The Geometry and Dynamics of Lifelogs: Discovering the Organizational Principles of Human Experience

Sreekumar, Vishnu; Dennis, Simon; Doxas, I.; Zhuang, Yuwen; Belkin, Mikhail

doi:10.1371/journal.pone.0097166

Cited by 28 publications

(55 citation statements)

References 19 publications

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“…This gap is propagated through the rest of the results as a relative lack of image pairs that are multiples of ∼15 h apart. In prior work, we analyzed the structure of lifelogged images and demonstrated that image pairs taken from identical spatiotemporal locations occupied a lower dimensional manifold than those image pairs taken from separate spatiotemporal locations (19). By removing image pairs separated by less than 100 m and 15.6 h, we reduced the possibility that the images themselves would give rise to the present results as a consequence of within-and between-episode image properties.…”

Section: Methodsmentioning

confidence: 81%

“…S1) with our custom lifelogging software that captured images along with their global positioning system (GPS) coordinates and timestamps (19). We collected an average of 5,414 ± 578 SEM images per subject, primarily from the Columbus, Ohio metropolitan area (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Image pairs with spatial distances less than 100 m were excluded because these distances are below the reliability of the GPS radios in these smartphones. Image pairs with temporal distances below 15.6 h were excluded based on prior work because of a discontinuity in the spatiotemporal distribution of image pairs (19) (Fig. S2B).…”

Section: Methodsmentioning

confidence: 99%

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Human hippocampus represents space and time during retrieval of real-world memories

Nielson

Smith

Sreekumar

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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Memory stretches over a lifetime. In controlled laboratory settings, the hippocampus and other medial temporal lobe brain structures have been shown to represent space and time on the scale of meters and seconds. It remains unclear whether the hippocampus also represents space and time over the longer scales necessary for human episodic memory. We recorded neural activity while participants relived their own experiences, cued by photographs taken with a custom lifelogging device. We found that the left anterior hippocampus represents space and time for a month of remembered events occurring over distances of up to 30 km. Although previous studies have identified similar drifts in representational similarity across space or time over the relatively brief time scales (seconds to minutes) that characterize individual episodic memories, our results provide compelling evidence that a similar pattern of spatiotemporal organization also exists for organizing distinct memories that are distant in space and time. These results further support the emerging view that the anterior, as opposed to posterior, hippocampus integrates distinct experiences, thereby providing a scaffold for encoding and retrieval of autobiographical memories on the scale of our lives.hippocampus | representational similarity analysis | lifelogging | episodic memory T he hippocampus plays a critical role in remembering the events of our lives (1). Direct evidence from single-neuron recordings in rats indicates that cells in the hippocampus fire in specific spatial locations (2-6) or at specific times during a temporal delay (7,8). Single-neuron and functional MRI (fMRI) studies in individuals navigating virtual environments have confirmed that cells coding for spatial location are also present in the human hippocampus (9-11). Similarly, place-responsive cell activity recorded in the hippocampus of patients with epilepsy during navigation of a virtual town was shown to reinstate during episodic memory retrieval of the previous virtual navigation (12). Together, these studies provide evidence that the same neurons in the medial temporal lobe (MTL) that are active during an experience also help represent the memory for that experience. These results, however, are limited to simple events in laboratory settings that occur on the scale of minutes and meters, thereby leaving unanswered whether we harness similar mechanisms in more natural settings and over larger temporal and spatial scales.Recent studies have used more naturalistic designs with incidentally acquired memories recorded via lifelogging devices that automatically capture photographs from the participants' lives (13,14). The typical finding is increased hippocampal activation when participants view images from their cameras as opposed to images from other participants' cameras (15-17), and this activation decays over the course of months (14). Still, there is no evidence to date that the hippocampus or other MTL structures actually represent space or time of autobiographical experiences. We a...

