- Email: [email protected]
Task initiation and amplitude of the contingent negative variation (CNV)
Electroencephalography and Clinical Neurophysiology, 1973, 34:587 592 @) Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
TASK INITIATION NEGATIVE
AND AMPLITUDE
VARIATION
587
OF THE CONTINGENT
(CNV) 1
CHARLES E. HAMILTON 2, JON F. PETERS AND JOHN R . KNOTT
Department of Po'chiato ~, Division of EEG and Clinical Neurophysiology, University o[~Iowa, hm'a CiO', Ia. 52240 (U.S.A.) (Accepted for publication: November 21, 1972)
The contingent negative variation (CNV) is classically elicited under experimental conditions in which a warning stimulus ($1) is presented to the subject, followed, after a short interval, by an imperative stimulus ($2) to which the subject has been instructed to respond. Walter et al. (1964) first reported the existence of the CNV utilizing this model, which is a simple reaction time paradigm. Other investigators have used a discriminative reaction time paradigm; when S 2 follows $1 a motor response is made, and when it follows Sta no response is made. In a later report, Walter (1967) used a procedure in which a CNV was elicited when the subject spontaneously initiated the trials. Under those conditions, a negative DC shift preceded the subject's voluntary initiating movement (closing a switch), and this shift persisted until the occurrence of $1 0.5 sec later, when a second negative shift, the CNV preceding $2 appeared. Walter termed the early shift preceding the movement the "intention wave". In some subjects, the "intention wave" could itself be used as a trigger to initiate the trial. Referring to the procedure in which the experimenter initiates each trial as ExperimenterStart (ES) and the alternative described above as Subject-Start (SS), it is manifest that the latter involves interactions of the classical CNV with preceding "readiness" or "motor" potentials (Kornhuber and Deecke 1965; Gilden et al. 1966). Supported in part by Grant COS1P GY 6168, N.S.F. to Coe College providing released time to Charles E. Hamilton. -~Visiting professor. Permanent address: Department of Psychology, Coe College, Cedar Rapids, Ia. 52402 U.S.A. (Reprint requests to this address.)
A limited number of studies have employed the SS procedure either because of its appropriateness relative to the variables under consideration (Lacey and Lacey 1973; Naitoh et al. 1973; Naitoh and Johnson 1972) or to ensure that subjects maintained optimal attention to complex stimuli (McAdam and Rubin 1971). Walter (1967) said that both the amplitude and the wave form of the CNV seen under SS conditions resembled very closely those seen during the ES trials. However, Naitoh and Johnson (1972) originally reported that CNV under the SS condition was reduced after one night of total sleep loss which was preceded by 3 nights of either slow wave or REM stage sleep deprivation. Later, Naitoh et al. (1972) found that both the SS and ES CNVs were reduced. Naitoh (1972, personal communication) has indicated to us that the SS condition led to a greater reduction in CNV than ES. The purpose of the present study was to record the CNV under the SS and ES procedures, giving consideration to the delay interval between the subject's initiative key press and $1 and the hand involved in the initiating and the responding acts. METHODS
Subjects were 24 male, right-handed paid volunteers recruited through the University of Iowa student employment office. They ranged in age from 21 to 35 years (mean age, 24.3 years). All subjects were free from any known neurological defects and none had any prior contact with CNV recording procedures. Slow potential changes were recorded using
5N8
Beckman Biopotential electrodes, attached with collodion-impregnated gauze patches, at Cz, C~ and C4 (see McAdam and Rubin 1971). The reference was linked electrodes on the left and right mastoid processes. Eye movements were recorded using a lead above and one below the right eye referred to an electrode on the right ear lobe (Peters et al. 1970). The AC impedance of each electrode was determined (using a Grass EZM) to be less than 5 k(2. A Grass Model 7 polygraph with 7P-1 chopper-stabilized pre-amplifiers operating in the 1 MQ DC mode was used to record the slow potentials. The 7DA driver amplifiers had an upper frequency level set at 75 c/sec. Obviously, the upper limit of the system is determined by the chopper frequency of the 7P-1 pre-amplifier and is less than 60 c/sec. Off-line data storage was via a Precision Instrument 6100 FM tape recorder. Those trials which the on-line paper record showed to be free of eye movement and other artifacts were then played back from FM tape, in reverse time, and averaged over an 8 sec epoch (512 points) with a PDP- 12 computer 3. No fewer than 10, nor more than 15, trials were averaged, per subject in each condition. The high attrition rate (40 SS and 40 ES trials were given) was predominantly due to eye movement. On SS trials this was a serious problem; also, on SS trials, the experimenter might be balancing a channel to correct for electrode drift at the moment the subject initiated the sequence. Following data collection from each subject, a series of 25 ~tV calibration pulses (Erode 1964) was stored on the F M tape. This off-line calibration was necessary because SS trials could not include the usual pre-S~ calibration which normally would appear at the point in time now occupied by the ramp of the motor potential which preceded the key press. These calibration signals were averaged in a manner analogous to that of the CNV and for the same number of trials per subject. The CNVs and calibration pulses were plotted on a Houston Instrument Model 2000 X-Y recorder. Amplitudes were The authors acknowledge the kindness of Maurice 1. Mendel, Ph.D., Department of Otolaryngology and Maxillo facial Surgery. University of Iowa, for permitting us to utilize lhe PDP-12 for data analysis.
