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Journal ArticleDOI

Transfer of the curvature aftereffect in dynamic touch.

01 Oct 2008-Neuropsychologia (Elsevier Limited)-Vol. 46, Iss: 12, pp 2966-2972

TL;DR: The existence and intermanual transfer of curvature aftereffects for dynamic touch were investigated and it is concluded that the representation of object information depends on the exploration mode that is used to acquire information.

AbstractA haptic curvature aftereffect is a phenomenon in which the perception of a curved shape is systematically altered by previous contact to curvature. In the present study, the existence and intermanual transfer of curvature aftereffects for dynamic touch were investigated. Dynamic touch is characterized by motion contact between a finger and a stimulus. A distinction was made between active and passive contact of the finger on the stimulus surface. We demonstrated the occurrence of a dynamic curvature aftereffect and found a complete intermanual transfer of this aftereffect, which suggests that dynamically obtained curvature information is represented at a high level. In contrast, statically perceived curvature information is mainly processed at a level that is connected to a single hand, as previous studies indicated. Similar transfer effects were found for active and passive dynamic touch, but a stronger aftereffect was obtained when the test surface was actively touched. We conclude that the representation of object information depends on the exploration mode that is used to acquire information.

Topics: Curvature (58%)

Summary (4 min read)

1. Introduction

  • A haptic curvature aftereffect is a phenomenon in which a flat surface feels concave after the prolonged touching of a convex surface, and vice versa.
  • Later, they showed that the aftereffect also occurred when small variations in the exploration manner were applied, but no aftereffect was found when the adaptation and test stimuli were touched by different hands (Vogels, Kappers, & Koenderink, 1997).
  • Existence of an aftereffect when curved surfaces were statically touched by only a single fingertip (Van der Horst et al., 2008).

1.1. Exploration modes to perceive curvature

  • The haptic perception and representation of curvature has been investigated for several manners of exploration.
  • This exploration manner is appropriate to obtain information from highly curved surfaces.
  • Psychophysical studies have shown that this exploration manner is opsych B.J. van der Horst et al. /.
  • Nevertheless, the shape of weakly curved stimuli can be perceived by static touch when the contact length with the stimulus is increased by placing the whole finger or several fingers together on the stimulus surface (Pont, Kappers, & Koenderink, 1997; Pont et al., 1999).
  • The thresholds decreased with increasing contact length, up to about 0.5 m−1 for a contact length of 15 cm.

1.2. Representation of curvature information

  • Static and dynamic touch provide different ways to acquire shape information from an object.
  • This suggests that curvature information is processed in a different way for dynamic touch.
  • The representation level of the curvature information may depend on the exploration mode.
  • More insight into the representation of curvature information can be obtained by studying the aftereffect and its transfer.
  • In vision, establishing aftereffect transfer has successfully uncovered the representation of perceived phenomena like motion (see e.g., Mather, Verstraten, & Anstis, 1998; Moulden, 1980; Tao, Lankheet, van de Grind, & van de Wezel, 2003; Wade, Swanston, & de Weert, 1993).

1.3. Active and passive dynamic touch

  • A distinction is made between active and passive dynamic touch.
  • In active dynamic touch, the subject moves the finger over the surface of a fixed stimulus; in passive dynamic touch, the stimulus moves underneath a finger that the subject keeps at a fixed position.
  • Passive dynamic touch shares with active dynamic touch that there is an analogous moving contact between the finger and the stimulus.
  • Therefore, similar results might be expected for active and passive dynamic touch.
  • Passive dynamic touch has in common with static touch that the finger stays in the same location.

2. Experiment 1

  • In the first experiment, the authors studied the existence and transfer of a dynamic aftereffect in active and passive dynamic touch.
  • The first goal was to demonstrate the existence of a curvature aftereffect in dynamic touch.
  • Having the same ability to acquire shape information does not necessarily imply that this information is represented at the same level.
  • Thus, the transfer pattern might deviate from the transfer characteristics of static aftereffects, as previously reported (Van der Horst et al., 2008; Vogels et al., 1997).
  • The shape could not be deduced from the immediate contact between the finger and the stimulus, but movement was required.

2.1.1. Design

  • Four conditions were studied in a two × two design.
  • The exploration mode was either active or passive dynamic touch.
  • In the active mode, the stimuli were explored by a self-induced movement with the index finger over the surface of a stationary stimulus.
  • A further distinction was made between the employment of either a single finger or different fingers.
  • In the same-finger mode, the same index finger was used to touch both the adaptation and the test stimulus; in the oppositefinger mode, the right index finger touched the adaptation stimulus, and the left index finger touched the test stimulus.

2.1.2. Setup

  • Subjects were seated behind a table, with their arms resting on a support.
  • Only the right slit was used in the same-finger mode.
  • The platform remained in position in the active conditions.
  • Fig. 1 illustrates the setup of the experiment.

2.1.4. Procedure

  • During a trial, the adaptation stimulus was touched by the index finger of the right hand for 11 s.
  • Three back-and-forth movements were made during the adaptation phase.
  • After 4 s, the test stimulus was touched with an index finger for a single side-to-side movement.
  • Practice trials were conducted to accustom the subjects to the proper exploration time.
  • The order in which the experimental conditions were conducted was partly counterbalanced.

2.1.5. Subjects

  • Eight, paid subjects participated (four male and four female, mean age 21 years).
  • All subjects were right-handed, as established by a standard questionnaire (Coren, 1993).

