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Blink frequency and speech motor activity
N~ogia, Vol. 18,pp. 603-4306 © Perpmon Press Ltd., 1980.Printedin Great Britain
0028-3932/80/1001-0603$02.00/0
NOTE BLINK FREQUENCY AND SPEECH MOTOR ACTIVITY DETLEV VON CRAMON and UwE SCHURI Max-Planck-lnstitute for Psychiatry, Neurological Department, KraepelinstraBe 10, D-8000 Miinchen 40, W. Germany
(Received 24 March 1980) Abstract--There is a relationship between blink rate and speech motor activity possibly dependent on the articulatory difficulty of the task. This relationship might be caused by a simultaneous activation of the topologically adjacent motor channels for lid and speech movements.
INTRODUCTION SIR ARTHUR HALL [1] found significantly elevated mean blink frequencies of normal persons during conversation. He attributed this increase to the fact that the conversation was conducted with an unknown person. He related his findings to the observations made by POND~ and KENNI~Y [2"] who had.observed a distinct increase in the mean blink frequency in witnesses undergoing cross-examination. In both cases, the feeling of inmginary or real threat w a s considered to be decisive for the increase in the frequency of lid movements, In this context, he discussed BLotm'r's findings [3] according to which, in animals, the "hunting" are supposed to have a lower blink frequency in many cases than the "hunted". In an earlier investigation one of us [4] was able to show that the mean blink frequency in normal subjects also increased significantly when the conversation was conducted with persons well known to them. A hypothesis was formulated which deviated from Hall's interpretation and which specified that the significant increase in blink frequency during conversation is an expression of a simultaneous activation of lid and speech motor activity. The aim of this paper was to evaluate this hypothesis by experimental means.
METHOD Subjects Twenty normal subjects (Ss) participated in each of two experiments. Experiment 1 included 12 females and 8 males, experiment 2 involved 11 females and 9 males ranging in age from 19 to 44 yr. The Ss were paid for participating in the test. They were informed prior to the experiment that their electroencephalogram was to be measured in darkness.
Apparatus The experiment was performed on Ss in a sound-reduced room ( < 35 dB) which was darkened completely. The humidity and temperature of the experimentation room were held constant and air movement was minimized. The Ss lay on a bed with the upper part of their body at a semi-reclined angle of 30°. At the be~i'nning of the experiment, the Ss were instructed to keep their eyes open during the entire duration of the experiment. This was monitored with the aid of an electrooculogram and corrected, if necessary, by the experimenter. The Ss were given instructions about various tasks by a Revox tape recorder via a loudspeaker located at the level oftbe S's head and centered behind him. The responses of the Ss were transmitted to the experimenter with the aid of a microphone. If necessary, additional instructions could be given via intercom. Tasks and procedure Two different tasks were used: (A) The Ss were to recite slowly the alphabet until interrupted after 1 rain by a signal from the experimenter. (B) The Ss were to recite numbers upwards of 100 slowly for 1 rain. 603
NOTE Both tasks were performed under two conditions: with permanent loud verbalization (A +, B +) and without speaking aloud (A-, B- ). In 10 of the Ss tasks were performed in the order A +, A - , B +, B - while for the other 10 Ss the sequence was A - , A +, B-, B ÷. The experiments started with a 5 rain rest period followed by a l0 sec instruction segment for each task. The tasks were followed by a 5 rain rest period.
Reoistration of the electrooculooram (EOG) and dam evaluation The frequency of bilateral lid movements (blinks) was registered with the aid of the EOG. For the registration of the vertical EOG Beckman miniature biopotential skin electrodes were placed on the supra- and infraorbital ridges in the vertical axis of the right and let't pupils (gain 40 pV/mm). The electrodes were applied about 30 rain prior to the experiment. Electrode resistance never exceeded 5 kOhms at the start of the experiment. The corneo-retinal d.c. potentials derived from the subjects were recorded externally of the experimentation room (Beckman Polygraph R 611/Philipe Analogband 714) and evaluated on-line (PDP 11/40). The blinks were detected and processed according to a procedure described by YON CRAMONand NEUe^U~ [5]. To compare the mean blink frequencies during performance of the tasks with the mean frequencies during rest periods prior to and after tasks, the computer defined segments of equal length. The cited values were examined for significant differences with the aid of t-tests for correlated means; P <0.01 was accepted as the level of significance (mutrked with an asterisk in Fig. 1).
