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PERCEPTUAL-MOTOR SKILLS

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Project 67 - Timing and Control of Skilled Movement in Normality and Pathology

67.1 Handwriting (Nimmo-Smith, Wing)

Even though we initially acquire skills such as handwriting by direct guidance based on a standard "model", an individual, personal style usually emerges as skill develops. Such between-individual variation is, in the case of handwriting, the basis for forensic determination of authorship of documents. A study of children's acquisition of cursive writing [322] points to the influence of penhold as one source of developing individual differences in letter formation, probably because different grips constrain pen movements in different ways. A second study [323] identifies certain changes in children's writing with their need to write faster as they get older.

At present forensic document examination relies mainly on qualitative aspects of letter formation. But as computer-based automated comparisons become practicable, basic data on quantitative variation will be required. Some of the issues that will require attention are illustrated in an analysis of data collected under an earlier Home Office contract [314]. One significant finding is that higher-level, linguistic factors influence the variability of pen strokes that, in terms of their lower-level movement description, are ostensibly the same. Thus automated comparison of writing samples will need to take account of text content. Other recent research on handwriting at the Unit has focussed on higher-level processes relating to the representation and selection of letterforms. A single-case study [111] provides evidence that different forms of the same letter (allographs) are stored separately. A neurological patient who had suffered a stroke was left with agraphia associated with constructional apraxia. However his writing deficits were selective, affecting lower-case rather than block capitals. This suggests that the storage of letterforms is organised according to letter context rather than being purely alphabetical.

67.2 Hand Positioning (Nimmo-Smith, Wann, Wing)

The fastest means of covering a given distance between two points is to use maximum acceleration followed by maximum deceleration. However, the resulting movement is likely to be abrupt, jerky and hard to control. Thus individual movements in highly-practised skills, such as handwriting, are not generally executed as rapidly as possible. A promising new line of investigation has been the evaluation of the time course of unconstrained movements in terms of a criterion that minimises mean square jerk (which is defined as the rate of change of acceleration). Estimates of jerk are lower for children whose handwriting is rated more highly by their teachers; poorer writers exhibit more jerk [305]. In adults, drawing movements in the production of ellipses are consistent with the minimisation of jerk [310]. The latter study also provided evidence of departures from a relationship between the speed and curvature of movement widely known as the "two-thirds power" law (see also [306]).

67.3 Motor Rehabilitation (Lough, Wing)

Voluntary arm movements often improve after hemiplegia consequent to stroke, and the literature provides several qualitative descriptions of recovery. However kinematic details of the time course of movements and quantitative estimates of recovery curves have not been established. Long-term evaluation of changes in upper limb function after stroke indicates the value of characterising recovery of voluntary movement (visually-guided hand positioning) in terms of peak angular velocity of the elbow [313]. Clinically, spasticity is often characterised by a postural synergy of flexed shoulder and elbow; however the recovery of elbow function in voluntary movements is uninfluenced by shoulder movement.

67.4 Force (Wing)

Despite the pervasive importance of the use of force (for example, in grasping objects) and the fact that impulsive force development is a basis for rapid, aimed, ballistic movements of the kind that are frequently studied by psychologists, the control of force is a largely neglected topic in research on psychological mechanisms of motor control. A relation between these two aspects of motor control is implied, for example, by the fact that, in parkinsonian bradykinesia, characteristic slowness in carrying out a movement is linked to a reduction in the ability to make abrupt changes in grip force [311]. A new quantitative theory, the parallel force unit model [304], has been formulated. It predicts the expected form of brief force impulses as a summation of a large number of noisy output channels. The theory is of potential importance not only in its own right, but also as a route to understanding relations between speed and accuracy in rapid, aimed movement.

Project 68 - Organization and Development of Skilled Performance

68.1 Reaching (Wing)

Many activities require concurrent execution of two or more psychologically distinct elements. One view holds that low-level coordinative structures link the simultaneous performance of separate actions and that these links are modified as skill advances. A continuing research effort at the Unit has been the demonstration of the existence of such links and of ascertaining their functional nature. The prototypical task that we employ is reaching for objects in the environment. This has two components, transport of the hand towards the object and shaping of the hand into a grasp, that are quite distinct. Indeed it has been suggested that these separable aspects are regulated by two independent visuo-motor channels. However, APU research demonstrates a dependence of mean hand aperture on the transport component [315, 319]. Changes in hand aperture provide a degree of compensation for inaccuracies in the transport component. Preliminary correlational analyses indicate that the hand aperture-transport dependence is predictive or feed-forward in nature and not due to feedback corrections made during movement. As such the dependence represents a control algorithm of potential interest to engineers working in robotics [318] and suggestions have been put forward for the definition of a criterion task for the evaluation of reach and grasp performance of teleoperated manipulator systems [325].

