Abstract:
A touch screen system for the vision-impaired provides a speed list in which each of the virtual buttons on a screen are duplicated in a line along one edge of the screen to provide rapid access to the virtual buttons while taking advantage of their logical grouping among multiple screens to assist both vision-impaired and fill-sighted individuals.

Description:
This invention was made at the Trace R&amp;D Center of the University of Wisconsin Madison with United States Government support awarded by DED Grant #H133E30012 
     The United States has certain rights in this invention. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to computer systems using touch screens, and in particular, to a touch screen system suitable for use by the vision-impaired. 
     BACKGROUND OF THE INVENTION 
     An electronic touch screen provides an alternative to a standard typewriter-style electronic keyboard for the entry of data into a computer. With a touch screen system, the user enters data by touching virtual buttons displayed on the computer display. The touch screen eliminates the need for a separate keyboard, and the space required for the keyboard, and may offer a more intuitive interface to users unfamiliar with computer operation. 
     With a touch screen system, the type, size, and number of the virtual buttons may be readily changed by changing computer&#39;s program without changes in the associated hardware. Thus, the touch screen system offers a user-interface that may be flexibly tailored to a particular application. The ability to divide virtual buttons among different screens and to display only those screens needed by the user&#39;s particular task can simplify data entry. The combination of text and graphical elements on the screen along with the virtual buttons can help to further guide the user through the steps of data input. 
     Normally, a touch screen system uses a touch screen panel which is placed directly over the viewing area of a standard computer display, for example, a CRT or a liquid crystal display (“LCD”). The touch screen panel provides a signal to a computer associated with the computer display indicating where on the surface of the display a stylus or finger is placed. This signal may be generated, for example, by acoustic systems detecting absorption of sound by a finger on the surface of the display or by systems using crossed beams of infrared light arrayed along x and y axes which are broken by the finger, or by laminated transparent electrodes which are physically compressed against each other to provide a point electrical contact that may be interpreted as an x and y coordinate. 
     Despite the advantages of touch screen systems in certain applications, they present an insurmountable barrier to the vision-impaired user who perceives only the featureless surface of the display screen knowing that it may contain one or more virtual buttons of arbitrary placement and function. 
     In contrast, a typewriter-style electronic keyboard, with its tactilely distinguishable keys and standard layout, can be used by both full-sighted and vision-impaired individuals. 
     It would be desirable to find a method of making touch screen systems accessible to both full-sighted and vision-impaired individuals, that preserves some of the advantageous aspects of a touch screen system in simplifying data entry tasks and in providing a flexible user interface. It would also be desirable to make such systems usable by those who can see but who cannot effectively read the text which is displayed and which is necessary for system use. 
     SUMMARY OF THE INVENTION 
     The present invention provides a touch screen usable by both full-sighted and vision-impaired individuals. In the invention, the spatial extent and location of the touch screen&#39;s buttons are indicated by a distinctive sound (“audio ridge”) triggered when a user&#39;s finger crosses into or out of the button boundaries separate from a spoken message which identifies the function of the button. A background sound identifies points on the screen which are outside any virtual button. 
     The possibility of confusing, multiple audio ridge signals, such as might be created by a touch position neither clearly in nor out of the virtual button, are eliminated by defining separate button boundaries for entry and exit of the button with the exit boundaries being somewhat larger. Intelligibility of the spoken message identifying the function of the virtual button is ensured by providing two modes of operation upon leaving a virtual button. If upon leaving the button the screen is still contacted, the spoken message is truncated facilitating the ability to move between buttons without the need to fully play each button&#39;s spoken message. If the touch point is removed, i.e., the finger is lifted from the screen, the message continues to play to alert the user of any new button that may have been entered even instantaneously before lifting the finger. 
     The arbitrary spatial arrangement of the buttons may be compressed into a linear format termed a “speed list” that works in conjunction with the normal virtual buttons of the touch screen but enables the user to move quickly between the various buttons. The speed list may be aligned with a guide ridge at the edge of the screen, the guide ridge including tactile separators to further aid the user in moving between these buttons. 
