On 2016 Oct 08, Lydia Maniatis commented:

The authors state in their conclusion that: "At each contrast level, the perceived depth first increases with the magnitude of disparity modulation up to a critical value and then decreases gradually with further increases in the magnitude of disparity modulation. "

As is well-known, perceived depth is largely mediated by stimulus structure. The stimuli used by Chen et al (2016) have a structure that produces a 3D impression. Do the "single-cycle" and the "corrugated" version, produce the same depth impression as forms, i.e. viewed in outline monocularly? Then this would have to be factored in to the conclusions re disparity and contrast. Are the authors claiming that they have controlled for this factor? Then this should be stated. Otherwise, their results can only be said to hold for the particular stimuli they employed, not for perception in general. In this case, there are no principles being investigated here; results have no predictive value; conclusions are purely ad hoc.

The most simple illustration of the role of luminance structure (combined with the principles instantiated in the visual system) is what happens in a completely homogeneous visual field, produced by a flat surface - in other words one with zero contrast. In this case, we perceive a cloudy, 3D space. A small luminance variation on that surface collapses the perceived fog into a flat perceived surface. If we converted that surface into an image that we would refer to as trompe l'oeil, we would have a very strong impression of 3D structure with zero disparity. At low contrast or high contrast, if structure implies depth, we'll see depth, and vice versa.

With respect to subjects, as is very common in psychophysics, there were very few - three here - and one of them was an author. The participation of authors is odd especially in light of the fact that we're told explicitly that the other two subjects were "naive to the purpose of this study." If it's important that the observers be naive, then why is an author a subject; if it's not important, why mention it?

Other points: The authors fail to consider the distinction between luminance contrast and perceived constrast. They modulate the luminance contrast between dots and background. We know that small elements, like thin lines, tend to produce assimilation with the background, i.e. lowers perceived contrast.

The authors mention that previous studies, using various stimuli and conditions, have produced inconsistent results. Despite these studies, we're told, " it is still difficult to infer the effect of luminance contrast effect on perceived depth in a scene..." So the question the authors seem to be asking is "what is the effect of luminance contrast on perceived depth in a scene?" But if the previous studies show anything, it is that conditions matter; so a search for "the effect" seems inappropriate. Picking a set of conditions out of a hat and testing them will only tell us about the luminance contrast effect under those conditions. The set of possible conditions is infinite.

The authors state in their intro that "as shown in signal detection theory (Green & Swets, 1966; Chen & Tyler, 2001), the threshold measurement constituting stereoacuity depends not only on the intensity of the stimulus but also on the internal noise." Neither Green & Swets (1966) nor Chen & Tyler (2001) have shown that there is noise in the visual system, and they have certainly not shown that this putative internal noise is maintained and expressed in the percept. The "internal noise" claim has generated no evidence (it is not even clear what this evidence would look like, including in terms of physiological measurements), and is maintained on the basis of studies employing a narrow set of conditions generating crude datasets whose results are highly overinterpreted.

On 2016 Oct 08, Lydia Maniatis commented:

The authors state in their conclusion that: "At each contrast level, the perceived depth first increases with the magnitude of disparity modulation up to a critical value and then decreases gradually with further increases in the magnitude of disparity modulation. "

As is well-known, perceived depth is largely mediated by stimulus structure. The stimuli used by Chen et al (2016) have a structure that produces a 3D impression. Do the "single-cycle" and the "corrugated" version, produce the same depth impression as forms, i.e. viewed in outline monocularly? Then this would have to be factored in to the conclusions re disparity and contrast. Are the authors claiming that they have controlled for this factor? Then this should be stated. Otherwise, their results can only be said to hold for the particular stimuli they employed, not for perception in general. In this case, there are no principles being investigated here; results have no predictive value; conclusions are purely ad hoc.

The most simple illustration of the role of luminance structure (combined with the principles instantiated in the visual system) is what happens in a completely homogeneous visual field, produced by a flat surface - in other words one with zero contrast. In this case, we perceive a cloudy, 3D space. A small luminance variation on that surface collapses the perceived fog into a flat perceived surface. If we converted that surface into an image that we would refer to as trompe l'oeil, we would have a very strong impression of 3D structure with zero disparity. At low contrast or high contrast, if structure implies depth, we'll see depth, and vice versa.

With respect to subjects, as is very common in psychophysics, there were very few - three here - and one of them was an author. The participation of authors is odd especially in light of the fact that we're told explicitly that the other two subjects were "naive to the purpose of this study." If it's important that the observers be naive, then why is an author a subject; if it's not important, why mention it?

Other points: The authors fail to consider the distinction between luminance contrast and perceived constrast. They modulate the luminance contrast between dots and background. We know that small elements, like thin lines, tend to produce assimilation with the background, i.e. lowers perceived contrast.

The authors mention that previous studies, using various stimuli and conditions, have produced inconsistent results. Despite these studies, we're told, " it is still difficult to infer the effect of luminance contrast effect on perceived depth in a scene..." So the question the authors seem to be asking is "what is the effect of luminance contrast on perceived depth in a scene?" But if the previous studies show anything, it is that conditions matter; so a search for "the effect" seems inappropriate. Picking a set of conditions out of a hat and testing them will only tell us about the luminance contrast effect under those conditions. The set of possible conditions is infinite.

The authors state in their intro that "as shown in signal detection theory (Green & Swets, 1966; Chen & Tyler, 2001), the threshold measurement constituting stereoacuity depends not only on the intensity of the stimulus but also on the internal noise." Neither Green & Swets (1966) nor Chen & Tyler (2001) have shown that there is noise in the visual system, and they have certainly not shown that this putative internal noise is maintained and expressed in the percept. The "internal noise" claim has generated no evidence (it is not even clear what this evidence would look like, including in terms of physiological measurements), and is maintained on the basis of studies employing a narrow set of conditions generating crude datasets whose results are highly overinterpreted.