RESULTS During the rest period prior to task A, the mean blink rate (BR) was 0.39 blinks per second (SE+_0.07), the corresponding value for task B was 0.40 blinks per second (SE +0.10). There was no significant difference between BR during rest periods prior to and after tasks. The average changes in BR between rest and the stimulus periods are pre~umted in Fig. 1. Significant BR respomes can be observed under the stimulus conditions A - , B +, B-. Although a significant increase of mean BR was only seen when counting aloud was required (B + : t (19),ffi5.42), tlmre was alto a tendency for the mean BR to increase when the ABC was recited. In contrast, performing tasks A and B without ~¢akin 5 led to a sigllificant decrease of the mean BR (A- : t (19) = - 5.00; B - : t (19) -- - 5.64).
ABC
COUNTINO
IN~0J
( N~OI
ft,S.
g..2 ,o UJ 0 Z "IU
v
z g
-t
o
-I
0
A.
A-
B-
B-
TASK
FIo. 1. Average BR-change (blps) between rest and the stimulus periods A +, A - , B ÷, B-.
DISCUSSION Bilateral lid movements (blinks) constitute a heterogeneous group'of movements. A differentiation must be made between voluntary-conmcious self-motion, involuntary-spontaneous self-motion and involuntary-reflex motion of the lids. According to the findings of PONDER and K~NEDY [2], it can be assumed that the spontaneous self-motion of the lids comprise the major portion of the lid motion of a person when awake.
NOTE
605
The experimental set-up selected was intended to reduce as far as possible the proportion of blink reflexes conducted through the afferent optical, auditory and trigeminal nerves. The experiment was therefore performed in a dark, sound-reduced room at constant temperature and humidity while extensively excluding any draughts, dust and smoke. Conducting the experiment in darkness, however, was chosen primarily to avoid disruptive interferences with visual perception [6]. The mean blink frequencies measured, therefore, consist predominantly of the voluntary-conscious and involuntary-spontaneous self-motion of the lids. Having the Ss recite the alphabet aloud results in a tendency for the mean blink frequency to increase, without reaching the accepted level of significance. If speech motor activity is intensified by introducing polysyllabic words containing consonant clusters--as is the case when reciting numbers upwards of 100--the mean blink frequency increases significantly. It may be conjectured, therefore, that there is a relationship hetwcen speech motor and lid motor activity. The magnitude of the observed ¢fl'¢~ could depend on the difficulty in articulating. Counting numbers upwards of 100 is likely to require a more complex articulatory pruces~ng than reciting the ABC. If the subjects are asked to perform both tasks without speaking aloud, a significant dccrc~u~ in the mean blink frequency compared to the preceding rest period value is found. According to K~rNAI,.D and GL,,,S~R [6], an inhibition in blink activity demonstrates the withdrawal of attention from the environment. With regard to the possible mechanisms of the observed relationship between lid motor and speech motor activity we propose the following considerations. Kr~o and MlCaanR.s[7"Jwere able to demonstrate that an increase in motor activity in the hand (hand grip)resulted in a significant increase in the mean blink frequency. This finding was explained by a theory presented of MEYER [g'l concerning the interaction of simultaneous reactions. ME¥~g [8] postulated the facilitation of lid motor activity by simultaneous activation in topologically adjacent motor channels. He made references in this context to the specially strategic position of the eye lid in the primary motor cortex where it is bordered on the one side by the area of representation of the hand and on the other side by those of the larynx, tongue and face. However, the simultaneous activation of both speech motor and lid motor "channels" was not taken into consideration by these authors. The simultaneous activation of adjacent motor channels or, formulated somewhat differently, the deficient inhibition between adjacent motor charmels does not have to occur in the primary motor cortex, but may also occur in subcortical motor relay nuclei or may even occur first in the facial nuclei of the caudal pons. The oral and perioral muscles and, consequently, peripheral facial nerve neurons undoubtedly play a decisive pan in articulation. The innervation of facial nerve neurons, which are necessary for speech motor activity, might not be limited to oral branches, but also include simultaneously orbicular branches. This topological question, however, cannot he decided on the basis of the data available at present. It can be said in conclusion that there is a relationship between speech motor and lid motor activity. The mean blink frequency appears to increase as the difficulty in articulating the task increases. The increase in the mean blink frequency during conversation can simply he explained by this relationship. There is no need, so far, for the assumptions of HALL [1] even if emotional factors may influence lid motor activity substantially.
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8.