C . E . HAMILTON et al.
measured in millimeters and converted to microvolts from these plots. The subjects were run in a differential reaction time paradigm in which $1 was either a high (800 c/sec) or low (400 c/sec) tone, 250 msec in duration, with an intensity of 75 dB SPL (measured at the subject's ear). The subject was instructed to press a telegraph key as fast as possible to $2 which was a single flash of a Grass PS-2 photostimulator (intensity "2", located 1.2 m in front of the eyes) following the high tone $1 and not to press when $2 followed the low tone (SeA). The response-nonresponse trials were randomly intermixed and delivered in two blocks of 40 trials, with a short rest period (4-5 min) between the 20th and 21st trials. The subject initiated the $1-$2 sequence on either the first or second block of 40 trials (SS) and the experimenter initiated the sequence on the remaining trials (ES). One half of the subjects started the trials with their right hand and responded to $2 (when appropriate) with their left hand. The other half were run under the reverse condition. The responding hand was constant for both ES and SS trials. Under the SS condition the subjects were instructed to initiate the trials whenever they felt like it, but to try to maintain at least 15 sec between trials without counting the interval. The mean inter-trial interval for SS trials actually was 30.39 sec (range 11.27 67.14) as compared to 23.92 sec (range 19.9129.38) for the ES trials. The delay interval between the subject's key press and the occurrence of S~ was fixed at either 0.0, 0.5 and 3.5 sec. The S~-S 2 interval was a constant 1.5 sec for all subjects in all conditions. Reaction times (RT) were measured by gating a C.M.C. Model 1125A counter to count a 1000 c/see sine wave. During the session, the subject was seated in a comfortable armchair inside a darkened, sound dampened chamber. Subjects were told to fixate their gaze on a cross drawn in the center of the shield of the PS-2 lamp. The tone stimuli were delivered from a speaker mounted directly behind the PS-2 lamp. Fig. 1 presents the X-Y plot (C z electrode) from the SS condition, using a 0.0 sec delay, for one subject and illustrates the scoring scheme used. Baseline for the motor potential (RP) and for one measure of CNV was determined by vi-
589
TASK INITIATION AND CNV AMPLITUDE
v
. . . .
'
71 Kt~
IqS~
Sl
Fig. 1. Sample response showing scoring scheme, a: Readiness Potential (RP). b: Baseline to peak negativity measure (CNVB). c: Peak positivity to peak negativity (CNVP). Negativity in this and subsequent figures represented by an upward deflection. C3'
Cz
ES~
5; S N R i
::~,~
A
F1
i<~ $I
/1
$2
;--~
~%~,%¢-
,-'.-~,w-v
KP $1
$2
A
rq
13
St
$2
Fig. 2. EEG responses from one subject for all conditions and electrodes (C~, Cz, C~.). Calibration 25/~V. Abbreviations: S , stimulus 1; $2, stimulus 2; KP, key press; ESR, Experimenter-Start response; ESNR, Experimenter-Start nonresponse; SSR, Subject-Start response; SSNR, Subject Start nonresponse.
sually "averaging" the first 0.5 sec of the 8 sec epoch. Motor potentials (RP) were measured as the difference between the baseline and amplitude of the signal at key press. If no RP was evident, the measurement was of the voltage occurring at the time of keypress. Two measures o f " C N V " were employed, one (designated CNVB) used the voltage difference between baseline (defined above) and the peak negativity (smoothed by visual evaluation) occurring between S~ (or S1A) and $2. The other (designated CNVP) used the voltage difference
between the peak positivity occurrin9 after $1 (or SIA) and the peak negativity precedin9 $2, as described above. The way in which these measurements were made is illustrated in Fig. I. Of the 24 subjects, 5 yielded potential shifts which failed to return to or exceed the pre-trial baseline. These data were not included in the analysis of
the CNV amplitude measure employing the baseline reference (CNVB) since the values were positive. However, measurements above the positive maximum (CNVP) could be obtained for all subjects. Wave forms recorded from the C~, and C~ electrodes were measured in the same manner. RESULTS
Fig. 2 presents the averages obtained from one subject for the four conditions and the three electrode locations. The basic CNVB and CNVP group data are presented in Table I. A Type VI ANOVA (Lindquist 1953) was performed on the CNVB (measured from baseline), CNVP (measured from peak positivity), and RP (measured from baseline) data to assess the effects of order in
c.E. HAMILTONel al.
590 TABLE I Group means and standard deviations (S.D.) for the two measures of CNV amplitude CNVB and CNV P in microvolts. The different values of N are explained in the text. Condition
C.~
C~
C4
ESR
~
ESNR
-
SSR -
-"
SSNR
v
~ ~--
30.0--
>
2S.O-
Z
CNVB (N - 19) ESR Mean S.D. ESNR Mean S.D. SSR Mean SD. SSNR Mean S.D. CNVP ( N - 24) ESR Mean S.D. ESNR Mean S.D. SSR Mean S D
SSNR
Mean S.D.
