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Does a human being learn to differentiate between its senses at some stage in their development? Is there a time when it, for example, cannot tell if an input is a taste or a visual image?

The question came to me because food may taste different when the sense of smell is impaired, although these are two separate senses with their own receptor organs. Is it possible for other senses to be mixed up in a similar way?

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  • $\begingroup$ Taste is really not a separate sense. Taste receptors on the tongue only react to a few things - sweet, sour, salty, bitter and umami, IIRC. (And possibly chili peppers, though IMHO that probably involves pain receptors :-)) Everything else is really smell. $\endgroup$ – jamesqf Apr 13 '17 at 5:03
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    $\begingroup$ there may be another taste that responds to starches. researchgate.net/publication/… $\endgroup$ – John Apr 13 '17 at 13:12
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Short Answer: Though the concept of development of perception in children is known (Vernon et al, 1961), the process of differentiation between different senses is largely innate, though some disorders related to sensory processing may be acquired during infancy.

Background: The processes involved here are sensory processing and sensory integration. Sensory processing is a process that organizes sensation from one’s own body and the environment, thus making it possible to use the body effectively within the environment (Stein et al, 2009). It deals with how the brain processes multiple sensory modality inputs, like proprioception, vestibular system, auditory system, vision, etc. into usable functional outputs.

The second process is known as sensory integration. Sensory integration is the process through which the brain organizes different sensory informations. In short, it is the organization of different sensations for use by the brain (Ayres et al, 2005). The theory of sensory integration was put forward by Anna Jean Ayres.

As it seems obvious now, sensory integration is an innate process (Cronin et al, 2015). However, sensory integration disorders can be acquired by a child in the early stages of life. This can cause results similar to what you say. For example, according to a 2009 study, every 1 in 6 children has sensory issues which make it difficult for them to process different sensory stimuli. In fact, some symptoms which are common for children with sensory processing disorders are4:

  • They can’t sit still through a half-hour lesson and disrupt the class.

  • They often seem distracted and don’t pay attention to what teacher is saying.

  • They bump into kids in the lunch line, making them angry.

  • They can’t hold a pencil correctly, so they struggle with handwriting.

  • They get upset when asked to switch from one activity to another.

  • They melt down during assemblies and have to leave the gym.

Such activities are often seen as indications of problems with sensory processing and sensory integration i.e. they cannot differentiate between different senses or have problem organizing these sensory inputs to get meaningful output. However, I didn't find a case study where a person is unable to tell whether the input stimulus is touch or taste. This might be because (mostly) different senses are processed in different areas of the brain (Pirotte et al, 2008).

References:

  1. M. D. Vernon, The development of perception in children, Educational Research 3 (1961), no. 1, 2–11.

  2. Stein BE, Stanford TR, Rowland BA (December 2009). "The neural basis of multisensory integration in the midbrain: its organization and maturation". Hear. Res. 258 (1-2): 4–15. doi:10.1016/j.heares.2009.03.012

  3. Ayres, A. Jean (2005). Sensory integration and the child : understanding hidden sensory challenges (25th anniversary ed., rev. and updated / by Pediatric Therapy Network ; photographs by Shay McAtee. ed.). Los Angeles, CA: WPS. ISBN 978-087424-437-3.

  4. A. Cronin and M.B. Mandich, Human development and performance throughout the lifespan, Cengage Learning, 2015.

  5. How Sensory Processing Issues Affect Kids in School - Child Mind Institute

  6. Pirotte B, Voordecker P, Neugroschl C, et al. (June 2008). "Combination of functional magnetic resonance imaging-guided neuronavigation and intraoperative cortical brain mapping improves targeting of motor cortex stimulation in neuropathic pain". Neurosurgery. 62 (6 Suppl 3): 941–56. doi:10.1227/01.neu.0000333762.38500.ac

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Mixing up input from different senses is actually a known neurological phenomenon called synesthesia. Synesthetes (ie. adults experiencing synesthesia) might see numbers in colors for example. Some may even "taste" colors as you say.

Now do all infants have synesthesia before some stage in development is another question. It is actually a rather old hypothesis called "neonatal synesthesia". One piece of evidence comes from this study which tested shape/color association in infants. I do not see any other study concerning this hypothesis though. I guess the main reason might be the difficulty to develop an objective experimental design on small infants who hardly communicate...

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  • $\begingroup$ Nice answer, +1! According to Wikipedia, synesthesia is a neurological phenomenon in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway. which is IMO different from mixing up of two different sensory stimuli. $\endgroup$ – another 'Homo sapien' Apr 13 '17 at 10:38
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    $\begingroup$ Thanks. That's true. I was meaning that signals "mix up" in the brain and stimulate two senses when it should only stimulate one. But that's not clear you're right. $\endgroup$ – francoiskroll Apr 13 '17 at 10:53
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    $\begingroup$ Indeed the signals do not "mix up". As per one theory, when a stimulus activates a specific brain area, another area gets cross-activated by the first receiving area of brain. According to ideasthesia theory, synesthesia is fundamentally a semantic phenomenon. Don't misinterpret this, I just wanted to clarify it (all points from wikipedia). $\endgroup$ – another 'Homo sapien' Apr 13 '17 at 12:20
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    $\begingroup$ To me, this would suggest that senses are not "learned", but are automatic and controlled by the brain. You can't, for example, choose not to feel something, there has to be a problem with the wiring in your body. This would suggest to me that a human can't mix up its sensory inputs through lack of learning on a basic level. $\endgroup$ – SGR Apr 13 '17 at 12:48
  • $\begingroup$ @another'Homosapien' I was saying that based on your answer I feel my response to OPs question would be that human's don't "learn" to distinguish their senses, the brain does it for them. Humans may have to learn what the feelings mean, but the feels themselves aren't confused naturally. $\endgroup$ – SGR Apr 13 '17 at 13:05

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