How we feel affects what we see

People who place an emphasis on positive things and are generally optimistic are sometimes said to "see the world through rose-tinted glasses". According to a new study by Canadian researchers, this is more than just an idiom. The study, which has just been published in the Journal of Neuroscience, provides the first direct evidence that the mood we are in affects the way we see things by modulating the activity of the visual cortex. Their findings show that putting on the proverbial rose-tinted glasses of a good mood is not so much about colour, but about the broadness of the view.

A number of behavioural studies have already shown that emotions can have an effect on perception. When, for example, observers are asked to selectively pay attention to a target at the centre of the visual field while ignoring surrounding "distractor" objects, the prior induction of a positive emotional state leads to more interference from the surrounding objects than does induction of a negative mood. Likewise, positive moods are associated with a tendency to perceive global components, and negative moods with the local components, of a visuospatial stimulus.

However, the exact neural mechanisms of these phenomena are unclear. One possibility is that mood has a "top-down" effect on vision, such that higher order cognitive processes impinge on the visual areas of the brain. Alternatively, mood may have a direct effect on the early stages of visual processing. Taylor Schmitz of the Affect and Cognition Laboratory at the University of Toronto and his colleagues hypothesized that positive emotional states would broaden the field of view, whereas negative states would have the opposite effect. To test their hypothesis, the researchers recruited 14 participants and used functional magnetic resonance imaging (fMRI) to monitor their visual cortical activity whilst they looked at various images.

The participants were shown photographs of faces expressing positive, negative or neutral emotions. Each of these was presented for 2 seconds, and followed by a composite image consisting of a face at the centre surrounded by photographs of houses or places. The first image of each pair served to induce a specific mood; participants were asked to report the emotion induced by each face, and also to judge the sex of the faces in the composite images, so that they focused their attention at the centre rather than the periphery. This experimental design exploited the knowledge that the fusiform face area (FFA) and parahippocampal place area (PPA) are selectively activated in response to faces and novel places, respectively, and so enabled the researchers to directly examine the effect of positive and negative emotional states on the encoding of composite images.

The researchers found a strong correlation between the participants' self-reported moods and the magnitude of the PPA response. The positive mood induced by the photographs of faces was positively correlated with increased processing of the novel places depicted in the composite images which followed, as revealed by increased activity in the left PPA (above). By contrast, negative moods had the opposite effect - they were associated with reduced PPA activity. In other words, inducing a good mood in the participants caused an increase in the scope of their field of vision, whereas inducing a negative mood reduced their visual field.

Thus, positive moods enhanced peripheral vision and increased the extent to which the brain encoded information in those parts of the visual field, to which the participants did not pay attention. Conversely, negative moods decreased the encoding of peripheral information. But does the enhanced peripheral vision that occurs because of positive mood induction come at the expense of central (or "foveal") vision? Schmitz and his colleagues compared FFA activity in the positive and negative mood induction trials, but found no difference. The enhanced peripheral vision following positive mood induction does not, therefore, occur as a result of a trade-off with central vision.

Evolutionarily, these effects might be explained as follows. A negative mood, such as fear or sadness, causes one's attention to be focused on specific details, at the expense of information in the periphery. An example of this is the so-called "weapon effect": those who witness a crime involving a weapon normally have an impaired memory for the appearance of the perpetrator, because their attention shifts to the weapon. The negative emotional content of the event enhances the visual processes by which the specific details (the weapon) are perceived and later remembered. This occurs at the expense of irrelevant peripheral information, which is suppressed, or filtered out. Such mechanisms would serve to increase one's vigilance in a possibly life-threatening situation.

On the other hand, positive emotions broaden the scope of the visual field, leading to increased breadth of attention; this new study shows that positive moods do so by directly modulating the visual system so that we can gain access to to more information. In psychology, the broaden-and build theory holds that positive emotions enhance one's awareness, and that this global perspective encourages novel thoughts and actions. This broadened behavioural repertoire in turn leads to increased creativity and inventiveness.

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Schmitz, T. et al (2009). Opposing Influences of Affective State Valence on Visual Cortical Encoding. J. Neurosci. 29: 7199-7207. DOI: 10.1523/JNEUROSCI.5387-08.2009.