Recreating Tactile Stimulus for Graphic Image: Basic Study

1Introduction

One of the goals for haptics researchers is to develop a multisensory display to convey not only visual information but also tactile information at the same time. There have been enormous studies on how to communicate sense of touch with various devices.
These devices are able to convey a variety of tactile information,
but it requires a rendering procedure to convert visual stimulus totactile stimulus. However, only a few rendering methods which associated with visual information have been examined so far. In thisstudy, a method is proposed to recreate tactile stimulus for visualinformation, especially by using the contour of the image. Because
the contour is one of the important information for both vision andtouch. As a starting point for a series of study, the stimulus durationof the shape and the perceived size was examined. Stimulus duration is one of the important factors because the perceived shape canbe directly affected by that.
In the following experiment, the passive high density Pin Matrix(PM) was used as a tactile display ,to convey tactile signal to thesubject[Nakatani et al. 2005]. This passive device is composed ofsteel pins 0.8 mm in diameter with 1.0 mm center-to-center spacing. The pins’ movement is constrained by close-ﬁtting holes inﬁberglass boards to prohibit the motion in horizontal direction andto allow free movement in the vertical direction. Each pin samples
the height information from the surface pattern and relays it to theﬁnger tip. The surface pattern was scanned by using a linear motor
stage, which can move only horizontal direction at speciﬁed speed.
In the following section, the experimental apparatus and the procedure is described then the result will be discussed.

2Susumu Tachi∗

Hiroyuki Kajimoto
Naoki Kawakami
The University of TokyoExperiment

Methods Four normal healthy adults (three males, one female) between 22 and 30 years olds attended the experiment . The experimental setup is shown in Figure 1 (a). A square shape (which is 25mm in width and 0.1 mm in height) stimulus was machine-milled
on aluminum plate. This stimulus plate was ﬁxed on a linear motor
stage which can move only in horizontal direction. A PM was ﬁxed
over the linear motor stage so that stimulus plate enables to touchthe bottom of each pin. The size of the PM was 10 x 20 mm, which
was enough size to cover whole contact area of the subject’s ﬁnger
pad. A reference plate was also developed by milling machine: thisplate had a series of strips with nine different widths (0.5, 1, 2, 4,6, 8, 10, 15, 20 mm) and they were all 0.1 mm in height. In thetrial, subjects placed right index ﬁnger on PM, and left index ﬁnger on reference stimulus plate. Then subjects were asked to matchthe subjective width to an assigned width on the reference stimulus plate shown in Figure 1 (a). Subjects could adjust the scanningspeed of the linear motor stage by verbally indicating ”speed up”
or ”speed down.” Each target width was examined ﬁve times in one
trial.
Results The data shown Figure 1 (b) indicated that the decrease intarget width resulted in an increase in the scanning speed of thestimulus plate. This result suggests that the perceived width of the∗ e-mail:{nakatani, kaji, kawakami, tachi}@star.t.u-tokyo.ac.jp

(a)

10mm
20mm(b)600

Scanning Speed [mm/s]

Masashi Nakatani

500
400
300
200
10000246810121416182022The target width [mm]Figure 1: (a): Top view of the experimental setup. The size ofthe Pin Matrix (PM) was 10 × 20mm, and the interval between twopins was 1.0mm. (b): The result of the experiment. The narrower
the width of the stimulus became, the higher the subjects tended toadjust the scanning speed of the stimulus plate on the linear motorstage.

stimulus can be affected by the stimulus duration. In addition, themagnitude of the variance increased as the target width decreased,
especially when the target width was smaller than 10 mm. Oneof the reasons can be that the scanning speed was faster than 200mm/s. The range of the speed at which people usually experience indaily life is reported as 50 - 200 mm/s. Therefore, outside this speed
range may result in misperceiving the size of the moving objects, ifpeople guess the size empirically.
In future work, a variety of machine-milled shapes can be use as
stimuli to investigate the possibility to represent different size ofthe shapes and textures with the same pattern. Moreover, a shapethat contains multiple contours will be examined to convey more
complicated shape information with various stimulus durations.

References
NAKATANI , M., K AJIMOTO , H., K AWAKAMI , N., AND TACHI ,S. 2005. Tactile sensation with high-density pin-matrix. In Proceedings of ACM Symposium on Applied Perception in Graphics
and Visualization, 169.