Visual awareness and emotion

How does the processing of emotional stimuli depend on awareness?

Behavior
It is commonly accepted that emotional stimuli are processed “subliminally” (i.e., without conscious awareness). In recent work, we have questioned this assumption. When awareness is measured in terms of objective criteria – in terms of signal detection theory sensitivity measures,  such as d’ or A’ (CONB, 2005)– we have shown that there is substantial inter-subject variability in their sensitivity to fearful faces (Emotion, 2005). Critically, a sizeable fraction of the subjects (50-75%) are capable of reliably detecting fearful faces shown for 33 ms, a duration that was typically associated with unaware conditions in the past.

Brain
In a recent fMRI study, we showed that amygdala responses actually depend on visual awareness (CC, 2005). Under conditions in which subjects were not aware of fearful faces flashed for 33 ms, no differential activation was observed in the amygdala. On the other hand, differential activation was observed for 67-ms fearful targets that the subjects could reliably detect. When trials were divided into hits, misses, correct rejects, and false alarms, target visibility was an important factor in determining amygdala responses to fearful faces. Taken together, these results further challenge the view that amygdala responses occur automatically.