images to videos to sound to location to ambient temperature, along with light levels and biosensor readings. In early systems (such as Lamming et al. 17), capturing people’s locations was a focus, involving users carrying or wearing small devices tracked by localized networked sensors. More recent wearable systems use head-mounted still and video cameras, 15 sensor-triggered still cameras worn around the neck14 (see the figure here), and audio-capture devices. 26 Yet others rely on instrumented environments that capture human activity through sensors or networks, as in MIT’s “PlaceLab” ( http://architecture.mit.edu/house_n/ placelab.html).

Situation-specific capture. These are more limited in scope, aiming to capture rich data in specific domains involving complex information. They can be viewed as a specialized form of lifelogging, aiming to record multiple kinds of data as completely and automatically as possible for specific activities or in particular places where the activity occurs. Most focus on recording activities during meetings, lectures, or other forms of work-related conversation, allowing “organizational knowledge” to be browsed and searched. 28 Early systems involved the simple indexing of recorded audio and pen-stroke data. More recent technology-enhanced meeting rooms capture video from multiple cameras and microphones, combining it with whiteboard content, slide capture, and digital pen strokes. Often included is software that automatically summarizes and extracts key events from the data.

Defining the Benefits: five Rs

Surprisingly, many lifelogging systems lack an explicit description of potential value for users, focusing instead on technical challenges (such as data capture and retrieval mechanisms). When claims are made about potential benefits, they tend to be ill-defined. Nevertheless, it is important to clarify what these claims might be. Here, we outline potential benefits for memory by describing the ways such systems might support “the five Rs,” or the activities we call recollecting, reminiscing, retrieving, reflecting, and remembering intentions:

Recollecting. Technology could help

surprisingly,
many lifelogging
systems lack an
explicit description
of potential value
for users, focusing
instead on technical
challenges.

us mentally “re-live” specific life experiences, thinking back in detail to past personal experiences (often called “episodic” memories25). Remembering aspects of a past experience can serve many practical purposes; examples include locating lost physical objects by mentally retracing our steps, recollecting faces and names by recalling when and where we met someone, or remembering the details of what was discussed in a meeting.

Reminiscing. As a special case of recollection, lifelogs could also help users re-live past experiences for emotional or sentimental reasons. This can be done by individuals or socially in groups, as an (often pleasurable) end in itself; examples are watching home videos and flipping through photo albums with friends and family.

Retrieving. Lifelogs promise to help us retrieve specific digital information we’ve encountered over the years (such as documents, email, and Web pages). Retrieval can include elements of recollection; for example, retrieving a document might require remembering the details of when we wrote it, when we last used it, or where we put it. Alternatively, retrieval might depend on inferential reasoning (such as trying to deduce keywords in a document or thinking about the document’s other likely properties, like type and size). Pondering information properties need not involve recollection of past experiences at all, as long as other ways are available for finding the desired information.

Reflecting. Lifelogs might support a more abstract representation of personal data to facilitate reflection on, and reviewing of, past experience. Reflection might include examining patterns of past experiences (such as about one’s behavior over time). Such patterns might provide useful information about our general level of physical activity or emotional states in different situations, allowing us to relate it to other data about, say, our health. Alternatively, reflection might involve looking at one’s past experiences from different angles or perspectives. Here, the value is not in re-living past events (as in recollecting) but in seeing things anew and framing the past differently. 13 The value is less about memory per se than it is about