Patent Publication Number: US-10319382-B2

Title: Multi-level voice menu

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of co-owned U.S. patent application Ser. No. 15/643,261, filed on Jul. 6, 2017, which is a continuation of co-owned U.S. patent application Ser. No. 15/130,827, filed on Apr. 15, 2016, which is a continuation of co-owned U.S. patent application Ser. No. 14/884,480, filed Oct. 15, 2015, which is a continuation of co-owned U.S. patent application Ser. No. 13/754,488, filed Jan. 30, 2013, all of which are hereby incorporated by reference in their entirety for all purposes. 
    
    
     BACKGROUND 
     Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
     Computing devices such as personal computers, laptop computers, tablet computers, cellular phones, and countless types of Internet-capable devices are increasingly prevalent in numerous aspects of modern life. Over time, the manner in which these devices are providing information to users is becoming more intelligent, more efficient, more intuitive, and/or less obtrusive. 
     The trend toward miniaturization of computing hardware, peripherals, as well as of sensors, detectors, and image and audio processors, among other technologies, has helped open up a field sometimes referred to as “wearable computing.” In the area of image and visual processing and production, in particular, it has become possible to consider wearable displays that place a graphic display close enough to a wearer&#39;s (or user&#39;s) eye(s) such that the displayed image appears as a normal-sized image, such as might be displayed on a traditional image display device. The relevant technology may be referred to as “near-eye displays.” 
     Wearable computing devices with near-eye displays may also be referred to as “head-mountable displays” (HMDs), “head-mounted displays,” “head-mounted devices,” or “head-mountable devices.” A head-mountable display places a graphic display or displays close to one or both eyes of a wearer. To generate the images on a display, a computer processing system may be used. Such displays may occupy a wearer&#39;s entire field of view, or only occupy part of wearer&#39;s field of view. Further, head-mounted displays may vary in size, taking a smaller form such as a glasses-style display or a larger form such as a helmet, for example. 
     Emerging and anticipated uses of wearable displays include applications in which users interact in real time with an augmented or virtual reality. Such applications can be mission-critical or safety-critical, such as in a public safety or aviation setting. The applications can also be recreational, such as interactive gaming. 
     SUMMARY 
     These as well as other aspects, advantages, and alternatives will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings. 
     HMDs can use a voice-navigable user interface. Phrases in the voice-navigable user interface that can be uttered by a user may be prompted by a “cue” displayed on a visible portion of the interface. Menu items in a voice menu of operations can be displayed textually and can operate as cues, providing a user with words or phrases to say to navigate the menu or to invoke commands. In some embodiments, menu items can include voice commands that can be invoked by a user. The commands may be grouped by categories. Displaying the available categories can provide cues to a user and inform a user of the menu items available to be uttered to navigate to available commands. In some embodiments, after commands are invoked, some commands may be displayed more prominently than other menu items. 
     In one aspect, a method is provided. The method comprising: at a head-mountable device (HMD) with a voice-navigable user interface, displaying a first visible menu comprising at least a portion of a voice navigable menu, wherein the voice navigable menu includes one or more menu items; receiving a first utterance at the HMD, the first utterance comprising a first menu item, wherein the one or more menu items comprise the first menu item; after receiving the first utterance, modifying the first visible menu to display one or more commands associated with the first menu item; receiving a second utterance at the HMD, the second utterance comprising a first command; and after receiving the second utterance, invoking the first command. 
     In another aspect, a head-mountable device (HMD) is provided. The HMD comprises: a processor; and a non-transitory computer-readable medium configured to store at least program instructions that, when executed by the processor, cause the HMD to carry out functions comprising: displaying a first visible menu comprising at least a portion of a voice navigable menu, wherein the voice navigable menu includes one or more menu items, receiving a first utterance, the first utterance comprising a first menu item, wherein the one or more menu items comprise the first menu item, after receiving the first utterance, modifying the first visible menu to display one or more commands associated with the first menu item, receiving a second utterance, the second utterance comprising a first command, and after receiving the second utterance, invoking the first command. 
     In yet another aspect, a non-transitory computer-readable medium is provided. The non-transitory computer readable medium is configured to store at least program instructions that, when executed by a processor, cause the processor to carry out functions comprising: displaying a first visible menu comprising at least a portion of a voice navigable menu, wherein the voice navigable menu includes one or more menu items; receiving a first utterance, the first utterance comprising a first menu item, wherein the one or more menu items comprise the first menu item; after receiving the first utterance, modifying the first visible menu to display one or more commands associated with the first menu item; receiving a second utterance, the second utterance comprising a first command; and after receiving the second utterance, invoking the first command. 
     The following clauses are offered as further descriptions of example embodiments: 
     Clause 1—a device, comprising a means for displaying a first visible menu comprising at least a portion of a voice navigable menu, wherein the voice navigable menu includes one or more menu items; a means for receiving a first utterance, the first utterance comprising a first menu item, wherein the one or more menu items comprise the first menu item; a means for, after receiving the first utterance, modifying the first visible menu to display one or more commands associated with the first menu item; a means for receiving a second utterance, the second utterance comprising a first command; and a means for, after receiving the second utterance, invoking the first command. 
     Clause 2—The device of clause 1, further comprising: a means for displaying at least a portion of a second visible menu, wherein the second visible menu includes the first command and at least one menu item of the one or more menu items; and wherein the second visible menu displays the first command above the at least one menu item. 
     Clause 3—The device of clause 2, further comprising: a means for receiving a third utterance, the third utterance comprising a second command, the second command differing from the first command; a means for, after receiving the third utterance, invoking the second command; a means for displaying at least a portion of a third visible menu, wherein the third visible menu includes the second command and at least one menu item of the one or more menu items, and wherein the third visible menu displays the second command above the at least one menu item. 
     Clause 4—The device of clause 3, wherein the third visible menu further includes the first command; and wherein an order in which the first command and the second command are displayed in the third visible menu is determined based on at least a frequency of use for the first command and a frequency of use for the second command. 
     Clause 5—The device of clause 3, wherein the third visible menu further includes the first command; and wherein an order in which the first command and the second command are displayed in the third visible menu is determined based on at least a recency of use for the first command and a recency of use for the second command. 
     Clause 6—The device of clause 3, wherein the third visible menu further includes the first command; and wherein an order in which the first command and the second command are displayed in the third visible menu is determined based on at least a combination of a frequency of use and a recency of use for the first command and a combination of a frequency of use and a recency of use for the second command. 
     Clause 7—The device of clause 1, wherein the means for displaying a first visible menu further comprises: a means for displaying at least a portion of the first visible menu in response to the HMD receiving a hotword utterance comprising a hotword. 
     Clause 8—The device of clause 1, wherein the first menu item comprises an identification of a category. 
     Clause 9—The device of clause 1, wherein at least one menu item of the one or more menu items comprises a command. 
     Clause 10—The device of clause 1, wherein at least one menu item of the one or more menu items comprises an identification of a category. 
     Clause 11—The device of clause 1, wherein the first command is associated with the first menu item. 
     Clause 12—The device of clause 1, wherein the means for modifying the first visible menu to display the one or more commands associated with the first menu item comprises a means for expanding the first visible menu to display the one or more commands in-line with the first menu item. 
     Clause 13—The device of clause 1, wherein the means for modifying the first visible menu to display the one or more commands associated with the first menu item comprises a means for displaying the one or more commands as a submenu. 
     These as well as other aspects, advantages, and alternatives will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings. Further, it should be understood that this summary and other descriptions and figures provided herein are intended to illustrative embodiments by way of example only and, as such, that numerous variations are possible. For instance, structural elements and process steps can be rearranged, combined, distributed, eliminated, or otherwise changed, while remaining within the scope of the embodiments as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates a wearable computing system according to an example embodiment. 
         FIG. 1B  illustrates an alternate view of the wearable computing device illustrated in  FIG. 1A . 
