Are faces preferentially attended when participants are unaware of being monitored?

Human faces convey a vast amount of information, including but not limited to age, gender, race, emotional state, and attractiveness. The perception of these attributes is important for our social interactions. For this reason, it has been argued that upright faces are a special class of stimuli that are preferentially attended. Preferential processing of fearful or sad expressions in clinical population of anxious individuals or those with severe depression have been reported; however the reports on healthy adult population have not been conclusive and appear to be largely affected by the experimental conditions and response mode.