The Human Vision System

Published Date: 02 Nov 2017

INTRODUCTION

The human vision system is one of the most complex systems in the central nervous system. The visual system includes the eyes, the connecting pathways through to the visual cortex and other parts of the brain, which will receive the reflected light from the surrounding things and configure the image. The presence of any defect in any part of the visual system can cause visual impairment or sometimes blindness. Blindness is defined as visual acuity of less than 3/60 (0.05) or corresponding visual field loss in the better eye with best possible correction (visual impairment categories 3, 4 and 5 in ICD-10). This corresponds to loss of walk about vision [1]. 285 million people are visually impaired worldwide: 39 million are blind and 246 million people have low vision and are at great risk of becoming blind [2]. cataract (47.9%) remains the leading cause of visual impairment in all areas of the world, except for developed countries. Other main causes of visual impairment in 2002 are glaucoma (12.3%), age-related macular degeneration (AMD) (8.7%), corneal opacities (5.1%), diabetic retinopathy (4.8%), childhood blindness (3.9%), trachoma (3.6%), and onchocerciasis (0.8%)[43]. Blindness and visual impairment are mainly due to birth defects and uncorrected refractive errors. In the first case, most of the causes are in the brain rather than in the eye while in the second one, they are conditions that could have been prevented if diagnosed and corrected with glasses or refractive surgery on time [11]. It is estimated that by the year 2020, all blind-related numbers will double [9]. The main reason that attracted the researchers to invent various technologies is the increasing number of people with vision disabilities in the world. It is hoped that these technologies can assist people in carrying out their every-day tasks like normal people. One of the main problems of the visually impaired is that most of them have lost their physical integrity, also they do not have confidence in themselves and they find themselves challenging to go out independently. Blind issue has become a sensitive issue and influential in the community in terms of economic and social loss. The economic loss due to un-accommodated blind people increased from $29 billion (2010) to $50 billion come (2013) [3]. Visually impaired people use their sense of hearing to compensate for their reduced eye sight, for instance they can recognize sound sources. Human spatial hearing was analyzed by many authors (Blauert 1999: More 1997) who established that both monaural and binaural attributes of the ear input signal contribute to forming the position of the auditory event [7]. The blind person in most cases uses the white cane to navigate the markings on the floor inside a building to find their way. This traditional method is not effective in all circumstances because the blind person must know their way, and if they fail to find the marking they may face some problems. It would be more complicated in the case if the blind person had problems in sensory organs. In addition, the white cane requires the user to actively scan the small area ahead of him/her. The white cane is also not suited for detecting potentially dangerous obstacles at head level. The traditional navigation method may not be sufficient for the blind person in these cases. The guide dog may be a solution, but the dog must be trained at least two years and trained guide dogs cost between $12,000 to $20,000 (In developed countries), and they are only useful for about five years [6], and the expense is unaffordable for many people. The growth of information technology plays a vital role in the recent development almost in all the fields, so the active navigation method may be helpful for the blind but it is important to appreciate as much as possible the needs and requirements of this community before starting to create devices for them. In today's society of social independence, the visually impaired like everyone else deserve independence. They require assistive devices for navigation, for reading signs and text to be independent. In particular, outdoor and indoor navigation has always been a challenging problem for their mobility. This navigation concern restricts the visually impaired right access to many buildings, precludes their use of public transit and makes their integration into local communities difficult [8]. Innumerable attempts have been made to leverage technology to supplement or replace these two "low-tech" aids. The resulting devices are commonly known as electronic travel aids (ETAS). In 1971 Dr Leslie Kay from New Zealand became the first engineer to invent a device for fish finding, a divers sonar and ultrasound device to listen to the heart moving and an ultrasound imaging system to look into metal [11]. Sonar techniques namely frequency modulation (FM) and pulsed echo techniques have been wildly used in ultrasonic blind mobility aids, because they are well suited for localizing objects. They use reflection as a key principal to determine the distance from an object.