12.08 7.18 10.82 5.61 11.58 6.88 6.80 4.05
15.31 8.52 10.11 5.98 14.90 6.43 8.26 4.51
12.64 5.42 10.23 5.66 I 1.26 8.12 10.06 8.36
20.47 5.82 17.04 5.55 14.13 5.62 10.87 3.31
29.62 8.59 21.80 6.56 21.59 7,62 16.36 6.78
22.89 7.45 16.37 5.91 13.53 6.40 12,74 5.79
which subjects received the conditions, response handedness, and delay between SS keypress and S r This yielded nine values of F none of which was significant at the 0.05 level of confidence. In addition, no significant interactions were found. A similar analysis using a Type I A N O V A showed RT to $2 not to differ significantly due to: order effect (F=0.6563, df= 1,22); responding hand ( F = 1.9338, df=l,22); nor delay between SS keypress and $1 (F=0.6563, d f = 2,2l). In addition, an A x S A N O V A showed no difference in R T between the SS and ES conditions (F = 0.2066, df= 1,23). In view of the absence of significant order, interval or handedness effects, all slow potential data were then pooled across these conditions. Mean CNV amplitude measured from baseline (CNVB) for the pooled data are shown in Fig. 3. An analysis with an A x B x S A N O V A revealed only one significant difference, that between SS and ES conditions (F=6.0710, df=3,54 P < 0.005). To assess differences between conditions at the three electrode locations, a critical difference ratio (Lindquist 1953) derived from the A N O V A yielded a minimum difference of 5.65/iV (P < 0.005). By this criterion, ESR and
c~ 2 0 . 0 - Z) J
15-0-13: Z CI:
lO.O-
S,OT C3'
1 CZ ELECTRODE
---
I~ C 4' ~
LOCnT ION
Fig. 3. Mean CNVB amplitude vs. electrode location for the four experimental conditions. Abbreviations as in Fig. 2. ESR
o.-o--o
SSR
ESNR
-~ -" -"
SSNR
v
v
30.0-
:~ 2 S . @ -
z 20.0F.-J
~ 15,oCl[
Z ¢12
~ [email protected]
S°OC3 ~
CZ
ELECTRODE LOCATION Fig. 4. Mean CNVP amplitude vs. electrode location for the
four experimental conditions. Abbreviations as in Fig. 2. SSR CNVs are significantly greater than SSNR at the Cz electrode. N o significant differences between conditions occurred at either C~ or C;.
591
TASK INITIATION AND CNV AMPLITUDE
A similar analysis carried out for the mean CNVP amplitude as measured from peak positivity to $1 (See Fig. 4) yielded significant differences between conditions (F = 27.1526, df= 3,69 P<0.005), and electrodes (F=41.5798,
df= 2,46 P < 0.005). The critical difference ratio obtained on the electrode data (4.37 #V) indicated the maximal CNVP amplitude to be at Cz. The differences between C~ and C~ were not significant. A similar analysis of the conditions (c.d.=5.48/~V) showed that ESR CNVs were larger than ESNR, and were also larger than SSR or SSNR. However, SSR CNVS were not significantly larger than SSNR CNVs. In contrast to the CNVB measure, these differences between conditions occurred at both the Cz and C~ electrodes. At the C~ electrode, ESR CNVs were larger than SSR and SSNR and ESNR amplitude was larger than SSNR. The pooled readiness potential (RP) data are shown in Table II and Fig. 5. Analysis with an A × B × S ANOVA failed to reveal any significant effects due to condition (SS Response and SS Non-Response) (F = 0.0073, dr= 1,23). Although the maximum amplitude of the RP was at Cz, no significant difference (F=1.5835, df-2,46) was obtained among the electrode locations nor was there evidence of laterality. SSR
10.0--
SSNR
>:q
~ ~
9.0--
Z
w r"q
8.0--
F-
QE
7.0--
(Z Z (X W
~-
6.0-
5.0-
I
C13~
C7 ELECTRODE
C14i LOCATION
Fig. 5. Mean RP amplitude v s . electrode location for the Subject-Start experimental conditions. Abbreviations as in Fig. 2
TABLE II Groupmeans and standard deviations (S.D.) for the motor potential(RP) data in microvolts. C3 Cz ................................... RP (N=24) Condition
SSR
SSNR
Mean S.D. Mean
S.D.
6.41 3.99 6.07 4.16
7.29 4.66 7.26 4.27
C4 6.24 3.95 6.40 5.53
---DISCUSSION
The results of this study demonstrate that when the subject initiates each trial at his own pace, the resulting CNVs are, on the average, smaller in amplitude than those obtained when the experimenter initiates each trial. One possible explanation would be based on the hypothesis that the negative-going readiness or motor potential, generated prior to key press in the SS procedure, carried over into the interval between $1 and $2. Thus, the magnitude of a further negative shift following the positive portion of the evoked potential to S t may be limited. This would be consistent with the findings of Otto and Leifer (1973) who reported smaller CNV amplitudes occurring on double response as compared to single response trials. McCallum and Papakostopoulos (1972) have also shown doubleresponse CNVs to be smaller than single response CNVs. The pre-S1 negativity may be another condition in which the "ceiling hypothesis" (Knott and Irwin 1967, 1968) operates. This has recently been supported by Low and Swift (1971). McAdam and Scales (1969) and, more recently, McAdam and Rubin (1971) have offered evidence in favor of a common neural substrate for the RP and the CNV. Thus, one may view any decrement in CNV amplitude during the SS trials as being due to either the relative refractoriness of some of the common neural pools involved in the generation of the RP and CNV, or to partial depolarization as a response involving RP, with later depolarization appearing as the CNV. Data obtained in the present experiment from C~ and C~ did not exhibit hemispheric asym-
