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 (sleep hallucinations: hypnagogic hallucinations occur in the profoundly relaxed state of transition from wakefulness to sleep, while hypnopompic hallucinations happen at the moment of waking). This excellent article also discusses the science of hypnagogia and other aspects. (Note: hypnagogic hallucinations occur quite normally from time to time for many people and don't necessarily indicate any kind of sleep disorder).

Two kinds of visions, synesthesia and hypnagogia: a comparison. An article by artist Carol Steen comparing synesthetic and entoptic/hypnagogic visions.

Go to the page on auditory-visual synesthesia

Readers’ comments - this page contains the comments on this article received between 2022 and 2025, with readers’ own experiences and some alternative possible explanations for why it happens

This page last updated: 18 April 2026