HALL, Sir A. The origin and purpnses of blinking. Br. J. Ophthal. 29, 445-467, 1945. PONI~R, E. and K E ~ ¥ , W. P. On the act of blinking. Q. JI exp. Physiol. 18, 89-110, 1928. Bl.ou~rr, W. P. Studies of the moveruent of the eyelids of animals: Blinking. Q. Jl exp. Physiol. 18, 111-125,1928. CRAMON, D. YON Die spontancn Lidbewegungen: ein Spiegel l~ychomotorischer Aktivitit? In: Emotionsforschuno im medizinischen Bereich. S. Davies-Osterkamp and E. P6ppel (Editors) Vandenhocck, G6ttingen, 1980. L-~AMON, D. YON and N ~ ' I ~ u ~ , H. Programmsystern zur automatischen Erkennung yon lateralen sakkadi~he~ Augenhew~ngen und Lidhewcgongen im EOG. EDV Med. Biol. 9, 96-100, 1978. KI~N~D, D. W. and G L ~ ' g , G. H. An analysis of eyelid moven~'nts. J. Nerv. Ment. D/s. 139, 31--48, 1964. KING,D. C. and MICHEl.S,K. M. Muscular tension and the human blink rate. J. exp. Psychol. 53,113-116,1957. MEYER,D. R. On the'interaction of simultaneous responses. Psychol. Bull. 50, 204, 220, 1953.
606
NOTE R68um6
:
On a constat6 une relation entre la fr6quence du clignement et l'activit6 mortice de la parole, relation qui d6pend peut ~tre de la difflcult6 articulatoire de la t&che. Cette relation pourrait ~tre d6termin6e par l'activation simultan~e des canaux moteurs topologiquewent voisin$ pour les mouvements des paupi~re$ et de la parole.
Zus~mmenfassunq Es w u r d e die Frage nach d e m Z u s a m m e n h a n g scher und s p r e c h m o t o r i s c h e r A u s f U h r u n g von 4 A u f g a b e n
zw£schen lidmotorl-
A k t i v i t ~ t gestellt.
W a h r e n d der
(Aufsagen des Alphabets,
Z~hlen auf-
warts yon 100; jeweils mlt und ohne Sprechen ausgefUhrt) wurden die b i l a t e r a l e n Blinkfrequenz
Lidbewegungen
aufgezeichnet.
$tieg mit der s p r e c h m o t o r i s c h e n
wobel der A n s t l e g yon der a r t i k u l a t o r l s c h e n Aufgabe abzuh~ngen
scheint.
Die m l t ~ l e r e
Aktivltat
an,
S c h w i e r i g k e i t der
0028-3932/80/1001-0603$02.00/0
NOTE BLINK FREQUENCY AND SPEECH MOTOR ACTIVITY DETLEV VON CRAMON and UwE SCHURI Max-Planck-lnstitute for Psychiatry, Neurological Department, KraepelinstraBe 10, D-8000 Miinchen 40, W. Germany
(Received 24 March 1980) Abstract--There is a relationship between blink rate and speech motor activity possibly dependent on the articulatory difficulty of the task. This relationship might be caused by a simultaneous activation of the topologically adjacent motor channels for lid and speech movements.
INTRODUCTION SIR ARTHUR HALL [1] found significantly elevated mean blink frequencies of normal persons during conversation. He attributed this increase to the fact that the conversation was conducted with an unknown person. He related his findings to the observations made by POND~ and KENNI~Y [2"] who had.observed a distinct increase in the mean blink frequency in witnesses undergoing cross-examination. In both cases, the feeling of inmginary or real threat w a s considered to be decisive for the increase in the frequency of lid movements, In this context, he discussed BLotm'r's findings [3] according to which, in animals, the "hunting" are supposed to have a lower blink frequency in many cases than the "hunted". In an earlier investigation one of us [4] was able to show that the mean blink frequency in normal subjects also increased significantly when the conversation was conducted with persons well known to them. A hypothesis was formulated which deviated from Hall's interpretation and which specified that the significant increase in blink frequency during conversation is an expression of a simultaneous activation of lid and speech motor activity. The aim of this paper was to evaluate this hypothesis by experimental means.
METHOD Subjects Twenty normal subjects (Ss) participated in each of two experiments. Experiment 1 included 12 females and 8 males, experiment 2 involved 11 females and 9 males ranging in age from 19 to 44 yr. The Ss were paid for participating in the test. They were informed prior to the experiment that their electroencephalogram was to be measured in darkness.
