Psychological Research (2003) 67: 291–302
DOI 10.1007/s00426-002-0129-y
O R I GI N A L A R T IC L E
Lucette Gullaud-Toussaint Æ Annie Vinter
The effect of discordant sensory information in graphic production:
two distinct subject groups
Received: 23 November 2000 / Accepted: 13 November 2002 / Published online: 19 February 2003
Springer-Verlag 2003
Abstract The present study investigated the underlying
processes used to cope with discordant sensory information induced in a mirror-drawing task. Two experiments were carried out in which adults copied simple
geometrical figures made up of either horizontal and
vertical segments or oblique segments meeting at a right
angle in both a normal and a mirror condition. Experiment 1 identified individual differences in relation to
preferred graphic movement directions; some subjects
preserved the visual directions that occurred in normal
drawing by reversing the direction of drawing movements (perceived-direction group), while others preserved normal drawing directions that produced
reversed visual directions (performed-direction group).
Experiment 2 was performed to elucidate whether these
two distinct behaviors resulted from different strategies
used to cope with visuo-proprioceptive discordances.
The main results showed that preference for the perceived directions led to longer pauses, slower movement
velocity, greater movement dysfluency, and greater
spatial orientation accuracy. By contrast, longer reaction time and greater angular accuracy characterized
performance in the performed-direction group. These
results were interpreted as indicating that two distinct
information-processing strategies can be used when resolving sensory discordance in graphic production.
Keywords Mirror drawing Æ Feedback control Æ
Feedforward control Æ Visuo-proprioceptive conflicts
L. Gullaud-Toussaint (&)
Laboratoire d’Analyse de la Performance Motrice Humaine,
MSHS, 99 Avenue du Recteur Pineau, 86000 Poitiers, France
E-mail: Lucette.Toussaint@mshs.univ-poitiers.fr
A. Vinter
Laboratoire d’Etude des Apprentissages et du Développement,
CNRS/UMR 5022, Dijon, France
Introduction
Are visual information and proprioceptive information
both used in graphic production? Van Doorn and Keuss
(Van Doorn, 1992; Van Doorn & Keuss, 1992, 1993)
suggested that subjects are able to compensate for the
absence of visual information in handwriting by an increased contribution of proprioceptive processing, as
revealed by the increase in axial pen force, movement
time, and writing size. Similarly, other experiments have
shown that subjects compensate for the absence of
proprioceptive cues through an increased contribution
of visual processing. Teasdale, Forget, Bard, Paillard,
Fleury, and Lamarre (1993) revealed that when vision
was available in a graphic task, a deafferented patient
and control subjects performed similarly, while without
vision, the spatial control of movements was more
strongly impaired in the patient than in the controls.
Thus, the movements of the hand within the limits of the
graphic space depend on afferent information provided
by the visual as well as by proprioceptive systems. This
raises the question of the respective role of each system
in drawing movement production.
Some authors have reported that visual and proprioceptive information may control different aspects of
movement execution. For example, Meulenbroek and
Thomassen (1991) suggested that two independent spatial reference systems were involved in straight-line
production. One system, designated as the anatomical
reference system, corresponded to the anatomical
structure of the effectors (the hand or the fingers), and
resulted in the preferential production of oblique lines.
The second system, called the geometrical reference
system, resulted in a bias towards horizontal and vertical
orientations. Meulenbroek and Thomassen (1991) have
suggested that oblique orientations are strong candidates for predominantly motoric control with a reduced
sensitivity to the availability of visual information, while
horizontals and verticals are more likely to be under
perceptual control, with a strong dependency on visual
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information. The authors demonstrated that the prevalence of visual control depended on the type of segments
to be drawn in a situation where visual and proprioceptive modalities were available.
Other studies revealed that the role played by visual
feedback on graphic accuracy concerns the topokinetic
component of movements (i.e., the spatial orientation),
while the morphokinetic component (i.e., the shape
production) seems to be preserved whatever the visual
exposure conditions (Broderick & Laszlo, 1987; Paillard,
1991; Van Doorn & Keuss, 1993). In a previous experiment devoted to the study of sensory information in
simple drawing production (geometrical figures composed of two segments meeting at a right angle), Gullaud (1998) confirmed that the withdrawal of visual
information did not modify the angular accuracy of
drawings (morphokinetic component), although vision
was necessary for calibration of the displacement of the
pen (line orientations or topokinetic component) within
the limits of the graphic space in the case of models
composed of horizontals and verticals. With regard to
oblique models, the author noted that, in the absence of
vision, compensatory strategies were sufficient to ensure
the spatial orientation accuracy of the drawings. These
strategies were probably based on an increase in proprioceptive control, as suggested by the increased
movement time and writing size (see also Van Doorn,
1992).
These overall results suggest that visual feedback
controls specific aspects of graphic movement execution.
