Sonification.deThe Sonification Handbook
Thomas Hermann, Andy Hunt, John G. Neuhoff Logos Publishing House, Berlin, GermanyISBN 978-3-8325-2819-52011, 586 pages Reference:Hermann, T., Hunt, A., Neuhoff, J. G., editors (2011). TheSonification Handbook. Logos Publishing House, Berlin,Germany.
Auditory Display in Assistive Technology
Alistair D. N. Edwards Auditory information can be of particular importance to people who cannot perceive other forms, notably those who are blind. This chapter mainly surveys some of the attempts to substitute visualinformation by sounds.
Reference:Edwards, A. D. N. (2011). Auditory display in assistive technology. In Hermann, T., Hunt, A., Neuhoff, J. G.,editors, The Sonification Handbook, chapter 17, pages 431–453. Logos Publishing House, Berlin, Germany.
Auditory Display in Assistive
Alistair D. N. Edwards This chapter is concerned with disabled people1. As soon as a label such as ‘disabled' is applied, questions are raised as to its definition. For the purposes of this chapter, no formaldefinition is required, rather it should suffice to say that the people we are writing abouthave the same needs as everyone else, it is just that in some instances their needs are moreintense and are sometimes harder to meet. If this book achieves anything, it should convincethe reader that sound can be an immensely powerful medium of communication and therelevance of this chapter is that the full potential of the use of sounds can often be morecompletely realized when aimed at meeting the needs of people with disabilities.
The immediately obvious use of sounds is as a replacement for other forms of communicationwhen they are not available. Specifically, blind people cannot access visual information.
Much of this chapter will deal with this form of substitution, but it will also demonstrate theuse of sounds in other applications.
It is a contention in this chapter that there is a great potential for the use of sound that hasnot yet been realized, but some progress has been made in the following areas which arereviewed in this chapter: 1Language is powerful and sensitive. No other literature is more sensitive to the needs of being politically correct than that which deals with disability. It is recognized that inappropriate use of language can cause harm andoffence, but at the same time perceptions of what is correct are constantly changing. For example, at the time of writing there are (sometimes fierce) arguments as to whether ‘disabled people' or ‘people with disabilities' is the better term. In this chapter we have attempted to be sensitive to all shades of opinion, and if we have failedand used any terminology felt to be inappropriate by any individual reader, then we can only apologize.
Then there are other potential uses and some of these are also discussed.
17.2 The Power of Sound
Of course, one of the most powerful (and the most used) form of auditory communication isspeech. Even though the emphasis of this book is on non-speech sounds, the role of speechcannot be ignored and it will be discussed in this chapter, in the context of where speech hasadvantages over non-speech.
The potential power of non-speech sound is illustrated by the following extract, written byJohn Hull, who is blind.
I hear the rain pattering on the roof above me, dripping down the walls to myleft and right, splashing from the drainpipe at ground level on my left, whilefurther over to the left there is a lighter patch as the rain falls almost inaudiblyupon a large leafy shrub. On the right, it is drumming with a deeper, steadiersound, upon the lawn. I can even make out the contours of the lawn, whichrises to the right in a little hill. The sound of the rain is different and shapesout the curvature for me. Still further to the right, I hear the rain soundingupon the fence which divides our property from that next door. In front, thecontours of the path and the steps are marked out, right down to the gardengate. Here the rain is striking the concrete, here it is splashing into the shallowpools which have already formed. Here and there is a light cascade as it dripsfrom step to step. The sound on the path is quite different from the sound ofthe rain drumming into the lawn on the right, and this is different again fromthe blanketed, heavy, sodden feel of the large bush on the left. Further out, thesounds are less detailed. I can hear the rain falling on the road, and the swish ofthe cars that pass up and down. I can hear the rushing of the water in the floodedgutter on the edge of the road. The whole scene is much more differentiatedthan I have been able to describe, because everywhere are little breaks in thepatterns, obstructions, projections, where some slight interruption or differenceof texture or of echo gives an additional detail or dimension to the scene. Overthe whole thing, like light falling upon a landscape, is the gentle backgroundpatter gathered up into one continuous murmur of rain. [1, p. 26-27]2 There are two important points to be taken from this extract. Firstly there is the immense amount of information that the writer was able to extract from sounds. Secondly, it has to beacknowledged that none of the attempts to use sounds in synthetic auditory displays has yetcome close to conveying that amount of information. It can be done; we do not yet know howto do it. It has to be acknowledged that most of the devices and ideas described in this chapterare not embodied in commercially available, commonly-used products. For various reasonsthey are not sufficiently useful for widespread adoption, and yet the above extract clearlydemonstrates the richness of information that can be usefully conveyed in non-speech sounds.
Tony Stockman also describes how blind people can make use of environmental sounds, putting them in the context of attempts to supplement these with technology-generated 2On Sight and Insight, John M. Hull, 1990, 1997. Reproduced by permission of Oneworld Publications.
Auditory Display in Assistive Technology 433 sounds in .
Sight is a very powerful sense. By any measure, the amount of information that can bereceived visually is vast. Yet it is not simply the raw bandwidth of sight that makes it sopowerful, it is the ability to (literally) focus on the information that is of relevance at anygiven time. Because of the amount of information available visually it is those people whodo not have access to visual information who are the most obvious candidates to use auditoryinformation as an alternative. There is a fundamental problem, though, in substituting forvisual information. The capacity of the non-visual senses (including hearing) simply doesnot match that of sight. This is often referred to as the bandwidth problem.
Thus, the fundamental restriction is that sounds cannot be used to convey the same amount of parallel information as the visual sense can. There are two principal approaches that canbe taken to address this problem: 1. Maximize the amount of information carried in the sounds; 2. Reduce the amount of information presented (i.e. filter it in some way).
Achieving (2) amounts to giving users a form of focus control corresponding to that of thevisual sense. While (1) is the main topic of this chapter, it cannot be divorced from the necessity to provide the control implied in (2).
