353 zyxwvut References Barlow, H.B. (1979) Reconstructing the visual image in space and time. Nature. 279: 189-190. Beck, J. and Halloran, T. (1985) Effects of spatial separation and retinal eccentricity on two-dot vernier acuity. Vision Res. 25: 1105-1111. Fomin, S.V., Sokolov, E.N. and Vaitkevi&us, H. (1979) Artificial sensors. Moskow, (In Russian). Klein, S.A. and Levi, D.M. (1985) Hyperacuity thresh- olds of 1 set: theoretical predictions and empirical validation. J.Opt.Soc.Am. A2: 1170-1190. Mart-, D. (1982) Vision, San Francisco. Pollen, D.A. and ROMer, S.P. (1983) Visual cortical neurones as localized spatial filters. IEEE Trans. and Syst. SMC-13: 907-916. Watt, RJ. and Morgan, MJ. (1983) Mechanisms responsible for the assessment of visual location: theory and evidence. Visual Res. 23: 97-109. Westheimer, G. (1975) Visual acuity and hyperacuity. InvestGpthalmol, 14: 570-572. EMG OF FACIAL MUSCLES IN SENSORIMOTOR TASKS D. Philipova, A. Angelov, V. Kolev, T. Vladova, V. Siljamova Brain Research Institute, Bulgarian Academy of Scien- ces, Acad. Bonchev str. 23, Sofia, Bulgaria Application of electromyographic investigation (EMG) to the polygmphic analysis of mental and emotional tension turns out to be an informative method for giving an assessment of the man’s adaptive capacities for varying neurophysiologic mental loads (Cacioppo 1981, Krauklis 1972, Klimova-Cherkasova 1982). The question we set before ourselves in the course of our investigations in the present experiment are the follow- ing: to what extent the facial EMG may reflect the functional state of brain in conditions of processing of sensory information and what is its relation to this processing. In order to answer these questions we studied twenty-one persons in several situations of tasks related to auditory stimulation: a) passive listen- ing b) a simple motor task in 100% series of low tones (800 Hz) - a quick respond to the tone by pressing a button with the thumb to the right hand. c) a selective motor task with stimuli of different probability charac- teristics - 75% high tones (1200 Hz) and 25% low tones (800 Hz) with a respond to the high tone by the left hand and to the low one by the right hand. d) a selective motor task in the same situation that in case “c” after the instruction for increase of motiva- tion. We recorded electromyograms in healthy volunteers of the m. frontalis dextra, m. triangularis dextra, m. masseter dextra (surface electrodes) and the behaviour indicator - reaction time; electroencephalograms from Cz and heart rate, which will serve as a basis for another report The researches were held with a Nichon Kohden apparatus. We recorded the bioelectric signals on paper and on a tape recorder for further processing. During the examination in chamber facial and jaw movements, as well as swallowing were observed exactly by video camera. The changes of facial muscles in sensorimotor tasks are complex, there are and individual variations, but generally the dynamic pattern of facial EMG in differ- ent situation of tasks may be characterized in the following way: In the series of passive listening no dynamics in the facial EMG has been registered. In situation of simple motor task half of investigated persons show slight activating changes in the direction of increasing the activity of the mm. triangular-isand/or frontalis. In situation of a selective motor task the changes are more complex - 11 out of 21 persons show increasing bioelectric activity predominantly of the mm. triangularis and/or frontalis, 3 of the investigated persons show decreasing activity and with the rest no significant dynamics in the facial EMG has been registrated. After the instruction for increase of motivation the nonspecific bioelectric activity in the facial muscles increases. The number of persons who show increasing of facial muscular tension (66% of persons), as well as the number of activated muscles are growing. Very often these changes ate registered in the region of oral pole - m. triangularis. We found out an interdepend- ence between the dynamics of this activity and the time of reaction - persons who shorted significantly the reaction time show higher non-specific activation of facial muscles and those who do not shorten reaction time do not show any change in the EMG dynamics in comparison with the series without an increased moti- vation. Probably these persons had the maximum level