Immediate vs. postponed visual feedback in practising a handwriting task

Human Movement North-Holland

Science 11 (1992) 563-592

563

Immediate vs. postponed visual feedback in practising a handwriting task Stanley

J. Portier

and Gerard

P. van Galen

NICI, University of Nijmegen, Nijmegen, The Netherlands

Abstract Portier, S.J. and G.P. van Galen, 1992. Immediate vs. postponed handwriting task. Human Movement Science 11, 563-592.

visual feedback

in practising

a

Two experiments are reported in which adult subjects practised the writing of four graphemes chosen from the Arabic alphabet. In both experiments the type of visual feedback was varied. In order to study the effects of feedback variation on the dynamics of the acquisition process, the absolute and relative changes of movement time and writing dysfluency across the first three segments of the graphemes were analyzed. The overall results of both experiments showed that movement time and writing dysfluency decreased, but that this decrease was significantly less for the first segment than it was for the second and the third segment. This finding corroborated the earlier exposed view (Portier et al. 1990) that the effects of practice may be described as a shift of programming strategies. The authors argued that advance serial element-to-element preparation prior to movement initiation gradually develops towards on-line retrieval of oncoming writing segments during real-time execution of the initial segments of a grapheme. At the acquisition level, the present data provide evidence that practising a handwriting task with immediate feedback induces most explicitly an on-line programming strategy, which can be identified from the differential effects on movement time and writing dysfluency. At the performance level, however, both experiments disclosed significant disadvantages of immediate feedback compared to postponed feedback, with regard to a fluent handwriting performance.

Conventional models of motor control have stressed the importance of visual feedback with regard to the reduction of movement errors. Visual information is considered to function in the detection of errors and also in the initiation of submovements designed to compensate for previous errors (Crossman and Goodeve 1983; Keele 1968). In educationally oriented theories of skill learning, the role of visual Correspondence to: S.J. Portier, Nijmegen, The Netherlands.

0167.9457/92/$05.00

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564

S.J. Portier,

G.P. em tiulen

/ Feedback

and practising

hundwriting

monitoring and feedback mechanisms has also been emphasized (Bilodeau 1966; Sovik 1981). Bilodeau (1966) mentioned that perceptual feedback is probably one of the most critical variables affecting skill acquisition. With the rise of processing accounts of motor behaviour, Adams (1971) proposed that in the acquisition of a perceptual motor skill, feedback and knowledge of results are used to develop (1) a memory trace for the selection and initiation of a movement, and (2) a perceptual trace to determine the accuracy of the movement. Schmidt’s (1975) closely related schema theory also posits two representations which are necessary for movement, one for initiation and one for error detection. Schmidt proposed the role of schema rules derived from practice, which can operate after the selection of a generalised motor program. In order to develop a good schema rule it is preferable to expose it to a large variety of similar movements. Feedback mechanisms are assumed to be involved in the selection of the relevant schema rule and also in the shaping of a selected schema, which is necessary for error reduction. Sovik and Teulings (1983) suggested that feedback is also involved in the acquisition of a complex motor skill like handwriting. They found that a training program which employed feedback (presented on a visual display) on the smoothness of handwriting movements enhanced writing speed, independently from writing accuracy or writing size. Recently, Smyth (1989) and Smyth and Silvers (1987) investigated the influence of visual deprivation on the handwriting process. Both studies revealed that visual deprivation increased the number of writing errors to a degree comparable to the effect of introducing a second, parallel task. The loss of orientation and alterations of the movement sequence led to the conclusion that visual information is involved in the on-line monitoring of handwriting tasks. Van Galen et al. (1989) found evidence that deprivation of visual feedback slowed down handwriting performance, especially in repetitive stroke patterns. The authors interpreted these results as evidence in favour of the view that visual feedback is involved in the on-line retrieval and ‘unpacking’ (Sternberg et al. 1978) of motor elements from a shortterm motor buffer (Henry and Rogers 1960) during real-time handwriting. The authors posit that the absence of visual feedback inhibits the on-line retrieval. As a consequence, real-time performance needs to be slowed down. Retrieval of handwriting elements is known to be hindered by their similarity (Van Galen 1984; Portier et al. 19901,

S.J. Portier, G.P. IYZ~Galen / Feedback and practising handwriting

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which seems to be corroborated in situations in which visual feedback is absent. Morikiyo and Matsushima (1990) showed that delayed visual feedback led to erroneous insertion of additional line elements or letter duplication, which may also be considered evidence for the view that visual feedback is involved in the retrieval of elements from the short-term motor buffer. The results of the studies described above generally present evidence on the role of visual feedback in familiar handwriting tasks. In the present study we will examine whether and in what sense visual feedback is involved in the acquisition of an unfamiliar handwriting task. To date, few research investigating this question has been published. According to Portier et al. (1990) the learning of a handwriting task can be characterized by two major processes. Firstly, practice leads to the integration of initially separate response segments in more comprehensive response chunks and secondly, preparation of oncoming segments is increasingly realized during real-time execution of the initial segment (on-line preparation). In a handwriting experiment on the learning of six unfamiliar handwriting patterns the authors analyzed the effects of practice across the consecutive segments of six artificial graphemes. Beside an overall increase of task efficiency, reflected by a smaller proportion of pauses between subsequent segments as well as by a decrease in the duration of these pauses, it was revealed that movement time and writing dysfluency decreased as a result of practice. This decrease was unequally distributed across consecutive grapheme segments, however. Movement time and writing dysfluency of an initial segment decreased relatively less compared to further segments. The results were considered to support the view that, in the case of learning a complex motor skill like handwriting, practice leads to a shift of the locus ofprogramming, i.e., the amount of on-line preparation of oncoming segments increases, and becomes relatively concentrated in the initial writing segment. For reasons of comprehension it is important to note that writing dysfluency refers to the technical term, used to measure the fluency of handwriting performance. The writing dysfluency of a segment is defined as the absolute number of velocity extremes, within the velocity profile of that specific segment (Meulenbroek and Van Galen 1988). In the present study our primary, theoretical aim was twofold: (1) to investigate the way in which movement time and writing dysfluency vary as a function of feedback conditions, and (2) to study the relation

