Patent Publication Number: US-10319072-B2

Title: Adaptation of presentation speed

Description:
BACKGROUND 
     Augmented reality applications allow a user to see a presentation of the world augmented with or superimposed by computer-generated content. The content may be graphical, textual, and/or audible. The presented world may be presented directly to the user, such as when the user is looking through a display, and the imagery is applied to or projected on the display. The world may also be presented indirectly, such as when a user is navigating previously captured images of the real world, rather than the world that is presently in front of the user. 
     A head mounted display (“HMD”) is a display device worn on or about the head. HMDs usually incorporate some sort of near-to-eye optical system to emit a light image within a few centimeters of the human eye. Single eye displays are referred to as monocular HMDs while dual eye displays are referred to as binocular HMDs. Some HMDs display only a computer generated image (“CGI”), while other types of HMDs are capable of superimposing CGI over a real-world view. This latter type of HMD can serve as the hardware platform for realizing augmented reality. With augmented reality the viewer&#39;s image of the world is augmented with an overlaying CGI, also referred to as a heads-up display (“HUD”), since the user can view the CGI without taking their eyes off their forward view of the world. 
     SUMMARY 
     This application relates to adaptation of presentation speed for content items associated with locations. Disclosed herein are aspects of systems, methods, and apparatuses for adapting presentation speed for content items associated with locations. 
     One aspect of the disclosed implementations is a system for audio presentation. The system includes a motion sensor, a speaker, a memory, and a processor. The memory stores instructions executable by the processor to cause the system to: obtain, from the motion sensor, an indication of motion in a space; adjust a presentation speed based on the indication of motion; and present, via the speaker, an audio content associated with a location in the space, wherein the audio content is presented using the adjusted presentation speed. 
     Another aspect is a method for content presentation. The method includes obtaining an indication of motion in a space; adjusting a presentation speed based on the indication of motion; and presenting a content item associated with a location in the space, wherein the content item is presented using the adjusted presentation speed. 
     Another aspect is a system for content presentation. The system includes a memory and a processor. The memory stores instructions executable by the processor to cause the system to: obtain an indication of motion in a space; adjust a presentation speed based on the indication of motion; and present a content item associated with a location in the space, wherein the content item is presented using the adjusted presentation speed. 
     These and other aspects of the present disclosure are disclosed in the following detailed description of the embodiments, the appended claims and the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views. 
         FIG. 1  is a diagram of an example of a space with locations associated with content items for presentation. 
         FIG. 2  is a block diagram of an example of a computing device configured to adjust presentation speed of content items based on motion of a user. 
         FIG. 3  is a flowchart an example of a process for adapting presentation speed of a content item associated with a location. 
         FIG. 4  is a flowchart an example of a process for presenting a content item associated with a location. 
         FIG. 5  is a flowchart an example of a process for adapting presentation speed based on motion data for a user. 
         FIG. 6  is a flowchart an example of a process for adapting presentation speed of a content item. 
         FIG. 7  is a flowchart an example of a process for adapting presentation speed of a content item based on a gaze direction. 
     
    
    
     DETAILED DESCRIPTION 
     In an augmented reality (AR) or virtual reality (VR) setting, audio presentation can be guided based on detected physical or virtual location. For example, the audio track may be changed as a person walks from one room to another as they walk around a museum to match the content of that new room. But walking pace varies from person to person, depending on many factors both physical and circumstantial (e.g., they are in a hurry, they are not interested in the content of a particular room, etc.). If an application is able to estimate the pace that a person is traveling through the physical or virtual environment, it may be used to change the pace of delivery of an accompanying audio track or other content item(s). If a user spends less time or walks briskly past a particular exhibit, the presentation speed of audio content can be accelerated or even stopped until the person returns to a more natural walking pace. There may be limits on how much faster the audio can be presented and remain intelligible. To make the presentation of audio content sound more natural when it is accelerated from a default presentation speed, pitch normalization processing may be applied to the audio content. 
