When you shine a torch to your hand, your fingers glow red. Amazingly, that same principle underlies the technology in EarGenie, and we thought you’d like to know about it.

Measuring baby brains

EarGenie uses light to measure brain activity in a technique called functional near-infrared spectroscopy (fNIRS).

Even though babies sometimes startle or react to sounds, those behaviours are unpredictable, though very cute, and have little diagnostic value. That’s why we use brain scans to test a baby’s hearing ability.

Currently, audiology clinics commonly use the auditory brainstem response (ABR) and the auditory steady state response (ASSR) to measure infant hearing. In these tests, electrodes (recording stickers) on the skin measure activity in the underlying hearing nerves—when the baby hears, the nerves fire. That neural activity is used to determine what sounds the baby can hear.

Unfortunately the ABR and ASSR have limitations, especially in babies with abnormal neural activity (see this factsheet on auditory neuropathy [live link]), or in babies wearing an electrical device such as a cochlear implant which causes interference.

That’s why we’re developing EarGenie—we’re using fNIRS to help streamline the diagnosis and management of infants with hearing loss.

Light is light, right?

Let’s go back to the torch. When you shine white light on your hand, your skin and bones don’t absorb the red portion of the light, so red light passes through your tissue and comes out the other side, hence the red glow.
However, there is one part of you that will absorb red light—the pigment in your blood, haemoglobin. When it comes to regular torchlight, your blood won’t soak up enough red to stop that eerie glow, but there are specific wavelengths of light your haemoglobin will happily absorb. Those wavelengths are called near-infrared light, and fNIRS exploits this characteristic to measure blood flow in the brain.


In fNIRS, small near-infrared light sources are embedded in a head-cap (imagine a high-tech waterpolo cap). Each little light source is paired with an equally small detector. At the click of a button, the lights shine on to the scalp. Some light gets absorbed by the blood, and some bounces back out and reaches a detector. When there’s more blood around, more light gets absorbed. And when is there more blood? When the brain is working hard and needs more food. Any part of the brain that’s active will demand more blood, and so generate a different fNIRS response to other less active areas.

fNIRS as an infant hearing test

When testing a baby with EarGenie, we intentionally arrange our fNIRS lights on the areas of the brain involved in hearing and language. Then we play sounds and if the baby’s brain gets activated by the sound, we know they heard it.

[Image: fNIRS caps contain little lights and detectors]

fNIRS allows us to test sounds of varying volume or pitch, and even whether the baby can hear the difference between words. This fabulous new technology offers insight into a baby’s language development and will help personalise the care of hearing impaired babies. It will improve tuning of hearing aids and cochlear implants, and facilitate individualised language therapy. The sooner we provide hearing impaired babies with the best possible care, the earlier they can learn to speak, and the brighter their future will glow.