Determination of Speed-Dependent Roadway Luminance for an Adequate Feeling of Safety at Nighttime Driving

The purpose of this work is to determine as a function of velocity the minimal roadway luminance that is required to be judged as being bright enough for a driver to perform a nighttime driving task with an adequate feeling of safety. In this context, it shall also be evaluated which areas of the vehicle forefield are most crucial for the driver’s general brightness perception. A field study with 23 subjects and dimmable LED headlights was conducted, in which the subjects were given the task to assess their perceived brightness for different luminance levels caused by the headlights’ low-beam distribution in the vehicle’s forefield on a 5-step rating scale. The experiments were repeated for three different driving velocities of 0 km h−1 (static case), 30 km h−1, and 60 km h−1, respectively. Results for the static case indicate that, for the roadway to be perceived as bright enough by 50% of the subjects, an average roadway luminance of 0.88 cd m−2 is required in an area up to 32 m in front of the vehicle. Furthermore, a significant effect of driving speed is observed. For example, at 60 km h−1, the luminance must be increased to 1.54 cd m−2 to be still perceived as sufficiently bright by 50% of the subjects.

Pupillary evidence reveals the influence of positive thoughts on brightness perception

Our visual experience often varies based on momentary thoughts and feelings. For example,when positive thoughts are invoked, visual objects may appear brighter. However, it remainsunclear whether this phenomenological experience is driven by a genuine top-down modulation of brightness perception or by a mere response bias. To investigate this issue, here we use pupillometry as a more objective measure of perceived brightness. We asked participants to judge the brightness level of an iso-luminant gray color patch after evaluating the valence of a positive or negative word. We found that the gray color patch elicited greater pupillary light reflex and more frequent “bright” responses after observers had evaluated the valence of a positive word. As pupillary light reflex is unlikely driven by voluntary control or response bias, these results suggest that positive concepts can genuinely modulate brightness perception.

Adaptive auditory brightness perception

Perception adapts to the properties of prior stimulation, as illustrated by phenomena such as visual color constancy or speech context effects. In the auditory domain, only little is known about adaptive processes when it comes to the attribute of auditory brightness. Here, we report an experiment that tests whether listeners adapt to spectral colorations imposed on naturalistic music and speech excerpts. Our results indicate consistent contrastive adaptation of auditory brightness judgments on a trial-by-trial basis. The pattern of results suggests that these effects tend to grow with an increase in the duration of the adaptor context but level off after around 8 trials of 2 s duration. A simple model of the response criterion yields a correlation of r = .97 with the measured data and corroborates the notion that brightness perception adapts on timescales that fall in the range of auditory short-term memory. Effects turn out to be similar for spectral filtering based on linear spectral filter slopes and filtering based on a measured transfer function from a commercially available hearing device. Overall, our findings demonstrate the adaptivity of auditory brightness perception under realistic acoustical conditions.

Research on Discrimination Threshold of Brightness for Different Color Temperatures

This article explores the experimental study on the relationship between human eye discrimination threshold of white light under different lighting levels and color temperatures by the psychophysical experimental method. The visual matching method was applied to study the subjective brightness perception under different lighting environments. We try to explore the internal connection between the physical intensity and subjective rating value. The experimental results will do help the development of dimming system for smart lighting.

Electrical neuromodulation biases brightness perception of flickering light

Human brightness estimation often pronouncedly dissociates from objective viewing conditions. Yet, the physiological substrate underlying subjective perception is still poorly understood. Rather than physical illumination, the subjective experience of brightness has been shown to correlate with temporal dynamics in the amplitude of cortical neural responses. Here, we aimed to experimentally manipulate visual flicker-evoked steady-state responses and related perception via concurrent modulation of cortical excitability by transcranial alternating current stimulation. Participants performed a brightness discrimination task of two visual flicker stimuli, one of which was targeted by same-frequency electrical stimulation at varying phase shifts. Transcranial electrical stimulation was applied with an occipital and a periorbital active control montage, based on finite-element method simulations of electric fields. Experimental results reveal that flicker brightness perception is modulated dependent on the phase shift between sensory and electrical stimulation, solely under stable flicker entrainment and exclusively under occipital electrical stimulation. The degree of induced brightness modulation was positively correlated with the strength of neuronal phase locking to the flicker, recorded prior to electrical stimulation. This finding was corroborated by a neural network model, demonstrating a comparable dependency between flicker-evoked phase synchronization and amplitude modulations of entrained neural rhythms by phase shifted visual and electric inputs. Our data suggest a causal role of the amplitude of neural activity in visual cortex for brightness perception in humans. This finding provides an important step towards understanding the basis of visual perception and further confirms electrical stimulation as a tool for advancing controlled modulations of neural excitability and related behavior.