Vision seems to play a dominant role in calibrating the
topokinetic component of drawing, especially when the
figures are composed of horizontal and vertical segments
(geometrical reference system, Meulenbroek & Thomassen, 1991; Gullaud, 1998). The role of proprioception in graphic movement execution is less known owing
to methodological difficulties in isolating proprioceptive
information. In order to elucidate the role of proprioception, the use of a discordant sensory information
paradigm appears appropriate, because the resolution of
visuo-proprioceptive conflicts implies the dominance of
either the visual or the proprioceptive modality (Uhlarik
& Canon, 1971; Redding & Wallace, 1988a, 1988b).
Lajoie, Paillard, Teasdale, Bard, Fleury, Forget and
Lamarre (1992) provided an illustration of visual information dominance when drawing under a mirror condition. Using a six-pointed star, these authors observed
that a deafferented patient had no problem in copying
the pattern, while controls encountered certain difficulties in producing fast and accurate movements. The
authors suggested that the greater difficulty encountered
by controls in the production of obliques as opposed to
vertical segments revealed the dominance of vision, because resolving the conflict implied a multiple directional
choice for obliques (combination of up, down, left, and
right directions), whereas it implied a binary choice for
verticals (reversal of the top-down and down-top directions). Before being able to reach a level of performance similar to the deafferented patient, the control
participants had to learn how to use reversed visual
feedback by recalibrating their proprioceptive map.
Gullaud and Vinter (1996, 1998) examined the mirror-drawing production of simple open geometrical figures, which were visually less constraining than the
closed figures used in the Lajoie et al. experiment (1992).
They were interested by the syntactical level, which describes graphic behavior in terms of a system of rules
(Van Sommers, 1984), i.e., starting rules (start at the
topmost and/or leftmost point), progression rules (draw
from top to bottom and/or from left to right), and a
threading rule (draw without pen-lifts). These rules
govern drawings and result from an interaction between
biomechanical and visual constraints (Thomassen, Tibosch & Maarse, 1989; Vinter & Meulenbroek, 1993). For
instance, going from left to right induces less biomechanical constraints (flexion movements) and optimal
visual control. In some situations, subjects have to
choose between biomechanical facilities and visually
guided movement, as was the case in Gullaud and Vinter’s experiments (1996, 1998), where the mirror-drawing
condition induced left to right and right to left reversals.
The directional analysis of graphic movement showed
that two subject groups could be distinguished. Some
subjects seemed to favor vision (the perceived-direction
group): they visually preserved the perceived movement
directions as they occurred in the normal condition,
which thus induced a reversal of the directions drawn on
the sheet of paper. In contrast, other subjects seemed to
favor biomechanical constraints (the performed-direction
group): they tended to preserve the directions drawn on
the sheet of paper as they did in the normal condition,
this strategy provoking a reversal of the directions perceived in the mirror.
Thus, the current literature suggests that visual
dominance may vary as a function of the geometrical
figure to be drawn (horizontal-vertical versus oblique
figures) as well as of the type of subjects (perceivedversus performed-direction group). Using a directional
analysis, Experiment 1 aimed to show that two groups of
subjects effectively emerge in a mirror-drawing task. The
Gullaud and Vinter experiment (1996) included too few
subjects in each group to provide substantial information. A more systematic study performed with a larger
sample of participants was needed. As previously observed, we expected that most of the subjects would visually preserve the movement directions and movement
sequences of mirror-drawing production as they do under the normal condition (perceived-direction group),
while directions and movement sequences should be
preserved and not be strongly dependent on the presence
of the mirror for the other subjects (performed-direction
group). The analysis of errors in mirror production
seemed appropriate in the present experiment. The great
difficulties encountered by the perceived-direction group
when drawing oblique segments in the mirror condition
could reveal the dominance of vision (Lajoie, Paillard,
Teasdale, Bard, Fleury, Forget & Lamarre , 1992), while
the performed-direction group should encounter greater
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difficulties in the production of horizontal and vertical
segments, visual control being dominant for these types
of segment (Meulenbroek & Thomassen, 1991; Gullaud
& Vinter, 1998).
Experiment 1
Method
Subjects
Thirty-two right-handed adults (mean age 23.9 years, range 18–28
years) who were students at the University of Bourgogne participated in the experiment, for which they received course credits.
They were unaware of the aims of the study. All of them spontaneously used their right hand to write their name on a sheet of
paper, were familiar with a language using only left-to-right
handwriting and did not have visual or motor problems.
Stimuli
Fig. 1 Illustration of the experimental set-up used in the mirrordrawing task. An opaque box was positioned over the paper sheet,
which prevented the subject from having a direct view of the model,
his writing hand, and the pen. An opening at the left of the opaque
box allowed the subject to visually control his/her movement from
a mirror located at the left (8 cm) of the sheet. The small rectangle
at the far end of the mirror is the place where the models appeared.
