Visual search under scotopic lighting conditions

• Published in: Vision research (Oxford) Vol. 113; no. Pt B; pp. 155 - 168
• Main Authors: Paulun, Vivian C., Schütz, Alexander C., Michel, Melchi M., Geisler, Wilson S., Gegenfurtner, Karl R.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.08.2015
• Subjects: Adult; Analysis of Variance; Attention - physiology; Contrast Sensitivity - physiology; Eye movements; Eye Movements - physiology; Female; Fixation, Ocular - physiology; Fovea Centralis - physiopathology; Humans; Lighting; Male; Night Vision - physiology; Photic Stimulation - methods; Scotopic sensitivity; Scotopic vision; Visual Fields - physiology; Visual search; Young Adult; Scotopic vision; Scotopic sensitivity; Eye movements; Visual search
• ISSN: 0042-6989; 1878-5646
• DOI: 10.1016/j.visres.2015.05.004

•Scotopic contrast sensitivity is lower, with a functional scotoma in the fovea.•Scotopic visual search shows longer lasting and less distributed fixations.•An ideal searcher behaves differently under photopic and scotopic conditions.•Human fixation patterns are qualitatively similar to ones of an ideal searcher.•The brain adjusts visual search behavior to meet some properties of rod vision. When we search for visual targets in a cluttered background we systematically move our eyes around to bring different regions of the scene into foveal view. We explored how visual search behavior changes when the fovea is not functional, as is the case in scotopic vision. Scotopic contrast sensitivity is significantly lower overall, with a functional scotoma in the fovea. We found that in scotopic search, for a medium- and a low-spatial-frequency target, individuals made longer lasting fixations that were not broadly distributed across the entire search display but tended to peak in the upper center, especially for the medium-frequency target. The distributions of fixation locations are qualitatively similar to those of an ideal searcher that has human scotopic detectability across the visual field, and interestingly, these predicted distributions are different from those predicted by an ideal searcher with human photopic detectability. We conclude that although there are some qualitative differences between human and ideal search behavior, humans make principled adjustments in their search behavior as ambient light level decreases.