         FIG. 1C  illustrates another wearable computing system according to an example embodiment. 
         FIG. 1D  illustrates another wearable computing system according to an example embodiment. 
         FIGS. 1E to 1G  are simplified illustrations of the wearable computing system shown in  FIG. 1D , being worn by a wearer. 
         FIG. 2A  is a simplified block diagram of a computing device according to an example embodiment. 
         FIG. 2B  shows a projection of an image by a head-mountable device, according to an example embodiment. 
         FIG. 3A  shows an example voice navigable menu, according to an example embodiment. 
         FIG. 3B  shows an example voice navigable menu, according to an example embodiment. 
         FIG. 4  shows an example visible menu, according to an example embodiment. 
         FIG. 5  shows an example visible menu, according to an example embodiment. 
         FIG. 6  shows an example visible menu, according to an example embodiment. 
         FIG. 7  shows an example visible menu, according to an example embodiment. 
         FIG. 8A  shows an example visible menu, according to an example embodiment. 
         FIG. 8B  shows an example visible menu, according to an example embodiment. 
         FIG. 9A  shows an example visible menu, according to an example embodiment. 
         FIG. 9B  shows an example visible menu, according to an example embodiment. 
         FIG. 9C  shows an example visible menu, according to an example embodiment. 
         FIG. 10  is a flow chart illustrating a method, according to an example embodiment. 
         FIG. 11  is a flow chart illustrating another method, according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Example methods and systems are described herein. It should be understood that the words “example” and “exemplary” are used herein to mean “serving as an example, instance, or illustration.” Any embodiment or feature described herein as being an “example” or “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or features. In the following detailed description, reference is made to the accompanying figures, which form a part thereof. In the figures, similar symbols typically identify similar components, unless context dictates otherwise. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. 
     The example embodiments described herein are not meant to be limiting. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     A. Overview 
     Some user interfaces, such as head mounted displays (“HMDs”), can place a visual display or displays close to one or both eyes of a wearer. Such displays may occupy part or all of a wearer&#39;s field of view. Due to size limitations, the display may have room for presenting only a limited amount of visible text. 
     HMDs can use a voice-navigable user interface (VNUI). The VNUI can include one or more microphones to capture audible input, such as speech uttered by a user or wearer of the HMD. Upon receiving audible input, the HMD can attempt to recognize the input as a speech command and process the command accordingly; for example, by converting the audible input to text and operating on the text. The speech input can represent commands to the HMD, such as commands to search, navigate, take photos, record videos, send messages, make telephone calls, etc. 
     One example scenario includes a VNUI, in which a user can invoke the VNUI of the HMD by uttering a phrase, such as “ok glass.” In other words, “ok glass” in this instance is a “hotword” to trigger activation of a VNUI. 
     The phrase “ok glass,” as well as other phrases in the VNUI that can be uttered by a user, may be prompted by a “cue” displayed on a visible portion of the interface. The cue can be simply the textual phrase displayed on the visual display. 
     In some embodiments, invoking the VNUI can provide access to a voice menu of operations. The voice menu of operations can, in turn, be displayed in the visible portion of the VNUI. Menu items can be displayed textually and can operate as cues, providing a user with words or phrases to speak in order to navigate the menu or invoke commands. 
     If the number of menu items is relatively small, the entire menu may be able to be displayed in the visible portion of the VNUI. If, however, there are more menu items than can be displayed by the VNUI, the VNUI can have a helpful system for organizing or simplifying the presentation of the menu items. 
     In some embodiments, the menu items include voice commands that can be invoked by a user. One way to organize voice commands is to group the voice commands by contextually related categories. To maintain simplicity, a menu, such as a top-level menu, for example, can display the categories without necessarily displaying each command within each category. Such a presentation can simplify the visible menu by showing a user fewer menu items than a list of all available commands. 
     Displaying the available categories can provide cues to a user and inform a user of the menu items available to be uttered to navigate to available commands. In other words, a user can visually see available categories, and can efficiently navigate through the voice command menu without needing to guess at which categories or commands may be available via the VNUI. 
     Example categories can include (i) Camera, (ii) Communication, and (iii) Information Retrieval (such as Internet searching or navigation). 
     Each category can then include one or more commands. Continuing the example above, example Camera category commands can include (i) “take a photo” and (ii) “record a video.” Under the Communication category, example commands can include (i) “send a message” and (ii) “make a call.” And under the Information Retrieval category, example commands can include (i) “Internet search” and (ii) “navigate.” Other categories and commands are possible as well. 
     Accordingly, commands can be invoked via the VNUI by uttering a sequence such as “ok glass, open camera, take a photo.” 
     Using categories can provide a readily navigable, hierarchical user interface display to remind users of possible vocal phrases and commands. The display can help new users learn phrases and commands, and can remind prior users of phrases and commands infrequently or not recently used. The display can speed adoption of the voice-navigable user interface, let users/wearers know about new commands/categories of commands, and provide visual feedback that spoken menu items have been properly processed by the HMD. 
     B. Example Wearable Computing Devices 
     Systems and devices in which example embodiments may be implemented will now be described in greater detail. In general, an example system may be implemented in or may take the form of a wearable computer (also referred to as a wearable computing device). In an example embodiment, a wearable computer takes the form of or includes a head-mountable device (HMD). 
     An example system may also be implemented in or take the form of other devices, such as a mobile phone, among other possibilities. Further, an example system may take the form of non-transitory computer readable medium, which has program instructions stored thereon that are executable by at a processor to provide the functionality described herein. An example system may also take the form of a device such as a wearable computer or mobile phone, or a subsystem of such a device, which includes such a non-transitory computer readable medium having such program instructions stored thereon. 
     An HMD may generally be any display device that is capable of being worn on the head and places a display in front of one or both eyes of the wearer. An HMD may take various forms such as a helmet or eyeglasses. As such, references to “eyeglasses” or a “glasses-style” HMD should be understood to refer to an HMD that has a glasses-like frame so that it can be worn on the head. Further, example embodiments may be implemented by or in association with an HMD with a single display or with two displays, which may be referred to as a “monocular” HMD or a “binocular” HMD, respectively. 
       FIG. 1A  illustrates a wearable computing system according to an example embodiment. In  FIG. 1A , the wearable computing system takes the form of a head-mountable device (HMD)  102  (which may also be referred to as a head-mounted display). It should be understood, however, that example systems and devices may take the form of or be implemented within or in association with other types of devices, without departing from the scope of the invention. As illustrated in  FIG. 1A , the HMD  102  includes frame elements including lens-frames  104 ,  106  and a center frame support  108 , lens elements  110 ,  112 , and extending side-arms  114 ,  116 . The center frame support  108  and the extending side-arms  114 ,  116  are configured to secure the HMD  102  to a user&#39;s face via a user&#39;s nose and ears, respectively. 
     Each of the frame elements  104 ,  106 , and  108  and the extending side-arms  114 ,  116  may be formed of a solid structure of plastic and/or metal, or may be formed of a hollow structure of similar material so as to allow wiring and component interconnects to be internally routed through the HMD  102 . Other materials may be possible as well. 
     One or more of each of the lens elements  110 ,  112  may be formed of any material that can suitably display a projected image or graphic. Each of the lens elements  110 ,  112  may also be sufficiently transparent to allow a user to see through the lens element. Combining these two features of the lens elements may facilitate an augmented reality or heads-up display where the projected image or graphic is superimposed over a real-world view as perceived by the user through the lens elements. 
     The extending side-arms  114 ,  116  may each be projections that extend away from the lens-frames  104 ,  106 , respectively, and may be positioned behind a user&#39;s ears to secure the HMD  102  to the user. The extending side-arms  114 ,  116  may further secure the HMD  102  to the user by extending around a rear portion of the user&#39;s head. Additionally or alternatively, for example, the HMD  102  may connect to or be affixed within a head-mounted helmet structure. Other configurations for an HMD are also possible. 