Apparatus The experiment was performed on Ss in a sound-reduced room ( < 35 dB) which was darkened completely. The humidity and temperature of the experimentation room were held constant and air movement was minimized. The Ss lay on a bed with the upper part of their body at a semi-reclined angle of 30°. At the be~i'nning of the experiment, the Ss were instructed to keep their eyes open during the entire duration of the experiment. This was monitored with the aid of an electrooculogram and corrected, if necessary, by the experimenter. The Ss were given instructions about various tasks by a Revox tape recorder via a loudspeaker located at the level oftbe S's head and centered behind him. The responses of the Ss were transmitted to the experimenter with the aid of a microphone. If necessary, additional instructions could be given via intercom. Tasks and procedure Two different tasks were used: (A) The Ss were to recite slowly the alphabet until interrupted after 1 rain by a signal from the experimenter. (B) The Ss were to recite numbers upwards of 100 slowly for 1 rain. 603
NOTE Both tasks were performed under two conditions: with permanent loud verbalization (A +, B +) and without speaking aloud (A-, B- ). In 10 of the Ss tasks were performed in the order A +, A - , B +, B - while for the other 10 Ss the sequence was A - , A +, B-, B ÷. The experiments started with a 5 rain rest period followed by a l0 sec instruction segment for each task. The tasks were followed by a 5 rain rest period.
Reoistration of the electrooculooram (EOG) and dam evaluation The frequency of bilateral lid movements (blinks) was registered with the aid of the EOG. For the registration of the vertical EOG Beckman miniature biopotential skin electrodes were placed on the supra- and infraorbital ridges in the vertical axis of the right and let't pupils (gain 40 pV/mm). The electrodes were applied about 30 rain prior to the experiment. Electrode resistance never exceeded 5 kOhms at the start of the experiment. The corneo-retinal d.c. potentials derived from the subjects were recorded externally of the experimentation room (Beckman Polygraph R 611/Philipe Analogband 714) and evaluated on-line (PDP 11/40). The blinks were detected and processed according to a procedure described by YON CRAMONand NEUe^U~ [5]. To compare the mean blink frequencies during performance of the tasks with the mean frequencies during rest periods prior to and after tasks, the computer defined segments of equal length. The cited values were examined for significant differences with the aid of t-tests for correlated means; P <0.01 was accepted as the level of significance (mutrked with an asterisk in Fig. 1).
RESULTS During the rest period prior to task A, the mean blink rate (BR) was 0.39 blinks per second (SE+_0.07), the corresponding value for task B was 0.40 blinks per second (SE +0.10). There was no significant difference between BR during rest periods prior to and after tasks. The average changes in BR between rest and the stimulus periods are pre~umted in Fig. 1. Significant BR respomes can be observed under the stimulus conditions A - , B +, B-. Although a significant increase of mean BR was only seen when counting aloud was required (B + : t (19),ffi5.42), tlmre was alto a tendency for the mean BR to increase when the ABC was recited. In contrast, performing tasks A and B without ~¢akin 5 led to a sigllificant decrease of the mean BR (A- : t (19) = - 5.00; B - : t (19) -- - 5.64).
ABC
COUNTINO
IN~0J
( N~OI
ft,S.
g..2 ,o UJ 0 Z "IU
v
z g
-t
o
-I
0
A.
A-
B-
B-
TASK
FIo. 1. Average BR-change (blps) between rest and the stimulus periods A +, A - , B ÷, B-.
DISCUSSION Bilateral lid movements (blinks) constitute a heterogeneous group'of movements. A differentiation must be made between voluntary-conmcious self-motion, involuntary-spontaneous self-motion and involuntary-reflex motion of the lids. According to the findings of PONDER and K~NEDY [2], it can be assumed that the spontaneous self-motion of the lids comprise the major portion of the lid motion of a person when awake.