In this chapter a number of research projects are described in which non-speech soundsare used to convey information to blind people. In comparison to the example from JohnHull, above, it will be evident that these attempts are quite crude. Nevertheless, this issurely a stage that has to be gone through in order to understand the nature of this style ofcommunication, with the hope that eventually we will be able to create vast, rich and useablesoundscapes.
17.3 Visually Disabled People
There are a large number of people with visual impairments. Although exact figures are hard to find, Tiresias  estimate that there are approximately six million people in Europe with a visual disability. Visual disabilities take a number of forms and the number of blind people - those with no useful sight - is relatively small (one million in Europe, according to Although the number with an impairment short of blindness (variously referred to as ‘visually impaired' or ‘partially sighted') is relatively large, the number of different forms of impair-ment make it difficult to meet their needs. (An impression of the effects of different forms ofimpairment can also be found on the Tiresias website, ). For instance, an adjustment thathelps some people (such as text enlargement for people with cataracts) can even make vision worse for others (enlargement further reduces the material in view to someone with tunnelvision, perhaps due to glaucoma).
It might be suggested that any interaction that makes no use of vision - such as an auditory 3The figures are open to debate. For instance,  estimated the number of visually disabled Europeans as 2,000,000, while the proportion of people with visual disabilities has been estimated variously as 1.6% (in Europe, ) and4.1% (in the USA, ). Also, one must beware that the population of Europe has changed since 1993 with the accession of new states.
interface designed for users who are completely blind - would be equally accessible to those with some vision. However, the fact is that those with some sight generally prefer to make as much use of that sight as possible. In other words, they do not need substitution of the visualinformation, but its enhancement to match their visual abilities.
Thus, this chapter really addresses the needs of those who must have an auditory substitute for visual forms of information, those who are blind - even though they are the minority ofthose with visual disabilities.
Visually disabled people have a variety of needs for non-visual information. This chapter looks at access to computers (through screen readers), electronic travel aids and otherapplications which make use of sounds.
17.4 Computer Access
Most human-computer interfaces are ‘visually dominated' in that the principal channel forcommunication from the computer to its user is the monitor screen. For a blind user, all theinformation that is displayed on a computer screen has to be substituted by non-visual formsof communication, either tactual or auditory.
The dominant form of tactual communication is braille. Braille is mainly a translation of printable text. The greatest barrier to the use of braille, though, is the small number of (blind)people who have the skills to read it. Again accurate statistics are hard to compile, but Bruceat al.  suggest that in the UK the proportion of blind people who can read braille is as lowas 2%. Computer braille displays are available . These usually consist of 40 or 80 braillecells. They are electro-mechanical devices and are thus quite expensive and are also bulkyand heavy.
While there is a significant community of enthusiastic braille users - including those who use braille for computer access - auditory interfaces have a lot of features which make them veryattractive compared to braille, notably: Ease-of-use: Unlike braille, sounds essentially require no training. Of course this is
not strictly true of some of the more complex uses of sounds discussed in this book (e.g. chapters but the simplest sounds including speech can be usedwithout training. Auditory interfaces are effectively accessible to 100% of blind people - as long as they do not also have a hearing impairment.
Cost: Sound cards are a standard component of all modern PCs, therefore the only addi-
tional cost is that of any special software.
Braille was originally designed for the presentation of literary text - that which can beexpressed in the 26 letters of the alphabet plus 10 digits and a small number of punctuationmarks. Its extension to other forms of communication (e.g., mathematics or music) issomewhat clumsy and labored. There is a similar problem with sound when applied to thecomplex information that can be displayed on a computer screen. On any computer screenthere may be hundreds of different elements visible. The sighted user can cope with thislarge amount of information because they have the ability (literally) to focus on the item ofinterest at any time. Thus, the user can take in the information of importance and filter outthat which is currently irrelevant. The non-visual senses (and here we are mainly concerned Auditory Display in Assistive Technology 435 with hearing) do not have that ability.
In other words, if we were to take a simple-minded approach to the adaptation of a visualdisplay for blind users we might try to associate a sound with each item on the screen. Toglance at such a screen would imply having every one of those items make its sound. Clearlythis would be a cacophony. Sounds would interact and mask each other and it would not bepossible to spatially separate the sounds in the same way that vision can do.
Computer access for blind people is achieved by using a piece of software called a screenreader. Essentially this examines the contents of the screen and converts it into sounds4.
Screen readers were first developed about the same time as the PC became available. Theoperating systems of the time (predominantly MS-DOS) were text-based. That is to say thatthe screen displayed text and commands were typed in on the keyboard. For instance, todisplay the contents of the current directory, the user would type DIR, or the contents ofthe file foo.txt could be displayed (typed) on the screen by entering TYPE FOO.TXT.
It was relatively easy to render this kind of interaction (i.e., the text of the command lineand the contents of the text file displayed in response to the command) in sounds by using ascreen reader linked to a speech synthesizer. Some of these first-generation screen readersmade some use of non-speech sounds. For example, the Hal screen reader  used beeps ofdifferent tones to guide the user between the different lines on the screen, but most of thesescreen readers relied mainly on speech.
The screen reader represented a major advance for blind people. The access to the computer that it gave, generated a degree of equality in job opportunities; jobs that had been inaccessiblenow became feasible for blind workers.
The next major development in the personal computer was the graphical user interface (GUI).
This was firstly implemented commercially on the Apple Macintosh, but eventually was also found on ‘IBM-compatible' PCs in the form of MicrosoftWindows. At first the GUI wasseen as a real threat to blind people. The form of interaction was completely different andvery much visually orientated. The mouse pointing device was added to the keyboard andscreen. It was necessary to point at objects on the screen. The design and positions of thoseobjects carried meaning. These properties and their meanings could not easily be translatedinto auditory forms. The emancipation that blind workers had experienced was in danger ofbeing lost.
