Do letters have colors for you? Do numbers have locations in space? Do sounds have smells? If so, you might have synesthesia. And, as it turns out, you might also be more likely to have autistic traits.

Synesthesia is a tendency to automatically associate information across different senses. Commonly, people with synesthesia associate letters, words, numbers or musical notes with colors. However, there’s a diverse array of different kinds of synesthesia involving all senses, including touch, smell and taste.

For a while, psychology researchers have been interested in finding ways the brains of people with synesthesia are different. For example, there’s some evidence that synesthetes may be more intelligent on average.

Now, a new study published in in the journal Cortex by researchers from the UK suggests that people with synesthesia may also have more autistic traits. The researchers gathered together a large group of people with a range of different kinds of synesthesia.

First, the researchers surveyed the participants about the extent to which they showed signs of two kinds of autistic traits: sensory sensitivity and attention to detail. These traits are more or less what they sound like – a tendency to be sensitive to sensations (sounds or tactile sensations for example), and a tendency to focus on specific details. Both are considered core features of autism spectrum disorders.

And in the study, both were associated with synesthesia. Not only did people with synesthesia tend to score higher on both kinds of traits, but people with more types of synesthesia tended to score even higher than people with fewer types of synesthesia.

Next, the researchers had participants complete two perceptual tests. The first tested people’s ability to detect subtle changes in visual scenes. The second challenged people to find shapes embedded in larger visual scenes.

These tests involve attention to local sensory details, and people with autism tend to outperform people without autism on both. As it turned out, people with synesthesia also outperformed people without synesthesia, reinforcing the idea that people with synesthesia resemble people with autism in how they process sensory information.

The researchers are quick to emphasize that even though people with synesthesia score higher on autistic traits, most people with synesthesia don’t actually have an autism spectrum disorder. That said, the findings do suggest that people with synesthesia may be at higher risk for autism and that synesthesia and autism may have interesting neurological similarities.

Image: Flickr/Jason Brennan