Autonomic responses correlate to motor anticipation

ELSEVIER

Behavioural Brain Research 63 (1994) 71-79

BEHAVIOURAL BRAIN RESEARCH

Autonomic responses correlate to motor anticipation C. Collet ~', C. Deschaumes-Molinaro", G. Delhomme b, A. Dittmar b, E. Vernet-Maury ~''* '~l, ahoratoire de Phrsiologie Neuroxensorielle. C/YRS. Univervit( Claude Bernard. L I'oH 1. F-69622 1/711eurham~e ('e&'~. France b Lahorahdre de Thermor~;gulation et Energ(tique de I'Everch'e, C N R S , 8 A vemw Rock/~,lh, r. 1"-69373 L voH Ce&' \ ,~', France

Received 17 December 1993: revised 21 April I994: accepted 21 April 1994

Abstract New findings have stated that autonomic nervous system (ANS) functioning may reflect some cognitive processes observed in real time analysis. Four ANS variables plus instantaneous heart rate and respiratory' frequency were quantified by original techniques and indices on 11 subjects during a coincidence-anticipation task, performed on a computer screen under six difl'erent, randomly-presented modalities (3 modalities describing the spot moving along a parabola at 2 speeds). Tonic levels and phasic responses corresponding to each trial were recorded continuously. Results showed that skin resistance tonic level evolution gave evidence of vigilance changes. Thus, performance can be related to subjects' vigilance. An autonomic response was always observed during performance of an anticipation task. The six task modalities were distinguished by performance values. Simultaneously recorded ANS responses fully differentiated these same modalities for 10 subjects out of 11. These ANS responses were fnrthermorc related to performance. Ten subjects out of 11 possess at least one Autonomic variable which can differentiate the six task modalities, confirming Lacey's h y p o thesis on ANS preferential response, and suggesting ANS specificity. ANS functioning may reveal some brain functions through a specific autonomic channel, characterizing each subject. The behavioral output of an individual may thus be reflected by such a functioning. Key word, s: Autonomic nervous sxstem response specificity'; Electrodermal response; Thermovascular response: Cardiorespiratory response; Human skill: Coincidence-anticipation task

1. Introduction P r e p r o g r a m m i n g is the process of preparing the m o t o r program for motion initiation. The person selects, organizes and initiates an action program, after information processing, which will p r o d u c e a series of muscular activities resulting in an action [24]. In view of the speed at which manx of these activities are carried out (particularly in sporting activities), much information processing must occur prior to critical events. A c c o r d i n g to this model, the program must be structured completely or almost completely before the m o v e m e n t can be initiated. Allen and T s u k a h a r a [2], have p r o p o s e d that the basal ganglia and lateral cerebellum are implied, with the associative cortex, in movement planning and programming. Every dax life activities usually require a large amount of perceptual information to be processed in relatively short periods of time in order to be successful. F o r this

* Corresponding author. Fax: /33) 78 94 95 85. 0166-4328.94 S7.00 {) 1994 Elscxier Science B.V. All rights reserved S S D I 0 1 6 n - 4 3 2S( 94)001)5 5- K

reason, accurate anticipatory skills haxe been frequently a d v a n c e d as being important for success in sporting activities [ 1]. The role played by the autonomic nerwms system ( A N S ) in m o t o r anticipating m e c h a n i s m s has been known for a long time [17]. Yet the analysis of autonomic responses has often given ambiguous and erroneous results considering both inter- or intra-subject correlations. In the last decade, new concepts and techniques have brought about better understanding of this autonomic functioning, with reliable results. First, Mulder [19] hypothesized that each emotion induced its own pattern of response in the A N S . This hypothesis was to be strongly d e m o n s t r a t e d 11) years later by E k m a n [12], who proved that the recorded autonomic response distinguished not only between positive and negative emotions, but also among negative emotions. This finding led to the postulation that autonomic responses were not indifferentiated, as claimed by' C a n n o n [3], and challenged theories on emotions that have failed to address the implications o f autonomic differentiation in emotions.