Edwards [10, 11] experimented with an auditory version of the GUI, Soundtrack. This wasnot a screen reader, but a word processor which retained most of the interactions of the GUI (windows, icons, scrollbars etc.) but represented them in an auditory form. The first level of interaction was based on tones of varying pitch, giving relative spatial information, butat any time the user could click the mouse and hear a spoken label. Double-clicking wouldactivate the current object.
Soundtrack remains one of the few attempts to make mouse-based interaction with a GUIaccessible in a non-visual form, but it was only a word processor, and not a generalized toolfor making GUIs accessible. However, screen readers were eventually developed such thatthe modern GUI interface is about as accessible as the former text-based ones were. GUIscreen readers obviate the need to use the mouse by taking over control of the cursor, which 4Most screen readers can also render the information on a braille display [7, 8], but that is outside the scope of this is controlled through the keyboard. They also still tend to rely to a large extent on syntheticspeech with minimal use of non-speech sounds.
Syntha-Voice's WindowsBridge was a screen reader which attempted to make the Windowsoperating system accessible through the mouse. Positional feedback on the cursor wasgiven using musical tones, and mouse movements could be filtered so that only vertical andhorizontal movements were detected (i.e. no diagonal movements). However, few users usedthis feature and, indeed, the product is no longer available.
Non-speech sounds were used more extensively in some experimental screen readers, notably Mercator and Guib. The contrasting approaches behind these different systems is written up in , but both tended to use the style of non-speech sound known as the auditory icon  (chapter The Guib Project culminated in a commercial screenreader, Windots, but it did not make much use of the non-speech sounds developed in Guib.
Windots was never a great success commercially and is no longer available. In practice the most popular Windows screen reader is Jaws for Windows5. Jaws has quite extensivefacilities for the use of non-speech sounds. A Speech and Sound Manager allows users toassociate different utterances or sounds with screen objects. These include: Control types These are widgets, such as buttons, scrollbars, check boxes.
Control state Widgets can be rendered differently depending on their state, a button that
is pressed or a check box that is checked or not.
Attributes Different font attributes can be signaled.
Font name Changes in font can be signaled.
Color The color of the current item can be signaled.
Indentation An indication of the depth of indentation is presented.
HTML Different HTML elements (in webpages) can be signaled.
All of these properties can be rendered in different ways. Speech may be used (i.e., an explicit description of the attribute) or a change in the current voice, but there is also theoption of playing a sound. Sounds are simply played from .wav files and a number of theseare provided with the Jaws software. These include auditory-icon-style sounds such asrecordings of door bolts being opened or closed (sample a lamp being switched on (sample the thump of a rubber mallet (sample and the like. There are also musical sounds, such as a piano playing one or two notes (e.g., sample that can beused in a more earcon-style of soundscape.
Different ‘Speech and Sound' configurations can be created and stored. This means thatusers can load particular configurations for different purposes. For instance, they may wishto use one configuration when word processing and a different one when writing programs.
Configurations can be stored in files. This means that they can easily be swapped andshared between users. A number of configurations are provided with the Jaws softwareand it is interesting that these make minimal use of the sounds option; they are (again)speech-driven.
Microsoft Windows is the operating system of choice for most blind users; it is best supported 5Freedom Scientific Auditory Display in Assistive Technology 437 by available screen readers. The Unix world has been slow to recognize the needs of blindusers, but this changed with the advent of the Linux Gnopernicus Project which aimed toenable users with limited vision, or no vision, to use the Gnome 2 desktop and applicationseffectively. However, this project appears to have stalled due to lack of funding.
As mentioned above, the advent of the GUI was seen at the time as a serious blow to the emancipation of blind computer users. Apple Computers were responsible for theintroduction of the GUI to the consumer market, with the release of the Macintosh. Althougha screen reader (OutSpoken) was released for the Macintosh, it has never been used by manyblind users (and is no longer marketed). However, in the release of Version 10.4 of its OS Xoperating system, Apple included VoiceOver, a built-in screen reading facility. Controversyexists regarding the efficacy of this screen reader [14, 15], but its use is growing as it is nowpart of the iPhone and the iPad. As with most screen readers, it is heavily speech-based, butdoes include the use of non-speech sounds.
A common theme in this book is that the true potential for the use of non-speech sounds has yet to be realized. This is clearly true in the application of computer access for blindindividuals. Most screen readers have facilities for the use of non-speech sounds; however,few people use them. This implies that the kinds of sounds being used and the informationthey are providing is not perceived as valuable to the users.
17.5 Electronic Travel Aids
The need to access computers is growing, but is still a relative minority activity compared to moving around the world. There are two aspects to this for blind people: short-rangeobstacle avoidance and the broader-scale of navigating to desired destinations. Technologies (sometimes referred to as Electronic Travel Aids or ETAs) can be used in both of these By far the most popular technology for obstacle-avoidance is the guide cane (also knownas the white cane). There are a number of reasons why this is so popular, which will bediscussed in contrast to higher-technology approaches below. For a person walking throughan environment, it is vital to know whether there are any obstacles in the path ahead. This is what the guide cane provides. Canes come in different lengths from approximately 60cm to 160cm. Shorter canes are symbolic-only, carried by the user (who is likely to have somevision) as a signal to others that they may need special assistance. It is only the longer onesthat are used for obstacle avoidance.
The cane communicates information mainly through the haptic senses. In other words, the user detects forces on the cane handle as its tip collides with objects. However, it is importantto be aware that there is an auditory component to the communication also. The sound thatthe cane makes as the tip is tapped on surfaces can communicate a lot of information. Forinstance the texture of the path (e.g., concrete versus grass) will be apparent from the soundthe tip makes. Also the sounds generated will be modulated by the environment. A closedarea surrounded by walls will generate echoes, whereas an open one does not. The amount ofinformation available from such natural auditory sources should not be underestimated. JohnHull describes  how he can recognize when he is walking by railings by the intermittent echo that they generate6. Snow is sometimes described as ‘the blind person's fog' - becauseit dampens sounds rather as fog blocks sighted people's vision.
