There are various sensory channels through which object attributes can be accessed. For example, sight and touch can learn the shape of an object. This raises an important question about the neural organization of object representation: Can the human brain create a shared representation of object shape abstracted from the senses, or is the shape representation formed from different senses separated from each other in the brain?
We can detect the shape of an object by touch or by sight. Previous studies have suggested that the inferolateral occipitotemporal cortex (ILOTC) implements supramodal shape representation because it is more responsive to seeing or touching objects than shapeless textures.
However, such activation in the anterior part of the ventral visual pathway can be brought about by the conceptualization of an object or the visual imagery evoked by touching an object.
A recent study directly compared shape and conceptual representation in early blind and sighted participants to explore these possibilities. 48 native Italian speakers with no history of neurobiological or psychiatric problems were included in the fMRI study. Of the 32 participants, 16 were born blind prematurely.
Scientists looked at how and where shape representations are stored in the brain and how they differ from mental representations of identically constructed objects. They tested in early blind people whether occipital regions implement shape representation independently of visual experience or imagery, or whether early visual loss causes “visual” cortex to reprogram its activity for conceptual representation.
The scientists found that the bilateral ILOTC in both groups was more strongly activated during the shape test than during a conceptual verification task based on the names of the same constructed objects. In addition, ILOTC-encoded shape similarity contained dispersive activity between objects, but not conceptual relatedness. In addition to the ILOTC, the scientists found RU representation in both groups’ bilateral ventral premotor cortices and the intraparietal sulcus (IPS), a frontoparietal circuit associated with object grasping and haptic processing.
The left perisylvian brain network associated with language processing was activated in both groups throughout the conceptual verification test. Interestingly, however, Cuenius was active only in early blind subjects. The ILOTC formed a modular structure with a focus on shape representation, with a stronger functional connection to the frontoparietal circuit than to the left perisylvian network.
Scientists pointed out, “Our results thus favor the hypothesis that ILOTC implements supramodal shape representation and argue against alternative hypotheses that such activation depends on visual imagery or conceptual associations based on functional relevance. These results echo various views suggesting that object representations in the brain are organized according to behaviors.”
- Xu Y, Vignali L, Sigismondi F, Crepaldi D, Bottini R, Collignon O (2023) Similar object shape representation encoded in the inferolateral occipitotemporal cortex of sighted and early blind people. PLoS Biol 21(7): e3001930. DOI: 10.1371/journal.pbio.3001930