72

C. (Adler et al.

Behavioural Brain Re.vearch 63 1t;94 " 1 - 7 9

Secondly, research by Lidberg and Waltin [ 18], Wallin and Fagius [30], based on the recording of sympathetic units activities with a micro-electrode, concluded that ANS is a highly differentiated, rapidly activated system, with subdivisions specialized in regulating different organ functions, in response to the changing demands of the internal and external milieu. Thirdly, our team [8] verified Lacey's hypothesis on individual AN S response: each subject responds through a preferential ANS channel, whatever the stimulus [15]. Taking into account these new results, 6 ANS variables were quantified by Dittmar and Vernet-Maury by an original device, and new indices were developed [28]. The authors were able to verify Lacey's hypothesis of individual response specificity [8,15,27]. This means that the effect of the stimulus situation also depends on the subject. It thus seems obvious that several ANS variables must be recorded. It is now well known that autonomic responses are components of behavioral responses. Recent results have led us to consider autonomic activity as reflecting cognitive processes [6,7,16,22,25,30]. Moreover, the main role of ANS in preparing an action has already been put forward, but ANS functioning has yet to be explained [ 17]. The aim of this experiment was to study autonomic responses while subjects performed a perceptual-anticipation task involving different modalities. It was expected to demonstrate that Autonomic responses are correlated with a subject's performance (accurate or inaccurate) on the one hand, and that continuous recording should be able to show autonomic responses distinguishing among anticipation task modalities.

2.

Methods

2.1. Subjects The 11 subjects, 6 females and 5 males, aged from 17 to 31, were from the direct laboratory environment, in order to guarantee a high level of motivation. They were students and were not paid for their participation, They were unaware of the aim and the hypothesis of the experiment before the test.

2.2. A N S parameters Six autonomic parameters were selected for quantification - electrodermal response: skin potential and resistance. - thermovascular parameters: skin blood flow and skin temperature. - cardio-respiratory parameters: instantaneous heart rate and respiratory frequency.

2.2.1. Potential responsex Skin potential was recorded using Beckman sclf~ adhesive 78 mm z electrodes. Electrode positioning was in compliance with traditional recontmendations [t3], The active electrode was placed on the hypothenar eminence of the subject's non-dominant hand. after alcohol-ether cleaning of the skin. The reference electrode was placed lit cm higher on the wrist. The signal processing for electrodermal potential variations was carried out using Svder code [9], which permitted classification of elementar~ responses according to their form. sign tpositivc el ncgative), and duration. As far as potential variations were concerned, only this index was used. the others being tess satisfactory or even redundant with indices simultane~ msiv recorded. According to this code. 3 positive and a ,,/egatire skin potential forms werc considered [2~1. 2.2.2. Resistance responses Cutaneous resistance was recorded using 30 ram: nnpolarizable round Capsulex electrodes placed on the second phalanx of the index ano of the third digit of the non-dominant hand, held by adhesive tape. Resistance was measured with 15 /,A DC current. A new temporal index was defined since response anaplitude depends on the prestimulation value [14]. ,\ similar observation of thermovascular indices made it possible to define the time during which the subject "'responds" to stimuli without referring to the initial value Ior tonic levell. This Ohmic Perturbation Duration or O P D index of skin resistance. reveals the emotional toad of stimulation [23], In order to eliminate an~ interference between skin potential and resistance and other artefacts, par~uneters ~ere recorded by means of a high rate common reiecuon mode differential "isolation" amplifier (Analog Devices AD 293 Bl. Likewise, recorder inputs were of the differential mode. and resistance circuit supply was of the floating type. Skin resistance measurement current passed between the index and the third digit while skin potential was measured between the hypothenar eminence and the inner side of the forearm. 2.2.3. Superticial skOl blood tto~ This was assessed using the original Hematron patented sensor (Dktmar. 1985. CNRS ANVAR. Patent 85 15932), The non-invasive sensor was placed on the skin with adhesive tape. on the thenar eminence of the non-dominant hand. The transducer consisted of a disc 25 mm in diameter and 4 mm thick. The measming surface in contact with the skin was made up of two parts: the reference area at the peripher} el" the disc and lhe measurement area al lhe center of the disc. The temperature difference betx~ecn these two areas was measured using 16 thcrmocouple

73

C. Collet et al. /Behavioural Brain Research 63 (1994) 71-79

junctions. A very low thermal inertia flat heater was located in the central part of the disc. A proportional, integral and derivative device controlled the heating power in order to maintain a constant temperature difference of 2 °C between the central area and the periphery. The size and shape of the heater were designed in such a manner that a thermal field was induced within the capillary network. The power necessary to maintain the temperature difference constant depends on skin blood flow: heat was transferred through the skin and washed out by the blood flow. At all times, electric power was proportional to the heat evacuated by the tissue blood flow [10]. Skin blood flow variations were measured: -by the difference (positive or negative) between the pre- and post-stimulation values expressed in W , m ~. C - 1 - by the duration of the oscillations perturbation (expressed in seconds).

