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A Vacuum-Tube Oscillatorfor Frequency Calibration ofElectroencephalo-Graphic andElectromyographic RecordsLouis William Max aa Department of Psychology , New York UniversityPublished online: 04 Nov 2012.

To cite this article: Louis William Max (1941) A Vacuum-Tube Oscillator for FrequencyCalibration of Electroencephalo-Graphic and Electromyographic Records, The Journalof General Psychology, 24:1, 225-226, DOI: 10.1080/00221309.1941.10544372

To link to this article: http://dx.doi.org/10.1080/00221309.1941.10544372

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The Journal of General Psychology, 1941, 24, 225-226.

A VACUUM-TUBE OSCILLATOR FOR FREQUENCY CALIBRATION OF ELECTROENCEPHALO­

GRAPHIC AND ELECTROMYOGRAPHIC RECORDS*

Department of Psychology, New York University

Louis WILLIAM MAx

In many of the recent studies of the electroencephalogram, the method commonly used for quantitative calibration of the records has been to impress upon the amplifier-recorder system a single pulsation of known microvoltage. Such a method is not quite accu­rate, for, as has previously been shown in another connection ( 1, p. I65n), voltage calibration of an amplifier at one frequency does not necessarily calibrate for physiological waves of other frequencies. The usual amplifier has a tendency to discriminate against lower frequencies and hence will amplify the alpha waves less than the betas. A more accurate method of calibration would be to register on the objective record the same known voltage at both the 10-cycle and 25-cycle frequencies. Since, however, a laboratory may need amplifier-recorder systems for electromyographic as well as for elec­troencephalographic research, a useful device would be one which would provide calibrating potentials at alpha, beta, and electromyo­graphic frequencies. We have built such a device for our own laboratory where it has been in successful use for some time. It is here briefly described.

The underlying principle of operation is the same as that of the 50-cycle oscillator previously described (I, Figure 3). In the present model, with C 1 = 0.5 mfd. (cf., ibid. Figure 3 and Table 1), an audio transformer1 is used instead of L 1, and a switch introduces in parallel therewith at C4 a capacity of 0.022 mfd. for the 50-cycle cali­bration, plus an additional 0.080 mfd. for 25 cycles, and a further increment of 0.395 mfd. for the alpha or 10-cycle frequency. These electrical values were determined for this particular transformer and circuit.

*Received in the Editorial Office on August 31, 1939. 1This is a Bremer-Tully "Euphonic" Interstage audio-transformer, made

by the Bremer-Tully Mfg. Co., Chicago.

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226 JOURNAL OF GENERAL PSYCHOLOGY

The whole unit is housed in a crackle-painted metal shield which also contains the batteries; the instrument is thus self-contained and portable. The particular electromyographic frequency here selected was 50 c.p.s. because we were primarily interested in the flexores digitorum (2, 3) ; but by varying the capacity C4 in accordance with

1 the formula f = any other desired frequency can of course

21ryLC be obtained.

Since the purchase price of the components of this oscillator comes to less than $25.00, it might well replace the currently used but less accurate expedient of calibrating with a single pulsation.2

REFERENCES

1. MAX, L. W. An experimental study of the motor theory of conscious­ness: II. Method and apparatus. J. Gen. Psychol., 1935, 13, 159-175.

2. . An experimental study of the motor theory of consciousness: Ill. Action-current responses in deaf-mutes during sleep, sensory stimulation, and dreams. J. Comp. Psycho/., 1935, 19, 469-486.

3. . An experimental study of the motor theory of consciousness: IV. Action-current responses in the deaf during awakening, kinaes­thetic imagery, and abstract thinking. J. Comp. Psycho/., 1937, 24, 301-34-4.

675 West End Avenue New York City

2A reliable attenuator-circuit for measuring the potential of the fre­quencies in terms of microvolts and millivolts has already been described (1, Figure 4). We have, on several occasions, checked the accuracy of the No. 546A Microvolter manufactured by the General Radio Company for this purpose, and have found that its microvolt ranges are subject to exten­sive para~itic voltages in an AC environment.

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