One of the major disadvantages of the traditional cane is that it operates only within a verynarrow vertical range. That is to say that it will generally detect obstacles at ground level.
While that is sufficient in many environments, there is clearly a danger from any obstacles up to head height. This is one advantage that high-technology sensors can have; they can scanthe entire path ahead of the user.
There is then the question as to how to communicate the information to the user, in a non-visual form. Sound is the obvious medium to use . There are, however, two particular problems with sound: auditory interference and the bandwidth problem.
A question arises as to how to present the auditory feedback from a guidance device. Head- phones may seem the obvious choice. They can present the information privately. This isimportant because the information is not of any use to anyone else in the vicinity and istherefore likely to annoy them. More importantly, any audible sounds would draw attention tothe person generating them and might be perceived as a label of their blindness. Headphonescan also be used to present information spatially, either using simple binaural stereo orthree-dimensional spatializations. Finally since the advent of the portable stereo player, ithas become socially acceptable to wear headphones in public, so that their use is not a socialfaux pas.
However, headphones are in practice not necessarily appropriate. The main problem is thatthey are tend to interfere with environmental sounds. There are various headphones availabledesigned to avoid this problem by not blocking external sounds , but their effectivenessis open to question.
Conspicuity and aesthetics are important factors, the importance of which are easy tounderestimate. Most people do not like to stand out in the crowd, and this is just as true ofpeople with visual disabilities as for sighted people. Modern white canes are usually foldable.
That is to say that they can be dismantled and folded into a package around 20cm in length.
This means that their visibility is under the user's control. As illustrated by the symbol cane, one of the features of the white cane is that it can be positively used as a signal to otherpeople that the owner has a visual disability. However, on the other hand, the user can alsochoose to fold the cane away, removing that signal.
Some high-technology devices are not so discreet. For instance, the Kaspa  is a box worn on the forehead. While improvements in miniaturization will almost undoubtedly make it possible to conceal such devices better, most users will still not want to wear equipmentthat is too visible. Any such device makes the user stand out, clearly indicates that there issomething different about them (it may not be obvious that the person has a visual disability)and may make them seem to be quite odd and freakish.
The importance of aesthetics should also not be underestimated; even a device which is very positive in the assistance and power that it gives the user, will be rejected by many if it is toougly. (See also Chapter There has already been mention above of changing attitudes towards headphones, which 6Another interesting example is the experiments by McGrath et al.  in which it was found that blind people could locate and accurately describe objects (a sheet of aluminium, a sheet of aeroboard and a leather football)in a dark room using only the sound of their voice.
Auditory Display in Assistive Technology 439 also suggests a fashion element. With the advent of the Sony walkman in the 1980s, itbecame acceptable (at least among young people) to wear headphones in public. For themost part they were small, discreet, and not very noticeable. Now the wearing of headphonesis common. In fact, in some environments (such as on public transport) there may be asmany people wearing headphones or earphones as not. Yet fashion has also moved on. Thereare those now who prefer not to wear barely visible earphones, but rather large, highlyconspicuous headphones. They would, no doubt argue that their choice is based on acoustics,that the sound reproduction is so much better, but at the same time, the headphones areusually high quality ones - of sleek design and with the accompanying clear brand labels. Inother words, there is an element of boasting in the wearing of these devices.
It would be ideal if the same kind of positive kudos could be attached to aids for visuallydisabled people. In other words, the device could become something ‘cool' and not a labelof deficiency. The headphones example illustrates, though, that aesthetics and fashion caninvolve complex interactions.
Yen  provides a comprehensive list of ETAs, some of which are explored in more detail in the following sections. While the emphasis is on the technical specification of these devices,it should be apparent that other factors - including aesthetics - are also important.
17.5.1 Obstacle Avoidance
There are a number of devices which operate as obstacle detectors. It is significant that the same approach to obstacle avoidance - a portable sensor generating auditory signals -has been tried many times. There is no point in trying to provide an exhaustive list of suchexperiments, but several devices are reviewed in , and  including: Russell Pathsounder, Nottingham Obstacle Detector, Two exceptional examples are the Bat ‘K' Sonar-Cane7 and the UltraCane8, exceptional in that they are commercially available products. The ‘K' Sonar is a hand-held deviceresembling a flashlight or torch that can be clipped to a white cane. It has a cable connectionto two miniature earpieces. The pitch of the echo sounds is proportional to distance: high-pitched sounds relate to distant objects and low-pitched sounds related to near objects.
(Examples are provided, see Table One feature of many of these hand-held devices is that they are directional. That is to say thatthey generate feedback about obstacles only when they are within the (narrow) beam of thedevice. This means that spatial information is given directly by the device (i.e., through the Scanning a 4cm-diameter plastic pole at 1.5m from left to right and back.
Walking towards a glass door from a distance of 5m to 1.5m and then retracing steps back to 5m.
Person approaching from 5m to the halt position and then retracing his steps.
Standing in front of a wooden fence with spacing between small panels and scanning the torch to the left and right to ‘shine' the beam along thefence line.
Scanning the torch down onto a grass lawn and up again.
Standing in front of a 50cm wide tree. The tree has only a thin layer of bark and a thin (4cm) shoot growing out at the base of the tree; a clumpof short flax on the other side. As the ultrasonic beam scans across itproduces a strong ‘warbling' sound from the trunk, a soft mushy soundfrom the flax, and a soft short whistle from the shoot.
Standing in front of a concrete block wall with large thick well-developed ferns at the side of the standing position. The torch scanned across theferns onto the wall and back again. The wall produces a tone sound. Theferns made a strong mushy sound.
Table 17.1: Sample K-Sonar sounds.
kinesthetic information that the user has about the position of the hand grasping the device).
There is no requirement to encode spatial (directional) information in the auditory signal.