2.2.4. Superficial skh~ temperature

This was measured by a low inertia thermistor (10 K3 M C D2 Betatherm). A 4 mm 2 sensor was placed with non-caustic glue on the middle of the palm of the nondominant hand. A variation of approximately one thousandth of a degree can be detected under such conditions. The amplitude and duration of the responses were measured. 2.2.5. Instantaneous heart rate

This was recorded from 3 silver electrodes in the precordial position. The D2 derivation signal (the interval between 2 consecutive R waves) was processed and delivered in the form of instantaneous heart frequency. The smallest appreciable variation was 0.5 of a beat per minute and the calibrated scale ranged from 0 to 200 b.p.m. In this way, heart rate frequency increase or decrease is easily put forward and the relationship between the stimulus impact and heart rate instantaneous response established.

2.2.7. Recording apparatus

This was made up of a Ytse 460 type BBC (Brown Boveri) 6-channel potentiometric D C recorder fitted with an event tracer, and an automatic synchronization appliance which cancels out temporal differences between the 6 markers. The paper width was 250 ram, and unwinding speed was 0.001 m/s. 2.3. Procedure

In order to make the subjects program a motor response, a perceptive task which could be performed on a computer screen was devised. The aim of the task was to intercept a moving spot on a parabolic trajectory when it reached a fixed target at the end of the parabola, on the right side of the screen. On feeling ready, the subject began each trial by pressing the spacebar of the keyboard, in order to start the spot, as shown by Fig. 1. Response was obtained in the same way, when the subject believed the spot had reached the target. Results in milliseconds were displayed on the screen after each trial. These were negative if the response was too fast, and positive if too slow. The software was devised in a way permitting the spot to move within a series of 4 high speeds V1, (between 0.17 and 0.33 m/s), or 4 low speeds, V2 (between 0.09 and 0.12 m/s). The speed was chosen at random for each trial in order to prevent familiarization and learning. Parts of parabola are drawn on Fig. 1, in order to show the 3 different spot trajectories. There is actually no remanence, and only the spot is visible on the screen during the experiment. The spot trajectory could be fully visible (3/3), or partly hidden. Thus, the subject only saw the first third part of the trajectory (1/3), or its first two thirds (2/3). In such cases, the subject had to construct mentally the

SCREEN COMPUTER HIGH LOW

SPEED V1 SPEED V2

2.2,6. Instantaneous respiratory frequency

This was recorded from a thermistor (Betatherm 10 K3 M C D2 3 mm length and 0.5 mm diameter), placed at the entrance of the left nostril with hypoallergenic adhesive tape. This thermistor is self heated (several degrees above ambient temperature) by its measuring current (0.5 mA). The exhaled air cools the thermistor at each respiratory cycle. The same signal processing as that of heart rate was used for recording the instantaneous respiratory frequency. Here again, variability is well evidenced and conversely to Instantaneous heart rate response, respiratory frequency variation was increased by different kinds of stimuli.

[

SPACE

BAR

J

Spot start and response

Fig. I. The six experimental modalities: 3 modalities describing the spot moving along parts of a parabola. 1/3, 2/3, 3/3, at 2 speeds, V1, V2: VI-~ 3, V1-2~, V1-33, V2-L~. V2-2~, and, V2-~~. The spot following the parabola randomly describes one of the 3 parts of the curve. The subject is asked to press the space-bar when he thinks the spot has reached its goal.

74

C. Collet er al. / Behavioural Brain Research 63 19941 7 1 - 7 9

hidden part of the parabola in order to respond at the right moment. Thus, combination of speeds and visible parts of parabola resulted in several alternatives which could be set out in 6 modalities. Finally, six crossed modalities were defined: Vl-~/3, V12/3, V1-3,3, V2-1,3, V2-2/3, V2-s/3. The experiment implied coincidence-anticipation, in order to obtain efficient results. It thus required the subject to prepare to respond by processing actual visual information.

