Abstract
Spatial relations are commonly divided in two global classes. Categorical relations concern abstract relations which define areas of spatial equivalence, whereas coordinate relations are metric and concern exact distances. Categorical and coordinate relation processing are thought to rely on at least partially separate neurocognitive mechanisms, as reflected by differential lateralization patterns, in particular in the parietal cortex. In this study we address this textbook principle from a new angle. We studied retinotopic activation in early visual cortex, as a reflection of attentional distribution, in a spatial working memory task with either a categorical or a coordinate instruction. Participants were asked to memorize a dot position, with regard to a central cross, and to indicate whether a subsequent dot position matched the first dot position, either categorically (opposite quadrant of the cross) or coordinately (same distance to the centre of the cross). BOLD responses across the retinotopic maps of V1, V2, and V3 indicate that the spatial distribution of cortical activity was different for categorical and coordinate instructions throughout the retention interval; a more local focus was found during categorical processing, whereas focus was more global for coordinate processing. This effect was strongest for V3, approached significance in V2 and was absent in V1. Furthermore, during stimulus presentation the two instructions led to different levels of activation in V3 during stimulus encoding; a stronger increase in activity was found for categorical processing. Together this is the first demonstration that instructions for specific types of spatial relations may yield distinct attentional patterns which are already reflected in activity early in the visual cortex.
Highlights
The ability to process spatial relations between objects in our environment is crucial to successfully execute behaviours like navigation, visual search, and object location memory
Spatial relations can be divided into two types; categorical and coordinate relations
We suggest that the particular spatial relation instructions in these tasks affect to which location spatial attention is directed, which in turn modulates the specific contents of working memory
Summary
The ability to process spatial relations between objects in our environment is crucial to successfully execute behaviours like navigation, visual search, and object location memory. Coordinate spatial relations involve precise and metric properties, making use of exact distances, such as ‘the car is two meters away from the house’. These two types of spatial relations are thought to be processed by two at least partially different subsystems. The left hemisphere is typically better in processing categorical information, whereas the right hemisphere commonly shows an advantage in processing coordinate information (see [2] for a review) This dissociation as exposed by opposing hemispheric biases, has been shown convincingly in behavioural experiments This dissociation as exposed by opposing hemispheric biases, has been shown convincingly in behavioural experiments (e.g. [3,4,5,6]), and by means of neuroimaging and TMS measurements (e.g. [7,8,9])
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