592 m e t r y of C N V , w h i c h is c o n s i s t e n t w i t h t h e r e p o r t s of L o w et al. (1966) a n d C o h e n (1969). O t t o a n d Leifer ( 1 9 7 2 ) w e r e a b l e to d e m o n s t r a t e l a t e r a l i z e d C N V r e l a t i v e to r e s p o n s e h a n d e d n e s s o n l y w h e n d a t a w e r e p o o l e d a c r o s s several c o n ditions. O u r p o o l e d d a t a did n o t yield s i m i l a r findings, h o w e v e r . The present data did not reveal laterality of R P in r e l a t i o n to r e s p o n s e h a n d e d n e s s , as prev i o u s l y r e p o r t e d ( K o r n h u b e r a n d D e e c k e 1965; G i l d e n et al. 1966). T h e small n u m b e r of trials a v e r a g e d h e r e (10-15) m a y a c c o u n t for t h i s ; t h e p r e v i o u s studies e m p l o y e d 400 trials. SUMMARY W h e n a subject is a l l o w e d to i n i t i a t e t h e o c c u r r e n c e of the S~ S 2 s e q u e n c e in a C N V experiment, significantly smaller CNVs are g e n e r a t e d t h a n w h e n t h e e x p e r i m e n t e r initiates t h e trials. It is h y p o t h e s i z e d t h a t t h e d e c r e m e n t in C N V a m p l i t u d e is d u e t o a pre-S~ n e g a t i v e shift in t h e D C level o f t h e b r a i n w h i c h limits subsequent negativity. RESUME INITIATION DE LA TACHE ET AMPLITUDE DE LA VARIATION CONTINGENTE NEGATIVE (CNV) L o r s q u ' i l est d e m a n d 6 "a un sujet de p r o v o q u e r la s u r v e n u e de la s S q u e n c e S 1 - S 2 d a n s une e x p d r i e n c e de C N V , o n o b t i e n t des C N V significativement plus petites que lorsque c'est l ' e x p 6 r i m e n t a t e u r qui i n d u i t les sSquences, Les a u t e u r s f o n t l ' h y p o t h S s e q u e la d i m i n u t i o n de l ' a m p l i t u d e C N V est d u e b, une d S f l e x i o n prS-S~ du n i v e a u D C d u c e r v e a u q u i l i m i t e la nSgativit6 ultSrieure.
REFERENCES COHEN, J. Very slow brain potentials relating to expectancy: the CNV. In E. DONCHIN and D. B. LINDSEEY (Eds.), Average evoked potentials., methods, results and evaluations. NASA SP-191, U. S. Government Printing Office, Washington, D. C., 1969: 143.--148. EMDE,J. W. A time locked low level calibrator. Electroenceph. clin. Neurophysiol., 1964, 16: 616-618. GILDEN, L., VAUGHANJR., H. G. and COSTA,L. D. Summated human EEG potentials with voluntary movements. Electroenceph. clin. Neurophysiol., 1966, 20: 433438.
('. E. HAMILTON et al.
KNOTT,J. R. and IRWIN,D. A. Anxiety, stress and the contingent negative variation. Electroenceph. clin. Neurophysiol., 1967, 22: 188. KNOTT,J. R. and IRWIN, D. A. Anxiety, stress and the contingent negative variation (CNV). Electroenceph. olin. Neurophysiol., 1968, 24:286 287. KORNHUBER,H. H. und DEECKE,L. Hirnpotential/inderungen bei Wilkfirbewegungen und passiven Bewegungen des Menschen: Bereitschaftspotential und reafferente Potentiale. Pfliigers Arch. ges. Physiol., 1965, 284:1 17. LACEV,J. I. and LACEY,B. C. Experimental association and dissociation of phasic bradycardia and vertex-negative waves: A psychophysiological study of attention and response-intention. Eleetroenceph. elin. Neurophysiol., 1973, Suppl. 33, in press. EINDQUIST, E. F. Design and analysis" ~¢' experiments in psychology and education. Houghton Mifflin Co., Cambridge, 1953: 93, 237 238, 268 273, 293 296. Low, M. D. and SWIFT, S. J. The contingent negative variation and the ~'resting" D. C. potential of the human brain: effects of situational anxiety. Neuropsyehologia, 1971, 9: 203-208. Low, M. D., BORDA,R. P., FROSTJR., J. D. and KELLAWAY,P. Surface-negative, slow-potential shift associated with conditioning in man. Neuroloqy (Minneap.), 1966, 16: 771 782. MCCALLUM,W. C. and PAPAKOSTOPOULOS,P. The effects of sustained motor activity on the contingent negative variation. Electroenceph. olin. Neurophl'viol., 1972, 33: 446. McADAM, D. W. and RUB1N, E. H. Readiness potential, vertex positive wave, contingent negative variation and accuracy of perception. Electroenceph. olin. Neurophysiol., 1971, 30:511 517. MCADAM, D. W. and SEALES,D. M. Bereitschaftspotentiat enhancement with increased level of motivation. Electroenceph, olin. Neurophysiol., 1969, 27:73 75. NAITOH, P. and JOHNSON, L. C. Effects of total and sleep stage deprivation on the CNV. Electroenceph. clin. Neurophysiol., 1972, 32:99 100. NAITOH, P., JOHNSON, L. C. and LUBIN, A. The effect of selective and total sleep loss on the CNV and its psychological and physiological correlates. Electroenceph. elin. Neurophysiol., 1973, Suppl. 33, in press. OTTO, D. A. and LEIFER, L. J. The effect of modifying response and performance feedback parameters on the CNV in humans. Eleetroenceph. c/in. Neurophysiol., 1973, Suppl. 33, in press. PETERS,J. F., KNOTT,J. R., MILLER, L. H., VAN VEEN,W. J. and C~HEN, S. I. Response variables and magnitude of the contingent negative variation. Eh'etroenceph. clin. Neuroph3wiol., 1970, 29:608 611. WALTER, W. G. Slow potential changes in the human brain associated with expectancy, decision and intention. Electroenceph. olin. Neurophrs'iol., 1967, Suppl. 26: 123 130. 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 (Lond.), 1964, 203: 380. 484.