     The presentation speed for other types of content items (e.g., video or slideshow content) may also be adjusted based on an indication of motion of a user in a space (e.g., a real space or a virtual space). In some implementations, the visual content is presented synchronously with audio content and the presentation speed for all the content items may be adjusted together. 
     Content items presented to a user may be associated with respective locations in a space. The user moving into proximity to a location may trigger the initiation of the presentation of a content item associated with the location. The presentation speed for the content item may be adjusted at the start of the presentation and/or the presentation speed may continue to be adjusted as the content item is presented. When a presentation speed is adjusted after the content item has started playing, the presentation speed may be updated gradually by interpolating the presentation speed between a current value and an adjusted value in small increments over an interval of time to avoid an abrupt change in presentation speed that could be noticeable and disruptive. 
     For example, the presentation speed for a content item may be adjusted based on a ratio of time spent in proximity to one or more prior locations visited by the user and durations of respective prior content items for those prior locations. The presentation speed for a content item may be adjusted within a limited range (e.g., between 1× and 2× a default presentation speed for the content item). Additional information about the attention of a user, such as a gaze angle of the user, may also be used to adjust a presentation speed for content items (e.g., including audio content). 
     Some implementations may provide advantages over prior augmented reality or virtual reality systems, such as tailoring content items to an individual user&#39;s interests and behavioral patterns automatically. Some implementations may streamline user interactions and make those interactions faster. 
       FIG. 1  is a diagram of an example of a space  100  with locations associated with content items for presentation. A user  110  moves in the space  100 . The user  110  wears a wearable interface  120  that is configured to present content items (e.g., audio content, video content, or slideshow content) to the user  110 . The space includes a first location  130  with a first proximity zone  132  around it, a second location  140  with a second proximity zone  142  around it, a third location  150  with a third proximity zone  152  around it, and a fourth location  160  with a fourth proximity zone  162  around it. One or more external motion sensors  170  are also positioned in the space  100  and are configured to detect motion of the user  110  in the space  100 . 
     For example, the space  100  may be in a museum and the locations ( 130 ,  140 ,  150 , and  160 ) may be associated with respective exhibits in the museum. The locations may be associated with respective content items (e.g., audio content, video content, or slideshow content that expound on a respective exhibit). A content item associated with one of the locations (e.g., the first location  130 , the second location  140 , the third location  150 , or the fourth location  160 ) may be presented to the user  110  via the wearable interface  120  when the user  110  is in proximity to the location. A presentation speed for the content item may be adjusted based on an indication of motion of the user  110  in the space  100 . 
     The wearable interface  120  may include headphones or another type of speaker for presenting audio content. In some implementations, the wearable interface  120  includes a wearable display (e.g., an HMD) configured to display images to the user  110  for presenting video content, slideshow content, etc. The wearable interface  120  may include motion sensors (e.g., accelerometers, gyroscopes, magnetometers, and/or a global positioning system receiver) for detecting motion of the user  110  through the space  100 . The wearable interface  120  may include an eye tracking sensor for detecting a gaze direction of the user  110 . For example, the wearable interface  120  may include the computing device  200  of  FIG. 2 . 
     The proximity zones ( 132 ,  142 ,  152 , and  162 ) may be defined as circular areas with configured radii centered at respective locations ( 130 ,  140 ,  150 , and  162 ). For example, the radii determining the size of the proximity zones ( 132 ,  142 ,  152 , and  162 ) may be configured by a curator that provides the content items associated with the respective locations ( 130 ,  140 ,  150 , and  162 ). 
     The external motion sensors  170  may include one or more cameras configured to capture images of the user  110  as the user moves through the space  100 . An estimate of motion of the user  110  in the space  100  may be determined based on image data from one or more cameras of the external motion sensors  170 . A presentation speed of a content item associated with a location (e.g., the second location  140 ) may be adjusted based on the estimate of motion of the user  110  in the space  100 . For example, a computing device configured to adjust the presentation speed for the content item may receive image data from a camera of the external motion sensors  170 . The image data may include views of the user  110  moving in the space  100 . The computing device may determine an estimate of motion of the user  110  in the space  100  based on the image data. This estimate of motion may in turn be used to determine an adjustment to the presentation speed. 
