1. The primary visual cortex also receives auditory inputs.
One defining characteristic of the brain is that it integrates information from different sources and modalities in order to give us a unitary perception of the world. For example, when you’re watching a movie, you don’t process the images and the voices separately. Instead, your brain somehow matches the voices to the characters and processes everything together to give you a nice story. This is an example of multisensory integration, in this case the two senses being auditory and visual.
But the question that has been puzzling scientists for a while is: where is this information put together in the brain? (We know this has to be in the brain, because we’ve already settled on the fact that eyes can’t perceive sounds or ears images.) There are a few reasons to care about that. For one, understanding how the brain integrates information brings us a bit closer to solving the big mystery of how the brain works. Plus, quite a few neuropsychiatric disorders, such as schizophrenia, ADHD, or autism include sensory processing issues.
Up until relatively recently, scientists believed that low-level areas, such as the primary visual cortex, are unisensory, while higher-order areas are multisensory. But with advances in neuronal tracing techniques, this view has begun to shift. In particular, neuronal tracing studies conducted in monkeys have proven that there are direct connections from the primary auditory to the primary visual cortex.
In humans, non-invasive methods, such as EEG and fMRI, point in the same direction, i.e. that the primary visual cortex receives auditory inputs. While more work needs to be done to better understand the underlying mechanisms, these findings could already provide a good explanation for why humans react faster to visual stimuli paired with sounds compared to those presented alone.
2. A large number of psychology and neuroscience studies cannot be reproduced.
A defining characteristic of science is reproducibility. Basically, if a result is reliable, we should observe it every single time when we perform an experiment under similar conditions. But in recent years more and more papers across various fields have begun to show that this isn’t necessarily the case.
But why is it that so many studies cannot be reproduced? And what steps have scientists begun to take in order to address this problem? As this is a highly complex issue, we’ve dedicated an entire separate blog post to it. In case you’ve missed it, you can read it here.
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Majka, P., Rosa, M. G., Bai, S., Chan, J. M., Huo, B. X., Jermakow, N., … & Mitra, P. P. (2019). Unidirectional monosynaptic connections from auditory areas to the primary visual cortex in the marmoset monkey. Brain Structure and Function, 224(1), 111-131.
Murray, M. M., Thelen, A., Thut, G., Romei, V., Martuzzi, R., & Matusz, P. J. (2015). The multisensory function of primary visual cortex in humans. Neuropsychologia.