The Purpose of the Thesis

The main objective of this work is to help blind or visually impaired people to navigate safely and quickly among obstacles and other hazards. In order to do this an innovative approach based on the integration of electronic components on the textile structures have been investigated. With this approach, the design of a new wearable obstacle detection system that is flexible and comfortable for the human body has been developed.

The proposed system provides three services, the first one provides a voice warning of obstacles and facilitates the selection of the clear path by using a helmet containing ultrasound sensors in its surrounding. The sensors send ultrasound signals which can be reflected by obstacles and receive the reflected waves. Secondly, the developed system helps blind people to sense and estimate the distance between them and anything that can be harmful, by using a vibration based bandage worn on the hand. Thirdly, a GPS (Global Positioning System) is used to support the communication system and determine the location of the blind person.

Functional Description

During operation, the user wears the helmet system on the head, and wears the bandage around his/her wrist. So while walking the user can make his/her hand move forward and turn in different directions to the left or right setting the direction of the sensor to a lower level to detect the area nearer the ground. The helmet position is fixed on the head and it senses the higher level of the human body. The same function allows the user to find a passable way, for example, the door opening. With these functions it is possible to guide the bind to travel safely and not to come into contact with any obstacles.

Chapter 1 is the introduction. Chapter 2 provides a literature search on the topic. Chapter 3 is about the hardware design of the system developed by the author. Chapter 4 is about the software details of the system. Chapter 5 provides the test results and discussions about the system. Finally, Chapter 6 is the conclusion.

CHAPTER 2

LITERATURE REVIEW

It is important for the visually impaired to be comfortable and hands free during their navigation, thus the usable electronic aid would work best by being embedded into wearable fabrics. The research that has been done on this with regards to the implementation of electronic components into textile structures is not detailed, however they consider attaching the component on to the wearable fabrics[5].

This review comprises devices developed from the Second World War, when the development of sensors played an important role in the human life, until nowadays. The background and history of ETA (electronic travel aids) started In, TVSS (Tactile Vision substitution System) are studied at Smith-Ketlewell Labs. L.KAY’ s Sonic Torch is produced as the first practical ETA device and continues in following famous commercial models, MOWAT sensor, Laser Cane, and so on. These ETA devices are basically surrounding distance transfer device, which gives distance information along pointed direction back to user with converted tone, sound modulation or mechanical vibrations. In addition, not only portable device, there exists travel guidance system in building as functional welfare facility, which gives voice announce about the important location and attribute information to the visually impaired by detecting sensor under the floor or street with electric cane[39].

2.1 GuideCane

The Guide Cane: is a device designed to help blind or visually impaired users navigate safely and quickly among obstacles and other hazards. During operation, the user pushes the lightweight Guide Cane forward. When the Guide Cane’s ultrasonic sensors detect an obstacle, the embedded computer determines a suitable direction of motion that steers the Guide Cane and the user around it. The steering action results in a very noticeable force felt in the handle, which easily guides the user without any conscious effort on his/her part [12].

2.2 Bionic Eyeglass

A bionic eyeglass is a device that helps blind and visually impaired people by converting visual information into speech. The indoor and outdoor situations and tasks have been selected by a technical committee consisting of blind and visually impaired persons, considering their most important needs and potential practical benefits that an audio guide can provide. Two types of cellular wave computing algorithms are used: general spatial-temporal event detection by analogic subroutines, and recently developed multi-channel mammalian retinal model followed by a classifier The basic idea is to mimic the way the nervous system discriminates relevant information from the irrelevant - namely realize an attention model. Typical indoor and outdoor event detection processes are considered and explained through examples. We present advances in adaptive color processing and number recognition [14]. .