2.4. Data analysis As two different kinds of results were to be obtained: subjects' performances, on the one hand, and physiological responses for each subject, on the other hand, two different statistical tests were used. With regard to the subjects' performances, classical statistics, such as a two-way variance analysis (speed and spatial modality) were made. The present design is a repeated measurement design. The number of performance values is up to 30, and distribution is thought to be gaussian. This kind of variance analysis as well as the Bonferroni corrected P-value calculation are thus justified. It is now well known that ANS characterizes an individual's response profile: the study by Lacey et al. [ 15] was confirmed by Vernet-Maury et al, [27] and later by Deschaumes-Molinaro et al. [8]. This has led us to adopt a particular approach for statistical treatment of results: only non-parametric computation is carried out in order to take into account the size of the experimental population, and to respect individual differences (non gaussian distribution). Thus, only the Kruskal-Waltis H and Mann-Whitney U tests are used.

Table 1 S u b j e c t s ' r e s p o n s e s to t h e six e x p e r i m e n t a l m o d a t i t i e s (in m s J

Subjects

V' I -

V 1-~ ~

V1

V'2-

V2-.

\;2-,

$2

202

179

-t6

339

165

4t

$3 $4

206 261

229 160

4(~ t,~

449 637

2(~(~ 119

~htj

$5

- =75

124

4.

449

Jl_

he)

$6 $7

~(i 110

73 96

~1 87

t66 ~,90

~" 110

'," s~l

$8 S')

1411 "~

134 119

~t ~-

- 483 q27

2(/2 9(,

24 -'-'

45a

S10

I(15

59

t,(,

128

a7

SII

2(/2

55

92

325

t23

t~

S, l_~

122

134

~

214

25i

Mean

161

S.D

(71,

,

" -

124

"2

- a|b

i<.l

44

(53J

(221

(115}

(70)

(16)

V a l u e s w e r e p o s m v e or n e g a t i v e w h e n the s u b j e c t r e s p o n d e d alter o r b e f o r e a r r i v a l o f t h e spot. R e s p o n s e s ma~ also c o i n c i d e with the spot. W h e n t h e c u r v e is r e d u c e d to its lirst t m r d . only n e g a u v e v a l u e s m~o highly a n t i c i p a t e d r e s p o n s e s l w e r e obser~.ed. M o r e a c c u r a t e results w e r e o b t a i n e d w h e n the s p o t I r a j e c t o r 5 w a s c o m p l e t e , w h a t e v e r the s p e e d (VI-= 3 a n d V2-~ ,).

ms 200 •

lOOt

- 100

°I

-200

-300 "'400 -500

V1 1 / 3

Vl 2/3

Vl 3/3

V2 1 / 3

V2 2/3

V2 313

Task modafities Fig. 2. M e a n results o f the e x p e r i m e n t a l p o p u l a t i o n to the 0 m o d a t i l i e s (in m s k See c o m m e n t s in T a b l e 1

3. Results

3.1. Perfi)rmance values Results in milliseconds evidenced that only 1/3 modality provided negative results which means that excessively anticipated responses were not coincident for the 2 speeds [subject's responses occurred too early). Each subject's results are summarized in Table 1. Mean values and standard deviation of the experimental population are shown by Fig. 2. A two-way analysis of variance showed that the difference within the group means was extremely significant (F= 119.3, P < 0.0001 for the experimental population). For V l, median values (standard deviation) were respectively -161 ms (71 ms), 124 ms (53 ms) and 52 ms (22 ms) for 1/3, 2/3 and 3/3 of parabolas. For V2, median values

(standard deviation)were respectively -418 ms (115 ms). 154 ins (70 ms) and 44 ms (16 ms) for 1:3. 2 3 and 3/3 of parabolas. Speed and spatial modatity effects had thus to be analyzed separately, in relation to performance.

3. I.I. Speed effect For the low spatial modality only (1/3), highly significant differences were obvious after the Bonferroni corrected P-value calculation: mean difference= 260, P < 0.001. Subjects were all more accurate in high speed than in low speed, mean values (standard deviation) being respectively 161 ins (71 ms) and -418 ms (115 ms). There is no significant difference between the two speeds V1 and V2 for 2/3 and 3 3 modalities. For 2/3. the mean difference. -30.6. P>0.05. was non-significant. Mean

75

C. Collet et al. / Behavioural Brain Research 63 (19941 71-79

values (standard deviation) were respectively 124 ms

3.2. A u t o n o m i c variables

(53 ms) and 154 ms (70 ms). For 3/3, the mean difference is 7.7, P > 0 . 0 5 , n o n significant. M e a n values (standard

