What affects what we consciously see? In a recent paper (see citation) Jolij and Meurs show that mood must be added to the influences. Here is the abstract:
Visual perception is not a passive process: in order to efficiently process visual input, the brain actively uses previous knowledge (e.g., memory) and expectations about what the world should look like. However, perception is not only influenced by previous knowledge. Especially the perception of emotional stimuli is influenced by the emotional state of the observer. In other words, how we perceive the world does not only depend on what we know of the world, but also by how we feel. In this study, we further investigated the relation between mood and perception. We let observers do a difficult stimulus detection task, in which they had to detect schematic happy and sad faces embedded in noise. Mood was manipulated by means of music. We found that observers were more accurate in detecting faces congruent with their mood, corroborating earlier research. However, in trials in which no actual face was presented, observers made a significant number of false alarms. The content of these false alarms, or illusory percepts, was strongly influenced by the observers mood. As illusory percepts are believed to reflect the content of internal representations that are employed by the brain during top-down processing of visual input, we conclude that top-down modulation of visual processing is not purely predictive in nature: mood, in this case manipulated by music, may also directly alter the way we perceive the world.
The subjects were instructed to be conservative and not to indicate a happy or sad face unless they were sure they had seen one the opposite of a forced choice. Therefore it is surprising that they saw faces that were not there. We know that top-down processes can give predictive effects but seeing non-existent faces matching the music mood does not seem to be an affect of prediction. It appears that top-down modulation of perceptual processing is not just driven by visual context, memory, or expectation but also by emotional state.
When I think about this, the question that comes to mind is how do we consciously become aware of a good mood or a bad mood? Probably there are many ways such as sensory clues from our bodies but a clear signal is whether we see things/people/events in a positive way indicating good mood or see them in a negative way indicating a bad mood. So it is not be too surprising that our conscious awareness of faces is coloured by our mood.
Jolij, J., & Meurs, M. (2011). Music Alters Visual Perception PLoS ONE, 6 (4) DOI: 10.1371/journal.pone.0018861