Kojima, S., Hiratsuka, S., Shiraki, N., Higuchi, K. et al., "Spatio-Temporal Frequency Characteristics Measurement of Contrast Sensitivity for Smart Lighting," SAE Technical Paper 2016-01-1420, 2016, doi:10.4271/2016-01-1420.
This study aims at the development of a projection pattern that is capable of shortening the time required by a driver to perceive a pedestrian at night when a vehicle’s high beams are utilized. Our approach is based on the spatio-temporal frequency characteristics of human vision. Visual contrast sensitivity is dependent on spatiotemporal frequency, and maximum contrast sensitivity frequency varies depending on environmental luminance. Conventionally, there are several applications that utilize the spatio-temporal frequency characteristics of human vision. For example, the National Television System Committee (NTSC) television format takes into consideration low-sensitivity visual characteristics. In contrast, our approach utilizes high-sensitivity visual characteristics based on the assumption that the higher contrast sensitivity of spatio-temporal frequencies will correlate more effectively with shorter perception times. To test this hypothesis, we conducted experiments aimed at determining maximum contrast sensitivity frequencies under simulated nighttime lighting levels using a Campbell-Robson chart, which allowed us to change spatial frequency and contrast levels smoothly. We then changed the brightness levels of specific temporal frequencies using this chart, and asked test participants to plot threshold lines showing the maximized contrast sensitivity of each temporal frequency. Next, we extracted the spatio-temporal frequencies showing the highest contrast sensitivity for each test subject, and investigated the frequency distribution. We found out that maximum sensitivity spatial frequency is around 1 cycles/degree, and the maximum sensitivity temporal frequency is around 6 Hz. In our future studies, we will evaluate the time required for drivers to perceive pedestrians at night using these frequencies.