This makes the signal simpler - and hence generally easier to comprehend. In other words a hand-held device sends out a one-dimensional beam and scanning it horizontally addsa second dimension of information, whereas a representation of the entire scene includesall three dimensions. These might be represented directly by spatialization of the auditoryrepresentation (as in the Kaspa, ) or by applying some other modulation to the signal.
The UltraCane is also important in that it is commercially available. It avoids the problems of auditory output discussed above by presenting its information haptically. As such, it isoutside the scope of this book, but it is interesting in that it possibly illustrates an attemptto sidestep some of the disadvantages of using sound. Sounds - and headphones - are notused, so there is no masking of the natural acoustic environment. The mapping of obstaclesto vibrations of different buttons in the cane handle, with strength indicating separation, is anatural one.
As mentioned earlier, despite the advent of clever electronic aids, the white cane remains the most popular device. It is worthwhile looking at reasons for this. Differences between guidecanes and electronic alternatives are summarized in Table The NavBelt is an experimental device of interest because of the ways it operates [23, 24, 25, 26, 27]. It takes the form of a belt worn around the user's waist. The belt contains an array ofsonar devices. The sonars measure the distance to obstacles. NavBelt operates in two modes.
In Guidance Mode it is designed to actively guide the user around obstacles towards a target, while in Image Mode it substitutes an auditory scene for the visual scene (more akin to the Auditory Display in Assistive Technology 441 kinds of visual substitution systems explored in the next section).
The sonars detect obstacles from which the NavBelt calculates the polar obstacle density, a measure which combines the size of obstacles and distance to them. In Guidance Mode, theNavBelt calculates the area with the lowest polar obstacle density near the direction of traveland guides the user in that direction. In other words, Guidance Mode works best when thetarget is known. This might be achieved by integrating the NavBelt with a navigation aid.
Bornstein  lists this as a potential future development, but there is no evidence of thishaving been subsequently implemented. In the absence of an absolute means of specifyingthe target, the device uses heuristic approaches to infer the intended direction of travel.
Electronic obstacle detector Inexpensive. Losing one or accidentally Expensive. The ‘K' Sonar costs of the swapping with another owner is not a ma- order of €500 or $650, and the Ultracane jor problem. It is feasible to own more is around €750 or $900.
than one in case of loss or damage. Astandard guide cane costs of the order of €20 or $30.
Subject to faults and requiring mainte-nance.
Does not interfere with hearing.
Acoustic signals may block natural cues.
Senses only at ground level.
Can be designed to sense up to headheight, but may not detect some impor-tant ground-level obstacles (e.g., kerbs).
Extensive training required - over 100 Estimates and claims as to the amount of training required vary.
Short-range - effectively the length of the Can be designed to operate at longer cane (1 - 2 meters).
ranges. Typical sonar devices can oper-ate up to 10 meters. Video-based systemstheoretically can operate up to the visualhorizon.
Requires constant active exploration.
Requires constant active exploration.
Table 17.2: Comparison between the features of the traditional guide cane and electronic It is interesting that technological orientation devices have been under development for atleast thirty years (e.g. ). The ‘K' Sonar had achieved sales of 1550 up to 20109 - butthis is a tiny proportion of the market.
The guidance information is presented to the user as binaural sounds on headphones with interaural time difference to create the impression of directionality. In Guidance Mode thepitch and amplitude of the sounds are proportional to the recommended travel speed. Theprinciple is that higher pitch and amplitude attract attention so that the user will instinctivelyslow down and concentrate on the direction of the signal. A special low-pitch signal (250 Hz,near to middle C) is generated when the direction of motion is approximately correct (i.e., 9Personal communication Table 17.3: Average walking speeds (ms-1) under different conditions. ‘Sighted' refers to the speed of the average sighted walker. The other figures relate to the evaluation ofthe NavBelt in its two modes, both in simulations and in physical traversal ofa laboratory. Note that the figure for Image Mode (Physical) was only attainedafter ‘several hours' of training.
within ±5°). This provides simple positive feedback when the user is going in the correct direction. At the same time, using a low-frequency tone will have less of a masking effect onenvironmental sounds.
Image Mode is designed to invoke the impression of a virtual sound source sweeping across 180° in front of the user. The sweep is completed in 37 discrete steps separated by 5°.
The sounds used are square waves modulated by amplitude, pitch and duration . The duration of a signal varies between 20 and 40ms, where 20ms indicates the longest distanceto an obstacle (5 meters) and 40ms indicates a very close object (0.5m). The amplitudevaries inversely with the range reading from the corresponding sonar sector. Sixteen discreteamplitudes can be selected, where the lowest value (silence) represents no threat to the userfrom that direction, whereas the maximum value indicates a high risk. The intention is that ‘the user's mind creates a mental picture of the environment that adequately describes the obstacle density around the user.' [24, p. 113].
Evaluations of the NavBelt have been based on simulations. In navigating randomly selected (simulated) maps the average travelling speed was 0.52ms-1 (compared to an average sighted person's walking pace of around 1.3ms-1). It was evident that the walking speed depends verymuch on the complexity of the environment. A more complex environment requires greatercognitive effort by the user and apparently leads to a slower walking speed. At the same timethere appeared to be a learning effect, whereby experienced NavBelt users attained higherspeeds. It was also noted, though, that users with ‘reduced auditory perception capabilitiestravel slower than highly skilled people.' . As well as the simulations, experiments werealso carried out using the actual NavBelt in which blindfolded participants travelled fromone side of the laboratory to the other. Walking speeds were slower than in the simulationbecause participants were more cautious. ‘However, after a training period of several hoursthey traveled safely through the controlled environment of the laboratory with an averagespeed of 0.4ms-1.' (ibid.) Simulation evaluations of Guidance Mode showed an average travel speed of 0.76ms-1 andan average deviation from the recommended direction of 7.7°. In similar experiments withthe real prototype NavBelt whereby participants travelled 12 meters across the laboratorythe average speed was 0.45ms-1. A more-realistic experiment was carried out in an officebuilding corridor with which the participants were familiar. The length of the path was 25meters and included several corners. No obstacles were positioned initially in the corridor, Auditory Display in Assistive Technology 443 but passers-by did walk down the corridor. Participants were also able to avoid obstaclesand attained an average walking speed of 0.6 ms-1. The walking speeds attained under thevarious conditions are summarized in Table 17.5.2 Visual Substitution
Developers of the NavBelt have experimented with two approaches to guidance. Its ImageMode is an example of the approach whereby the idea is to generate an auditory fieldrepresenting the entire visual scene that a sighted person would see. The visual picture canbe captured through video cameras and then translated into an auditory form.