     Specifically, the touch screen of the present invention provides an electronic display screen having a display area positioned beneath a touch panel commensurate with the display area and providing a coordinate output indicating a touch point in the display area. The electronic display screen, the touch panel and audio circuitry are connected to an electronic computer which executes a stored program to identify a boundary of a virtual button with respect to the display screen and when the touch point crosses the boundary, to instruct the audio circuitry to generate an audio ridge signal delineating the boundary. The electronic computer then instructs the audio circuitry to generate a spoken message identifying the virtual button while the touch point is within the boundary. 
     A first audio ridge signal may be generated when the touch point crosses into the boundary of the virtual button and a second audio ridge signal may be generated when the touch point crosses out of the boundary. Further, the audio circuitry may generate a background sound while the touch point is outside the boundary. 
     Thus, it is one object of the invention to allow the user to scan the touch point across the screen and, through the use of audio ridge signals combined with a spoken message, obtain a mental map of button placement, size and function. The use of an audio ridge signal that is distinct from the spoken message separates the concepts of the button space and button function, improving the user&#39;s understanding of the screen. 
     The electronic computer may identify a first inner boundary and a second outer boundary of the virtual button, and the audio circuitry may be instructed to generate the audio ridge signal only when the touch point is crossing into the inner boundary or when the touch point is crossing out of the outer boundary. 
     Thus, it is another object of the invention to provide the benefits of a separate audio ridge signal without the risk of generating ambiguous tones if the boundary is only partially crossed. By moving the boundary point, depending on the direction of entry or exit from the virtual button, multiple accidental crossings of the boundary are eliminated, aiding in intelligibility. 
     The electronic computer may display plurality of first virtual buttons having arbitrary locations on the display screen and may activate one of the virtual buttons to execute an associated software routine when the touch point is at the location of the activated virtual button. The computer may also generate a plurality of second virtual buttons having a one-to-one correspondence with the first plurality virtual buttons, but arranged on the display screen in the linear array. When the touch point is within the location of one of the second virtual buttons, a subroutine associated with the one virtual button and with one of the first virtual buttons is activated. 
     The electronic screen may further include a frame extending around the display surface and providing a ridge along which a finger may be drawn and the plurality of second virtual buttons may be arranged on the display screen adjacent and parallel to the ridge. The ridge may also include a plurality of embossments, and the virtual buttons may be arranged on the display screen to align with one each of the plurality of embossments. 
     Thus, it is another object of the invention to provide a duplicate set of virtual buttons on the screen arrayed in a fashion to facilitate use by a vision-impaired individual. This second list, besides being in a straight line, may have standard spacing and a limited extent. Thus the user, by running his or her finger or stylus along this line, can determine all the possible buttons on that screen. 
     The electronic computer may generate a spoken message identifying a virtual button when the touch point crosses into the virtual button. When the touch point then crosses out of the virtual button the message may be truncated. However, if the touch point disappears off the screen the message will be completed. 
     Thus, it is yet another object of the invention to ensure that a complete message is communicated to the user when the user&#39;s finger is lifted from the touch screen, for example, prior to confirmation of button selection, and yet to allow the user to move quickly from message to message without the need to listen to the complete message. It will be understood that this feature, as well as others to be described, will be of benefit not only to the vision-impaired but also to those who have trouble reading the text messages for any reason including unfamiliarity with the written language. 