A videotape (experiment 1) and an xy digitizer connected to a
computer (experiment 2) were used to record the drawing
productions
Eight models composed of two segments meeting at a right angle
were used in this experiment. Half of the models, called ‘‘hv
structure,’’ were composed of the four possible combinations of
horizontal and vertical line segments (e.g., the four corners of a
square shape), whereas the other half, called ‘‘ob structure,’’ were
composed of the four possible combinations of oblique line segments (e.g., the four corners of a diamond shape). The line segment
length was 1 cm for all models. Each model was printed in black
ink on a 6·6 cm white card, and models were presented one at a
time. Subjects were instructed to copy each model one at a time and
as accurately as possible. The starting points, movement directions,
and movement sequences were free and pen-lifts were allowed between two segments.
Procedure
The subjects participated in two successive conditions within a
single experimental session. In the normal condition, they were able
to look normally at their drawing performance. In the mirror
condition, they performed the experimental task looking at the
model, their hand, and the trace through a mirror. The mirror was
located at the left of the sheet of paper and was placed perpendicular to the graphic workplane. As illustrated in Fig. 1, a mask
prevented the subjects from having a direct view of the model and
of their drawing movements.
The subjects began the task by copying four random series of
the eight models in the normal condition. In a second phase and in
order to familiarize them with the difficulties involved in the mirror
task, they copied 12 one-segment models (four horizontals, four
verticals, and four obliques) in the mirror condition. After
familiarization, they drew the eight models presented in a random
order four times under the mirror-drawing condition. Because one
of the 32 subjects was unable to draw in the mirror condition despite numerous trials, 1,984 drawings (31 subjects · 2 conditions · 4
trials · 8 models) were retained for the analysis.
Data analysis
Each drawing was recorded by means of a videotape. For each
model, we coded the direction and the sequence of the drawing
movements. The mean frequencies of occurrence of verticals [to
the top (90) and to the bottom (270)], horizontals [to the right
(0) and to the left (180)] and obliques [from bottom left to top
right (45), from top left to bottom right (315), from top right
Fig. 2 Illustration of discordances between ‘‘performed’’ and
‘‘perceived’’ movement directions
to bottom left (225) and from bottom right to top left (135)]
were thus computed. In the coding of movement directions,
minor angular deviations were not considered. We were mainly
interested in coding whether a vertical was drawn, for instance,
in the 90 or in the 270 direction. For convenience, we will term
performed movements the movements realized on the sheet of
paper, and perceived movements those visible in the mirror. As
illustrated in Fig. 2, the performed and perceived drawing
movements are conflicting in the mirror-drawing condition. Exceptions are for the vertical directions (90, 270). Because the
same information is given by an analysis of either the performed
or the perceived movement directions, we restricted the analysis
to the frequencies of occurrence of performed movement directions only.
The tape recording allowed us to pick up and compute the
number of errors in movement direction. Errors were characterized by an entire movement or by a ‘‘micro–movement’’ (minimum length of 1 mm) performed in the wrong direction or
orientation when compared with the model. In the latter case, a
deviation of 22.5 on both sides of each standard segment (i.e., 0,
45, 90, 135, 180, 225, 270, and 315) was defined, and an
error was coded when the segment orientation exceeded this deviation.
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Fig. 3 Simultaneous representation of subjects and graphic movement directions as a function of the first and second factorial axis.
Numbers 1–31 indicate the individual subjects. D0, D45, D90,
D135, D180, D225, D270, and D315 correspond to movement
directions performed to 0, 45, 90, 135, 180, 225, 270, and
315, respectively
Results
Movement directions
The main goal of the first experiment was to check
whether two groups of subjects could be identified in the
mirror condition on the basis of the reversal or nonreversal of performed movement directions, as observed in
a previous study (Gullaud & Vinter, 1996). Consequently, for each subject, the frequency of occurrences
of each direction (0, 45, 90, 135, 180, 225, 270,
and 315) produced on the sheet of paper (performed
directions) when drawing in the mirror condition was
computed. The data were collected in a 31 (number of
Fig. 4 Polar representation of
the frequency of performed
movement directions as a
function of Condition (normal
vs mirror) and Group
(perceived-direction vs
performed-direction)
subjects) by 8 (number of directions) frequency table.
This table was composed of 248 cells, including the
frequency of occurrences of each direction for each
subject. It was analyzed using a correspondence analysis
(a type of principal component analysis using frequency
tables as data; for details on the procedure and analysis,
see Greenacre, 1984; Benzécri, 1973). This procedure
illustrates the presence of different groups of subjects as
a function of the movement directions they mainly used
in the mirror condition. The results are presented in
Fig. 3.
The first factorial axis explained 47.99% of the variance. As expected, this axis divided subjects into two
groups. The first group included 16 subjects who predominantly produced left-oriented segment directions
(135, 180, and 225). In contrast, the second group
included the 15 remaining subjects who predominantly
produced right-oriented segment directions (0, 45, and
315). The first and second groups were termed the
perceived-direction and performed-direction groups
respectively. Subjects in the perceived-direction group
might have favored left-oriented performed movement
directions because the resulting perceived directions
agreed with those realized in the normal condition. By
contrast, subjects in the performed-direction group
might have favored left-oriented perceived movement
directions because the resulting performed directions
agreed with those realized in the normal condition. This
interpretation was tested in the following part by an
examination of the frequency of performed directions.
