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Intercorrelation of CNV Variables
Intercorrelation of CNV Variables F. H. M. VERHEY, Th. B. LAMERS and P. M. J. EMONDS
Clinical Psychophysiology Department, Regional Psycho-Medical Centre Vijverdal. Maastricht (The Netherlands)
In preparing a CNV project in psychiatry we registered CNVs in a standardised way in 2 groups of patients: group I, 102 patients; group 11, 79 patients. All raw data being stored on tapes for processing on PDP-12 and correlating with clinical data we decided to use these data as well for statistical intercorrelation. Apart from sex, age and reaction time, 3 CNV parameters were included: (a) mean amplitude in the 100 msec period just prior to S, (A); (b) mean amplitude of post-imperative negativity in the period from 350 to 450 msec after S, (PINV); (c) mean amplitude of post-imperative negativity corrected to RT in the period from 350 to 450 msec after S, +reaction time (PINV C). The baseline was determined in 3 different ways: (1) mean of samples 1 sec prior to S , ; (2) mean of samples 0.5 sec prior to S,; (3) mean of 3 samples around 350 msec after S, (“take-off” point). CNV parameters were calculated from these baselines (Al, A2, A3; PINV1, PINV2, PINV3; PINV C1, PINV C2, PINV C3). Standard deviations (S.D.s) were also calculated. Two paradigms were employed: group I (N= 102): IS1 1500 msec; no emphasis on RT. group I1 (N=79): IS1 1000 msec; emphasis on RT. All data were correlated on a Burrough B77 computer in a Spearman correlation program. METHOD Group I: 102 psychiatric patients admitted to the mental hospital were examined; the age ranging from 13 to 75 years (mean 40.2 and S.D. 13.2 years). Male 60, female 42. Group II: 79 psychiatric inpatients; age ranging from 15 to 74 years (mean 39.2 and S.D. 13.6 years). Male 48, female 31. During data collection the patient was seated in a comfortable armchair inside a semi-darkened, sound-damped, air-conditioned chamber. Instructions were given to all subjects by the same male technician, always in the same way. Subjects had to concentrate with eyes opened on the center of a grey disc with an opening of 1 cm diameter at a distance of 100 cm. S, was a tone (1000 Hz, 50 msec from a loudspeaker behind stroboscope, 1 m in front of subject); S , intermittent light flashes at an 18 Hz rate provided by the 1 cm central opening in the grey disc; duration 2 sec
532 unless terminated by button press. Motor response had to be given by button press with the right hand. Silver-silver chloride electrodes (Burden type) were attached to the vertex and the left earlobe for reference. Skin to be cleaned with aceton and drilled with blunt needle. Non-abrasive electrode jelly. Skin impedance less than 1 kQ. Similar electrode placed 2 cm below pupil of left eye (on orbital ridge) monitored eye movements. CNV and eye movements were recorded with Elema-Schonander amplifiers (TC: 11 sec; HF: 75 c/sec). Data were processed in line by a PDP-12 computer (sampling rate 128/sec). The paradigm was controlled by this PDP-12: Group I: pre S,: 1000 msec; ISI: 1500 msec; post S,: 3500 msec. Group 11: pre S,: 1000 msec; ISI: 1000 msec; post S,: 2000 msec. Intertrial interval varied randomly and predetermined from 7 to 25 sec. Eight successful trials were averaged. A cancelling program refused all trials with eye movement potentials exceeding 64 pV (corresponding with eye deviation in any direction more than 20 cm from light circle at 100 cm distance). Ail trials with channel artefact or button press not within 2 sec after S, were also rejected. Average CNV, eye movement potentials and standard deviation were plotted by an HP X-Y plotter; parameters calculated for 3 baselines and standard deviations were printed out by teletype. RESULTS Some significant correlations were obtained (sign. level < 2%): (A) CNV amplitude correlates with reaction time. (B) Amplitude 3 correlates with standard deviation reaction time (group I). (C) Amplitudes 1, 2 and 3, PINV1, 2, 3 and PINV C1, 2, 3 intercorrelate. (D) Amplitude 1, 2, 3 correlate with PINV1, 2, 3. (E) Amplitude 1, 2, 3 correlate with PINV C1, 2, 3. (F) S.D. amplitude 1, 2, 3 correlate with S.D. PINV1, 2, 3. (G) S.D. amplitude 1, 2, 3 correlate with S.D. PINV C1, 2, 3. (H) Age correlates with S.D. amplitude, S.D. PINV, S.D. PINV C (group I). (I) Age correlates with reaction time (group I). (J) Sex correlates with amplitude 3 (group 11). (ad A) There has been discussion in the past about possible relations between CNV amplitude and reaction time. A survey of the literature concerning the relationship between CNV and reaction time led to the conclusion that those two events are, for the most part, independent and reflect the activity of different psychological processes (Rebert and Tecce, 1973). We obtained an inverted correlation (sign. < 0.6%) between amplitude 1, 2, 3 and reaction time (both groups). (ad B ) An alternative method of measuring amplitude was devised in which a feature of the EEG response was assumed to be the “take off point” of the CNV (470 msec, Rebert and Knott, 1970; 350 msec, Loveless, 1973). In this correlation project we tried out the CNV amplitude calculation referred to this 350 msec point (A3) as an alternative to the usual calculations (Al, A2). Only amplitude 3 correlates inverted with S.D. of reaction time, sign. < 1.4%, r 0.21 (group I). (ad C) Concern is often expressed over the multiplicity of methods employed for quantifying the CNV. The question of what constitutes a satisfactory baseline from which to measure is the key issue (Peters et al., 1976). A1 and A2 intercorrelate (sign. <0.1%, r 0.98). A1 and A3 intercorrelate (sign. <0.1%, r 0.30).