3.2.1. Tonic values

deviation) were respectively 52 ms (22 ms) and 44 ms

As subjects could prepare themselves before the start of each trial, but did not know what kind of stimulus would

(16 ms).

occur, tonic values could not be considered as taskspecific. Conversely, autonomic tonic variables are well

3.1.2. Spatial modality e{/ect

Subjects anticipated their responses when stimulus duration was low, for both speed categories. They were all

k n o w n for their indication of activation versus relaxation. The most reliable index to be used is skin resistance.

more accurate when the spatial modality was longer. The

Skin resistance tonic level was recorded throughout the

difference was statistically significant between 1/3, and 2/3, and between 1/3 and 3/3, when using the Bonferroni

test and values of the first part of the experiment were compared to those of the second part for each subject.

corrected P-value. For the high speed, (V1) the mean dif-

Skin resistance level did not differ in the two parts of

ference between 1/3 and 2/3 was - 2 8 5 , P < 0 . 0 0 1 (mean

the experiment for subjects 2, 4, 5 and 8: group 1 ( M a n n -

161 ms and 124 ms); the mean

Whitney non-parametric U-test: P > 0.05 for all these sub-

difference between 1/3 and 3/3 is - 2 1 3 , P < 0 . 0 0 1 , (mean

jects). A significant decrease in skin resistance was neverthe-

values being respectively

values being respectively -161 ms and 52 ms). The difference between 2/3 and 3/3 was not significant: the mean difference was 72, P > 0.(15, (mean values being respectively 124 ms and 52 ms). In the same way, comparisons were made for the low speed (V2): the mean difference between 1/3 and 2/3 was -575, P < 0.00 l, (mean values being respectively - 4 1 8 ms and 154 ms); the mean difference between 1/3 and 3/3 was 465, P < (1.001, (mean values being respectively - 4 1 8 ms and 44 ms). The difference between 2/3 and 3/3 was not significant but near a significant threshold: the mean difference was 110, P > 0.05, (mean values being respectively

less observed in 5 subjects (3, 6, 9, 10 and 12: second group) and an equally significant increase for 2 subjects (7 and 11: third group). P < 0 . 0 0 0 1 for all subjects. Subjects who maintained their skin resistance at a constant level (group 1) showed no significant differences in performance. Conversely, subjects from the second and third groups improved or worsened their performance (except subject 11 who showed an increase in skin resistance tonic level without any significant modification of his performances in both parts of the experiment). Thus, skin resistance evolution throughout the test is mainly correlated to performance. Table 2 summarizes these results.

154 ms and 44 ms).

Table 2 Relationships between skin resistance tonic level and task performances Skin resistance (S.D.) Ist part

2nd part

$2 $3 $4 $5 S(~

63.1 (1.8) 88.8 (4.2) 168.8 (11.2) 130.9 (5.5) 61.5 (5.5)

60.6 (2.2) 79.6 (1.51 171.2 (8.9) 128.6 (9.2) 53.5 (2.11

$7

167.3 (29)

$8 St) SII) Sll S12

Statistical significance

Performances (S.D.)

Statistical significance

Explanation

Activation at a constant level From activation to stress Activation at a constant level Activation at a constant level From relaxation to optimal level of activation From stress to optimal level of activation Activation at a constant level From activation to stress From relaxation to optimal level of activation ? From activation to stress

1st part

2nd part

N.S. **** N.S. N.S. ****

- 220 (220) - 165 (270) 715 (1441 - 275 (207) -495 (183)

275 (1871 - 77(I (330) -495 (209) 495 (237) 193 (1341

N.S. * N.S. N.S. **

240.6 (45.7)

****

55(1 (1861

-220 (1441

**

171.1 (16.2 1~17.2 (4.3) 81.7 (3.3)

168.2 (21.9) 98.9 (4.7) 68.8 (4.6)

N.S. **** ****

495 (237) -300 (155) -495 (1531

275 (172) -495 (1551 165 (335)

N.S. ** **

318 (59) 72.6 (2)

436 (62) 65.9 (3.8~

**** ****

-275 (260) 55 (224)

357 (1721 - 110 (2161

N.S. ***

The activation level evolution is thought to be related to performance (Duffy [11]): (a) an optimal level of activation implies the best performances; (b) an excessivelyhigh level of activation impliesweaker performancc as well as an excessivelylow level of activation. Results obtained during the first (trials I to 45) and thc second part (trials 46 to 90) of the experiment are compared. From left to right: skin resistance tonic level and P-values: task performance (ms) and P-values. Relationships between skin resistance values and performance (lst and 3rd colunm). **** P<0.001II;*** P-(I.01:** P 0.(12:*P=0.05.

