Touch-Sound Synesthesia: A Definition and Comprehensive Overview
Synesthesia is an extraordinary neurological condition where the stimulation of one sensory or cognitive pathway leads to involuntary experiences in another. For instance, some synesthetes “see” sounds, “taste” colors, or even “feel” flavors. What is synesthesia? Synesthesia is a phenomenon that causes sensory crossovers, such as tasting colors or feeling sounds. Some people describe it as having “wires crossed” in their brain because it activates two or more senses when there’s only a reason for one sense to activate.
When you listen to a symphony, do you see a vivid display of colors dancing before your eyes? Or perhaps when you smell a freshly baked apple pie, you not only savor its aroma but also “taste” its vibrant shades of red and brown?
Understanding How Synesthesia Works
To understand synesthesia (pronounced “sin-ess-THEE-zh-uh”), it helps to understand how your senses work. Your brain relies on your five main senses - sight, sound, smell, taste or touch - to know what’s happening around you. That involves the following steps:
- Detection: Your senses pick up something happening around you. An example would be using your eyes to look at your surroundings or using your ears to listen for certain sounds.
- Signaling: Your senses send a signal to your brain describing what they’re experiencing. For example, your eyes would describe the colors and shapes of the things you can see nearby, or your ears would send signals that describe how loud a sound is, if it’s high- or low-pitched, etc.
- Processing: Your brain receives those signals and routes them to a certain area for processing. The area that does the processing connects to areas that help you understand what you’re seeing. Examples of this are recognizing a stop sign by its shape and/or color or recognizing that a sound is a piece of music or someone’s voice.
In short, your senses describe to your brain what they pick up, and your brain creates its own understanding of the world around you from those descriptions. But people with synesthesia experience the processing step differently. Their brains process the same information through two or more brain areas at once. That causes a primary and at least one secondary effect:
- Primary effect: The primary effect is what you experience because of sensory input. An example of this would be hearing sounds and recognizing them as music.
- Secondary effect: People with synesthesia experience a secondary effect (or more than one) that seems like it’s one of their senses working, but there’s no input from that sense that should be causing it. An example of this would be seeing colors because you hear music.
Visual synesthesia can also happen in different ways. Some people experience visual synesthesia like a “projection,” meaning their brain directly combines the secondary effect into their sense of sight. That causes them to experience it as if they actually see it. Other people have an “internal screen” effect. They can automatically picture it in their head but don’t experience it as if they were seeing it directly.
Exploring Different Forms of Synesthesia
While you have five main senses, there are many different things you can identify with each sense. These are perception abilities. Some examples include:
- Sight: Colors, patterns, textures, shapes.
- Hearing: Volume, pitch, frequency.
- Touch: Temperatures, pressure, textures, vibrations, pain.
Some perception abilities involve more than one sense, like balance. Your perception abilities can also involve concepts you understand using your senses, such as time, numbers and language. Because there are so many possible combinations between your senses and perception abilities, researchers can identify at least 60 different forms of synesthesia. Some experts estimate there are more than 150 different forms. This is also why many people with synesthesia have it but don’t know what it is or that it’s unusual.
Some forms of synesthesia are better known or are more common.
Common Types of Synesthesia
- Grapheme-Color Synesthesia: In this form, alphabets and numbers are seen as inherently colored. “Grapheme” is the word for the smallest part of a written language, like a letter, number or symbol. Some people see different graphemes with specific colors. People who experience visual synesthesia’s projection effect often see graphemes as different colors.
- Chromesthesia: Here, sounds, often musical notes, conjure specific colors.
- Lexical-Gustatory Synesthesia: This type is truly fascinating. Words trigger a specific taste in the mouth.
- Ordinal Linguistic Personification (OLP): In OLP, ordered sequences, like numbers, days of the week, or months, are associated with distinct personalities and sometimes even genders.
- Mirror-Touch Synesthesia: People with mirror-touch synesthesia experience the same sensation another person feels. Mirror-touch synesthesia is when you see something happen to someone else and physically feel it, too. It works similarly to the reflexive cringe you might have if you see someone trip and face-plant in front of you. However, the effect is much stronger. Some people can watch another person being touched on the arm or hand and they also feel it. Other people can actually feel pain that others describe or pain from visible injuries. This form is more likely to be disruptive if it causes you to feel pain as a secondary effect.