TASK INITIATION NEGATIVE
AND AMPLITUDE
VARIATION
587
OF THE CONTINGENT
(CNV) 1
CHARLES E. HAMILTON 2, JON F. PETERS AND JOHN R . KNOTT
Department of Po'chiato ~, Division of EEG and Clinical Neurophysiology, University o[~Iowa, hm'a CiO', Ia. 52240 (U.S.A.) (Accepted for publication: November 21, 1972)
The contingent negative variation (CNV) is classically elicited under experimental conditions in which a warning stimulus ($1) is presented to the subject, followed, after a short interval, by an imperative stimulus ($2) to which the subject has been instructed to respond. Walter et al. (1964) first reported the existence of the CNV utilizing this model, which is a simple reaction time paradigm. Other investigators have used a discriminative reaction time paradigm; when S 2 follows $1 a motor response is made, and when it follows Sta no response is made. In a later report, Walter (1967) used a procedure in which a CNV was elicited when the subject spontaneously initiated the trials. Under those conditions, a negative DC shift preceded the subject's voluntary initiating movement (closing a switch), and this shift persisted until the occurrence of $1 0.5 sec later, when a second negative shift, the CNV preceding $2 appeared. Walter termed the early shift preceding the movement the "intention wave". In some subjects, the "intention wave" could itself be used as a trigger to initiate the trial. Referring to the procedure in which the experimenter initiates each trial as ExperimenterStart (ES) and the alternative described above as Subject-Start (SS), it is manifest that the latter involves interactions of the classical CNV with preceding "readiness" or "motor" potentials (Kornhuber and Deecke 1965; Gilden et al. 1966). Supported in part by Grant COS1P GY 6168, N.S.F. to Coe College providing released time to Charles E. Hamilton. -~Visiting professor. Permanent address: Department of Psychology, Coe College, Cedar Rapids, Ia. 52402 U.S.A. (Reprint requests to this address.)
A limited number of studies have employed the SS procedure either because of its appropriateness relative to the variables under consideration (Lacey and Lacey 1973; Naitoh et al. 1973; Naitoh and Johnson 1972) or to ensure that subjects maintained optimal attention to complex stimuli (McAdam and Rubin 1971). Walter (1967) said that both the amplitude and the wave form of the CNV seen under SS conditions resembled very closely those seen during the ES trials. However, Naitoh and Johnson (1972) originally reported that CNV under the SS condition was reduced after one night of total sleep loss which was preceded by 3 nights of either slow wave or REM stage sleep deprivation. Later, Naitoh et al. (1972) found that both the SS and ES CNVs were reduced. Naitoh (1972, personal communication) has indicated to us that the SS condition led to a greater reduction in CNV than ES. The purpose of the present study was to record the CNV under the SS and ES procedures, giving consideration to the delay interval between the subject's initiative key press and $1 and the hand involved in the initiating and the responding acts. METHODS
Subjects were 24 male, right-handed paid volunteers recruited through the University of Iowa student employment office. They ranged in age from 21 to 35 years (mean age, 24.3 years). All subjects were free from any known neurological defects and none had any prior contact with CNV recording procedures. Slow potential changes were recorded using
5N8
Beckman Biopotential electrodes, attached with collodion-impregnated gauze patches, at Cz, C~ and C4 (see McAdam and Rubin 1971). The reference was linked electrodes on the left and right mastoid processes. Eye movements were recorded using a lead above and one below the right eye referred to an electrode on the right ear lobe (Peters et al. 1970). The AC impedance of each electrode was determined (using a Grass EZM) to be less than 5 k(2. A Grass Model 7 polygraph with 7P-1 chopper-stabilized pre-amplifiers operating in the 1 MQ DC mode was used to record the slow potentials. The 7DA driver amplifiers had an upper frequency level set at 75 c/sec. Obviously, the upper limit of the system is determined by the chopper frequency of the 7P-1 pre-amplifier and is less than 60 c/sec. Off-line data storage was via a Precision Instrument 6100 FM tape recorder. Those trials which the on-line paper record showed to be free of eye movement and other artifacts were then played back from FM tape, in reverse time, and averaged over an 8 sec epoch (512 points) with a PDP- 12 computer 3. No fewer than 10, nor more than 15, trials were averaged, per subject in each condition. The high attrition rate (40 SS and 40 ES trials were given) was predominantly due to eye movement. On SS trials this was a serious problem; also, on SS trials, the experimenter might be balancing a channel to correct for electrode drift at the moment the subject initiated the sequence. Following data collection from each subject, a series of 25 ~tV calibration pulses (Erode 1964) was stored on the F M tape. This off-line calibration was necessary because SS trials could not include the usual pre-S~ calibration which normally would appear at the point in time now occupied by the ramp of the motor potential which preceded the key press. These calibration signals were averaged in a manner analogous to that of the CNV and for the same number of trials per subject. The CNVs and calibration pulses were plotted on a Houston Instrument Model 2000 X-Y recorder. Amplitudes were The authors acknowledge the kindness of Maurice 1. Mendel, Ph.D., Department of Otolaryngology and Maxillo facial Surgery. University of Iowa, for permitting us to utilize lhe PDP-12 for data analysis.