     Consider a space with N exhibits respectively associated with locations in the space (e.g., the first location  130 , the second location  140 , the third location  150 , and the fourth location  160  in the space  100 ). These exhibits can be notated by the index iϵ(0, . . . N−1). The space can span a single room or multiple rooms. A location (e.g., the second location  140 ) associated with an exhibit has position coordinates of (x_i, y_i). A proximity zone (e.g., the second proximity zone  142 ) may be configured for the location as a circular region with radius r_i centered at the location&#39;s position coordinates (x_i, y_i). 
     A content item (e.g., an audio track) for exhibit i has a duration, d_i. The content item may be presented at a presentation speed, v_i (e.g., v_i=1=&gt;normal speed, v_i=2=&gt;twice playback speed, etc.). 
     Let t_i be the time spent by the user  110  in a proximity zone of the ith exhibit/location. If the user  110  spends more time, t_i, in a proximity zone than the duration of the corresponding content item, d_i, one could infer that time was not an issue. However, if t_i, &lt;d_i one can infer that the visitor was not interested in this exhibit, or they got bored with the presentation of the content item. Other cues may be used to differentiate these cases. For example, a gaze direction of the user  110  could be monitored to see if the user  110  is looking elsewhere. For example, the user  110  may be deemed to be interested in an exhibit, where they spend time reading an explanation placard of the exhibit. In some scenarios, the presentation speeds for content items of current and/or future exhibits may be increased in an attempt to retain the interest of the user  110 . 
     An example scheme for adjusting presentation speed of content items is:
         For all exhibits visited so far where we determine that the user  110  is interested, calculate the proportion of the respective content item (e.g., audio track) that they listened to, P_iϵ(0,1).   Let P′ be the average of all P_i for all the exhibits visited so far.   Determine a presentation speed for a content item of an exhibit as follows:   If (P′&lt;0.5) v_i=2.0   else v_i=1/P′
 
In this scheme, the presentation speed is capped 1.0&lt;=v_i&lt;=2.0 for audio since double presentation speed may be a sensible upper limit for presentation speed to retain intelligibility.
       

     In some implementations, a dampening mechanism may be used to gradually apply adjustments into the presentation speed update to avoid irritating abrupt changes in presentation speed to the user  110 . 
     Other available sensory information may be utilized to inform the adjustment of the presentation speed of content items. For example, precise positions of the user  110  could be used to infer that other people or objects are impeding a view of an exhibit at a location. For example, a relative position of the user and an exhibit explanation placard together with viewer gaze direction can be used to infer whether they have read/are reading the information on the placard and use this in the decision process. 
     This scheme is equally applicable in an AR scenario, a VR scenario, or a real-world scenario. The specific sensory information that is available may be different in these cases. In the VR world, positions are known implicitly whereas in the real-world position has to be sensed in some way. 
       FIG. 2  is a block diagram of an example of a computing device  200  configured to adjust presentation speed of content items based on motion of a user. The computing device may include or be part of a system for content presentation (e.g., audio presentation). The computing device  200  can be in the form of a computing system including multiple computing devices, or in the form of a single computing device, for example, a VR headset, a mobile phone, a tablet computer, a laptop computer, a notebook computer, a desktop computer, and the like. 
     A CPU  202  in the computing device  200  can be a central processing unit. Alternatively, the CPU  202  can be any other type of device, or multiple devices, capable of manipulating or processing information now-existing or hereafter developed. Although the disclosed implementations can be practiced with a single processor as shown, e.g., the CPU  202 , advantages in speed and efficiency can be achieved using more than one processor. 
     A memory  204  in the computing device  200  can be a read-only memory (ROM) device or a random access memory (RAM) device in an implementation. Any other suitable type of storage device can be used as the memory  204 . The memory  204  can include code and data  206  that is accessed by the CPU  202  using a bus  212 . The memory  204  can further include an operating system  208  and application programs  210 , the application programs  210  including at least one program that permits the CPU  202  to perform the methods described here. For example, the application programs  210  can include applications 1 through N, which further include a content item presentation application that performs the methods described here (e.g., implementing the process  300  of  FIG. 3 ). 