     The foregoing and other objects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof and in which there is shown by way of illustration, a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference must be made therefore to the claims herein for interpreting the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified blocked diagram of a typical touch screen system such as may be used in a kiosk showing the position of the touch panel in front of a display screen with a separate confirmation button positioned at the bottom of the screen; 
     FIG. 2 is a front elevation view of the display screen of FIG. 1 showing an example set of virtual buttons together with particular touch points and trajectories associates with features of the invention; 
     FIG. 3 is an enlarged detail from FIG. 2 showing a touch path across a particular virtual button and the expansion and contraction of the button boundary depending on the direction of the trajectory of the touch point; 
     FIG. 4 is a figure similar to that of FIG. 3 showing two button boundaries different only in vertical dimension for a nondisplayed speed list button; 
     FIG. 5 is a timing diagram showing the generation of audio ridge signals, background sound, and spoken messages as a touch point moves across virtual buttons; 
     FIG. 6 is a simplified flow chart showing the parsing of touch trajectories into zone changes which affect process actions; 
     FIG. 7 is a state diagram showing the process actions invoked by various changes in zones of FIG. 6; 
     FIG. 8 is a representation of a table contained in memory defining each virtual button displayed on display screen; and 
     FIG. 9 is a detailed enlargement of the screen of FIG. 2 showing a speed list made visible together with embossments providing ready access to the list members. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, a touch screen system  10  includes an electronic display  12  having a generally planar and rectangular display area  14  on which text and graphics may be displayed. Such displays  12  are well known in the art and may make use of a cathode ray terminal (“CRT”) or a liquid crystal display (“LCD”). 
     Positioned in front of the display area  14  is a touch panel  16  having an active area  18  commensurate in size with the display area  14 . The display area  14  may be seen through the active area  18 , and a user touching the display area  14  with a finger or stylus (not shown) must pass the finger or stylus first through the active area  18 . Touch panels  16  are also well known in the art and may employ a number of different technologies, including those employing crossed beams of infrared light (which detect the finger by the interruption of one or more beams), and those employing layered transparent electrodes (which detect the finger by its deforming the layers and causing the electrodes to touch). 
     Preferably, in the present invention, the touch panel  16  provides a high resolution X-Y coordinate signal indicating the position of the finger on the display area  14 , and “no stylus signal” when the finger is removed. Thus, the location of a touch point of a finger against the display area  14  can be accurately assessed. 
     A confirmation button  20 , being a single-pole single-throw momentary push button switch is mounted beneath the touch panel  16  in a prominent and uniform location to be accessible to a sight impaired individual. 
     Flanking the display  12  are one or more speakers  22  directed toward the user of the touch screen system  10  so that speech and tones generated by the speakers  22  may be heard by the user. 
     Each of the various components  12 ,  16 ,  20  and  22  are connected to an internal computer bus  24  by commercially available adapter cards  26 . The confirmation button  20  is connected to the bus  24  by a standard mouse or keyboard port  28  whereas the signal from the touch screen is received by a serial port  30 . A video card  32  provides the interface between the bus  24  and the display  12  and a sound card  34  provides an interface between the computer bus  24  and the speakers  22 . The sound card  34  may include an on-board amplifier, to provide sufficient volume to the speakers  22 , and may include a standard FM synthesizer chip as well as a digital-to-analog converter (“ADC”) for synthesizing arbitrary wave forms from a stored sound look up table. This latter feature permits, for example, generating spoken words from text according to readily available speech synthesis software. 
     Also attached to the computer bus  24  is a microprocessor  38  and associated computer memory  40  for holding a stored program executed by the microprocessor  38  together with variables used in that stored program. 
     A modem  42  connects the computer bus  24  to a telephone line  44  to provide access to a remote computer, such as a central bank computer, if for example, the touch screen system  10  is used as a remote terminal in an automated teller machine (“ATM”) or the like. 
     Referring now to FIGS. 1 and 2, the processor  38  may display on the display area  14  a number of virtual buttons  46  arranged arbitrarily over the surface of the display area and divided into one or more “screens” displayed on at a time on the display area  14 . The virtual buttons  46  are grouped on the display area  14 , for example, by function, to improve their ease of use. The virtual buttons  46  are also grouped among different screens, for example, to divide the user&#39;s interaction the touch screen system  10  into discrete logical stages. 
     The virtual buttons  46 , in their simplest embodiment, are rectangular images containing an alphanumeric label. These images are formed by the video card  32  receiving instructions from the microprocessor  38  which most typically simply relays an image previously stored in memory  40 . 
