How do blind people represent rainbows? Disentangling components of conceptual representations

Abstract

How do we represent information that has no sensory features? How are abstract concepts like "freedom", devoid of external perceptible referents, represented in the brain? To address the role of sensory information in the neural representation of concepts, we investigated how people born blind process concepts whose referents are imperceptible to them because of their visual nature (e.g. "rainbow", or "red"). We find that the left dorsal anterior temporal lobe (ATL) shows preference both to typical abstract concepts ("freedom") and to concepts whose referents are not sensorially-available to the blind ("rainbow"), as compared to partially sensorially-perceptible referents (e.g. "rain"). Activation pattern similarity in dorsal ATL is related to the sensorial-accessibility ratings of the concepts in the blind. Parts of inferior-lateral aspects of ATL and the temporal pole responded preferentially to abstract concepts devoid of any external referents ("freedom") relative to imperceptible objects, in effect distinguishing between object and non-object concepts. The medial ATL showed a preference for concrete concepts ("cup"), along with a preference for partly perceptible items to the blind ("rain", as compared with "rainbow"), indicating this region's role in representing concepts with sensory referents beyond vision. The findings point to a new division of labor among medial, dorsal and lateral aspects of ATL in representing different properties of object and non-object concepts. IntroductionHow do we represent concepts that extend beyond our perceptual experience, concepts like "freedom" and "justice", which have no clear external referent? And how do blind people represent concepts such as rainbow, whose referent is perceptible only visually and comprised of colors, which are uniquely visual qualia?Various studies have addressed the neural correlates of concrete and abstract concepts 1-4 . Because concrete concepts, like "cup", have perceptible features, such as shape, size and color, whereas abstract concepts, like "freedom", lack sensory features, it has been proposed that the latter type of concepts rely more heavily on semantic or verbal information 5,6 . Therefore, the inspection of how abstract concepts are represented has been considered an important way to understand language and knowledge representation in the brain. Traditionally, this has been tested by comparing brain responses to abstract concepts to those generated by concrete ones (like "cup"). This comparison has revealed large-scale networks of regions associated with abstract concepts involving language areas and concrete concepts involving modality-specific areas 2,7-10 .However, there are additional differences between abstract and concrete concepts beyond the existence of external sensory referents. Abstract concepts tend to be learned later in life, be less familiar 11,12 and some of them refer to emotional contents 13,14 , potentially providing an emotional (internal) "sensory" referent. Furthermore, abstract concepts are more ambiguous and...