Intern. J . Neuroscience, 1979, Vol. 9, pp. 175-183 0320-7454/79/0903-0175$04.50/0
8 1979, Gordon and Breach Science Publishers, Inc. Printed in Great Britain
THE EFFECTS OF SELF-REGULATION OF SLOW CORTICAL POTENTIALS ON PERFORMANCE IN A SIGNAL DETECTION TASK WERNER LUTZENBERGER, THOMAS ELBERT, BRIGITTE ROCKSTROH and NIELS BIRBAUMER
Int J Neurosci Downloaded from informahealthcare.com by University of Otago on 01/09/15 For personal use only.
lnstitute of’Psycholog)*,University of Ttibingen, Federal Republic of Germany (Received December 18, 1978)
Results from research on slow cortical potentials, especially CNV research, suggest that attention may be increased with increased cortical negative shifts. The present study investigates the relationship between performance in a signal detection task and slow cortical potentials. Cortical shifts were varied by means of a biofeedback procedure. 22 subjects received continuous visual feedback or their slow cortical potentials (SCP) during intervals of 6 sec, 1I yoked control subjects received “false feedback” of the SCP of a matched experimental partner. Minimal changes of the feedback stimulus presented for 100rnsec a t different times during the feedback interval served as signals to be detected. The experiment consisted of 240 trials. Experimental subjects learned to shift their cortical level towards more or less negativity or positivity depending on the frequency of a signal tone. Mean differences were, however, small ( 5 pv> compared to previous results on self-regulation of SCP. All subjects showed a P300 if a signal was detected correctly, whereas no positive wave occurred if “false alarms” were made. Experimental subjects showed a highly significant inverted U-shaped relationship between SCP-shift and signal detection Performance, i.e., were better during small negative shifts than during strong negative or small positive shifts. No relationship was found in yoked control subjects who also showed no variation of SCP. Furthermore, yoked control subjects showed a performance decrement compared to experimental subjects. It is suggested that a shifting of cortical potentials facilitates attentional processes. The lack of a systematic variation of SCP in yoked control subjects also may be responsible for the lack of relationship between SCP and signal detection performance in yoked control subjects.
Atientional processes may be divided roughly into focused attention during short time intervals and long-lasting alertness as described for example by the tcrm “vigilance” (Mackie, 1977; Bilodeau & Bilodeau, 1968). Research on slow cortical potentials (SCP) suggested an interpretation of cortical negative shifts as reflecting attentional processes, cortical arousal, information processing, expectancy and response preparation (see for example Tecce, 1972; McCallum, 1969; Loveless, 1978;
_--
Pribrani & McGuinness, 1975; Gaillard, 1978). Cortical positivity, on the other hand, was discussed as a sign of cortical inhibitory processes and deactivation (Prince, 1974). While experiments on SCP involving the reactiontime or two-stimulus paradigm usually concentrate on focused attention, the relationship between longlasting attention or vigilance and SCP seems not to have been investigated. The present experiment was performed t o investigate a functional relationship between SCP and the performance in a signal detection task as an example of a vigilance task requiring long-lasting alertness. On the background of results and interpretations of SCP it was hypothesized that cortical slow potential shifts covary with performance in a signal detection task: performance was assumed to be better during periods of pronounced negativity as to periods Of less negative or positive shifts.
-
Research was supported by the Deutsche Forschungsgemeinschaft and the Stiftung Volkswagenwerk. Requests for reprints should be sent to: Niels Birbaumer, Ph.D., Professor Psychologisches InStitUt der Universitat Tubingen, Arbeitsbereich Klinische Psychologic und Psychophysiologie, Gartenstrasse 29, 7400 Tubingen. F.R.G. 175
Int J Neurosci Downloaded from informahealthcare.com by University of Otago on 01/09/15 For personal use only.
17G
W. LUTZENBERGER et al.
A basic idea of testing this hypothesis was to induce different levels of cortical activity, i.e., more or less negative SCP at the vertex, by means of a biofeedback procedure and to investigate the performance in signal detection as the dependent variable. Several experiments demonstrated that healthy human subjects are able to change, i.e., to control instrumentally, their SCP level through a biofeedback procedure (Elbert, Birbaumer, Lutzenberger, & Rockstroh, 1978; Elbert, Rockstroh, Lutzenberger, & Birbaumer, 1978b). This procedure, therefore, seems appropriate for the specific induction of different potential shifts. For the present experiment this biofeedback procedure was combined with a signal detection task.