76

('. ('oiler et al. ' Behavioural Brain Re,~earch 63 (1994~' 7 1 - 7 9

3.2.2. Phasic' values

Only phasic responses may be task related. The issue here is to analyse the autonomic phasic responses in relation to each task modality. A decrease in skin resistance was systematically observed. Independently of spontaneous activity, other variables showed different fluctuations (increase or decrease), before recovering their initial level. Fig. 3 shows an example of a recording of autonomic responses while the subject performs the task. According to autonomic response quantification methods described previously and to the six task modalities, autonomic responses were compared. The KruskallWallis H-test was calculated for each subject and each index. All variables were not capable of differentiating the six modalities. Only one or two variables were task-specific for a particular subject, thus responding via a specific autonomic variable. Skin resistance differentiated the 6 modalities in 5 subjects out of 11 (4, 5, 9, 10, 12). Instantaneous respiratory frequency was the preferential variable for 3 subjects (8, 9, 11). The 2 indices of this

STIMULUS 30s. 1

200 SKIN RESISTANCE

180 Kg

160 140 i

0.9 W , m 1.°C4

0.7 SKIN BLOOD FLOW

0.5 34.2 °C

13

i

~

55 b.p.m.

autononuc variable (amplitude and duration) distinguished the task modalities. Skin blood flow differentiated the 6 modalities of the task for 2 subjects (6 and 7). Amplitude and duration of instantaneous heart rate differentiated the 6 task modalities in subject 2, The form of skin potential responses distinguished the task modalities in subject 12. Skin temperature responses were not correlated to the task modalities for this experimental population. Table 3 shows that the 11 subjects showed at least one index distinguishing the six modalities of the task. Thus. preferential autonomic variables are correlated to the task modalities.

SKIN TEMPERATURE

34.0 mV

Each subject responded through one n~r 2t autonomic channelt s). In thl> experimental population, skin resistance index u a s the more reliable. whereas Skin Temperature was not apec~lic lno subjecl responded through this channell.

3.3. Per/brmances and autonomtc responses relationshq)s

I

34.1 15 14

"Fable 3 Specific A N S variables distinguished among the 6 modalines

'

~

~

INSTANTANEOUS HEART RATE

45 20 %,

18J-

~

SKIN POTENTIAL

';

~-I-L~L~

r

.NSTANTANEOUS P'RATOYPREOUENC¥

Fig. 3. Subject 8: A N S responses recorded during a successful trial: 0 = coincidental response. Skin resistance, skin blood flow, and skin temperature values decreased: skin potential increased; instantaneous heart rate increased and instantaneous respiratory frequency decreased

Taking mto account the variable which differentiates the 6 task modalities for each subject, autonomic responses were correlated with the best perlbrmances (no difference between spot arrival and subject's responsel on the one hand. and the least good performances on the other hand (more than -330 msl. Statistical analysis using the M a n n - W h i m e ) /_.,'-test showed that Autonomic resptmses were different according to subjects" performances, except for subject 3. None of this subject's autonomic indices were capable of separating accurate performances from inaccurate ones. Performances and autonomic responses relationships could be summarized as follow.-.: the O P D index was significantly longer in inaccurate -

C. Collet et al.

Behavim~ral Brain Research 63 (1994) 71-79

performances for 3 subjects among those whose preferential variable was skin resistance. Subject 4, P < 0.04, median values being respectively 8 s for inaccurate performances and 4 s for accurate ones; subject 9, P < 0.03, median values being respectively 9 s for inaccurate performances and 4 s for accurate ones; subject 12, P < 0 . 0 1 , median values being respectively 8 s for inaccurate performances and 4 s for accurate ones. - Skin blood flow responses were always negative. Differences in amplitude occurred between both inaccurate and accurate performances. Subject 6, P<0.05, median values being respectively -0.08 W . m - ~. ° C - ~ and -0.30 W-m I.~C ~); subject 7, P<0.01, median values being respectively -0.08 W . m - ~ . ° C i and -0.32 W.m i °C ~, thus higher in accurate performances. - Respiratory indices: response durations were correlated to performances for subjects 8, 9 and 11. They were longer in accurate responses than in inaccurate ones. Subject 8, P < 0.01, median values were respectively 12 and 18. Subject 9, P < 0 . 0 2 , median values were respectively 14 and 21. Subject 11 , P < 0 . 0 1 , median values were respectively 11 and 22. - No correlation was found between performance and Autonomic preferential variable for subject 3. In conclusion, this study evidenced that each subject "responded" through a specific autonomic variable. Considering each preferential variable, performance was shown to be related to Autonomic response, except for one subject.