     The HMD  102  may also include an on-board computing system  118 , an image capture device  120 , a sensor  122 , and a finger-operable touch pad  124 . The on-board computing system  118  is shown to be positioned on the extending side-arm  114  of the HMD  102 ; however, the on-board computing system  118  may be provided on other parts of the HMD  102  or may be positioned remote from the HMD  102  (e.g., the on-board computing system  118  could be wire- or wirelessly-connected to the HMD  102 ). The on-board computing system  118  may include a processor and memory, for example. The on-board computing system  118  may be configured to receive and analyze data from the image capture device  120  and the finger-operable touch pad  124  (and possibly from other sensory devices, user interfaces, or both) and generate images for output by the lens elements  110  and  112 . 
     The image capture device  120  may be, for example, a camera that is configured to capture still images and/or to capture video. In the illustrated configuration, image capture device  120  is positioned on the extending side-arm  114  of the HMD  102 ; however, the image capture device  120  may be provided on other parts of the HMD  102 . The image capture device  120  may be configured to capture images at various resolutions or at different frame rates. Many image capture devices with a small form-factor, such as the cameras used in mobile phones or webcams, for example, may be incorporated into an example of the HMD  102 . 
     Further, although  FIG. 1A  illustrates one image capture device  120 , more image capture device may be used, and each may be configured to capture the same view, or to capture different views. For example, the image capture device  120  may be forward facing to capture at least a portion of the real-world view perceived by the user. This forward facing image captured by the image capture device  120  may then be used to generate an augmented reality where computer generated images appear to interact with or overlay the real-world view perceived by the user. 
     The sensor  122  is shown on the extending side-arm  116  of the HMD  102 ; however, the sensor  122  may be positioned on other parts of the HMD  102 . For illustrative purposes, only one sensor  122  is shown. However, in an example embodiment, the HMD  102  may include multiple sensors. For example, an HMD  102  may include sensors  102  such as one or more gyroscopes, one or more accelerometers, one or more magnetometers, one or more light sensors, one or more infrared sensors, and/or one or more microphones. Other sensing devices may be included in addition or in the alternative to the sensors that are specifically identified herein. 
     The finger-operable touch pad  124  is shown on the extending side-arm  114  of the HMD  102 . However, the finger-operable touch pad  124  may be positioned on other parts of the HMD  102 . Also, more than one finger-operable touch pad may be present on the HMD  102 . The finger-operable touch pad  124  may be used by a user to input commands. The finger-operable touch pad  124  may sense at least one of a pressure, position and/or a movement of one or more fingers via capacitive sensing, resistance sensing, or a surface acoustic wave process, among other possibilities. The finger-operable touch pad  124  may be capable of sensing movement of one or more fingers simultaneously, in addition to sensing movement in a direction parallel or planar to the pad surface, in a direction normal to the pad surface, or both, and may also be capable of sensing a level of pressure applied to the touch pad surface. In some embodiments, the finger-operable touch pad  124  may be formed of one or more translucent or transparent insulating layers and one or more translucent or transparent conducting layers. Edges of the finger-operable touch pad  124  may be formed to have a raised, indented, or roughened surface, so as to provide tactile feedback to a user when the user&#39;s finger reaches the edge, or other area, of the finger-operable touch pad  124 . If more than one finger-operable touch pad is present, each finger-operable touch pad may be operated independently, and may provide a different function. 
     In a further aspect, HMD  102  may be configured to receive user input in various ways, in addition or in the alternative to user input received via finger-operable touch pad  124 . For example, on-board computing system  118  may implement a speech-to-text process and utilize a syntax that maps certain spoken commands to certain actions. In addition, HMD  102  may include one or more microphones via which a wearer&#39;s speech may be captured. Configured as such, HMD  102  may be operable to detect spoken commands and carry out various computing functions that correspond to the spoken commands. 
     As another example, HMD  102  may interpret certain head-movements as user input. For example, when HMD  102  is worn, HMD  102  may use one or more gyroscopes and/or one or more accelerometers to detect head movement. The HMD  102  may then interpret certain head-movements as being user input, such as nodding, or looking up, down, left, or right. An HMD  102  could also pan or scroll through graphics in a display according to movement. Other types of actions may also be mapped to head movement. 
     As yet another example, HMD  102  may interpret certain gestures (e.g., by a wearer&#39;s hand or hands) as user input. For example, HMD  102  may capture hand movements by analyzing image data from image capture device  120 , and initiate actions that are defined as corresponding to certain hand movements. 
     As a further example, HMD  102  may interpret eye movement as user input. In particular, HMD  102  may include one or more inward-facing image capture devices and/or one or more other inward-facing sensors (not shown) that may be used to track eye movements and/or determine the direction of a wearer&#39;s gaze. As such, certain eye movements may be mapped to certain actions. For example, certain actions may be defined as corresponding to movement of the eye in a certain direction, a blink, and/or a wink, among other possibilities. 
     HMD  102  also includes a speaker  125  for generating audio output. In one example, the speaker could be in the form of a bone conduction speaker, also referred to as a bone conduction transducer (BCT). Speaker  125  may be, for example, a vibration transducer or an electroacoustic transducer that produces sound in response to an electrical audio signal input. The frame of HMD  102  may be designed such that when a user wears HMD  102 , the speaker  125  contacts the wearer. Alternatively, speaker  125  may be embedded within the frame of HMD  102  and positioned such that, when the HMD  102  is worn, speaker  125  vibrates a portion of the frame that contacts the wearer. In either case, HMD  102  may be configured to send an audio signal to speaker  125 , so that vibration of the speaker may be directly or indirectly transferred to the bone structure of the wearer. When the vibrations travel through the bone structure to the bones in the middle ear of the wearer, the wearer can interpret the vibrations provided by BCT  125  as sounds. 
     Various types of bone-conduction transducers (BCTs) may be implemented, depending upon the particular implementation. Generally, any component that is arranged to vibrate the HMD  102  may be incorporated as a vibration transducer. Yet further it should be understood that an HMD  102  may include a single speaker  125  or multiple speakers. In addition, the location(s) of speaker(s) on the HMD may vary, depending upon the implementation. For example, a speaker may be located proximate to a wearer&#39;s temple (as shown), behind the wearer&#39;s ear, proximate to the wearer&#39;s nose, and/or at any other location where the speaker  125  can vibrate the wearer&#39;s bone structure. 
       FIG. 1B  illustrates an alternate view of the wearable computing device illustrated in  FIG. 1A . As shown in  FIG. 1B , the lens elements  110 ,  112  may act as display elements. The HMD  102  may include a first projector  128  coupled to an inside surface of the extending side-arm  116  and configured to project a display  130  onto an inside surface of the lens element  112 . Additionally or alternatively, a second projector  132  may be coupled to an inside surface of the extending side-arm  114  and configured to project a display  134  onto an inside surface of the lens element  110 . 
     The lens elements  110 ,  112  may act as a combiner in a light projection system and may include a coating that reflects the light projected onto them from the projectors  128 ,  132 . In some embodiments, a reflective coating may not be used (e.g., when the projectors  128 ,  132  are scanning laser devices). 
     In alternative embodiments, other types of display elements may also be used. For example, the lens elements  110 ,  112  themselves may include: a transparent or semi-transparent matrix display, such as an electroluminescent display or a liquid crystal display, one or more waveguides for delivering an image to the user&#39;s eyes, or other optical elements capable of delivering an in focus near-to-eye image to the user. A corresponding display driver may be disposed within the frame elements  104 ,  106  for driving such a matrix display. Alternatively or additionally, a laser or LED source and scanning system could be used to draw a raster display directly onto the retina of one or more of the user&#39;s eyes. Other possibilities exist as well. 