The bandwidth problem was described above. The same problem applies in this application.
Sensors such as video cameras can provide large amounts of (visual) information. Thequestion is how much of that information to provide to the user. The more information, thegreater the user's freedom to navigate, but the harder it becomes to interpret and understand.
Obstacle detectors, such as those described above, can generate quite simple sounds, givingan indication of the location of the size and location of objects. At the other end of the scalethere have been attempts to render the entire scene sonically.
One example is the Voice Project (see [29, 30] and the Voice web site10). This creates arepresentation of the visual picture pixel-by-pixel. The vertical positions of pixels are repre-sented by pitch, horizontal positions (left-to-right) are represented by time, and brightness isrepresented by loudness. The sound effectively scans horizontally across the image so that avertical column of pixels are all presented in a single, complex sound. The start of a scan ismarked by a ‘click' and the scanning repeatedly loops. An example of this sonification isshown in Figure This simple mapping is quite raw, implying minimal processing of the image. The system relies instead on brain plasticity. The intention is that with practice the user will learn tointerpret the auditory scenes naturally. Some support for this approach is given in  whichdescribes the examination of functional magnetic resonance images (fMRI) of the brains ofblind and sighted participants performing sound localization tasks. They observe that blindpeople demonstrate a shift in activated brain areas towards more posterior areas - the areasthat are involved in visual processing in sighted people11.
González-Mora et al. [31, 37] have experimented with a prototype device which incorporatesvideo cameras and headphones mounted on a pair of spectacles. Their sonification isdescribed as follows: ‘The basic idea of this prototype can be intuitively imagined as trying to emulate,using virtual reality techniques, the continuous stream of information flowing tothe brain through the eyes, coming from the objects which define the surroundingspace, and which is carried by the light which illuminates the environment. In 11Modern brain imaging techniques such as fMRI have enabled researchers to shed new light on the idea that blind people's non-visual senses are in some ways heightened. Previously there was some skepticism about thisapparent phenomenon (e.g., ) but now there is an increasing body of knowledge which suggests that the areaof the brain usually referred to as the visual cortex is devoted largely to the processing of visual informationsimply because in sighted people that is the predominant source of stimulation. In people deprived of sight,the same area can be reassigned to the processing of non-visual information. Examples of this work include[33, 34, 35, 36].
Figure 17.1: Sample graphic which is sonified by the Voice system as illustrated in Sam- ple Note that the blurred style of the picture is deliberate, reflecting thepixel-by-pixel translation to sound.
this scheme two slightly different images of the environment are formed on theretina, with the light reflected by surrounding objects and processed by the brainto generate its perception. The proposed analogy consists of simulating thesounds that all objects in the surrounding space would generate' [31, p. 371-372].
Of course in a real environment, inactive objects do not generate sounds, but in the prototypesystem a click sound is used: ‘When a person is in front of a particular scene, he/she receives an acoustic inputconsisting of a set of a set of auralized12 "clicks", with a randomized order ofemission, corresponding to the calculated 3-D coordinates of the objects. Thisset of "clicks" is sent to the person in a time period of 153ms, after which thenext acoustic image is sent. Depending on the number of coordinates that theobjects occupy inside the perception field, there is a variable interclick interval,never less than 1 ms.' (ibid. p. 374).
Interestingly, in the context of the earlier quote from John Hull, the perceived effect isdescribed as resembling ‘a large number of rain drops striking the surface of a pane ofglass'.
Spatial information is reproduced by spatialization of the sounds, using individualized head-related transfer functions (HRTFs)13. A field of 80° horizontally by 45° vertically is presented with a resolution of 17 × 9 and 8 levels of depth (although higher resolutions are being 12The authors appear to use the word ‘auralized' to mean ‘spatialized'.
13Every individual is different in the way they perceive spatial sounds because of the shape of their ears and head.
This can be modeled for artificially spatialized sounds by creating their HRTF. Best results are achieved usingindividual HRTFs, although an ‘average' HRTF can be used, but it will be less effective.
Auditory Display in Assistive Technology 445 Evaluations have yielded results which are claimed to be encouraging regarding blind people'sability to perceive the layout of a test room - although the evaluation is not described in detail.
It is interesting that some participants reported experiencing apparent synaesthesic effects, whereby the sonification evoked a visual perception of ‘luminous sparkles' coinciding with the spatial location of the sound sources. The system is very much a prototype and not yet areleased product.
Sighted people rely on light reflecting off objects in the environment entering their eyesand forming an image on the retina. Babies learn to interpret these images through activeexploration of their environment and hence learn to rely on them in interacting with the world.
Visual substitution systems aim to create a similar representation using sounds. Most objects do not make sound, though, so there is no natural acoustic ‘light', so instead a visual imageis translated by technology into sound. The hope is that people can learn to interpret thesesoundscapes as well and as naturally as visual scenes. There is some hope for this approachin that the plasticity of the brain in interpreting acoustic input has been well demonstratedby the success of cochlear implants for deaf people. A cochlear implant generates artificialsensations in the auditory nerves. There is no reason to believe that the sensations thusgenerated resemble those generated by natural hearing, and yet - with practice - peoplebecome quite adept at interpreting those inputs as if they are (low fidelity) sounds .