     The computing device  200  can also include one or more output devices, such as a display  218 . The display  218  may be, in one example, a touch sensitive display that combines a display with a touch sensitive element that is operable to sense touch inputs. The display  218  can be coupled to the CPU  202  via the bus  212 . Other output devices that permit a user to program or otherwise use the computing device  200  can be provided in addition to or as an alternative to the display  218 . When the output device is or includes a display, the display can be implemented in various ways, including by a liquid crystal display (LCD), a cathode-ray tube (CRT) display or light emitting diode (LED) display, such as an organic LED (OLED) display. In some implementations, the display  218  is a wearable display (e.g., an HMD integrated in glasses or goggles). 
     The computing device  200  can also include or be in communication with a motion sensor  220 , for example an inertial measurement unit, or any other motion sensor  220  now existing or hereafter developed that can detect motion of a user in a space. The motion sensor  220  can be configured to be worn by a user operating the computing device  200 . For example, the motion sensor  220  may include accelerometers, gyroscopes, magnetometers, and/or a global positioning system receiver. 
     The computing device  200  can also include or be in communication with a speaker  222 , for example headphones, or any other sound-making device now existing or hereafter developed that can generate sounds in response to signals from the computing device  200 . The speaker  222  can be positioned such that it is directed toward a user operating the computing device  200  and can be configured to present audio content (e.g., music or an audio track) associated with a location when the user is in proximity to the location. For example, video content may be presented, via the display  218  (e.g., a wearable display), synchronously with audio content presented via the speaker  222 . 
     The computing device  200  can also include or be in communication with an eye tracking sensor  226 , for example an optical sensor, or any other eye tracking sensor  226  now existing or hereafter developed that can detect eye orientation or gaze direction. For example, the eye tracking sensor  226  may include a video camera that detects light (e.g., infrared light) reflected from an eye and outputs image data. The image data may be analyzed to determine a relative orientation of the eye. In some implementations, the eye tracking sensor  226  may use electric potentials measured with electrodes placed around the eyes. Electric signal that can be derived using two pairs of contact electrodes placed on the skin around one eye is called an electrooculogram (EOG). For example, an indication of gaze direction for a user may be determined based on an EOG and data describing the position and orientation of a user&#39;s head in a space. An indication of gaze direction for a user may be obtained from the eye tracking sensor  226  and a presentation speed for a content item may be determined based in part on the indication of gaze direction. 
     The computing device  200  can also include a communications interface  230 , which may enable communications with a content server and/or external sensors (e.g., the external motion sensors  170 ). For example, the communications interface  230  may be used to receive image data from a camera. The image data may include views of a user moving in a space. For example, the communications interface  230  may be used to receive content items (e.g., audio content, video content, and/or slideshow content) from a content server for presentation to a user. For example, the communications interface  230  may include a wired interface, such as a high-definition multimedia interface (HDMI), a universal serial bus (USB) interface, or a FireWire interface. For example, the communications interface  230  may include a wireless interface, such as a Bluetooth interface, a ZigBee interface, and/or a Wi-Fi interface. 
     Although  FIG. 2  depicts the CPU  202  and the memory  204  of the computing device  200  as being integrated into a single unit, other configurations can be utilized. The operations of the CPU  202  can be distributed across multiple machines (each machine having one or more processors) that can be coupled directly or across a local area or other network. The memory  204  can be distributed across multiple machines such as a network-based memory or memory in multiple machines performing the operations of the computing device  200 . Although depicted here as a single bus, the bus  212  of the computing device  200  can be composed of multiple buses. Further, secondary storage can be directly coupled to the components of the computing device  200  or can be accessed via a network and can comprise a single integrated unit such as a memory card or multiple units such as multiple memory cards. The computing device  200  can thus be implemented in a wide variety of configurations. 