Figure 4 illustrates the mean frequencies of occurrence for performed directions produced by each group.
ANOVAs were carried out with Group (perceived direction versus performed direction) as the betweensubjects factor, and with Condition (normal versus
mirror) and Block of trials (four blocks) as the withinsubjects factors. Significant interactions were investigated by means of Newman-Keuls post hoc tests.
All subjects performed left-oriented movements more
frequently in the mirror than in the normal condition
[horizontal, F(1, 29)=86.86, p<.001; oblique 45–225,
F(1, 29)=33.62, p<.001; oblique 135–315, F(1,
29)=198.42, p<.001]. A significant interaction between
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Fig. 5 Illustration of the
dominant movement sequences
realized by perceived-direction
vs. performed-direction groups
for each model in normal
(standard sequence) and mirror
conditions (performed and
perceived sequences). For a
given model, dotted drawing
showed that performed or
perceived sequences never
occurred in the normal
condition, while bold
continuous drawing showed
that the standard sequences
were preserved in mirror
production
Group and Condition for horizontals [F(1, 29)=10.08,
p<.005], top left to bottom right obliques [F(1,
29)=41.84, p<.001] and top right to bottom left obliques
[F(1, 29)=10.87, p<.005] showed that the left-oriented
movement directions were more frequent in the perceived-direction group than in the performed-direction
group when drawing in the mirror. Whatever the segment
orientation, no other significant effect was observed, and
in particular there was no effect of Block of trials (p>.09).
Movement sequencing
For each model and condition, the dominant movement
sequences observed in the perceived-direction and
performed-direction groups were established. The results
are presented in Fig. 5. The standard sequence corresponds to the usual movement sequence produced in the
normal condition. Because no differences were observed
between the groups for each model (p>.22), the frequencies of occurrence of the dominant sequences in the
normal condition were averaged for all subjects (second
column), thereby simplifying graphic presentation. The
perceived and performed sequences correspond to
movements as they were seen in the mirror or realized on
the sheet of paper respectively. Note that whatever the
models, the dominant movement sequences were produced without pen-lifts. Figure 5 shows that the models
composed of horizontals and verticals only (models a, b,
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c, d) were reversed in the mirror, because of the mirror
transformations induced on the left-right and right-left
horizontal directions.
Figure 5 reveals that, for both groups, the standard
movement sequences were preserved in the mirror
condition for the models c, d, g, and h [F(1, 29)=1.77,
p>.19]. By contrast, performance varied as a function
of Condition and Group for models a, b, e, and f [F(1,
29)>16.02, p<.001]. For each of these four models,
subjects in the perceived-direction group visually preserved the sequences used in the normal condition for
the same model (indicated by bold continuous drawing
on Fig. 5). But because of the mirror transformation,
the resulting performed sequences were new in comparison to the normal condition (indicated by dotted
drawing on Fig. 5). Subjects in the performed-direction
group preserved the performed sequences as they did in
the normal condition for the same model (models a, b,
e, and f). Their movement sequence choices did not
seem to depend on what they saw in the mirror, the
perceived sequences never being preserved (as illustrated by dotted drawings).
Number of errors
No error was recorded in the normal condition. The
mean number of errors (i.e., entire movement and micro-movement performed in the wrong direction or
orientation) made in the mirror-drawing task was computed. An ANOVA was carried out with Group as the
between-subjects factor, and Structure and Block of
trials as the within-subjects factors. Whatever the
Group, the mean number of errors was greater for oblique models (1.44) than for horizontal-vertical ones
(0.87) [F(1, 29)=24.45, p<.001], and decreased with
practice (block 1=1.8, block 2=1.1, block 3=1.0, block
4=0.7) [F(3, 87)=16.69, p<.001]. Contrary to our
expectations, no effect of Group was observed (p>.12).
However, differences between groups appeared with
regard to on-line movement corrections: the micromovements were more frequently observed in the
perceived-direction group (57%) than in the performeddirection group [39.7%; v2(2)=9.23, p<.005].
Discussion
Experiment 1 showed that two distinct subject groups
were observed when participants had to cope with
visuoproprioceptive discordance in a mirror-drawing
task. Some subjects preserved the visual directions and
sequences that occurred in normal drawing by reversing
the direction of drawing movements (perceiveddirection group), while others preserved normal drawing directions and sequences, which produced reversed
visual directions (performed-direction group). The
analysis of movement directions and sequences suggests
that vision could be the principal determinant for the
perceived-direction group when resolving the visuoproprioceptive conflicts, to the detriment of biomechanical constraints. An additional argument supporting
the idea of the visual guidance of graphic movements in
the mirror-drawing condition for this group was provided by the occurrence of micro-movements for segments produced in the wrong direction when compared
with the model. By contrast, subjects in the performeddirection group produced significantly less on-line
movement corrections, the drawing of the requested
model being reversed in consequence. These latter
subjects noted that their drawing did not match the
model only when it was entirely completed.
