Abstract
Scene imagery features prominently when we recall autobiographical memories, imagine the future and navigate around in the world. Consequently, in this study we sought to better understand how scene representations are supported by the brain. Processing scenes involves a variety of cognitive processes that in the real world are highly interactive. Here, however, our goal was to separate semantic and spatial constructive scene processes in order to identify the brain areas that were distinct to each process, those they had in common, and the connectivity between regions. To this end, participants searched for either semantic or spatial constructive impossibilities in scenes during functional MRI. We focussed our analyses on only those scenes that were possible, thus removing any error detection that would evoke reactions such as surprise or novelty. Importantly, we also counterbalanced possible scenes across participants, enabling us to examine brain activity and connectivity for the same possible scene images under two different conditions. We found that participants adopted different cognitive strategies, which were reflected in distinct oculomotor behaviour, for each condition. These were in turn associated with increased engagement of lateral temporal and parietal cortices for semantic scene processing, the hippocampus for spatial constructive scene processing, and increased activation of the ventromedial prefrontal cortex (vmPFC) that was common to both. Connectivity analyses showed that the vmPFC switched between semantic and spatial constructive brain networks depending on the task at hand. These findings further highlight the well-known semantic functions of lateral temporal areas, while providing additional support for the previously-asserted contribution of the hippocampus to scene construction, and recent suggestions that the vmPFC may play a key role in orchestrating scene processing.
Highlights
During our lives we accrue knowledge and build expectations about the appearance of the visual world
While the 1way-RM-ANOVA showed a significant effect of experimental condition (F (3,96) = 22.9, p < 0.0001), the two key planned post-hoc analyses showed no difference in accuracy between the semantic and spatial constructive possible scenes (t = 0.4, df = 96, p = 0.92), or between the semantic and spatial constructive impossible scenes (t = 1.9, df = 96, p = 0.11)
We found that participants looked at possible scenes differently depending on whether they were searching for semantic or spatial constructive impossibilities
Summary
During our lives we accrue knowledge and build expectations about the appearance of the visual world. One way we can learn about how this critical knowledge is supported by the brain is by examining what happens when violations occur. In an early positron emission tomog raphy study, Schacter et al (1995) had participants study drawings of novel single objects and they had to judge whether they were structur ally possible or impossible. Using similar stimuli, Lee and Rudebeck (2010) examined how the objects were processed by two patients, one with bilateral hippocampal damage and the other with similar lesions that extended into perirhinal cortex. The patient with the perirhinal damage was impaired on the task, with the deficit being a failure to identify impossible objects while performance on possible objects was not significantly different to control participants
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