Motion After Effect in Tactile Sensation
Junji Watanabe
Hiroyuki Kajimoto

Seiichiro Hayashi
Susumu Tachi

Introduction

The University of Tokyo, Japan
E-mail: junji@star.t.u-tokyo.ac.jp

Adaptation (m oving stimulus)

In vision, after prolonged seeing of motion in one direction, illusory
motion in the opposite direction is observed in physical static pattern(known as “waterfall illusion”). This phenomenon is referred to as Motion
After Effect (MAE) [1][2], (see also Fig. 1.).
Although some visual illusions have been observed also in tactileperception [3], obvious tactual MAE has not been reported [4]. We,
however, found clear and robust MAE in tactile sensation by using dynamic
vibration of ambiguous motion as the test stimulus of MAE [5].

Test (static stimulus)

VisionIllusory motion

TactileExperiment
Subject : 3 naïve subjects
Apparatus :Illusory motion???

(issue of current presentation)

Finger pad of the forefinger was mounted
on three pins, which vibrate vertically as in5mm
right figure. The diameter of the rod was 1.0 mm.
The spatial intervals of the pins were 5 mm.
Vibration generators
The frequency of vibration
was 60 Hz, and the amplitude of vibration was 0.06 mm.

Fig. 1 Motion After Effect (MAE)

200ms

Procedure :

266ms
400ms

Three 60 Hz vibrations (each has 200 ms duration) weresequentially presented from fingertip (downward condition in Fig. 2a)or to fingertip (upward condition in Fig. 2b). The inter-stimulus onset
interval of the vibrations was 100 ms.

400ms

・・・

600ms

2000ms100ms(b) Upwardcondition

2 AFC
answer
Upward orDownward ?

・・・

600ms

2000mscondition

Result :Figure 3 shows the rate of response “Upward”. The horizontal axis
represents vibration amplitude of the top pin. Blue, green and redlines indicates the average of each 20 trials in Downward adaptation,
Upward adaptation and No adaptation condition, respectively.

We found obvious Motion After Effect in tactile sensation, which
occurs when tested by dynamic vibrations of ambiguous motion.
Tactual MAE can help to investigate further insight in tactile
information processing, as visual MAE has been useful probe tostudy human brain mechanism for visual motion perception.

References[1] A. Wohlgemuth :On the aftereffect of seen movement, British Journal ofPsychology, Monograph Supplement, Vol. 1, pp. 1-117, 1911.
[2] G. Mather, F.A.J. Verstraten, S.M. Anstis: The Motion Aftereffect: A Modern
Perspective, Cambridge, Mass: The MITPress, 1998.
[3] A. Bicchi, D. Dente. E.P. Scilingo :Haptic illusions induced by tactile flow,
Proceedings of EuroHaptics 2003, pp. 2412-2417, 2003.
[4] E.A. Lerner, J.C. Craig :The prevalance of tactile motion aftereffects,
Somatosensory & Motor Research, Vol.19, No.1, pp.24-29, 2002.
[5] J. Watanabe, S. Hayashi, H. Kajimoto, S. Tachi: Tactile motion perception:
psychophysical study using tactual motion after effect, (in preparation).

2 AFCanswer
Upward orDownward ?

No Adaptation stimulus(c) No adaptation condition

In the data of No adaptation (Blue), when the vibration amplitudeof the top pin was the same as the other pins, the rate of answer“Upward” is about 0.5. If downward vibration is presented in
adaptation phase (Green), more “Upward” responses is obtained.
On the other hand, in upward condition (Red), the rate of “Upward”
decreases. These tendencies are observed for a wide range of top
1
pin amplitude. This strongly suggests that perceived motion direction
for the test stimulus is affected by the upward or downward motion Rate of
0.9
adaptation, i.e. clear evidence of tactual motion after effect.
“Upward ” 0.8

Conclusions

2 AFC
answer
Upward orDownward ?

133ms

After 30 times adaptation, test stimulus was presented. In the test (a) Downward
stimulus, middle stimulus was firstly presented, and then, both top
and bottom stimuli were simultaneously presented after 133 ms. The
amplitude of the middle and bottom stimuli were 0.06 mm, while thatof top pin was varied from 0.02 mm through 0.15 mm.
Subjects answered whether upward or downward motion wasperceived. The answer was 2 Alternative forced choice (AFC).
20 trials were performed for each amplitude.
3 conditions x 8 amplitude x 20 trials = total 480 trials for 1 subject.

1 timeTest stimulus

30 times
Adaptation stimulus

0.7
0.6
0.5
0.4
0.3
0.2
0.1
0Fig.2 Experimental Time Charts
Downward
Upwardconditioncondition

No adaptation condition

0.02 0.024 0.03 0.04

0.06

0.09 0.12 0.15

Fig. 3 Results of one subject
Horizontal axis: vibration amplitude of the top pin [mm].
Vertical axis: rate of response “Upward”