On 2016 Sep 25, Lydia Maniatis commented:

I would respectfully ask the authors to justify their fundamental assumption, as this is straightforwardly asserted in their opening sentence:

“Visual sensitivity is limited by both the strength of the neural signals, and the noise in the visual nervous system1 (Levi DM, Klein SA, Chen I. 2005).”

I am interested in the reference to “the noise in the visual nervous system.” What is the basis of the claim that “noise in the visual nervous system" affects the percepts generated under the conditions of this study? What is the nature of this noise, where does it occur, and what is the evidence for it?

The single reference provided for the claim doesn’t provide answers as it, too, takes the it for granted. It does provide two other supporting references; but on inspection, these are equally inadequate.

According to Levi et al (2005) :

“It has been recognized for well over a century that visual perception is limited by both the strength of the neural signals, and by the noise in the visual nervous system…The notion that internal noise in the visual system acts like light, even in the absence of a stimulus, i.e., dark light, led Barlow (1957) to formulate a very influential model of visual detection which posits that visual sensitivity is limited “by the difficulty of distinguishing a weak signal from the background of spurious signals, or ‘noise’, which occurs without any light signal at all”. Barlow (1957) quantified the dark noise by determining the amount of actual light that produced the same amount of noise in the eye that is present in the dark, using the now widely used prescription for quantifying the noise, known as the equivalent input noise technique (Pelli, 1990).”

To clarify, Barlow (1957) is suggesting that there are “low levels of intrinsic retinal noise even in complete darkness.” He is interested in absolute thresholds. He states that his results “fit the theoretical predictions for the case of stimuli of short duration and small area (against a background of large area) for a range of background intensities up to about 10 scotopic trohinds [i.e. very, very low intensities].”

Levi, Klein and Chen (2005) however, are not referring to absolute thresholds or to retinal noise. They tell us that Pelli (1990); Pelli (1981) provided a new description of the equivalent input noise as a contrast function.

The theoretical rationale provided by Pelli (1990) is as follows:

Thus [in the case of electronic amplifiers] we can measure [“specify” would be more accurate] the intrinsic noise by finding an equivalent input noise. This is sometimes called 'referring the amplifier's noise to its input'. Essentially the same approach can be applied to vision. Indeed, this is analogous to Barlow's (1957) dark light measurements. By a similar analogy we can apply this idea to the contrast domain.”

More casual assumptions follow as Pelli (1990) elaborates the application of this analogy to the human visual system.

I submit that vague analogies should not be admitted the status of theoretical arguments.

It should be noted that Zomet et al (2016) in no way test the casually adopted and elaborated assumption that I am challenging. They simply interpret data as though it were true; their procedure can’t tell if it’s false. (The claim is, in fact, so vague that it’s not clear how one would go about testing it).

Postscript: The criteria for publication in Scientific Reports are that: "In this journal a paper is not assessed based on its perceived importance, significance or impact, but it is enough to be just scientifically valid." Testable hypotheses, and testing of assumptions prior to applying them as though they were true, is a fundamental criterion of scientific validity, which I believe is absent in the present case.

On 2016 Sep 25, Lydia Maniatis commented:

I would respectfully ask the authors to justify their fundamental assumption, as this is straightforwardly asserted in their opening sentence:

“Visual sensitivity is limited by both the strength of the neural signals, and the noise in the visual nervous system1 (Levi DM, Klein SA, Chen I. 2005).”

I am interested in the reference to “the noise in the visual nervous system.” What is the basis of the claim that “noise in the visual nervous system" affects the percepts generated under the conditions of this study? What is the nature of this noise, where does it occur, and what is the evidence for it?

The single reference provided for the claim doesn’t provide answers as it, too, takes the it for granted. It does provide two other supporting references; but on inspection, these are equally inadequate.

According to Levi et al (2005) :

“It has been recognized for well over a century that visual perception is limited by both the strength of the neural signals, and by the noise in the visual nervous system…The notion that internal noise in the visual system acts like light, even in the absence of a stimulus, i.e., dark light, led Barlow (1957) to formulate a very influential model of visual detection which posits that visual sensitivity is limited “by the difficulty of distinguishing a weak signal from the background of spurious signals, or ‘noise’, which occurs without any light signal at all”. Barlow (1957) quantified the dark noise by determining the amount of actual light that produced the same amount of noise in the eye that is present in the dark, using the now widely used prescription for quantifying the noise, known as the equivalent input noise technique (Pelli, 1990).”

To clarify, Barlow (1957) is suggesting that there are “low levels of intrinsic retinal noise even in complete darkness.” He is interested in absolute thresholds. He states that his results “fit the theoretical predictions for the case of stimuli of short duration and small area (against a background of large area) for a range of background intensities up to about 10 scotopic trohinds [i.e. very, very low intensities].”

Levi, Klein and Chen (2005) however, are not referring to absolute thresholds or to retinal noise. They tell us that Pelli (1990); Pelli (1981) provided a new description of the equivalent input noise as a contrast function.

The theoretical rationale provided by Pelli (1990) is as follows:

Thus [in the case of electronic amplifiers] we can measure [“specify” would be more accurate] the intrinsic noise by finding an equivalent input noise. This is sometimes called 'referring the amplifier's noise to its input'. Essentially the same approach can be applied to vision. Indeed, this is analogous to Barlow's (1957) dark light measurements. By a similar analogy we can apply this idea to the contrast domain.”

More casual assumptions follow as Pelli (1990) elaborates the application of this analogy to the human visual system.

I submit that vague analogies should not be admitted the status of theoretical arguments.

It should be noted that Zomet et al (2016) in no way test the casually adopted and elaborated assumption that I am challenging. They simply interpret data as though it were true; their procedure can’t tell if it’s false. (The claim is, in fact, so vague that it’s not clear how one would go about testing it).

Postscript: The criteria for publication in Scientific Reports are that: "In this journal a paper is not assessed based on its perceived importance, significance or impact, but it is enough to be just scientifically valid." Testable hypotheses, and testing of assumptions prior to applying them as though they were true, is a fundamental criterion of scientific validity, which I believe is absent in the present case.