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We can read:

The visual cortex is located in the occipital lobe of the brain and is primarily responsible for interpreting and processing visual information received from the eyes. The amount of visual information received and processed by the visual cortex is truly massive. Nearly half of the brain is in some way dedicated to vision—either direct communication pathways from the retina of the eyes to the occipital lobe, or to indirect visual processing and visual skills. The visual cortex is divided into six critical areas depending on the structure and function of the area. These are often referred to as V1, V2, V3, V4, V5, and the inferotemporal cortex. The primary visual cortex (V1) is the first stop for visual information in the occipital lobe.

We can read:

The primary auditory cortex is the first region of cerebral cortex to receive auditory input.

Perception of sound is associated with the left posterior superior temporal gyrus (STG). The superior temporal gyrus contains several important structures of the brain, including Brodmann areas 41 and 42, marking the location of the primary auditory cortex, the cortical region responsible for the sensation of basic characteristics of sound such as pitch and rhythm. We know from research in nonhuman primates that the primary auditory cortex can probably be divided further into functionally differentiable subregions.[36][37][38][39][40][41][42] The neurons of the primary auditory cortex can be considered to have receptive fields covering a range of auditory frequencies and have selective responses to harmonic pitches.[43] Neurons integrating information from the two ears have receptive fields covering a particular region of auditory space.

The primary auditory cortex is surrounded by secondary auditory cortex, and interconnects with it. These secondary areas interconnect with further processing areas in the superior temporal gyrus, in the dorsal bank of the superior temporal sulcus, and in the frontal lobe. In humans, connections of these regions with the middle temporal gyrus are probably important for speech perception. The frontotemporal system underlying auditory perception allows us to distinguish sounds as speech, music, or noise.

On top of that it is known that the structure of the neurons in the cortex is the same where ever you look (though the division of the visual system is structure-based as can be read above). The information processing is just different in both (the neurons have different connection strengths).

How do the two processes, though implemented on the same structure, differ from one another? Is the process of hearing more a serial parallel process due to the serial character of sound? How are the connection strengths between neurons involved? Wat makes sound different from vision?

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Visual and auditory senses are processed completely independently, up to a point. Obviously, they rely on different physical quantities (air pressure for sounds, photons for vision), are sensed by different organs (cochlea for sounds, retina for vision). Finally they reach the brain in different areas (mostly, but not exclusively, V1 for vision and A1 for audition). We are pretty sure they are processed completely independently up to this point. Then it becomes less clear.

Psychologically there are known interactions between the visual and auditory senses (the ventriloquist effect or the McGurk effect for examples). Physiologically there are areas that respond to both and demonstrated effects of one modality on the other in most areas, including by the way V1 at least in rodents. Although it is still unclear what these interactions are and whether they exists in all species.

For the rest, these questions are way too broad to be answered without providing a complete lecture on the state of knowledge in the field. But basically because these senses are processed independently at early stages, there is good evidence that they are processed quite differently. But as they obviously interact in the cortex they must be converted into some sort of common framework at some point. This "common framework" is most likely modality-specific (spatial localization, time perception, language etc.) because of the functional specialty of cortical areas.

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  • $\begingroup$ I have another question. Are the visual and auditory regions placed arbitraririly? I mean, the visual region is straight behind the back of your eyes, on the other side of the brain. Does the same hold for the auditory region? +1 by the way! $\endgroup$ Jul 29 at 19:53
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    $\begingroup$ No, V1 is the most posterior area of the brain (so the farthest possible). If you touch the pointy bone at the back of your skull, V1 is right behind it. It's not really "on the other side of the brain". It is contra-lateral to the visual scene (neurons processing the left half of the scene are in the right hemisphere and conversely), but they respond the half of each retina, which are combined in the Lateral geniculate Cortex prior to reaching V1. More or less the same is true for audition: signals from each cochlea are combined in relays prior to reaching the cortex. $\endgroup$ Jul 29 at 20:04
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    $\begingroup$ But there is still some lateralization (though not as marked as in the visual cortex). Decussation (the crossing of nerves) is a general property of the nervous system and holds true for all organs (including your muscles which are controlled by the contra-lateral hemisphere). As for the localization of A1 it is on the superior bank of the temporal sulcus, more or less where your temples are. And their "arbitrary" localization is an accident of evolution, just like decussation. $\endgroup$ Jul 29 at 20:08
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    $\begingroup$ That's a complicated question. Yes it is bilateral but at least in humans, who have language, the left hemisphere (in right-handed subjects) seems to have a much more prominent role. But at this point, and I say that kindly, I can only invite you to take a neuroscience intro class because those are broad and complicated questions, often without a clear answer as yet. $\endgroup$ Jul 29 at 20:14

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