The Synesthesia Tree: Seeing flashes on hearing loud or sudden sounds

(It can also happen on being touched unexpectedly or feeling pain)

(This phenomenon is not synesthesia)

Some people report that when lying in bed with their eyes closed, about to fall asleep, if they hear a loud or sudden noise they sometimes see a flash of white light, a bright colour or a pattern of lines or stripes. There can be different colours or patterns, but the most common visual reaction seems to be a white flash. This visual reaction to sound is not synesthesia. The cause could be pressure generated by an ocular contraction reflex on being surprised by the loud or sudden sound, creating a phosphene effect similar to the one you might see if you close your eyes and press your fingers lightly against your eyelids.

These phosphene patterns can also sometimes be generated by a blow to the head (“seeing stars”), a sharp pain or even, for some people, being unexpectedly touched by someone.

This is what Sean Day says about this subject in his book Synesthetes (2016/2021):

"There are indications that people in general – that is, regardless of whether they are congenital synesthetes or not – have hypnagogic synesthetic experiences at least two or three times per year. Such experiences are usually ‘sound à visual’; most commonly, a loud noise, such as a door slamming, produces a synesthetic visual flash. There are other possibilities for hypnagogic synesthetic experiences, though, such as a touch to the body making you think someone is calling your name. Research is currently underway on this topic1."
1 See, for example, Sagiv & Ben-Tal (forthcoming).

There are also people who are especially sensitive to what is called the “sound-induced flash illusion”, which has been the subject of scientific experiments: on watching a single flash of light and hearing two beeps, they see two consecutive flashes.

Here is some information on the sound-induced flash illusion and a test to see whether it happens to you.

More information on entoptic phenomena (visual effects originating within the eye itself) and other related topics:

Closed-eye hallucinations

Hypnagogia (the hypnagogic state is the state of transition from wakefulness to sleep, a state of profound relaxation in which visual phenomena of this type can spontaneously occur. This article also talks about sleep hallucinations (hypnagogic and hypnopompic hallucinations).

An article by Carol Steen comparing synesthetic and entoptic/hypnagogic visions

This article and its comments are an interesting read about loud or sudden sounds creating flashes, and related phenomena

Go to the page on auditory-visual synesthesia

This page last updated: 27 March 2022

4 comments:

AnonymousSeptember 4, 2022 at 5:09 PM
In my case, the eye flash following a loud or sudden sound is often immediately followed by a sharp alkaline feeling on my tongue, as if I just licked a weak 9V battery. This would seem to discount the ocular contraction as the sensory source.
JudyMay 12, 2023 at 10:52 AM
I wake up from the flash of light whenever my air-conditioner decides to make some sudden noise, and it's annoying.
AnonymousJune 4, 2023 at 6:49 PM
I get these whenever my eyes are closed, regardless of whether I'm falling asleep or not, and they look nothing like the phosphenes from pressing my finger on the eyelid, nor anything like "seeing stars". It's evenly spread out across the entire vision field, and most often looks like TV static. Sometimes it's geometric patterns like a checkerboard or (rarely) more elaborate patterns. I also get the same when one of my muscles suddenly twitches.