Exp Brain Res (2009) 193:483–489
DOI 10.1007/s00221-009-1711-y

R ES EA R C H N O T E

Haptic localizations for onset and oVset of vibro-tactile stimuli
are dissociatedJunji Watanabe · Masashi Nakatani · Hideyuki Ando ·Susumu Tachi

Received: 9 February 2008 / Accepted: 9 January 2009 / Published online: 6 February 2009
© Springer-Verlag 2009

Abstract When humans explore the external world, handand arm movements play important roles. Spatio-temporalarrangements of the environment are perceptually generated mainly by means of the sensory–motor integration of
the internal model of these movements with the information
obtained during the movements. In order to investigate themechanisms of this integration process, localization tasks
have been studied, and previous studies have suggested thatthe integration process does not work properly around thetime of a hand movement. In particular, when a transient
vibro-tactile stimulation is presented before, during, or after
a hand movement, the stimulus is systematically mislocalized. However, it is debatable whether the tendency tomislocalize a transient stimulus indicates a general failureof the sensory-motor integration process. Here we investigated the generality of the tendency towards mislocalization

J. Watanabe (&)
PRESTO Japan Science and Technology Agency,
3-1 Morinosato-Wakamiya, Atsugi,
Kanagawa 243-0198, Japane-mail: watanabe@avg.brl.ntt.co.jp
J. Watanabe
Human and Information Science Laboratory,
NTT Communication Science Laboratories,
NTT Corporation, 3-1 Morinosato-Wakamiya,
Atsugi, Kanagawa 243-0198, Japan
M. Nakatani · S. Tachi
Graduate School of Information Science and Technology,
The University of Tokyo, 7-3-1, Hongo, Bunkyo,
Tokyo 113-8656, Japan
H. AndoGraduate School of Information Science and Technology,
Osaka University, 2-1, Yamadaoka, Suita,
Osaka 565-0871, Japanby observing haptic localizations to diVerent target types,
the onset and oVset of continuous vibro-tactile stimuli. We
found similar types of mislocalizations in responses to thetransient vibration and the onset of a continuous vibration,
and a clear diVerence in the types of mislocalizations in
responses to the onset and oVset of continuous vibrations.
Keywords Haptic localization · Hand movement ·Internal representation · Sensory–motor system ·Vibro-tactile stimulation

Introduction
Humans move the hand, a sensitive and active probe, forperceiving spatio-temporal arrangements in a dynamic
environment. When the hand is moved from one position toanother and makes contact with an object during the movement, humans can localize the contact position even without visual guidance. This is because the sensory–motor
system can integrate the internal hand movement information with the temporal information about the contact fromthe periphery. The internal representation of the arm andhand is fundamental for accurate motor movements andspatial cognition (Paillard and Brouchon 1968; Horch et al.
1975; Sittig et al. 1987; Cordo 1990; Cordo et al. 1994;
Krakauer et al. 1999; Haggard et al. 2000). Internal modelsof hand movements, mainly forward models, have been
intensively studied (Kawato et al. 1987; Wolpert et al.
1995; Flanagan and Lolley 2001; Johnson et al. 2002).
Spatial localization tasks and temporal order judgmenttasks are eVective techniques for investigating how theinternal representation of the movement and the information obtained during the movement are integrated in thebrain (McCloskey et al. 1983; Jirsa et al. 1992; Dassonville

123

484

1995; Azuma and Haggard 1999; Nijhawan and Kirschfeld2003). In such tasks, a visual, auditory, or vibro-tactile
stimulus is presented around the time of a hand movement,
and participants are asked to point out the stimulated position or compare the stimulation timing with the timing of
the hand movement. These previous reports indicated thatthe sensory–motor integration does not work perfectly. In
particular, when a transient vibro-tactile stimulation waspresented before, during, or after the hand movement, thestimulus was systematically mislocalized (Dassonville1995). The participants localized the stimulus toward the
direction of the hand movement around the time when the
movement began, even when the stimulus was presented
before the hand movement.
However, it is debatable whether the errors in localization to a transient stimulation suggest a general failure of
the sensory–motor integration process. SpeciWc eVect arising from the transient stimulus itself may contribute to the
localization errors. Typical environments exhibit a highdegree of spatio-temporal coherence, and the localization tocontinuous stimuli may tend to diVer, as observed in visual
localization at the time of oculo-motor movement (See Cai
et al. 1997; van Beers et al. 2001; Watanabe et al. 2005).
Here we investigated the generality of the mislocalization
tendency by observing haptic localizations in response todiVerent target types. In our experiments, the onset timing,
the oVset timing, and the duration of the vibration were systematically varied. We asked participants to manually point
to the perceived position of the onset or oVset of a presented vibration. In the Wrst experiment, the time course of
the localization to a transient vibration was measured, andthe measured time course served as the basis for comparing
the data with subsequent experiments. In the second andthird experiments, a continuous vibration was presented
until long after, or from long before the hand movement,
and the onset or oVset of the vibration was varied. The participants localized the onset or oVset of the continuous
vibration.

