Looking for neural correlates of sustained inattentional blindness with single trial per subject design in fMRI.

An inability to notice an extra salient item once the attention is engaged in some other task, called Inattentional Blindness (IB; Mack & Rock, 1998), is widely used in research on visual awareness. However, the neuroimaging of IB is limited due to technical issues, including the possible number of trials per subject. Since the IB decreases once the participant is informed about the effect, a single trial per subject design is usually implemented in psychophysics. FMRI studies of IB so far have either substantially changed the original paradigm (Thakral, 2011) or didn't measure the IB effect while scanning (Todd et al., 2005; Matsuyoshi, Ikeda, 2010). Our research aimed at investigating the neural correlates of IB in multiple object tracking (MOT) task preserving the design of a single trial. In the scanner participants traced eight moving white and black circles and counted bounces of the white circles off the edges of the screen. In experimental group an extra item (a dark grey square) traveled across the screen for 7 seconds. It was neither verbally reported nor recognized by 69% of 23 observers (the IB effect). BOLD signal evoked by the unnoticed stimulus in 16 IB subjects was compared with the signal in 16 control subjects who were not presented with an extra item. Greater activation (p< 0.001 uncorrected, k=3 voxels) was found in both left and right FEF in the control condition. Separate analysis of the activation in experimental and control group demonstrated clear and significant (p< 0.05 FWE corrected) neural signature of the MOT task (Howe et al., 2009; Culham et al., 2001) including the bilateral V5, IPS, SPL and PMA/FEF areas. Thus our results advocate the feasibility of a single trial per subject design in fMRI and its potential use for research on the unconscious information processing in IB. Meeting abstract presented at VSS 2015.