Patterns of neural response in face regions are predicted by low-level image properties.

Models of face processing suggest that the neural response in different face regions is selective for higher-level attributes of the face, such as identity and expression. However, it remains unclear to what extent the response in these regions can also be explained by more basic organizing principles. Here, we used functional magnetic resonance imaging multivariate pattern analysis (fMRI-MVPA) to ask whether spatial patterns of response in the core face regions (occipital face area - OFA, fusiform face area - FFA, superior temporal sulcus - STS) can be predicted across different participants by lower level properties of the stimulus. First, we compared the neural response to face identity and viewpoint, by showing images of different identities from different viewpoints. The patterns of neural response in the core face regions were predicted by the viewpoint, but not the identity of the face. Next, we compared the neural response to viewpoint and expression, by showing images with different expressions from different viewpoints. Again, viewpoint, but not expression, predicted patterns of response in face regions. Finally, we show that the effect of viewpoint in both experiments could be explained by changes in low-level image properties. Our results suggest that a key determinant of the neural representation in these core face regions involves lower-level image properties rather than an explicit representation of higher-level attributes in the face. The advantage of a relatively image-based representation is that it can be used flexibly in the perception of faces.

An image-invariant neural response to familiar faces in the human medial temporal lobe.

The ability to recognise familiar faces with ease across different viewing conditions contrasts with the inherent difficulty in the perception of unfamiliar faces across similar image manipulations. Models of face processing suggest that this difference is based on the neural representation for familiar faces being more invariant to changes in the image, than it is for unfamiliar faces. Here, we used an fMR-adaptation paradigm to investigate neural correlates of image-invariant face recognition in face-selective regions of the human brain. Participants viewed faces presented in a blocked design. Each block contained different images of the same identity or different images from different identities. Faces in each block were either familiar or unfamiliar to the participants. First, we defined face-selective regions by comparing the response to faces with the response to scenes and scrambled faces. Next, we asked whether any of these face-selective regions showed image-invariant adaptation to the identity of a face. The core face-selective regions showed image-invariant adaptation to familiar and unfamiliar faces. However, there was no difference in the adaptation to familiar compared to unfamiliar faces. In contrast, image-invariant adaptation for familiar faces, but not for unfamiliar faces, was found in face-selective regions of the medial temporal lobe (MTL). Taken together, our results suggest that the marked differences in the perception of familiar and unfamiliar faces may depend critically on neural processes in the medial temporal lobe.

Activity in the right fusiform face area predicts the behavioural advantage for the perception of familiar faces.

People are extremely proficient at discriminating the identity of familiar faces, but are significantly worse with unfamiliar faces. Despite this clear behavioural difference in perception, the neural correlates of the advantage for familiar faces remain unclear. Here, we use an individual differences approach to explore the link between neural responses in face-selective regions and the behavioural advantage for the perception of familiar faces. First, we compared performance on an identity matching task with either familiar or unfamiliar faces. We found that participants were significantly better at matching the identity of familiar compared to unfamiliar faces. Next, we used fMRI to measure the response to familiar and unfamiliar faces. Consistent with the behavioural data, there was a significant difference in the neural response to familiar and unfamiliar faces in face-selective regions. Finally, we asked whether interindividual variation in behavioural performance could be predicted by corresponding variation in fMRI response. We found a significant correlation in the right fusiform face area (rFFA) between the difference in response to familiar and unfamiliar faces and corresponding differences on the face-matching task. That is, participants who showed a larger response to familiar compared to unfamiliar faces in the rFFA also matched familiar faces much more accurately than unfamiliar faces. No other face-selective region showed a correlation between neural and matching accuracy. These results provide a link between activity in the rFFA and the perception of familiar faces.