Materials and methods
Participants
Four right-handed participants (three naive males, and one
male author), aged from 22 to 26 years, performed all
experiments.
Apparatus
A small disk-shaped vibrating motor (NEC TOKIN Corporation, Miyagi, Japan, TYPE33) was mounted on the nail of theright index Wnger of the participant with double-sided sticky

123

Exp Brain Res (2009) 193:483–489

tape. The vibration motor was 16 mm in diameter, 4 mm inwidth, and 4 g in weight, and the vibration frequency was
130 Hz. The participant was instructed to make a rapid rightward hand movement with the right arm along an aluminum
bar, as shown in Fig. 1a. The motor was activated at aroundthe time of the hand movement. A thin electric wire that connected the motor to a microcomputer (Microchip Technology
Inc., Arizona, USA, PIC18F452), which controlled the
motor. The position of the index Wnger was measured using alaser displacement sensor (KEYENCE, Osaka, Japan, LK500). The sampling rate of the sensor was 1,024 samples per
second. Data from the microcomputer and the laser displacement sensor were collected in a PC using a data logger(KEYENCE, Osaka, Japan, NR-2000) after irrelevant noise
had been removed from the data by a low-pass Wlter (cut-oV
frequency, 2.5 kHz). The sampling rate of the logger was
1,000 samples per second. The timings of the vibration andtime course of Wnger movement were recorded together.
Procedure
A participant sat with his right index Wnger on a thin aluminum bar. At the beginning of each trial, an audio signal(100 Hz) was presented, and the participant immediately
made a rightward hand movement along the bar. A vibrotactile stimulus was presented before, during, or after thehand movement. After the hand movement, the participantmanually pointed to the stimulus location with their rightindex Wnger. When the location had been decided, theypushed a button with their left Wnger to record the indicatedlocation and then placed their right index Wnger at the initial
position on the aluminum bar (The initial position wasmarked with sticky tape). When they were ready, theypushed the button again, and the next trial began.
Participants performed all experiments with their eyes
closed, and the vibration was inaudible, so that they could
only perform the localization using internal sensory–motor
information. The trip length and duration of the hand movement were about 400 mm and 300 ms, respectively. The
participants practiced performing the appropriate hand
movement (with a clear start and termination and with stable length and duration) before the experiments.
We used three types of vibro-tactile stimuli. Figure 1b
shows the timings of these stimuli. In the Wrst condition(S1), the duration of the stimulus was 20 ms, which was
similar to the duration of the transient vibration used by
Dassonville (1995). This vibration duration was suYcientfor detecting the stimulus, even during hand movement. In
the second condition (S2), the vibration began around thetime of the hand movement and continued for about 1 s
after it. The participants indicated the onset position of thecontinuous vibration. In the third condition (S3), thevibration started long before the hand movement initiation

Exp Brain Res (2009) 193:483–489
Fig. 1 a Experimental conWguration. b Timing charts ofpresented vibro-tactile stimuli.
c When the latency for the onset
is longer than that of the eVerent
copy, a mislocalization toward
the hand movement can beobserved before the hand
movement. d When the latency
for the oVset is shorter than thatof the eVerent copy, amislocalization in the direction
opposite to the hand movement
can be observed around the endof the hand movement.
e Reaction times in response to
the transient vibration (left),vibration onset (center), andvibration oVset (right) inmilliseconds. The vibrations
were presented to the nail of theright index Wngers with thehands static. Then, theparticipants immediately pushed
the button with their left index
Wngers. The averages andstandard errors for 60 trials areshown. (*p < 0.05, **p < 0.01)

