Forehead Retina System
Hiroyuki Kajimoto∗
The University of Tokyo

1

Yonezo Kanno†
EyePlusPlus, Inc.

Susumu Tachi‡
The University of TokyoIntroduction

The goal of our project is to provide a cheap, lightweight, yet fully
functional system that provides rich and dynamic 2D environmental information to the blind. The Forehead Retina System (FRS)composed of a small camera and 512 electrodes on the foreheadcaptures the view in front, extracts outlines from the view, and converts the outlines to tactile sensation by electrical stimulation. Using this device, the users can ”see” the surrounding environment
with their forehead skin, without using their eyes.

2Related Works

Figure 1: 512 (32 × 16) electrodes module for the forehead.

The vision to tactile conversion system was first developed byCollins [Collins 1970], who used 400 vibration motors on the skinof the back and a CCD (Charge Coupled Device) camera. He called
the system a tactile vision substitution system (TVSS).
However, although many similar systems have been proposed sincethen, they have not become widely used for the following two reasons: One is the technical aspect of the stimulation. For tactiledevices using a large number of mechanical actuators, the system
becomes heavy, expensive, and requires a considerable amount ofpower. To solve this problem, we applied electrical stimulation.
The electrical stimulation is lightweight, cheap, scalable, and consumes much less energy. At the same time, it does not generatesound and is free from mechanical resonance.
The other reason pertains to the region of stimulation. Many previous proposals placed vibration motors on the back. Although awaistcoat with the motors is definitely ”wearable,” its use is not soeffortless. For this problem, we propose to use the forehead as astimulation point. Although electrical stimulation has a long history, stimulation of forehead skin is a new approach. However, inreality, it is quite reasonable because of the ease in putting the system on and taking it off. Furthermore, if the stimulation is appliedon the back, finger, or tongue, the coordinate system transformation
to change the image on the skin to that on an absolute coordinate
system is complicated. However, if we use the forehead, this transformation becomes unnecessary.

3SystemA CCD camera attached on a pair of sunglasses captures the viewin front. A laptop PC extracts the edges and converts it to a tactile
stimulation pattern. The pattern is transmitted to the driver circuit
via a standard serial port. 512 electrodes (Fig.1)are driven sequentially to create the tactile pattern. The entire process is triggered by
the image capture event, which occurs every 33 [ms] (30 [fps]). The
basic electrical stimulation technology is inherited from ”SmartTouch”[Kajimoto et al. 2003] which is a visual-to-tactile conversion
systems for the skin on the finger.
∗ e-mail: kaji@star.t.u-tokyo.ac.jp† e-mail:kanno@eyeplus2.com‡ e-mail:tachi@star.t.u-tokyo.ac.jp

Figure 2: Wearing Forehead Retina System (FRS).

In one case, the luminance information is used for edge extraction.
In other case, color key is used to extract specific color. The outline
edge is extracted by an ordinary Laplacian of Gaussian (LOG) filter.
After that, the image is scaled down to a resolution of 32 × 16.
Using threshold, we obtain a black and white binary pattern.
We must note that although many useful algorithms have been proposed in the field of computer vision, we cannot always use them
unconditionally. The processing must be performed realtime (atmost 33 [ms] or one frame latency), and the system must be small
and power efficient for portability. Therefore, we believe that rather
than incorporating elegant but expensive algorithms, the combination of bare minimum image processing and training is practical.
We are beginning to test the system with the visually impaired todetermine the most appropriate balance as good human interfaces
have always achieved.

References
C OLLINS , 1970. Tactile television - mechanical and electricalimage projection. IEEE Trans. Man-Machine Systems MMS-11,1 (Mar.), 65–71.
K AJIMOTO ET AL ., 2003. Smarttouch: A new skin layer to touchthe non-touchable. In Conference Abstracts and Applications of
SIGGRAPH, CD–ROM.