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Roberto Caldara, Rob Jenkins, David Brennan, Barrie Condon, Donald Hadley, Eugene Mayer; Gaze direction is in the eye of the Superior Temporal Sulcus. Journal of Vision 2008;8(6):403. doi: https://doi.org/10.1167/8.6.403.
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Human eyes have a unique morphology and play a crucial role in social interactions and communication. The importance of the eyes for processing facial identity and expression has been clearly established with behavioural, image classification (e.g., Bubbles) and brain imaging studies. Humans are also highly sensitive where another person is looking, and functional Magnetic Resonance Imaging (fMRI) studies have consistently reported gaze related responses in the right Superior Temporal Sulcus (rSTS). Yet, whether information processed from the eyes during perception of facial identity, expression or gaze is coded by the same neural substrates is not yet understood. To address this question we tested PS, a pure case of acquired prosopagnosia with lesions sparing the neural substrates sensitive to eye gaze (rSTS) (Sorger et al., 2007), using a gaze adaptation paradigm and fMRI. We previously revealed with Bubbles (Gosselin & Schyns, 2001) that PS does not use the eyes but only the mouth to identify short-term familiar faces (Caldara et al., 2005) and to categorize facial expressions, even fear in which the eyes are highly diagnostic for normal observers (Caldara et al., 2006). Consequently, the PS case represents a unique opportunity to test whether the distributed neural face system relies on a unique set of substrates for coding information from the eyes. Adaptation to averted gaze eliminates perception of gaze in the adapted direction (Jenkins et al. 2006). Strikingly, PS showed sensitivity to gaze direction, but no gaze adaptation effect. Contrary to intuition however, PS showed larger activations in the rSTS for averted gaze than for direct gaze and eyes closed conditions. These data suggest separable functional routes for gaze information, with gaze adaptation requiring the integrity of the occipito-temporal face-sensitive network. Critically, sensitivity to gaze direction is independently coded in the rSTS.
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