              Junji Watanabe†
PRESTO Japan Scienceand Technology Agency / NTT  
One way in which we explore the external world is through oursense of touch. The fingertips contain sensitive tactile sensors, andwhen the fingers touch an object and are moved across its surface,
the information sequentially presented to the fingertips is integrated
into the total shape of the object. This perceptual integration isbased on the important assumption that an object is static duringexploratory hand movements. However, if the object moves duringthe hand movement, the assumption leads to an illusory perceptionof the object’s shape. As shown in Fig 1(a), when the object moves
in the same direction as the hand movement, the object is perceived
to elongate, since the width is basically judged from the initial andfinal positions of the moving edges. On the other hand, when theobject moves in the opposite direction as in Fig. 1(b), its width isperceived to shrink. Our discovery of this phenomenon led us todevelop a novel tactile display called the Embossed Touch Displaythat can provide any given width of an object by moving the object
according to the hand movement.
The Embossed Touch Display features advanced object control performed in accordance with measured hand movements. We implemented the display with a laser distance sensor and a liner slider.
The sensor measures the distance between it and the finger, andliner slider is controlled in accordance to the distance. Using
this display, we can present realistically rigid edges. We can alsopresent continuous surfaces, which is difficult for prior tactile devices.

   We investigated the parameter for presenting any given width using
this device. The relationship between perceived width and object’s
velocity is described in Fig. 2. The perceived width and the object’s velocity are represented by the ratio to the real width and thefinger velocity, respectively. The dashed line is the expected value
obtained by Y 1 1 X . Where X and Y are the ratio of object’s velocity and perceived width. For example, when the object
moves in the same direction as the finger at the half velocity of thefinger, say X 05, the perceived width would be double (Y 2).
On the other hand, the width of the object would be perceived tohalf (Y 05) when the object moves in the opposite direction at1.
the same velocity, X
The results of three subjects are plotted in the vicinity of the expected value (dashed line). This indicates that when the object is e-mail: (hide,t-amemiya,maeda)@avg.brl.ntt.co.jp† e-mail:watanabe@avg.brl.ntt.co.jp‡ e-mail:nakatani@star.t.u-tokyo.ac.jp

Masashi Nakatani‡
The Universityof TokyoTomohiro Amemiya* Taro Maeda*
NTT Communication
Science Laboratories

moved during active touch movements, the object’s width can beperceived as equal to the distance of the finger movement. Therefore we can display any given width by controlling the velocity ofthe object.
SAME direction(a) Perceptually elongated width
OPPOSITE direction

㧔b㧕Perceptually shrunk width

Figure 1: Conceptual figure of display principle.

Perceived width Ratio

Hideyuki AndoNTT Communication
Science Laboratories

2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
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0-2:Subject A:Subject B:Subject C-1.5-1-0.500.5
Velocity ratio of finger and object

1.0

Figure 2: Velocity ratio and perceived width.

   We have proposed a method where the tactile shape is presented bymoving an object according active touch by the finger. In addition,
we examined the relation of the object velocity and the perceived
object width by experiment. From the results, we confirmed thatwidth is perceived with an almost complete correspondence to theamount of finger movement. It is possible that this method presents
shape while the object is traced directly by the finger. We believethat arbitrary two-dimensional shape can be presented using a linear
stage of two dimensions.