vestibular systems leading to a significant interaction. However, the clear tendency of smaller effects of WBV on the amplitudes P2 and Nl-P2 with the visual condition B suggests a certain modification of this interaction by vision. In addition, the lack of average changes of the AEP-amplitude during WBV under visual condition B contradict to the assumption that mechanism 1, i.e. changes in the inner ear, is of major importance. The increase of latencies was an effect occurring uniformly during WBV, namely, with the stimulation of the vestibular system. The question remains open to which extent the non-significant differences between AEP amplitudes at N, D and B during WBV might be linked with different changes of the arousal too. One hypothesis is that the unusual condition B has caused an activation, compensating partially the de-arousing effect of low-frequency WBV. In summary, the results suggest the dominance of vestibular-auditory interactions, compared with visual-auditory ones, although a modulating influence of the latter and possibly different directions of attention cannot safely be excluded.
ACKNOWLEDGEMENT This work was done in the Temporary International Research Team on Combined Effects of
Noise and Vibration of the Council of Mutual Economic Assistance of the Socialist Countries.
REFERENCES Allen, G.R. and Sussmann, E.D. (1975) Addendum to: International Standard IS0 2631 - Evaluation of Exposure to Whole-body Vibration Below I Hz. (ISO/TC lOS/SC 4, Secretariat 18), Geneva, October 1975. Griffin, M.J. (1986) Evaluation of vibration with respect to human response. SAE Technical Paper Series, 860047, P174, Passenger Comfort, Convenience and Safety: Test Tools and Procedures, pp. 11-34. Kohl. R.L. (1983) Sensory conflict theory of space motion sickness: an anatomical location for the neuroconflict. Auiat. Space Environ. Med., 54: 464-465. Meredith, M.A. and Stein, B.E. (1986) Visual, auditory, and somatosensory convergence on cells in superior colliculus results in multisensory integration. J. Neurophysiol., 56: 640-662. O’Hanlon, J.F. and McCauley, M.E. (1974) Motion sickness incidence as a function of the frequency and acceleration of vertical sinusoidal motion. Aerospace Med., 45: 366-369. Ovsjanik, V.P., Bakaj, E.A., Gurik, V.V., Karimov, R.S., Udovik, S.L. and Kovalenko, L.S. (1987) Effect of adequate stimulation of the vestibular apparatus on medium-latent acoustic evoked potentials. Kosm. Biol. i Auiakosm. Med., 21: 80-82. Schaefer, K.-P. (1985) Neurophysiologische Gnmdlagen des Orientierungsverhaltens und der multisensorischen Koordination. Funkt. Biol. Med., 14: 14-36. Ullsperger, P. and Seidel, H. (1980) On auditory evoked potentials and heart rate in man during whole-body vibration. Eur. J. Appl. Physiol., 43: 183-192. Ullsperger, P., Seidel, H. and Menzel, G. (1986) Effect of whole-body vibration with different frequencies and intensities on auditory evoked potentials and heart rate in man. Eur. J. Appl. Physiol., 54: 661-668. Yonekawa, Y. and Miwa, T. (1972) Sensational responses of sinusoidal whole body vibrations with ultra-low frequencies. Ind. Health. 10: 63-76.
of Psychophysiology,
81
9 (1990) 81-84
PSYCHO 00264
The effect of low-frequency whole-body vibration under different visual conditions on auditory evoked potentials Helmut
Seidel, Uwe Schuster,
Departments
Gerhard
Menzel, Peter Ullsperger
and Ralph Bliithner
of Occupational Hygiene and Occupational Physiology, Central Institute for Occupational Medicine of the GDR, Berlin (G. D. R.) (Accepted 20 March 1989)
Key words: Whole-body vibration; Auditory evoked potential; Vision; Sensory interaction
Auditory evoked brain potentials (AEP) were recorded from 9 healthy males during sinusoidal whole-body vibration (WBV) in the longitudinal (*a,) direction with 0.6 Hz, 1.85 ms-*rms (Fl), 1.01 Hz, 4.27 ms-*rms (F2) and without WBV (F3) under 3 visual conditions - homogeneous bright visual field (B), normal vision (N), and complete darkness (D). The sequences of the different experimental conditions were arranged according to a 9 X 9 Latin Square design. A subtraction technique was used to eliminate vibration-synchronous activity from the EEG. The Nl and NlP2 amplitudes decreased during Fl and F2, compared to F3. The latencies of Nl and P2 increased during Fl and F2. The effects of Fl and F2 did not differ. The visual conditions exhibited no systematic effect on the AEP. The results suggest (1) Fl and F2 to be equivalent exposure conditions and (2) the dominance of vestibular-auditory interactions, compared with visual-auditory ones.