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between feedback manipulation and the shift of the locus ofprogramming as an effect of practice. More specifically, it is questioned whether the results of practice, in terms of a differential decrease of movement time and writing dysfluency can be influenced by the kind of feedback which is provided. To this end, we report two experiments in which adult, Dutch subjects had to practise four graphemes of Arabic script under different conditions of visual feedback. These four graphemes were used in both experiments. In general, Arabic script has little resemblance to Latin script, because of its opposite writing direction. Nevertheless, the isolated graphemes do show some visual resemblances with graphic patterns of Latin script that actually originated from the same historical roots (Gelb 1952). Our secondary aim was to investigate the role of pattern features of letter forms in the acquisition process. Several studies showed, that apart from feedback and instruction conditions, pattern features of motor actions also play an important role in motor performance. Examples are found in morse-sign responses (Klapp and Wyatt 1976), in speech (Abbs and Gracco 1983; Abbs et al. 1984; Hulstijn 1987; Sternberg et al. 19781, and in studies on handwriting (Van Galen 1984; Van Galen et al. 1989; Wing et al. 1979). The handwriting studies showed that repetition of identical letters and strokes slows down handwriting performance. Portier et al. (1990) found that a left-right mirroring of the first segment at the last segment position led to even longer movement times than repetition of these segments did. These repetition effects appeared to be independent from effects of practice. In order to explore whether pattern features like similarity of consecutive elements interacted with effects of feedback, we varied the similarity of individual grapheme elements at two levels, by means of using (1) graphemes which contained a repetition of the initial element, and (2) graphemes with a non-repetitive structure. Our prediction here is that movement time will be relatively extended in patterns with a repetitive structure compared to patterns with a non-repetitive structure. This extension, however, will be unrelated to the acquisition process. A further pattern feature that is known to influence writing performance, is the degree of curvature of grapheme elements. Viviani and Terzuolo (1980) found that the degree of curvature is a more important factor for the determination of writing time, than trajectory length is. It appeared that writing velocity was inversely related to the

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curvature of a written trajectory. In a post-hoc analysis Portier et al. (1990) found independence between curvature and practice effects, which led to the conclusion that curvature must be considered an output parameter which does not affect the storage of graphemes in motor memory. In order to explore the effects of curvature on the learning process here, we varied the degree of curvature of the consecutive grapheme elements at two levels: (1) graphemes composed of highly curved elements vs. (2) graphemes composed of elements with a relatively low degree of curvature.

Experiment

1

Three groups of 12 subjects participated in experiment 1. During the acquisition phase, one group received immediate feedback (IF), a second group received postponed feedback (PF), and a third group was provided with both feedback forms (IPF). All feedback conditions were mediated through a visual display in front of the subject. In the experiment, IF was defined as a dynamic, on-line visual presentation of the writing trajectory, depicted simultaneously with the production of the written trace, and PF as a static visual presentation of the written trace, immediately after it was completed. The IPF group received both the immediate, as well as the postponed visual presentation. First, we hypothesize that different forms of feedback will have a differential effect on the acquisition of a handwriting task. Visual deprivation does not only slow down the handwriting process (Van Galen et al. 1989), but also hinders the real-time monitoring of qualitative aspects of handwriting (Smyth 1989; Smyth and Silvers 1987). At the same time, intermittent correction models of movement control predict a larger number of adjustments in full vision conditions than in situations in which the subject is deprived of vision (Keele 1968, 1981). If we assume that postponing the feedback delays movement speed and inhibits the number of adjustments (reflected by the number of dysfluencies), we predict that when subjects are deprived of immediate feedback (PF) they will be more fluent but also slower. A further expectation is that the acquisition of a handwriting skill characterized by a differential decrease of movement time and writing dysfluency (Portier et al. 1990) will be most explicitly evident if immediate feedback is provided (IF or IPF).

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Method

An experiment was run in which subjects practised the writing of four Arabic graphemes. The experiment was extended over two training sessions, each session consisting of 160 trials. Subjects

Thirty-six adult subjects, all graduate students, who may be considered as skilled writers, served as paid volunteers in the experiment. All subjects were right handers, and unfamiliar with Arabic script. During the experiment the subjects were not aware of the purpose of the investigation. Design

In the experiment, we studied the effects of two learning variables: (1) Feedback, by means of providing three different forms of feedback, and (2) Practice, by having two training sessions of 160 trials each. Additionally, we investigated the effects of three task variables: (1) grapheme Similarity, and (2) grapheme Curvature, through the choice of the stimulus material, and (3) segment Position. Feedback was varied by using three forms of feedback. One group of 12 subjects received Immediate Feedback (IF), by on-line visual presentation of the dynamic writing trajectory as a cumulative trace. A second group of 12 subjects received Postponed Feedback (PF), by presenting the static written trace, immediately after it was completed. The third and last group of 12 subjects received both Immediate and Postponed Feedback (IPF). Similarity between grapheme elements was varied by manipulating the degree of repetition of the two initial grapheme elements: (a) repetition of the first element (see fig. 1; patterns 1 and 21, and (b) alteration of the first element (see fig. 1; patterns 3 and 4). The element boundaries for each grapheme were defined at those locations where the vertical coordinate of the pen position reached a maximum value. The degree of Curvature of the graphemes was also varied at two levels: graphemes containing curved elements (see fig. 1; patterns 2 and 4) vs. relatively less-curved elements (see fig. 1; patterns 1 and 3). The experimental variables were introduced according to a completely hierarchical design, with 40 repeated measurements for each

S.J. Portier, G.P. ~‘an Galen / Feedback and practising handwriting

Stimulus

569

graphemes

I/x

2

3

Fig. 1. The Arabic graphemes as presented to the subjects. Similarity of the first and last element was varied by (a) repetition of the first drawn element (1 and 21, and (b) alteration of the first drawn element (3 and 4). The degree of curvature was varied at two levels: (a) graphemes composed of less curved elements (1 and 3), and (b) graphemes composed of curved elements (2 and 4). Subjects were instructed to write from the right to the left, as in original Arabic script. The first element refers to the first element drawn by the subject. Element boundaries are indicated by squares.

