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Caroline Blais, Frédéric Gosselin, Martin Arguin, Daniel Bub, Daniel Fiset; Optimal viewing positions for upright and inverted face recognition. Journal of Vision 2009;9(8):536. doi: 10.1167/9.8.536.
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Upright faces are easier to recognise than inverted faces. Eye-tracking studies have shown that the same pattern of ocular fixations across the stimulus are obtained with inverted and upright faces, suggesting that the inversion effect cannot be explained by a difference in the features fixated as a function of orientation (Williams & Henderson, 2007; but see Barton, Radcliffe, Cherkasova, Edelman & Intriligator, 2006). One possibility, however, is that the areas fixated with inverted faces are not optimal for recognition, in contrast to fixations with upright faces. Here, we tested this hypothesis using the optimal viewing position paradigm. Five participants were first familiarized with the stimulus set, made of the faces of five female and five male famous actors. First, the exposure duration needed by each participant to identify upright faces centered at fixation with an accuracy of 90% was determined using QUEST (Watson & Pelli, 1983). Then, upright or inverted faces were displayed for this duration (less than 100 ms for all subjects) at random positions within a distance of 7.8 deg of visual angle horizontally and 11.7 deg of visual angle vertically relative to fixation. A mask made of the average of the ten faces in the stimulus set was displayed immediately after target offset. Participants were asked to identify the target face. Each participant completed 3,000 trials for each orientation. We then determined correct response probabilities as a function of viewing position. The results show, for example, that the optimal viewing area is smaller for inverted than for upright faces. Implications of these results for the face inversion effect will be discussed (e.g., Sekuler, Gaspar, Gold, & Bennett, 2004; Willenbockel et al., 2008).
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