Synesthesia heightens connections between sensory experiences

Researchers from Emory University have discovered that people who experience synesthesia, the mixing of senses, are more sensitive to associations between shapes and the sound of words.

Synesthesia, a trait found in between one and four percent of the population, is an inheritable condition that, in its most common form, causes people to draw connections between particular colors, words, numbers or sounds. Many famous artists and composers, such as Michel Gagné and Kanye West, have shared their experiences with the condition, and the most common issues synesthetes report are difficulties associated with reading.

The team of Emory University researchers, led by neurologist Dr. Krish Sathian, asked a group of 17 synesthetes and 18 controls to complete implicit association tests (IAT). While the test is often used to elicit hidden prejudices such as sexism, racism and homophobia, the IAT is also equipped to assess “crossmodal perceptions.”

A crossmodal perception, or cross-modal correspondence, is a connection formed between two or more different sensory modalities. This phenomenon is quite prevalent in our daily lives. One example of a cross-modal correspondence is the association of some musical notes as “high” and others as “low.” While musical notes, and sounds in general, have no spatial differentiation, we tend to connect different pitches with words that signify positions in a multidimensional space where sound cannot physically be. Similarly, studies have shown that we are more likely to associate soft letter sounds, such as “m” and “l,” with round shapes, and hard letter sounds, like “k” and “t,” with angular shapes.

Sathian says that there is still much debate in the scientific field regarding synesthesia. Some question whether the associations synesthetes have are entirely different from what the rest of the population experiences, or if their experiences are just more extreme, more frequent versions of cross-modal correspondences.

Participants in the study were recruited through advertisements on the Emory campus and self-identified as synesthetes. Each prospective participant took an online test called the Synesthesia Battery to confirm whether or not he or she had consistent associations.

To determine whether or not people with synesthesia were more sensitive to purely sensory associations between sound pitch and size or position of shapes, the research team tested and monitored the time of the associations between congruent and incongruent pairs of sounds and spacial positions. Examples of congruent pairs include a high pitch with a high position in space or a low pitch with a low position in space. If there was a significant difference in response time between congruent and incongruent pairs, the scientists would conclude that people with synesthesia were more sensitive to purely sensory associations between pitch and shapes.

From the data collected, Sathian and his team observed that people with synesthesia are more sensitive to correspondences between the sounds of pseudowords, words that have no meaning in English, and shapes. This suggests that the effects of their synesthesia have an impact on other parts of their neural networks and are connecting sounds, not just colors, to different sensory cues.

The team also observed that there was no significant difference in the purely sensory association domain. This means that the time differences between associations of congruent and incongruent pairs were not significant enough to suggest that synesthesia had an effect on response time.

The most common form of synesthesia in the Emory study was “grapheme-color,” the association between visual symbols and colors. This often originates in an individual’s childhood depending on how symbols, letters especially, are learned at a young age. For instance, a previous study had confirmed that a popular brand of refrigerator alphabet magnets had an influence on the associations people with grapheme-color synesthesia developed.

Previous brain imaging studies have shown that people with synesthesia are wired differently and have increased neural connections between the senses, which is what causes their unusual sensory experiences. These hyperconnections, based upon Dr. Sathian’s study, have an effect on other neural connections that synesthetes have.

As such, we can expect that in the future, scientists will continue to pursue the origins of synesthesia to develop a better understanding of its effects, in the hopes that any new findings can be applied to create better therapies for those with learning difficulties or individuals devoid of certain senses.