of the four graphemes. according to a completely

Presentation randomized

of the graphemes block design.

was done

Procedure and apparatus Prior to the actual experiment, each subject was allowed to practise two dummy-graphemes, in order to become familiar with the experimental procedure, the apparatus and the pen. The experiment was subdivided in two sessions of 50 minutes each, which were held on two consecutive days. In each session a subject performed four blocks of 40 trials each. The graphemes were presented by a computer managed visual display, about 100 cm in front of the subject, during a presentation interval of four seconds. A high tone at the end of the stimulus

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S.J. Portier, G.P. uzn Galen / Feedback and practising handwriting

presentation interval indicated the start of the execution interval, which lasted for a fixed interval of four seconds in each trial. In all three feedback groups the subject’s writing hand was covered by a black, opaque box, in order to ensure that visual feedback was only provided by the display. The subject was instructed to look at the screen while writing. Further instructions were given to produce a legible and at the same time fluent handwriting. There was no explicit time pressure, except for a restricted execution interval of four seconds. In the IF condition the written trace appeared on-line on the display. During the full execution interval of four seconds the subjects received IF. For reasons of clarification it should be noted that IF has a threefold nature. Firstly, it includes the time interval that passed between the starting tone and the actual start of handwriting (i.e., reaction time). Secondly, it includes the on-line, dynamic visualization of the written trajectory, and thirdly (if the subject completed the grapheme within the restricted interval of four seconds) it also encompassed the remaining time between the completion of the grapheme and the end of the execution interval. In the PF condition only a static reproduction of the written trace was presented for four seconds, immediately after the execution interval. The subjects who received IPF were shown an immediate cumulative trace of the written trajectory as well as the after-trial static reproduction. Subjects wrote with a stylus (Maarse et al. 19881, with an inbuilt registration apparatus, on a CALCOMP 9240 digitizer tablet (spatial resolving power 0.025 mm). The stylus and digitizer tablet were interfaced with a DIGITAL MicroVax 3100 computer. The X- and Y-position of the pen, as well as the axial pen pressure exerted on the pen point (21, were all sampled at 100 Hz. Data analysis Data records were filtered using a low-pass FIR-filter (Rabiner and Gold 1975) of 12 Hz., which provided an accurate estimation of the spatial trajectory that was actually performed by the subject (Teulings and Maarse 1984). The writing trajectories were displayed for inspection and analyzed by means of an interactive computer program. Segment boundaries were located by searching for the minima within the absolute velocity pattern of the recorded writing movement. Segment boundaries should not be mixed up with the element boundaries that were defined earlier. For the location of element bound-

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Absolutevelocity "

"

123

"

4

2.5 set

5

Fig. 2. An example of the output of the data analysis procedure of one record. The pen position was sampled with a frequency of 100 Hz. The recordings were filtered with a low-pass filter of 12 Hz. The written grapheme is depicted together with the corresponding absolute velocity and axial pen pressure pattern. Circles indicate segment boundaries which were used to measure the dependent variables of the target segments within the grapheme. The consecutive segments are numbered according to the order in which the subjects produced the grapheme. The corresponding segment number is also indicated in the velocity and pen pressure profile.

aries we used spatial criteria, while the criteria for locating segment boundaries were of a kinematic nature. A quadratic interpolation technique (Teulings and Maarse 1984) was used to determine more accurately the exact location of the velocity minima between two successive samples. An output example of the segmentation procedure of one record is illustrated in fig. 2. For each grapheme segment, movement time and writing dysfluency were determined as kinematic measures of the writing process. Writing size, writing slant, and the standard deviation of the curvature were also computed. These spatial measures were used as control variables, in order to examine whether or not kinematic effects could be attributed to spatial variability. Consequently, we were able to determine the independency of the kinematic measures from the

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spatial measures. Such independency warrants that kinematic effects can more reliably be attributed to cognitive demands and not to biomechanical or spatial aspects of the task. Finally, the performed degree of curvature was computed in order to control the reliability of the experimental variation of the degree of curvature. The analyses of the dependent variables were restricted to the first three segments of the graphemes, because earlier experiments (Hulstijn and Van Galen 1983; Van Galen et al. 1986) showed that movement times of final segments were lengthened by the oncoming stop at the end of the grapheme. Each grapheme was visually checked by the experimenter as to its correct production. Graphemes which were not written correctly were marked as an error. Records were defined as an error either when segments were missing or incorrectly inserted. Written graphemes that contained segments with a different rotation (clockwise versus counter-clockwise) as compared to the stimulus grapheme were also marked as an error. Error trials were excluded from the kinematic analyses. The dependent variables were analyzed separately using analysis of variance (ANOVA) on the means of 40 replications according to a 3 forms of feedback (FB) x 12 subjects (SS) x 2 days (DAY) X 2 degrees of similarity (SIM) X 2 degrees of curvature (CUR) X 3 segment positions (SGP) design. Student Newman Keuls tests (SNK a; p < 0.05) were performed in order to test the significance of differences between factor levels. Results and Discussion Errors Error trials were rejected from the kinematic analyses. The criterion to reject a trial was when either segments were missing or incorrectly written (e.g., trials that were written according to the Latin script movement direction). It appeared that the mean error rates amounted 12%, 9% and 6.5% for the IF, IPF and PF group, respectively. Effects of pattern features on movement time and writing size Prior to the analyses on effects of curvature we examined whether the experimental assumption that the degree of curvature was higher in patterns 2 and 4 than in patterns 1 and 3 was acknowledged by the degree of curvature of the written trajectories. Analysis of variance