INTRODUCTION Up to now, the evaluation of very low-frequency whole-body vibration (WBV) has given rise to controversy (Allen and Sussmann, 1975; Griffin, 1986; Yonekawa and Miwa, 1972). Its effects have been much less investigated than responses to higher frequencies. WBV below 1 Hz is known to be a potential cause of motion sickness (O’Hanlon and McCauley, 1974). A better knowledge of human response to WBV is essential for a better understanding of motion sickness and its related symptoms. Sensory mismatch between the ongoing sensory experience and long-term memory (Kohl, 1983) has been considered an important mechanism responsible for the development of motion sickness.
Correspondence: H. Seidel, Zentralinstitut fur Arbeitsmedizin der DDR, Noldnerstr. 40/42, 1134 Berlin, G.D.R. 0167-8760/90/$03.50
Auditory evoked brain potentials (AEP) proved to be informative measures for studying the human response to WBV (Ullsperger and Seidel, 1980; Ullsperger et al., 1986). The amplitude of AEP diminished with decreasing frequencies of WBV between 8 and 1 Hz (Ullsperger et al., 1986). With decreasing frequency and constant acceleration of WBV, sensory afferent patterns change due to a decrease of somatosensory input and simultaneous increase of visual input resulting from increasing displacements, whereas vestibular afferences are supposed to remain constant. The question has remained open to which extent sensory interactions between the visual input and other afferences contribute to the changes of central nervous information processes during WBV (Ullsperger et al., 1986). The present study aimed at (1) comparing the effects of WBV-exposures with 0.6 and 1 Hz; (2) examining the consequences of different visual inputs on these effects.
0 1990 Elsevier Science Publishers B.V. (Biomedical Division)
82
MATERIALS Nine years
AND
healthy
participated
METHODS
males
aged
between
in the experiment.
23 and Except
31 for
one subject, they had no previous experience with WBV. Vertical sinusoidal WBV in the Z-axis was generated by an electronically controlled electrohydraulic vibrator. The subjects were exposed to WBV with 0.6 Hz and 1.85 msK2 rms (Fl), 1.01 Hz and 4.27 msK2 rms (F2) and control conditions without WBV (F3 = 0 Hz), each under 3
a computer, the peak amplitudes of the AEP’s were measured against a baseline calculated across a prestimulus part of 200 ms from which the vibration-synchronous (component windows:
activity was eliminated too Nl 50-200 ms, P2 150-250
ms). During the exposure, subjects were asked to keep their sitting posture as constant as possible and not to pay attention to the auditory stimuli. All data were tested by multifactorial analyses of variance (ANOVA) and r-tests for paired sam-
different visual inputs: homogeneous t ight visual field without the possibility of the perception of motion (B), normal vision (N), and complete dark-
ples.
ness (D). The visual conditions were realized by means of dust-protection spectacles and ad-
RESULTS
ditional illumination (B only). The spectacles fitted close to the head and restricted the peripheral
Fig. 1 shows the AEP grand mean waveforms for the conditions tested, averaged across all sub-
visual field. During B and D, the glasses of the spectacles were covered with white or black paper,
jects and experiments. The gross AEP waveform remained unchanged under all conditions tested.