2.1.6. Analysis

  • For each subject and condition, the responses in the convex adaptation trials were separated from the responses in the concave adaptation trials.
  • A psychometric function (cumulative Gaussian) was fitted to the data to determine the point of subjective equality (PSE).
  • In the active conditions, the adaptation and test stimuli were stimuli moved underneath the index finger.
  • The dark bars represent the results for nger.
  • The PSEs and the magnitude of the aftereffect are indicated.

2.2. Results

  • The mean results for each condition are given in Fig. 3a.
  • The error bars represent the standard errors.
  • Visual inspection of this graph shows that an aftereffect was obtained in all conditions.
  • In addition, the magnitude of the aftereffect was higher in the active conditions compared to the passive conditions.

2.3. Discussion

  • This experiment shows the existence of a dynamic curvature aftereffect and, most surprisingly, a full transfer of this effect.
  • This result differs from the partial transfer of the static curvature aftereffect, as obtained in their previous study (Van der Horst et al., 2008).
  • To place the finding in a broader perspective, only some specific visual motion aftereffects show a full interocular transfer.
  • In general, there is only partial transfer of the effect, the strength of which depends on several stimulus and measurement parameters (Tao et al., 2003; Wade et al., 1993).
  • Furthermore, the difference in magnitude of the aftereffect indicates that there are differences in curvature representation of active and passive dynamic touch.

3. Experiment 2

  • In the second experiment, the transfer between active and passive dynamic touch was investigated.
  • In the passive–active condition, the order was reversed.
  • In both conditions, subjects used only their right hands for adaptation and testing.
  • Before the experiment, the authors formulated two main hypotheses.
  • Second, a higher aftereffect could be obtained in the active–passive condition; this would suggest that active and passive touch share the same representation, but adaptation is stronger for active touch.

3.1. Methods

  • The same setup was used for this experiment as in the previous experiment.
  • The authors did not use the ±1.8 m−1 stimuli but increased the number of repetitions per stimulus.
  • The order in which the experiment was performed was counterbalanced among subjects.
  • There were eight, right-handed subjects (four male and four female, mean age 21 years), none of whom were involved in the first experiment.

3.2. Results

  • The mean results for each condition are presented in Fig. 3b.
  • Independent samples t-tests were performed in order to compare the results of the second experiment to the same-finger results of the first experiment.
  • The result for the passive–active condition was not significantly different from that of the active condition but was significantly higher than that of the passive condition (t14 = 0.7, p = 0.5 and t14 = 3.9, p = 0.001, respectively).

3.3. Discussion

  • This experiment reveals an aftereffect transfer from active to passive dynamic touch, and vice versa.
  • The magnitude of the effect was higher in the passive–active condition than in the active–passive condition.
  • The correspondence between the first and the second experiment is that a stronger aftereffect is obtained when the test stimulus is actively explored, irrespective of the manner of touching the adaptation stimulus.

4.1. The existence of a dynamic curvature aftereffect

  • The authors demonstrated the occurrence of an aftereffect when curved surfaces are dynamically touched with a single index finger.
  • This finding is a considerable extension of the original discovery of Gibson (1933), since the authors employed a quantitative approach and displayed the existence of the effect for a relatively short adaptation time.
  • The dynamic curvature aftereffect is similar to previously reported static curvature aftereffects (Van der Horst et al., 2008; Vogels et al., 1996).

4.2. Dynamic touch versus static touch

  • One of the most important findings of this study is the complete intermanual transfer of the dynamic curvature aftereffect.
  • Since the immediate contact of a single finger is insufficient, curvature information must be derived from the dynamic contact between the finger and the stimulus surface.
  • The point of contact is displacement is too small to provide sufficient information.
  • The remaining sources cannot individually provide information about the shape of the stimulus, since they are indistinguishable for convex and concave shapes.

4.3. Active dynamic touch versus passive dynamic touch

  • Intermanual transfer of the aftereffect was found for both active and passive dynamic touch.
  • In the previous section, the authors argued that information about the direction of movement is essential to distinguish a weakly curved shape.
  • The correspondence between these findings is that a smaller aftereffect was obtained when the test stimulus was touched passively instead of explored actively.
  • A related aspect is that active and passive dynamic touch require different sensorimotor involvement.
  • Following adaptation to a convex shape to convex curvature information, the pressure profile of exploring a flat surface corresponds to that of a slightly concave surface without adaptation.

4.4. Conclusion

  • The current study demonstrates the existence of a haptic dynamic curvature aftereffect and a complete intermanual transfer of this effect, which suggests that dynamically obtained curvature information is represented at a high level in the brain.
  • A comparison between active and passive dynamic touch shows a larger aftereffect for actively tested curvature.
  • In conclusion, this study provides evidence that the representation of object information depends on the exploration mode that is used to obtain that information.
  • The definition of passive dynamic touch as used in the current study differs from the more strict definitions of passive touch, in which there is no role for the efferent commands (Chapman, 1993; Loomis & Lederman, 1986, chapter 31).