       FIG. 1C  illustrates another wearable computing system according to an example embodiment, which takes the form of an HMD  152 . The HMD  152  may include frame elements and side-arms such as those described with respect to  FIGS. 1A and 1B . The HMD  152  may additionally include an on-board computing system  154  and an image capture device  156 , such as those described with respect to  FIGS. 1A and 1B . The image capture device  156  is shown mounted on a frame of the HMD  152 . However, the image capture device  156  may be mounted at other positions as well. 
     As shown in  FIG. 1C , the HMD  152  may include a single display  158  which may be coupled to the device. The display  158  may be formed on one of the lens elements of the HMD  152 , such as a lens element described with respect to  FIGS. 1A and 1B , and may be configured to overlay computer-generated graphics in the user&#39;s view of the physical world. The display  158  is shown to be provided in a center of a lens of the HMD  152 , however, the display  158  may be provided in other positions, such as for example towards either the upper or lower portions of the wearer&#39;s field of view. The display  158  is controllable via the computing system  154  that is coupled to the display  158  via an optical waveguide  160 . 
       FIG. 1D  illustrates another wearable computing system according to an example embodiment, which takes the form of a monocular HMD  172 . The HMD  172  may include side-arms  173 , a center frame support  174 , and a bridge portion with nosepiece  175 . In the example shown in  FIG. 1D , the center frame support  174  connects the side-arms  173 . The HMD  172  does not include lens-frames containing lens elements. The HMD  172  may additionally include a component housing  176 , which may include an on-board computing system (not shown), an image capture device  178 , and a button  179  for operating the image capture device  178  (and/or usable for other purposes). Component housing  176  may also include other electrical components and/or may be electrically connected to electrical components at other locations within or on the HMD. HMD  172  also includes a BCT  186 . 
     The HMD  172  may include a single display  180 , which may be coupled to one of the side-arms  173  via the component housing  176 . In an example embodiment, the display  180  may be a see-through display, which is made of glass and/or another transparent or translucent material, such that the wearer can see their environment through the display  180 . Further, the component housing  176  may include the light sources (not shown) for the display  180  and/or optical elements (not shown) to direct light from the light sources to the display  180 . As such, display  180  may include optical features that direct light that is generated by such light sources towards the wearer&#39;s eye, when HMD  172  is being worn. 
     In a further aspect, HMD  172  may include a sliding feature  184 , which may be used to adjust the length of the side-arms  173 . Thus, sliding feature  184  may be used to adjust the fit of HMD  172 . Further, an HMD may include other features that allow a wearer to adjust the fit of the HMD, without departing from the scope of the invention. 
       FIGS. 1E to 1G  are simplified illustrations of the HMD  172  shown in  FIG. 1D , being worn by a wearer  190 . As shown in  FIG. 1F , when HMD  172  is worn, BCT  186  is arranged such that when HMD  172  is worn, BCT  186  is located behind the wearer&#39;s ear. As such, BCT  186  is not visible from the perspective shown in  FIG. 1E . 
     In the illustrated example, the display  180  may be arranged such that when HMD  172  is worn, display  180  is positioned in front of or proximate to a user&#39;s eye when the HMD  172  is worn by a user. For example, display  180  may be positioned below the center frame support and above the center of the wearer&#39;s eye, as shown in  FIG. 1E . Further, in the illustrated configuration, display  180  may be offset from the center of the wearer&#39;s eye (e.g., so that the center of display  180  is positioned to the right and above of the center of the wearer&#39;s eye, from the wearer&#39;s perspective). 
     Configured as shown in  FIGS. 1E to 1G , display  180  may be located in the periphery of the field of view of the wearer  190 , when HMD  172  is worn. Thus, as shown by  FIG. 1F , when the wearer  190  looks forward, the wearer  190  may see the display  180  with their peripheral vision. As a result, display  180  may be outside the central portion of the wearer&#39;s field of view when their eye is facing forward, as it commonly is for many day-to-day activities. Such positioning can facilitate unobstructed eye-to-eye conversations with others, as well as generally providing unobstructed viewing and perception of the world within the central portion of the wearer&#39;s field of view. Further, when the display  180  is located as shown, the wearer  190  may view the display  180  by, e.g., looking up with their eyes only (possibly without moving their head). This is illustrated as shown in  FIG. 1G , where the wearer has moved their eyes to look up and align their line of sight with display  180 . A wearer might also use the display by tilting their head down and aligning their eye with the display  180 . 
       FIG. 2A  is a simplified block diagram of a computing device  210  according to an example embodiment. In an example embodiment, device  210  communicates using a communication link  230  (e.g., a wired or wireless connection) to a remote device  240 . The device  210  may be any type of device that can receive data and display information corresponding to or associated with the data. For example, the device  210  may be a heads-up display system, such as the head-mounted devices (HMDs)  102 ,  152 ,  172 , or  252  described with reference to  FIGS. 1A-1G and 2B . 
     Thus, the device  210  may include a display system  212  comprising a processor  214  and a display  216 . The display  210  may be, for example, an optical see-through display, an optical see-around display, or a video see-through display. The processor  214  may receive data from the remote device  240 , and configure the data for display on the display  216 . The processor  214  may be any type of processor, such as a micro-processor or a digital signal processor, for example. 
     The device  210  may further include on-board data storage, such as memory  218  coupled to the processor  214 . The memory  218  may store software that can be accessed and executed by the processor  214 , for example. 
     The remote device  240  may be any type of computing device or transmitter including a laptop computer, a mobile telephone, or tablet computing device, etc., that is configured to transmit data to the device  210 . The remote device  240  and the device  210  may contain hardware to enable the communication link  230 , such as processors, transmitters, receivers, antennas, etc. 
     Further, remote device  240  may take the form of or be implemented in a computing system that is in communication with and configured to perform functions on behalf of client device, such as computing device  210 . Such a remote device  240  may receive data from another computing device  210  (e.g., an HMD  102 ,  152 , or  172  or a mobile phone), perform certain processing functions on behalf of the device  210 , and then send the resulting data back to device  210 . This functionality may be referred to as “cloud” computing. 
     In  FIG. 2A , the communication link  230  is illustrated as a wireless connection; however, wired connections may also be used. For example, the communication link  230  may be a wired serial bus such as a universal serial bus or a parallel bus. A wired connection may be a proprietary connection as well. The communication link  230  may also be a wireless connection using, e.g., Bluetooth® radio technology, communication protocols described in IEEE 802.11 (including any IEEE 802.11 revisions), Cellular technology (such as GSM, CDMA, UMTS, EV-DO, WiMAX, or LTE), or Zigbee® technology, among other possibilities. The remote device  240  may be accessible via the Internet and may include a computing cluster associated with a particular web service (e.g., social-networking, photo sharing, address book, etc.). 
     C. Example Image Projection 
       FIG. 2B  shows an example projection of UI elements described herein via an image  280  by an example head-mountable device (HMD)  252 , according to an example embodiment. Other configurations of an HMD may be also be used to present the UI described herein via image  280 .  FIG. 2B  shows wearer  254  of HMD  252  looking at an eye of person  256 . As such, wearer  254 &#39;s gaze, or direction of viewing, is along gaze vector  260 . A horizontal plane, such as horizontal gaze plane  264  can then be used to divide space into three portions: space above horizontal gaze plane  264 , space in horizontal gaze plane  264 , and space below horizontal gaze plane  264 . In the context of projection plane  276 , horizontal gaze plane  260  appears as a line that divides projection plane into a subplane above the line of horizontal gaze plane  260 , a subplane a subspace below the line of horizontal gaze plane  260 , and the line where horizontal gaze plane  260  intersects projection plane  276 . In  FIG. 2B , horizontal gaze plane  264  is shown using dotted lines. 
