Review
Segmentation in the perception and memory of events

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People make sense of continuous streams of observed behavior in part by segmenting them into events. Event segmentation seems to be an ongoing component of everyday perception. Events are segmented simultaneously at multiple timescales, and are grouped hierarchically. Activity in brain regions including the posterior temporal and parietal cortex and lateral frontal cortex increases transiently at event boundaries. The parsing of ongoing activity into events is related to the updating of working memory, to the contents of long-term memory, and to the learning of new procedures. Event segmentation might arise as a side effect of an adaptive mechanism that integrates information over the recent past to improve predictions about the near future.

Section snippets

Making sense by segmenting

Imagine walking with a friend to a coffee shop. If asked to describe this activity in more detail you might list a few of the events that make it up. The events listed could be broken up by changes in the physical features of the activity, such as location: ‘We started out by going down to the laboratory. We grabbed our coats and put them on. Then we walked out of the building to the corner by the subway station…’ Or, they could be broken up by changes in conceptual features, such as your

Events and their boundaries

By ‘event’ we mean a segment of time at a given location that is conceived by an observer to have a beginning and an end [1]. In particular we focus on the events that make up everyday life on the timescale of a few seconds to tens of minutes – things like opening an envelope, pouring coffee into a cup, changing the diaper of a baby or calling a friend on the phone. Event Segmentation Theory (EST) [2] (see Glossary) proposes that perceptual systems spontaneously segment activity into events as

Automatic event segmentation

Does asking people for conscious judgments about event boundaries really tell us anything about ongoing perception outside the laboratory? Event segmentation tasks have good intersubjective agreement [10] and reliability [11], which suggests they tap into ongoing processing. Nonetheless, a basic limitation of directly applying segmentation tasks is that they might interfere with the ongoing perceptual processes they attempt to measure. Stronger evidence that event segmentation is automatic

Memory for events

Event boundaries relate systematically to both the online maintenance of information (working memory) and the permanent storage of information for later retrieval (long-term memory). According to EST [2], this is because at event boundaries people update representations of the current event, which frees information from working memory, and orient to incoming perceptual information, which encodes it particularly strongly for long-term memory. Evidence for working memory updating at event

How does segmentation help?

Why do people segment ongoing activity into events? Segmentation results from the continual anticipation of future events. This anticipation enables you adaptively to encode structure from the continuous perceptual stream, to understand what an actor will do next, and to select your own future actions [53]. Segmentation simplifies, enabling you to treat an extended interval of time as a single chunk. If you segment well, this chunking saves on processing resources and improves comprehension.

Acknowledgements

Preparation of this article was supported in part by grants R01-MH070674 and T32 AG000030–31 from the National Institutes of Health. We thank Devarajan Sridharan for providing figure materials, and thank the following colleagues for thoughtful comments on the manuscript: Dare Baldwin, Joe Magliano, G.A. Radvansky, Stephan Schwan, Ric Sharp, Khena Swallow and Barbara Tversky.

Glossary

Event model
an actively maintained representation of the current event, which is updated at perceptual event boundaries.
Event segmentation
the perceptual and cognitive processes by which a continuous activity is segmented into meaningful events.
Temporal grain
events can be perceived on a range of temporal grains, or timescales, from a second or less to tens of minutes.

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