     Virtual buttons  46  may be “pressed” by a user touching the display area  14  (as is Ada detected by the touch panel  16 ) causing the microprocessor  38  to execute a predetermined set of instructions associated with that button. For example, referring to FIG. 2, the screen includes a keypad  52  composed of number keys from 0 to 9. As each number key is pressed, the microprocessor  38  may, for example, receive and store that number and/or transmit it via modem  42  to a central computer. 
     As is understood in the art, each virtual button  46  may include a “pressed” and “unpressed” image reflecting its two possible states. A shadow box around the button  46  changes with these different modes to suggest the shading that would obtain with a real button being depressed or released. 
     Other than the differences between the “pressed” and “unpressed” images, the simplest form of virtual buttons  46  are essentially static: staying in the same place and having the same alphanumeric label on a given screen. Generally, however, a given screen may also include nonstatic virtual buttons, for example, a scrolling list of text  48 . The virtual buttons, further, need not look like conventional buttons but may include for example, animated graphical elements that may move across the screen. Area  48  may be separated into smaller virtual buttons  46  whose location is fixed but whose contents, i.e., the alphanumeric label and the set of instructions executed by the microprocessor  38  change as the display scrolls. In addition, the screen may include printed plain text instructions  50 , which, during non-audio mode (to be described) and unlike the above virtual buttons  46 , generally are not pressed to invoke the execution of a set of predetermined instructions by the microprocessor  38 . Henceforth the term virtual button will be considered to generally embrace any defined field on the screen which may be activated by a touch to cause the computer to initiate a predefined set of instructions. Thus the text field  50  and the scrolling area  48  are virtual buttons  46 . 
     In a non-audio mode, the microprocessor  38  displays a given screen with its virtual buttons  46  and monitors the X-Y coordinate generated by the touch panel  16  comparing the coordinate against a map of button locations contained in memory  40  and associated with that particular screen. If a touch point occurs within the outline of a particular virtual button, that button is considered to have been pressed and the microprocessor  38  executes the instructions associated with that button. 
     In the present invention, an audio mode may be activated in which audio queues are provided to assist the vision-impaired user. In the preferred embodiment the audio mode is entered by a standard gesture in which a stylus (e.g., a finger or pen) is pressed against the upper right hand corner of the display area  14  at point  56  and drawn leftward at least half way across the top of the display area  14  as indicated by arrow  58 . This gesture is selected to be simple and to start at a readily determinable position on the display area  14  and yet to be unlikely to be accidentally invoked. An opposing gesture, in which the finger is pressed against the upper left hand side of the screen  60  and drawn rightward at least three quarters of the way across the top of the screen as indicated by arrow  62  is used to convert back to a non audio mode. Canceling the audio mode intentionally, thus requires a somewhat greater effort by the user than activating the audio mode so as to prevent accidental cancellation and to allow the user the greatest possible latitude in moving a finger around on the screen. 
     When the audio mode has been invoked, generally the touch point will be used to trigger audio cures enabling the vision-impaired individual or the individual who has difficulty reading, improved access to the information and capabilities of the touch  5  screen. In the audio mode of the present invention, the user is provided with audio clues as to the location of the touch point with respect to the defined virtual buttons  46 . Referring now to FIG. 8, the microprocessor  38 , evaluates the touch point signal from the touch panel  16 , against a table  131  stored in memory  40  and indicating the locations (and sizes) of the virtual buttons  46  and providing a spoken message  80  identifying the button&#39;s function. The virtual buttons  46  listed in table  131  are arranged by screens, and each screen is associated with a spoken description  134  describing the general layout of the screen. Thus, the table  131  includes a set of entries  130  for each screen display including a text description of the screen  134  such as may be provided to the sound card  34 . After the audio mode has been invoked, the description  134  of the screen currently displayed by the microprocessor  38  on the display  12  may be played by touching the screen in the upper left hand corner and releasing the touch screen without sliding the finger rightward or downward as indicated by arrows  62  and  33 . The verbal screen description for the screen of FIG. 2, for example, might be: 
     This screen provides for the withdrawal of money from your account or the determination of an account balance. In the lower right hand comer is a telephone type keypad. Above this keypad is a scrolling menu of different account types including: checking and savings accounts. In the lower left hand corner additional buttons allow the numbers on the key pad to be entered or cleared or invoke a help screen or return you to the main menu. Above these buttons are a text description of this screen. 