     Additionally, a dividing plane, indicated using dividing line  274  can be drawn to separate space into three other portions: space to the left of the dividing plane, space on the dividing plane, and space to right of the dividing plane. In the context of projection plane  276 , the dividing plane intersects projection plane  276  at dividing line  274 . Thus the dividing plane divides projection plane into: a subplane to the left of dividing line  274 , a subplane to the right of dividing line  274 , and dividing line  274 . In  FIG. 2B , dividing line  274  is shown as a solid line. 
     Humans, such wearer  254 , when gazing in a gaze direction, may have limits on what objects can be seen above and below the gaze direction.  FIG. 2B  shows the upper visual plane  270  as the uppermost plane that wearer  254  can see while gazing along gaze vector  260 , and shows lower visual plane  272  as the lowermost plane that wearer  254  can see while gazing along gaze vector  260 . In  FIG. 2B , upper visual plane  270  and lower visual plane  272  are shown using dashed lines. 
     The HMD can project an image for view by wearer  254  at some apparent distance  262  along display line  282 , which is shown as a dotted and dashed line in  FIG. 2B . For example, apparent distance  262  can be 1 meter, four feet, infinity, or some other distance. That is, HMD  252  can generate a display, such as image  280 , which appears to be at the apparent distance  262  from the eye of wearer  254  and in projection plane  276 . In this example, image  280  is shown between horizontal gaze plane  264  and upper visual plane  270 ; that is image  280  is projected above gaze vector  260 . In this example, image  280  is also projected to the right of dividing line  274 . As image  280  is projected above and to the right of gaze vector  260 , wearer  254  can look at person  256  without image  280  obscuring their general view. In one example, the display element of the HMD  252  is translucent when not active (i.e. when image  280  is not being displayed), and so the wearer  254  can perceive objects in the real world along the vector of display line  282 . 
     Other example locations for displaying image  280  can be used to permit wearer  254  to look along gaze vector  260  without obscuring the view of objects along the gaze vector. For example, in some embodiments, image  280  can be projected above horizontal gaze plane  264  near and/or just above upper visual plane  270  to keep image  280  from obscuring most of wearer  254 &#39;s view. Then, when wearer  254  wants to view image  280 , wearer  254  can move their eyes such that their gaze is directly toward image  280 . 
     D. An Example User Interface for an HMD 
     The display  216  of device  210  may be available as part of a user interface for an HMD, such as one of example HMDs  102 ,  152 ,  172 , and  252 , as discussed above in more detail in the context of at least  FIG. 2A . The display  216  of device  210  can be used to display portions of a VNUI (voice-navigable user interface)  220 , which can include display  216 , input device(s)  222 , such as microphone(s), to receive speech input, and output device(s)  224  such as the display, speaker(s), and/or BCT(s) for audio and/or video output. In an example operation, a user or wearer of an HMD may utter words or phrases displayed on a voice navigable menu to interact with the VNUI  220 . 
       FIGS. 3A and 3B  show an example voice navigable menu  300 , which VNUI  220  can present on the display  216 . The voice navigable menu  300  can include one or more categories  301 ; e.g., “Category 1,” “Category 2,” “Category 3,” and “Category 4” as shown in  FIG. 3A . As used herein, a “category,” for example, is a menu item that can describe or can be associated with one or more sub-items. For instance, a restaurant menu category “Breakfast” may describe a number of restaurant menu items for breakfast, such as eggs, toast, oatmeal, bacon, etc. 
     The voice navigable menu  300  can include menu items, such as categories  301  and commands  302  in  FIGS. 3A and 3B . The menu items may be organized into “top-level” menu items and “sub-level” menu items. A top-level menu item is, generally, a menu item with which other menu items are associated. In some cases, a top-level menu item is a menu item that can be expanded to reveal lower level menu items, such as sub-level menu items. A sub-level menu item is, generally, a menu item that is associated with another menu item, such as a top-level menu item. 
     In some cases, the voice navigable menu  300  can have a parent-child hierarchy, in which top-level menu items correspond to a parent menu item and sub-level menu items correspond to a child menu item. In some cases, top-level menu items are displayed on one physical level of the menu, such as a root or base level, while sub-level menu items are displayed on a second physical level of the menu. In some embodiments, the voice navigable menu  300  displays top-level menu items as the left-most items in a display. 
     In some embodiments, the categories  301  comprise top-level menu items, as shown in  FIGS. 3A and 3B . As shown in  FIG. 3B , the categories  301 —top-level menu items—can be displayed as the left-most (or least-indented) menu items. 
     Each category can include or be associated with one or more commands  302 , and each command  302  can be associated with one or more of the categories  301 . In some embodiments, the commands  302  can be sub-level menu items, as shown in  FIG. 3B . As shown in  FIG. 3B , the commands  302 —sub-level menu items—can be displayed further to the right (or further indented) as compared to the top-level menu items. 
     The categories  301  and commands  302  can be some or all of the menu items in the voice navigable menu  300 . For example, other menu items can include identifications of files. Other examples are possible as well. 
     Some or all of the menu items of the voice navigable menu  300  can be displayed to a wearer on the display  216 . In some cases, an HMD may interpret certain head-movements as being wearer input, such as nodding, or looking up, down, left, or right. VNUI  220  may, in turn, interpret such movements as wearer input directing the voice navigable menu  300  to scroll, such that menu items previously not visible on display  216  become visible. In some cases, displayed menu items can also serve as cues to a wearer, by providing the wearer with a word or phrase that the wearer can utter to navigate the menu or invoke a command. 
     Such utterances by wearer(s) can include the categories  301  and the commands  302 . In response to an utterance comprising one of the categories  301 , VNUI  220  may display, on the display  216 , the command or commands  302  associated with the uttered category. In response to an utterance comprising one of the commands  302 , VNUI  220  may invoke the uttered command. 
       FIG. 4  shows an example display  216 . The example display  216  can include a visible menu  305 . The visible menu  305  can include all or a part of the voice navigable menu  300 . For example, in some embodiments, all of voice navigable menu  300  can be visible on the display  216  as visible menu  305 . In other embodiments, only a portion of the voice navigable menu  300  may be visible on the display  216  as the visible menu  305 . For example, space limitations on the display  216  and/or the length of the voice navigable menu  300  can limit visible menu  305  to displaying only a portion of voice navigable menu  300 . 
     The visible menu  305 , like the voice navigable menu  300 , can include one or more menu items. In some embodiments, the visible menu  305  can display menu items from the voice navigable menu  300  in a modified or rearranged order. In some embodiments, the visible menu can display sub-level menu items above and/or as top-level menu items. 
     The visible menu  305  of  FIG. 4  depicts, in this example, three example categories displayed as top-level menu items: Camera  310 , Communication  320 , and Information Retrieval  330 . Other categories are possible as well. The visible menu  305  may include other menu items, such as commands, for example. 
     As discussed, a wearer can interact with the VNUI  220  by uttering a menu item, such as an identification of a category. In an example operation, a wearer may utter a phrase such as “ok glass, open camera” to address the HMD by saying “ok glass” and then requesting the HMD access a camera by saying “open camera.” 
     In response, VNUI  220  may then display in the visible menu  305  the available commands associated with the uttered category. For example, as shown in  FIG. 5 , example commands associated with the Camera category  310  may include “take a photo”  410  and “record a video”  420 . Other commands are possible as well. 
     In some embodiments, when a wearer opens a category, VNUI  220  can show the commands associated with the category as sub-level menu items in-line with the top-level menu items, as shown in  FIG. 5 . In particular,  FIG. 5  shows the “take a photo”  410  and “record a video”  420  sub-level commands in-line with the Camera  310  and Communication  320  top-level categories in the visible menu  305 . 
     In this example, the VNUI associates a set of commands with a category by showing the commands below the associated category and slightly indented. Other ways of showing top-level menu items and sub-level menu items, and of differentiating top-level menu items from sub-level menu items, are possible as well. The visible menu  305  also includes another category, Communication  320 , which is not associated with the displayed commands and which is displayed below the commands. 
