The ventral occipito-temporal cortex (VOTC) is well-known to display topographically organized responses to distinct visual categories (e.g. faces, places, tools etc.). What factors shape this categorical organization?
Some have suggested that the main driver is a preference for some specific visual features (e.g. spatial frequencies, eccentricity, curvatures etc.). Others suggested that part of this categorical response cannot be explained by visual features only.
With the CPP (Crossmodal Perception and Plasticity, https://cpplab.be/ ) lab, Stefania Mattioni thought to tackle the problem by investigating the categorical response of VOTC in absence of vision; by presenting sounds of different categories in sighted and congenitally blind people.
They reasoned that if the categorical organization of VOTC does not entirely depend on vision, a similar functional profile should emerge when the categories are presented acoustically, even in people without visual experience!
They carried out a comprehensive mapping of the representational geometry underlying low-level (acoustic or visual features) and categorical responses to images and sounds in the VOTC of sighted and blind people.
They first demonstrated that the topographical response to sounds in the sighted and the blind look like the one observed in sighted in vision.
Using Representational Similarity Analyses based on category decoding, they further showed that the representational format of our different categories was similar across groups/sensory inputs.
Interestingly, they observed that blind people show higher decoding accuracies and higher inter-subject consistency in the representation of auditory categories, and that the representational structure of visual categories in sighted was significantly closer to the structure of the auditory categories in blind than in sighted group.
VOTC shows similar large-scale representational connectivity profiles when processing images in sighted and sounds in sighted and blind people. They suggest this may be a mechanism to drive the categorical org of sounds even in blinds
Digging further, they demonstrated that categorical membership is the main factor that predicts the representational structure of sounds in VOTC in blind people, rather than lower-level acoustical attributes of sounds.
Then, they provided a qualitative exploration of the structure of the categorical representation in the VOTC. Despite similarities, interesting things emerge here like the fact that the representation of animals is closer to tools in the blind.
In sum, sounds trigger categorical responses in the VOTC of congenitally blind and sighted people that match the topography and functional profile of visual responses, despite qualitative nuances between modalities and groups.
To conclude, there is more in the occipital cortex than meets the eye!
VOTC functional profile. Different ways of visualizing the representation of different categories in the ventral-occipito temporal cortex. (B1) Researchers looked at how distinguishable (i.e. decodable) is the representation of each category from the representation of each other category. High columns means that the representation of the 2 categories are different and can be distinguished with an high level of accuracy. (B2) Summary of the previous graph within one single matrix. Each line and column represent one category. Each square in the matrix contains the accuracy value between 2 categories. Blue color means low degree of accuracy (i.e. the representations of the 2 categories are similar), Yellow color means high degree of accuracy (i.e. the representations of the 2 categories are different). (B3) Multidimensional scaling (MDS) visualization. The categories have been arranged such that their pairwise distances approximately reflect response pattern similarities. Categories placed close together are based on low decoding accuracy values (similar response patterns). Categories arranged far apart generated high decoding accuracy values (different response patterns). (B4) Binary decoding dendrogram. We performed hierarchical cluster analysis (based on the accuracy values) to assess if VOTC response patterns form clusters corresponding to natural categories in the 3 groups (SCv: top; EBa: center; SCa: bottom).