C . E . HAMILTON et al.
measured in millimeters and converted to microvolts from these plots. The subjects were run in a differential reaction time paradigm in which $1 was either a high (800 c/sec) or low (400 c/sec) tone, 250 msec in duration, with an intensity of 75 dB SPL (measured at the subject's ear). The subject was instructed to press a telegraph key as fast as possible to $2 which was a single flash of a Grass PS-2 photostimulator (intensity "2", located 1.2 m in front of the eyes) following the high tone $1 and not to press when $2 followed the low tone (SeA). The response-nonresponse trials were randomly intermixed and delivered in two blocks of 40 trials, with a short rest period (4-5 min) between the 20th and 21st trials. The subject initiated the $1-$2 sequence on either the first or second block of 40 trials (SS) and the experimenter initiated the sequence on the remaining trials (ES). One half of the subjects started the trials with their right hand and responded to $2 (when appropriate) with their left hand. The other half were run under the reverse condition. The responding hand was constant for both ES and SS trials. Under the SS condition the subjects were instructed to initiate the trials whenever they felt like it, but to try to maintain at least 15 sec between trials without counting the interval. The mean inter-trial interval for SS trials actually was 30.39 sec (range 11.27 67.14) as compared to 23.92 sec (range 19.9129.38) for the ES trials. The delay interval between the subject's key press and the occurrence of S~ was fixed at either 0.0, 0.5 and 3.5 sec. The S~-S 2 interval was a constant 1.5 sec for all subjects in all conditions. Reaction times (RT) were measured by gating a C.M.C. Model 1125A counter to count a 1000 c/see sine wave. During the session, the subject was seated in a comfortable armchair inside a darkened, sound dampened chamber. Subjects were told to fixate their gaze on a cross drawn in the center of the shield of the PS-2 lamp. The tone stimuli were delivered from a speaker mounted directly behind the PS-2 lamp. Fig. 1 presents the X-Y plot (C z electrode) from the SS condition, using a 0.0 sec delay, for one subject and illustrates the scoring scheme used. Baseline for the motor potential (RP) and for one measure of CNV was determined by vi-
589
TASK INITIATION AND CNV AMPLITUDE
v
. . . .
'
71 Kt~
IqS~
Sl
Fig. 1. Sample response showing scoring scheme, a: Readiness Potential (RP). b: Baseline to peak negativity measure (CNVB). c: Peak positivity to peak negativity (CNVP). Negativity in this and subsequent figures represented by an upward deflection. C3'
Cz
ES~
5; S N R i
::~,~
A
F1
i<~ $I
/1
$2
;--~
~%~,%¢-
,-'.-~,w-v
KP $1
$2
A
rq
13
St
$2
Fig. 2. EEG responses from one subject for all conditions and electrodes (C~, Cz, C~.). Calibration 25/~V. Abbreviations: S , stimulus 1; $2, stimulus 2; KP, key press; ESR, Experimenter-Start response; ESNR, Experimenter-Start nonresponse; SSR, Subject-Start response; SSNR, Subject Start nonresponse.
sually "averaging" the first 0.5 sec of the 8 sec epoch. Motor potentials (RP) were measured as the difference between the baseline and amplitude of the signal at key press. If no RP was evident, the measurement was of the voltage occurring at the time of keypress. Two measures o f " C N V " were employed, one (designated CNVB) used the voltage difference between baseline (defined above) and the peak negativity (smoothed by visual evaluation) occurring between S~ (or S1A) and $2. The other (designated CNVP) used the voltage difference
between the peak positivity occurrin9 after $1 (or SIA) and the peak negativity precedin9 $2, as described above. The way in which these measurements were made is illustrated in Fig. I. Of the 24 subjects, 5 yielded potential shifts which failed to return to or exceed the pre-trial baseline. These data were not included in the analysis of
the CNV amplitude measure employing the baseline reference (CNVB) since the values were positive. However, measurements above the positive maximum (CNVP) could be obtained for all subjects. Wave forms recorded from the C~, and C~ electrodes were measured in the same manner. RESULTS
Fig. 2 presents the averages obtained from one subject for the four conditions and the three electrode locations. The basic CNVB and CNVP group data are presented in Table I. A Type VI ANOVA (Lindquist 1953) was performed on the CNVB (measured from baseline), CNVP (measured from peak positivity), and RP (measured from baseline) data to assess the effects of order in
c.E. HAMILTONel al.
590 TABLE I Group means and standard deviations (S.D.) for the two measures of CNV amplitude CNVB and CNV P in microvolts. The different values of N are explained in the text. Condition
C.~
C~
C4
ESR
~
ESNR
-
SSR -
-"
SSNR
v
~ ~--
30.0--
>
2S.O-
Z
CNVB (N - 19) ESR Mean S.D. ESNR Mean S.D. SSR Mean SD. SSNR Mean S.D. CNVP ( N - 24) ESR Mean S.D. ESNR Mean S.D. SSR Mean S D
SSNR
Mean S.D.