       FIG. 3  is a flowchart an example of a process  300  for adapting presentation speed of a content item associated with a location. The process  300  includes obtaining  310  an indication of motion in a space; adjusting  320  a presentation speed based on the indication of motion; and presenting  330  a content item associated with a location in the space, wherein the content item is presented using the adjusted presentation speed. For example, the process  300  may be implemented by the wearable interface  120  of  FIG. 1 . For example, the process  300  may be implemented by the computing device  200  of  FIG. 2 . 
     The process  300  includes obtaining  310  an indication of motion in a space. In some implementations, the space may be a real space (e.g., a space in a museum that includes exhibits). For example, the indication of motion may be based on data from motion sensors (e.g., accelerometers, gyroscopes, magnetometers, and/or a global positioning system receiver) worn by a user as the user moves through the space. In some implementations, the space may be a virtual space (e.g., that user moves through using a virtual reality application and control interface). For example, the indication of motion may be based on control signals from a user detected with a virtual reality control interface (e.g., including motion sensors worn by the user, buttons, a mouse, and/or a joystick). The indication of motion may include a position, an orientation, and/or a velocity in the space. In some implementations, the indication of motion may include specification of a path through the space traversed by the user. 
     The process  300  includes adjusting  320  a presentation speed based on the indication of motion. In some implementations, the presentation speed may be adjusted  320  to present a content item faster when the user is moving through the space faster than expected. For example, the when the average velocity of the user in the space over a time interval or as the user moves between two locations is greater than an expected average velocity, the presentation speed may be increased by factor proportional to the excess average velocity. In some implementations, the presentation speed may be adjusted  320  based on analysis of the amount of time the user has spent in proximity to other locations associated with content items. For example, the presentation speed may be adjusted  320  by implementing the process  500  of  FIG. 5 . Adjusting  320  the presentation speed may include checking that the adjusted presentation speed is less than a limit (e.g., 2× or 3× a default presentation speed for the content item). Enforcing a limit on the presentation speed may serve to preserve intelligibility of the content item. 
     The process  300  includes presenting  330  a content item associated with a location in the space. The content item may be presented  330  using the adjusted presentation speed. The content item may include at least one of audio content, video content, and slideshow content. For example, content item may include audio content and may be presented  330  by playing the audio content with a speaker (e.g., the speaker  222 ). When audio content is presented  330  using a presentation speed higher than the default presentation speed for the content item (e.g., playback at 1.5× speed), pitch normalization processing may be applied to the audio content to mitigate distortion of voices in the audio content. For example, content item may include video content and/or slideshow content and may be presented  330  by displaying the video content and/or slideshow content on a display (e.g., the display  218 ). In some implementations, video content is presented  330 , via a wearable display (e.g., an HMD), synchronously with audio content. For example, the content item may be presented  330  when the user is in proximity to the location by using the process  400  of  FIG. 4 . 
       FIG. 4  is a flowchart an example of a process  400  for presenting a content item associated with a location. The process  400  includes determining  410  a user position in the space; checking  420  whether the user position is in proximity to the location; and initiating  430  presentation of the content item based on the user position entering proximity to the location. For example, the process  400  may be implemented by the wearable interface  120  of  FIG. 1 . For example, the process  400  may be implemented by the computing device  200  of  FIG. 2 . 
     The process  400  includes determining  410  a user position in the space. For example, the user position may be determined  410  based on coordinates from a global positioning system. In some implementations, the user position in the space may be determined  410  by tracking the evolution of the user&#39;s position from a known starting point based on data from motion sensor(s) worn by the user. For example, accelerometer and gyroscope measurements may be integrated to track the evolution of a user position. In a virtual space, the position of the user may be determined  410  by retrieving a position data structure from a virtual reality application being used by the user. 
