Categories: Science Facts

Face Selectivity in the Blind Brainon August 30, 2020 at 7:00 pm

Why do particular brain areas tend to adopt particular roles? Is the brain “wired” by genetics to organize itself in a certain way, or does brain organization emerge from experience?

One part of the brain has been the focus of a great deal of nature-vs-nurture debate. It’s called the fusiform face area (FFA) and, as the name suggests, it seems to be most active during perception of faces.

It’s broadly accepted that the FFA responds most strongly to faces in most people, but there’s controversy over why this is. Is the FFA somehow innately devoted to faces, or does its face specialization arise through experience?

In the latest contribution to this debate, a new study argues that the FFA doesn’t need any kind of visual experience to be face selective. The researchers, N. Apurva Ratan Murty et al., show that the FFA activates in response to touching faces, even in people who were born blind and have never seen a face.

Murty et al. designed an experiment in which participants — 15 sighted and 15 congenitally blind people — could touch objects while their brain activity was recorded with fMRI. A 3D printer was used to create models of faces and other objects, and the participants could explore these with their hands, thanks to a rotating turntable.

fMRI tactile stimuli from Murty et al. (2020)

The key result was that touching the faces produced a similar pattern of activity in both the blind and sighted people, and this activity was also similar to when sighted people viewed faces visually:

Similar face-selective activity between visual and touch, and touch in congenitally blind people. From Murty et al. (2020)

In a follow-up experiment with n=7 of the congenitally blind participants, Murty et al. found that the same face-selective areas in these individuals also responded to “face-related” sounds, such as laughing or chewing sounds, more than other sounds. (This replicates earlier work.)

Finally, Murty et al. show that the functional connectivity of the FFA is similar across blind and sighted participants, and that functional connectivity predicts face-selectivity in both groups.

They conclude that the selectivity of the FFA for faces is not driven by any kind of visual experience, but that it may be guided by “top-down connections” from other brain areas, although this isn’t directly shown.

The authors acknowledge that this study doesn’t prove that the FFA’s face-selectivity is innate. The congenitally blind participants may have never seen faces, but they have touched them before, so it’s not as if they have zero experience with faces.

However, I would say that these data do challenge the theory that the FFA is only selective for faces because we are “face experts.” On this theory, the FFA is actually an “expertise area,” responding to any category of objects that we are highly familiar with — including faces. This expertise theory makes sense for sighted people, as most of us probably see dozens of faces every day, but it seems unlikely that blind people have tactile experience of that many faces.

That said, the number of participants included in this study is quite small by modern fMRI standards, although in the case of the congenitally blind participants, it is understandable that these are difficult to recruit. But I would still say that these results are going to be difficult to reconcile with any theory that proposes that the FFA’s function is purely a product of visual experience.