Tracking irregular acoustic patterns by finger tapping

International Elsevier

Journal of Psychophysiology,

6 (1988) 327-330,

327

PSP 00217

Tracking irregular acoustic patterns by finger tapping Marek FranEk 2, Tom% Radil Institutes

of ’ Physiology and 2 Theory and History

acoustical

Indra ’

of Art, Czechoslovak Academy of Sciences, Prague (Czechoslovakia)

(Accepted

Key words: Tracking

* and Miroslav

rhythm;

17 May 1988)

Finger

tapping;

Time interval

generation

Acoustical sequences were divided by time intervals of various durations, and the performance of finger tappings following the stimuli were recorded. The results proved that it is difficult to synchronize finger tapping with irregular acoustical patterns. The subjects tended to transform the irregular stimulus patterns into more regular response patterns shifted toward interval proportions close to 1 : 1 or 2 : 1

INTRODUCTION In our previous paper (FranEk et al., 1987) regular rhythmic acoustical sequences were generated, and the time instant of finger tapping was compared with the onset of these acoustical stimuli. The rhythmic elements that the stimulation sequences consisted of, were of equal duration and they were repeated regularly so that it was easy to follow them. The problem adhered to in the present paper is the extent to which subjects can follow irregular acoustical sequences by finger tapping. It has been previously found (Fraisse, 1946, 1947, 1956; Summers, 1975; Povel, 1981) that it is difficult to generate irregular rhythms. These previous studies, however, made use of the method of rhythm production or reproduction, where no stimuli are given during tapping proper. In the present experiments, in contrast, the subjects were constantly listening to the rhythms they had to follow as well as to the acoustical feedback signals of their own tapping. Thus systematic devi-

Correspondence: M. Fra&k, Institute of Theory and History of Art, Department of Musicology, Na PerStyn6 1, 110 00 Praha 1, Czechoslovakia. 0167-8760/88/$03.50

0 1988 Elsevier Science

Publishers

ations from the external rhythms could point to features of timing mechanisms involved in the brain.

METHODS Twenty-three subjects, 15 males and 8 females (aged 18-30 years) participated in the experiThey came from a group of musical ments. amateurs, having played any musical instrument from 6 to 8 years of age, used in our previous experiments (Franek et al., 1987) and well acquitted of similar tasks. Four stimulation sequences each consisting of 3 element (ii, i,, i3) patterns (Fig. 1) were used. Stimulus patterns consisted of intervals of different lengths (values in ms): 470-330-330; 470-330-380; 380-420-520 and 470-470-470 (the control sequence). In the 3 experimental sequences the approximate interval relationships within the patterns were: 1 :0.7:0.7; 1 :0.7:0.8 and 1 : 1.1 : 1.4. The pattern always started by a 300-ms tone (ti) and was followed by two 50-ms tones (t 2, t3) of equal frequency (400 Hz), timbre and intensity. The stimulation pattern was repeated many times in a regular way forming the

B.V. (Biomedical

Division)

328 TABLE

I

Grand means for stnndurd deviations of Inter-tapping ms) for the whole group of subjects

I

Significances 1.

intervals (in

at 5% level are given. For details see text and Fig.

I : 0.7: 0.8

2

Stimulatron

sequence

S.D. of inter-tapping

interval for

(stimuluspattern elements)

I : 1.1: 1.4

3

i

*

I

i

*

810

410 I

’

’

470 I

I

I:1

COnllOl i

:

I

i

of acoustical stimulation seFig. 1. Schematic representation quences used in the experiments (hatched field, tone; open field, silence). Vertical fines delineate the stimulus patterns (always two consecutive patterns are shown); dots, their elements (which are of unequal duration); t, represents the longer, t 2 the shorter tone. For details see text.

