The saying, “Things are not always as they appear” is more true than your typical platitude. Seeing is not something that we do with only our eyes - in fact, the eyes are a fraction of the process involved in what we constitute as “seeing”. As much as we may want to believe that there is one objective “reality”, perception is something that cannot be divorced from what the eyes see and is ruled by many factors. One factor I address here is the role of the emotional state on perception and seeing.
Typically, emotions and visual perception are thought to be mechanisms operating independently of each other; however, one’s current emotion state can affect how an environment is perceived. For example, most of the time, people have a tendency to process their surroundings globally; however, stressed conditions seems to minimize the spatio-temporal field, thus narrowing attention. In 1959, psychologist J.A. Easterbrook proposed his hypothesis that “the range of cues attended to is inversely related to the degree of arousal; that is, in a state of increased arousal, attention narrows and fewer environmental stimuli are focused on.” (Easterbrook)
Conversely, findings since Easterbrook’s hypothesis have supported the notion that positive emotion encourages global attention. When researchers induce a happy or stressed mood by having participants reflect on and write about a happy or stressful event from their lives, those in positive moods perceived their environment in a global perceptual style, whereas participants in stressed moods adopted a local perceptual style.
A common test to measure global and local perception is the Kimchi test, wherein participants are shown a geometric figure made up of three small squares arranged in the overall shape of a triangle. People are then asked which of the comparison figures is most similar: a triangle composed of small triangles or a square composed of small squares. The local response would be to elect the figure with squares, the global response being the figure with the triangles.
To read more about the Easterbrook study, this is a good starting point:
Easterbrook J.A. The effect of emotion on cue utilization and the organization of behavior. Psychological Review. 1959;66(3):183–201.