On 2015 Sep 11, Lydia Maniatis commented:

The authors describe this study as having measured “the effect of context on the mapping between luminance and lightness.” This description unacceptably vague, though not uncommon in lightness research. “Context” is always varied in any experiment in any field, and can mean a million things. Without a clear rationale for the particular choices made, the statement lacks relevant content; but such a rationale is lacking in this study, where the authors justify their choice of stimuli by saying that “we follow in the tradition that uses checkerboard scenes as a model system for studying perceived lightness...” This may not be the best tradition to follow; very poor use of it is made here.

The authors apparently didn't exploit their own visual system to assess the effects of their stimuli, which clearly produce illumination/transparency/luminosity effects of varying ambiguity. When, therefore, in the introduction to their study, they state that their stimuli “are missing the geometric factors that, in natural scenes, are associated with a strong impression of different fields of illumination...” and that their study allows them to investigate “the extent to which photometric manipulation in the absence of such geometric cues affects perceived lightness,” it is unclear whether they mean to imply that the themselves effects are absent, or only that known cues are absent. Since the effects are obviously present, and since they are necessarily contingent on the surface luminance structure – the geometry – of the stimuli, the latter do, in fact, contain unanalyzed “geometric cues” to differential illumination/transparency.

On the basis of an exceptionally crude data-set – observers are asked to rate only the central square while the remaining 24 are varied semi-randomly, the authors, after extended and strenuous mathematical engagement with their data, do, indeed, come to the conclusion that “... observers' lightness matches are consistent with the visual system treating the photometric variation in checkerboard context as spatial variation in the illumination." This was probably the most roundabout way possible to come to a self-evident conclusion (though it should be noted that the apparent illumination changes in their stimuli are not limited to the groups of squares the investigators lightened or darkened as a block – the stimuli are also full of accidental effects.)

In general, the results are “broadly consistent” with what was already known. Where they are supposed to be “novel,” they are so only if scission is treated as not occurring: “Other features of our data are novel. First is the manner in which the shape of the CTFs varies with context. Early proposals about how context affects lightness focused on the notion that lightness is computed via a ratio to some reference luminance (Land, 1986; Wallach, 1948, see Brainard & Wandell, 1986) or as a fixed function of contrast. These models predict that the CTFs will plot as lines of slope 1 in the type of log–log representation we employ and are clearly contradicted by the data.” Obviously, a simple or even not so simple ratio rule or contrast concept is a straw man given the self-evident and semi-acknowledged scission effects. Perhaps this is the reason for the implausible hedging on the question of whether these illumination/transparency effects did, in fact, arise: “However, inferences about how the visual system parsed the stimuli into separately illuminated regions must remain speculative, since our stimuli were not constructed as simulations of illuminated surfaces nor did we measure either the observers' estimates of the illumination or the perceived lightness at locations in the checkerboard context other than the central target patch.” It is very difficult to see what was the point of all this trouble, except to obscure the obvious.

A blind eye is also turned toward luminosity effects. Radonjic et al (2011) had unconvincingly explained away the perception of luminosity in high range stimuli by attributing it to the use of an emissive display, without, however, explaining why the same did not occur for targets of similar luminance in low-range displays. In the present study, the problem of potential luminosity is dealt with by discounting very high reports because they “did not correspond to a palette paper.” Thus, the data are not allowed to show luminosity effects.

It would have been interesting and worthwhile if the authors had made better use of the checkerboard tradition and attempted to analyze the why scission effects occur in stimuli without penumbras or apparent overlap of figural boundaries.

On 2015 Sep 10, Lydia Maniatis commented:

None

On 2015 Sep 10, Lydia Maniatis commented:

None

On 2015 Sep 11, Lydia Maniatis commented:

The authors describe this study as having measured “the effect of context on the mapping between luminance and lightness.” This description unacceptably vague, though not uncommon in lightness research. “Context” is always varied in any experiment in any field, and can mean a million things. Without a clear rationale for the particular choices made, the statement lacks relevant content; but such a rationale is lacking in this study, where the authors justify their choice of stimuli by saying that “we follow in the tradition that uses checkerboard scenes as a model system for studying perceived lightness...” This may not be the best tradition to follow; very poor use of it is made here.

The authors apparently didn't exploit their own visual system to assess the effects of their stimuli, which clearly produce illumination/transparency/luminosity effects of varying ambiguity. When, therefore, in the introduction to their study, they state that their stimuli “are missing the geometric factors that, in natural scenes, are associated with a strong impression of different fields of illumination...” and that their study allows them to investigate “the extent to which photometric manipulation in the absence of such geometric cues affects perceived lightness,” it is unclear whether they mean to imply that the themselves effects are absent, or only that known cues are absent. Since the effects are obviously present, and since they are necessarily contingent on the surface luminance structure – the geometry – of the stimuli, the latter do, in fact, contain unanalyzed “geometric cues” to differential illumination/transparency.

On the basis of an exceptionally crude data-set – observers are asked to rate only the central square while the remaining 24 are varied semi-randomly, the authors, after extended and strenuous mathematical engagement with their data, do, indeed, come to the conclusion that “... observers' lightness matches are consistent with the visual system treating the photometric variation in checkerboard context as spatial variation in the illumination." This was probably the most roundabout way possible to come to a self-evident conclusion (though it should be noted that the apparent illumination changes in their stimuli are not limited to the groups of squares the investigators lightened or darkened as a block – the stimuli are also full of accidental effects.)

In general, the results are “broadly consistent” with what was already known. Where they are supposed to be “novel,” they are so only if scission is treated as not occurring: “Other features of our data are novel. First is the manner in which the shape of the CTFs varies with context. Early proposals about how context affects lightness focused on the notion that lightness is computed via a ratio to some reference luminance (Land, 1986; Wallach, 1948, see Brainard & Wandell, 1986) or as a fixed function of contrast. These models predict that the CTFs will plot as lines of slope 1 in the type of log–log representation we employ and are clearly contradicted by the data.” Obviously, a simple or even not so simple ratio rule or contrast concept is a straw man given the self-evident and semi-acknowledged scission effects. Perhaps this is the reason for the implausible hedging on the question of whether these illumination/transparency effects did, in fact, arise: “However, inferences about how the visual system parsed the stimuli into separately illuminated regions must remain speculative, since our stimuli were not constructed as simulations of illuminated surfaces nor did we measure either the observers' estimates of the illumination or the perceived lightness at locations in the checkerboard context other than the central target patch.” It is very difficult to see what was the point of all this trouble, except to obscure the obvious.

A blind eye is also turned toward luminosity effects. Radonjic et al (2011) had unconvincingly explained away the perception of luminosity in high range stimuli by attributing it to the use of an emissive display, without, however, explaining why the same did not occur for targets of similar luminance in low-range displays. In the present study, the problem of potential luminosity is dealt with by discounting very high reports because they “did not correspond to a palette paper.” Thus, the data are not allowed to show luminosity effects.

It would have been interesting and worthwhile if the authors had made better use of the checkerboard tradition and attempted to analyze the why scission effects occur in stimuli without penumbras or apparent overlap of figural boundaries.