It has to be stated that there is a dearth of formal evaluations of most of the systems describedin this section. This is clearly a weakness in research terms, but furthermore there mustalways be a fear that the systems are ineffective and that to pursue them further would be a waste of time.
17.5.3 Navigation Systems
The obstacle avoidance and visual substitution systems described above are predominantly concerned with short-range mobility, mainly the avoidance of obstacles. A different problemis that of navigating to a chosen destination. For instance, when a person arrives by trainin a strange city, they may need to know how to get to an office block which is known tobe walking distance from the station. This is a problem for all travelers, but sighted peoplecan rely on maps and similar aids to work out and follow the correct route. It is increasinglycommon now for car drivers faced with such navigation problems to rely on a SatNav globalpositioning device and the same option is available for blind pedestrians.
A number of systems have been developed. One feature which they all seem to share, though, is a reliance on the use of speech, and apparent minimal use of non-speech sounds.
Some of the systems developed are: Trekker: Based on the Maestro, which is a PDA designed to be accessible to blind users,
the Trekker is a talking GPS addition. Further details are available at BrailleNote GPS: BrailleNote is a portable braille PDA which also has an optional GPS
attachment. It displays information in speech and braille. It is also available fromHumanware and  is a (somewhat dated) com-parative evaluation of Trekker and BrailleNote GPS.
Sendero: This company markets accessible GPS software for a number of devices, in-
cluding the BrailleNote, the VoiceSense PDA, Windows Mobile and Symbian phonesas well as non-mobile devices - the desktop PC for route planning These rely almost entirely on voice output.
Mobic: Mobic was an experimental system developed with funding from the European
Union. An evaluation of the system is documented in , but the output was entirelyspoken.
Satellite navigation is a technology developed to assist in navigation tasks by providing theuser's location in the world accurate to the nearest few meters. Originally this was for militarypersonnel operating in unfamiliar territory (presumably because they had just invaded theterritory!). However, it did not take long for developers to realize that the technology mightbe a valuable aid for those whose navigation problems arise from their not being able to see.
The systems listed above are examples of this. Further developments and improvementswill no doubt occur and it would seem to be an application in which there is potential for the use of non-speech sounds. The street is an environment in which naturally occurringsounds are invaluable to a blind pedestrian. Guidance information presented in a way whichis complementary to the natural soundscape would be most valuable; it must be possible toimprove on plain speech.
17.6 Other Systems
There are a variety of other attempts to translate graphical materials into sounds. They are all research projects which have not yet found their way into everyday use, but brief details aregiven here, along with links to further information.
A Cartesian graph is a simple but rich visual representation of information. See Figure for instance. Many people have had the idea that the curve of such a graph could berepresented by a soundgraph or auditory graph based on a sound, the pitch of which varies with the height of the curve, but one of the first published suggestions was . A number of different groups have implemented the idea, including [42, 43, 44]. Walker & Mauneypresent guidelines on soundgraph design in . (See also chapters A powerful visual facility is that of the glance. In other words, the viewer can look briefly at a visual representation and get an overall (but imprecise) impression of its meaning.
Playing the waveform of the soundgraph curve, as in Sample gives a similar overallimpression of the curve's shape. To gain more precise information the user might interact with the sound. Thus a sound cursor can be moved left and right along the curve and by listening for the point of highest pitch, the user might locate the maximum in the curve inFigure Having located the point, its coordinates could be found using speech.
The soundgraph implementation of Edwards and Stevens  facilitated the location of such turning points (maxima and minima) by allowing the user to hear the derivative of thecurve. At a turning point the slope of the curve is zero and hence its derivative is a constant.
Listening to the derivative, it should have constant pitch at such a point. Grond et al. have taken this idea a step further by displaying the first m terms of the Taylor Series of a Auditory Display in Assistive Technology 447 Figure 17.2: A graph of y = sin(x) + x/2, a typical curve, which might be represented as a soundgraph. A sound representation of this graph can be found as Sam-ple function. This work is in its early stages but the authors conclude that for suitable students (essentially those with experience of auditory media) ‘the sonified functions are very sup- portive to grasp important characteristics of a mathematical function' [46, p. 20]. Examplesof these sonifications are available at A good soundgraph implementation should have the advantage of giving the user a feeling of very direct interaction with the mathematics. For instance, the user can move along thecurve, sensing significant points (e.g., a maximum turning point) just by hearing the variationin the pitch (rising then falling). This contrasts with other representations such as algebra, where the requirement to manipulate the symbols can interfere with the appreciation of the mathematics that they represent. Yu, Ramloll, and Brewster  have gone a step further infacilitating direct interaction with soundgraphs by adding haptic interaction via the Phantomforce-feedback device.
Soundgraphs have generally been used to represent curves on Cartesian graphs. Anotherform of graph is the scatter plot. Riedenklau et al. have developed a very novel non-visualrepresentation of the scatter plot that uses sounds and Tangible Active Objects (TAOs) . A TAO is a small plastic cube with on-board processing and wireless communication facilities.
Placed on a Tangible Desk (tDesk) surface they can be tracked by camera. Scatter plots canbe represented on the surface and the position of the TAO relative to clusters is fed back in anauditory form as a sonogram . Sighted testers (who were blindfolded for the experiment)matched the TAO representation of different scatter plots to visual representations with a77% success rate. Again this work is in its early stages and further developments - includingtesting with blind people - are proposed.
Audiograph [50, 51, 52] was a system originally designed to test how much information could be conveyed in non-speech sound, but it was soon realized that the most appropriateapplication would be as a means of presenting graphical information to blind people.
The following graphical information is communicated for each graphical object: 1. the position of each object; 2. the type, size and shape of each object; 3. the overall position of the objects using various scanning techniques.
All these used a similar metaphor - a coordinate point is described by using a musical mapping from distance to pitch (a higher note describing a larger coordinate value), and xand y co-ordinates are distinguished by timbre (Organ and Piano).
