Project summary
Our group in the Colour & Vision Research Laboratories (Andrew Stockman, Chris Dainty, Peter West and Bruce Henning) at the Institute has today been awarded a second, concurrent 3-year, BBSRC project grant (BB/M01858X/1) this time to investigate: "At and beyond the neural limits: visual psychophysics using an adaptive-optics visual stimulator." This grant will enable us to measure visual performance beyond the limits normally imposed by the optical imperfections of the eye. We will design and build a user-friendly, adaptive-optics (AO) visual stimulator that will correct for the optical imperfections and will enable us simultaneously to image the retina at high resolution and to present high-resolution visual stimuli. The optical system will be capable of running at about 120 Hz with a resolution of 1920 x 1080 pixels and with 12-bits of resolution per channel, thus allowing us to generate images with high temporal and spatial resolution, high dynamic range and wide colour gamut over an extended intensity range. Once the device is constructed, we will embark on a series of standard measurements of human visual performance. Rather than trying to measure the response to complex visual scenes, we will measure an observer’s sensitivity to simple spatial patterns made up of periodic patterns of light and dark. These simple “sinusoidal” patterns are the building blocks from which we can predict the responses to any complex stimuli. To fully characterise the vast space of possible visual scenes, the simple sinusoidal patterns will be systematically varied from coarse to fine. For each pattern, we will determine how much contrast the observer needs to just see the pattern. From these measurements, we derive the spatial contrast sensitivity function (or spatial CSF) that defines the visual performance of the human observer. The importance of the AO system is that we can use it to measure spatial contrast sensitivities without the measurements being limited by the optics of the eye. Moreover, we can make those measurements for chromatic stimuli, achromatic stimuli and stimuli detected by single classes of light-sensitive detectors. By using different stimuli, we can investigate different neural pathways in the visual system. As well as going beyond the optical limit, the AO stimulator will also allow us to investigate human vision beyond the usual neural limits of the system. Visual patterns produced by the AO stimulator that are too fine to be seen directly (and are therefore “invisible”) can be seen indirectly due to interactions between pairs of patterns or due to changes in apparent intensity when a pattern is turned on and off. Using these patterns we will be able to investigate the underlying properties of the neurons in the visual system. The indirect detection of these “invisible” patterns allows us to probe the inner working of the pathways answer specific questions about how the retina works.