critical issue of the relationship between brain physiology and conscious experience will be discussed.

EARLY CORTICAL AUDITORY EVOKED POTEN-

TIALS (ECAEPS) ARE INFLUENCED BY CENTRAL

VESTIBULAR STIMULATION

Th. Prohst

Inst. of Physiol. Psychology. Dept. of Exp. Biol. Psychol.

University of Dusseldorf. D-4000 Diisseldorf. F.R.G.

The aim of the experiments reported here was to confirm

electrophysiologically the results of psychophysical experi-

ments. in which a pronounced vestibular stimulation led to a

marked increase in threshold of simultaneous auditory

object-motion perception. Because of the basic difficulty to

record scalp-hiosignals the generation of which depends upon

the perception of motion of an auditory stimulus. ECAEPs

were recorded by acoustic click stimuli lacking the specific

quality of motion under two vestibular stimulus conditions:

(1) f~~ripheru/ly triggered vestihular stimulation by passive

sinusoidal head oscillations at a frequency of 1 Hz (AmpI.:

k 20 o ) with peak accelerations of about 790 O/s’ could not

show a sensory interaction between auditory and vestibular

afferences because of the distinct myogenic contamination of

the interesting components of the ECAEP being otherwise of

mainly neurogenic origin. (2) Cenfrall~ triggered vestihular stimulation by visually

induced self-motion perception (circularvection) in the objec-

tively stationary observer where no head movements were

made showed a significant reduction in amplitude of the

ECAEP-component N,, /PC, (Latency: 25 msl, which is mainly

intracranial in origin as a neurogenic response of the primary

auditory cortex. The results obtained under the circularvection condition

support the hypothesis that an inhihitory interaction already

demonstrated for i,isuu( perception exists for auditory pro-

cessing as well.

BIOPIIYSICAL AND NEURONAL MECHANISMS OF VISCERAL PAIN

0. Piill, L.-P. Erasmus. M. Escrihuela-Branz and R. H&l

MPI of Psychiatry, Munich. Germany

Visceral hyperalgesia is an important part of psychophysiolog- ical syndromes like the irritable bowel syndrome. After

Ritchie’s attempt to explain it by lowered bowel compliance had heen only partially successful, ‘central’ hypotheses have

heen favored. The studies summarized here show that his

results are still relevant if mechanisms of peripheral transduc-

tion of distension stimuli are analysed more carefully and with improved methods. In two subsequent studies with Sl irritable

colon patients and h5 healthy controls previous findings of lowered tolerance of colon distension could be replicated in

terms of volume at tolerance limits. However. corresponding

intraluminal pressures were consistently higher in patients.

This contradicts a simple hypersensitivity model and must be

interpreted as adaptation to higher stimulation levels of vis-

ceral stretch receptors due to reduced bowel compliance.

Therefore, visceral hyperalgesias of the irritable bowel type

should not be attributed prematurely to central variables

without specifying functional changes at the peripheral trans-

duction site.

THE PSYCHOPHYSIOLOGY OF VISUAL-MOTOR CO-

ORDINATION

T. Radii. Z. Bohdanecky. M. Indra and J. Mates

Institute of Physiology. Czechoslovak Academy of Sciences,

Prague. Czechoslovakia

Computer controlled methods have been developed for dis-

playing moving targets (T) and recording hand movements

(HM) in human subjects during tracking the stimulus. The influence of T speed. trajectory dimension (ID, 2Dl. respec-

tively, type of trajectory (line, circle. square). type of T move- ment (1D sinusoidal, ID ramp). T versus HM direction (equal,

reversed) and dependence of TM on HM (feedback control of T size and T speed) have been analyzed and corresponding

psychophysiological parameters measured. Correlations be-

tween tracking errors. respectively. their correction and cor- dial cycle phase and heart rate as well as EEG slow potential

shifts have heen described.

TEMPORAL STRUCTURE IN ACOUSTICAL-MOTOR

FOLLOWING

T. Radil. E. Poppel ’ and J. Mates

Institute of Physiology, Czechoslovak Academy of Sciences,

Prague. Czechoslovakia and ’ Institute of Medical Psychology.

LMU. Munich, F.R.G.

Rhythmic acoustical sequences have been generated by means

of a computer and the ability of subjects to follow them by

finger tapping analyzed. Usually tapping onset preceded stim- ulus onset. The duration of this anticipation interval de-

creased to values close to zero when the pause between the

preceding finger contact with the response key and the follow-

ing stimulus onset became short (fast tapping. prolongation ol

stimulus tones combined with an instruction to hold the key) and increased when the task became more difficult (stimulus

sequences with missing tones, false feedback on tapping). Timing of key holding depended on the temporal structure of

tonal sequences. short tones were overestimated. long ones

underestimated. usually. Humans possess an ahility of follow- ing rhythmic stimulus sequences with high accuracy. they do

transform, however. the objective temporal structure into a subjective one. The results are interpreted in the frame of a

theory on hierarchical mechanisms of timing in the human brain.