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Neuropsychologia 46 (2008) 2966–2972
Contents lists available at ScienceDirect
Neuropsychologia
journal homepage: www.elsevier.com/locate/neuropsychologia
Transfer of the curvature aftereffect in dynamic touch
Bernard J. van der Horst
, Wouter P. Willebrands, Astrid M.L. Kappers
Helmholtz Instituut, Universiteit Utrecht, Department of Physics of Man, Princetonplein 5, 3584 CC Utrecht, The Netherlands
article info
Article history:
Received 18 April 2008
Received in revised form 4 June 2008
Accepted 9 June 2008
Available online 14 June 2008
Keywords:
Active touch
Haptic
Perception
Shape representation
abstract
A haptic curvature aftereffect is a phenomenon in which the perception of a curved shape is systematically
altered by previous contact to curvature. In the present study, the existence and intermanual transfer of
curvature aftereffects for dynamic touch were investigated. Dynamic touch is characterized by motion
contact between a finger and a stimulus. A distinction was made between active and passive contact of
the finger on the stimulus surface. We demonstrated the occurrence of a dynamic curvature aftereffect
and found a complete intermanual transfer of this aftereffect, which suggests that dynamically obtained
curvature information is represented at a high level. In contrast, statically perceived curvature information
is mainly processed at a level that is connected to a single hand, as previous studies indicated. Similar
transfer effects were found for active and passive dynamic touch, but a stronger aftereffect was obtained
when the test surface was actively touched. We conclude that the representation of object information
depends on the exploration mode that is used to acquire information.
© 2008 Elsevier Ltd. All rights reserved.
1. Introduction
A haptic curvature aftereffect is a phenomenon in which a flat
surface feels concave after the prolonged touching of a convex
surface, and vice versa. The occurrence of this phenomenon has
been demonstrated for different exploration modes. Gibson (1933)
reported that when subjects ran their fingers along the edge of
a convexly curved cardboard for three minutes, the subsequently
explored flat edge felt concave. Recent studies have focused on
the properties of static rather than dynamic curvature afteref-
fects.
Vogels, Kappers, and Koenderink (1996) studied the charac-
teristics of an aftereffect when curved surfaces were touched by
static contact with the entire hand. They found a linear depen-
dence of the magnitude of the aftereffect on the curvature of the
adaptation stimulus. In addition, they showed that the magni-
tude of the aftereffect increased with adaptation time (up to about
10 s) but decreased with increasing interstimulus intervals. Later,
they showed that the aftereffect also occurred when small varia-
tions in the exploration manner were applied, but no aftereffect
was found when the adaptation and test stimuli were touched
by different hands (Vogels, Kappers, & Koenderink, 1997). Finally,
they demonstrated that two consecutively presented adaptation
surfaces together contributed to the magnitude of the aftereffect
(Vogels, Kappers, & Koenderink, 2001). Recently, we presented the
Corresponding author. Tel.: +31 30 2537715; fax: +31 30 2522664.
E-mail address: b.j.vanderhorst@uu.nl (B.J. van der Horst).
existence of an aftereffect when curved surfaces were statically
touched by only a single fingertip (Van der Horst et al., 2008). Fur-
thermore, we found a significant effect when the adaptation and
test stimuli were touched by different fingers, but the magnitude
of this transferred aftereffect was only about 20–25% of the original
effect.
In the present study, we investigated the existence and transfer
of an aftereffect when curved surfaces were explored dynamically
by a single finger. Studying the aftereffect and its transfer can pro-
vide more insight into the representation of perceived curvature
information.
1.1. Exploration modes to perceive curvature
The haptic perception and representation of curvature has been
investigated for several manners of exploration. In this section, we
consider a numb er of studies on static and dynamic curvature per-
ception.
One way to perceive the shape of an object is through static
contact of a single fingertip on a curved stimulus. This exploration
manner is appropriate to obtain information from highly curved
surfaces. Neurophysiological studies have provided evidence that
curvature information is processed on the basis of the response
profile of the population of mechanoreceptors in the fingerpad.
This response profile correlates to the contact shape and the force
that is applied to the finger (Goodwin, Browning, & Wheat, 1995;
Goodwin, Macefield, & Bisley, 1997; Jenmalm, Birznieks, Goodwin,
& Johansson, 2003; LaMotte & Srinivasan, 1993). However, psy-
chophysical studies have shown that this exploration manner is
0028-3932/$ see front matter © 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.neuropsychologia.2008.06.003

