On 2017 Mar 05, Lydia Maniatis commented:

“The present findings demonstrate that it is difficult to tease apart low-level (e.g., contrast) and midlevel (e.g., transparency) contributions to lightness phenomena in simple displays… Dissociating midlevel transparency explanations from low-level contrast explanations of the crispening effect will always be problematic, as by definition information is processed by “low-level” mechanisms before higher visual processing areas responsible for the midlevel segmentation of surfaces.”

As the above passage indicates, the authors of this article are endorsing the (untenable but common) notion that, within a visual percept, some features are reflections of “low-level” processes, i.e. activities of neurons at anatomical levels nearer to the retinal starting point, while other features are reflections of the activities of “mid-level” neurons, later in the anatomical pathway. Still others, presumably, are reflections of the activities of “high-level” neurons. Thus, when we observe that a grey square on a dark grey background appears lighter than the same grey square on light grey background, this is the result of “low-level” firing patterns, while if we perceive a grey film overlying both squares and backgrounds (an effect we can achieve by simply making certain alterations in the wider configuration, leaving the "target" area untouched), this is a consequence of “mid-level” firing activity. And so on. Relatedly, the story goes, we can effectively observe and analyze neural processes at selected levels by examining selected elements of the percepts to which various stimuli give rise.

These assumptions are not based on any evidence or rational arguments; the arguments, in fact, are all against.

That such a view constitutes a gross and unwarranted oversimplification of an unimaginably complex system whose mechanics, and the relationships between those mechanics and perception, we are not even close to understanding, should be self-evident.

Even if this were not the case, the view is paradoxical. It’s paradoxical for many reasons, but I’ll focus on one here. We know that at any given location in the visual percept – any patch – what is perceived – with respect to any and all features – is contingent on the entire area of stimulation. That is, with respect to the percept, we are not dealing with a process of “and-sum.” This has been demonstrated ad infinitum.

But the invocation of “low-level” processes is simultaneously an invocation of “local” processes. So to say that the color of area “x” in this visual percept is the product of local process “y” is tantamount to saying that for some reason, the normal, organized feedback/feedforward response to the retinal stimulation stopped short at this low-level. But when and how does the system decide when to stop processing at the lower-level? Wouldn't some process higher up, with a global perspective, need to ok this shutting down of the more global process (to be sure, for example, that a more extended view doesn’t imply transparency)? And if so, would we still be justified in attributing the feature to a low-level process?

In addition, the “mid-level segmentation of surfaces” has strong effects on perceived lightness; are these supposed to be added to the “low-level contrast effects” (with the "low-level" info simultaneously underpinning the "mid-level" activity)? A rationale is desperately needed.

Arbitrarily interpreting the visual percept in terms of piecemeal processes for one feature and semi- global processes for another and entirely global processes for a third, and some or all at the same time is not a coherent position.

On 2017 Mar 05, Lydia Maniatis commented:

“The present findings demonstrate that it is difficult to tease apart low-level (e.g., contrast) and midlevel (e.g., transparency) contributions to lightness phenomena in simple displays… Dissociating midlevel transparency explanations from low-level contrast explanations of the crispening effect will always be problematic, as by definition information is processed by “low-level” mechanisms before higher visual processing areas responsible for the midlevel segmentation of surfaces.”

As the above passage indicates, the authors of this article are endorsing the (untenable but common) notion that, within a visual percept, some features are reflections of “low-level” processes, i.e. activities of neurons at anatomical levels nearer to the retinal starting point, while other features are reflections of the activities of “mid-level” neurons, later in the anatomical pathway. Still others, presumably, are reflections of the activities of “high-level” neurons. Thus, when we observe that a grey square on a dark grey background appears lighter than the same grey square on light grey background, this is the result of “low-level” firing patterns, while if we perceive a grey film overlying both squares and backgrounds (an effect we can achieve by simply making certain alterations in the wider configuration, leaving the "target" area untouched), this is a consequence of “mid-level” firing activity. And so on. Relatedly, the story goes, we can effectively observe and analyze neural processes at selected levels by examining selected elements of the percepts to which various stimuli give rise.

These assumptions are not based on any evidence or rational arguments; the arguments, in fact, are all against.

That such a view constitutes a gross and unwarranted oversimplification of an unimaginably complex system whose mechanics, and the relationships between those mechanics and perception, we are not even close to understanding, should be self-evident.

Even if this were not the case, the view is paradoxical. It’s paradoxical for many reasons, but I’ll focus on one here. We know that at any given location in the visual percept – any patch – what is perceived – with respect to any and all features – is contingent on the entire area of stimulation. That is, with respect to the percept, we are not dealing with a process of “and-sum.” This has been demonstrated ad infinitum.

But the invocation of “low-level” processes is simultaneously an invocation of “local” processes. So to say that the color of area “x” in this visual percept is the product of local process “y” is tantamount to saying that for some reason, the normal, organized feedback/feedforward response to the retinal stimulation stopped short at this low-level. But when and how does the system decide when to stop processing at the lower-level? Wouldn't some process higher up, with a global perspective, need to ok this shutting down of the more global process (to be sure, for example, that a more extended view doesn’t imply transparency)? And if so, would we still be justified in attributing the feature to a low-level process?

In addition, the “mid-level segmentation of surfaces” has strong effects on perceived lightness; are these supposed to be added to the “low-level contrast effects” (with the "low-level" info simultaneously underpinning the "mid-level" activity)? A rationale is desperately needed.

Arbitrarily interpreting the visual percept in terms of piecemeal processes for one feature and semi- global processes for another and entirely global processes for a third, and some or all at the same time is not a coherent position.