NOTE
605
The experimental set-up selected was intended to reduce as far as possible the proportion of blink reflexes conducted through the afferent optical, auditory and trigeminal nerves. The experiment was therefore performed in a dark, sound-reduced room at constant temperature and humidity while extensively excluding any draughts, dust and smoke. Conducting the experiment in darkness, however, was chosen primarily to avoid disruptive interferences with visual perception [6]. The mean blink frequencies measured, therefore, consist predominantly of the voluntary-conscious and involuntary-spontaneous self-motion of the lids. Having the Ss recite the alphabet aloud results in a tendency for the mean blink frequency to increase, without reaching the accepted level of significance. If speech motor activity is intensified by introducing polysyllabic words containing consonant clusters--as is the case when reciting numbers upwards of 100--the mean blink frequency increases significantly. It may be conjectured, therefore, that there is a relationship hetwcen speech motor and lid motor activity. The magnitude of the observed ¢fl'¢~ could depend on the difficulty in articulating. Counting numbers upwards of 100 is likely to require a more complex articulatory pruces~ng than reciting the ABC. If the subjects are asked to perform both tasks without speaking aloud, a significant dccrc~u~ in the mean blink frequency compared to the preceding rest period value is found. According to K~rNAI,.D and GL,,,S~R [6], an inhibition in blink activity demonstrates the withdrawal of attention from the environment. With regard to the possible mechanisms of the observed relationship between lid motor and speech motor activity we propose the following considerations. Kr~o and MlCaanR.s[7"Jwere able to demonstrate that an increase in motor activity in the hand (hand grip)resulted in a significant increase in the mean blink frequency. This finding was explained by a theory presented of MEYER [g'l concerning the interaction of simultaneous reactions. ME¥~g [8] postulated the facilitation of lid motor activity by simultaneous activation in topologically adjacent motor channels. He made references in this context to the specially strategic position of the eye lid in the primary motor cortex where it is bordered on the one side by the area of representation of the hand and on the other side by those of the larynx, tongue and face. However, the simultaneous activation of both speech motor and lid motor "channels" was not taken into consideration by these authors. The simultaneous activation of adjacent motor channels or, formulated somewhat differently, the deficient inhibition between adjacent motor charmels does not have to occur in the primary motor cortex, but may also occur in subcortical motor relay nuclei or may even occur first in the facial nuclei of the caudal pons. The oral and perioral muscles and, consequently, peripheral facial nerve neurons undoubtedly play a decisive pan in articulation. The innervation of facial nerve neurons, which are necessary for speech motor activity, might not be limited to oral branches, but also include simultaneously orbicular branches. This topological question, however, cannot he decided on the basis of the data available at present. It can be said in conclusion that there is a relationship between speech motor and lid motor activity. The mean blink frequency appears to increase as the difficulty in articulating the task increases. The increase in the mean blink frequency during conversation can simply he explained by this relationship. There is no need, so far, for the assumptions of HALL [1] even if emotional factors may influence lid motor activity substantially.
REFERENCES 1. 2. 3. 4. 5. 6. 7. 8.
HALL, Sir A. The origin and purpnses of blinking. Br. J. Ophthal. 29, 445-467, 1945. PONI~R, E. and K E ~ ¥ , W. P. On the act of blinking. Q. JI exp. Physiol. 18, 89-110, 1928. Bl.ou~rr, W. P. Studies of the moveruent of the eyelids of animals: Blinking. Q. Jl exp. Physiol. 18, 111-125,1928. CRAMON, D. YON Die spontancn Lidbewegungen: ein Spiegel l~ychomotorischer Aktivitit? In: Emotionsforschuno im medizinischen Bereich. S. Davies-Osterkamp and E. P6ppel (Editors) Vandenhocck, G6ttingen, 1980. L-~AMON, D. YON and N ~ ' I ~ u ~ , H. Programmsystern zur automatischen Erkennung yon lateralen sakkadi~he~ Augenhew~ngen und Lidhewcgongen im EOG. EDV Med. Biol. 9, 96-100, 1978. KI~N~D, D. W. and G L ~ ' g , G. H. An analysis of eyelid moven~'nts. J. Nerv. Ment. D/s. 139, 31--48, 1964. KING,D. C. and MICHEl.S,K. M. Muscular tension and the human blink rate. J. exp. Psychol. 53,113-116,1957. MEYER,D. R. On the'interaction of simultaneous responses. Psychol. Bull. 50, 204, 220, 1953.
606
NOTE R68um6
:
On a constat6 une relation entre la fr6quence du clignement et l'activit6 mortice de la parole, relation qui d6pend peut ~tre de la difflcult6 articulatoire de la t&che. Cette relation pourrait ~tre d6termin6e par l'activation simultan~e des canaux moteurs topologiquewent voisin$ pour les mouvements des paupi~re$ et de la parole.
Zus~mmenfassunq Es w u r d e die Frage nach d e m Z u s a m m e n h a n g scher und s p r e c h m o t o r i s c h e r A u s f U h r u n g von 4 A u f g a b e n
zw£schen lidmotorl-
A k t i v i t ~ t gestellt.
W a h r e n d der
(Aufsagen des Alphabets,
Z~hlen auf-
warts yon 100; jeweils mlt und ohne Sprechen ausgefUhrt) wurden die b i l a t e r a l e n Blinkfrequenz
Lidbewegungen
aufgezeichnet.
$tieg mit der s p r e c h m o t o r i s c h e n
wobel der A n s t l e g yon der a r t i k u l a t o r l s c h e n Aufgabe abzuh~ngen
scheint.
Die m l t ~ l e r e
Aktivltat
an,
S c h w i e r i g k e i t der