stimulus sequence continued for 2.5 min. A PDP 11/40 computer was used for generating the stimulus sequences, which were recorded on one channel of a tape recorder. Subjects were asked to listen to the auditory stimulus through headphones and to synchronize with the rhythm by finger tapping (with the index finger of the right hand) on a metal plate. The pulses derived from the plate were transformed by means of a sinewave generator into tones of the same frequency of 400 Hz but of different timbre (and of duration corresponding to the contact with the plate), which were presented through the headphone as well. Thus the subjects heard the stimulation tones and had an acoustical feedback of their performance as well. Response rhythms were recorded on the second channel of the tape recorder (Tesla B 113). The data were processed by means of a SM 4/20 computer using a special program (Indra et al., 1985) measuring temporal relationships between onsets of tones in both channels and performing the statistics. The subjects were sitting in a quiet room, with the response plate in front of them. After a short training session first the control sequence and then the 3 stimulation sequences were presented, in random order. The subjects were required to

i,-i,-i,

470-330-330 470-330-380 380-420-520 470-470-470

il

i2

i-3

;!l]

Z;)

;;l]]

listen to a rhythm and to start tapping as soon as possible according to the stimuli. After each sequence the subjects had to characterize the temporal relationship among the elements i 1 : i, : i, of the stimulus pattern by musical notation.

RESULTS The average duration and standard deviation of intertapping intervals (ITI) corresponding to the stimulus elements i,, i 2, i, were computed for each subject and from them grand means of average values and of standard deviations have been expressed. IT1 variability (Table I) was higher for irregular stimulus sequences in comparison with the regular one. Average values of IT1 did differ from stimulus values (Table II). Correct following of the

TABLE

II

Grand means for average values of inter-tapping for the whole group of subjects Stimulation sequence (stimulus pattern elements)

intervals (in ms)

Average inter-tapping interval for

il-t2-i3

ii

iz

ij

470-330-330 470-330-380 380-420-520 470-470-470

437 437 430 478

364 379 412 471

334 367 486 466

329

irregular stimulus patterns used was only exceptionally found. The difference between stimulation and tapping rhythms was more expressed for the irregular sequences. We did confirm, however, our previous finding that IT1 intervals are different from inter-stimulus intervals for regular stimulation patterns as well, although to a lesser degree. Although in our previous study (FranZk et al.,

TABLE

III

Incidence of correct and incorrect musical notations element duration within pattern For details Pattern i,-iz-i,

see text. Correct

Incorrect

1 0 0

12 11 12

Considered regular

No res Considered Irregular in a wrong

ponse

way

Is’ PATTERN SllMtJlAllON

470-330-330 470-330-380 380-420-520

PIITERN

RESPONSE

I 094

asslmllatlnn 0.63 n=l4

d&on

I 062:O.r5 n-3 correct

I 07207

n=7

ZadPRTIERN STtYtJlRTlON

PRTTERN

RESPONSE

ail II084

awmhtlon 097092 I 083

n-9 n=4

correct OJl8

1 072

n=3

3rd PATTERN STtMUlAltON

I

RESPONSE

I

of stimulus

‘11

14

asvmllatlon 102 102 n.12

PATTERN

I360

420

5201

dIStInCtIOn

1

I correct I16 I39

a11 bll

0.96 072

I6 069

n.6 n.3

n-l

Figs. 2-4. Incidence of IT1 durations; close to interstimulus intervals within the stimulus pattern (vertical line); approaching proportion 1: 1 (‘assimilation’); and 2 : 1 (‘distinction’). Fig. 2 for stimulus pattern 470-330-330 ms, Fig. 3 for 470-330-380 ms, Fig. 4 for 380-420-520 ms. For details see text.

8 8 4

2 4 7

1987) we found prevailing anticipation of the onset of stimuli, in synchronization with non-regular patterns the anticipation appeared only exceptionally. Our subjects were divided into 3 groups according to the relative proportion of IT1 durations corresponding to the stimulus elements ii, i,, i, within the patterns (Figs. 2-4). The first group was characterized by more-or-less correct following, the second one by a tendency toward equalization of ITIs within the pattern of the type 1 : 1: 1 (called according to Fraisse, 1956 ‘assimilation’), the third group by a tendency toward doubling or halving the intervals, i.e. by proportions 2 : 1 or 1 : 2 among them (called ‘distinction’). The number of cases with correct following decreased with increasing complexity of the stimulation pattern, ‘assimilation’ being more usual in general, and ‘distinction’ occurring more often for the most complex pattern (1 : 1.1 : 1.4) than for the two simpler ones (1 : 0.7 : 0.8 and 1 : 0.7 : 0.7). The differences in the incidence of the described groups were not significant, however, due to the number of subjects available and a few intermediate cases observed as well. No intra-individual stability could be found with respect to the 3 basic types of interval proportions. Thus the basic finding was that the subjects did transform the irregular stimulus patterns into a more regular response pattern, which was closer to interval proportions 1:l or2:l. The results of judgements on stimulus timing represented by musical notations recorded by the subjects (Table III) did demonstrate that the sub-

