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> Backpropagation itself is not biologically plausible because, among other things, real neurons can’t just stop processing the external world and wait for back

> Backpropagation itself is not biologically plausible because, among other things, real neurons can’t just stop processing the external world and wait for backpropagation to begin — if they did, we’d end up with lapses in our vision or hearing. Counterpoint: Our brain works around "lapses in our vision" constantly. See https://en.wikipedia.org/wiki/Chronostasis https://en.wikipedia.org/wiki/Chronostasis or https://en.wikipedia.org/wiki/Blind_spot https://en.wikipedia.org/wiki/Blind_spot. (Not saying that makes backpropagation biologically plausible, but as phrased, their argument is not convincing.)

mjburgess 5y ago
The relevant sense of "stop" is stop /processing/. And the relevant object is the neurone, not the perception. ie., our visual field lags during, eg., a saccade; but all the neurones backing the visual system are still responsive to light. And it isnt that the visual field is blank, nor the eye/neurones unresponsive. The neurones are in constant continuous contact with environmental stimuli -- they don't just stop being causally activate.
- soraki_soladead 5y ago
  Indeed. Neurons don't stop processing during events like saccades. They are hyperpolarized by inhibitory neurons. This suppresses further spikes but it's not a separate mode of operation.
- MauranKilom 5y ago
  > And the relevant object is the neurone, not the perception. The argument given in the article is very much that you would perceive an interruption if your neurons were momentarily doing something else, but you don't, so they don't ("A -> B, not B, therefore not A"). I'm contesting this implication. You merely presented statements equivalent to "neurons don't do that" ("not A"), which misses the point. Or, phrased another way: How do you know that "[neurons] don't just stop being causally activate"? It is not inherently implausible that, at any given time, some neurons in our brain are "on backpropagation maintenance", so to speak. ANNs can be trained just fine with dropout after all (and for ANNs, we intentionally add dropout because it's beneficial!). I have no evidence for this claim (and I don't believe it to be true in the slightest), but "you'd notice a momentary loss of perception" is simply not an argument against it.

mjburgess 5y ago

The relevant sense of "stop" is stop /processing/. And the relevant object is the neurone, not the perception. ie., our visual field lags during, eg., a saccade; but all the neurones backing the visual system are still responsive to light. And it isnt that the visual field is blank, nor the eye/neurones unresponsive. The neurones are in constant continuous contact with environmental stimuli -- they don't just stop being causally activate.

soraki_soladead 5y ago
Indeed. Neurons don't stop processing during events like saccades. They are hyperpolarized by inhibitory neurons. This suppresses further spikes but it's not a separate mode of operation.
MauranKilom 5y ago
> And the relevant object is the neurone, not the perception. The argument given in the article is very much that you would perceive an interruption if your neurons were momentarily doing something else, but you don't, so they don't ("A -> B, not B, therefore not A"). I'm contesting this implication. You merely presented statements equivalent to "neurons don't do that" ("not A"), which misses the point. Or, phrased another way: How do you know that "[neurons] don't just stop being causally activate"? It is not inherently implausible that, at any given time, some neurons in our brain are "on backpropagation maintenance", so to speak. ANNs can be trained just fine with dropout after all (and for ANNs, we intentionally add dropout because it's beneficial!). I have no evidence for this claim (and I don't believe it to be true in the slightest), but "you'd notice a momentary loss of perception" is simply not an argument against it.