The Colour & Vision Research laboratory database originated at the University of California at San Diego in 1995. In 2001, the database and CVRL moved to the Institite of Ophthalmology at University College London, where they continue today.
Our primary research goal is to understand how the human visual system works. Our approach is to use carefully-designed perceptual experiments with which we investigate how changes in the visual stimulus seen by a human observer changes his or her perception of that stimulus. By characterizing the relationship between the visual input (the stimulus) and the visual output (the perception), we can infer the properties of the intervening visual mechanisms that process visual information. For example, if we vary the wavelength of a stimulus and measure how it affects the observer's ability to detect that stimulus, we can estimate the "spectral sensitivity" of the underlying visual mechanisms; or if we vary the temporal and/or spatial frequency of the stimulus, we can determine their temporal and/or spatial contrast sensitivities. In more complex experiments, we can combine visual stimuli detected by different visual mechanisms to characterise how those mechanisms interact. For example, we can choose pairs of visual stimuli one of which is detected only by rods and the other of which is deteced only by cones to investigate how rod and cone systems interact. Many other experimental manipulations are possible.
Much can also be revealed by investigating how perception is altered when the visual system goes wrong—as occurs in clinical cases. By contrasting perception in clinical cases with perception in normal "control" observers, we can learn not only more about the clinical deficits but also more about normal visual processing. Now that many visual deficits have been linked to missing proteins or enzymes, this approach has become more powerful. By comparing perception in observers lacking a particular molecule with that of normal observers, we can characterise the role of that molecule in visual processing.
Through this work, we are developing and refining a model of the early or "low level" stages of the visual pathway. For particular examples of our experimental work, please refer to our publications.
In addition to this low-level work, we investigate higher levels of visual processing and, in particualr, how time-varying signals are encoded at cortical levels. For example, by measuring how signals from different sensory modalities (visual and auditory) interact, we can gain insights into how those signals are processed before their cortical site of interaction.
Several studies are ongoing. One focuses on the changes in colour appearance that can be perceived when lights are flickered. These changes depend strongly on the how fast the flicker is turned on and how fast it is turned off. Such colour changes have led to a new approach of modelling colour vision and colour pathways that considers colour changes as being limited by a “slew” rate (a limiting rate of change of colour). Another study, previously funded by the BBSRC, takes advantage of "non-linearities" within the visual system to analyze and "dissect" the human visual pathway. When an input signal passes through a non-linear site, new signal components are introduced that were absent before the non-linearity. (A slow burst of high-frequency flicker, for example, which has no low-frequency components, will produce a low-frequency signal corresponding to the duration of the burst at the non-linear site.) These new signal components, since they are produced within the visual pathway, can be used to measure separately the properties of the stages of visual pathway before and after the non-linear site. By localizing such nonlinear sites we can reveal how separate stages of the visual system contribute to visual processing. Another continuing study is the characterization of the visual deficits suffered by various types of clinical patients with known genetic defects. Through these characterisations, we can explicitly link the visual loss to the nature of the genetic loss and the underlying molecular mechanism.
Other areas of research include:
UCL Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK