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Weina Zhu, Jan Drewes, Yue Li, Karl R. Gegenfurtner; Rapid object recognition in the absence of conscious awareness. Journal of Vision 2013;13(9):504. doi: 10.1167/13.9.504.
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The visual system has a remarkable capability to extract categorical information from complex natural scenes (Thorpe, Fize et al. 1996). To investigate whether rapid object recognition is limited to conscious perception, we recorded event-related potentials (ERPs) on both conscious and unconscious conditions. A continuous flash suppression (CFS) paradigm was used to ensure the target image was suppressed during the experiment (Tsuchiya and Koch 2005), in which the target was displayed in one eye to compete against flashed masks presented to the other eye. We equated the luminance and contrast of the images by using the SHINE toolbox to minimize potential low-level confounds in our study (Willenbockel, Sadr et al. 2010). In experiment 1, the duration of suppression was measured during CFS. We found animal images to be perceived earlier than non-animal under identical suppression masking (1666ms vs. 1728ms). This suggests a privileged processing of animal images exists even during suppression. In experiment 2, image contrast was adaptively controlled to ensure 50% of the images were seen during CFS. Subjects were to decide/guess the presence of an animal in the shown images. Accuracy was 77% vs. 49% for "seen" and "unseen", confirming subjects were truly unaware of "unseen" images. ERP results showed animal images induced bigger amplitude (150ms-350ms) than non-animal images on "seen" condition, but smaller amplitude than non-animal images on "unseen" condition (p(animal×seen) =0.034). The amplitude of animal images was significantly different between seen and unseen condition (p=0.011), but not for the non-animal images. The trial-by-trial correlation between seen/unseen condition and EEG amplitude for both animal and non-animal images is significant before 380ms (p<0.05). Our results indicate the brain has different responses on animal and distractor (non-animal) images even in unawareness, and the rapid processing of animal images might be different in conscious and unconscious conditions.
Meeting abstract presented at VSS 2013
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