B.J. van der Horst et al. / Neuropsychologia 46 (2008) 2966–2972 2967
unsuitable to perceive the shape of weakly curved surfaces, i.e.,
when the curvature is below the 84% threshold of about 7 m
1
(Goodwin, John, & Marceglia, 1991; Pont, Kappers, & Koenderink,
1999).
Nevertheless, the shape of weakly curved stimuli can be per-
ceived by static touch when the contact length with the stimulus
is increased by placing the whole finger or several fingers together
on the stimulus surface (Pont, Kappers, & Koenderink, 1997; Pont et
al., 1999). The thresholds decreased with increasing contact length,
up to about 0.5 m
1
for a contact length of 15 cm.
A different way to perceive the shape of an object is by dynamic
contact between a single fingertip and the object surface. In a
number of psychophysical studies, the curvature of the stimuli
was below the threshold for static touch with a single fingertip
(Davidson, 1972; Gordon & Morison, 1982; Pont et al., 1999). Hence,
movement was required to perceive the shape of the surface. Also in
this case, the discrimination threshold decreased with the increas-
ing contact length. For a contact length of 20 cm, a discrimination
threshold of 0.4 m
1
was found. Similar thresholds were found for
static and dynamic touch, when the same contact length was used
(Pont et al., 1999).
Several other studies have investigated curvature perception by
dynamic touch, but the curvature of the stimuli that were used var-
iedfrom19to120m
1
, which is above the threshold for static touch
with a single finger (Bodegård, Geyer, Grefkes, Zilles, & Roland,
2001; Bodegård et al., 2000; Provancher, Cutkosky, Kuchenbecker,
& Niemeyer, 2005; Van der Horst & Kappers, 2007; Van der Horst
& Kappers, 2008). In such cases, dynamic contact was not required
to perceive the shape of the stimulus, but it might have improved
the accuracy.
1.2. Representation of curvature information
Static and dynamic touch provide different ways to acquire
shape information from an object. Higher performance can be
achieved for dynamic touch than for static touch, in which only
a single finger is used. Dynamic contact b etween the finger and the
stimulus provides additional information about the shape of the
stimulus. This suggests that curvature information is processed in a
different way for dynamic touch. Consequently, the representation
level of the curvature information may depend on the exploration
mode.
More insight into the representation of curvature information
can be obtained by studying the aftereffect and its transfer. In
vision, establishing aftereffect transfer has successfully uncovered
the representation of perceived phenomena like motion (see e.g.,
Mather, Verstraten, & Anstis, 1998; Moulden, 1980; Tao, Lankheet,
van de Grind, & van de Wezel, 2003; Wade, Swanston, & de Weert,
1993). In haptics, the aftereffect transfer paradigm has only scarcely
been employed. Our recent study on the static curvature aftereffect
demonstrated a partial transfer of this effect. We suggested that an
important part of the representation is situated at a neural level
that is directly connected to the processing of the responses of the
mechanoreceptors in the individual finger; a small part of the rep-
resentation is located at a higher, bimanual stage (Van der Horst et
al., 2008).
Analogous to the static aftereffect, establishing the existence
and transfer characteristics of a dynamic curvature aftereffect could
provide information about the representation of dynamically per-
ceived curvature. If similar results are obtained for dynamic touch
as were found for static touch, this would suggest that, irrespective
of the differences in exploration mode, curvature is represented at
similar levels. In contrast, finding different patterns would indicate
that curvature representation occurs in different ways, depending
on the mode of exploration.
1.3. Active and passive dynamic touch
A distinction is made between active and passive dynamic touch.
In active dynamic touch, the subject moves the finger over the sur-
face of a fixed stimulus; in passive dynamic touch, the stimulus
moves underneath a finger that the subject keeps at a fixed posi-
tion. Passive dynamic touch shares with active dynamic touch that
there is an analogous moving contact between the finger and the
stimulus. Therefore, similar results might be expected for active
and passive dynamic touch. However, passive dynamic touch has in
common with static touch that the finger stays in the same location.
If self-induced movement is an important factor, then the results
for passive touch should deviate from the results for active touch.
2. Experiment 1
In the first experiment, we studied the existence and transfer of
a dynamic aftereffect in active and passive dynamic touch.
The first goal was to demonstrate the existence of a curvature
aftereffect in dynamic touch. Gibson (1933) reported the occur-
rence of an aftereffect after three minutes of adaptation. However,
in the current study, we used a shorter adaptation time (11 s), com-
parable to the adaptation times that have been used in studies on
the static aftereffect.
The second purpose of this experiment was to establish whether,
and to what extent, the dynamic aftereffect transfers between both
hands. The transfer characteristics might be similar to those of the
static aftereffect, since the ability to perceive curvature is compa-
rable for static and dynamic touch, when there is controlled for
contact length. However, having the same ability to acquire shape
information does not necessarily imply that this information is rep-
resented at the same level. Moreover, no comparable results were
found for static and dynamic touch when only a single finger was
used. Thus, the transfer pattern might deviate from the transfer
characteristics of static aftereffects, as previously reported (Van der
Horst et al., 2008; Vogels et al., 1997). In order to make a proper
distinction between static curvature representation and dynamic
curvature representation, we use d stimuli in the curvature range
below the threshold for single-finger static touch.Consequently, the
shape could not b e deduced from the immediate contact between
the finger and the stimulus, but movement was required.
The third goal was to determine whether active and passive
dynamic touch demonstrate similar aftereffects. The same results
might be obtained, since there is a comparable moving contact
between the finger and the stimulus. However, there might be
differences in the magnitude of the aftereffect and the extent of
transfer, since there is self-induced movement in the active but not
in the passive case.
2.1. Methods
2.1.1. Design
Four conditions were studied in a two (exploration) × two (finger) design. The
exploration mode was either active or passive dynamic touch. In the active mode, the
stimuli were explored by a self-induced movement with the index finger over the
surface of astationary stimulus. In the passive mode, the stimuli moved underneath a
statically sustained finger. A further distinction was made between the employment
of either a single finger or different fingers. In the same-finger mode, the same index
finger was used to touch both the adaptation and the test stimulus; in the opposite-
finger mode, the right index finger touched the adaptation stimulus, and the left
index finger touched the test stimulus.
2.1.2. Setup
Subjects were seated behind a table, with their arms resting on a support. The
stimuli could be placed in two slits on a platform in front of the support. Only the
right slit was used in the same-finger mode. In the opposite-finger mode, the adapta-
tion stimulus was placed in the right slit, and the test stimulus was placed in the left
slit. In the passive conditions, the platform moved back and forth at a constant speed