533
EES 2 (3)A N l d CIS
ZVaS
Fig. 1. Diagram of significant results.
It seems there is no difference between A1 and A2 as the mean values and S.D.sfor A1 and A2 are the same. A3 correlates with r 0.30 with A1 and there is a different S.D. (ad D,E) This result seems to confirm the thesis that post-imperative negativity should always be considered in relation to CNV amplitude. The r value (0.4) implicates that a certain number of cases are deviating. This opens the possibility for the supposition that in certain (pathological?) cases PINV behaves in a deviating way (Timsit-Berthier et al., 1972; Dubrovsky and Dongier, 1976). (ad F, G) The high correlation (sign. 0.1%) and the parity of the mean, S.D. and range of standard deviations A l , 2, 3, PINV1, 2, 3, and PINV C1, 2, 3 indicate that no extra variables appear in the post-imperative period (EDR) (Venables and Martin, 1964; Picton and Hillyard, 1972). (ad H ) As there is no relation between age and amplitude and a significant inverted correlation between age and standard deviation of amplitude and PINV (C), it seems that with advancing age CNV becomes more constant (in group I). (ad I ) Though in group I no emphasis was given on reaction time, it is remarkable that with advancing age reaction time increases. (ad J ) Females had higher A3 in group 11.
534 REFERENCES Dubrovsky, B. and Dongier, M. (1976) Evaluation of event-related slow potentials in selected groups of psychiatric patients. In The Responsive Brain, W. C. McCallum and J. R. Knott (Eds.), Wright, Bristol, pp. 150-154. Loveless, N. E. (1973) The contingent negative variation related to preparatory set in a reaction time situation with variable period. Electroenceph. elin. Neurophysiol., 35: 369-374. Peters, J. F., Knott, J. R.and Hamilton, Ch. E. (1976) Further thoughts on measurements of “the” CNV. In The Responsive Brain, W. C. McCallum and J. R. Knott (Eds.), Wright, Bristol, pp. 15-20. Picton, T. W. and Hillyard, S. A. (1972) Cephalic skin potentials in electroencephalography. Electroenceph. din. Neurophysiol., 33: 419-424. Rebert, Ch. S . and Knott, J. R. (1970) The vertex non-specific evoked potential and latency of contingent negative variation. Electroenceph. elin. Neurophysiol., 28: 561-565. Rebert, Ch. S. and Tecce, J. J. (1973) A summary ofCNV and reaction time. Electroenceph. d i n . Neurophysiol., SUPPI. 33: 173-179. Timsit-Berthier, M.,Konincx, N., Delaunoy, J. and Rousseau, J. C. (1972) New statistical studies of the negative variation in psychiatry. Rev. EEG Neurophysiol., 2 333-339. Venables, P. H. and Martin, I. (1964) Skin Resistance and Skin Potential. North-Holland Publ., Amsterdam. Verhey, F., Lamers, Th. en Emonds, P. (1975) Ontwerp voor een ondenoek naar de betekenis van bepaalde langzame hersenpotentialen voor de psychiatrische diagnostiek. Bulletin, 2 33-38. Verhey, F., Lamers, Th. and Emonds, P. (1975) Standard Deviation as a Methodological Tool in CNV Studies. Gain, Paris.