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revealed that the level of curvature was significantly higher in patterns 2 and 4 than in patterns 1 and 3 (F(l,ll) = 52.84, p < O.OOl>, which is in accordance with the experimental variation of the degree of curvature. The movement time and writing size analysis both revealed main effects for pattern similarity (F(l,ll) = 264.93, p < 0.001; F(l,ll) = 68.54, p < 0.001, respectively). It appeared that repetition of segments led to shorter movement times and smaller writing sizes than alteration of grapheme segments, which is in contrast with our prediction. The effects for pattern similarity did not interact with the movement time effects for practice (F(2,22) = 1.09, p > 0.05). Furthermore, the movement time and writing size results showed that a higher degree of curvature led to (1) a longer movement time (F(l,ll) = 133.20, p < O.OOl), and (2) a larger writing size (F(l,ll) = 243.60, p < 0.001). Variation in the degree of curvature interacted significantly with movement time effects of practice, across segment positions. This interaction will be presented in more detail in the next section. Effects of practice on the spatial properties of writing In order to control explicitly for the independency between changes in spatial and kinematic features of the writing performance during the acquisition phase, we analyzed the effects of practice on three spatial measures of the writing tasks: writing size, writing slant, and standard deviation of curvature. Analysis of variance showed neither significant main effects of practice, nor significant interactions between practice and feedback on writing size (F(l,ll) = 0.28, p > 0.05; F(2,22) = 1.88, p > 0.051, writing slant (F(l,ll) = 0.91, p > 0.05; F(2,22) = 0.85, p > O.OS>,and standard deviation of curvature (F( 1,ll) = 0.00, p > 0.05; &X2,22) = 1.70, p > 0.05). Thus, we may conclude that practice and feedback effects which will eventually be revealed in the analyses of movement time and writing dysfluency are independent of fluctuations in the spatial features mentioned above. General kinematic effects of practice across segments The main effects of practice on movement time and writing dysfluency for the initial three segments are summarized in table 1. The movement time analysis revealed a main effect for practice (F(l,ll) = 11.11, p < 0.01) and a practice by segment position interaction (F(2,22) = 11.60, p < 0.01). A more detailed SNK-analysis showed

514

S.J. Portier, G.P. ~:an Galen / Feedback and practising handwriting

Table 1 Means and standard deviations of movement time (MT) and writing function of segment position (SGP) and practice (Day 1, Day 2). SGP

MT (ms) M

dysfluency

(WD),

as a

WD (nvinv/seg) SD

M

SD

1.71 1.76 2.09

0.79 0.87 1.13

1.74 1.60 1.93

0.85 0.76 1.02

Day I 1 2 3

425 430 471

125 123 144 Day 2

1 2 3

423 403 440

14.5 140 160

that movement time decreased less for the first segment than for the second and third segment (p < 0.05). The movement time decrease for the second and third segment was not significantly different. These results are further corroborated by the writing dysfluency results, which showed a significantly smaller decrease for the first segment compared with the second and third segment (SNK a; p < 0.05). The effect of practice on movement time across writing segments is illustrated in fig. 3. Additionally, the differential movement time decrease appeared to be of a dissimilar nature in less curved graphemes than in highly curved graphemes (F(2,22) = 5.19, p < 0.051, which may reflect that the degree of curvature is not only a performance parameter but may also be involved in the acquisition of an unfamiliar writing task. The movement time data of the first segment revealed a decrease of 10 ms as an effect of practice for the less curved graphemes, but an increase of 5 ms for the highly curved graphemes. Summarizing briefly, movement time and writing dysfluency decreased significantly as a result of practice, but these effects were unequally distributed across segment positions. For both dependent variables, the decrease was relatively less in the first segment compared to the second and third segment. These results replicate the findings of Portier et al. (1990) and acknowledge the theoretical viewpoint that practice leads to a shift of processing load towards the

S.J. Portier, G.P. van Galen / Feedback and practising handwriting

o o .._.,..

575

SGP 1 SGP 2 SGP3

460 1

i!

i= E

440

E zi 5

0. 420

.,

0

0

:

0

400 I

2

1 Fig. 3. Mean movement

time for each segment

position

as a function

of practice.

initial writing segment. With increased proficiency, the preparation of forthcoming segments seems to proceed more and more during realtime execution of the initial segment. The present experiment also revealed evidence that the degree of curvature may not only be an output parameter, but additionally seems to be involved in the motor programming process. More specifically, a high degree of curvature slows down performance speed, but may also provide more opportunities for concurrent (on-line) programming of oncoming segments. Kinematic effects of feedback conditions and interactions with practice

The means and standard deviations of movement time and writing dysfluency as a function of segment position, feedback and practice are summarized in table 2. The movement time analysis revealed neither a significant differential effect for feedback conditions (F(2,22) = 1.09, p > O.OS), nor a significant feedback by practice interaction (F(2,22) = 0.70, p > 0.05).

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Table 2 Means and standard deviations of movement time (MT) and writing dysfluency function of segment position (SGP), feedback and practice (Day 1, Day 2). SGP

as a

Day 2

Day 1 MT (ms) M

(WD)

SD

WD (nvinv/seg)

MT (ms)

M

M

SD

(WD) (nvinv/seg) SD

M

SD

2.38 2.23 2.83

1.03 0.91 1.23

1.39 1.25 1.44

0.46 0.29 0.37

1.47

0.54 0.47 0.52

Immediate feedback (IF) 1 2 3

392 427 469

122 118 147

2.40 2.62 3.24

0.92 0.97 1.24

389 384 413

139 121 155

Postponed feedback (PF) 1 2 3

455 452 502

119 122 143

1.32 1.32 1.54

0.32 0.28 0.39

455 432 4x4

144 140 143

Immediate and postponed feedback CIPF) 1 2 3

428 411 441

130 130 138

1.40 1.33 1.49

0.46 0.40 0.38

424 392 423

149 154 151

1.33 1.51

Writing dysfluency, on the contrary, was significantly affected by feedback conditions (F(2,22) = 22.11, p < 0.001). Further analysis showed that writing dysfluency was highest when subjects received IF, followed with significant gaps by the IPF group and the PF group (SNK a; p < 0.05). The writing dysfluency analysis also revealed a significant interaction between feedback conditions and practice (F(2,22) = 3.88, p < 0.05). In order to investigate this interaction in more detail we performed a partial analysis on writing dysfluency for each feedback group separately. The mean writing dysfluency as a function of practice, segment position, and feedback condition, is illustrated in fig. 4. Immediate

feedback

(IF)