2968 B.J. van der Horst et al. / Neuropsychologia 46 (2008) 2966–2972
Fig. 1. Experimental setup. The arms rested on a support that was 19 cm above the
tabletop. The stimuli were placed in slits on a platform, which was 14 cm above the
tabletop. The distance between the centres of the slits was 40 cm. In this example, the
subject explores the concave adaptation stimulus with the right index finger before
touching the test stimulus with the opposite index finger. In the active conditions,
the stimuli remained in a fixed position; in the passive conditions, a computer con-
trolled stepping motor moved the platform. The surface of the stimuli was circularly
curved. The length of the stimuli was 200 mm, and the width was 20 mm. The height
at the side of the stimuli was 40 mm.
of 0.11 m/s, driven by a computer controlled stepping motor. The platform remained
in position in the active conditions. Fig. 1 illustrates the setup of the experiment.
2.1.3. Stimuli
The stimuli were produced from polyvinyl chloride (PVC). The top surface was
a circular cylinder part, which curved either outward (convex) or inward (concave).
One convex adaptation stimulus and one concave adaptation stimulus were used,
with curvature values of +3.8 and 3.8 m
1
, respectively. The curvature of the 10
test stimuli varied from 1.8to+1.8m
1
, in steps of 0.4 m
1
.
2.1.4. Procedure
During a trial, the adaptation stimulus was touched by the index finger of the
right hand for 11 s. Three back-and-forth movements were made during the adap-
tation phase. After 4 s, the test stimulus was touched with an index finger for a
single side-to-side movement. The task of the subject was to indicate whether this
test stimulus felt convex or concave. Practice trials were conducted to accustom the
subjects to the proper exploration time. No feedback was provided.
Each condition consisted of 10 repetitions of a group of 20 trials (2 adaptation
stimuli × 10 test stimuli). The presentation order of the trials within a group was
randomized. A complete condition was measured in a single session, which took
Fig. 2. Examples of two psychometric curves of one subject in an active, same-
finger condition. The response is plotted against the curvature of the test stimulus.
The psychometric curves were obtained by fitting cumulative Gaussians to the data.
The circular data points represent the response when adaptation was performed
with the convex adaptation stimulus; the square data points result from adaptation
with the concave adaptation stimulus. The points of subjective equalities are given
by P
V
and P
C
, respectively. The magnitude of the aftereffect (AE) is defined as the
difference between P
V
and P
C
.
about 90 min. The order in which the experimental conditions were conducted was
partly counterbalanced. One half of the subjects first performed the active con-
ditions followed by the passive conditions; the other half of the subjects started
with the passive conditions. The order in which the same-finger conditions and
the opposite-finger conditions were conducted was counterbalanced among the
subjects.
2.1.5. Subjects
Eight, paid subjects participated (four male and four female, mean age 21 years).
All subjects were right-handed, as established by a standard questionnaire (Coren,
1993).
2.1.6. Analysis
For each subject and condition, the responses in the convex adaptation trials
were separated from the responses in the concave adaptation trials. The fraction of
“convex” responses was calculated for each curvature value of the test stimuli. A
psychometric function (cumulative Gaussian) was fitted to the data to determine
the point of subjective equality (PSE). The PSE is the curvature value that is judged
as convex in 50% of the cases and as concave in 50% of the cases. In other words,
on average, this curvature value is judged as flat. The magnitude of the aftereffect is
defined as the difference between the PSE resulting from convex adaptation (P
V
) and
from concave adaptation (P
C
). Fig. 2 shows an example of the psychometric curves
Fig. 3. (a) Mean results of the aftereffect for eight subjects. The error bars represent the standard errors. In the active conditions, the adaptation and test stimuli were
explored by self-induced exploration with the index finger. In the passive conditions, the stimuli moved underneath the index finger. The dark bars represent the results for
the conditions in which the adaptation and test stimuli were touched by the same index finger. The light bars represent the results for the conditions in which the adaptation
stimulus was touched by the right index finger and the test stimulus was touched by the opposite index finger. (b) Mean results of the aftereffect for eight subjects. In the
active–passive condition, the adaptation stimulus was explored actively, while the test stimulus was touched passively. In the passive–active condition, passive contact with
the adaptation stimulus was followed by active exploration of the test stimulus.

