Changes in reaction time and search time with background luminance in the mesopic range

Area of Science:

• Vision Science
• Human Perception
• Photobiology

Background:

• Human vision utilizes rod and cone signals across diverse lighting conditions.
• Understanding visual task performance at different light levels is essential.

Purpose of the Study:

• To investigate how reaction time and visual search performance vary with luminance contrast and background luminance.
• To evaluate mesopic visual performance models using colored stimuli.

Main Methods:

• Measured reaction times and search times with achromatic targets under varying luminance conditions.
• Assessed the spectral dependence of performance using colored stimuli.
• Compared experimental data to predictions from two mesopic visual performance models.

Main Results:

• Visual search performance was more robust to luminance changes than reaction time.
• Search performance could be rendered invariant by adjusting contrast scaling.
• Reaction time varied significantly across the mesopic range.
• The 'effective contrast' model accurately predicted spectral dependencies for both reaction and search times.
• A mesopic luminous efficiency model based on reaction times showed limitations in predicting spectral dependence when chromatic signals were influential.

Conclusions:

• Visual search is more adaptable to luminance fluctuations than simple reaction time in mesopic conditions.
• The 'effective contrast' model provides a good framework for understanding spectral influences on mesopic visual tasks.
• Further refinement of mesopic luminous efficiency models is needed to account for chromatic signal contributions.