Clinical Psychophysiology Department, Regional Psycho-Medical Centre Vijverdal. Maastricht (The Netherlands)
In preparing a CNV project in psychiatry we registered CNVs in a standardised way in 2 groups of patients: group I, 102 patients; group 11, 79 patients. All raw data being stored on tapes for processing on PDP-12 and correlating with clinical data we decided to use these data as well for statistical intercorrelation. Apart from sex, age and reaction time, 3 CNV parameters were included: (a) mean amplitude in the 100 msec period just prior to S, (A); (b) mean amplitude of post-imperative negativity in the period from 350 to 450 msec after S, (PINV); (c) mean amplitude of post-imperative negativity corrected to RT in the period from 350 to 450 msec after S, +reaction time (PINV C). The baseline was determined in 3 different ways: (1) mean of samples 1 sec prior to S , ; (2) mean of samples 0.5 sec prior to S,; (3) mean of 3 samples around 350 msec after S, (“take-off” point). CNV parameters were calculated from these baselines (Al, A2, A3; PINV1, PINV2, PINV3; PINV C1, PINV C2, PINV C3). Standard deviations (S.D.s) were also calculated. Two paradigms were employed: group I (N= 102): IS1 1500 msec; no emphasis on RT. group I1 (N=79): IS1 1000 msec; emphasis on RT. All data were correlated on a Burrough B77 computer in a Spearman correlation program. METHOD Group I: 102 psychiatric patients admitted to the mental hospital were examined; the age ranging from 13 to 75 years (mean 40.2 and S.D. 13.2 years). Male 60, female 42. Group II: 79 psychiatric inpatients; age ranging from 15 to 74 years (mean 39.2 and S.D. 13.6 years). Male 48, female 31. During data collection the patient was seated in a comfortable armchair inside a semi-darkened, sound-damped, air-conditioned chamber. Instructions were given to all subjects by the same male technician, always in the same way. Subjects had to concentrate with eyes opened on the center of a grey disc with an opening of 1 cm diameter at a distance of 100 cm. S, was a tone (1000 Hz, 50 msec from a loudspeaker behind stroboscope, 1 m in front of subject); S , intermittent light flashes at an 18 Hz rate provided by the 1 cm central opening in the grey disc; duration 2 sec
532 unless terminated by button press. Motor response had to be given by button press with the right hand. Silver-silver chloride electrodes (Burden type) were attached to the vertex and the left earlobe for reference. Skin to be cleaned with aceton and drilled with blunt needle. Non-abrasive electrode jelly. Skin impedance less than 1 kQ. Similar electrode placed 2 cm below pupil of left eye (on orbital ridge) monitored eye movements. CNV and eye movements were recorded with Elema-Schonander amplifiers (TC: 11 sec; HF: 75 c/sec). Data were processed in line by a PDP-12 computer (sampling rate 128/sec). The paradigm was controlled by this PDP-12: Group I: pre S,: 1000 msec; ISI: 1500 msec; post S,: 3500 msec. Group 11: pre S,: 1000 msec; ISI: 1000 msec; post S,: 2000 msec. Intertrial interval varied randomly and predetermined from 7 to 25 sec. Eight successful trials were averaged. A cancelling program refused all trials with eye movement potentials exceeding 64 pV (corresponding with eye deviation in any direction more than 20 cm from light circle at 100 cm distance). Ail trials with channel artefact or button press not within 2 sec after S, were also rejected. Average CNV, eye movement potentials and standard deviation were plotted by an HP X-Y plotter; parameters calculated for 3 baselines and standard deviations were printed out by teletype. RESULTS Some significant correlations were obtained (sign. level < 2%): (A) CNV amplitude correlates with reaction time. (B) Amplitude 3 correlates with standard deviation reaction time (group I). (C) Amplitudes 1, 2 and 3, PINV1, 2, 3 and PINV C1, 2, 3 intercorrelate. (D) Amplitude 1, 2, 3 correlate with PINV1, 2, 3. (E) Amplitude 1, 2, 3 correlate with PINV C1, 2, 3. (F) S.D. amplitude 1, 2, 3 correlate with S.D. PINV1, 2, 3. (G) S.D. amplitude 1, 2, 3 correlate with S.D. PINV C1, 2, 3. (H) Age correlates with S.D. amplitude, S.D. PINV, S.D. PINV C (group I). (I) Age correlates with reaction time (group I). (J) Sex correlates with amplitude 3 (group 11). (ad A) There has been discussion in the past about possible relations between CNV amplitude and reaction time. A survey of the literature concerning the relationship between CNV and reaction time led to the conclusion that those two events are, for the most part, independent and reflect the activity of different psychological processes (Rebert and Tecce, 1973). We obtained an inverted correlation (sign. < 0.6%) between amplitude 1, 2, 3 and reaction time (both groups). (ad B ) An alternative method of measuring amplitude was devised in which a feature of the EEG response was assumed to be the “take off point” of the CNV (470 msec, Rebert and Knott, 1970; 350 msec, Loveless, 1973). In this correlation project we tried out the CNV amplitude calculation referred to this 350 msec point (A3) as an alternative to the usual calculations (Al, A2). Only amplitude 3 correlates inverted with S.D. of reaction time, sign. < 1.4%, r 0.21 (group I). (ad C) Concern is often expressed over the multiplicity of methods employed for quantifying the CNV. The question of what constitutes a satisfactory baseline from which to measure is the key issue (Peters et al., 1976). A1 and A2 intercorrelate (sign. <0.1%, r 0.98). A1 and A3 intercorrelate (sign. <0.1%, r 0.30).
