Time-Locked Psychophysics: Speeded Responses to Visual Stimuli

Northeastern University, Boston MA

Investigators

Abstract

Color is central to human experience, influencing our moods, our choices of foods, clothes, and indeed all our visual behavior. But much about how humans process color is still a mystery. A better understanding of human color vision has many practical applications in imaging, materials and textiles, architecture and lighting design. Many of these models are only loosely tied to basic human color mechanisms, in part because of a lack of good models of fundamental color processes. The human brain contains millions of nerve cells that respond when an event occurs in the environment. For visual stimuli, the neural responses start in the retina of the eye and are transmitted to the brain where they create our conscious awareness of the world around us. Among other things, the neural activity signals the color of the light. This process is fast, but not instantaneous. This project uses novel procedures to measure behavioral responses that are triggered by color in the very first fraction of a second of nerve activity in the eye and study how those responses change over time over a range of colors, contrasts, and adapting backgrounds. This research uses innovative psychophysical methods to explore how light adaptation and the bifurcation of neural visual signals underlie chromatic detection and color categorization. One goal is to explore whether the fastest behavioral responses are triggered by the very early activity in the light-sensitive cells of the retina of the eye. A second goal rests on the hypothesis that neural responses to the start and end of a stimulus are carried in two different nerve pathways to the brain (the ON and OFF pathways). The aim is to test whether the ON and OFF responses can be measured and studied separately, by determining whether responses triggered by the start and end of a stimulus can have different colors even though the physical stimulus is the same for both. Results from all experiments will be analyzed using advanced computational methods and compared with the known properties of nerve cells in the eye. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.