2.3 Wheelchair(1980)

This device utilizes ultrasonic and laser technology to provide wheelchair users with information about obstacles in their path. The aid consists of two units, a Master and a Slave. The two units slide onto brackets mounted on clamps to the sides of the wheelchair. Having a unit on each side enhances the ability of the unit to detect drop offs as well as forward and side obstacles. The Slave unit emits a high pitched signal; the Master has a lower tone. The controls are on the Master unit. The system includes a rechargeable nickel cadmium battery and a low powered gallium arsenide solid state injection laser. The ultrasonic portion can be set for a range of 4 feet or 8 feet. When an obstacle is detected, alarms on both the Master and Slave units are activated. WEIGHT: Each unit weighs less than a pound [40].

2.4 Sonic Pathfinder(1984)

The Sonic Pathfinder is similar to the (SonicGuide) but pre-processes the sensor data and presents "only that information which is of immediate practical interest to the moving pedestrian . The information is presented as simplified audio signals which are less likely to interfere with environmental sounds. Despite its simplicity training was still shown to be critical for correct use [15].

2.5 K' Sonar

The 'K' Sonar is a small electronic travel device in the size of cell - phone. It sends out from the upper transducer a spreading beam of high frequency sound that the human ear cannot detect. This sound spreads out something like the light from an ordinary torch. Any object in that beam will reflect some of the sound back to the sonar and the lower transducer will transform the sound echo into tiny electrical signals, which will be amplified and processed. This is so that, eventually they can be used to produce sound in the earpiece, which will now be audible to the human ear [16].

2.6 Trisensor (1978)

but is now known as the KASPA system (Kay's Advanced Spatial Perception Aid). KASPA represents object distance by pitch, but also represents surface texture through timbre. Use is made of echo location through frequency-modulated (FM) signals. The improved, but still modest, resolution probably positions Kay's work somewhere between obstacle detection and environmental imaging. The best angular resolution is about one degree in the horizontal plane (azimuth detection) for the central beam, which is quite good, but vertical resolution (elevation) is poor - making the ``view'' somewhat similar to constrained vision with binocular viewing through a narrow horizontal slit [14].

2.7 Sonic Torch (1965)

A battery operated hand held device basically operates by transmitting the ultrasound in the forward direction and receiving the reflected sound beam from the nearest object(s) [41].

2.8 Mowat Sensor (1973)

It is a light weight, hand held, pocket size device. Like a sonic torch a Mowat sensor also detects nearby object by sending high frequency ultrasound and receiving the reflected beam. The user can identify the distance of the object by the rate of vibration that is produced by the device[17].

2.9 Smart Cane

Smart Cane is one invention which was originally the creation of a common blind cane but it is equipped with a sensor system. This invention resembles Guide Cane where this invention has a number of ultrasonic sensors and servo motors. This invention is designed with the aim at helping the blind in navigating. Ultrasonic sensors need to detect and avoid obstacles or objects located in front of the user. Meanwhile the fuzzy controller is required to determine the instructions that will be executed for example to turn right, left or stop. Like Guide Cane, this invention also has a control button on the handle, and the button has four different directions. This invention has the same weaknesses as the Guide Cane where there will be a problem to save space or to place the smart cane [4].

2.10 Miniguide Holder(1980)

The Miniguide holder allows the aid to be attached to canes, walking frames and wheel chairs. The diameter of the cane can range from 12mm to 25mm (half inch to one inch). The angle of the Miniguide can be adjusted by releasing the cam lever [42].

2.11 UltraCane

The Ultra Cane gives mobility assistance to blind and partially-sighted people by emitting ultrasonic waves, just like the echolocation system used by bats and dolphins. In fact, it was from the knowledge and understanding of bats that the Ultra Cane was first developed. The bat emits an ultrasonic pulse and times how long it takes for the echo to return. By its implicit knowledge of the velocity of sound in air, the bat is able to calculate the distance to the object. This knowledge has been transferred to the Ultra Cane, which works in a similar way [18].