68.2 Timing (Nimmo-Smith, Wann, Wing)

In many skills (including handwriting - [324, 309] the accurate timing of successive movements is critical. A task that allows assessment of the variability of timing is periodic finger tapping of a response key at various predetermined rates. Recently, additional complexity has been introduced into the tasks employed in order to develop an understanding of the coordination of a number of separate response streams [312]. Subjects had to produce accurately timed intervals by tapping with one hand or by using the two hands in alternation. The latter yields more variable performance. In alternate hand tapping, simulation modelling of the sequences of interresponse times suggests the existence of two internal clocks that interact with one another. This postulate of two "equi-potential" controllers departs from the strictly hierarchical view of motor control often associated with the information processing approach [317].

68.3 Space and Action (Marcel with M. Brouchon, Marseille)

Perceptual-motor space appears to have two major divisions: left and right, and near and far, but the basis of such distinctions remains problematic. Marcel and Brouchon have studied double dissociations between near and far space in visually guided motor tasks in patients with optic ataxia and in normal subjects; results suggest that the most relevant variable is the intentional nature of the task (touching, grasping, throwing, pointing) rather than distinctions related to the object or objective distance. Thus, relative spatial accuracy in peri- and extra¬corporal space can be reversed if patients are enabled to grasp far objects with an extendable pincer or forced to point to near objects. In normal subjects the nature of spatial errors in speeded tasks has been shown to depend on (a) whether the instructions are to grasp, point to, or touch objects, and (b) the strategy of hand utilization necessitated by the mutual proximity of targets; these differences mirror those found in performance in peri- versus extra-corporal space. The major difference between tasks differentiating near and far space appears to be between manipulation and deixis (indication). Preliminary work on hemineglect suggests that this intentional distinction may illuminate divisions in the horizontal plane. While right-parietal/left visual field neglect is observed much more than left-parietal/right neglect, almost all indices of neglect concern peri-corporal space and non-deixic tasks. Interestingly, when given deixic tasks in extra-corporal space, two out of three left parietal patients showed (previously unobserved) right neglect.

68.4 Influence of Intention on Accessibility and Fluency of Action (Marcel with C. Garvie, Rehabilitation Unit, Addenbrooke's Hospital)

In Ideomotor Apraxia, actions which cannot be produced on request or by imitation are often produced or improved when performed as a component of normal activities. Marcel has explored the extent of occurrence of such phenomena in a range of neurological patients, one application being identification of appropriate eliciting conditions for therapy. Patients showing the phenomenon were filmed in a variety of situations. Dual-task conditions (appropriate to each patient's impaired behaviour) suggested that, in general, the performance difference is not due to "over-attention". When an activity was induced of which the relevant behaviour was a component, improvement was obtained in all cases. Unexpectedly a further significant improvement was observed when the action performed had social or personal significance. These findings suggest that motor control is strongly influenced by the nature of the intention.

REFERENCES

Refereed Journal Articles

296. Anderson, M. and LOUGH, S. (1986) A psychological framework for neurorehabilitation. Physiotherapy Practice, 2, 74-82.

297. ELDRIDGE, M., NIMMO-SMITH, I., WING, A.M. and Totty, R.N. (1985) The dependence between selected categorical measures of cursive handwriting. Journal of the Forensic Science Society, 25, 217-231.

298. HAGGARD, P. (1989) How linkages and computation specify movement patterns. Human Movement Science, 8, 381-391.

299. HAGGARD, P. and WING, A.M. Assessing and reporting the accuracy of position measurements made with optical tracking systems. Journal of Motor Behavior, in press.

300. LOUGH, S. (1987) Visual control of arm movement in the stroke patient International Rehabilitation Research, 10.4, 113-119.

301. LOUGH, S. and Lough, F. (1985) The efficacy of physiotherapy to recovery of arm function following stroke. International Journal of Rehabilitation Research, 8, 402-403.

302. McLeod, P., McLAUGHLIN, C. and NIMMO-SMITH, I. (1985) Information encapsulation and automaticity: Evidence from the visual control of finely timed actions. In M.I. Posner and O. Marin (Eds.), Attention and Performance XI. Hillsdale, N.J.: Lawrence Erlbaum Associates, pp.391-406.

303. POULTON, E.G. (1988) The Journal of Motor Behavior in the 1960s and the 1980s. Journal of Motor Behavior, 20, 75-78.

304. Ulrich, R. and WING, A.M. A recruitment theory of force-time relations in the production of brief force pulses: The parallel force unit model. Psychological Review, in press.

305. WANN, J.P. (1987) Trends in the refinement and optimization of fine-motor trajectories: Observations from an analysis of the handwriting of primary school children. Journal of Motor Behavior, 19, 13-37.

306. WANN, J. (1989). The appraisal of the velocity-curvature relation in children's hand movements: A research note. Journal of Motor Behavior, 21, 145-150.