>>
1
METHOD Subjects There were 33 male student volunteers that participated in the experiment which lasted for 3 h. Students who were currently taking any medication or who suffered from cardiovascular or central nervous abnormality were excluded. They received a gratuity depending on their performance during the experiment and were randomly assigned to one of two groups: 22 subjects were assigned to an experimental group receiving SCP-feedback, while I 1 subjects formed a yoked control group receiving “false feedback” of SCP of a matched experimental partner. Design and Procedure Feedback of SCP was provided by the outline of a little rocket-ship moving from the left to the right across a TV-screen in front of the subjects during intervals of 6sec each. Subjects were asked to direct the rocket into one of two goals marked on the right side of the TV-screen depending on the frequency of a signal tone: a high (1 200 Hz,65 dB) or low (400 Hz,65 dB) tone signaled that the upper goal or the lower goal had to be hit. The relation of signal tone and required goal was counterbalanced across subjects, signal tones appeared in randomized order within subjects. Each feedback interval was followed by a reinforcement interval of 9 sec: a score demonstrated the amount of successful trials (win points) in which the rocket reached the required goal and failures (loss points), trials in which the wrong goal was hit. The difference between win and loss points was con-
FIGURE 1 Visual feedback of slow cortical potentials: directing the rocket into the upper or lower goal (bars on the right side) required a change of SCP level towards negativity or positivity (less negativity). For signal detection the interruptions of the outline of the rocket (see examples at the bottom of the figure) appeared for I 0 0 msec.
verted into money after the experiment. Additionally, the word “good” appeared above win points and the word “bad” above loss points (see Figure 1 ; see also Elbert et al., 1978b). Reaching one goal required a negative cortical shift, reaching the other a change of the cortical level towards reduced negativity or positivity. The actual height of the rocket during the feedback interval was a function of the actual cortical shift: the height of the rocket at time t was a linear function of the integral of the EEG from the onset of the signal tone to the actual time t during the 6-sec flight of the rocket across the TV-screen. Specific procedures were included so that artifactitious influences-especially of ocular origin-could be excluded: integration was stopped if the rocket was moving toward the required goal and EOG shifts of the same polarity as SCP were recorded simultaneously (see Elbert et al., 1978 and 1978b for a detailed description of the algorithm). This resulted in a conditioning of eye movements: subjects were successful in reaching the required goal only if there were no EOG deflections (
8 1979, Gordon and Breach Science Publishers, Inc. Printed in Great Britain
THE EFFECTS OF SELF-REGULATION OF SLOW CORTICAL POTENTIALS ON PERFORMANCE IN A SIGNAL DETECTION TASK WERNER LUTZENBERGER, THOMAS ELBERT, BRIGITTE ROCKSTROH and NIELS BIRBAUMER
Int J Neurosci Downloaded from informahealthcare.com by University of Otago on 01/09/15 For personal use only.
lnstitute of’Psycholog)*,University of Ttibingen, Federal Republic of Germany (Received December 18, 1978)
Results from research on slow cortical potentials, especially CNV research, suggest that attention may be increased with increased cortical negative shifts. The present study investigates the relationship between performance in a signal detection task and slow cortical potentials. Cortical shifts were varied by means of a biofeedback procedure. 22 subjects received continuous visual feedback or their slow cortical potentials (SCP) during intervals of 6 sec, 1I yoked control subjects received “false feedback” of the SCP of a matched experimental partner. Minimal changes of the feedback stimulus presented for 100rnsec a t different times during the feedback interval served as signals to be detected. The experiment consisted of 240 trials. Experimental subjects learned to shift their cortical level towards more or less negativity or positivity depending on the frequency of a signal tone. Mean differences were, however, small ( 5 pv> compared to previous results on self-regulation of SCP. All subjects showed a P300 if a signal was detected correctly, whereas no positive wave occurred if “false alarms” were made. Experimental subjects showed a highly significant inverted U-shaped relationship between SCP-shift and signal detection Performance, i.e., were better during small negative shifts than during strong negative or small positive shifts. No relationship was found in yoked control subjects who also showed no variation of SCP. Furthermore, yoked control subjects showed a performance decrement compared to experimental subjects. It is suggested that a shifting of cortical potentials facilitates attentional processes. The lack of a systematic variation of SCP in yoked control subjects also may be responsible for the lack of relationship between SCP and signal detection performance in yoked control subjects.