2.12 Indoor Navigation and Object Identification System

The basic aim of our research is to allow object identification for the blind and to improve their indoor navigation abilities using local sensor information in combination with 3D models of the environment. The components of the architecture will be described in detail in the following subsections. Color is an important object feature for the blind, even tough this may not be easily understandable for people with normal vision. But when considering clothes, food, traffic lights or weather conditions it becomes obvious why the blind frequently talk about color - even those who have never seen any color. A lot of object features, such as the size of an object or its surface structure, are accessible to different senses. The problem with color for the blind is that this object feature is only available to the sense of vision. In contrast, the size or the weight of objects are also accessible to our tactile sense. But there is no other means for the perception of color except seeing. Perhaps this is the reason why color is so important and also fascinating for the blind. A lot of objects and materials have a characteristic color or their color is within a typical range, like for example the colors of skin, metals and fruit. This suggests the use of color for the detection of objects [55].

2.13 Real-time path and obstacle detection

system designed to help the visually impaired through the use of a navigation aid. This system helps the blind to navigate indoor and outdoor, such that the users can be warned of obstacles on the path where they walk. Although the proposal of the Smart Vision project aimed at detecting obstacles at a distance between 2 and 5 meters, we have increased the distance to 8 meters, as this allows to warn to the user sooner, and the algorithms perform as well up to 8 meters. The implemented system has shown a robust performance, both in- and outdoor. When no clear path is present in the image, it is difficult to find useful borders. However, in this case a default window in front of the user is applied. This does not interfere with the user’s navigation, as in an open space he can walk freely, and possible obstacles in front can still be detected. For example, corners can be a problem, although even if the path borders are only partially present in the image, the obstacle detection algorithms will perform very well. Path detection will only look for straight lines, but this can also be improved. Although it performs well on moderately curved sidewalks, the performance in case of very curved sidewalks can be improved in future work. The performance on homogeneous grounds is very good, but there is a need for improving the results on pavements with multiple textures, although in most of the test sequences the system worked fine [56].

2.14 Real–Time Assistance Prototype

new prototype for being used as a travel aid for blind people. The system is developed to complement traditional navigation systems such as white cane and guide dogs. The system consists of two stereo cameras and a portable computer for processing the environment AL information. The aim of the system is to detect the static and dynamic objects from the surrounding environment and transform them into acoustical signals. Through stereophonic headphones, the user perceives the acoustic image of the environment, the volume of the objects, moving object direction and trajectory, its distance relative to the user and the free paths in a range of 5m to 15m. The acoustic signals represent short train of delta sounds externalized with non-individual Head- Related Transfer Functions generated in an anechoic chamber. Experimental results show that users were able to control and navigate with the system safety both in familiar and unfamiliar environments [57].

2.13 Drishti: An Integrated Indoor/Outdoor Blind Navigation System

Drishti uses a precise position measurement system, a wireless connection, a wearable computer and a vocal communication interface to guide blind users and help them travel in familiar and unfamiliar environments independently and safely. Outdoors, it uses DGPS as its location system to keep the user as close as possible to the central line of sidewalks of campus and downtown areas; it provides the user with an optimal route by means of its dynamic routing and rerouting ability. The user can switch the system from an outdoor to an indoor environment with a simple vocal command. An OEM ultrasound positioning system is used to provide precise indoor location measurements. Experiments show an in-door accuracy of 22 cm. The user can get vocal prompts to avoid possible obstacles and step-by-step walking guidance to move about in an indoor environment. This paper describes the Drishti system and focuses on the indoor navigation design and lessons learned in integrating the indoor the outdoor system [58].

2.14 Prototype of assistive device offering to Blind People

Assistance devices designed to aid visually impaired people need to deal with two different

issues: at first they need to capture contextual information (distance of an obstacle, position of the user, environment around the user), at second they need to present the user with this information. Presentation method must be adapted to blind users and must be suitable for a continuous use. It generally means that the system should be fast in order to cut user from obstructions, information have not to be too much detailed in order to keep user’s perception channels free and finally passing of the information must be well pronounced [59].