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Section: Methodsmentioning

confidence: 81%

Section: Resultsmentioning

confidence: 99%

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Human hippocampus represents space and time during retrieval of real-world memories

Nielson

Smith

Sreekumar

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

217

213

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“…Natural signals contain potentially useful information over a wide range of temporal scales (e.g., Alvarez-Lacalle, Dorow, Eckmann, & Moses, 2006;Sreekumar, Dennis, Doxas, Zhuang, & Belkin, 2014;Voss & Clarke, 1975). Mathematical scaleinvariance, the property that memory does not have a characteristic scale, has been argued to be a central principle of cognitive psychology (Anderson & Schooler, 1991;Chater & Brown, 2008;Kello et al, 2010) and is a key feature of many behavioral models of timing, conditioning and episodic memory (Brown et al, 2000(Brown et al, , 2007Gallistel & Gibbon, 2000;Gibbon, 1977;Miall, 1989).…”

Section: The Representation Of History Is Scale-invariantmentioning

confidence: 99%

A distributed representation of internal time.

Howard¹,

Shankar²,

Aue³

et al. 2015

Psychological Review

134

156

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This article pursues the hypothesis that a scale-invariant representation of history could support performance in a variety of learning and memory tasks. This representation maintains a conjunctive representation of what happened when that grows continuously less accurate for events further and further in the past. Simple behavioral models using a few operations, including scanning, matching and a "jump back in time" that recovers previous states of the history, describe a range of behavioral phenomena. These behavioral applications include canonical results from the judgment of recency task over short and long scales, the recency and contiguity effect across scales in episodic recall, and temporal mapping phenomena in conditioning. A growing body of neural data suggests that neural representations in several brain regions have qualitative properties predicted by the representation of temporal history. Taken together, these results suggest that a scale-invariant representation of temporal history may serve as a cornerstone of a physical model of cognition in learning and memory.

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“…The fact that nearby neurons exhibit similarly sized place fields (Jung et al 1994;Kjelstrup et al 2008) suggests that there is a characteristic segment size for a species that moves through space at a particular rate. It is possible that salient events tend to happen at regular temporal or spatial intervals (Sreekumar et al 2014). Alternatively, the segment size may depend upon internal limitations of hippocampal processing, for example, the limited amount of time in which information can be held across a delay or a limited amount of time a cell can fire at a faster rate than the overall population (Geisler et al 2010).…”

Section: Theta Sequences Code For Behaviorally Relevant Spatial Segmentsmentioning

confidence: 99%

Hippocampal Mechanisms for the Segmentation of Space by Goals and Boundaries

McKenzie

Buzsáki

2016

Research and Perspectives in Neurosciences

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In memory, the continuous flow of experience is punctuated at meaningful boundaries between one episode and the next. When salient events are separated by increasing amounts of space or time, memory systems can accommodate in two ways. One option is to increase the amount of neural resources devoted to longer event segments. The other is to maintain the same neural resources with sacrificed spatiotemporal resolution. Here we review how the spatial coding system is affected by the segmentation of space by goals and boundaries. We argue that the resolution of the place code is dictated by the amount of space encoded within periods of theta. Thus, the theta cycle is viewed as a 'neural word' that segregates segments of space and its cognitive equivalents (memory, planning). In support of this conclusion, we report that, as rats traverse a linear track, the beginning of a journey is represented at the falling phase of theta whereas the journey's end is represented on the ascending phase. The current location is represented in the temporal context of the past and future event boundaries. These results are discussed in relation to the changes in physiology observed across the longitudinal axis of the hippocampus, with a special consideration for how sequence information could be integrated by downstream 'reader' neurons.

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The Geometry and Dynamics of Lifelogs: Discovering the Organizational Principles of Human Experience

Cited by 28 publications

References 19 publications

Human hippocampus represents space and time during retrieval of real-world memories

Human hippocampus represents space and time during retrieval of real-world memories

A distributed representation of internal time.

Hippocampal Mechanisms for the Segmentation of Space by Goals and Boundaries

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