www.lesswrong.com/posts/xWTSHJASRaLABgHWc/neuroscience-basics-for-lesswrongians
2 corrections found
A big difference, with the sound reaching the right ear first, indicates the sound came from the left.
This sentence reverses the direction of the cue. If a sound reaches the right ear first, that indicates a source on the right, not the left.
Full reasoning
The article is describing interaural time differences (ITDs), which are used to localize sounds horizontally. On this cue, the leading ear indicates the side the sound came from.
Authoritative explanations say that a sound source on the left reaches the left ear before the right ear, and that sounds separated by tiny ITDs are perceived as coming from the side of the leading ear. So if the right ear receives the sound first, the source is on the right, not the left.
This appears to be a simple left/right mistake, but as written it gives readers the opposite relationship from the real one.
2 sources
- Integrating Information from the Two Ears - Neuroscience - NCBI Bookshelf
Psychophysical experiments show that humans can actually detect interaural time differences as small as 10 microseconds; two sounds presented through earphones separated by such small interaural time differences are perceived as arising from the side of the leading ear.
- Interaural Time Difference - Introduction to Sensation and Perception
The first is based on interaural time differences (ITD) and relies on the fact that a sound source on the left will generate sound that will reach the left ear slightly before it reaches the right ear.
For example, in normal mammals, the neurons in the visual cortex are organized into “ocular dominance columns,” but these fail to form if the animal is raised in darkness.
This overstates the role of visual experience. Ocular dominance columns are not present in all mammals, and in primates such as macaques they can still form without visual experience, including after dark rearing.
Full reasoning
This sentence makes two broad claims that are not correct as stated.
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Ocular dominance columns are not a universal feature of “normal mammals.” A review in The Neuroscientist notes that ocular dominance columns are present in some mammalian species but absent in others, including rat, mouse, rabbit, sheep, and goat.
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Dark rearing does not generally make ocular dominance columns “fail to form.” The same review states that ocular dominance columns form without visual experience. Scholarpedia gives the species-specific detail: dark rearing can reduce or abnormalize segregation in kittens, but in monkeys a normal pattern of ocular dominance stripes has been found after rearing in darkness.
So the article's blanket statement is too strong. A more accurate version would be that ocular dominance-column development depends on species and developmental conditions; it is not true in general that these columns fail to form whenever an animal is raised in darkness.
2 sources
- Ocular Dominance Columns: Enigmas and Challenges - PMC
It has been established clearly that they form without visual experience... They were found in the owl monkey, marmoset... ferret, and mink. However, they were absent in the rat, mouse, tree shrew, squirrel, possum, rabbit, sheep, and goat.
- Ocular dominance column - Scholarpedia
Like eye-specific retinogeniculate projections, ocular dominance columns do not require visual experience to form... This does not seem to be true for monkeys where it has been found that a normal pattern of ocular dominance stripes developed in a macaque monkey reared in darkness after birth.