On 2017 May 15, Lydia Maniatis commented:

Below I comment on some serious conceptual and methodological problems with this publication.

1. Observers are asked to decide which of four briefly presented images is the most blurred, in a forced choice task. Why? The authors tell us that "blur perception is an elemental feature of the human visual system" because it drives accommodation and vergence. The problem, of course, is that we don't perceive the blur driving these responses - at least I don't, as I look around me. So the term "blur perception" isn't valid. In fact, the authors are not talking, here, about the retinal stimulation just preceding and producing proper accommodation etc, but, rather, images that, even post-accommodation, lack sharpness due to the manner in which they were produced or designed. They are asking observers for a conscious assessment of the relationship between an image and the objects of which it might be an imperfect projection. They can call this "blur perception," but this is obviously a very different definition than 'the retinal stimulation preceding accommodation and vergence.' So from a theoretical point of view, I submit that at least the first five paragraphs of this article are irrelevant. The definition of blur perception shifts at paragraph 6, which refers to psychophysical studies. (Given the irrelevance of the exposition, we are left, of course, with the question of the theoretical interest of the present measurements).

2. In paragraph 6, to accommodate the second definition of blur perception, we are referred to "the variance discrimination model of blur." This model "assumes that the visual system is attempting to estimate the local variance of the luminance profile of an image from a set of luminance samples. Each of these samples is, however, perturbed by some level of internal noise or intrinsic blur." The reference to "internal noise or intrinsic blur" is to be taken on faith (and is part of the untenable "signal detection" view of perception, see below). At best, the idea has never been tested and it is not clear how it could be tested. It is my suspicion that adherence to forced-choice paradigms in the area of psychophysics implicitly serves the purpose of ensuring that something that can be interpreted as "noise" (i.e. the shots in the dark by observers) will be present in the data. The same goes for the very brief presentations (which are also uncritically an irrationally assumed to tap into "lower levels" of visual processing).

3. "This model well describes the dipper data and is grounded in signal detection theories of sensory discrimination and decision making (Green & Swets, 1966)." Again, signal detection "theories," are not remotely corroborated or conceptually valid. They date from the sixties when perception was crudely analogized to radar operators trying to decide whether a particular blip was a whale or a ship, and judging from the reference provided have apparently not been further developed since. The "model" along with methods amenable to producing data of the right shape in the context of multiple free parameters and post hoc adjustments was simply adopted uncritically. The concept, with its treatment of neurons as "noisy detectors" has been criticized by Teller (1984). I've discussed the problems in various comments, including here: https://pubpeer.com/publications/8B2F3402AFA4F136252567815CB415. The notion is implicitly homuncular, the homunculus observing neural firing rates at various levels of the visual system and assigning them meaning, presumably via other firing rates...

4. Here's how you explain away discrepancies: "Overall, Intrinsic Blur estimates with our dead leaves stimuli were greater than those reported for border blur discrimination (Watson & Ahumada, 2011) or for blur discrimination with fractal patterns (Mather, 1997), suggesting that blur perception with naturalistic stimuli may be mediated by receptive fields with larger space constants (Mather & Smith, 2002)." It's that easy. Note that the term "naturalistic stimuli" is undefined. Many scholarly perception publications include in this category photos of buildings, sidewalks and shrubbery on college campuses. Not to mention that the "dead leaves" stimulus does not look remotely natural, nor would anyone spontaneously relate it to leaves.

On 2017 May 15, Lydia Maniatis commented:

Below I comment on some serious conceptual and methodological problems with this publication.

1. Observers are asked to decide which of four briefly presented images is the most blurred, in a forced choice task. Why? The authors tell us that "blur perception is an elemental feature of the human visual system" because it drives accommodation and vergence. The problem, of course, is that we don't perceive the blur driving these responses - at least I don't, as I look around me. So the term "blur perception" isn't valid. In fact, the authors are not talking, here, about the retinal stimulation just preceding and producing proper accommodation etc, but, rather, images that, even post-accommodation, lack sharpness due to the manner in which they were produced or designed. They are asking observers for a conscious assessment of the relationship between an image and the objects of which it might be an imperfect projection. They can call this "blur perception," but this is obviously a very different definition than 'the retinal stimulation preceding accommodation and vergence.' So from a theoretical point of view, I submit that at least the first five paragraphs of this article are irrelevant. The definition of blur perception shifts at paragraph 6, which refers to psychophysical studies. (Given the irrelevance of the exposition, we are left, of course, with the question of the theoretical interest of the present measurements).

2. In paragraph 6, to accommodate the second definition of blur perception, we are referred to "the variance discrimination model of blur." This model "assumes that the visual system is attempting to estimate the local variance of the luminance profile of an image from a set of luminance samples. Each of these samples is, however, perturbed by some level of internal noise or intrinsic blur." The reference to "internal noise or intrinsic blur" is to be taken on faith (and is part of the untenable "signal detection" view of perception, see below). At best, the idea has never been tested and it is not clear how it could be tested. It is my suspicion that adherence to forced-choice paradigms in the area of psychophysics implicitly serves the purpose of ensuring that something that can be interpreted as "noise" (i.e. the shots in the dark by observers) will be present in the data. The same goes for the very brief presentations (which are also uncritically an irrationally assumed to tap into "lower levels" of visual processing).

3. "This model well describes the dipper data and is grounded in signal detection theories of sensory discrimination and decision making (Green & Swets, 1966)." Again, signal detection "theories," are not remotely corroborated or conceptually valid. They date from the sixties when perception was crudely analogized to radar operators trying to decide whether a particular blip was a whale or a ship, and judging from the reference provided have apparently not been further developed since. The "model" along with methods amenable to producing data of the right shape in the context of multiple free parameters and post hoc adjustments was simply adopted uncritically. The concept, with its treatment of neurons as "noisy detectors" has been criticized by Teller (1984). I've discussed the problems in various comments, including here: https://pubpeer.com/publications/8B2F3402AFA4F136252567815CB415. The notion is implicitly homuncular, the homunculus observing neural firing rates at various levels of the visual system and assigning them meaning, presumably via other firing rates...

4. Here's how you explain away discrepancies: "Overall, Intrinsic Blur estimates with our dead leaves stimuli were greater than those reported for border blur discrimination (Watson & Ahumada, 2011) or for blur discrimination with fractal patterns (Mather, 1997), suggesting that blur perception with naturalistic stimuli may be mediated by receptive fields with larger space constants (Mather & Smith, 2002)." It's that easy. Note that the term "naturalistic stimuli" is undefined. Many scholarly perception publications include in this category photos of buildings, sidewalks and shrubbery on college campuses. Not to mention that the "dead leaves" stimulus does not look remotely natural, nor would anyone spontaneously relate it to leaves.