     The process  400  includes checking  420  whether the user position is in proximity to a location. For example, checking  420  whether the user position is in proximity to the location may include determining a distance between the user position and the location. If the distance is below a threshold that has been configured for the location (e.g., 1 meter, 5 meters, or 10 meters), then the user is determined to be in proximity to the location. Checking  420  whether the user position is in proximity to the location may include determining whether the user position is within a proximity zone configured for the location. For example, the proximity zone (e.g., the second proximity zone  142 ) for a location (e.g., the second location  140 ) may be configured as a circle around the center point of the location. Other shapes may be configured for proximity zones. For example, a proximity zone may be configured to match the shape of a room. Checking  420  whether the user position is in a proximity zone for a location may include testing whether the coordinates of the user position are a member of the set of coordinates defining the proximity zone. 
     The process  400  includes initiating  430  presentation of the content item based on the user position entering proximity to the location. When the user position transitions from outside to inside of proximity to the location, presentation of the content item associated with the location may be initiated  430 . The content item may be presented using a presentation speed that has been adjusted (e.g., using the process  400 ) based on an indication of motion of the user in the space. The presentation of the content item may continue until entire content item is presented or until the user position exits proximity to the location. 
     In some implementations, the presentation speed may continue to be adjusted (e.g., using the process  400 ) during the ongoing presentation of the content item. For example, the presentation speed may continue to be adjusted based on changes in the average velocity of the user over a sliding time window or based on other information about the user&#39;s interaction with something (e.g., an exhibit) at the location, such an estimate of a gaze angel of the user. When a presentation speed is adjusted during an ongoing presentation of a content item the adjustment may be implemented through a dampening mechanism to avoid abrupt changes that in the presentation speed. For example, the presentation speed may be updated to an adjusted value in a series of small steps by interpolating the presentation speed from a current value to the adjusted value over an interval of time. 
       FIG. 5  is a flowchart an example of a process  500  for adapting presentation speed based on motion data for a user. The process  500  includes determining  510  a time period that a user was in proximity of a prior location in the space, wherein the prior location is associated with a prior content item with a duration; determining  520  a ratio of the time period to the duration; updating  530  an average ratio based on the ratio; and determining  540  the presentation speed based on the ratio. For example, the process  500  may be implemented by the wearable interface  120  of  FIG. 1 . For example, the process  500  may be implemented by the computing device  200  of  FIG. 2 . 
     The process  500  includes determining  510  a time period that a user was in proximity of a prior location in the space. The prior location may be associated with a prior content item with a duration. For example, referring to  FIG. 1 , the user  110  may have previously moved through the third proximity zone  152  of the third location  150  and through the fourth proximity zone  162  of the fourth location  160 , before entering the second proximity zone  142  of the second location  140 . A time history of the user positions of user  110  may indicate that the user  110  was in proximity of the third location  150  (e.g., in the third proximity zone  152 ) for a time period, t_3, and was in proximity of the fourth location  160  (e.g., in the fourth proximity zone  162 ) for a time period, t_4. In this scenario, the time history of the user positions of the user  110  may be analyzed to determine  510  the time period t_4 and/or the time period t_3. For example, the third location  150  may be associated with a prior content item, CI_3, of duration d_3 and the fourth location  160  may be associated with a prior content item, CI_4, of duration d_4. 
     The process  500  includes determining  520  a ratio of the time period to the duration. For example, a ratio may be determined  520  for the latest prior location. In the above scenario, a ratio, R_4, for the fourth location  160  may be determined as R_4=t_4/d_4. In some implementations, ratios may also be determined  520  for earlier prior locations. In the above scenario, a ratio, R_3, for the third location  150  may be determined as R_3=t_3/d_3. 
     The process  500  includes updating  530  an average ratio based on the ratio. For example, an average ratio, R_avg, for the user may be updated  530  based on the ratio for the latest prior location. In the above scenario, latest ratio, R_4, may be used to update  530  the average ratio, R_avg, For example, R_avg may be updated  530  as R_avg[n+1]=α*R_4+(1−α)*R_avg[n], where 0&lt;α&lt;1. In some implementations, a list of ratios for prior locations may be maintained and an average ratio may be updated  530  based on all available ratios for prior locations in the list. In the above scenario, the average ratio may be updated as R_avg=0.5*R_3+0.5*R_4. 
