Traditional ways of testing a person's hearing include tuning fork tests, speaker distance examination, and pure-tone threshold tests. These tests involve reflexes, such as raising the hand or pressing a button on hearing a particular sound.
However, these methods that require a response from the person who is having the hearing test may not fit people who are unable to respond, such as adults with stroke, young people with developmental problems, or babies.
A team of researchers led by Dr. Singh Bala from the Institute of Neuroscience at the University of Oregon came up with an alternative way of testing someone's hearing that requires an eye examination instead of a direct response.
Bala and his colleagues started from the observation that barn owls dilate their pupils when they discern sounds.
The researchers discovered this in their previous work, which they conducted almost two decades ago. So, in this new study, the team hypothesized that the same would be true in humans. The team published the experiment's results in the Journal of the Association for Research in Otolaryngology.
To test their hypothesis, the scientists used eye-tracking technology to examine the pupils of 31 adults, with an average age of 24 years old, who had no hearing loss. The experimenters used an infrared video camera to monitor the participants' pupils as they were taking a standard hearing test.
The participants were asked to press a button if they heard noises at the frequency of 1, 2, 4, and 8 kilohertz (kHz), respectively. During the test, the participants also had to gaze at a computer screen.
A dot appeared on the screen, followed by tones at random delays, which prevented the participants from predicting when they would hear the sound. When the participants saw the dot turning into a question mark on the screen, they had to indicate if they had heard the sound or not.
The researchers found that pupils started to dilate at about 0.25 of a second after the sound.
In a report published by The Medical News Today website, Dr. Bala said: "The fact that the pupil dilation was so quick enabled the researchers to see and establish causality."
For his part, study co-author Terry Takahashi commented on the relevance and usefulness of the findings, saying, "A pupil dilation test is not as useful in adults who can communicate with the tester."
