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Conative control of the contingent negative variation
Electroencephalography and Clinical Neurophysiology Elsevier Publishing Company, Amsterdam - Printed in The Netherlands
CLINICAL
AND
LABORATORY
NOTES
CONATIVE CONTROL OF THE CONTINGENT NEGATIVE VARIATION DALE W . MCADAM, DONALD A . IRWIN, CHARLES S. REBERT AND JOHN R . KNOTT Division o f Electroencephalography and Neurophysiology, Department o f Psychiatry, University o f Iowa, Iowa City, Iowa ( U . S . A . )
(Accepted for publication: February 21, 1966)
The "contingent negative variation" (CNV), originally described by Walter et al. (1964), is a slow potential shift occurring during the foreperiod; i.e., between warning and response signals, in a reaction time experiment. It is customarily recorded between an "active" vertex electrode and a "reference" electrode on the mastoid process. It appears as vertex negativity which begins in the late phases of the evoked potential to the first, or warning, stimulus, and which persists until a response is made to the second stimulus. The CNV has been reported to vary systematically with several experimental manipulations and, as a result, has been linked with psychological constructs such as "expectancy" (Walter 1964), "motivation" (Irwin et al. 1966) and "conation" (Low et al. 1966). On some occasions, "in group" personnel, i.e., the experimenters themselves, have been used as subjects in these experiments. Whereas the "trained observer" is often more useful than the "naive subject", the inadvertent biasing of data is always a danger when the former is employed. The purpose of the present study was to investigate the extent to which an experimenter-subject could control his CNV.
would, if CNVs were under voluntary control, generate a plot of CNV magnitude against blocks of trials which would have the form of a "W". RESULTS Fig. 1 presents a graph of the mean magnitude of the CNV in #V when the experimenter-subjects were asked to "think high CNV", or to "think low CNV" alternately. The experimenter-subjects were indeed able to generate a W-shaped curve, and a sign test (Siegel 1956, p. 68-75) of the differences between "think high" and "think low" points was statistically significant at the p < 0.015 level. Experimenter-subject D.M. reported that, in order to generate a high CNV, he "attempted to gauge the interval between stimuli exactly, and to make the response exactly coincident with the second stimulus". Experimenter-sub-
25-
METHODS Silver silver chloride electrodes were applied, using collodion, to the vertex and mastoid process of each of the first three authors. Experimenter-subjects were seated in a comfortable chair and a telegraph key was placed below the fingers of the right hand. "Warning" and "imperative" stimuli were flashes from a Grass PS-2 photostimulator lamp separated by a 1.5 sec interval. EEGs were recorded with a Grass Model 7P1 low level DC pre-amplifier and its attendant driver amplifier. "Averages" of 10 trials were made using an Enhancetron. A 25 /~V calibration pulse was superimposed on each trace (Erode 1964), and the magnitude of the CNV was measured as the maximum departure of the trace during the inter-stimulus interval from the pre-trial baseline. Experimenter-subjects were instructed to produce, for successive blocks of 10 trials, large, small, large, small and large amplitude CNVs. It was predicted that this procedure
15" •. ~ .
~.
%. ~:~. %.
i
"THINK:-'~" High
.~i~.~ ~ .~... ~ .... ~,
i
~ .~
I
Low High CONDITIONS
I
Low
High
Fig. 1 Mean/~V of CNV during conditions when experimentersubjects were instructed to "think high CNV", or "think low CNV". N -- 3. Electroenceph. clin. Neurophysiol., 1966, 2 1 : 1 9 4 - 1 9 5
CONTROL OF CNV ject C.R. stated that, when instructed to "think high CNV", he "imagined that the second stimulus was very difficult to detect, and that he must push the key as hard and fast as possible". Experimenter-subject D.I. "concentrated on perceiving the second stimulus and making a fast response to it" in order to generate a high CNV. All three experimenter-subjects reported relaxing their vigilance and their speed efforts to generate low CNVs 1. DISCUSSION Since sophisticated subjects ("trained observers") are able to control their CNVs "at will" through adopting the appropriate "mental sets", results of experiments which use such subjects (especially those having a prior knowledge of the predicted results) must be interpreted with extreme caution. Wherever feasible, it would be advisable to use persons who are not familiar with the CNV phenomenon to explore and elucidate its psychological correlates.