respectively. N means the normal visual surrounding of the laboratory with an illumination of about
The results of the ANOVA and comparisons of mean values of the AEP amplitudes and the peak
600 lux. Each
latencies
run lasted
5 min. The sequence
the experimental runs was arranged 9 x 9 Latin square (9 experimental
of
according to a conditions, 9
subjects). Auditory stimuli (1 kHz, 50 ms, 86 dB, interstimulus interval 7 s) were presented via headphones to both ears. The background noise amounted to 50 dB. The EEG signal was recorded from the vertex with a right mastoid reference, preamplified near the electrodes and amplified in
are presented
in Table
I. Amplitudes,
as
well as peak latencies were influenced by the factor ‘Frequency of WBV’. The factor ‘Visual condition’ had no significant effect. During WBV exposures with Fl and F2, the amplitudes P2 and Nl-P2 decreased; increased.
the
latencies
of Nl
and
P2
the frequency band from 0.1 Hz to 15 Hz (resulting time delay caused by analog filters: 30 ms) and online averaged (sampling interval 2 ms) for epochs
of 600 ms, including
prestimulus
parts
of
200 ms. Possible changes of the DC-level due to WBV could not be detected because of the low cutoff frequency. After excluding artifacts on the basis of excessive amplitudes, the vibration-synchronous activity was automatically eliminated by a subtraction technique similar to that described earlier (Ullsperger and Seidel, 1980; Ullsperger et al., 1986). This subtraction method was also performed in runs without WBV in order to have a signal-to-noise ratio comparable to that during WBV. Thirty treated EEG-epochs were averaged to obtain the evoked potential for each run. Using
Fig. 1. Grand mean waveforms of auditory evoked potentials (AEPs) averaged across all 9 subjects. AEPs obtained during whole-body vibration (WBV) with frequencies 0.6 Hz (Fl), 1.01 Hz (F2) and control without WBV (F3) under visual conditions of a homogeneous bright visual field (bright). normal vision (normal), and complete darkness (dark).
83 TABLE
tudes was pronounced during the visual conditions N and D. The changes of latencies were independent of the visual condition. Effects of Fl and F2 did not differ.
I
F-ratios calculated by multi-factorial analysis of variance for the AEP amplitudes NI, P2, NI - P2 and their peak latencies Significant differences between mean values are indicated by the exposure conditions Fl (WBV 0.6 Hz), F2 (1.01 Hz), and F3 (0 Hz, control).
DISCUSSION
Source
Subject
Visual condition
Amplitudes Nl 2.23
Frequency
Significant differences
1.91
0.56
_
7.89 * 6.43 *
0.88 2.56
5.79 * 3.64 *
FliF3F2F3 Fl>F3F2>F3
P2 Nl-P2
Ullsperger et al. (1986) previously discussed 4 mechanisms by which WBV possibly affects AEP: (1) direct mechanical action on the inner ear, (2) changes of peripheral gating mechanisms, (3) sensory interactions, and (4) changes in central nervous activation. The internal mechanisms of multisensory integration are poorly understood at present (Meredith and Stein, 1986; Schaefer, 1985). In the case of vestibulo-auditory interactions, Ovsjanik et al. (1987) found the changes of medium latent acoustic potentials to depend on individual characteristics too. Therefore, the possibility that identical changes of AEP indicate different underlying processes cannot be excluded. With re-
* Significant F-ratios.
