title: A shared, flexible neural map architecture reflects capacity limits in both visual short-term memory and enumeration.
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.
authors: Center for Mind/Brain Sciences, University of Trento, I-38068 Rovereto, Italy, Department of Psychology, Humboldt University of Berlin, D-12489 Berlin, Germany, knops.andre@gmail.com.
authors: André
authors: A
authors: Knops
authors: Center for Mind/Brain Sciences, University of Trento, I-38068 Rovereto, Italy, National Institute of Health and Medical Research, Unit 992, Cognitive Neuroimaging Unit, F-91191 Gif/Yvette, France, Atomic Energy and Alternative Energies Commission, Departement of Life Sciences (DSV)/Biomedical Imaging Institute (I2BM), NeuroSpin Center, F-91191 Gif/Yvette, France, and.
authors: Manuela
authors: M
authors: Piazza
authors: Center for Neural and Cognitive Sciences, University of Hyderabad, 500046 Hyderabad, India.
authors: Rakesh
authors: R
authors: Sengupta
authors: National Institute of Health and Medical Research, Unit 992, Cognitive Neuroimaging Unit, F-91191 Gif/Yvette, France, Atomic Energy and Alternative Energies Commission, Departement of Life Sciences (DSV)/Biomedical Imaging Institute (I2BM), NeuroSpin Center, F-91191 Gif/Yvette, France, and.
authors: Evelyn
authors: E
authors: Eger
authors: Center for Mind/Brain Sciences, University of Trento, I-38068 Rovereto, Italy.
authors: David
authors: D
authors: Melcher
mesh_terms: D000293:Adolescent; D000328:Adult; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D009415:Nerve Net / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods*; D011597:Psychomotor Performance / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult