Comments and responses to "Theoretical approaches to lightness and perception".

A common theoretical framework for brightness and lightness perception In a review of the brightness/lightness literature, Kingdom (2011) noted that " Divided into different camps, each with its own preferred stimuli, methodology and theory, the study of LBT [lightness, brightness, transparency] is sometimes more reminiscent of the social sciences with its deep ideological divides than it is of the neurosciences " (page 652). Methodology and theory clearly separate our work from that of Gilchrist as described by Kingdom. The similarity of the underlying problems, however, has led us to investigate the roots of these differences and to propose a framework to bridge the divide and advance the field (Blakeslee & McCourt, 2015). The common question for brightness/lightness research is: how, and under what circum­ stances, is the visual system able to differentiate the physically invariant reflectance of a surface from its potentially changing illumination? The visual system lacks direct access to either quantity, being given only their product which determines the retinal luminance (intensity) distribution. The recovery of surface reflectance and illumination is thus an inverse problem with no algorithmic solution, and observers must therefore employ knowledge or prior assumptions (conscious or unconscious, learned or innate) about these variables to approximate a solution. We propose a framework for brightness/lightness research that resolves many of the confusions that have plagued communication between research groups (for details see Blakeslee & McCourt, 2015). The core ideas of this framework are that: (1) much of the confusion in the brightness/lightness literature stems from groups using different definitions of the central variables (brightness and lightness); (2) the term 'lightness', when defined simply as apparent reflectance, is underspecified with regard to illumination and is often used to refer to three independent and incomparable types of judgments. We discuss the above confusions and the false dichotomy between brightness and lightness research paradigms that they create, in relation to the preceding paper (Gilchrist, 2015). (1) A false divide has been created by how the terms brightness and lightness are used and understood by different research groups The Commission Internationale de l'Ėclairage (CIE, 1970) defines the term brightness as the attribute of a visual sensation according to which a given visual stimulus appears to be more or less intense, or according to which the area in which a visual stimulus is presented appears to emit more or less light (Wyszecki, 1986; Wyszecki & Stiles, 1982). 'Lightness', on the other …