Perceptual and Motor

Skills,1998,86,1395-1401. O Perceptual and Motor Skills 1998

INTERACTIONS: TIMING AND FORCE CONTROL OF FINGER-TAPPING SEQUENCES' NOBUYUKI INUI

TAKUYA ICHIHARA

Department of Humaru Motor Control Naruto Uruiuersity of Education

Graduate School of Education Naruto Uruiuersity of Education

IAKAHISA MINAMI AND ATSUNORI MATSUI Department of Human Motor Control Naruto Uniuersity of Education

Summary.-This study examined effects of combinations of intertap interval and in sequences of equally paced finger taps. 12 male college students tapped a force plate connected to strain gauges. Subjects firstly tapped the plate at a preferred pace and force for 12 sec. Next, subjects tapped the plate by half or double the preferred pace. A series of finger-tapping tasks then consisted of nine combinations of pace and force. Analysis showed that, although variations in intertap interval were considerably accurately controlled across conditions, those in peak forces were not. Movement timing of tapping sequences hence appeared to be independent of force conrol. For six of 12 subjects, on the other hand, positive correlations between spontaneous variations in intertap interval and in forces were noted. Then, although motor timing was independent of force control in conditions of low pace and weak force, there were strong interactions between muscle force on interactions between two factors

the tu.o factors under high pace conditions.

Movement timing and control of muscle force are two main factors in motor coordination that differentiate people across a variety of movements. Little research has been reported on motor timing and its relation to control of force; however, these factors have been studied separately in the field of human motor control (Billon, Semjen, & Stelmach, 1996; Keele, Ivry, & Pokorny, l9B7; Semjen & Garcia-Colera, 1986). Motor timing and production of force clearly interacted when analyzed as single movements such as single arm flexions or extensions (Gottlieb, Corcos, & Agarwal, 1992). The relationship between timing and control of force may have different characteristics when one considers complex serial actions

or

drumming. For example, Sloboda (19$) showed that pianists could independently vary keystroke times and forces. In earlier work, Fraisse and Oleron (1954) also reported that in periodic tapping changes in the force of tapping had no effect on the intertap intervals. such as playing the piano

Keele, Pokorny, Corcos, and Ivry (1985) asked people tAddress

to make regular

enquiries to N. Inui, M.D., Department of Human Motor Control, Faculty of Health

and Living Sciences. Naruto University of Education, Takashima, Naruto-cho, Naruto-shi,7728502, Japan or e-mail ([email protected]).

t396

N. INUI, ET AL.

tapping responses with the finger or foot. Over subjects, the variance of intertap intervals correlated significantly betu,een the finger and foot. In addition, control of force achieved with the finger was correlated with that achieved with the forearm or foot (Keele, et al., 1987). They found, however, that accuracy of controlling force was not correlated with accuracy of motor timing. Some authors also reported, on the other hand, that there were some interactions between timing and control of force during a task of periodic tapping (Billon, et al,. 1996; Keeie, et al., 1987; Semjen & Garcia-Colera, 1986). \X/hen subjects were required to press or tap at a moderate rate (intertap interval of 4OO or 600 msec.), stronger force pulses were preceded by a shortened interval and followed by u lengthened interval (Keele, et al., 1987; Semjen & Garcia-Colera, 1986). But an accent lengthened the preceding interval and delayed the next response when the subject was required to tap at a fast rate, the intertap interval being 180 msec. (Semjen, Garcia-Colera, & Requin, 1984). Thus, the interactions of motor timing and control of muscle force in tapping sequences at a slow rate are likely to differ from those at a fast rute so the present study examined effects of nine combinations of intertap intervai and force on interactions between the two factors in sequences of equally paced finger taps. Merrroo Apparatus

A force plate (3.zby 10 cm) tapped by subjects consisted of two metal rings (5 cm in diameter) connected to four strain gauges. Tapping responses were then recorded by a personal computer (Macintosh LCIII, Apple) through an amplifier (MCC-8A, KYO\7A) and an A/D converter (Mac Lab MKIII, AD Instruments Pty, Ltd). Measurements

Fig. 1 shows the definition and measurement of the dependent variables. The trace shows the same record after amplification and filtertng at a frequency cut-off of 10 Hz. The output of an amplitier was sampled and digitized at a frequency of 200 Hz by an A/D converter. Intertap interval, peak force, press duration, and time to peak force were automatically measured in each task. Intertap interval were measured by the onset-to-onset times of the tap. The force of each tap uras measured as the peak output voltage from the strain gauge. And, the ratio of time to peak force to duration of press was computed. Although subjects tapped a force plate for 12 sec. in each task , data for the initial 2 sec. were discarded from the calculations.

TIMING, FORCE CONTROL OF FINGER TAPPING

l.Hl lTime to r Peak Force t.(l-------------_

lPress Duration

t)97

l

lntertap lnterval Frc.

1.

The definition and measurement of the dependent variables

Procedure

Subjects were seated facing the force plate, and subjects' palms lay on the support (6 cm in height), Subjects made tapping movements by a slight extension-flexion pulse of the index finger about the metacarpophalangeal joint. Subjects firstly tapped a force plate with the index tinger at a preferred pace and force for 12 sec. Accurate timing of the taps with equal intertap intervals \r/as then encouraged. Next, subjects tapped the plate by half

or double the preferred rate without feedback about their tapping

re-

A series of finger-tapping tasks thus consisted of nine combinations of pace and force. The order of the combinations presented to subjects was sponses.

randomly varied. Sample

The sample consisted of 12 healthy male college students and graduate students. Their chronological ages ranged from 2l to 25 yearc, with a mean of 22.7 yr. Rnsurrs

Table 1 shows means and standard deviations of intertap intervals and force under nine conditions. First, to examine the differences among conditions for intertap interval a one-w^y rcpeated-measures analysis of variance was performed. There u/ere significant (p