Research
DO LAB F. M. Kirby Neurobiology Center | Boston Children's Hospital | Harvard Medical School
RESEARCH
The visual system may be considered in two parts: one that resolves patterns, and one that detects the overall level of illumination, or irradiance. Pathways for pattern vision have mechanisms for discarding irradiance information. This helps to maintain a constancy of perception despite the vast differences in light level that are typical of the environment, such as between sun and shade or morning and evening. On the other hand, pathways for irradiance detection tend to smooth over patterns in light intensity such that, for example, the body clock is not altered by a passing cloud.
PATTERN VISION
Visual perception entails the resolution of detail in space, time, and wavelength. The resolving power of human vision, like that of many other primate species, is impressive. For example, it outstrips the spatial acuity of cats by 10-fold and that of mice by 100-fold. We study the origin of this performance in the cone photoreceptors of the fovea, a specialized domain of the retina.
The figure illustrates how the tiny and densely-packed foveal cones form a pixel array that is suitable for image resolution (top right; a recording electrode is also present). By contrast, the peripheral cones are large and widely spaced (top left; the small cells are rod photoreceptors). We are comparing the functional properties of foveal and peripheral cones (examples of light responses are shown at the bottom). These data are from G. Bryman, a predoctoral student in the lab.
IRRADIANCE DETECTION
The intensity of illumination changes over many orders of magnitude with each rotation of the earth, driving differences in environmental parameters such as temperature and the types of species that are active. Tracking intensity therefore provides a survival advantage, and mammals do so in order to regulate their physiology and behavior. Producing an accurate representation of the overall light level entails integration over space, time, and wavelength—quite distinct from the resolution that is characteristic of pattern vision. We investigate the mechanisms of signal integration and ask whether they differ across diurnal and nocturnal species.
Irradiance detection is supported by intrinsically photoreceptive retinal ganglion cells (ipRGCs), which express a receptor called melanopsin (image by E. Milner, a predoctoral student in the lab).