1 A further set of data were obtained on the fourth author-subject. Excellent CNVs were generated at a 1.5 sec inter-stimulus interval, even under conditions of overall low vigilance, i.e., drowsiness. However, with a 4 sec interval, no CNV could be generated, even by utilizing specific anticipatory techniques to gauge the interval, and by concentrating on fast and firm responses. This suggests that temporal, as well as other, including conative, factors are involved in control of CNV amplitude.
195 SUMMARY
Experiments are described in which experimentersubjects were able to control the amplitude of the contingent negative variation "at will". It is urged that any investigations of the psychological correlates of the CNV which make use of "trained observers" should be interpreted with this possible source of bias in mind, and replicated, where feasible, using unbiased, naive subjects. REFERENCES EMDE, J. W. A time locked, low level calibrator. Electroenceph, elin. Neurophysiol., 1964, 16: 616-618. IRWIN, D. A., REBERT, C. S., MCADAM, D. W. and KNoTr, J. R. Slow potential changes (CNV) in the human EEG as a function of motivational variables. Electroenceph. clin. Neurophysiol., 1966, 2l : in press. Low, M. D., FROST, J. D., BORDA, R. P. and KELLAWAY, P. Surface negative slow potential shift associated with conditioning in man and sub-human primates. Electroenceph, din. Neurophysiol., 1966, 21: in press. SIEGEL, S. Nonparametric statistics for the behavioral sciences. McGraw-Hill, New York, 1956, 312 p. WALTER, W. G. Slow potential waves in the human brain associated with expectancy, attention and decision. Arch. Psychat. Nervenkr., 1964, 206: 309-322. WALTER, W. G., COOPER, R., ALDRIDGE, V. J., MCCALLUM, W. C. and WINTER, A. L. Contingent negative variation: an electric sign of sensorimotor association and expectancy in the human brain. Nature (Loud.), 1964, 203: 380-384.
Reference: MCADAM, D. W., IRWIN, D. A., REa~RT, C. S. and KNoa'r, J. R. Conative control of the contingent negative variation. Electroenceph. clin. Neurophysiol., 1966, 21: 194-195.
CLINICAL
AND
LABORATORY
NOTES
CONATIVE CONTROL OF THE CONTINGENT NEGATIVE VARIATION DALE W . MCADAM, DONALD A . IRWIN, CHARLES S. REBERT AND JOHN R . KNOTT Division o f Electroencephalography and Neurophysiology, Department o f Psychiatry, University o f Iowa, Iowa City, Iowa ( U . S . A . )
(Accepted for publication: February 21, 1966)
The "contingent negative variation" (CNV), originally described by Walter et al. (1964), is a slow potential shift occurring during the foreperiod; i.e., between warning and response signals, in a reaction time experiment. It is customarily recorded between an "active" vertex electrode and a "reference" electrode on the mastoid process. It appears as vertex negativity which begins in the late phases of the evoked potential to the first, or warning, stimulus, and which persists until a response is made to the second stimulus. The CNV has been reported to vary systematically with several experimental manipulations and, as a result, has been linked with psychological constructs such as "expectancy" (Walter 1964), "motivation" (Irwin et al. 1966) and "conation" (Low et al. 1966). On some occasions, "in group" personnel, i.e., the experimenters themselves, have been used as subjects in these experiments. Whereas the "trained observer" is often more useful than the "naive subject", the inadvertent biasing of data is always a danger when the former is employed. The purpose of the present study was to investigate the extent to which an experimenter-subject could control his CNV.