     In other embodiments, when a wearer opens a category, VNUI  220  can show the commands as a stand-alone submenu on the display  216 , as shown in  FIG. 6 . In particular, as seen in  FIG. 6 , the visible menu  305  includes commands associated with a particular category, but no categories or other menu items. 
     Minimizing the number of menu items in the visible menu  305  can increase focus on commands likely to be invoked and so allow more efficient invocation of those commands. For example, the two commands “take a photo”  410  and “record a video”  420  presented in the visible menu  305  of  FIG. 6  may be the two commands a wearer is most likely to want to invoke (based on, for example, the wearer uttering an identification of the Camera  310  category). 
     In addition, by minimizing menu items in the visible menu  305 , VNUI  220  may make navigating the menu more efficient. For example, a minimal or reduced number of menu items may keep a wearer from reading or mentally processing additional and potentially unneeded menu items. 
     In any case, VNUI  220  can highlight or more prominently display certain menu items. To do so, VNUI  220  can, for example, display the menu item at the top of the visible menu  305 . In other embodiments, VNUI  220  can emphasize the menu item compared to one or more other menu items, without necessarily displaying the menu item at the top of the visible menu  305 . 
     For example, once a wearer has invoked a command, VNUI  220  can “bubble-up” the command to the top of the visible menu  305  or to a position above another command or a category. In particular, the next time a wearer invokes the menu, VNUI  220  can present, for example, a most recently used and/or a most frequently used command above other menu items. In some cases, VNUI  220  can present the command at or near the top of the visible menu  305 . 
       FIG. 7  shows an example menu in which the visible menu  305  includes the command “take a photo”  410  above the categories Camera  310 , Communication  320 , and Information retrieval  330 . In  FIG. 7 , VNUI  220  has bubbled-up the command “take a photo”  410  to a position above the displayed categories. There may also be other menu items available but not displayed in the visible menu  305 . 
       FIG. 8A  shows an example menu in which the visible menu  305  includes the commands “take a photo”  410  and “send a message”  430  above the categories Camera  310  and Communication  320 . Here, VNUI  220  has bubbled-up the commands “take a photo”  410  and “send a message”  430  to a position above the displayed categories. There may also be other menu items available but not displayed in the visible menu  305 . 
     In any case, once a wearer has used VNUI  220  to navigate to and invoke one or more commands, the visible menu  305  can include both available categories and commands. In some embodiments, the visible menu can display both available categories and commands as top-level menu items, as in  FIGS. 7 and 8A . 
     By bubbling up or prominently displaying one or more menu items, VNUI  220  can present the one or more menu items in a manner that attempts to predict a wearer&#39;s intent when using the VNUI. In particular, the VNUI can determine a command likely to be used, and the VNUI can display the command to appear more prominently than other menu items. 
     VNUI  220  can use any number of various criteria to determine which command or commands a wearer is likely to invoke. As one example, the VNUI can determine a command likely to be used based on how frequently commands are used by the wearer. In particular, the VNUI may bubble up the command or commands used most frequently by a wearer, such that a more frequently invoked command appears at the top of the menu. 
     As another example, the VNUI can determine a command likely to be used based on how recently a wearer has used the command. In particular, the VNUI may bubble up the command or commands used most recently by a wearer, such that a more recently invoked command appears at the top of the menu. 
     As yet another example, VNUI  220  can bubble up the commands based on some combination of criteria. For instance, the VNUI can bubble up commands based on a first criteria of how recently a wearer has used the command, and then, for those commands with similar frequencies of use, based on a second criteria of how recently a wearer has used the command or commands. 
     Taking the visible menu  305  of  FIG. 6  as one particular example, VNUI  220  may have determined that a wearer is more likely to use the “take a photo”  410  command than other menu items. Accordingly, the VNUI can, in this example, display the “take a photo”  410  command above the other menu items in the visible menu  305 . 
     Taking the visible menu  305  of  FIG. 8A  as another particular example, VNUI  220  may have determined that a wearer is more likely to use the “take a photo”  410  and “send a message”  430  commands than other menu items (such as other commands). Accordingly, VNUI  220  can, in this example, display the “take a photo”  410  and “send a message”  430  commands above the other menu items in the visible menu  305 . 
     VNUI  220  may also have determined that a wearer is more likely to use the “take a photo”  410  command than the “send a message”  430  command. Accordingly, the VNUI can, in this example, display the command “take a photo”  410  above the command “send a message”  430  in the visible menu  305 . 
     In addition, as one or more commands or menu items bubble up, other commands or menu items can “bubble down.” For example, commands that have previously been bubbled up can be displaced by newly bubbled up commands. In some cases, a displaced command can be displayed below a newly bubbled up command. In other cases, the displaced command can be displayed only once a wearer utters the name of a category with which the displaced command is associated. Other examples are possible as well. 
     By bubbling up commands, the VNUI also encourages a wearer to speak the command directly from the top-level menu. If a wearer sees the command in a visible menu with top-level menu items, the wearer should not need to navigate to a submenu to view commands associated with a category before invoking the command. Accordingly, bubbling up commands may make the VNUI more efficient for a wearer. 
     As an example, a wearer can directly invoke a command that has been bubbled up to the top-level menu. In particular,  FIG. 7  shows the command “take a photo”  410  bubbled up in the visible menu  305 . A wearer can directly invoke this command via VNUI  220  by uttering a sequence such as “ok glass, take a photo,” instead of having to navigate to the command by uttering the sequence “ok glass, open camera, take a photo.” 
     Regardless of whether a command has been bubbled up or displayed more prominently, wearers of some embodiments can invoke a command directly from the top-level menu-without needing to navigate to a category. Some embodiments of the VNUI can incorporate a “hotword” approach to voice recognition. Each command can be treated as a hotword, and the VNUI can recognize and carry out the command, even if the command is not displayed on the visible menu  305 . 
     As an example, other commands may not be visible in the visible menu  305  of  FIG. 8A , although they may be available. In particular, VNUI  220  may include the command “record a video,” which VNUI  220  may not display in the visible menu  305 . A wearer can also directly invoke this command via VNUI  220  by uttering a sequence such as “ok glass, record a video,” instead of having to navigate to the command by uttering a sequence such as “ok glass, open camera, record a video.” Accordingly, the system allows a wearer to utter a command directly, without the command being visible on the menu. 
     The system also allows for a wearer to be able to invoke commands from one category while viewing commands from another category. For example, the visible menus  305  of  FIG. 5  and  FIG. 6  display commands in the category “Camera”  310 . A wearer can also directly invoke, via VNUI  220 , a command from another category, such as the command “send a message”  430  from the category Communication  320 . In particular, from the visible menus  305  of  FIG. 5 or 6 , a wearer can utter a sequence such as “ok glass, send a message” to directly invoke the “send a message” command, even if that command is not displayed on the visible menu  305 . 
     In some embodiments, a wearer may also use VNUI  220  to navigate to a category that is not in the visible display. For example, the visible menu  305  of  FIG. 5  shows the category Camera  310  and the category Communication  320 , but not the category Information Retrieval  330  (as shown in  FIG. 4 ). In this example, from the visible menu  305  of  FIG. 5 , a wearer can utter a sequence such as “ok glass, open information retrieval” to view available commands in that category. 
     Associating commands with categories, bubbling up the command(s) most likely to be used, and allowing commands to be invoked from anywhere within the available menu can help the scalability of voice navigable menus. Such a system can allow for more voice commands to be added with minimal impact on the ability of the VNUI and visible display to efficiently guide a wearer through the menu. 
     The menu items in the visible menu  305  can act as cues for a wearer of the voice navigable menu  300 . In other words, the items in the visible menu  305  can tell a wearer what to say to invoke a command or to navigate the menu. For example, by speaking a command, a wearer can invoke the command. And by speaking a category, a wearer can navigate to the available commands in that category. 