330

jects were unable to evaluate the rhythm. Two types of wrong answers could be differentiated: those characterized by considering stimulation patterns regular (like 2/4 or 3/4 bars) or irregular but in a wrong way. In many cases the subjects could not express the stimulus timing by musical notation at all. Differences in the level of theoretical preparation in music among subjects and inherent ambiguity in notation have to be taken into consideration, however.

DISCUSSION The results mentioned prove that it is very difficult to follow irregular acoustical patterns, although repeated regularly, by finger tapping. That was true irrespective of the fact that the subjects were constantly listening to the stimulus sequence with which they had to synchronize their tapping. The rhythms presented have been transformed into different, i.e. more regular ones. Our results do confirm those of Fraisse (1946-1947) showing that it is a hard task to generate irregular tapping sequences spontaneously (i.e. without any stimuli), as well as a tendency toward equalizing consecutive ITIs and also those demonstrating (1946) that when asked to form IT1 sequences consisting of 2-6 different intervals the subjects did reduce the task to alternating just one long and one short interval of the relative duration of approximately 2 : 1. When stimulus sequences consisting of long and short intervals of different duration had to be reproduced (Fraisse, 1956) the subjects tended to generate just two periods: a long and short one. On the basis of similar findings two principles of rhythm construction have been formulated: ‘assimilation’ -a tendency toward equalizing the duration of two close intervals; and ‘distinction’-a tendency toward doubling or halving the intervals and approaching proportions 2 : 1. The preference of certain rhythmic structures is typical for Western art music (Fraisse, 1956) the relationship of tonal lengths being close to the proportion 2 : 1 in 86% of typical muscial samples analyzed. The above results have been confirmed by Summers (1975)

who asked the subjects to reproduce rhythmic patterns of the proportion 5 : 1 : 1; they tended to generate intervals of the proportion 2 : 1 : 1. Patterns 5 : 5 : 1 could not be reproduced at all. In other experiments (Povel, 1981) the task of the subjects was to reproduce sequences made of rhythmic patterns consisting of two or 3 intervals (like 1 : 2, 1 : 3, 2 : 3, 2 : 5, etc.). They adopted the rhythm, however, to proportions close to 1 : 2. It follows from the experiments mentioned that humans do prefere certain rhythms. Our experiments, in which the subjects could constantly compare the stimulus sequence (always present) with the feedback provided by their own performance, prove that besides rhythm preference humans are incapable of generating sequences of time intervals of certain proportions, i.e. their timing ability is rather limited, probably due to the inefficiency of the underlying neuronal programs. In contradistinction to the above experiments limitations of memory mechanisms could not influence the results gained, in our case. Repeated tests in the same subjects demonstrated that equal stimulus rhythms could be adopted in different ways. It was also clear that various subjects do change the same rhythm differently. The tendency to ‘assimilate’ and to ‘make distinct’ the rhythms in the described way was, however, typical.

REFERENCES Fraisse, P. (1946) Contribution & l’etude du rythme en tant que forme temporelle. J. de Psychol. Norm. Pathol., 39: 283-304. Fraisse, P. (1946-47) Mouvements rythmiques et arythmiques. Ann. Psycho/., 47-48: 11-21. Fraisse, P. (1956) Les Structures Rythmrques. Edition Universitaires, Louvain. Frantk, M., Radil, T., Indra, M., LBnsk$, P. (1987) Following complex rhythmic acoustical patterns by tapping. Int. J. Psychophysiol., 5: 187-192. Indra, M., FranEk, M., Radil, T. (1985) Measuring the ability of reproducing given rhythms. Actia. New., supl., 27: 124-125. Povel, D.J. (1981) Internal representation of simple temporal patterns. J. Exp. Psychol.: Human Percept. Perform., 7: 3-18. Summer, J.J. (1975) The role of timing in motor program representation. J. Mot. Behau., 7: 229-241.