would, if CNVs were under voluntary control, generate a plot of CNV magnitude against blocks of trials which would have the form of a "W". RESULTS Fig. 1 presents a graph of the mean magnitude of the CNV in #V when the experimenter-subjects were asked to "think high CNV", or to "think low CNV" alternately. The experimenter-subjects were indeed able to generate a W-shaped curve, and a sign test (Siegel 1956, p. 68-75) of the differences between "think high" and "think low" points was statistically significant at the p < 0.015 level. Experimenter-subject D.M. reported that, in order to generate a high CNV, he "attempted to gauge the interval between stimuli exactly, and to make the response exactly coincident with the second stimulus". Experimenter-sub-
25-
METHODS Silver silver chloride electrodes were applied, using collodion, to the vertex and mastoid process of each of the first three authors. Experimenter-subjects were seated in a comfortable chair and a telegraph key was placed below the fingers of the right hand. "Warning" and "imperative" stimuli were flashes from a Grass PS-2 photostimulator lamp separated by a 1.5 sec interval. EEGs were recorded with a Grass Model 7P1 low level DC pre-amplifier and its attendant driver amplifier. "Averages" of 10 trials were made using an Enhancetron. A 25 /~V calibration pulse was superimposed on each trace (Erode 1964), and the magnitude of the CNV was measured as the maximum departure of the trace during the inter-stimulus interval from the pre-trial baseline. Experimenter-subjects were instructed to produce, for successive blocks of 10 trials, large, small, large, small and large amplitude CNVs. It was predicted that this procedure
15" •. ~ .
~.
%. ~:~. %.
i
"THINK:-'~" High
.~i~.~ ~ .~... ~ .... ~,
i
~ .~
I
Low High CONDITIONS
I
Low
High
Fig. 1 Mean/~V of CNV during conditions when experimentersubjects were instructed to "think high CNV", or "think low CNV". N -- 3. Electroenceph. clin. Neurophysiol., 1966, 2 1 : 1 9 4 - 1 9 5
CONTROL OF CNV ject C.R. stated that, when instructed to "think high CNV", he "imagined that the second stimulus was very difficult to detect, and that he must push the key as hard and fast as possible". Experimenter-subject D.I. "concentrated on perceiving the second stimulus and making a fast response to it" in order to generate a high CNV. All three experimenter-subjects reported relaxing their vigilance and their speed efforts to generate low CNVs 1. DISCUSSION Since sophisticated subjects ("trained observers") are able to control their CNVs "at will" through adopting the appropriate "mental sets", results of experiments which use such subjects (especially those having a prior knowledge of the predicted results) must be interpreted with extreme caution. Wherever feasible, it would be advisable to use persons who are not familiar with the CNV phenomenon to explore and elucidate its psychological correlates.
1 A further set of data were obtained on the fourth author-subject. Excellent CNVs were generated at a 1.5 sec inter-stimulus interval, even under conditions of overall low vigilance, i.e., drowsiness. However, with a 4 sec interval, no CNV could be generated, even by utilizing specific anticipatory techniques to gauge the interval, and by concentrating on fast and firm responses. This suggests that temporal, as well as other, including conative, factors are involved in control of CNV amplitude.
195 SUMMARY
Experiments are described in which experimentersubjects were able to control the amplitude of the contingent negative variation "at will". It is urged that any investigations of the psychological correlates of the CNV which make use of "trained observers" should be interpreted with this possible source of bias in mind, and replicated, where feasible, using unbiased, naive subjects. REFERENCES EMDE, J. W. A time locked, low level calibrator. Electroenceph, elin. Neurophysiol., 1964, 16: 616-618. IRWIN, D. A., REBERT, C. S., MCADAM, D. W. and KNoTr, J. R. Slow potential changes (CNV) in the human EEG as a function of motivational variables. Electroenceph. clin. Neurophysiol., 1966, 2l : in press. Low, M. D., FROST, J. D., BORDA, R. P. and KELLAWAY, P. Surface negative slow potential shift associated with conditioning in man and sub-human primates. Electroenceph, din. Neurophysiol., 1966, 21: in press. SIEGEL, S. Nonparametric statistics for the behavioral sciences. McGraw-Hill, New York, 1956, 312 p. WALTER, W. G. Slow potential waves in the human brain associated with expectancy, attention and decision. Arch. Psychat. Nervenkr., 1964, 206: 309-322. WALTER, W. G., COOPER, R., ALDRIDGE, V. J., MCCALLUM, W. C. and WINTER, A. L. Contingent negative variation: an electric sign of sensorimotor association and expectancy in the human brain. Nature (Loud.), 1964, 203: 380-384.
Reference: MCADAM, D. W., IRWIN, D. A., REa~RT, C. S. and KNoa'r, J. R. Conative control of the contingent negative variation. Electroenceph. clin. Neurophysiol., 1966, 21: 194-195.