The operations and processes that the human brain employs to achieve fast visual categorization remain a matter of debate. A first issue concerns the timing and place of rapid visual categorization and to what extent it can be performed with an early feed-forward pass of information through the visual system. A second issue involves the categorization of stimuli that do not reach visual awareness. There is disagreement over the degree to which these stimuli activate the same early mechanisms as stimuli that are consciously perceived. We employed continuous flash suppression (CFS), EEG recordings, and machine learning techniques to study visual categorization of seen and unseen stimuli. Our classifiers were able to predict from the EEG recordings the category of stimuli on seen trials but not on unseen trials. Rapid categorization of conscious images could be detected around 100 ms on the occipital electrodes, consistent with a fast, feed-forward mechanism of target detection. For the invisible stimuli, however, CFS eliminated all traces of early processing. Our results support the idea of a fast mechanism of categorization and suggest that this early categorization process plays an important role in later, more subtle categorizations, and perceptual processes.
Keywords: visual awareness, rapid categorization, continuous flash suppression, EEG
Citation: Kaunitz LN, Kamienkowski JE, Olivetti E Murphy B Avesani P and Melcher DP (2011) Intercepting the first pass: rapid categorization is suppressed for unseen stimuli. Front. Psychology 2:198. doi: 10.3389/fpsyg.2011.00198
Received: 27 February 2011; Accepted: 04 August 2011;
Published online: 23 August 2011.
Edited by:Rufin VanRullen, Centre de Recherche Cerveau et Cognition, France
Reviewed by:Thomas Carlson, University of Maryland, USA
Copyright: © 2011 Kaunitz, Kamienkowski, Olivetti, Murphy, Avesani and Melcher. This is an open-access article subject to a non-exclusive license between the authors and Frontiers Media SA, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and other Frontiers conditions are complied with.
*Correspondence: Lisandro Nicolas Kaunitz, Center for Mind/Brain Sciences (CIMeC), University of Trento, Via delle Regole 101, 38060 Mattarello (TN), Italy. e-mail: firstname.lastname@example.org