Seminar Series

Summation and Suppression of Luminance Contrast in Early Vision

In the early 1980s research in spatial vision was dominated by the view that the retinal image is processed by a set of independent cortical filter-elements (mechanisms) each tuned to various image properties at specific retinal coordinates. Summation and masking experiments were used to estimate mechanism characteristics, such as size, number and bandwidth. A mask was supposed to probe the detecting mechanism by exciting it, and authors appealed to probability summation to account for low-level summation between them. However, by the 1990s it had become clear that the basic mechanisms were not independent, but were subject to various interactions. I shall describe a series of masking and summation experiments that have investigated these interactions across the following dimensions: orientation, spatial frequency, position, eyes, and colour. These experiments and models show that: (i) our interpretation of previous masking studies is wrong, (ii) spatial summation is more extensive than once thought, (iii) there are multiple routes to suppression, (iv) the relation between probability summation and the slope of the psychometric function is not as straightforward as is often thought. Example papers Probability summation (Meese & Williams, 2001; Meese & Summers, 2007; Meese, Summers & Baker, in prep) Cross-orientation suppression (Meese & Holmes, 2007; Baker, Meese & Summers, 2007) Linear suppression (Meese & Holmes, 2002; Holmes & Meese, 2004; Meese & Challinor, in prep) Binocular summation (Meese, Georgeson & Baker, 2006; Baker, Meese & Georgeson, 2007; Baker & Meese, 2007; Meese, Summers & Baker, in prep) Area summation (Meese, 2004; Meese et al, 2005; Meese & Hess, 2007; Meese & Summers, 2007; Meese, Summers & Baker, in prep) Contextual modulation (Meese & Hess, 2004; Meese et al, 2007)