ABSTRACT
The fate of deprived sensory cortices - visual regions in the blind and auditory regions in the deaf - exemplifies the extent to which experience can change brain regions. These regions are frequently seen to activate during tasks involving other sensory modalities, leading many accounts to infer that these regions have started processing sensory information of other modalities. However, such observations can also imply that these regions are now activating to any task event regardless of the sensory modality. Activating to task events, irrespective of the sensory modality involved, is a feature of the multiple-demands (MD) network. These are a common set of regions within the frontal and parietal cortices that activate in response to any kind of control demand. Thus, demands as diverse as attention, perceptual difficulty, rule-switching, updating working memory, inhibiting responses, decision-making, and difficult arithmetic - all activate these same set of regions that are thought to instantiate domain-general cognitive control and underpin fluid intelligence. We investigated if deprived sensory cortices, or foci within them, become part of the MD network. We tested if the same foci within the visual regions of the blind and auditory regions of the deaf activated to different control demands. We found that control demands related to updating auditory working memory, difficult tactile decisions, time-duration judgments, and sensorimotor-speed - all activated the entire bilateral occipital regions in the blind but not in the sighted. These occipital regions in the blind were the only regions outside the canonical fronto-parietal MD regions to show such activation to multiple control demands. Further, compared to the sighted, these occipital regions in the blind had higher functional connectivity with fronto-parietal MD regions. Early deaf, in contrast, did not activate their auditory regions to different control demands, showing that auditory regions do not become MD regions in the deaf. We suggest that visual regions in the blind do not take a new sensory role but become part of the MD network, and this is not a response of all deprived sensory cortices but a feature unique to the visual regions.
ABSTRACT
Why do we divide ('chunk') long tasks into a series of shorter subtasks? A popular view is that limits in working memory (WM) prevent us from simultaneously maintaining all task relevant information in mind. We therefore chunk the task into smaller units so that we only maintain information in WM that is relevant to the current unit. In contrast to this view, we show that long tasks that are not constrained by WM limits are nonetheless chunked into smaller units. Participants executed long sequences of standalone but demanding trials that were not linked to any WM representation and whose execution was not constrained by how much information could be simultaneously held in WM. Using signs well-known to reflect beginning of new task units, we show that such trial sequences were not executed as a single task unit but were spontaneously chunked and executed as series smaller units. We also found that sequences made of easier trials were executed as longer task units and vice-versa, further suggesting that the length of task executed as one unit may be constrained by cognitive limits other than WM. Cognitive limits are typically seen to constrain how many things can be done simultaneously e.g., how many events can be maintained in WM or attended at the same time. We show a new aspect of these limits that constrains the length of behaviour that can be executed sequentially as a single task-unit.