Contrary to our expectations, a higher number of
errors (in the mirror condition) for oblique models
when compared with horizontal-vertical models was
observed in both groups. Recall that, in accordance
with Lajoie and co-workers’ hypothesis (1992), the
greater difficulties observed for obliques could suggest
the dominance of visual information when resolving
discordances. From a visual point of view, obliques
are effectively the most complex segments to draw
because the conflict entails a multiple choice, whereas
for horizontals resolving the conflict entails a binary
choice. The aforementioned result of the present study
suggests the dominance of visual information when
resolving the conflict, whatever the movement direction favored by the subjects. Moreover, the distinction
between the geometrical and the anatomical systems of
reference reported by Meulenbroek and Thomassen
(1991) in straight line production was not confirmed
when simple geometrical figures were drawn through a
mirror. It may be that the complexity induced by the
conflicting task leads subjects to favor vision, the
‘‘Queen of the senses,’’ whatever the line-segment
orientation (horizontal-vertical or oblique).
Taken together, these results suggest that although
visual information was important regardless of the
movement directions favored by the subjects in the
mirror condition, it may have played a different role for
each group. As suggested by movement directions and
on-line corrections, performance of subjects in the perceived-direction group could have been under visual
guidance in the mirror drawing task. By contrast, the
important number of directional errors of entire movements produced in the mirror condition for the performed-direction group shows that these subjects used
visual information before and later during movement
production, probably to check whether their graphic
production and the models were congruent. It is possible
that biomechanical constraints are stronger in the latter
group, which could explain the preservation of performed movement directions and the necessity for the
subjects to plan the resolution of visuoproprioceptive
discordance before drawing production. This hypothesis
was investigated in the second experiment, by analyzing
spatial accuracy and temporal features of drawing
movements.
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Experiment 2
The second experiment investigated the underlying
processes used by the perceived-direction and performed-direction groups when solving visuoproprioceptive conflicts. As already mentioned, the availability
of visual information during movement execution is
determinant with regard to the topokinetic component
of graphic behavior, whereas the morphokinetic component seems to be preserved whatever the visual
exposure conditions (Paillard, 1991; Gullaud, 1998). We
thus expected that the importance of on-line visual
control in the perceived-direction group would be
manifested through a greater accuracy of spatial orientation than in the performed-direction group.
In the present experiment, the analysis of temporal
features of drawing production, including movement
programming and movement execution, was considered
of prime importance in understanding how both groups
proceeded to solve visuoproprioceptive conflict. Did the
subjects solve the sensory discordance before or during
graphic production, illustrating a programming-based
strategy or a feedback-based strategy respectively? Not
just the latency phase (reaction time) but also later parts
of the response (movement time and duration of pauses
between two segments) needed to be analyzed to answer
this question. We expected that the greater importance
of on-line visual corrections for the perceived-direction
group would be reflected in longer movement time, numerous velocity peaks, and longer duration of pauses,
the last-mentioned being necessary in order to recalibrate the movement in another direction. By contrast, if
the preservation of performed movement directions has
some basic determinants grounded in the biomechanical
system (performed-direction group), this should imply
the elaboration of a feedforward plan taking into account the mirror transformations before movement initiation, in order to respect the syntactical rules.
In a previous experiment, Plamondon and Clément
(1991) showed that movement directions affect movement time without disturbing performance accuracy.
They reported that more time was needed to produce
right to left than left to right graphic progressions.
Consequently, the location of the starting point and the
movement direction were imposed on participants in
Experiment 2, in order to explore how changes in
movement directions affected graphic performance in the
mirror-drawing task for both groups. The reader is
reminded that each group behaves differently with regard
to the directions most often produced on the paper sheet
when mirror drawing (Gullaud & Vinter, 1996), with
right to left directions in the perceived-direction group
and left to right directions in the performed-direction
group. For each model, participants were thus forced to
use their preferred movement sequence on the paper
sheet (i.e., from the left in the perceived-direction group,
and from the right in the performed-direction group) and
their nonpreferred sequence (i.e., from the right in the
perceived-direction group, and from the left in the performed-direction group).
Method
Subjects
Eighteen of the 31 subjects who participated in the first experiment
were selected on the basis of the frequency of movement directions
favored in the mirror-drawing condition. This frequency was
computed using models a, b, e, and f (see Experiment 1, Fig. 5), for
which subjects behaved differently and preserved either a performed or a perceived movement sequence. Ten subjects in the
perceived-direction group of Experiment 1 were kept in Experiment
2 because in more than 62.5% of cases (mean 84.8%) they adopted
the same perceived movement sequence as in the normal condition.
The eight remaining subjects were from the performed-direction
group of Experiment 1. They preserved a performed movement
sequence in more than 62.5% of the cases (mean 75%).
Stimuli and apparatus
As mentioned previously, four models of Experiment 1 (models a,
b, e, and f) were retained in the second experiment. Two models
were composed of horizontal and vertical line segments (‘‘hv’’
structure), and the two remaining models were made up of oblique
line segments (‘‘ob’’ structure).
