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Tristan S Yates, Cameron T Ellis, Nicholas B Turk-Browne; Counting sheep: Perceptual narrowing of other-species faces in infant fMRI. Journal of Vision 2021;21(9):2632. doi: https://doi.org/10.1167/jov.21.9.2632.
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© ARVO (1962-2015); The Authors (2016-present)
Infants have less expertise than adults in perceiving human faces, but this reduced specialization trades off with a greater ability to distinguish individuals of other species. These differences between infants and adults diminish by the end of the first year. How does the brain support such perceptual narrowing? Developmental changes in the tuning of sensory cortex may be responsible, affecting which bottom-up features are available for perception. We test this hypothesis using an fMRI repetition suppression design in young infants, older infants, and adults. Face-selective regions tend to show reduced BOLD activity when the same face identity is viewed repeatedly compared with when different identities are viewed, suggesting that these regions are tuned to individual identities. We applied this adaptation logic while participants viewed short blocks containing human faces, sheep faces, or scenes. In the face conditions, half of the blocks presented the same identity multiple times sequentially (Repeat) whereas the other half presented a matched number of faces each from a unique identity (Novel). The difference in BOLD activity for Novel minus Repeat blocks provides an index of repetition suppression. We expected adults to show more repetition suppression than infants for human faces, but infants to show more repetition suppression than adults for sheep faces. Data collection is ongoing toward planned sample sizes, but we conducted preliminary analyses with available data. Consistent with our predictions, adults but not younger or older infants showed repetition suppression for human faces in fusiform and occipital face areas. This suggests that the tuning of visual regions for human faces emerges on a more protracted timescale than behavioral discrimination. Inconsistent with our predictions, although younger infants showed repetition suppression to sheep faces in face-selective regions, so too did older infants and adults. These preliminary results motivate further work exploring the mechanisms of perceptual narrowing.
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