Figure 1.
Faces (or words) of different emotional valence are embedded within a premask and a postmask followed by a confidence rating (low, medium, high) and a forced choice test (target, none, distracter). To ensure that participants do not respond automatically (i.e. without attending to the stimuli), the duration of the fixation cross varies, and a blank screen was added between the postmask and the confidence rating with varying duration.
Figure 2.
Happy compared to neutral and negative faces enhance conscious reportability measures (confidence and accuracy).
When faces are presented for 32 ms, participants are more confident of seeing happy versus sad faces, and more accurate in identifying happy versus sad faces. Similarly, when faces are presented for 80 ms, participants are more confident of seeing happy versus neutral faces, and more accurate in identifying happy versus neutral faces and also happy versus sad faces. In this young cohort the 32 ms and the 80 ms conditions were both consciously perceived (i.e. participants are above chance when identifying the faces). N = 30. Error bars indicate standard error of the mean.
Figure 3.
No effect of different emotional stimuli on confidence or accuracy when stimuli are presented subliminally.
When faces are presented for 16 ms, which is subliminal in this cohort (i.e. participants are at chance when identifying the faces), we do not see an effect of emotion in terms of confidence and accuracy. N = 15. Error bars indicate standard error of the mean.
Figure 4.
Positive compared to neutral words enhance conscious reportability.
When words are presented for 80 ms, participants are more confident of seeing positive versus neutral words, and more accurate in identifying positive versus neutral words. When words are presented for 16 ms, we do not see an effect of emotion on confidence and accuracy. N = 15, all native English speakers. Error bars indicate standard error of the mean.
Figure 5.
A region of the ACC shows significant differences mirroring behavioural effects with regards to conscious reportability.
(A) Magnetic resonance imaging showing the location of the bilateral electrodes in the patient's brain normalised to MNI space with four electrode points (in black) in the ACC and nearby white matter. (B, C) The behavioural results in the patient showed that he was more confident of seeing faces in conscious (83 ms) versus subliminal (33 ms) trials, and more accurate in identifying faces in conscious versus subliminal trials. In the conscious trials, the patient was more confident of seeing happy versus sad faces, and also more accurate in identifying happy versus sad faces. In the subliminal trials we found no effect of emotion on conscious reportability. (D) Mirroring the behavioural findings, we found significant differences in the local field potentials between the two deepest electrodes in the ACC after 400 ms (lasting around 70 ms) when comparing conscious (83 ms) and subliminal (33 ms) trials. (E) Similarly, in the conscious trials, we found significant differences slightly later after 496 ms (lasting 30 ms) between happy and sad faces. (F) Importantly, this significant effect of emotion was not found in the subliminal trials. (G–I) When we applied a lowpass-filter with a 100 Hz cut of frequency the comparisons yielded the same results as in D–F where a 30 Hz cut of frequency was used (see Methods). (J) To rule out potential effects on LFP activity by the difference in stimulus presentation time in subliminal and conscious trials, we reanalysed this comparison linked to end of postmask, rather than start of the stimuli, and found the same significant difference in LFP activity between conscious and subliminal trials.
Table 1.
Word Stimuli.
Table 2.
Matching of Positive, Neutral and Negative Words.