     The process  500  includes determining  540  the presentation speed based on the ratio. For example, the presentation speed may be determined  540  by scaling a default presentation speed for the content item by a factor that is inversely proportional to the ratio. In some implementations, the presentation speed scale factor is determined  540  as inversely proportional to the ratio for the latest prior location (e.g., R_4 in the above scenario). In some implementations, the presentation speed scale factor is determined  540  as inversely proportional to an average ratio prior locations (e.g., R_avg in the above scenario), which in turn depends on the latest ratio. For example, the presentation speed for the current content item may be determined  540  to be inversely proportional to the average ratio within a range between a minimum presentation speed and a maximum presentation speed. For example, the presentation speed for the current content item may be determined  540  by implementing the process  600  of  FIG. 6 . 
       FIG. 6  is a flowchart an example of a process  600  for adapting presentation speed of a content item. The process  600  includes determining the presentation speed to be inversely proportional to the ratio within a range between a minimum presentation speed and a maximum presentation speed. For example, the process  600  may be implemented by the wearable interface  120  of  FIG. 1 . For example, the process  600  may be implemented by the computing device  200  of  FIG. 2 . 
     The process  600  includes determining  610  a ratio of attention to content duration(s). For example, the ratio may be determined  610  as the ratio of linger time t_4 to content duration d_4 for the last prior location (e.g., as described in relation to operation  520 ). For example, the ratio may be determined  610  as an average of ratios for prior locations (e.g., as described in relation to operation  530 ). 
     The process  600  includes checking  615  whether the ratio is below a minimum threshold (e.g., 0.5), and if it is below the threshold, setting  620  the presentation speed to a maximum speed (e.g., 2× the default presentation speed for the content item associated with the current location). Otherwise, the ratio is checked  625  to determine whether the ratio is above a maximum threshold (e.g., 1), and if it is above the threshold, setting  630  the presentation speed to a minimum speed (e.g., the default presentation speed for the content item associated with the current location). 
     If the (at  615  and  625 ) the ratio is between the minimum and maximum thresholds, then the presentation speed is determined  632  as inversely proportional to the ratio. For example, the presentation speed may be determined  632  as v_i=v_0_i/R, where v_i is the presentation speed for the content item of the current location, v_0_i is a default presentation speed for the content item of the current location, and R is the ratio. 
       FIG. 7  is a flowchart an example of a process  700  for adapting presentation speed of a content item based on a gaze direction. The process  700  includes obtaining  710  an indication of gaze direction for a user; and determining  720  the presentation speed based in part on the indication of gaze direction. For example, the process  700  may be implemented by the wearable interface  120  of  FIG. 1 . For example, the process  700  may be implemented by the computing device  200  of  FIG. 2 . 
     The process  700  includes obtaining  710  an indication of gaze direction for a user. For example, the indication of gaze direction may be obtained  710  by receiving an estimate of gaze direction from an eye tracker (e.g., including the eye tracking sensor  226 ) in a device worn by the user. In some implementations the indication of gaze direction may be obtained  710  by combining eye orientation data from an eye tracking sensor (e.g., the eye tracking sensor  226 ) with user head orientation data from a motion sensor (e.g., the motion sensor  220 ) worn by the user. This orientation data may be combined to obtain  710  a gaze direction expressed in world coordinates of the space. The indication of gaze direction may reflect whether the user is looking in the direction of an object (e.g., a placard for an exhibit or central object at the location) in the proximity of the current location. 
     The process  700  includes determining  720  the presentation speed based in part on the indication of gaze direction. A ray in the indicated gaze direction from the user position in the space may be checked for intersection with known objects of interest at or near the location. For example, if the indicated gaze direction intersects with a placard for an exhibit associated with the current location, then a presentation speed for a content item associated with the location may be reduced. For example, if the indicated gaze direction points away from the location without intersecting with objects of interest at or near the location, then a presentation speed for a content item associated with the location may be increased. In some implementations, the presentation speed for a content item that is already being presented may be gradually reduced or increased (e.g., by interpolating between a current presentation speed and a new presentation speed that has been determined  720 .