The task was performed on an xy digitizer (Calcomp Drawingboard) connected to an IBM-PC computer. The xy coordinates
were sampled at a frequency of 100 Hz, with a spatial accuracy of
0.2 mm (for technical details, see Teulings & Maarse, 1984).
Procedure
The experimental conditions were similar to those used in the first
experiment: a normal and a mirror condition. Each drawing trial
started with a high-frequency acoustic signal, which indicated to
the subjects that they had to begin their drawing production. When
they had finished, an interactive recording procedure allowed the
experimenter to stop the process of data acquisition.
As illustrated in Fig. 6, two opposite movement sequences were
used in this experiment and the starting point as well as the movement
directions were imposed for each model by arrows. The term preferred sequence indicates that subjects copied the model using a
sequence that they spontaneously produced in the mirror task
(Experiment 1), the reverse being true for the nonpreferred sequence.
Because two distinct behaviors (reversal vs nonreversal of performed sequences) were observed in the mirror condition as a
function of the Group, the preferred sequence was the visually
perceived one in the perceived-direction group, while it corresponded to the performed sequence in the performed-direction
group. It should be remembered that, as shown in Experiment 1, all
the subjects behaved similarly in the normal condition.
In this experiment, 64 models were drawn by subjects (4 models
· 2 sequences · 4 trials · 2 conditions). The total number of recorded movement sequences was 1,152. All models were presented
in a random order in each condition.
Data analysis
Each drawing was identified and smoothed with a second-order
filter with a transition band between 8 and 20 Hz. The filtered
data were displayed alongside tangential velocity profiles. An
interactive analysis program1 was used to extract different temporal variables for each segment. The temporal variables were
1
The recording apparatus (interface and pen), acquisition and data
analysis programs were made by the Nijmegen Institute for Cognition and Information (NICI).
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Fig. 6 Illustration of the models used in experiment 2 and of the
preferred versus nonpreferred sequence for each model. These two
sequences were determined as a function of subjects’ performance
spontaneously realized in the first experiment. Arrows indicated the
starting point and the movement directions for each model
the reaction time (ms) and the duration of pauses (ms) between
the two segments of each model, the tangential velocity (cm/s),
and the number of velocity peaks for each segment (each peak
being due to successive acceleration and deceleration phases in
drawing movements). Two measures of drawing accuracy were
computed: the spatial orientation of the drawing in the workspace and the size of the angles (in degrees). For both of these
dependent variables, the root mean square error (RMSE) was
analyzed, because it is considered the best overall measure of
performance accuracy (Henry 1975; Schmidt 1988). The other
variables were the mean number of errors, as computed in the
first experiment (the total number of entire movements and
‘‘micro-movements’’ performed in the wrong direction or orientation when compared with the model) and the frequency of
micro-movements only (on-line movement corrections).
The dependent variables were analyzed by means of separate ANOVAs with Group (perceived direction vs performed
direction) as the between-subjects factor, and Condition (normal
vs mirror), Structure of models (hv vs ob), and Sequence (preferred vs nonpreferred) as within-subjects factors. NewmanKeuls post hoc tests were used to investigate the significant
interactions.
Fig. 8A, B RMSE of the spatial orientation of models (A) and of
angular accuracy (B) as a function of Group (perceived-direction vs
performed-direction), Condition (normal vs mirror), and Structure
(hv vs ob)
Fig. 7 Mean number of errors produced in the mirror-drawing
condition as a function of Group (perceived-direction vs performed-direction), Structure (hv vs ob) and Sequence (preferred vs
nonpreferred)
Results
Spatial accuracy of drawing productions
As presented in Fig. 7, most of the errors were made
when subjects used a nonpreferred sequence and when
they drew oblique models [F(1, 16)=6.83 and 19.72,
p<.001, respectively]. However, the occurrence of errors
tended to be greater for oblique models than for horizontals and verticals when subjects in the performeddirection group drew in a nonpreferred direction [Group
· Sequence · Structure, F(1, 16)=3.81, p=.066].
A qualitative analysis of errors confirmed the
importance of visual guidance of mirror-drawing
movements for the perceived-direction group. Micromovements were more frequent in the perceived-direction group (42.37%) than in the performed-direction
group (7.5%) [v2(2)=17.12, p<.001]. These results
reproduced those of Experiment 1.
The subsequent analyses included the drawings produced without errors, that is 1,053 drawings out of the
1,152 collected. The RMSE relative to the spatial orientation of models in the workspace is displayed in Fig. 8A.
On average, the RMSE was higher in the mirror
299
Fig. 9A–D Reaction times (A), duration of pauses (B), tangential
velocity (C), and mean number of velocity peaks (D) as a function
of Group (perceived-direction vs performed-direction), Condition
(normal vs mirror), and Sequence (preferred vs nonpreferred)
condition [F(1, 16)=28.45, p<.001], for oblique models
[F(1, 16)=31.68, p<.001], and in the performed-direction group [F(1, 16)=5.48, p<.05]. The difference
between groups mainly resulted from mirror-drawing
productions [Group · Condition, F(1, 16)=4.17,
p=.058]. Both groups performed differently as a function
of Structure [Group · Structure, F(1, 16)=6.54, p<.025].