307. WANN, J.P., Dejong, M. and Harrison, A.B.C. (1986) The cumulative effects of high altitude on motor performance: A comparison between Caucasian visitors and native highlanders. Journal of Human Movement Studies, 12, 139-144.

308. WANN, J.P. and Jones, J.G. (1986) Space-time invariance in handwriting: Contrasts between primary school children displaying advanced or retarded handwriting acquisition. Human Movement Science, 5, 275-296.

309. WANN, J.P. and NIMMO-SMITH, I. Evidence against the relative invariance of timing in handwriting. Quarterly Journal of Experimental Psychology, in press.

310. WANN, J.P., NIMMO-SMITH, I. and WING, A.M. (1988) Relation between velocity and curvature in movement: Equivalence and divergence between a power law and a minimum-jerk model. Journal of Experimental Psychology: Human Perception and Performance, 14, 622-637.

311. WING, A.M. (1988) A comparison of the rate of pinch grip force increases and decreases in Parkinsonian Bradykinesia. Neuropsychologia, 26, 479-482.

312. WING, A.M., Church, R.M. and Centner, D.R. (1989) Variability in the timing of responses during repetitive tapping with alternate hands. Psychological Research, 51, 28-37.

313. WING, A.M., LOUGH, S., Turton, A., Fraser, C. and Jenner, J.R. Recovery of elbow function in voluntary positioning of the hand following hemiplegia due to stroke. Journal of Neurology, Neurosurgery and Psychiatry, in press.

314. WING, A.M. and NIMMO-SMITH, I. (1987) The variability of cursive handwriting measures defined along a continuum: Letter specificity. Journal of the Forensic Science Society, 27, 297-306.

315. WING, A.M., Turton, A. and Fraser, C. (1986) Grasp size and accuracy of approach in reaching. Journal of Motor Behavior, 18, 245-260.

C - Invited Chapters and Commentaries

316. WANN, J.P., NIMMO-SMITH, I. and WING, A.M. (1989) Why are "Strategies" "Sensitive"? Smoothing the way for a raison d'etre. Behavioral and Brain Sciences, 12, 235-236.

317. WING, A.M. (1987) Hierarchies in an information-processing perspective of the control of movement. C.P.C. Cahiers de Psychologie Cognitive, 7,211-213.

318. WING, A.M. Coordination in normal and prosthetic reaching. In S.T. Venkataraman and T. Iberall (Eds.), Dextrous Robot Hands. New York: Springer-Verlag, in press.

D - Conference Proceedings

319. Athenes, S. and WING, A.M. (1989) Knowledge directed coordination in reaching for objects in the environment. In S. Wallace (Ed.), Perspectives on the Coordination of Movement. Amsterdam: Elsevier Science Publishers, B.V. (North-Holland), pp.285-301.

320. LOUGH, S. and WING, A.M. (1985) Recovery of voluntary arm function following stroke. Journal of Physiology, June Issue, p.3P.

321. MCLAUGHLIN, CM. (1986) Vision and the timing of interceptive actions. In J. Watkins, T. Reilly and L. Burwitz (Eds.), Sports Science (Proceedings of the VIII Commonwealth and International Conference on Sport, Physical Education, Dance, Recreation and Health, Glasgow, 18-23 July 1986). London: E and F N Spon., pp.337-342.

322. Sassoon, R., NIMMO-SMITH, I. and WING, A.M. (1986) An analysis of children's penholds. In H.S.R. Kao, CP. van Galen and R. Hoosain (Eds.), Graphonomics: Contemporary Research in Handwriting. Elsevier Science Publishers B.V. (North-Holland), pp.93-106.

323. Sassoon, R., NIMMO-SMITH, I. and WING, A.M. (1989) Developing efficiency in cursive handwriting: An analysis of't' crossing behaviour in children. In R. Plamondon, CY. Suen and M.L. Simner (Eds.), Computer Recognition and Human Production of Handwriting. Singapore: World Scientific Publishing, pp.287-297.

324. WANN, J.P. (1986) Handwriting disturbances: Developmental trends. In H.T.A. Whiting and M.G. Wade (Eds.), Themes in Motor Development, (Proceedings of the NATO ASI on Motor Skill Acquisition in Children, Maastricht, The Netherlands, July 1985). Dordrecht, The Netherlands: Martinus Nijhoff Publishers, pp.207-223.

325. WING, A.M. and Fraser, C. (1988) Artificial hand usage in grasp and release phases of reaching. In C.A. Mason (Ed.), Teleoperation and Control. Proceedings of the International Symposium. IFS Publication, Springer-Verlag, pp.107-112.

E - Technical Reports, Theses and Tests

326. MCLAUGHLIN, CM. (1987) Visual and motor processes involved in the control of collisions. Unpublished PhD Thesis, University of Cambridge.

327. WANN, J.P. (1988) The control of fine-motor trajectories. Unpublished

PhD Thesis, University of Cambridge.