In the immediate feedback condition, an analogous writing dysfluency result was obtained compared to the overall result. We found an almost significant effect that in this feedback condition writing dysfluency decreased with practice (F(l,ll) = 4.07, p = 0.07). Similar to the overall result, a practice by segment position interaction was found

S.J. Portier. G.P. van Galen / Feedback and practising handwriting

Immediate $ Postponed Feedback

Postponed Feedback

Immediate Feedback

577

IIIIII2

1 Day

2

1 Day

Fig. 4. Mean writing dysfluency for each segment position feedback group (immediate feedback, postponed feedback back) separately.

2

1 Day

as a function of practice, for each and immediate + postponed feed-

(F(2,22) = 5.67, p < 0.05). Writing dysfluency decreased significantly less in segment 1 than in segment 2 and 3 (SNK a; p < 0.05). The decrease was not significantly different for segment 2 and segment 3. Postponed feedback (PF) For the postponed feedback condition, the writing dysfluency analysis showed no significant main effects for practice (F(l,ll) = 0.51, p > 0.05). The practice by segment position interaction, however, appeared to be significant (F(2,22) = 3.74, p < 0.05). The effect of practice was significantly different for segment 1, compared to segment 2 and 3 (SNK a; p < 0.05), in the sense that writing dysfluency increased in segment 1, but decreased in both other segments. Immediate feedback and postponed feedback combined (IPF) In the condition where subjects received both immediate feedback and postponed feedback, no significant effects of practice on writing

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dysfluency were found (F(l,ll) = 0.36, p > 0.05). The interaction between practice and segment position was also statistically nonsignificant (F(2,22) = 1.64, p > 0.05). Summarizing the kinematic effects as a result of practice and feedback, it was found that the number of writing dysfluencies was lower in the condition in which immediate feedback was absent (PF). This result is in agreement with our prediction deduced from the intermittent correction models (Keele 1968, 1981) of motor control. We did not find any main effect of feedback condition on movement time which does not correspond to our expectation. Furthermore, the results showed a significant writing dysfluency decrease as an effect of practice, particularly in the IF group. Analogous to the general effects of practice, the writing dysfluency decrease was different across segment positions: the first writing segment improved relatively less than the second and third writing segment. This result confirms the prediction derived from Smyth (1989) and Smyth and Silvers (19871, that posits the need for visual feedback in the acquisition of a handwriting skill. The differential improvement across segment positions was evident in the immediate feedback group but not in the group that received immediate as well as postponed feedback. The latter result is not in accordance with our prediction, that the acquisition of a handwriting task identified by a differential decrease of movement time and writing dysfluency would be more evident if immediate visual feedback is provided. It may be that the combination of immediate and postponed feedback does not unite the independent advantages of each separate feedback type. The two feedback types may even inhibit each other’s functionality. We will return to this issue in the general discussion. The results seem to indicate that conditions of immediate visual feedback provide more opportunities for adjustments, leading to a less fluent handwriting performance. In contrast, practice leads to a larger improvement in writing dysfluency in the condition in which only immediate visual feedback is presented. The differential decrease of writing dysfluency, reflecting a shift towards on-line processing also seems to be most evident in the immediate feedback condition. A possible objection to this interpretation of the results is the contamination between temporal placement of the feedback (immediate versus postponed) and its nature (dynamic versus static). In order to disentangle the effect of temporal placement and the nature of the feedback, a second experiment is indispensable.

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In this experiment the temporal placement of the feedback will be varied, but the dynamic nature will be held constant. In contrast with experiment 1 in which the effects of practice were measured by comparing two complete sessions, we used a pretest-posttest comparison in experiment 2.

Experiment

2

An additional group of 12 graduate students participated in experiment 2. Now, two types of dynamic visual feedback were mediated. The first type of feedback, which was also used in experiment 1, was immediate dynamic feedback and the second type of feedback was postponed dynamic feedback. Both feedback conditions were presented through a visual display in front of the subject. Analogous to experiment 1, immediate feedback is defined as a dynamic, on-line visual presentation of the written trajectory simultaneously with the production of the written trace (IF). In the condition of postponed, dynamic feedback the kinematic features of every writing trace were sampled and stored during real-time production, in order to be visually displayed to the subject, immediately following the completion of the writing task. The postponed dynamic feedback is different from the postponed feedback used in experiment 1, in the sense that the visual presentation of the written trace is no longer of a static but of a dynamic nature (PDF). The speed at which the cumulative trace was depicted, was identical to real-time writing velocity. Both types of feedback were presented dynamically in order to verify that the results in experiment 1 can be allocated to variation in temporal placement (immediate versus postponed) of the feedback and not to a different nature (dynamic versus static). A further important difference compared to experiment 1 was that in the present experiment feedback conditions were varied within subjects, as to control for between-subject differences. According to studies performed by Sovik (19761, Wright and Wright (19801, and LaNunziata et al. (1985) dynamic feedback would lead to a larger effectiveness in the acquisition of a handwriting task than static feedback. The results of experiment 1 seem to acknowledge the results of these latter studies, although the combined immediate and postponed feedback (IPF) results do not. In the present experiment we will examine whether independent varia-