485

a

c

Vibrator

Beep

hand trajectory

400 mmhand movement
IP

b

TP

Beep

efferent copy

Longerlatencyfor onset

Mislocalization

hand trajectory

Time

d

Beep
Shorterlatencyfor offset

hand trajectory

Vibration positionTimeeefferent copy

S1
S2
S3
Transient Onset Offset

Reaction Time (ms)*** * MN

300

MS

**
**

Mislocalization
TU

JY

Time

200
100
0

S1

S2

S3

S1

S2

S3

(about 2–4 s before, randomized) and ceased around thetime of the hand movement. The oVset position of thevibration was localized.
The total number of trials for each stimulus condition was
240, divided into eight blocks of 30 trials (8 £ 30). The orderof the stimulus conditions was randomized between blocks,
and the same type of stimulus was presented in a block.
Data analysis
We excluded trials in which the participants moved theirWnger over too short or long a distance (shorter than
350 mm or longer than 450 mm), for too short or long a
duration (shorter than 200 ms or longer than 400 ms), or forearly or late latency (shorter than 200 ms or longer than
500 ms). The start and end times of hand movement were
deWned as time that hand movement speed exceeded andbecame lower than 500 mm/s, respectively.

Results
All results in the three stimulus conditions are shown in
Figs. 2 and 3. The same data are plotted with regards to

S1

S2

S3

S1

S2

S3

absolute reported position in Fig. 2 and localization error in
Fig. 3. The individual data points for each participant (MN,
MS, JY, TU) are shown in Figs. 2a–c and 3a–c. Averages
across the four participants are shown in Figs. 2d and 3d.
The horizontal axis represents the time diVerence from theinitiation of the hand movement to the time the onset(Figs. 2a, b, 3a, b) or oVset (Figs. 2c, 3c) of the vibro-tactile
stimulus was presented in milliseconds. A negative valuemeans that the stimulus was presented before the hand
movement. The yellow areas (0–300 ms on the horizontalaxis) indicate the time range of the hand movement. The
vertical axes represent the reported absolute position in
Fig. 2 and amount of localization error in Fig. 3 inmillimeters.
The results of transient vibration localizations (S1) are
shown in the Wrst column from the left (Figs. 2a, 3a).
Mislocalizations toward hand movement were observed in
the data for all participants. The mislocalizations initiatedabout 100 ms before the hand movement and continued
until the end of the hand movement. The amount of mislocalization was maximized in the early time range of thehand movement (around 0–100 ms). These results are
consistent with those reported by Dassonville (1995),
although the amount of mislocalization was smaller than in

123

486
Fig. 2 Localization results.
Horizontal and vertical axes represent the time to hand movement initiation in milliseconds
and the reported location inabsolute coordinate in millimeters, respectively. a Transient
vibration condition (S1).
b Vibration onset condition (S2).
c Vibration oVset condition (S3).
Results of all valid trials andcurves and data points that show
the averages of the data in
100-ms bins are shown. The
solid curve denotes the meantime course of the hand
movement. The numbers ofvalid trials, obtained after thedata analysis, are shown in the
Wgures. d Curves and data points
that average the data in the
100-ms bins across the four
participants. The individual data
were normalized to the standard
amplitude (400 mm) before
averaging. Red circles, green
triangles, and blue crosses
represent the averaged data fortransient vibration, vibration
onset, and vibration oVset,
respectively

Exp Brain Res (2009) 193:483–489

aTransient Vibration (S1)
Absolute
position (mm)
n=179
500
400
300
200
100
0
MN
−100
−200
−200
0
200
400
500
400
300
200
100
0
−100
−200
−200
500
400
300
200
100
0
−100
−200
−200
500
400
300
200
100
0
−100
−200
−200

n=217

MS

0

200

400
n=158

JY

0

200

400
n=197

TU

0

200

400

b

Vibration Onset (S2)Absolute
position (mm)
n=222
500
400
300
200
100
0
MN
−100
−200
−200
0
200
400
500
400
300
200
100
0
−100
−200
−200
500
400
300
200
100
0
−100
−200
−200
500
400
300
200
100
0
−100
−200
−200

n=200

MS

0

200

400
n=142

JY

0

200

400
n=201

TU

0

200

400

c

Vibration Offset (S3)Absolute
position (mm)
n=226
500
400
300
200
100
0
MN
−100
−200
−200
0
200
400
n=191

