Human brain activity time-locked to perceptual event boundaries. Zacks, Braver, Sheridan, Donaldson, Snyder, Ollinger, Buckner, Raichle. NatNeuro 2001

  1. “Here we present evidence that a network of brain regions is tuned to perceptually salient event boundaries, both during intentional event segmentation and during naive passive viewing of events”
  2. When watching someone else undertake a task, knowledge about the task allows us to fill in missing information
    1. But this task involves continuous, dynamic, unsegmented data
    2. How to do we segment this continuum of stimulus into discrete items?
  3. Even infants can divide continuous activity into discrete events
  4. “Event segmentation exhibits a hierarchical structure, with segments at a coarse temporal grain corresponding to groups of fine-grain segments.”
  5. fMRI study on people watching videos of everyday activities
    1. After passive watching in fMRI, they were asked to segment video in terms of both coarse and fine temporal grain (also in fMRI)
    2. They were not told about the segmenting task before passive viewing
    3. fMRI data and segmentations were then compared
  6. “The data revealed transient changes in neural activity at event boundaries, during both passive viewing and active segmentation.  Throughout the activated network, responses were greater to coarse unit boundaries than to fine unit boundaries.”
  7. “All areas that showed transient changes in activity during passive viewing also showed reliable changes during the active segmentation runs…”
  8. Specified coarse temporal boundaries tended to align with fine boundaries
  9. fMRI activity was more strongly correlated at coarse boundaries than fine ones
  10. “One possibility is that physical correlates of object and actor motion lead to the detection of fine unit boundaries, whereas cognitive representations of events determine how fine units group together into large units… However, the data are consistent with another possibility. The observed transient changes in cortical activity may reflect bottom-up processing of physical features of the activity that correlate with natural event segmentation. Based on this view, the possible involvement of the MT complex can be taken as evidence that features of the motion signal are important for
    conscious event segmentation, and the activity of the right frontal region can be interpreted as due to shifts of gaze or visual attention due to object or actor motion.”
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