     Referring still to FIG. 8 within the entries  130  for each screen are entries  136  defining the various virtual buttons on the screen by their location of their boundaries  138  and providing a text message  80  usable by the sound card  34  if that virtual button is pressed. The location data includes the necessary information defining an inner and outer boundaries of the button (as will be described). The message data  80  is normally the same as that printed in the image of the virtual button  46  but in the case of text block  50  is a short description of the text, for example, “text field” so that the user is not burdened with listening to the entire text message corresponding to the printed text within the text block  50  text. 
     Generally in the audio mode, the microprocessor  38  will identify the screen being displayed and based on a comparison of the touch point to the locations  138  for that screen will play the message  80  associated with that button. As mentioned, when the touch point  57  in the upper left hand corner of the display area  14  is pressed the description  134  associated with that screen will be played. 
     Consider now the virtual buttons  46  providing number keys  1  and  2  for the keypad  52 . The touch point may move in a trajectory  66  from a position to the left of number key  1  in an area not occupied by any other virtual button  46  then across the left most boundary of the general number key  1  and across the surface of the number key  1  and out of its right boundary into a space not occupied by any other button  46 . Continuing the trajectory  66  may cross the left boundary of the number key  2  and prior to exiting the number key  2 , the finger may be lifted as indicated by the trajectory  66  becoming dotted. 
     Each point of the trajectory  66  is associated with an audio queue indicated by audio track  72 . Generally for points of the trajectory  66  in area  51  outside of any virtual button  46 , a background sound  74  is generated. Such a background tone may, for example, be white noise which is perceived as a gentle hissing sound. The purpose of the background sound  74  is to establish that a touch signal on the screen is in fact being generated but not within any virtual button; This is particularly important in some touch screens which require moderate pressure to be activated. The background sound  74  further establishes that the audio mode has been invoked and that the basic hardware is working. 
     When the trajectory  66  crosses the left most boundary of the number key  1 , an audio ridge signal  76  is generated. Any easily recognized tone may be used, however, in the preferred embodiment it is a short duration signal in keeping with its purpose for providing immediate and accurate indication of the crossing of a button boundary. 
     Conversely when the trajectory passes out of one button, a second audio ridge signal  78  may be generated, preferably having different characteristics than the audio ridge signal  76  so as to allow the user to discern the entry from the exits of a button. For example, audio ridge signal  76  may be a slightly higher pitched tone suggesting a rising or a lifting as might occur if a real button were crossed and audio tone  78  may be a lower pitched tone suggesting a dropping as if the finger or stylus were passing off of an elevated button. The audio ridge tones  76  and  78  may be further varied to indicate the type of virtual button (e.g., to distinguish between keypad buttons and the text field  50 ). 
     A spoken message  80 , in this case “one”, is begun once the trajectory  66  is within the number key  1 . Also, in this case, where the trajectory passes out of number key  1  into a background area  51  and then immediately into the number key  2 , the message  80  is truncated upon the occurrence of the audio ridge signal  78 . Thus if the user is simply “scanning” the surface of the touch screen or is not interested in the remainder of the description of the button  46 , the user may simply move the finger further along causing the message of previous virtual buttons  46  to the silenced. 
     In contrast, if the finger is lifted prior to the crossing out of a button  46 , the message continues to play. For example, as a trajectory  66  crosses the left most boundary of the number key  2 , the audio ridge signal  76 ′ is invoked and a spoken message  80 ′. When the finger is lifted, for example, at instant  82 , the message  80 ′ continues to play to completion. This prevents the user from being confused as to which virtual button  46  was the last button pressed if the user&#39;s finger briefly touches another button as it is removed from the screen. In particular, when a finger is used as the stylus, a second button may be inadvertently pressed as the user&#39;s finger rolls upward from the touch screen. It has been determined that if the message is truncated on this second button, the user may be confused as to the identity of the last button pressed. In a system where the last button pressed is confirmed by pressing the confirmation button  20 , any confusion in the identity of the last button pressed may cause the wrong program to be initiated. 