500
400
300
200
100
0
−100
−200
−200

MS

0

JY

0

0

350
300
250
200
150
100
50

0

100

200

300

400

Time to hand movement start time (ms)

123

400

TU

400

-100

200

n=179

500
400
300
200
100
0
−100
−200
−200

Normalized absolute position (mm)

0
-200

400
n=146

500
400
300
200
100
0
−100
−200
−200

Time to hand movement start time (ms)

d

200

500

200

400

Exp Brain Res (2009) 193:483–489
Fig. 3 Localization results
represented as amount of error.
Horizontal and vertical axes
represent the time to hand
movement initiation in
milliseconds and the amount oflocalization error in millimeters,
respectively. a Transient
vibration condition (S1).
b Vibration onset condition (S2).
c Vibration oVset condition (S3).
Results of all valid trials andcurves and data points that show
the averages of the data in
100-ms bins are shown. dCurves and data points that
average the data in the 100-ms
bins across the four participants.
Error bars indicate the standard
errors. The individual data werenormalized to the standard
amplitude (400 mm) before
averaging. Red circles, green
triangles, and blue crosses
represent the averaged data fortransient vibration, vibration
onset, and vibration oVset,
respectively

487aTransient Vibration (S1)Amount of
localization error (mm)
n=179
300

b

Vibration Onset (S2)Amount of
localization error (mm)
n=222
300

c

200

200

200

100

100

100

0

0

0

−100
−200
−200

MN

0

200

400

−100

n=217

300

MN

−200
−200

0

200

400
n=200

300

Vibration Offset (S3)Amount of
localization error (mm)
n=226
300

−100
−200
−200

200

200

100

100

100

0

0

0

−200
−200

MS

0

200

400

−100
−200
−200

n=158

300

MS

0

200

400
n=142

300

−200
−200

200

200

100

100

0

0

0

JY

0

200

400

−100

n=197

300

JY

−200
−200

0

200

400
n=201

300
200

200

100

100

100

0

0

0

−100

−100

−200
−200

TU

0

200

400

TU

−200
−200

0

200

400

0

200

−200
−200

400
n=146

JY

0

200

400
n=179

300

200

−100

MS

−100
−200
−200

400
n=191

300

100

−200
−200

200

−100

200

−100

0

300

200

−100

MN

TU

0

200

400

Time to hand movement start time (ms)dAmount of localization error (mm)
100

50

0

-50
-200

-100

0

100

200

300

400

500

Time to hand movement start time (ms)

123

488

Dassonville’s experiments, in which the hand traveled a
longer distance (520 mm) than in our experiment (400 mm).
The results of onset localizations (S2) are shown in thesecond column from the left (Figs. 2b, 3b). Generally, theerrors in localization to the onsets of the continuous vibrotactile stimuli showed the same tendency as those inlocalization to the transient vibrations. Errors in the same
direction as the hand movement started around 100 ms
before the hand movement and continued until the end of
the hand movement. The maximum magnitudes of mislocalizations were comparable to or larger than those to thetransient vibration in the data for all participants.
The results of oVset localizations (S3) are shown in thethird column from the left (Figs. 2c, 3c). Although the data
were more scattered and the magnitude of the localization
error was smaller than in the other conditions, these errors
showed a diVerent tendency from those in the previous two
conditions. SpeciWcally, in addition to the mislocalizations
toward the direction of the hand movement observed in theearly range of the hand movement, the mislocalizations in
the opposite direction were observed in the later range ofthe hand movement.
The averaged data across the four participants (Figs. 2d,3d) clearly demonstrate the diVerence in the localizations to
the onset and oVset of vibrations. The curve of oVset localization always falls below the other curves in absolutereported position (Fig. 2d), and widely diverges from thoseof the other conditions in the amount of localization error(Fig. 3d).
In summary, our results showed a similar trend in mislocalizations to the transient vibration and to the onset of acontinuous vibration; mislocalization in the same directionin the early time range was the dominant component. The
results also showed a clear diVerence in the trend in mislocalizations to the onset and oVset of continuous vibrations;mislocalization to the oVset was observed both in the same
direction in the early time range and in the opposite direction in the later time range. It appears that the mislocalizations to the oVset exhibit a bifurcation, with some of themin the same direction and others in the opposite direction of
the hand movement.

