A shared, flexible neural map architecture reflects capacity limits in both visual short-term memory and enumeration. Knops, A., Piazza, M., Sengupta, R., Eger, E., & Melcher, D. J Neurosci, 34(30):9857–9866, 2014.
doi  abstract   bibtex   
Human cognition is characterized by severe capacity limits: we can accurately track, enumerate, or hold in mind only a small number of items at a time. It remains debated whether capacity limitations across tasks are determined by a common system. Here we measure brain activation of adult subjects performing either a visual short-term memory (vSTM) task consisting of holding in mind precise information about the orientation and position of a variable number of items, or an enumeration task consisting of assessing the number of items in those sets. We show that task-specific capacity limits (three to four items in enumeration and two to three in vSTM) are neurally reflected in the activity of the posterior parietal cortex (PPC): an identical set of voxels in this region, commonly activated during the two tasks, changed its overall response profile reflecting task-specific capacity limitations. These results, replicated in a second experiment, were further supported by multivariate pattern analysis in which we could decode the number of items presented over a larger range during enumeration than during vSTM. Finally, we simulated our results with a computational model of PPC using a saliency map architecture in which the level of mutual inhibition between nodes gives rise to capacity limitations and reflects the task-dependent precision with which objects need to be encoded (high precision for vSTM, lower precision for enumeration). Together, our work supports the existence of a common, flexible system underlying capacity limits across tasks in PPC that may take the form of a saliency map.
@Article{Knops2014,
  author      = {Knops, Andr\'e and Piazza, Manuela and Sengupta, Rakesh and Eger, Evelyn and Melcher, David},
  journal     = {J Neurosci},
  title       = {A shared, flexible neural map architecture reflects capacity limits in both visual short-term memory and enumeration.},
  year        = {2014},
  number      = {30},
  pages       = {9857--9866},
  volume      = {34},
  abstract    = {Human cognition is characterized by severe capacity limits: we can
	accurately track, enumerate, or hold in mind only a small number
	of items at a time. It remains debated whether capacity limitations
	across tasks are determined by a common system. Here we measure brain
	activation of adult subjects performing either a visual short-term
	memory (vSTM) task consisting of holding in mind precise information
	about the orientation and position of a variable number of items,
	or an enumeration task consisting of assessing the number of items
	in those sets. We show that task-specific capacity limits (three
	to four items in enumeration and two to three in vSTM) are neurally
	reflected in the activity of the posterior parietal cortex (PPC):
	an identical set of voxels in this region, commonly activated during
	the two tasks, changed its overall response profile reflecting task-specific
	capacity limitations. These results, replicated in a second experiment,
	were further supported by multivariate pattern analysis in which
	we could decode the number of items presented over a larger range
	during enumeration than during vSTM. Finally, we simulated our results
	with a computational model of PPC using a saliency map architecture
	in which the level of mutual inhibition between nodes gives rise
	to capacity limitations and reflects the task-dependent precision
	with which objects need to be encoded (high precision for vSTM, lower
	precision for enumeration). Together, our work supports the existence
	of a common, flexible system underlying capacity limits across tasks
	in PPC that may take the form of a saliency map.},
  doi         = {10.1523/JNEUROSCI.2758-13.2014},
  keywords    = {Adolescent; Adult; Brain Mapping, methods; Brain, physiology; Female; Humans; Male; Memory, Short-Term, physiology; Nerve Net, physiology; Photic Stimulation, methods; Psychomotor Performance, physiology; Visual Perception, physiology; Young Adult},
  language    = {eng},
  medline-pst = {ppublish},
  pmid        = {25057189},
  school      = {Center for Mind/Brain Sciences, University of Trento, I-38068 Rovereto, Italy.},
  timestamp   = {2016.09.20},
}

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