533
EES 2 (3)A N l d CIS
ZVaS
Fig. 1. Diagram of significant results.
It seems there is no difference between A1 and A2 as the mean values and S.D.sfor A1 and A2 are the same. A3 correlates with r 0.30 with A1 and there is a different S.D. (ad D,E) This result seems to confirm the thesis that post-imperative negativity should always be considered in relation to CNV amplitude. The r value (0.4) implicates that a certain number of cases are deviating. This opens the possibility for the supposition that in certain (pathological?) cases PINV behaves in a deviating way (Timsit-Berthier et al., 1972; Dubrovsky and Dongier, 1976). (ad F, G) The high correlation (sign. 0.1%) and the parity of the mean, S.D. and range of standard deviations A l , 2, 3, PINV1, 2, 3, and PINV C1, 2, 3 indicate that no extra variables appear in the post-imperative period (EDR) (Venables and Martin, 1964; Picton and Hillyard, 1972). (ad H ) As there is no relation between age and amplitude and a significant inverted correlation between age and standard deviation of amplitude and PINV (C), it seems that with advancing age CNV becomes more constant (in group I). (ad I ) Though in group I no emphasis was given on reaction time, it is remarkable that with advancing age reaction time increases. (ad J ) Females had higher A3 in group 11.
534 REFERENCES Dubrovsky, B. and Dongier, M. (1976) Evaluation of event-related slow potentials in selected groups of psychiatric patients. In The Responsive Brain, W. C. McCallum and J. R. Knott (Eds.), Wright, Bristol, pp. 150-154. Loveless, N. E. (1973) The contingent negative variation related to preparatory set in a reaction time situation with variable period. Electroenceph. elin. Neurophysiol., 35: 369-374. Peters, J. F., Knott, J. R.and Hamilton, Ch. E. (1976) Further thoughts on measurements of “the” CNV. In The Responsive Brain, W. C. McCallum and J. R. Knott (Eds.), Wright, Bristol, pp. 15-20. Picton, T. W. and Hillyard, S. A. (1972) Cephalic skin potentials in electroencephalography. Electroenceph. din. Neurophysiol., 33: 419-424. Rebert, Ch. S . and Knott, J. R. (1970) The vertex non-specific evoked potential and latency of contingent negative variation. Electroenceph. elin. Neurophysiol., 28: 561-565. Rebert, Ch. S. and Tecce, J. J. (1973) A summary ofCNV and reaction time. Electroenceph. d i n . Neurophysiol., SUPPI. 33: 173-179. Timsit-Berthier, M.,Konincx, N., Delaunoy, J. and Rousseau, J. C. (1972) New statistical studies of the negative variation in psychiatry. Rev. EEG Neurophysiol., 2 333-339. Venables, P. H. and Martin, I. (1964) Skin Resistance and Skin Potential. North-Holland Publ., Amsterdam. Verhey, F., Lamers, Th. en Emonds, P. (1975) Ontwerp voor een ondenoek naar de betekenis van bepaalde langzame hersenpotentialen voor de psychiatrische diagnostiek. Bulletin, 2 33-38. Verhey, F., Lamers, Th. and Emonds, P. (1975) Standard Deviation as a Methodological Tool in CNV Studies. Gain, Paris.