In collaboration with Suzuki (President and CEO Toshihiro Suzuki), Professor Makoto Miyazaki of the Faculty of Informatics, Shizuoka University, Daiki Yoshioka (graduate student) of the Graduate School of Science and Technology, Shizuoka University, and Associate Professor Shigeki Takeuchi of the Faculty of Business Information, Jobu University announced that they have identified the brain activity associated with experiencing glare (strong brightness) when exposed to intense light. Their findings were based on the results of electroencephalographic studies the group performed. Glare experienced during activities such as driving may become the cause of an accident. This research result is expected to help in preventing such events. The results were published on August 17 in "Automotive Technology Association Proceedings Vol. 52, No. 5," published by the Society of Automotive Engineers of Japan.
The discomfort and diminished visual ability resulting from intense light, such as high beams from oncoming cars, during night-time motor vehicle driving is known as glare. This phenomena can be responsible for traffic accidents. Engineering evaluation methods have been proposed as countermeasures, but these methods only use the variables of the light stimulus (such as the brightness of the light source and the distance from the light source). Neurophysiological changes in the brain were not considered until now. A compounding issue is that, in recent years, since the adoption of liquid crystal displays that constantly emit light in automobile meters, Suzuki has received customer feedback that the displays are "blinding." In an attempt to solve the issue, the company has been using conventional engineering evaluation methods to design displays such as meters. However, individual differences in the perception of glare made it difficult to overcome this the problem.
In response to this issue, the research group focused on brain activities that create individual differences in the perception of glare. First, the researchers aimed to identify the brain region that is activated when humans experience "glare" by experimentally measuring brain waves (evoked potential test). Thirty individuals aged 19-27 years (24 males and 6 females, mean age 21.5 years) participated in the experiment. All participants were right-handed and had normal or corrected-to-normal visual acuity.
In the experiment, participants performed a glare judgment task for white light stimuli emanating from an ultra-high brightness display (maximum luminance 2500 cd/square meter) in a shaded, sound-resistant, electromagnetic shield room over 2 days. On the first day, the glare threshold of each participant (the brightness at which "glare" is felt at a rate of 50%) was investigated by presenting eight levels of brightness. On the second day, five levels of luminance were set for each participant based on their thresholds, and their electroencephalograms were recorded. Specifically, each participant was presented with a light stimulus at a luminance corresponding to their glare threshold.
Participants judged that half the trials were "blinding (due to glare)" and the other half of the trials were "not blinding." Subsequently, the brain waves obtained during the "not blinding" stimuli were subtracted from brain waves obtained during the "blinding" stimuli. Thus, brainwaves specific to the "blinding" state were obtained. The electroencephalograms were recorded with the subjects wearing an electroencephalography cap with 63 electrode channels.
Analysis showed increased glare-related brain activity in the right occipitotemporal (approximately 100 ms after onset of the light stimulus presentation), left occipitotemporal (between 130 and 300 ms after onset), and prefrontal regions (between 180 and 190 ms after onset). Among the subjects, the prefrontal region was located directly above Brodmann areas 10 and 11 of the brain, which are known to be involved in various higher cognitive functions and reported to be activated in relation to pain. This suggests that the increased brain activity in the prefrontal cortex reflects the neural response of the discomfort associated with "glare." However, the electroencephalogram recorded in the occipital temporal region was considered to reflect the activity of the visual region known as the inferior temporal gyrus. It also reflected the neural response associated with the light intensity and a 'bright' texture.
This study revealed the brain regions and time latencies where brain activity is recorded when an individual experiences the sensation of "glare." In the future, it is expected that the objective data can be used for product development by clarifying the relation between individual characteristics such as age and sex differences, life factors such as fatigue and sleep time, and glare based on associated brain activity.
Professor Miyazaki said, "While the electroencephalogram measurements performed in this study have an excellent temporal resolution, their spatial resolution is low, and they limit us to rough site identification. We expect that more detailed site identification will be possible by performing MRI measurements with an excellent spatial resolution. Going forward, by clarifying the relationship of glare with personal characteristics such as age and sex, it will be possible to prevent discomfort while maintaining the visibility of liquid crystal displays, which are expected to be increasingly adopted in the future. We believe that these findings will be useful not only the automobile industry but also in a wide range of situations related to daily life such as applications in cities, houses, and in home appliances."
This article has been translated by JST with permission from The Science News Ltd.(https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.