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tion of temporal placement of feedback can replicate the results of experiment 1. If the assumption is correct that immediate feedback provides more opportunities for on-line movement control than postponed feedback, we expect that the mere variation of temporal placement of feedback will lead to analogous results as those presented in experiment 1. At the acquisition level, we predict that the differential dysfluency and movement time decrease will be most explicitly evident for the immediate feedback condition. At the performance level, handwriting performance will be less dysfluent if postponed dynamic feedback is provided. Effects of variation in pattern features (degree of similarity and curvature), which were already tested in experiment 1, will not be investigated in the present experiment. Method Subjects Twelve adult subjects, all graduate students, who may be considered as skilled writers, served as paid volunteers. None of these subjects participated in experiment 1. As a selection criterion all of the subjects had to be right-handed, and unfamiliar with Arabic script. During the experiment the subjects were not aware of the purpose of the investigation. Design In the present experiment, we studied the effects of two learning variables: (1) Feedback, by means of varying the temporal placement at two positions, and (2) Practice, by comparing a pretest and a posttest of 40 trials each (4 graphemes x 10 replications). Within the pre- and posttest two graphemes were allocated to the Immediate Feedback (IF) condition, and two graphemes were presented under Postponed Dynamic Feedback (PDF). The two feedback conditions were presented according to a block design. Within each feedback block the presentation order of the two graphemes was random. The combination of feedback condition and graphemes was counterbalanced between subjects. Between the pre- and posttest a training session of 160 trials (4 graphemes X 40 replications) was conducted, in which the feedback-grapheme combination, as well as the presentation order of the graphemes were analogous to the pre- and posttest.

S.J. Portier, G.P. can Calen / Feedback and pructising handwriting

PRETEST

TRAINING SESSION

POSTTEST

20 trials

(IF)

80 trials (IF)

20 trials (IF)

20 trials

(PDF)

80 trials

20 trials (PDF)

Fig. 5. The experimental

within-subjects

(PDF)

581

design as used in experiment

2. (n = 12.)

Feedback was varied by using two types of feedback. Immediate Feedback (IF), by on-line visual presentation of the dynamic writing trajectory as a cumulative trace, and Postponed Dynamic Feedback (PDF) by presenting a dynamic cumulative written trace, immediately after the trial was completed. Feedback was varied within subjects. An illustration of the experimental within-subjects design is presented in fig. 5. In contrast with traditional pretest-posttest designs, we varied the temporal placement of feedback within the pre- and posttest as well as within the training session, in order to be able to measure performance effects as a function of feedback and also the effects of feedback on the acquisition process, which can be identified from the interaction between practice and feedback. Procedure

and apparatus

Prior to the actual experiment, each subject was allowed to practice two dummy-graphemes, in order to become familiar with the experimental setting. The experiment was subdivided in three sessions, a pretest and a posttest of 40 trials each and a training session of 160 trials in between. Stimulus presentation, execution interval and instruction were identical to experiment 1. In the IF condition the written trace appeared dynamically (on-line) on the visual display. Presentation of IF lasted during the execution interval of 4 seconds. In the PDF condition a dynamic reproduction of the written trace was presented in real-time writing speed, immediately after the execution interval. The apparatus was the same as used in experiment 1. Data analysis

Filtering and segmentation procedures were performed according to analogous criteria to those used in experiment 1. To determine the effects of practice and feedback for pretest as well as for posttest and

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for each grapheme segment separately, we analyzed movement time and writing dysfluency as kinematic measures of the writing process. Writing size, writing slant, and the standard deviation of the curvature were computed as control variables, in order to check whether or not effects on movement time and writing dysfluency could be attributed to spatial effects. The analyses of the dependent variables were performed on the first three segments of the graphemes as in experiment 1. Further data analyses consisted of analysis of variance (ANOVA) on the means of 20 replications according to a 2 types of feedback (FB) X 12 subjects (SS) X 2 tests (TST) X 3 segment positions (SGP) design. Student Newman Keuls tests (SNK a; p < 0.05) were performed in order to test the significance of differences between factor levels. Results and Discussion Errors

Error trials were rejected from further analysis according to the same criteria as used in experiment 1. The proportion of errors was also comparable to the proportions we found in the previous experiment. Again, in the IF condition the subjects produced the largest amount of errors (13%), whereas the mean error rate for the PDF condition amounted 3%. Effects of practice and feedback on spatial properties of writing

Prior to the analyses of movement time and writing dysfluency, we investigated the influence of practice and feedback on writing size, writing slant and standard deviation of curvature. Analyses of variance revealed that writing size decreased as a function of practice (F(l,ll) = 5.40, p < 0.05). This outcome did not interact with effects of feedback, however (F(l,ll) = 0.27, p > 0.05). Writing slant was neither affected by practice (F(l,ll) = 0.21, p > 0.051, nor by variation of feedback (F(l,ll) = 1.25, p > 0.05). The feedback by practice interaction was also nonsignificant (F(l,ll) = 0.11, p > 0.05). As a final spatial measure, the standard deviation of curvature appeared to be significantly larger if postponed dynamic feedback was provided (F(l,ll) = 5.28, p < 0.05). The latter result was not influenced by the amount of practice, which was confirmed by the nonsignificant interaction between practice and feedback (F(l,ll) = 0.97, p > 0.05). Ac-

S.J. Portier, G.P. can Galen / Feedback and practising handwriting

Table 3 Means and standard deviations of movement time (MT) and writing dysfluency function of segment position (SGP), feedback and practice (Pretest, Posttest). SGP

Pretest

(WD)

as a

Posttest

MT (ms) M

583

SD

WD (nvinv/seg)

MT (ms)

M

M

SD

WD (nvinv/seg) SD

M

SD

2.68 2.60 2.85

1.43 0.97 1.23

1.32 1.18 1.24

0.47 0.26 0.32

Immediate feedback (IF) 1 2 3

425 479 467

141 120 119

2.75 3.43 3.14

1.24 1.17 1.03

431 416 440

172 116 129

Postponed dynamic feedback (PDF) 1 2 3

461 411 466

159 131 170

1.39 1.24 1.43

0.54 0.25 0.45

415 367 378

152 143 161

cordingly, we may conclude that practice leads to smaller writing trajectories and mediation of postponed dynamic feedback to a larger variability in curvature. Nevertheless, interaction effects between practice and feedback, which may be revealed in movement time and writing dysfluency analyses are independent of analogous effects in writing size, writing slant, or deviation of curvature. Effects of practice and feedback on movement time and writing dysfluency across segments A summary of the means and standard deviations of movement time and writing dysfluency as a function of segment position, feedback and practice is presented in table 3. Furthermore, the movement time and writing dysfluency results for practice, segment position and feedback are illustrated in figs. 6 and 7. As main effects of practice both movement time and writing dysfluency decreased significantly (F(l,ll) = 14.51, p < 0.01; F(l,ll) = 6.76, p < 0.05). The writing dysfluency analysis revealed an effect for feedback (F(l,ll) = 51.36, p < 0.0011, in the sense that the number of writing dysfluencies appeared to be significantly less if PDF was provided compared to the IF condition. The decreases of movement time and writing dysfluency as a function of practice were unequally distributed across segment positions (F(2,22) = 4.68, p < 0.05; F(2,22)