Discussion
Since our experiments were performed without visual guidance, the only available information was the internal representation of the hand movement and the timing informationof the sensory input (the vibration stimulus on the nail).
The internal representation used for the localization task
would be the eVerent copy (the copy of a motor commandfrom the central nervous system to move the hand) (Sperry
1950; von Holst 1954), because the participants performed

123

Exp Brain Res (2009) 193:483–489

fast hand movements and aVerent information from theperiphery would be subjected to signiWcant delays due tothe transduction latency of the peripheral nerves. As suggested in the study by Dassonville (1995), the mislocalizations could be due to both an inaccurate representation of
the hand movement and the lack of a mechanism to register
the timing information. In agreement with this argument
and analogous investigations in the peri-saccadic mislocalization literature (Boucher et al. 2001; Georg et al. 2008),
our experimental results showed that the mislocalizations
diVered with diVerent target types.
How can the diVerence in the onset and oVset localizations be explained? Regardless of whether the internal representation is inaccurate or not, it seems that the sameinternal representation would be referred for the three localization tasks. If so, the dissociation of the time courses
between the onset and oVset localizations should be
ascribed to the diVerence in the timing information of thesensory input. It is, however, unclear at which level thediVerence could be generated; it could be in the level ofneural signal, encoding, or higher cognitive strategy.
Considering the diVerence in the level of neural signal,
since the time required for the mechanoreceptors to respondto the onset or oVset of the vibration makes little diVerence(Johansson and Westling 1987), the diVerence in the timingof neural signal, such as that induced by transduction
latency, might therefore be a key factor. As shown in
Figs. 1c and 1d, it could be assumed that the relatively
longer or shorter latencies of the sensory input comparedwith the latency of the eVerent copy result in a mislocalization in the direction of the hand movement before themovement begins, or a mislocalization in the opposite
direction during and after the movement, respectively.
However, the latencies measured in the simple reaction
time task (Fig. 1e and its legend) did not show a consistenttendency in conjunction with the localization results
between individuals, though some signiWcant eVects(p < 0.05) were observed within each individual data set.
Primarily, the assumption that the latency is constantthroughout a hand movement cannot explain the bifurcationof the oVset localization. Although it has been reported thatthe detection threshold (Dyhre-Poulsen 1975) and the subjective intensity of suprathreshold stimuli (Milne et al.
1988; Post et al. 1994) could be changed at around the timeof hand movement, the reason that the diVerent tendency
was observed only for oVset localization is still unclear.
This discrepancy between localization and latencies
might be due to the level of information encoding. An interesting report in the Weld of visual psychophysics could be
related to this discrepancy. Boucher et al. (2001) reported
that the mislocalization around the time of saccadic eye
movement could be changed by modulations in luminanceintensity, which caused Xuctuations in processing time inExp Brain Res (2009) 193:483–489

the brain, and that the amount of change in observed mislocalization did not coincide with the amount expected fromthe diVerences in processing time. As observed in the visual
modality (Jaskowski 1996; Nishida and Johnston 2002;
Terao et al. 2008), in the tactile modality as well, how thetiming information is encoded for perceptual tasks such as
localization may not directly reXect the timing of the neuralsignals.
Finally, the diVerence might be a result from a diVerencein the localization strategies, which are used at the cognitive level, rather than from the diVerence in the sensory
information processing. A diVerent strategy may be used
when the target is an oVset, namely, the oVset may be mislocalized as having occurred at the center of the hand
movement. Another possibility is that, although a typicalstrategy may be used regardless of target types, other strategies may be used in some trials only when the target is an
oVset.
In the current paper, we investigated the generality of themislocalization tendency by observing the haptic localizations in response to diVerent target types, i.e., the onset andoVset of continuous vibro-tactile stimuli. The novel Wnding
in this study is that the mislocalization can diVer with
diVerent target types. Our results suggest that the diVerence
cannot simply be ascribed to distortion in the timing of neural signals, such as that induced by latency diVerences, indicating instead that it could be explained by taking into
account the possibility of diVerences in the encoding oftiming information or in the cognitive strategies for localization.