- Number Form Synesthesia: In this type, numbers are visualized as points in space, forming a mental map.
- Auditory-Tactile Synesthesia: Certain sounds induce specific tactile sensations.
- Spatial Sequence Synesthesia: Individuals with this type perceive numerical sequences as points in space.
- Ticker-Tape Synesthesia: In this form, spoken words are seen as text, almost like subtitles in a movie.
- Hearing-motion synesthesia: Some people experience sounds related to seeing things moving. An example of this would be a person hearing a “whoosh” sound when watching something go past them.
- Sound-color synesthesia: Sound-color synesthesia is where you see specific colors when you hear certain sounds. It tends to be specific to certain sounds or music. Musicians and artists often describe having this form.
- Time-space synesthesia: This is a form of synesthesia where you visualize things in a very specific way. People who have this form of synesthesia often “see” sequences with specific patterns or forms. An example of this is visualizing a calendar or a string of numbers in a certain way. Some people can mentally “map” these out in vivid or detailed ways.
Synesthesia remains an immensely rich field, offering a kaleidoscope of ways to experience the world.
Touch-Sound Synesthesia: A Closer Look
Touch-sound synesthesia is when you hear specific sound depending on the texture or type of object they are touching. Surfaces have their own sounds and the sounds are different depending on how I touch the surface. "I can [hear] touch. Like when I'm swiping on my phone, or typing. Or touching my fingers, or my bedsheet, floor, scratching something, even I can hear sounds from touching inside my mouth using my tongue." touch screen I'll get a slightly jarring buzz sound. sound different based on their textures. or other sensitive skin areas, at least that's what has been on my radar."
Levels of Intensity in Synesthesia
Yes, synesthesia can affect people differently. Some people may only experience synesthesia under certain circumstances. Others may experience synesthesia for many reasons, or they might experience more than one secondary effect. In severe cases, synesthesia can be strong enough to affect your ability to concentrate or focus. Fortunately, this is rare. Synesthesia is usually short-lived, so it’s usually not disruptive to this degree.
The Genetics and Neural Basis of Synesthesia
Traditional views held that synesthesia was a form of “cross-talk” between different regions of the brain. However, recent neuroimaging studies have shown that the phenomenon is more complex than that. Researchers at the University of Sussex took this a step further. They discovered that people with synesthesia tend to have more grey matter in specific brain regions associated with sensory processing. Grey matter is pivotal in processing information in the brain, including sensory perception, decision-making, and self-control.
The role of genetics in synesthesia is a hot topic in scientific circles, and for good reason. Unlocking the genetic keys behind synesthesia could unravel a multitude of secrets about not only this condition but also sensory experiences and cognitive functions. Research shows a strong likelihood that synesthesia is hereditary, as it often appears within families. One groundbreaking study in the Journal of Neuropsychology even highlighted a genetic predisposition towards this sensory phenomenon.
Pioneering studies employing genome-wide association techniques (GWAS) are setting out to identify the specific genes tied to the diverse forms of synesthesia. This line of inquiry could dramatically shift our comprehension of how genetic makeup influences this unique condition. Beyond that, uncovering these genes could offer valuable insights into conditions that may be related to synesthesia, such as ASD.
Synesthesia and Autism Spectrum Disorders (ASD)
On the surface, synesthesia and autism appear to be distinct phenomena: the former involves a fusion of sensory experiences, while the latter is generally defined by difficulties in social interactions, repetitive behaviors, and challenges in speech and non-verbal communication. Yet, research indicates that synesthesia is nearly three times as prevalent in individuals with Autism Spectrum Disorders (ASD)-at 18.9%-as opposed to 7.2% in the general population.
Further scientific exploration suggests that both synesthesia and autism may stem from heightened neural connectivity and activity. While the genetic foundations and mechanisms for both conditions are not yet fully understood, some researchers propose that there could be an overemphasis on local brain connectivity, at the expense of global connections, in both scenarios.
| Condition | Prevalence in General Population | Prevalence in Individuals with ASD |
|---|---|---|
| Synesthesia | 7.2% | 18.9% |