This is a simple form of translation from visual pixel information to non-speech sounds of different pitch, similar to soundgraphs [53, 54, 55]. An auditory cursor sweeps acrossthe graphic horizontally. As it intersects a black pixel it makes a sound, the pitch of whichrepresents the vertical height of the pixel. Figures and and their accompanyingsound samples show how simple shapes are translated using this scheme.
Figure 17.3: A triangle, which is rendered in sound by Smartsight as Sample There is a constant (low) tone, representing the base of the triangle with rising andfalling tones representing the other sides.
Simple graphics, such as those above can be perceived quite easily without training, but thedevelopers claim that with training the same approach can be successfully used with muchmore complex layouts. Figure is an example of a more complex, compound shape,but the developers claim that with training listeners can even interpret moving, animatedgraphics.
Smartsight originated in research in the University of Manchester, Institute of Science and Technology (now part of the University of Manchester) but was transferred to a spin-off company which has the objective of commercializing the idea. As yet, though, commercialsuccess seems limited; during the writing of this chapter the company's web site disap-peared.
Auditory Display in Assistive Technology 449 Figure 17.4: A square, which is rendered by Smartsight as Sample Notice that this starts with a sharp chord, representing the left-hand vertical edge, followed by apair of notes representing the horizontal edges and finishes with another verticaledge.
Figure 17.5: Sample graphic that would translate to Sample using the Smartsight system. The picture is a stylized, symmetrical house, with a trapezoid roof, tworectangular windows and a door.
This chapter has been largely concerned with the use of hearing as a substitute for vision, but the two senses, and the stimuli which interact with them, are very different. The ‘bandwidthproblem' has been discussed earlier. Related to that is the fact that, in general, sight ispassive. That is to say that, except in artificial conditions of darkness, visual information isalways available. Thus, sighted people receive vast amounts of visual information constantly,and large parts of their brains are assigned to processing that information. Sound is alsoinherently temporal, while vision is more spatial. Of course sounds have a spatial origin andvisual objects can move over time, but the emphasis is different in each case.
Sound, by contrast, is active, inasmuch as something must be moving to generate the sound.
Most objects do not emit sounds and so to make them accessible to the auditory channelthey must be made noisy. Sometimes objects can be embodied in sounds - as in screenreaders which assign sounds to the elements of computer programs. Other systems work with the light analogy more directly. The Voice system operates on ambient light. It captures the visual scene, through video cameras, and converts them into sound, but in doing this itconverts from the spatial domain to the temporal. In other words, the pixels are presentedas an auditory raster scan, not in parallel. The problem is that the auditory sense is poorlyequipped to interpret a scene thus presented.
Other devices work rather more like flashlights. The ‘K' Sonar physically resembles a flashlight and it creates an auditory signal representing the portion of the environmentcaptured in its (very limited) ‘beam'. The signal presented is simple, but impoverished. Withtraining, users can presumably interpret the sounds well (Table but such perception ishardly comparable with vision.
The spatialized clicks of González-Mora's system are claimed to give a good picture. These are simple sounds. Serial presentation in a random order may overcome some of the problemsof translation from the visual (spatial) to the auditory (spatial and temporal) domain, but the work is still experimental and yet to be proved.
When the sense of sight is missing other senses must be recruited. Sight is a very powerful sense and so it is very difficult (perhaps impossible) to completely substitute for it. Neverthe-less, the auditory sense has great potential as an alternative. Much research effort has beenexpended into developing technologies which will do this, as described in this chapter. Yetit is significant that this chapter is almost solely concerned with the description of researchprojects; very few of the devices described are in commercial production and those whichare tend to sell in small numbers (see also ). In other words, the great potential for theuse of non-speech sounds as experienced in everyday life and highlighted by the passagefrom John Hull is not being realized.
This arrested development of auditory representation is a phenomenon which might be apparent in other chapters of this book; we authors and researchers know the potential forthe use of auditory displays and are enthusiastic about promoting their adoption - yet theusers are unconvinced. Within the context of this chapter specifically, one might expect thatthe users - those without sight - would in some senses be the easiest to convince, would bemost willing to adopt an alternative for the sense which they lack, even if the alternative isless-than-perfect. Yet this is not the case.
Furthermore, while this chapter is concerned with disabled people, it has concentrated onthose with visual disabilities. If auditory interaction has all the benefits and powers that weassert it has, then surely it could be a useful aid to those who have difficulties in interacting with technology due to other forms of impairment? Yet there seems to be almost no work that has demonstrated this to be the case.
It is not unusual for a researcher to conclude that what is required is more research, yetthat is not always a cynical attempt at self-preservation. So it is in this case that there is agenuine need. We can develop auditory interfaces that are as good as the simple white cane, which give as much information as the cane (including the auditory feedback as it clicks on surfaces), and interfaces which can provide as much richness as rain falling on a garden - butas yet we do not know how.
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Oral Tradition, 7/1 (1992):116-142 Latin Charms of Medieval England: Verbal Healing in a Christian Oral Tradition Lea Olsan This is an essay to open a discussion of medieval Latin charms as a genre rooted in oral tradition. It will concern itself solely with materials drawn from manuscripts made in England from about A.D. 1000 to near 1500. One reason for setting such limitations on the materials is that restricting the study chronologically and geographically will facilitate identification of features peculiar to the insular English tradition of Latin charms.1 For though Latin charms can be found throughout medieval Europe, to make cross-cultural comparisons prematurely might obscure distinctive regional features. To begin, it seems best to state what is meant by the word "charm" in this paper.
Letter from the Secretariat I, Anmol Kaur Bagga, Secretary General of TCET-MUN 2015, along with the Secretariat feel immense pleasure to welcome you to the TCET-MUN 2015. We feel honored to host you during the 3 days of ardent debate. Now in its fifth year, TCET-MUN has grown leaps and bounds from its humble beginnings in 2010. From a conference that simulated two committees back then, we are proud to have six committees this year. The conference is a culmination of dedication and commitment of many people, who worked to make this conference memorable and a quality learning experience.