References
Azuma R, Haggard P (1999) EVects of response type on coordinatedresponses during arm movement. Percept Psychophys 61:579–
590
Boucher L, Groh JM, Hughes HC (2001) AVerent delays and themislocalization of perisaccadic stimuli. Vision Res 41:2631–2644
Cai RH, Pouget A, Schlag-Rey M, Schlag J (1997) Perceived geometrical relationships aVected by eye-movement signals. Nature
386:601–604
Cordo PJ (1990) Kinesthetic control of a multijoint movement
sequence. J Neurophysiol 63:161–172
Cordo PJ, Carlton L, Bevan L, Carlton M, Kerr GK (1994) Proprioceptive coordination of movement sequences: role of velocity andposition information. J Neurophysiol 71:1848–1861
Dassonville P (1995) Haptic localization and the internal representation of the hand in space. Exp Brain Res 106:434–448
Dyhre-Poulsen P (1975) Increased vibration threshold before movements in human subjects. Exp Neurol 47:516–522
Flanagan JR, Lolley S (2001) The inertial anisotropy of the arm isaccurately predicted during movement planning. J Neurosci
21:1361–1369

489
Georg K, Hamker FH, Lappe M (2008) InXuence of adaptation stateand stimulus luminance on peri-saccadic localization. J Vis
8(1):15.1–15.11
Haggard P, Newman CS, Blundell J, Andrew H (2000) The perceived
position of the hand in space. Percept Psychophys 62:363–377
Horch KW, Clark FJ, Burgess PR (1975) Awareness of knee joint angle under static conditions. J Neurophysiol 38:1436–1447
Jaskowski P (1996) Simple reaction time and perception of temporalorder: dissociations and hypotheses. Percept Mot Skills 82:707–
730
Jirsa R, Radil T, Maras L (1992) Perception of timing of movement onset in a simple reaction time task. Neuroreport 3:524–526
Johansson RS, Westling G (1987) Signals in tactile aVerents from theWngers eliciting adaptive motor responses during precision grip.
Exp Brain Res 66:141–154
Johnson H, Van Beers RJ, Haggard P (2002) Action and awareness inpointing tasks. Exp Brain Res 146:451–459
Kawato M, Furukawa K, Suzuki R (1987) A hierarchical neural network model for the control and learning of voluntary movements.
Biol Cybern 56:1–17
Krakauer JW, Ghilardi MF, Ghez C (1999) Independent learning ofinternal models for kinematic and dynamic control of reaching.
Nat Neurosci 2:1026–1031
McCloskey DI, Colebatch JG, Potter EK, Burke D (1983) Judgments
about onset of rapid voluntary movements in man. J Neurophysiol
49:851–863
Milne RJ, Aniss AM, Kay NE, Gandevia SC (1988) Reduction in perceived intensity of cutaneous stimuli during movement: a quantitative study. Exp Brain Res 70:569–576
Nijhawan R, Kirschfeld K (2003) Analogous mechanisms compensate
for neural delays in the sensory and the motor pathways: evidence
from motor Xash-lag. Curr Biol 13:749–753
Nishida S, Johnston A (2002) Marker correspondence not processing
latency determines temporal binding of visual attributes. Curr
Biol 12:359–368
Paillard J, Brouchon M (1968) Active and passive movements in thecalibration of position sense. In: Freedman SJ (ed) Neurophysiolosy of spatinally oriented behavior. Dorsey, Homewood, pp 37–
55
Post LJ, Zompa IC, Chapman CE (1994) Perception of vibrotactile
stimuli during motor activity in human subjects. Exp Brain Res
100:107–120
Sittig AC, Denier van der Gon JJ, Gielen CCAM (1987) The contribution of aVerent information on position and velocity demonstrated
to the control of slow and fast human forearm movements. Exp
Brain Res 67:33–40
Sperry RW (1950) Neural basis of the spontaneous optokinetic
response produced by visual inversion. J Comp Physiol Psychol
43:482–489
Terao M, Watanabe J, Yagi A, Nishida S (2008) Reduction of stimulus
visibility compresses apparent time interval. Nat Neurosci
11:541–542
van Beers RJ, Wolpert DM, Haggard P (2001) Sensorimotor integration compensates for visual localization errors during smooth pursuit eye movements. J Neurophysiol 85:1914–1922
von Holst E (1954) Relations between the central nervous system andthe peripheral organs. Br J Anim Behav 2:89–94
Watanabe J, Noritake A, Maeda T, Tachi S, Nishida S (2005) Perisaccadic perception of continuous Xickers. Vision Res 45:413–430
Wolpert DM, Ghahramani Z, Jordan MI (1995) An internal model for
sensorimotor integration. Science 269:1880–1882

123