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S.J. Pm-tier, G.P. LWI Galen

/ Feedback

and practising

handwriting

Postponed Dynamic Feedback

Immediate Feedback 5q---TEq

350 I I

I

pretest

I

I

posttest

w

Practice Fig. 6. Mean movement time for each segment position feedback group (immediate feedback and postponed

pOSttf?St

Practice as a function of practice, for each dynamic feedback) separately.

= 5.21, p < 0.05). For both dependent variables the initial writing segment benefited significantly less from practice than the second and third segment. Moreover, both differential decreases interacted with the temporal placement of the feedback that was mediated (F(2,22) = 4.15, p < 0.05; F(2,22) = 4.90, p < 0.05, respectively). These interactions could not be attributed to parallel effects on writing size (F(2,22) = 1.70, p > 0.05). The movement time analysis within the IF condition revealed that the decrease was less in segment 1 and 3 than in segment 2 (SNK a; p < 0.05). Actually, movement time for segment 1 increased slightly as a result of practice. The movement time results for PDF, however, showed a decrease in all segments. The decrease was significantly less in segment 1 and 2 than in segment 3 (SNK cu; p < 0.05). The movement time results for the IF condition seem to show the largest similarity with the conventional movement time results which were considered evidence for a shift of motor programming load (Portier et al. 1990). The writing dysfluency results were

S.J. Portier, G.P. can Galen / Feedback and practising handwriting

Immediate Feedback g-$j -

posttest Practice

Postponed Dynamic Feedback

SGP SGP SCP

I

I

pretest

585

I

pretest

I

Practice

Fig. 7. Mean writing dysfluency for each segment position as a function of practice, for each feedback group (immediate feedback and postponed dynamic feedback) separately.

fairly analogous to the movement time results, in the sense that in the IF condition writing dysfluency improved relatively more in segment 2 than in segment 1 and 3 (SNK a; p < O,OS>,while for the PDF condition the writing dysfluency analysis revealed a similar but nonsignificant pattern as compared to movement time. In summary, both the movement time and the writing dysfluency results provide evidence in favour of the view that immediate feedback may be more beneficial in the acquisition of a handwriting task than postponed feedback. It appears that the characteristic shift of movement times of consecutive task segments towards a relatively longer duration of the initial segment is significantly more pronounced in the immediate feedback condition. The same finding was evidenced by the distribution of dysfluencies. From a performance point of view, however, it seems that immediate feedback may also be a hindering factor, which is reflected by an overall larger number of writing dysfluencies in the immediate feedback condition.

586

S.J. Portier, G.P. LWI Galen / Feedback and practising handwriting

General discussion The results of experiment 1 and 2 showed that movement time and writing dysfluency are sensitive measures for practice and feedback variation. Both experiments revealed a decrease of movement time and writing dysfluency as an effect of practice. A second, robust finding was that practice effects were differentially distributed across segment positions, in the sense that for both dependent variables the decrease was less for the first segment, compared to the second and third segment. In general, the results are in correspondence with the view presented earlier that practice leads to a shift of the locus of programming towards the initial writing segment(s) (Portier et al. 1990). The amount of on-line processing (preparation of oncoming segments during real-time execution) increases and becomes relatively concentrated in the initial writing segment. Consequently, movement time and writing dysfluency decrease relatively less in the initial segment compared to forthcoming segments. In experiment 1 the relative shift towards on-line preparation during the initial grapheme segment was significant for the dysfluency data only. In experiment 2, where practice effects may be more appropriately measured through the introduction of a separate pre- and posttest, movement time as well as dysfluency results were in accordance with the hypothesis that immediate feedback is more favourable to a hierarchical processing strategy. The findings of the present experiments can be related to a hierarchical model of handwriting production (Van Galen et al. 1986; Van Galen 1991; Thomassen and Van Galen 19921, which explains that preparation of a specific motor action (by descending the hierarchy in a top-down way) may occur concurrently to real-time execution of a previous action. A parallel theoretical view of movement organization is discussed by Inhoff et al. (1984) and by Rosenbaum et al. (1987). The latter groups of authors also argued that preparation of subsequent movements may occur during the execution of previous movements, by concurrent editing of parameters at lower levels of the hierarchical editor model. A strongly related practice mechanism, reported by Hulstijn and Van Galen (1988) is that practice leads to chunking of initially separate response elements into larger composite units. These units can be retrieved and stored in a transient motor buffer by means of a single retrieval and storage process. It is suggested that the retrieval of consecutive response elements initially