12.08 7.18 10.82 5.61 11.58 6.88 6.80 4.05
15.31 8.52 10.11 5.98 14.90 6.43 8.26 4.51
12.64 5.42 10.23 5.66 I 1.26 8.12 10.06 8.36
20.47 5.82 17.04 5.55 14.13 5.62 10.87 3.31
29.62 8.59 21.80 6.56 21.59 7,62 16.36 6.78
22.89 7.45 16.37 5.91 13.53 6.40 12,74 5.79
which subjects received the conditions, response handedness, and delay between SS keypress and S r This yielded nine values of F none of which was significant at the 0.05 level of confidence. In addition, no significant interactions were found. A similar analysis using a Type I A N O V A showed RT to $2 not to differ significantly due to: order effect (F=0.6563, df= 1,22); responding hand ( F = 1.9338, df=l,22); nor delay between SS keypress and $1 (F=0.6563, d f = 2,2l). In addition, an A x S A N O V A showed no difference in R T between the SS and ES conditions (F = 0.2066, df= 1,23). In view of the absence of significant order, interval or handedness effects, all slow potential data were then pooled across these conditions. Mean CNV amplitude measured from baseline (CNVB) for the pooled data are shown in Fig. 3. An analysis with an A x B x S A N O V A revealed only one significant difference, that between SS and ES conditions (F=6.0710, df=3,54 P < 0.005). To assess differences between conditions at the three electrode locations, a critical difference ratio (Lindquist 1953) derived from the A N O V A yielded a minimum difference of 5.65/iV (P < 0.005). By this criterion, ESR and
c~ 2 0 . 0 - Z) J
15-0-13: Z CI:
lO.O-
S,OT C3'
1 CZ ELECTRODE
---
I~ C 4' ~
LOCnT ION
Fig. 3. Mean CNVB amplitude vs. electrode location for the four experimental conditions. Abbreviations as in Fig. 2. ESR
o.-o--o
SSR
ESNR
-~ -" -"
SSNR
v
v
30.0-
:~ 2 S . @ -
z 20.0F.-J
~ 15,oCl[
Z ¢12
~ [email protected]
S°OC3 ~
CZ
ELECTRODE LOCATION Fig. 4. Mean CNVP amplitude vs. electrode location for the
four experimental conditions. Abbreviations as in Fig. 2. SSR CNVs are significantly greater than SSNR at the Cz electrode. N o significant differences between conditions occurred at either C~ or C;.
591
TASK INITIATION AND CNV AMPLITUDE
A similar analysis carried out for the mean CNVP amplitude as measured from peak positivity to $1 (See Fig. 4) yielded significant differences between conditions (F = 27.1526, df= 3,69 P<0.005), and electrodes (F=41.5798,
df= 2,46 P < 0.005). The critical difference ratio obtained on the electrode data (4.37 #V) indicated the maximal CNVP amplitude to be at Cz. The differences between C~ and C~ were not significant. A similar analysis of the conditions (c.d.=5.48/~V) showed that ESR CNVs were larger than ESNR, and were also larger than SSR or SSNR. However, SSR CNVS were not significantly larger than SSNR CNVs. In contrast to the CNVB measure, these differences between conditions occurred at both the Cz and C~ electrodes. At the C~ electrode, ESR CNVs were larger than SSR and SSNR and ESNR amplitude was larger than SSNR. The pooled readiness potential (RP) data are shown in Table II and Fig. 5. Analysis with an A × B × S ANOVA failed to reveal any significant effects due to condition (SS Response and SS Non-Response) (F = 0.0073, dr= 1,23). Although the maximum amplitude of the RP was at Cz, no significant difference (F=1.5835, df-2,46) was obtained among the electrode locations nor was there evidence of laterality. SSR
10.0--
SSNR
>:q
~ ~
9.0--
Z
w r"q
8.0--
F-
QE
7.0--
(Z Z (X W
~-
6.0-
5.0-
I
C13~
C7 ELECTRODE
C14i LOCATION
Fig. 5. Mean RP amplitude v s . electrode location for the Subject-Start experimental conditions. Abbreviations as in Fig. 2
TABLE II Groupmeans and standard deviations (S.D.) for the motor potential(RP) data in microvolts. C3 Cz ................................... RP (N=24) Condition
SSR
SSNR
Mean S.D. Mean
S.D.
