Luminance-dependent visual latency for the Hess effect, the Pulfrich effect, and simple reaction time

Area of Science:

• Visual perception
• Psychophysics
• Neuroscience

Background:

• The Hess effect is a monocular visual illusion.
• It involves the apparent displacement of a more illuminated target ahead of a less illuminated one during lateral motion.
• Previous research has not fully explored its characteristics across different light levels.

Purpose of the Study:

• To investigate the Hess effect under scotopic and photopic conditions.
• To compare the magnitude of the Hess effect with the Pulfrich effect.
• To analyze reaction time changes with stimulus intensity.

Main Methods:

• White targets on a black background were used.
• Stimuli were presented at scotopic (low light) and photopic (normal light) levels.
• Theoretical time-constants were calculated assuming a diffusion process and temporal centroid.

Main Results:

• The Hess effect magnitude was similar to the Pulfrich effect under photopic conditions.
• Reaction time decreased more rapidly with increasing stimulus intensity than predicted by either effect.
• Calculated time-constants for the Hess effect ranged from 0.145 to 0.165 seconds.

Conclusions:

• The Hess effect exhibits distinct properties compared to the Pulfrich effect, particularly concerning reaction time.
• The findings suggest a complex interplay between stimulus intensity, latency, and visual processing.
• A diffusion process followed by a non-linearity model provides a theoretical framework for understanding the Hess effect's temporal dynamics.