     The ability to efficiently guide a wearer through the voice navigable menu may be an especially important consideration for new or infrequent wearers. Likewise, even experienced wearers may be unfamiliar with available menu items such as commands or categories (such as, for example, if commands or categories are added to the voice navigable menu). 
     In particular, associating commands with categories can reduce the number of items displayed in, for example, a top-level menu. For instance, multiple commands can be associated with each category, and commands may be added to each category as the system develops. The number of categories will likely be less than the number of commands. A menu that displays some or all available categories may have fewer menu items than a menu that displays, for example, all available commands. 
     A menu with fewer menu items may be easier to navigate, especially on a smaller display of an HMD. In particular, an HMD may have a smaller display than other mobile computing devices. In some cases, an HMD may have a significantly smaller display than other computing devices. Accordingly, the display  216  and visible menu  305  of an HMD may also be smaller or significantly smaller than other computer devices. 
     Because of the smaller display  216 , fewer menu items may be able to be presented to a wearer on the visible menu  305 . Accordingly, the fewer menu items in the voice navigable menu  300 , the better chance that the visible menu  305  can include the entire voice navigable menu. Alternatively, if the visible menu  305  only includes a portion of the entire voice navigable menu  300 , minimizing the number of menu items in the voice navigable menu  300  should help increase the amount of the voice navigable menu  300  included in the visible menu  305 . 
     A wearer&#39;s efficiency in navigating a voice navigable menu should increase with a wearer&#39;s ability to see more of the voice navigable menu in the display  216 . In other words, the time spent by a wearer navigating the voice navigable menu should be less if the visible menu  305  includes more of the available categories and commands. 
     Bubbling up the command or commands most likely to be used can also help a wearer efficiently navigate a voice navigable menu. For example, the bubbled up commands may be the commands a wearer is most likely to want to invoke. In such a case, a wearer may be able to more quickly recall or invoke a command if the command is visually presented to the wearer—or visually presented to the wearer in a prominent way, such as at the top of a visible menu. 
     In particular, a wearer seeking a particular command may avoid having to navigate to that command. Instead, if that command is displayed in the top-level menu (at the top or in some other, prominent way), a wearer can immediately receive the visual cue for the command without having to navigate to the category. 
     In addition, allowing commands to be invoked from anywhere within the available menu can also reduce the need for a wearer to navigate to a particular category (or top-level visible menu) before invoking the command. 
     E. Updating the Example User Interface 
     Some embodiments also allow for the addition of applications or features, in some cases from third-parties. In such embodiments, the added applications can result in added commands. In the voice navigable menu, the added commands can be associated with an added command menu item, which can comprise an added command category in the voice navigable menu. 
     For discussion purposes, an added command can be distinguished from an original command. An original command can refer to a command that may have been originally provided in or, in some cases, previously added to a voice navigable menu. In addition, an added command menu item can be distinguished from an original menu item. An original menu item can refer to a menu item, such as a category, that may have been originally provided in or, in some cases, previously added to a voice navigable menu. 
     In some instances, the added applications can be treated collectively as a category in the voice-navigable menu (such as a “Glass Apps” category or an “Added Command” category, for example). In other cases, a third-party application or one or more added commands may be treated as its own category (such as a “Facebook” category, for example). 
     Turning to  FIG. 8B , as a more particular example, a category for added applications (such as third-party applications) can be Glass Apps  340 , and commands within that category may be, for example, (i) “post a tweet”  440  and (ii) “call an Uber car”  450 —commands associated with two different third-party features. 
     As shown in  FIG. 8B , in the visible menu  305 , uttering “ok glass, open Glass Apps” would show the added commands “post a tweet”  440  and “call an Uber car”  450 . Accordingly, added commands can be invoked via VNUI  220  by uttering a sequence such as “ok glass, open Glass Apps, post a tweet.” 
     As with other commands, added commands such as “post a tweet”  440  and “call an Uber car”  450  can be bubbled up in the top-level menu. As also with other commands, added commands can be directly invoked via VNUI  220  by uttering a sequence such as “ok glass, post a tweet,” instead of having to navigate to the added command by uttering the sequence “ok glass, open Glass Apps, post a tweet.” 
     In addition, a menu item for an added command can be the command itself, instead of an ambiguous menu item that merely opens an app or leads to further menu items. For example, a menu item such as the command “post a tweet” provides more guidance to a wearer than a menu item such as “open Twitter.” 
     A wearer may choose which additional or third-party applications or features to install or enable in a set-up portal for the HMD device. The set up portal may be part of the HMD or the VNUI  220  itself, or it may be accessed through interfaces of other devices (such as an Internet browser on a computing device). Additional or third-party applications may also be added to the VNUI automatically by a computing device executing suitable software. 
     If a wearer chooses particular additional or third-party applications or features, there may be a set-up sequence that asks a wearer to specify whether:
         I&#39;d like to use Glass to . . .
           . . . post a tweet [ON|OFF]   . . . call an Uber car [ON|OFF]
 
Accordingly, commands can be added to the voice navigable menu  300  based on the features that the wearer enables. Once added to the voice navigable menu  300 , the added commands can be displayed in the visible menu  305  and treated similarly to the commands discussed above.
   
               

     One unique property of this example set-up sequence is that the set-up flow uses the same verb form of a command that a wearer would utter when invoking the command. In particular, uttered commands (e.g., “post a tweet”) use the English imperative verb form, while the set-up flow (“I&#39;d like to use Glass to . . . ”) uses the English infinitive verb form, and each verb form is orthographically/lexicographically identical in English. In other words, a wearer can use the same verb form of “post a tweet” both during a set-up sequence (“I&#39;d like to use Glass to post a tweet”) and when invoking the command (“ok glass, post a tweet”). 
       FIGS. 9A-9C  depict an example set-up sequence that can be presented on the display  216  of VNUI  220 . In this example,  FIG. 9A  shows a menu item Add Glass Apps  332  in the visible menu  305 . To select the Add Glass Apps  332  menu item, a wearer can utter “ok glass, add glass apps.” 
     VNUI  220  may then present to the wearer the visible menu  305  of  FIG. 9B , which displays two available commands for selection: enable “post a tweet”  334  and enable “call an Uber car”  336 . To enable one of the available commands, a wearer can utter “ok glass, enable ‘post a tweet.’” 
     VNUI  220  may then present to the wearer the visible menu  305  of  FIG. 9C , which displays the “post a tweet”  440  command as a menu item. As discussed, the “post a tweet” command may also be added or associated with a category of added commands, such as the Glass Apps  340  category of  FIG. 8B . 
     Added commands (such as third-party or other added commands) may be merged into an existing library of voice commands. Because of the potentially large number of added or third-party commands, potential added commands can be selected and approved to maintain distinctiveness from other commands. One consideration may be selecting potential added commands that are long enough to provide phonetic distinctiveness from other commands (for example, “post a tweet” instead of “tweet”). 
     In addition, a computer executing suitable software can determine a phonetic distance between a potential added command set and existing commands, perhaps in an existing command set. If the smallest phonetic distance between commands in the potential added command set and an existing command set is greater than a threshold, the computer can determine that the potential added command set may be acceptable for addition in the command set. If the smallest phonetic distance is less than the threshold, however, then the computer can determine that the potential added command set may not be distinguishable from the existing command set by the speech recognition system. In some embodiments, the computer can identify command(s) in the potential added command set whose phonetic distance is within the threshold, and suggest those commands be modified or rejected for inclusion of the potential added command set into the existing command set. 
     The VNUI can be periodically updated with added commands as needed. 
     F. Example Methods of Operation 
       FIG. 10  is a flow chart illustrating a method  600 , according to an example embodiment. In  FIG. 10 , method  600  is described by way of example as being carried out by a wearable computer and possibly a wearable computer that includes a head-mounted display (HMD). However, it should be understood that example methods, such as method  600 , may be carried out by a wearable computer without wearing the computer. For example, such methods may be carried out by simply holding the wearable computer using the wearer&#39;s hands. Other possibilities may also exist. 