The difference between hv and ob structure in the
performed-direction group was only tendential
(Newman-Keuls, p=.066) and it disappeared in the
mirror condition, while oblique models were significantly
less accurate than horizontal-vertical models in both
normal and mirror conditions in the perceived-direction
group (p<.001). No other significant effect was observed,
and in particular there was no effect of Sequence (F<1).
Figure 8B depicts the RMSE of angular accuracy. No
main effect of Group was revealed by ANOVAs (F<1).
For all subjects, the angular error was higher in the
mirror condition [F(1, 16)=16.59, p<.001] and for oblique models [F(1, 16)=16.94, p<.001], but it was not
modified by Sequence (F<1). The RMSE varied as a
function of Condition and Structure [F(1, 16)=4.38,
p=.053], and between Group, Condition, and Structure
[F(1, 16)=4.29, p<.05]. The effect of Structure appeared
to be similar in the normal and mirror conditions in the
perceived-direction group (p>.26). By contrast, subjects
in the performed-direction group had difficulty in
drawing horizontal-vertical models in the mirror condition when compared to performances in the normal
condition [F(1, 16)=15.26, p<.001]. No other significant effect appeared.
Analysis of temporal variables
Mean reaction times are displayed in Fig. 9A. ANOVA
revealed that they were longer in the mirror than in the
normal condition [F(1, 16)=37.83, p<.001], and for a
nonpreferred sequence than for a preferred one
[F(1, 16)=9.81, p<.005]. However, the marginally significant interaction between Condition and Sequence
[F(1, 16)=3.98, p=.056] showed that the increase in
reaction times when using a nonpreferred sequence
mainly occurred in the mirror-drawing condition. Differences appeared between the perceived-direction and
the performed-direction group in the mirror task only
[F(1, 16)=4.48, p<.05], the increase in reaction times
being significantly more important in the performeddirection group. No effect of Structure [F(1, 16)=1.06,
p=.32] and no other interaction were revealed by the
ANOVAs ( p>.33).
The mean duration of pauses, illustrated in Fig. 9B,
also increased in the mirror condition for all subjects
[F(1, 16)=16.83, p<.001], but it increased significantly
more in the perceived-direction group than in the performed-direction group [F(1, 16)=4.58, p<.05]. When a
nonpreferred sequence was imposed, an increase in the
duration of pauses was observed [F(1, 16)=4.46,
300
p<.05], especially in the mirror condition and for the
perceived-direction group [Group · Condition · Sequence, F(1, 16)=3.98, p=.06]. No other significant
effect appeared.
As shown in Fig. 9C, slower movements were observed in the mirror-drawing condition [F(1, 16)=15.60,
p<.001], for a nonpreferred sequence [F(1, 16)=4.60,
p<.05], and in the perceived-direction group [F(1,
16)=5.90, p<.05]. In the mirror task, velocities decreased significantly more in the perceived-direction
group than in the performed-direction group [F(1,
16)=4.22, p<.05], especially for a preferred sequence
[Group · Condition · Sequence, F(1, 16)=8.33, p<.01].
For all subjects, the mean tangential velocity was higher
for oblique models (3.9 cm/s) than for horizontal-vertical models (3.6 cm/s) [F(1, 16)=14.88, p<.001].
Finally, the analysis of the mean number of velocity
peaks (Fig. 9D) revealed that movements were less
fluent in the mirror condition [F(1, 16)=27.86, p<.001]
and for oblique models [hv structure =2.4, ob structure =3.0; F(1, 16)=11.85, p<.005]. Movements tended to be more dysfluent in the mirror condition for
the perceived-direction group than for the performeddirection one [F(1, 16)=3.93, p=.064]. Moreover, the
significant interaction between Group, Condition, and
Sequence [F(1, 16)=6.27, p<.025] showed that the
increase in movement dysfluency in the mirror condition for the perceived-direction group was greater for
the preferred sequence, while this was true for the
nonpreferred sequence in the performed-direction
group. No other significant effect was revealed by the
ANOVAs (p>.23).
Discussion
Experiment 2 confirmed that subjects’ drawing behavior
differed as a function of their group (perceived-direction
versus performed-direction) with regard to temporal
parameters and performance accuracy. While no difference between groups appeared in the normal condition,
the subjects from each group reacted differently when
resolving the visuoproprioceptive discordance. The
occurrence of micro-movements, the longer duration of
pauses, the slower movement velocity, and the greater
movement dysfluency show that the perceived-direction
group encountered more difficulties during movement
execution in the mirror-drawing task. By contrast, the
major changes in reaction times observed in the performed-direction group show that much of the conflict
was resolved during movement planning.