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occurs in an element-to-element way. With increasing practice, however, the retrieval process will be more and more continuously organized and may occur during the execution of previous writing elements. The present experiments add to this view that the chunking into larger comprehensive units and the degree of on-line preparation is not only sensitive to practice, but also to feedback conditions. As main effects of feedback, both experiments revealed that subjects which received postponed feedback (either static or dynamic) produced a remarkably more fluent script than subjects which were provided with immediate feedback. The result that handwriting performance was more fluent in conditions in which immediate feedback was deprived is in agreement with our prediction, and also supports theories on vision-based adjustments in motor control (Keele 1968, 1981). While in the study of Van Galen et al. (1989) visual deprivation tended to delay movement time, this was not evident in our data. One explanation may be that the rather slow movement times may allow for extensive feedback processing, which is reflected in a more dysfluent performance, but does not additionally slow down handwriting. A second explanation could be that we did not give an explicit accuracy instruction to the subjects. Elliott et al. (1991) recently showed that depriving visual information in a manual aiming task delayed movement time more, when explicit instructions to move accurately were given. The lack of instruction to perform the task as accurately as possible and the absence of immediate feedback may have induced a subject’s expectation that the writing movement would be precise enough as to require no adjustments (Barrett and Glencross 1989), leading to a relatively fluent performance. As opposed to our results, Elliott et al. (1991) found no relation between the number of discrete adjustments and vision. The authors argued that visual control of single aiming movements may proceed in a more continuous fashion than sometimes is thought. Adjustments may still be there and may even be more frequent with visual occlusion, but are performed below the determination threshold (pseudo-continuous adjustments). For the acquisition of a handwriting task, the immediate feedback condition provides stronger evidence for a shift towards an on-line programming strategy than the postponed feedback condition. Since the differential movement time and writing dysfluency decrease is more explicitly present in the immediate feedback condition (experiment 1) and also provides evidence for a larger increase in program-

588

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and practising handwriting

ming load in the first writing segment (experiment 21, compared to the other feedback conditions, we contend that the acquisition of a handwriting task may proceed more towards on-line task performance when immediate feedback is given. This interpretation would support our predictions derived from the studies by Smyth (1989) and Smyth and Silvers (1987). An alternative explanation here, may be that the dual-task nature of the IF condition has a disrupting effect on performance, which could also explain the larger number of dysfluencies in this condition. Resource theories on dual-task performance (e.g., Wickens 1984) may also be able to explain the movement time decrease as a result of practice. Practice may lead to a resource trade-off in which the processing of feedback becomes less resource consuming, leaving more resources to share with actual movement performance. However, this alternative point of view cannot explain why the movement time decrease is less in the first segment compared to the second and third segment. The finding that the combination of immediate and postponed feedback, which was provided in experiment 1, did not lead to changes in dynamic measures may be explained by a theoretical suggestion of Winstein and Schmidt (1989) that an amount of extrinsic feedback (knowledge of results) would promote the dependence on that feedback, and thereby prevent the development of intrinsic response capabilities. A second interpretation, based on an educational viewpoint, could be that traditional methods of handwriting education are mainly product-oriented and do not provide feedback on the kinematic aspects of real-time handwriting. If immediate as well as postponed feedback is provided, subjects might focus their attention on the form of feedback which is most familiar to them. Both of these interpretations are, of course, consistent with the finding that fluency of writing was less disrupted when both immediate and postponed feedback were available compared to the condition in which only immediate feedback was presented. Summarizing briefly, as a performance measure the overall fluency data of both experiments provide evidence in favour of an instruction technique that provides postponed feedback. The acquisition of a handwriting task, however, seems to be stimulated more in conditions which provide immediate feedback. As an overall advantage of immediate feedback the data also showed a smaller standard deviation in the curvature of the written trajectories, which may reflect the role of immediate feedback in maintaining the constancy of letter forms. The

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589

latter also favours the view posited by Smyth (1989) and Smyth and Silvers (1987) that visual feedback is involved in the on-line monitoring of the task. At the same time, the on-line monitoring seems to induce more discrete adjustments causing more dysfluencies in handwriting performance. Although our experimental procedure does not provide information about the deviation between the subject’s written trajectory and the stimulus grapheme, we tried to examine spatial accuracy by analyzing the proportional number of error trials (which were excluded from the kinematic analyses) as a function of practice and feedback. As can be expected, the number of error trials decreased with practice. Surprisingly, however, subjects produced a larger number of error trials in conditions that provided immediate feedback. An explanation may be that the dual task nature of the immediate feedback condition (especially during the acquisition phase), hinders the accurate on-line retrieval of oncoming segments, leading to a larger number of errors. In conditions of postponed feedback the dual-task nature is absent and subjects might follow a perceptual image, according to a more serial element-to-element preparation strategy. Such a strategy would lead to a more fluent performance, a less explicit shift towards on-line preparation of the task, but also to less writing errors, because the retrieval of task segments is no longer hindered by on-line processing. We realize, that the number of error trials does not provide us with information about the spatial accuracy of the correctly written trials. In future research the accuracy of handwriting performance should be examined in more detail and for several feedback conditions, since it is known from other research on the role of vision in motor control, that visual deprivation has a much larger impact if an instruction for accurate performance has been given (Elliott et al. 1991). In general, our data suggest that temporal placement of feedback is indeed of significant importance for the performance of a handwriting task proper, as well as for the acquisition of such a task. Besides the traditional function of feedback as an error-elimination strategy, as proposed in closed-loop models of motor control (Adams 1971), it also appeared that especially immediate feedback contributed positively to a shift towards an on-line preparation strategy in which forthcoming segments are retrieved from the transient motor buffer during the real-time execution of a preceding segment. A final remark we would like to make, is the possible difference

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between artificial immediate feedback (as provided in the present experiments) and real-life immediate feedback (by looking at the moving writing hand and the dynamic construction of the writing trajectories). The question whether or not one would write more fluently with ‘real-life’ feedback than with artificially mediated feedback may be an interesting topic of future research.

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Viviani, P. and C. Terzuolo, 1980. ‘Space-time invariance in learned skills’. In: G.E. Stelmach and J. Requin (eds.), Tutorials in motor behaviour. Amsterdam: North-Holland. pp. 525-533. Wickens, C.D., 1984. Engineering psychology. Columbus, OH: Merrill. Wing, A.M., V.J. Lewis and A.D. Baddeley, 1979. The slowing of handwriting by letter repetition. Journal of Human Movement Studies 5, 182-188. Winstein, C.J. and R.A. Schmidt, 1989. ‘Sensorimotor feedback. In: D. Holding (ed.), Human skills. London: Wiley. pp. 17-47. Wright, CD. and J.P. Wright, 1980. Handwriting: The effectiveness of copying from moving versus still models. Journal of Educational Research 74, 95-98.