     Referring now to FIGS. 1,  3  and  6 , the steps taken by the microprocessor  38  in evaluating actions on the touch screen system  10  during the audio mode are broken into three phases. In the first phase, indicated by process block  90 , coordinates from the touch panel  16  are received and compared to the locations  138  in table  131  to determine the current state of the touch point as either: in a particular button  46  (“BUTTON”) in the background area  51  (“BLANK”) or off the screen (“NO TOUCH”) indicating that the finger is not touching the touch panel  16 . 
     Next, at process block  92 , the particular zone of the touch point is enrolled in a queue so that the immediate history of touch points over time may be determined. For example, if the current state of the touch point is NO TOUCH, the previous state may have been either BUTTON or BLANK with different responses by the microprocessor  38  attaching to each. 
     Next at process block  94 , the microprocessor  38  processes particular interface based on a review of the queue  92 . These actions include adjustment of the display  12  and the generation of the audio cues as has been described but not the execution of the underlying actions the buttons normally invoke when pressed in both the audio and nonaudio modes. 
     The text block  50  operate similarly to any other button  46  in their interface actions. When the touch point is within the text zone, a short description of the text message is read. The entire text message is read only when the button selection is confirmed, for example by pressing the confirmation button  20 . In the scrolling areas  48  the different zones represent buttons  46  which can announce their contents, however the contents of these buttons  46  generally change as a function of the scrolling. Thus the area in the table  131  normally reserved for the message instead includes a pointer, as is understood in the art, to a separate table (not shown) of scrolled items. 
     Generally, in the audio mode, the pressing of a button does not immediately invoke the underlying action that pressing the button invoked in the non-audio mode invokes. Instead, that process is broken into two portions, the portion which affects only the display area  14  and the audio cues is separated from the underlying action of the button, for example, the entering of data designated by that button. This two step process is mediated by the confirmation button  20  which must be pressed to confirm a particular action. Thus, the user&#39;s finger or stylus is free to wander about the display area  14  to identify the location and functions of the various buttons without fear of activating those buttons. When the confirmation button is pressed, the message  80  of the selection is repeated as a further confirmation. 
     At process block  96  the activation of the confirmation button  20  is checked. In a preferred embodiment of the invention, activation of the buttons is accomplished by entering within the boundary of a particular button, as has been described, and pressing the confirmation button  20  prior to leaving that boundary. Generally, the user may first touch a particular button  46  and then lift his or her stylus or finger to press confirmation button  20 , or in two-handed operation the user may hold his or her stylus or finger within the button  46  pressing confirmation button  20  with the second hand. 
     At process block  98 , if the confirmation button  20  has been pressed, the microprocessor  38  processes the underlying action to that button as if the button had been pressed in the non-audio mode. For text block  50 , when the confirmation button is pressed, the full text message of the text block is read. 
     Referring now to FIGS. 5 and 7, process block  94  determines the necessary audio actions according to the transition between three states of: NO TOUCH, BLANK, and BUTTON as has been described and as may be determined by the queue established in process block  92  and stored in memory  40 . Thus, if the touch point is currently at the BLANK state  100 , as determined by process block  90 , but was previously in the NO TOUCH state  102 , as determined from the queue of process block  92  (a transition indicated by arrow  110 ), then a background sound  74  is generated to indicate that the touch point is in the background area  51 . Similarly per arrow  109 , if the touch point is currently in the BLANK state but was previously in the BUTTON state  104 , background sound  74  is generated but also a down direction audio ridge signal  78  is produced and any message in process is truncated. 
     If the current state as determined at process block  90  is the BUTTON state  104  indicating that a touch point is within the boundary of a button  46  and if previously the touch point was in the BLANK state  100  (per arrow  105 ) then an up audio ridge signal  76  is generated and message  80  corresponding to the label of the button  46  is read. In contrast if the BUTTON state  104  is arrived at from the NO TOUCH state  102  (as indicated by arrow  107 ) the message  80  is read and a touch sound  79  is provided (indicating that the touch panel  16  has registered the touch and shown in FIG.  5 ), however, no up audio ridge  76  is generated. 