B.J. van der Horst et al. / Neuropsychologia 46 (2008) 2966–2972 2969
for one subject and one condition. The PSEs and the magnitude of the aftereffect are
indicated.
2.2. Results
The mean results for each condition are given in Fig. 3a. The
error bars represent the standard errors. Visual inspection of this
graph shows that an aftereffect was obtained in all conditions.
Most importantly, similar magnitudes of the aftereffect were found
in the same-finger conditions and in the opposite-finger condi-
tions, which points to a complete transfer of the aftereffect. In
addition, the magnitude of the aftereffect was higher in the active
conditions compared to the passive conditions. Statistical analy-
ses confirmed these observations. For each condition, a one-tailed,
one-sample t-test was conducted to determine whether the after-
effect deviated from zero. Significant aftereffects were found in all
conditions (t
7
= 5.4, p < 0.001 for the active same-finger condition;
t
7
= 4.2, p = 0.002 for the active opposite-finger condition; t
7
= 2.9,
p = 0.012 for the passive same-finger condition; t
7
= 9.0, p < 0.001
for the passive opposite-finger condition). A 2 × 2 ANOVA with a
repeated measures design showed a significant main effect for the
factor exploration (F
1,7
= 27.5, p = 0.001) but no significant effects
for the factor finger or for the interaction between exploration and
finger (F
1,7
=0.1,p = 0.7 and F
1,7
= 0.2, p = 0.7, respectively).
2.3. Discussion
This experiment shows the existence of a dynamic curvature
aftereffect and, most surprisingly, a full transfer of this effect. This
result differs from the partial transfer of the static curvature afteref-
fect, as obtained in our previous study (Van der Horst et al., 2008).
To place the finding in a broader perspective, only some specific
visual motion aftereffects show a full interocular transfer. In gen-
eral, there is only partial transfer of the effect, the strength of which
depends on several stimulus and measurement parameters (Tao et
al., 2003; Wade et al., 1993). Our finding of a complete transfer
suggests that curvature perception by dynamic touch is a complex
process that is represented at a high level in the brain. A further
account of this finding will be provided in the general discussion.
Complete intermanual transfer was found for both active and
passive touch, but the magnitude of the aftereffect was higher in
the active conditions than in the passive conditions. The fact that
we found a complete transfer of the aftereffect in both active and
passive dynamic touch suggests that curvature information is rep-
resented similarly in both exploration modes; however, analogous
phenomena do not necessarily share a common representation.
Furthermore, the difference in magnitude of the aftereffect indi-
cates that there are differences in curvature representation of active
and passive dynamic touch. Therefore, we performed a second
experiment to determine whether adaptation by active dynamic
touch induces an aftereffect in passive dynamic touch, and vice
versa.
3. Experiment 2
In the second experiment, the transfer between active and
passive dynamic touch was investigated. Two conditions were con-
sidered. In the active–passive condition, adaptation was performed
by active dynamic touch, and testing was performed by passive
dynamic touch. In the passive–active condition, the order was
reversed. In both conditions, subjects used only their right hands
for adaptation and testing.
Before the experiment, we formulated two main hypotheses.
One hypothesis was that there would not be a transfer between
active and passive touch. This would imply that the existence and
intermanual transfer of the aftereffect for active and passive touch
are analogous phenomena but do not share a common representa-
tion. The other hypothesis predicted that there would be a transfer
between active and passive touch, which would suggest that both
exploration modes share a common representation. In this case,
several results were possible. First, a similar aftereffect could be
found in both conditions; only the representation shared by active
and passive touch would be reflected by the aftereffect. Second, a
higher aftereffect could be obtained in the active–passive condi-
tion; this would suggest that active and passive touch share the
same representation, but adaptation is stronger for active touch.
Third, a stronger aftereffect could be found in the passive–active
condition. In this case, the manner of touch during the test phase,
not the exploration mode in the adaptation phase, determines the
magnitude of the aftereffect.
3.1. Methods
The same setup was used for this experiment as in the previous experiment. We
did not use the ±1.8 m
1
stimuli but increased the number of repetitions per stimu-
lus. As a result, each condition consisted of 192 trials in total (12 repetitions of a group
of 2 × 8 trials). The order in which the experiment was performed was counterbal-
anced among subjects. There were eight, right-handed subjects (four male and four
female, mean age 21 years), none of whom were involved in the first experiment.
3.2. Results
The mean results for each condition are presented in Fig. 3b.
Significant aftereffects were found in both conditions, as one-
tailed, one-sample t-tests demonstrated (t
7
= 4.8, p = 0.001 for the
active–passive condition; t
7
= 7.8, p < 0.001 for the passive–active
condition). A dependent-samples t-test showed that the magni-
tude of the aftereffect was significantly higher in the passive–active
condition than in the active–passive condition (t
7
= 2.8, p = 0.025).
Independent samples t-tests were performed in order to com-
pare the results of the second experiment to the same-finger results
of the first experiment. The magnitude of the aftereffect for the
active–passive condition did not differ significantly from the active
and passive conditions of the first experiment (t
14
= 1.4, p =0.18,
t
14
= 1.5, p = 0.16, respectively). The result for the passive–active
condition was not significantly different from that of the active con-
dition but was significantly higher than that of the passivecondition
(t
14
= 0.7, p = 0.5 and t
14
= 3.9, p = 0.001, respectively).
3.3. Discussion
This experiment reveals an aftereffect transfer from active to
passive dynamic touch, and vice versa. The magnitude of the
effect was higher in the passive–active condition than in the
active–passive condition. The correspondence between the first
and the second experiment is that a stronger aftereffect is obtained
when the test stimulus is actively explored, irrespective of the man-
ner of touching the adaptation stimulus.
4. General discussion
4.1. The existence of a dynamic curvature aftereffect
We demonstrated the occurrence of an aftereffect when curved
surfaces are dynamically touched with a single index finger. This
finding is a considerable extension of the original discovery of
Gibson (1933), since we employed a quantitative approach and dis-
played the existence of the effect for a relatively short adaptation
time. In this respect, the dynamic curvature aftereffect is similar to
previously reported static curvature aftereffects (Van der Horst et
al., 2008; Vogels et al., 1996).

2970 B.J. van der Horst et al. / Neuropsychologia 46 (2008) 2966–2972
4.2. Dynamic touch versus static touch
One of the most important findings of this study is the complete
intermanual transfer of the dynamic curvature aftereffect. The mag-
nitude of the aftereffects in the opposite-finger and same-finger
conditions was the same. In contrast, no intermanual transfer has
been demonstrated for the static whole-hand aftereffect (Vogels
et al., 1997); only partial transfer has been found for the static
single-finger aftereffect (Van der Horst et al., 2008). This dissim-
ilarity between the transfer of the dynamic curvature aftereffect
and transfer of the static curvature aftereffect indicates that the
representation of curvature perceived by dynamic touch deviates
considerably from the representation of curvature perceived by
static touch. The origin of this difference might be found at the basis
of curvature perception, namely, the way in which curvature infor-
mation is achieved by the finger(s). In the subsequent paragraphs,
we consider how curvature information can be derived from static
and dynamic contact with a stimulus surface.
When a single finger is in static contact with a stimulus sur-
face, the indentation profile of the stimulus on the finger is directly
related to the shape of the surface (Fig. 4a). The curvature of the
surface can be derived by assembling the responses of the cuta-
neous mechanoreceptor population in the finger pad (Goodwin &
Wheat, 2004; Van der Horst et al., 2008). For weakly curved stim-
uli, the local, immediate contact of the finger on the stimulus does
not provide sufficient information about the shape of the stimulus,
since the curvature of the stimulus is below the threshold for single-
finger static touch (Goodwin et al., 1991; Pont et al., 1999). However,
the shape can be perceived by static touch when the whole hand or
different parts of the hand are in contact with the stimulus surface.
In this case, the shape may be derived from combining the local
slant at each contact point with knowledge about the position of
the fingers (see Fig. 4a). Note that for single-finger static touch as
well as multi-finger static touch, the available information remains
constant in time.
The situation is different for dynamic touch. Since the immedi-
ate contact of a single finger is insufficient, curvature information
must be derived from the dynamic contact between the finger
and the stimulus surface. Several events occur simultaneously and
change over time when the finger makes a horizontal movement
over the stimulus surface: the finger skin slips and stretches; the
finger is displace d in the vertical direction; the orientation of the
finger with respect to the external space (rotation around the finger
axis) and to the stimulus surface (change in contact point) may be
altered (Fig. 4b).
The question is how the shape of the stimulus can be deduced
from various information sources. Theoretically, knowing the start-
ing position, the vertical displacement is the only information
Fig. 4. (a1) Illustration of convex and concave stimuli in contact with a single finger by static touch. There is a direct relationship between the shape of the stimulus and its
indentation profile on the finger. (a2) Static touch with different parts of the hand that contact the stimulus surface (in this case, three fingers). Local slant information from
each contact point must be combined with information about the position of the finger in order to obtain curvature information from the stimulus surface. (b) Illustrations of
information sources when there is dynamic contact between the finger and a stimulus. (b1) The finger slips and stretches due to friction between the finger and the stimulus.
The deformation depends on the direction of movement contact, as indicated by an arrow. (b2) The orientation of the finger with respect to the external space can change
(rotation), when the finger moves over the stimulus surface. In the example, the finger remains parallel to the stimulus surface. In this specific situation, the point of contact
on the finger does not change. Besides, the finger displaces in the vertical direction, but this displacement is too small to provide sufficient information. (b3) The orientation
of the finger with respect to the stimulus surface can change when the finger moves over the surface. As a consequence, the contact point can change. In the example, the
finger does not rotate.