4.

Discussion

Performance values will first be considered, then the relationship between performance and autonomic response will be discussed. During task performance, the period between spot disappearance and its arrival on target was, as defined above, between 934 and 1759 ms for high speed integration, and between 2472 and 3297 ms for low speed integration. In a reaction time {RT) paradigm (a few seconds or more), Quesada and Schmidt [21] obtained better results with a short foreperiod than with a longer one. The average RT with a constant 2-s foreperiod, was only 22 ms. Conversely, the same authors reported that Mowrer (1940) found RTs of about 230 ms for a very long foreperiod duration. When the foreperiods are long, an early response is prevented because the subject cannot anticipate the exact occurrence time. Thus, the accuracy of the response in an anticipation task depends on task characteristics. Present results confirm this finding, especially for the first third reduced parabola. In this case, foreperiod duration is longer for low speed than for high speed. Differences are

77

not statistically evidenced for the 2/3 and 3/3 modalities. For the latter two modalities, duration responsible for speed integration is longer; the foreperiod effect is thus weaker. Furthermore, retention of speed information in "working memory", lasts longer with low speed. This may explain differences in performance between V1 and V2. Sperling [26] showed that the quality of information retention in working memory is less than 50'~o, for a duration higher than 500 ms. This event is especially true when the curve is reduced to its first third. In this case, subjects see the moving spot for 311 ms in order to integrate the information of high speed. They must therefore retain information for 623 ms. For low speed, the integration duration is longer: 824 ms; thus, conservation duration is longer: 1648 ms. It may be concluded that duration allowed for speed integration is sufficient for both high and low speeds. Conversely, duration required to hold information is too long to produce an effective response, especially for low speed. This may explain not only differences in performances obtained with V1 and V2 speeds, when the parabola is reduced to its first third, but also differences evidenced in response to the spatial modality. Therefore, when spatial modality effect is analyzed, there is a strong relationship between it and response accuracy: the longer the stimulus presentation, the more accurate the response. Performance is significantly different among the three spatial modalities. This difference is nevertheless lower between 2/3 and 3/3, rather than 1/3 and 2/3 or between 1/3 and 3/3. It may therefore be supposed that two-thirds of the parabola are necessary but adequate to integrate speed information effectively. The last third here provides redundant information. In conclusion, results enable one to distinguish the six task modalities; the study of ANS responses was thus justified for the same six modalities. Performance can moreover be thus expressed by physiological measurements. As far as the relationship between autonomic variables and performances is concerned, tonic values--measured just before the start of each trial--characterize subject activation level. Electrodermal activity is well correlated to the evolution of vigilance: an increase in resistance associated with a decrease in potential tonic values is related to subjects' relaxation level. Conversely, a decrease in skin resistance and an increase in skin potential would characterize an activation phase. Skin blood flow and skin temperature are also concerned by an arousal mechanism. Skin temperature and skin blood flow increases are correlated to activation while decreases are related to relaxation. It is well known that skin resistance is the most reliable index of activation level. Finally, the tonic levels of ANS

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Behavioural Bra#7 Research 63 1994