     Finally if the NO TOUCH state  102  is the current state but the previous state was the BUTTON state  104  (per arrow  109 ) any message  80  is finished and no sound is generated by the sound card  34 . If however the NO TOUCH state  102  is reached by a previous BLANK state  100 , then only no sound is generated as indicated by arrow  110 . 
     Referring now to FIGS. 2 and 3, as has been described, the ability to accurately delineate the edges of the virtual buttons  46  so as to permit the user to obtain a sense of their spatial layout is provided by the audio ridge signal  76 ,  78  at the boundary of the button  46  separate from the message  80  provided by the button. Although it is desirable that the audio ridge  76  or  78  for the edge of the button be sensitive to small changes in the position of touch point so that there is sense of a sharp line where the button begins, nevertheless it is also important to prevent confusing multiple triggerings or chatter of the audio ridges  76  and  78  or message  80  at the boundary of the button. Such multiple triggerings may be caused by a touch point that straddles the boundary of the button and hence moves in and out of the boundary to create rapid minor crossing of the boundary. These multiple triggerings (which can also initiate the spoken message  80 ) clutter the audio channel that is relied on to inform the vision-impaired user. 
     Accordingly, in the present invention, two boundaries are used to define each button  46 . The first inner boundary  120 , generally but not necessarily coextensive with the visual boundary of the button  46 , may only be triggered by a passage from outside the boundary  120  to inside the boundary  120  as indicated by arrow  122 . Crossing boundary  122  invokes the up audio ridge signal  76  referred to in discussion of FIG.  5 . 
     Once boundary  120  has been crossed, the touch point is considered to be within the button  46  and additional crossings of boundary  120  are of no effect until a second larger boundary  124  outside of boundary  126  is crossed going from the inside of boundary  124  to the outside of boundary  124  as indicated by arrow  123 . The distance d 1    10  between boundaries  120  and  124  is selected to be sufficiently large that minor jitter in the movement of the touch point will not cause repeated triggerings of the buttons  46 . 
     When boundary  124  has been crossed from within the boundary to outside of the boundary, an audio down signal  78  is generated and boundary  124  may no longer be triggered by crossing until boundary  120  is again crossed from outside of boundary  120  to inside of boundary  120 . Thus, in effect, the boundary of the button moves between boundary  120  and  124  expanding from boundary  120  to  124  when the button is first entered and collapsing to boundary  120  when the button is first exited. 
     Referring now to FIGS. 2,  4  and  9 , although the two dimensional layout of some virtual buttons  46 , such as the keypad  52 , will be convenient to many users with impaired vision, often the three dimensional layout of the virtual buttons  46  will prove unnecessarily cumbersome to the vision-impaired. In these cases, the vision-impaired user will prefer simpler arrangement of the buttons yet as still grouped by different screens. The present invention therefore also provides a speed list that may be invoked by the user touching the upper left hand comer of the screen at point  57  (FIG. 2) and drawing his or her finger downward as indicated by arrow  33 . As shown in FIG. 9, the speed list, when displayed, provides duplicates of each virtual button  46 , with the duplicate buttons  46 ′ arranged vertically along an edge of a frame  152  surrounding the display area  14 . The speed list  150  thus contains a complete set of possible virtual buttons  46  found on the particular screen but arranged to be accessed by moving a finger or stylus upward or downward along a single vertical axes of the left side of the frame  152 , the frame  152  which forms a natural channel to guide the finger or stylus. 
     As each virtual button  46 ′ is invoked, the message  80  associated with the button  46  is played according to the rules previously described. That is, each virtual button  46 ′ has an inner boundary  120 ′ and an outer boundary  124 ′ (which differ only in their vertical dimension) and audio ridge signals  76  and  78  are generated when inner boundary  120 ′ is crossed vertically going into the boundary  120 ′ as indicated by arrow  122 ′ or when outer boundary  124 ′ is crossed vertically going out of the boundary as indicated by arrow  123 ′. Small embossments  154  in the left side of the frame  152  adjacent to the display area  14  may be used to locate the virtual buttons  46 ′ to allow rapid scanning upward and downward within the buttons without waiting for the audio queues of the audio ridges  76 ,  78  or the associated messages  80 . In all other respects the virtual buttons  46 ′ duplicate the virtual buttons  46  used when the touch screen system  10  is in the non-audio mode. 
