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5. MOTOR SKILL AND ACTION
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5.1 CONTROL AND TIMING OF MOVEMENT (Project 41) (Grudin, Hinton; Long, McLeod, Nimmo-Smith, Wing)
In a review of the literature Wing (415) found general support for the concept that accurate movement of the hand to a target takes place in two phases. An initial phase serves to cover distance rapidly while a second phase employs feedback to correct any discrepancy between actual and Intended hand position at the end of the first phase. A project being carried out in collaboration with Dr. Miller at Addenbrooke's Hospital is examining the relation between the two phases of movement using a procedure in which a discrepancy between hand and target is unexpectedly introduced by the experimenter in the course of the movement. In one study similarities in timing of movements in the two phases were found even though there were large differences in the amplitude of movement, (420). One interpretation of this result is that a single motor programme underlies both phases of movement. This idea is now being explored further by looking at corrective movements initiated at different points in the initial, distance-covering phase of movement.
In real life, movements are often made very quickly with no opportunity for feedback correction. A movement made without correction is called ballistic. In reaching for an object in the environment, vision is normally used to guide the hand so that the fingers encompass the object as the hand closes. However, if the movement must be made quickly such guidance is not possible. Wing, in collaboration with Turton and Fraser at Addenbrooke's Hospital (424 U), found that people compensate for the loss of feedback correction by opening the hand wider as it approaches the object so giving a greater margin for error.
McLeod et al (224) studied the timing of fast, ballistic movements used in hitting a moving ball with a bat. They observed a remarkably low degree of temporal variability in' the movements - less, for example than is found in typical reaction time tasks. They suggested that the low variability might be due to a task-specific process that operates unaffected by other, competing demands for information processing resources. This represents a particular theoretical view of the attention demands of movement; a general review of such theories may be found in (143).
One of the most serious theoretical problems in developing theories of motor control is the number of degrees of freedom involved. Computational models produced in robotics and artificial intelligence seem in general inappropriate as psychological models because of the long sequence of accurate numerical operations they require to program an appropriate movement. Hinton, in work performed while he was here developed a computational model which is much more psychologically plausible. The style of computation involved is iterative approximation using separate parallel processes for each degree of freedom. He showed that the number of iterations required can be greatly reduced by. adding processors that coordinate several joints at once.
The development of psychological theories about the control of movement is often aided by study of changes in the nature of performance with increasing skill. Long et al (204) documented the way in which the intervals between keystrokes in typing reduce with practice. On the basis of a detailed statistical analysis, they suggested two distinct processes were involved in generating the timing data, one responsible for fluent and the other for non-fluent keystrokes.
Other work on typing has focussed on the nature of errors in typing rather than the timing of keystrokes. Grudin (119) found that novice typists produce not only more errors but also a different pattern of errors from that produced by experts. He concluded that the differences were consistent with the development by the skilled typists of action units comprising several keystrokes at a time. It is interesting to note that, even among skilled typists, there is not just one pattern of errors; Indeed, as Grudin (121) has pointed out, error patterns are characteristic of the individual, and hence they should be of forensic interest.
Grudin's evidence of multicharacter typing units may be seen as a particular case of the general point made in (109). Performance of a sequence of movements usually involves more than just the stringing together of individual components. People impose structure on the sequences they perform to integrate the separate movements into a smooth, coordinated flow of action. In the area of movement control a frequently encountered candidate for describing -the structural relations between elements in a sequence of movements is the hierarchy (316; 317; 318). However, in the case of typing, Grudin (120) found the pattern of errors was not consistent with a hierarchical specification of finger movements.
In the motor skills discussed above, timing is not an explicit component. However satisfactory musical performance or interpretation does require accurate placing of movements in time. Using the simplified laboratory task of regular repetitive tapping as a model for more complex skills such as piano playing, Wing (414) presented a theoretical account of coordination of simultaneous two-handed tapping data based on a single central timekeeper. However, when the timing task involves two, asynchronous response streams such as two hands tapping in alternation, Wing, working in collaboration with Dr. Don Gentner, University of California, San Diego, has observed a degree of independence in the timing of movement In each stream. This is counter to the single timekeeper theory and is currently the subject of further investigation.
5.2 HANDWRITING (Project 10) (Eldridge, Nimmo-Smith, Wing)
Much of our research on handwriting has been concerned with its use in the applied area of identity verification. If handwriting in two documents, one of known origin the other perhaps unearthed in some criminal investigation, is similar, it may mean the two documents were written by the same person. But, in coming to a conclusion on this, a potential problem is that handwriting is inherently variable. To make reliable judgments, the forensic document examiner needs to know not only which handwriting features people produce in different ways but also whether they are produced consistently on different occasions. Under a contract with the Home Office to provide objective data in this area (422), Wing, Nimmo-Smith and Eldridge collected and analysed a set of cursive handwriting samples. A scheme for the classification of a selected set of cursive letters was developed and used to describe handwriting variability in terms of a discrimination index that summarizes variability within any one individual's handwriting relative to the variability observed between individuals. This index was used to rank the potential usefulness of different features of various letters, (98). Further analyses were run to determine the statistical dependence between different features. Such dependence affects the way in which the document examiner should combine evidence from different features in arriving at a single decision about authorship of a questioned document, (99).