In addition to these temporal differences, the groups
differed with regard to spatial accuracy. Subjects in
the performed-direction group were less accurate in
reproducing model orientation than those in the perceived-direction group, and they did not exhibit any
modifications of the morphokinetic component (angular
accuracy), especially when drawing the oblique models.
In accordance with the literature showing that on-line
visual feedback plays a major role in spatial orientation
accuracy (Broderick & Laszlo, 1987; Gullaud, 1998;
Paillard, 1991; Van Doorn & Keuss, 1993), the present
experiments confirm that the perceived-direction group
makes greater use of visual information than the performed-direction group in graphic movement production.
Differences between the production of oblique models and horizontal-vertical models were expected from
the literature. In straight line production (Meulenbroek
& Thomassen, 1991) and in simple geometrical drawing
tasks performed in nonconflicting conditions (Gullaud,
1998; Gullaud & Vinter, 1998), it was shown that the
visual system was dominant for horizontal and vertical
line segments, while motoric control was prevalent for
obliques. Consequently, we expected that horizontalvertical drawing production would be easier for the
perceived-direction group, and the drawing of obliques
easier for the performed-direction group. However, in
the present experiment no significant Group · Structure
of models interaction was revealed by the ANOVAs (on
errors and temporal variables). For both groups, errors
were more frequent for obliques than for horizontals
and verticals, and movements were less fluent for the
former than for the latter. These results suggest that
visual control predominates over motoric control for all
subjects, whatever the directions they spontaneously use
when drawing through a mirror.
Movement sequences (preferred vs nonpreferred)
were imposed on participants in order to explore how
changes in movement direction affected the graphic
performance of perceived-direction and performeddirection groups. As expected (Plamondon & Clement,
1991), graphic accuracy (i.e., spatial orientation and size
of angle) did not change as a function of left to right or
right to left movement progressions in either group,
while changes in movement execution parameters (i.e.,
tangential velocity and number of velocity peaks) were
mainly observed in the perceived-direction group for
preferred and nonpreferred sequences (Newman-Keuls,
p>.05). Thus, difficulties encountered in terms of
movement execution in the mirror task by the perceiveddirection group cannot be explained by the production
of movements from right to left. Increases in reaction
times in both groups and in the duration of pauses in the
perceived-direction group were observed when a nonpreferred sequence was used in the mirror condition.
These results suggest that when subjects were forced to
use a sequence that they did not spontaneously produce
in the mirror, they encountered more difficulties in the
planning of movement direction.
General discussion
Both experiments confirm that two different information-processing strategies appear when adults are
required to draw in a conflicting task. With regard to
movement sequence, some of them favor the visually
perceived sequence, while others favor the performed
301
sequence. The importance of visual guidance in the
perceived-direction group is revealed by the analysis of
the spatial accuracy of drawing production, especially
with regard to spatial orientation of movements in the
graphic workspace. Moreover, the temporal data show
that the perceived-direction group encounters more
difficulties during movement execution in the mirrordrawing task. These findings suggest that subjects in
the perceived-direction group rely mainly on a visual
feedback control of movement when they have to
resolve visuoproprioceptive discordances. By contrast,
visual guidance does not seem to play a major role in
the performed-direction group. The changes in reaction
times observed in this latter group show that much of
the conflict is resolved during motor programming.
Subjects in this group would rely mainly on a feedforward control of movements when drawing in the
mirror.
Such results seem in accordance with prism adaptation studies in which some authors have reported that
two motor control strategies can occur (Redding &
Wallace, 1996). In this case, when both starting and
target locations were simultaneously visible, the relative
difference between locations were used to initiate a
feedforward movement plan (i.e., feedforward control
strategy). When starting locations were not visible, the
differences between target location and effector location, when available, were directly used for feedback
corrections (i.e., feedback control strategy). However,
whereas the nature of strategic control appeared to be
task-specific in prism exposure, the present experiments
on mirror drawing suggest a more subject-dependent
approach to account for the type of strategies used to
solve visuoproprioceptive conflicts.
These results call for further investigations, and
especially for developmental experiments. Research in
motor development has revealed age-related differences
in the use of feedforward and feedback processes (Bard,
Hay & Fleury, 1985; Hay, 1979, 1984; Olivier, Audiffren
& Ripoll, 1998), with a critical period in development of
movement control at around 7–8 years. The changes in
spatial accuracy and timing in movements were interpreted as a changing dominance of pro- (5-year-olds)
and retroactive control (7-year-olds), followed by a
mixed control in older children (11-year-olds). Investigation of mirror-drawing production in children seems
interesting to observe how changes in feedforward and
feedback processes can affect performance in the case of
visuoproprioceptive conflicts. Before the age of 6 years,
most children should belong to the performed-direction
group because of the dominant role of feedforward
processes, while at 7–8 years most children should behave like the perceived-direction group because of the
dominant role of feedback processes. Moreover, we
might expect to observe a differential dichotomy in older
children, as was the case in adults. Wondering why
adults react differently when resolving visuoproprioceptive discordance also opens up a fruitful avenue of
research.
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