variables, especially skin resistance, express the arousal evolution through the activation/relaxation axis. Just before the start of each trial, the subject was unaware of its modality, so that tonic values could not reflect the programmed response of the subject's central nervous system. In previous studies on mental workload, tonic values distinguished two strategies: correct response or rapid response [29]. Moreover, tonic values during the concentration phase in olympic shooting were highly correlated with performance [7]. Such an observation can be explained by the fact that in this previous experiment, subjects were aware of what would occur and what they had to do. In the present study, subjects had to perform each trial as accurately as possible without knowing the modalities in advance. Thus, the variation of tonic values must only be analysed here in terms of activation/relaxation. The evolution of skin resistance tonic level was considered in 3 different groups. In terms of activation vs. relaxation, subjects who maintained their activation at a constant level, showed stable performances during both parts of the experiment (group 1). In the second group, subjects with a decreased tonic level (meaning increased activation) showed better performance. In this group, 2 subjects out of 5 began the test at a low level of activation (near relaxation), and increased, this level, progressively up to optimal activation. The other three subjects of the second group whose results weakened in the second part of the test showed an increased activation level, close to stress at the end of the test. This fact is especially observed in subject 3. This subject showed low skin resistance values associated with high potential values: these two electrodermal indices emphasize the presence of stress. This may' also explain that subject 3 was unable to distinguish the task modalities and consequently performed badly. In the third group, two subjects showed a decreased activation level. One of them improved his results, which means he was stressed in the first part of the test and then reached an optimal level of activation in the second part, in accordance with the U curve of the general YerkesDodson law [32]. The other subject in the group, with increased skin resistance values (almost relaxed) maintained his performances. It may be supposed, despite the relaxation, that the skin resistance level during the final part of the test was still sufficient to keep performances at the level of the first part of the experiment. In conclusion, the study of tonic level evolution evidenced a strong relationship between the evolution of skin resistance tonic level and performance. As far as phasic values of autonomic variables are concerned, it was shown that the "preferential" variable (subject specific) distinguished the six modalities of the task as

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a whole. These results are m compliance with kacey's hypothesis on ANS response specificity [15]. ANS responses are related to central information processing sincc they are correlated to performance values. Thus. thex reflect a part of CNS activity in real time, through a specific autonomic channel, characterizing each subject. Thus, gacey's hypothesis, already verified in the laboratory [27,8] is again confirmed m a new and original paradigm. O P D (ohmic perturbation duration l is particularl~ effective since it distinguished among the six modalities. for 5 subjects out of 11. These results confirm thc rclevance of the chosen autonomic variables, and also the efficiency of the methodolog). Relationships between AN S index values and pert\~rmance are evidenced: ANS responses related to accurate and inaccurate performances differ. For most subjects. lengthy OPD was observed for inaccurate results. Converserlv, a shorter O P D was correlated to the most accuratc results. It is clear that task duration was longer for low speed than lbr high speed. A clear relationship was established between (i) inaccurate results and low speed and (u) between accurate results and high speed, especially when the curve is reduced to its firsl third, so that in this experimem, il can be concluded that the O P D was taskrelated: the longer the task. the tonger the skin resistance response. It has already been shown that the O P D was long for correc~ performances aad short in bad performances, in a task for which the duration was always the same despite the subject's performance [7.2(t] Thus. it seems that autonomic variables are related to thc task ~md its modalities rather than to per[brmance itself With reference to recent findings, autonomm responses were shown to be correlated to performances Igood or bad. accurate or inaccurate, correct or incorrect .. L when subjects performed a repetitive task. Potential responses in terms of form analysis have already been correlated to skill perlimnance [7]: negative C-responses were in relation to the more accurate performances in shooting. This result cannot be confirmed in the present experiment, as only onc subjecl responded throughout the "'preferred" potential variable. Yet. potential responses analysis led to the same conclusion as those of skin resistance. A-forms were observed in accurate performances whereas C-forms were recorded in inaccurate ones: an A-form never exceeds 5 s: the response is short. Conversely, a C-form presents a long response duration. Resistance is related to the task durauon so that the longer the task. the longer the OPD. As inaccurme responses were obtained for low speed, i. u. a long task duration, long OPDs were obtained more often in inaccurate performances. A relationship could here be established betwecn long O P D and C-potential form. and between short O P D and A-potential form.

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The amplitude of skin blood flow responses was correlated to performance: high amplitude is related to inaccurate performances whereas a weak amplitude characterizes accurate ones. This was already observed in drivers: strong negative responses coincide with bad maneuvers (Collet et al., submitted). Instantaneous respiratory frequency is clearly shown to distinguish accurate from inaccurate responses. Perturbation duration is related to performance (except for subject 3). The better the performance, the longer the perturbation duration. These results confirm recent analysis of autonomic responses in mental imagery: in this experiment, they were correlated to subject performance [6,7]. Thus, autonomic responses could be considered to reflect a behavioral output. Their variations can be considered an inferential model in the study of the C N S [4].

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