The text used in collecting the handwriting samples included words with certain letters occurring at the beginning, middle and ends of the word. Wing et al (423) reported an analysis showing that the average variability of letter formation within the writing of a given individual is greater at the beginning than at the middle or end of a word. This implies that, in cursive writing, the basic model form for any letter is modulated to facilitate joining with the following letter.
Although statistically reliable, the magnitude of the effect reported was small (423), and it is possible that children, who have less firmly established internalised letter models, would be likely to display more letter form variability in letters at the beginning of words. Samples of children's handwriting have been collected by Wing and Nimmo-Smith in collaboration with a calligrapher working in Kent schools, Mrs. Rosemary Sassoon. Photographs of the children's pen grips were also taken in order to investigate a further issue: Training of handwriting as a motor skill receives little emphasis in school these days and, as a result, children tend to use a proliferation of writing grips. We are interested in determining how the nature of pen grip used affects the child's quality of writing.
A consultancy in this area was carried out in 1984 by Wing and Nimmo-Smith for Scicon on the human factors of automatic signature verification.
5.3 MOTOR DISORDERS (Project 48) (Lough, Wing)
5.3.1 Recovery of arm function following stroke
Our interest in disorders of voluntary movement is twofold. On the theoretical side Lough and Wing are interested in describing deficits in the control of movement that can be identified with different functional processes and the degree to which extant theories can account for the various types of movement disorder (417). They are also concerned with the more applied question of how function may be improved by changes In physical therapy.
In the U.K. it is estimated that two in every thousand suffer from a stroke each year. Of the 70% who survive, three quarters are left with a severe residual dysfunction of sensori-motor processes. Ten percent of the working time of hospital and community physiotherapists is spent attempting to maximise the recovery in this group of patients. The scale of this affliction in terms of sufferance of movement disability and cost to N.H.S. resources is second only to arthritis. However a review by Lough points out that aside from subjective clinical experience little is objectively known about the sensori-motor dysfunction caused by stroke, or about how the condition should be most effectively managed.
It has demonstrated that by applying the experimental techniques and theoretical constructs used in the behavioural analysis of normal motor skills to the study of hemiparetic movement, insights can be gained into the problems these patients face, and suggestions can be made as to how therapeutic Intervention might be Improved. This current project expands on these findings through a longitudinal behavioural analysis of recovery of hemiparetic upper limb function (185).
Lough and Wing, in collaboration with Fraser and Oenner of Addenbrooke's Hospital developed a method for assessing voluntary movement in hemiplegic stroke patients with only a minimal degree of movement (207). Data are currently being collected to provide a quantitative picture of the recovery of elbow function. Performance of a given patient is tested in a variety of movement contexts (e.g., with and without - ipsilateral shoulder movement, contralateral arm movement, or vision). Joint angle information and EHG data are recorded over several months of recovery to elucidate how muscle activation patterns change.
The ultimate goal of this project is to provide a database on arm recovery from which therapy can be assessed and improved. As the data are still being collected and analysed no firm conclusions can be offered at present. The picture of recovery which seems to be emerging is much more complex than has been previously described. It appears to suggest that current management policy for stroke patients may be failing to contend with problems in movement control which, with a change in therapy assessment and practice, could be resolved.
A symptom often associated with Parkinson's disease is bradykinesia or slowness of movement. The bradykinesia can result in more variable timing of repetitive movement. A detailed case study by Wing in collaboration with Keele and Margolin of the University of Oregon of a patient with bradykinesia affecting one side more than the other concluded the increased variability in timing should be identified with a deficit in timekeeping rather than being due to increased motor delay variability (419). Micrographla or small handwriting is another symptom that can occur in parkinsonian patients. The change in size of writing has been shown by Margolin & Wing (231) to be associated with progressive reduction in the force used for each pen stroke and this reduction in force is not completely compensated by taking more time to complete each stroke.
This work plus a review of other studies led Wing & Miller (421) to suggest that the basal ganglia lesions in Parkinson's disease affect the activation of movements that have been correctly programmed and are waiting to be initiated. To explore this hypothesis we are currently testing parkinsonian patients at Addenbrooke's Hospital. One group comprises patients with asymmetric symptoms so that the less affected side may be used as a comparison for the more parkinsonian side. Another study involves the comparison of the performance of patients before and after treatment for the disease. This work would benefit from availability of research assistance; all the paradigm development etc. is complete but patient testing is slow and time consuming.
The identification of a particular process or function underlying movement control with a given brain structure is not a prime aim of the present research. Rather we are interested in motor disorder insofar as a selective deficit can be revealing about the nature of normal movement control and also suggestive in regard to possible strategies for therapy. An illustration of this point is a case study carried out with Mrs. Carole Fraser at Addenbrooke's Hospital involving a girl with an artificial hand (418; 106). Despite mechanical differences between the operation of her natural hand and the artificial hand, it was shown that there were certain very significant similarities in reaching movements carried out with either hand. It was argued that the similarity clarified the reason for stability of the thumb relative to the index finger in the natural hand as the object was approached. A research proposal extending this approach to the training of artificial hand users has been prepared for submission to the DHSS.
Other sections in the 1981-1984 report
2. COGNITIVE PSYCHOLOGY
3. COGNITIVE ERGONOMICS/APPLIED COGNITIVE PSYCHOLOGY
4. HEARING
5. MOTOR SKILL AND ACTION
6. VISUAL PERCEPTION
7. PSYCH0PHYSIOL0GY SECTION