Every day we’re confronted with information that stimulates many of our senses at the same time, but we don’t perceive this information in its component parts. Rather, we perceive it as a whole without being conscious of doing so. But people with bipolar disorder struggle with this integration process, and this might make it hard for them to communicate.

Think about an explosion: the sight of the fireball might be sufficient to signal that an explosion has occurred, but we will know that it definitely has if we also hear a loud bang, smell smoke and feel heat from the fire.

It’s the integration of all these different kinds of sensory information that enables us to experience the world around us in all its glory. And this integration is vital if we are to understand other people.

Working together

We are inherently social beings and the emotional expressions of the people we encounter reach us through different sensory channels. Accurate perception of this emotional information is crucial for social communication.

To communicate effectively, we need to appreciate the meaning behind other people’s words, decipher the tones and inflections with which they are spoken, and relate these to the speaker’s facial expressions and body language. More importantly, we need to integrate the information quickly so our perceptions are coherent.

Most of the time, the information we see and hear has the same meaning. In some cases, perception from only one of the senses may be enough for emotional understanding. But cues from only one sense can often be ambiguous.

It would be difficult for us to tell that what we are encountering is an explosion, for instance, based on the smell of burning alone. And because of this occasional ambiguity, integration of information from different senses is vital for helping us better judge incoming information, and key to understanding others.

Sensory integration is particularly important when inputs to one of the senses are distorted, like when someone’s voice is muffled. In this case, it may become difficult to be certain about what the speaker may be thinking and feeling, but coupling the muffled voice with information from her face can help us to figure it out.

Integration is clearly handy any time we communicate with other people.

A curious difference

But some people have a permanent communication disadvantage that may affect them socially. An increasing number of studies show that in some people with psychiatric conditions such as bipolar disorder, interpersonal functioning is compromised.

It’s not clear why this is, but we think it may be related to potential difficulties in integrating different kinds of social information. Just as intact sensory integration can help improve our understanding of others, abnormal integration can impair it. Research shows at least some people with bipolar disorder have difficulty recognising other people’s facial and vocal emotional expressions.

A colleague and I wondered whether, in addition to these seemingly separate processes being impaired, it was also possible that there was impairment in the way the systems governing these different emotion perception skills interacted in people with bipolar disorder. We tested the idea by looking at how people with the disorder integrate emotional signals.

We asked a group of people who had bipolar disorder and a group of people who did not to quickly identify a series of facial expressions while ignoring a series of sentences spoken in an emotional tone at the same time.

Sometimes, the auditory information matched the visual information – a happy face paired with a happy voice, for instance – and sometimes it didn’t. Because conflicting information is likely to interfere with how well a stimulus is recognised, we expected sensory integration would be best reflected in quicker responses when the visual and auditory information were the same.

What we found

We found people who didn’t have bipolar disorder showed this effect, but the bipolar group failed to integrate emotional signals to the same extent. Whether the audio and visual information was the same or not made no difference to the responses of the bipolar group. They were, in fact, consistently and significantly slower than the control group at recognising facial emotional expressions.

In effect, the bipolar group didn’t show the usual information-processing boost that occurs when information of the same meaning is presented to different senses. This suggests that for people with bipolar disorder, meaningful information from different sensory channels isn’t integrated in the usual way.

It seems that when people with bipolar encounter ambiguous facial expressions, related auditory information is unlikely to help them identify the underlying emotional state of the person with whom they’re communicating. This could mean that the brain regions that process information from the senses do not communicate well in people who have this disorder.

The idea needs further investigation but, regardless of underlying causes, our results highlight a potential reason for why some people with bipolar disorder may experience interpersonal difficulties.