Figures (4)
Citations
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Journal ArticleDOI
TL;DR: This paper surveys the research literature on robust tactile and haptic illusions by briefly considering a number of important general themes that have emerged in the materials surveyed.
Abstract: This paper surveys the research literature on robust tactile and haptic illusions. The illusions are organized into two categories. The first category relates to objects and their properties, and is further differentiated in terms of haptic processing of material versus geometric object properties. The second category relates to haptic space, and is further differentiated in terms of the observer's own body versus external space. The illusions are initially described and where possible addressed in terms of their functional properties and/or underlying neural processes. The significance of these illusions for the design of tactile and haptic displays is also discussed. We conclude by briefly considering a number of important general themes that have emerged in the materials surveyed.

118 citations


Cites background from "Transfer of the curvature aftereffe..."

  • ...The haptic curvature aftereffect is a robust phenomenon that has received a fair amount of attention [112], [113], [114], [115]: a flat surface feels curved (convex/concave) after haptic exploration of a curved shape (concave/convex, respectively) that can last as long as 60 s [112] or as short as 10 s [113], [114], [115]....

    [...]

  • ...Typically, following some relatively brief ( 1 min) period of passive or active stimulation such as feeling a textured surface move across the skin or actively exploring a curved surface, a stationary stimulus presented to the same area of skin is perceived to move [212], [213] or a flat surface feels curved [115]....

    [...]


Journal ArticleDOI
TL;DR: The role of active touch in three aspects of shape perception and discrimination studies is focused on, and the presence of strong after-effects after just briefly touching a shape is addressed.
Abstract: In this paper, I focus on the role of active touch in three aspects of shape perception and discrimination studies. First an overview is given of curvature discrimination experiments. The most prominent result is that first-order stimulus information (that is, the difference in attitude or slope over the stimulus) is the dominant factor determining the curvature threshold. Secondly, I compare touch under bimanual and two-finger performance with unimanual and one-finger performance. Consistently, bimanual or two-finger performance turned out to be worse. The most likely explanation for the former finding is that a loss of accuracy during intermanual comparisons is owing to interhemispheric relay. Thirdly, I address the presence of strong after-effects after just briefly touching a shape. These after-effects have been measured and studied in various conditions (such as, static, dynamic, transfer to other hand or finger). Combination of the results of these studies leads to the insight that there are possibly different classes of after-effect: a strong after-effect, caused by immediate contact with the stimulus, that does only partially transfer to the other hand, and one much less strong after-effect, caused by moving over the stimulus for a certain period, which shows a full transfer to other fingers.

37 citations


Journal ArticleDOI
TL;DR: An organised overview of the main variables in touch experiments is presented, compiling aspects reported in the tactual literature, and attempting to provide both a summary of previous findings, and a guide to the design of future works on tactual perception and memory through a presentation of implications from previous studies.
Abstract: This paper reviews the literature on tactual perception. Throughout this review, we will highlight some of the most relevant aspects in the touch literature: type of stimuli; type of participants; type of tactile exploration; and finally, the interaction between touch and other senses. Regarding type of stimuli, we will analyse studies with abstract stimuli such as vibrations, with two- and three-dimensional stimuli, and also concrete stimuli, considering the relation between familiar and unfamiliar stimuli and the haptic perception of faces. Under the “type of participants” topic, we separated studies with blind participants, studies with children and adults, and also performed an overview of sex differences in performance. The type of tactile exploration is explored considering conditions of active and passive touch, the relevance of movement in touch and the relation between haptic exploration and time. Finally, interactions between touch and vision, touch and smell and touch and taste are explored in the last topic. The review ends with an overall conclusion on the state of the art for the tactual perception literature. With this work, we intend to present an organised overview of the main variables in touch experiments, compiling aspects reported in the tactual literature, and attempting to provide both a summary of previous findings, and a guide to the design of future works on tactual perception and memory, through a presentation of implications from previous studies.