6.41 3.99 6.07 4.16
7.29 4.66 7.26 4.27
C4 6.24 3.95 6.40 5.53
---DISCUSSION
The results of this study demonstrate that when the subject initiates each trial at his own pace, the resulting CNVs are, on the average, smaller in amplitude than those obtained when the experimenter initiates each trial. One possible explanation would be based on the hypothesis that the negative-going readiness or motor potential, generated prior to key press in the SS procedure, carried over into the interval between $1 and $2. Thus, the magnitude of a further negative shift following the positive portion of the evoked potential to S t may be limited. This would be consistent with the findings of Otto and Leifer (1973) who reported smaller CNV amplitudes occurring on double response as compared to single response trials. McCallum and Papakostopoulos (1972) have also shown doubleresponse CNVs to be smaller than single response CNVs. The pre-S1 negativity may be another condition in which the "ceiling hypothesis" (Knott and Irwin 1967, 1968) operates. This has recently been supported by Low and Swift (1971). McAdam and Scales (1969) and, more recently, McAdam and Rubin (1971) have offered evidence in favor of a common neural substrate for the RP and the CNV. Thus, one may view any decrement in CNV amplitude during the SS trials as being due to either the relative refractoriness of some of the common neural pools involved in the generation of the RP and CNV, or to partial depolarization as a response involving RP, with later depolarization appearing as the CNV. Data obtained in the present experiment from C~ and C~ did not exhibit hemispheric asym-
592 m e t r y of C N V , w h i c h is c o n s i s t e n t w i t h t h e r e p o r t s of L o w et al. (1966) a n d C o h e n (1969). O t t o a n d Leifer ( 1 9 7 2 ) w e r e a b l e to d e m o n s t r a t e l a t e r a l i z e d C N V r e l a t i v e to r e s p o n s e h a n d e d n e s s o n l y w h e n d a t a w e r e p o o l e d a c r o s s several c o n ditions. O u r p o o l e d d a t a did n o t yield s i m i l a r findings, h o w e v e r . The present data did not reveal laterality of R P in r e l a t i o n to r e s p o n s e h a n d e d n e s s , as prev i o u s l y r e p o r t e d ( K o r n h u b e r a n d D e e c k e 1965; G i l d e n et al. 1966). T h e small n u m b e r of trials a v e r a g e d h e r e (10-15) m a y a c c o u n t for t h i s ; t h e p r e v i o u s studies e m p l o y e d 400 trials. SUMMARY W h e n a subject is a l l o w e d to i n i t i a t e t h e o c c u r r e n c e of the S~ S 2 s e q u e n c e in a C N V experiment, significantly smaller CNVs are g e n e r a t e d t h a n w h e n t h e e x p e r i m e n t e r initiates t h e trials. It is h y p o t h e s i z e d t h a t t h e d e c r e m e n t in C N V a m p l i t u d e is d u e t o a pre-S~ n e g a t i v e shift in t h e D C level o f t h e b r a i n w h i c h limits subsequent negativity. RESUME INITIATION DE LA TACHE ET AMPLITUDE DE LA VARIATION CONTINGENTE NEGATIVE (CNV) L o r s q u ' i l est d e m a n d 6 "a un sujet de p r o v o q u e r la s u r v e n u e de la s S q u e n c e S 1 - S 2 d a n s une e x p d r i e n c e de C N V , o n o b t i e n t des C N V significativement plus petites que lorsque c'est l ' e x p 6 r i m e n t a t e u r qui i n d u i t les sSquences, Les a u t e u r s f o n t l ' h y p o t h S s e q u e la d i m i n u t i o n de l ' a m p l i t u d e C N V est d u e b, une d S f l e x i o n prS-S~ du n i v e a u D C d u c e r v e a u q u i l i m i t e la nSgativit6 ultSrieure.
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KNOTT,J. R. and IRWIN,D. A. Anxiety, stress and the contingent negative variation. Electroenceph. clin. Neurophysiol., 1967, 22: 188. KNOTT,J. R. and IRWIN, D. A. Anxiety, stress and the contingent negative variation (CNV). Electroenceph. olin. Neurophysiol., 1968, 24:286 287. KORNHUBER,H. H. und DEECKE,L. Hirnpotential/inderungen bei Wilkfirbewegungen und passiven Bewegungen des Menschen: Bereitschaftspotential und reafferente Potentiale. Pfliigers Arch. ges. Physiol., 1965, 284:1 17. LACEV,J. I. and LACEY,B. C. Experimental association and dissociation of phasic bradycardia and vertex-negative waves: A psychophysiological study of attention and response-intention. Eleetroenceph. elin. Neurophysiol., 1973, Suppl. 33, in press. EINDQUIST, E. F. Design and analysis" ~¢' experiments in psychology and education. Houghton Mifflin Co., Cambridge, 1953: 93, 237 238, 268 273, 293 296. Low, M. D. and SWIFT, S. J. The contingent negative variation and the ~'resting" D. C. potential of the human brain: effects of situational anxiety. Neuropsyehologia, 1971, 9: 203-208. Low, M. D., BORDA,R. P., FROSTJR., J. D. and KELLAWAY,P. Surface-negative, slow-potential shift associated with conditioning in man. Neuroloqy (Minneap.), 1966, 16: 771 782. MCCALLUM,W. C. and PAPAKOSTOPOULOS,P. The effects of sustained motor activity on the contingent negative variation. Electroenceph. olin. Neurophl'viol., 1972, 33: 446. McADAM, D. W. and RUB1N, E. H. Readiness potential, vertex positive wave, contingent negative variation and accuracy of perception. Electroenceph. olin. Neurophysiol., 1971, 30:511 517. MCADAM, D. W. and SEALES,D. M. Bereitschaftspotentiat enhancement with increased level of motivation. Electroenceph, olin. Neurophysiol., 1969, 27:73 75. NAITOH, P. and JOHNSON, L. C. Effects of total and sleep stage deprivation on the CNV. Electroenceph. clin. Neurophysiol., 1972, 32:99 100. NAITOH, P., JOHNSON, L. C. and LUBIN, A. The effect of selective and total sleep loss on the CNV and its psychological and physiological correlates. Electroenceph. elin. Neurophysiol., 1973, Suppl. 33, in press. OTTO, D. A. and LEIFER, L. J. The effect of modifying response and performance feedback parameters on the CNV in humans. Eleetroenceph. c/in. Neurophysiol., 1973, Suppl. 33, in press. PETERS,J. F., KNOTT,J. R., MILLER, L. H., VAN VEEN,W. J. and C~HEN, S. I. Response variables and magnitude of the contingent negative variation. Eh'etroenceph. clin. Neuroph3wiol., 1970, 29:608 611. WALTER, W. G. Slow potential changes in the human brain associated with expectancy, decision and intention. Electroenceph. olin. Neurophrs'iol., 1967, Suppl. 26: 123 130. 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 (Lond.), 1964, 203: 380. 484.