Table II presents the mean values of amplitudes and latencies for the 9 experimental conditions tested. The WBV-induced decrease of ampli-
TABLE II Mean values and standard deviations (in parentheses) of AEP-amplitudes with Fl = 0.6 Hz, F2 = 1.01 Hz and F3 = 0 Hz (control)
Nl, P2, NI-P2 and peak latencies during whole-body vibration
B: bright homogeneous visual field; N: normal visual field; D: darkness. Amplitude (pV) B Nl
P2
Nl-P2
Latency (ms) N
D
B
N
D
Fl
12.1
9.2
10.5
152
147
140
F2
(5.5) 12.3
(2.4) 9.6
(3.3) 11.0
(16) 141
(16) 142
(16) 140
F3
(4.5) 10.5
(2.9) 10.2
(4.0) 12.0
(17) 131
(19) 132
(20) 130
(2.2)
(4.8)
(8.5)
(13)
(13)
(16)
7.3
8.0
234
234
228
F2
9.3 (4.7) 9.6
(4.3) 6.9
(5.9) 7.6
(18) 226
(23) 228
(19) 214
F3
(6.5) 11.0
(4.1) 11.8
(3.5) 11.2
(23) 214
(27) 214
(30) 212
(4.2)
(5.6)
(2.5)
(21)
(18)
(21)
Fl
21.4
16.5
18.5
F2
(8.4) 21.9
(4.0) 16.5
(5.8) 18.6
F3
(9.5) 21.5
(5.2) 22.0
(2.6) 23.2
(5.1)
(9.6)
(4.2)
Fl
84
gard to the exposure conditions in the present experiment, mechanisms (3) and (4) seem to be of greatest significance. The equal effects of Fl and F2 indicate agreement with the frequency weighting proposed by Allen and Sussman (1975) and biological effects. WBV with both frequencies tested systematically acted on the AEP, whereas visual conditions did not. Considering mechanism 3, this is a surprising result, since vision is the most important human sense. It might hint at close links between the auditory and vestibular systems leading to a significant interaction. However, the clear tendency of smaller effects of WBV on the amplitudes P2 and Nl-P2 with the visual condition B suggests a certain modification of this interaction by vision. In addition, the lack of average changes of the AEP-amplitude during WBV under visual condition B contradict to the assumption that mechanism 1, i.e. changes in the inner ear, is of major importance. The increase of latencies was an effect occurring uniformly during WBV, namely, with the stimulation of the vestibular system. The question remains open to which extent the non-significant differences between AEP amplitudes at N, D and B during WBV might be linked with different changes of the arousal too. One hypothesis is that the unusual condition B has caused an activation, compensating partially the de-arousing effect of low-frequency WBV. In summary, the results suggest the dominance of vestibular-auditory interactions, compared with visual-auditory ones, although a modulating influence of the latter and possibly different directions of attention cannot safely be excluded.
ACKNOWLEDGEMENT This work was done in the Temporary International Research Team on Combined Effects of
Noise and Vibration of the Council of Mutual Economic Assistance of the Socialist Countries.
REFERENCES Allen, G.R. and Sussmann, E.D. (1975) Addendum to: International Standard IS0 2631 - Evaluation of Exposure to Whole-body Vibration Below I Hz. (ISO/TC lOS/SC 4, Secretariat 18), Geneva, October 1975. Griffin, M.J. (1986) Evaluation of vibration with respect to human response. SAE Technical Paper Series, 860047, P174, Passenger Comfort, Convenience and Safety: Test Tools and Procedures, pp. 11-34. Kohl. R.L. (1983) Sensory conflict theory of space motion sickness: an anatomical location for the neuroconflict. Auiat. Space Environ. Med., 54: 464-465. Meredith, M.A. and Stein, B.E. (1986) Visual, auditory, and somatosensory convergence on cells in superior colliculus results in multisensory integration. J. Neurophysiol., 56: 640-662. O’Hanlon, J.F. and McCauley, M.E. (1974) Motion sickness incidence as a function of the frequency and acceleration of vertical sinusoidal motion. Aerospace Med., 45: 366-369. Ovsjanik, V.P., Bakaj, E.A., Gurik, V.V., Karimov, R.S., Udovik, S.L. and Kovalenko, L.S. (1987) Effect of adequate stimulation of the vestibular apparatus on medium-latent acoustic evoked potentials. Kosm. Biol. i Auiakosm. Med., 21: 80-82. Schaefer, K.-P. (1985) Neurophysiologische Gnmdlagen des Orientierungsverhaltens und der multisensorischen Koordination. Funkt. Biol. Med., 14: 14-36. Ullsperger, P. and Seidel, H. (1980) On auditory evoked potentials and heart rate in man during whole-body vibration. Eur. J. Appl. Physiol., 43: 183-192. Ullsperger, P., Seidel, H. and Menzel, G. (1986) Effect of whole-body vibration with different frequencies and intensities on auditory evoked potentials and heart rate in man. Eur. J. Appl. Physiol., 54: 661-668. Yonekawa, Y. and Miwa, T. (1972) Sensational responses of sinusoidal whole body vibrations with ultra-low frequencies. Ind. Health. 10: 63-76.