     As shown in FIG. 2 generally the speed list  150  need not be displayed but consists merely of a plurality of touch points  156  in a linear arrangement. 
     The speed list  150  is updated according to the screen display simply by scanning the table  131  to identify the new buttons and messages available on a given screen. When the speed list  150  is invoked, a separate tone in messages  80  may flag those virtual buttons  46  which may change, for example, by scrolling without a screen change. Whenever the speed list appears or disappears its appearance or departure is announced in keeping with a requirement that all changes in existing displays are announced. 
     Referring again to FIG. 5, in an alternative embodiment in which confirmation button  20  is not used, confirmation of a given virtual button selection may be made by a sharp double tap  172  on the touch panel  16  timed to occur within certain time windows after the touch panel  16  is no longer touched. For example, with a touch trajectory  170  which passes from the background  51  to the surface of the number key  1  and then lifts off the screen to tap twice on the screen (e.g., on the center of the number key  2 ), a confirmation of the number key  1  may occur. In this case, the audio track changes from the background sound  74  and then provides an up audio ridge  76  and a message  80 ″. Because the touch point is removed from the screen, the message  80 ″ plays to completion. A short double tap  172  on button  2  and then a release is interpreted as a confirmation. The double tap could occur on any surface of the touch panel  16  but must occur within a predetermined time interval w 2  after completion of the message  80 , the taps must be no longer than a predetermined w 2  and must not be separate by more than w 3 . 
     This approach eliminates the need for a separate confirmation button  20  but can require a degree of timing that may make it unsuitable for certain situations or users. 
     It will be recognized that other methods of confirming a selected virtual key  46  may be used including the use of a landmark position on the touch panel  16  to provide a virtual confirmation button, for example, in the lower left hand corner of the display area  14  or the use of pressure sensitive touch panel  16  where a greater pressure may be interpreted to be a confirmation of a particular selection. 
     Referring again to FIG. 2, as has been described, when the text block  50  is pressed it will begin a recitation of the text within that block if the text is short. If the text printed in the block is long the field name is announced (indicating generally the type of field) and the confirmation button  20  must be pressed (or other confirmation signal provided) for the entire text to be spoken. For long messages it may also be desirable to allow the user to pause, fast forward or rewind the message. These features may be invoked by additional virtual buttons  46 ″ placed along the right most edge of the display area  14 . 
     In a preferred embodiment, the user moves toward the right side of the screen to locate a reference notch  200  and then touches the screen to invoke a vertical array of buttons  46 ″ like that of the speed list  150 . Moving down from the initial point of contact provides audio descriptions of the buttons  46 ″ which allow for the selection of a direction of movement within the spoken message (e.g., forward or backward) and for the increment of movement (e.g., paragraph, sentence, word, and letter). The confirmation button is used to select the direction and increment last touched. With each tap of the screen the message is incremented as selected. If the letter increment is chosen the message is spelled, a capability provided by storing the spoken message and its spelling or by using a text driven speech synthesizer. This same procedure may be used to navigate around in a table contained on the screen. In this case the buttons  46 ″ provide for movement up down left and right. 
     The above description has been that of a preferred embodiment of the present invention. It will occur to those that practice the art that many modifications may be made without departing from the spirit and scope of the invention. Clearly, the present invention is not limited to use with full sized computer terminals but may be used on any touch screen providing the necessary spatial resolution, for example, those used on cellular telephones, personal digital assistants (PDA&#39;s) or various pieces of standard office equipment such as copy or fax machines. The audio circuitry may share components with the computer and may rely on the computer for certain synthesis tasks. In order to apprise the public of the various embodiments that may fall within the scope of the invention, the following claims are made.