Atientional processes may be divided roughly into focused attention during short time intervals and long-lasting alertness as described for example by the tcrm “vigilance” (Mackie, 1977; Bilodeau & Bilodeau, 1968). Research on slow cortical potentials (SCP) suggested an interpretation of cortical negative shifts as reflecting attentional processes, cortical arousal, information processing, expectancy and response preparation (see for example Tecce, 1972; McCallum, 1969; Loveless, 1978;
_--
Pribrani & McGuinness, 1975; Gaillard, 1978). Cortical positivity, on the other hand, was discussed as a sign of cortical inhibitory processes and deactivation (Prince, 1974). While experiments on SCP involving the reactiontime or two-stimulus paradigm usually concentrate on focused attention, the relationship between longlasting attention or vigilance and SCP seems not to have been investigated. The present experiment was performed t o investigate a functional relationship between SCP and the performance in a signal detection task as an example of a vigilance task requiring long-lasting alertness. On the background of results and interpretations of SCP it was hypothesized that cortical slow potential shifts covary with performance in a signal detection task: performance was assumed to be better during periods of pronounced negativity as to periods Of less negative or positive shifts.
-
Research was supported by the Deutsche Forschungsgemeinschaft and the Stiftung Volkswagenwerk. Requests for reprints should be sent to: Niels Birbaumer, Ph.D., Professor Psychologisches InStitUt der Universitat Tubingen, Arbeitsbereich Klinische Psychologic und Psychophysiologie, Gartenstrasse 29, 7400 Tubingen. F.R.G. 175
Int J Neurosci Downloaded from informahealthcare.com by University of Otago on 01/09/15 For personal use only.
17G
W. LUTZENBERGER et al.
A basic idea of testing this hypothesis was to induce different levels of cortical activity, i.e., more or less negative SCP at the vertex, by means of a biofeedback procedure and to investigate the performance in signal detection as the dependent variable. Several experiments demonstrated that healthy human subjects are able to change, i.e., to control instrumentally, their SCP level through a biofeedback procedure (Elbert, Birbaumer, Lutzenberger, & Rockstroh, 1978; Elbert, Rockstroh, Lutzenberger, & Birbaumer, 1978b). This procedure, therefore, seems appropriate for the specific induction of different potential shifts. For the present experiment this biofeedback procedure was combined with a signal detection task.
>>
1
METHOD Subjects There were 33 male student volunteers that participated in the experiment which lasted for 3 h. Students who were currently taking any medication or who suffered from cardiovascular or central nervous abnormality were excluded. They received a gratuity depending on their performance during the experiment and were randomly assigned to one of two groups: 22 subjects were assigned to an experimental group receiving SCP-feedback, while I 1 subjects formed a yoked control group receiving “false feedback” of SCP of a matched experimental partner. Design and Procedure Feedback of SCP was provided by the outline of a little rocket-ship moving from the left to the right across a TV-screen in front of the subjects during intervals of 6sec each. Subjects were asked to direct the rocket into one of two goals marked on the right side of the TV-screen depending on the frequency of a signal tone: a high (1 200 Hz,65 dB) or low (400 Hz,65 dB) tone signaled that the upper goal or the lower goal had to be hit. The relation of signal tone and required goal was counterbalanced across subjects, signal tones appeared in randomized order within subjects. Each feedback interval was followed by a reinforcement interval of 9 sec: a score demonstrated the amount of successful trials (win points) in which the rocket reached the required goal and failures (loss points), trials in which the wrong goal was hit. The difference between win and loss points was con-
FIGURE 1 Visual feedback of slow cortical potentials: directing the rocket into the upper or lower goal (bars on the right side) required a change of SCP level towards negativity or positivity (less negativity). For signal detection the interruptions of the outline of the rocket (see examples at the bottom of the figure) appeared for I 0 0 msec.
verted into money after the experiment. Additionally, the word “good” appeared above win points and the word “bad” above loss points (see Figure 1 ; see also Elbert et al., 1978b). Reaching one goal required a negative cortical shift, reaching the other a change of the cortical level towards reduced negativity or positivity. The actual height of the rocket during the feedback interval was a function of the actual cortical shift: the height of the rocket at time t was a linear function of the integral of the EEG from the onset of the signal tone to the actual time t during the 6-sec flight of the rocket across the TV-screen. Specific procedures were included so that artifactitious influences-especially of ocular origin-could be excluded: integration was stopped if the rocket was moving toward the required goal and EOG shifts of the same polarity as SCP were recorded simultaneously (see Elbert et al., 1978 and 1978b for a detailed description of the algorithm). This resulted in a conditioning of eye movements: subjects were successful in reaching the required goal only if there were no EOG deflections (
