TOWARDS A COMPLETE MODEL OF PHOTOPIC VISUAL THRESHOLD PERFORMANCE

Based on a wide variety of fragmentary evidence taken from psychophysics, neurophysiology and electron microscopy, it has been possible to put together a widely applicable conceptual model of photopic visual threshold performance. Such a model is so complex that a single comprehensive mathematical version is cumbersome. It is, however, possible to set up related mathematical models, each of limited application but strictly known envelope of usage. Such models may be used for assessment of a variety of facets of visual performance when using display imagery, including effects and interactions of image quality, random and discrete display noise, viewing distance, image motion, etc. , both for foveal interrogation tasks and for visual search tasks. The specific model may be selected according to the assessment task in hand. The paper discusses the major facets of pre-perceptual visual processing and their interaction with instrumental image quality and noise. It then highlights the statistical nature of visual performance before going on to consider a number of specific mathematical models of partial visual function. These are compared with widely popular empirical models of visual function.