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Yoram S Bonneh, Gal Rosenzweig; Face familiarity revealed by oculomotor inhibition on the fringe of awareness. Journal of Vision 2019;19(10):13a. doi: https://doi.org/10.1167/19.10.13a.
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© ARVO (1962-2015); The Authors (2016-present)
Background: Involuntary eye movements during fixation of gaze are typically transiently inhibited following stimulus onset. This oculomotor inhibition (OMI), which includes microsaccades and spontaneous eye blinks, is known to be modulated by stimulus saliency and anticipation, with shorter inhibition for more salient stimuli and longer inhibition for oddballs or surprise. It is currently unknown whether the OMI is sensitive to familiarity, and whether the familiar stands out as salient or as surprising. Methods: We measured the OMI while observers (n=19) passively viewed a slideshow of one universally familiar and 7 unfamiliar facial images presented very briefly (10 ms) at 1Hz in random order. Initial experiments indicated that the OMI was often insensitive to familiarity when the facial images were highly visible. We therefore limited the visibility using backward masking (70ms SOA, two successive nature images), so that the faces were barely visible or at the fringe of awareness. We assessed statistical significance using a non-parametric permutation test. Results: The inhibition of both microsaccades and eye-blinks was significantly prolonged for the familiar face, as compared to the average of the non-familiar (~60ms, p=0.0005 for microsaccades; p=0.002 for blinks). We also found a small but significant effect of earlier (around ~100ms) micro-saccade inhibition onset with familiarity (p=0.01, 30ms difference). Conclusions: These findings demonstrate, for the first time, the sensitivity of the OMI to familiarity, with familiar faces prolonging the OMI similar to oddball stimuli. Because this can be measured on the fringe of awareness and in passive viewing, the OMI can be used as a novel physiological measure for studying hidden memories with potential implications for health, legal, and security purposes.
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