     Further, example methods, such as method  600 , may be carried out by devices other than a wearable computer, and/or may be carried out by sub-systems in a wearable computer or in other devices. For example, an example method may alternatively be carried out by a device such as a mobile phone, which is programmed to simultaneously display a graphic object in a graphic display and also provide a point-of-view video feed in a physical-world window. Other examples are also possible. 
     As shown in  FIG. 10 , method  600  begins at block  610 , where an HMD with a voice navigable user interface can display a first visible menu. The first visible menu can comprise at least a portion of a voice navigable menu. As discussed above, the first visible menu may comprise a portion of the voice navigable menu or the entire voice navigable menu. In addition, the voice navigable menu can include one or more menu items. The menu items can include both categories and commands. 
     At block  620 , the HMD can receive a first utterance. The first utterance can comprise a first menu item. The one or more menu items recited in block  610  can comprise the first menu item. In some cases, the first menu item may not be displayed on the visible menu when uttered. In other cases, the first menu item may be displayed on the visible menu when uttered. 
     At block  630 , after receiving the first utterance, the HMD can modify the first visible menu to display one or more commands associated with the first menu item. In some embodiments, the HMD can expand the first visible menu to display the one or more commands as sub-level menu items in-line with the first menu item. In other embodiments, the HMD can display the one or more commands as a stand-alone submenu. 
     At block  640 , the HMD can receive a second utterance. The second utterance can comprise a first command. 
     At block  650 , after receiving the second utterance, the HMD can invoke the first command. 
     In some embodiments, method  600  may further involve the HMD displaying at least a portion of a second visible menu. The second visible menu can include the first command and at least one menu item of the one or more menu items. In these embodiments, the second visible menu can display the first command above the at least one menu item. In other embodiments, the second visible menu can display the first command in a manner more prominent than the at least one menu item, but not necessarily above the at least one menu item. 
     In some embodiments, method  600  can additionally include receiving a third utterance at the HMD. The third utterance can comprise a second command, the second command differing from the first command. After receiving the third utterance, the HMD can invoke the second command. In addition, the method can include the HMD displaying at least a portion of a third visible menu. The third visible menu can include the second command and at least one menu item of the one or more menu items. And the third visible menu can display the second command above the at least one menu item. In some embodiments, the third visible menu can further include the first command. 
       FIG. 11  is a flow chart illustrating a method  700 , according to an example embodiment. In  FIG. 11 , method  700  is described by way of example as being carried out by a wearable computer and possibly a wearable computer that includes a head-mounted display (HMD). However, it should be understood that example methods, such as method  700 , may be carried out by a wearable computer without wearing the computer. For example, such methods may be carried out by simply holding the wearable computer using the wearer&#39;s hands. Other possibilities may also exist. 
     Further, example methods, such as method  700 , may be carried out by devices other than a wearable computer, and/or may be carried out by sub-systems in a wearable computer or in other devices. For example, an example method may alternatively be carried out by a device such as a mobile phone, which is programmed to simultaneously display a graphic object in a graphic display and also provide a point-of-view video feed in a physical-world window. Other examples are also possible. 
     As shown in  FIG. 11 , method  700  begins at block  710 , where an HMD with a voice navigable user interface can display a first visible menu. The first visible menu can comprise at least a portion of a voice navigable menu. As discussed above, the first visible menu may comprise a portion of the voice navigable menu or the entire voice navigable menu. In addition, the voice navigable menu can include one or more menu items. 
     The one or more menu items in block  710  can comprise an original menu item. The original menu item can be associated with one or more original commands. 
     At block  720 , the HMD can receive a first utterance. The first utterance can comprise an original command of the one or more original commands. In some cases, the first added command may not be displayed on the visible menu when uttered. In other cases, the first menu item may be displayed on the visible menu when uttered. 
     At block  730 , after receiving the first utterance, the HMD can invoke the original command. 
     At block  740 , the HMD can receive an added command menu item. The added command menu item can be associated with one or more added commands. At least one of the added commands can differ from the one or more original commands. In addition, the one or more added commands can comprise a first added command. 
     At block  750 , the HMD can add the added command menu item to the voice-navigable user interface of the HMD. 
     At block  760 , the HMD can receive a second utterance. The second utterance can comprise the first added command. In some cases, the first added command may not be displayed on the visible menu when uttered. In other cases, the first menu item may be displayed on the visible menu when uttered. 
     At block  770 , after receiving the second utterance, the HMD can invoke the first added command. 
     In some embodiments, method  700  may further involve the HMD receiving a third utterance. The third utterance can comprise an identification of the added command menu item. After receiving the third utterance, the HMD can modify the first visible menu to display the one or more added commands. 
     In some embodiments, method  700  can additionally include the HMD displaying at least a portion of a second visible menu. The second visible menu can include the first added command and at least one menu item of the one or more menu items. In addition, the second visible menu can display the first added command above the at least one menu item. 
     In some embodiments, the one or more added commands of method  700  can further comprise a second added command, the second added command differing from the first added command, and method  700  can further include receiving a fourth utterance at the HMD. The fourth utterance can comprise the second added command. After receiving the fourth utterance, the HMD can invoke the second added command. In addition, the method can further include the HMD displaying at least a portion of a third visible menu. The third visible menu can include the second added command and at least one menu item of the one or more menu items. And the third visible menu can display the second added command above the at least one menu item. In some embodiments, the third visible menu can also include the first added command. 
     G. Conclusion 
     The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. 
     The above detailed description describes various features and functions of the disclosed systems, devices, and methods with reference to the accompanying figures. In the figures, similar symbols typically identify similar components, unless context dictates otherwise. The example embodiments described herein and in the figures are not meant to be limiting. Other embodiments can be utilized, and other changes can be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     With respect to any or all of the ladder diagrams, scenarios, and flow charts in the figures and as discussed herein, each block and/or communication may represent a processing of information and/or a transmission of information in accordance with example embodiments. Alternative embodiments are included within the scope of these example embodiments. In these alternative embodiments, for example, functions described as blocks, transmissions, communications, requests, responses, and/or messages may be executed out of order from that shown or discussed, including substantially concurrent or in reverse order, depending on the functionality involved. Further, more or fewer blocks and/or functions may be used with any of the ladder diagrams, scenarios, and flow charts discussed herein, and these ladder diagrams, scenarios, and flow charts may be combined with one another, in part or in whole. 
     A block that represents a processing of information may correspond to circuitry that can be configured to perform the specific logical functions of a herein-described method or technique. Alternatively or additionally, a block that represents a processing of information may correspond to a module, a segment, or a portion of program code (including related data). The program code may include one or more instructions executable by a processor for implementing specific logical functions or actions in the method or technique. The program code and/or related data may be stored on any type of computer readable medium such as a storage device including a disk or hard drive or other storage medium. 
     The computer readable medium may also include non-transitory computer readable media such as computer-readable media that stores data for short periods of time like register memory, processor cache, and random access memory (RAM). The computer readable media may also include non-transitory computer readable media that stores program code and/or data for longer periods of time, such as secondary or persistent long term storage, like read only memory (ROM), optical or magnetic disks, compact-disc read only memory (CD-ROM), for example. The computer readable media may also be any other volatile or non-volatile storage systems. A computer readable medium may be considered a computer readable storage medium, for example, or a tangible storage device. 
     Moreover, a block that represents one or more information transmissions may correspond to information transmissions between software and/or hardware modules in the same physical device. However, other information transmissions may be between software modules and/or hardware modules in different physical devices. 
     The particular arrangements shown in the figures should not be viewed as limiting. It should be understood that other embodiments can include more or less of each element shown in a given figure. Further, some of the illustrated elements can be combined or omitted. Yet further, an example embodiment can include elements that are not illustrated in the figures. 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.