28 citations


Journal ArticleDOI
TL;DR: The nature of the aftereffects are investigated, demonstrating that they are orientation- and skin-region–specific, occur even when just one hand is adapted, do not transfer either contralaterally or across the palm and dorsum, and are defined in a skin-centered, rather than an external, reference frame.
Abstract: The stage at which processing of tactile distance occurs is still debated. We addressed this issue by implementing an adaptation-aftereffect paradigm with passive touch. We demonstrated the presence of a strong aftereffect, induced by the simultaneous presentation of pairs of tactile stimuli. After adaptation to two different distances, one on each hand, participants systematically perceived a subsequent stimulus delivered to the hand adapted to the smaller distance as being larger. We further investigated the nature of the aftereffects, demonstrating that they are orientation- and skin-region–specific, occur even when just one hand is adapted, do not transfer either contralaterally or across the palm and dorsum, and are defined in a skin-centered, rather than an external, reference frame. These characteristics of tactile distance aftereffects are similar to those of low-level visual aftereffects, supporting the idea that distance perception arises at early stages of tactile processing.

25 citations


Journal ArticleDOI
TL;DR: Curvature discrimination performance was best in the current study when dynamic cutaneous stimulation occurred in the absence of active movement, and for both age groups, the curvature discrimination thresholds obtained for passive touch were significantly lower than those that occurred during active touch.
Abstract: Our tactual perceptual experiences occur when we interact, actively and passively, with environmental objects and surfaces. Previous research has demonstrated that active manual exploration often enhances the tactual perception of object shape. Nevertheless, the factors that contribute to this enhancement are not well understood. The present study evaluated the ability of 28 younger (mean age was 23.1 years) and older adults (mean age was 71.4 years) to discriminate curved surfaces by actively feeling objects with a single index finger and by passively feeling objects that moved relative to a restrained finger. While dynamic cutaneous stimulation was therefore present in both conditions, active exploratory movements only occurred in one. The results indicated that there was a significant and large effect of age, such that the older participants’ thresholds were 43.8 percent higher than those of the younger participants. Despite the overall adverse effect of age, the pattern of results across the active and passive touch conditions was identical. For both age groups, the curvature discrimination thresholds obtained for passive touch were significantly lower than those that occurred during active touch. Curvature discrimination performance was therefore best in the current study when dynamic cutaneous stimulation occurred in the absence of active movement.

9 citations


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Abstract: On the basis of computational studies it has been proposed that the central nervous system internally simulates the dynamic behavior of the motor system in planning, control, and learning; the existence and use of such an internal model is still under debate. A sensorimotor integration task was investigated in which participants estimated the location of one of their hands at the end of movements made in the dark and under externally imposed forces. The temporal propagation of errors in this task was analyzed within the theoretical framework of optimal state estimation. These results provide direct support for the existence of an internal model.

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"Transfer of the curvature aftereffe..." refers background in this paper

  • ...An accurate movement can be made when the efferent copy of the outgoing motor command is integrated with afferent sensory information (Flanagan, Bowman, & Johansson, 2006; Gritsenko, Krouchev, & Kalaska, 2007; Wolpert, Ghahramani, & Jordan, 1995 )....

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"Transfer of the curvature aftereffe..." refers background in this paper

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TL;DR: The remarkable manipulative skill of the human hand is not the result of rapid sensorimotor processes, nor of fast or powerful effector mechanisms, Rather, the secret lies in the way manual tasks are organized and controlled by the nervous system.
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"Transfer of the curvature aftereffe..." refers background in this paper

  • ...Concerning the adaptation phase, it is not unlikely that both actively and passively acquired curvature information can cause a change in the movement planning during active testing, since information from different perceptual inputs can influence motor planning (see e.g., Flanagan et al., 2006; Goodwin & Wheat, 2004; Gordon, Forssberg, Johansson, & Westling, 1991)....

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Abstract: Motion perception lies at the heart of the scientific study of vision. The motion aftereffect (MAE), probably the best known phenomenon in the study of visual illusions, is the appearance of directional movement in a stationary object or scene after the viewer has been exposed to visual motion in the opposite direction. For example, after one has looked at a waterfall for a period of time, the scene beside the waterfall may appear to move upward when ones gaze is transferred to it. Although the phenomenon seems simple, research has revealed surprising complexities in the underlying mechanisms, and offered general lessons about how the brain processes visual information. In the last decade alone, more than 200 papers have been published on MAE, largely inspired by improved techniques for examining brain electrophysiology and by emerging new theories of motion perception. The contributors to this volume are all active researchers who have helped to shape the modern conception of MAE. Contributors: David Alais, Stuart Anstis, Patrick Cavanagh, Jody Culham, John Harris, Michelle Kwas, Timothy Ledgeway, George Mather, Bernard Moulden, Michael Niedeggen, Shin'ya Nishida, Allan Pantle, Robert Patterson, Jane Raymond, Michael Swanston, Peter Thompson, Frans Verstraten, Michael von Grunau, Nicolas Wade, Eugene Wist.

303 citations


"Transfer of the curvature aftereffe..." refers background in this paper

  • ...In vision, establishing aftereffect transfer has successfully uncovered the representation of perceived phenomena like motion (see e.g., Mather, Verstraten, & Anstis, 1998; Moulden, 1980; Tao, Lankheet, van de Grind, & van de Wezel, 2003; Wade, Swanston, & de Weert, 1993)....

    [...]


Frequently Asked Questions (2)
Q1. What contributions have the authors mentioned in the paper "Transfer of the curvature aftereffect in dynamic touch" ?

Van der Horst et al. this paper investigated the transfer of curvature aftereffect when curved surfaces were explored dynamically by a single finger. 

This finding raises interesting questions about the importance of self-induced movement in dynamic touch, which might be the subject of future studies.