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Bruce Bridgeman, Hema Kopalle, Lisa Clark, Nicolas Davidenko; The Mechanism of Lateral Gaze Bias for Faces. Journal of Vision 2016;16(12):725. doi: 10.1167/16.12.725.
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© ARVO (1962-2015); The Authors (2016-present)
In viewing faces, Left Gaze Bias (LGB) is a tendency to look at the right side of faces (looking left to see the right side). Two possible mechanisms for the bias are a fixed face-oriented visual exploration strategy, possibly centered in the Fusiform Face Area (FFA) or other right-hemisphere centers, or bias by the 'online' scanpath algorithm that drives all other visual exploration sequences. While both possibilities predict a LGB, they make different predictions for left-right reversed faces. The FFA strategy predicts no change in fixation bias, while the scanpath alternative predicts a right-gaze bias to the extent that the right side of a normal face is more informative. We showed 42 faces from a standard image database to 52 observers, half reversed across their vertical midline axis, and measured visual fixations with an eye monitor that superimposes gaze position on the image. A centered fixation cross was replaced by a face image when fixation was achieved. 73% of our observers showed a left bias for normal faces in the first lateral saccade. On left-right reversed faces, 50 observers showed the same bias as for normal faces, while 2 changed their bias. This clear evidence for the FFA strategy reflects an endogenous origin for first gaze. Subsequent to the first fixation, observers began exploring the other side of the face after a few fixations, indicating that the endogenous bias gives way to a more normal scanpath. Observers were generally unaware of their gaze biases, and a test with a different sample of observers from the same population showed no ability to distinguish normal from reversed faces with a forced-choice behavioral measure. In conclusion, observers show an unconscious bias to saccade first to a preferred side of a face, whether normal or left-right reversed, and later explore both sides.
Meeting abstract presented at VSS 2016
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