Expert: Dana Krempels, Ph.D. - 7/6/2008

Question
QUESTION: I understand no human taste receptor work exactly the same,does all the normal human taste receptor work differently among different people? when we taste the same flavour?

Animals have different taste receptor from us, since we are all human, does it mean our taste receptor produce the same taste sensation? Do we have the same kind of taste receptor in our tongue?

Some people might argue that human have different taste different food....but what if we like the same food? do we have the same tastebud? do we taste the same?

If two person like the same flavour....like sweet, do they share the same taste?

Most people like the taste of burger, fries and sweet stuffs, fastfood....does that mean human have the same preference?

and if human have the same preference over certain flavour, do we taste, the same thing?

Beside the level of intensity...Does my "sweet" generally the "sweet"taste by everyone?do we have identical or similar experience when we chew our food in our mouth..like "the feel of food in our mouth"?

The experience of chewy, sticky, crunchy..etc...do we share the same experience?

ANSWER: Dear Rambo,

Unfortunately, your question isn't answerable any more easily than the question "do we all perceive colors the same way?"  Because both color and taste/smell are psychophysical phenomena, the only way to know for sure if you see colors exactly the same way as another person or taste flavors the same way would be to get inside that other person's head.  And that's not possible.

We can make educated guesses.  Humans share a common evolutionary history, and during our evolution our ancestors who found the taste of fats and sugars to be pleasing ate more of these (relatively rare, then) foods than their relatives who didn't find them so appealing, and this may have been an evolutionary advantage if calories were scarce.  It helped our ancestors to survive.

It's still possible that we perceive flavors differently, since each individual has different proteins that comprise our sensory receptors.  And it's also likely that members of the same family (or people who are more closely related, in general) have more similar taste perceptions that those who are not related, since related people will have more similar proteins.  But this isn't certain, and it is impossible to test scientifically.  So all we can do is guess.  

Hope this helps!  Very interesting question.

Dana

---------- FOLLOW-UP ----------

QUESTION: Hi Dana, thanks for previous answer...I still want to ask...

- Basically all human taste show rejection to taste bitter...why is this so? do we perceive the same taste?
- How about other senses like touch, hearing and smell?  Does our receptor work differently?
- How do I prove that we have similar experience in smell?
- Is it possible for sensor to feel the same thing? like size,surface and temperature? is our perception the same?
-Do we perceive the same sound?
-How can I prove that I have the same experience as other?

-Last question, is there any evidence to prove that human perceive different or same experience?

ANSWER: Dear Rambo,

I'll take them one at a time:

- Basically all human taste show rejection to taste bitter...why is this so? do we perceive the same taste?

Actually, some humans actually *enjoy* a slight taste of bitterness.  Too much bitterness is almost always rejected, but a slight tang is often pleasurable to humans.

One reason for this could be that plant compounds containing medicinal or anti-bacterial properties often taste bitter.  Our ancestors who enjoyed that taste (or at least could tolerate it a little bit) may have had an advantage over conspecifics (members of the same species) who didn't, since they were killing possibly harmful bacteria when they ate those plants.  (It's interesting to note that people often are drawn to bitter flavors when they have an upset tummy!)

Too much bitterness, though, could mean that something is highly toxic.  So we pretty much universally are "programmed" to avoid very, very bitter tastes.

- How about other senses like touch, hearing and smell?  Does our receptor work differently?

Probably.  But again, there is no way to scientifically address differences in the perception of psychophysical phenomena (i.e., psychological perceptions elicited by physical factors, such as color, taste, smell, etc.).  We may all see the color "red" differently. But because we all learned to call that sensation "red," we don't indicate that there's a difference among us.  As I said before, the only way to know if there really is a difference would be to get inside the other person's head and look out.  And that's impossible.

Touch, hearing and smell are the same thing.  It is possible that we all experience stimuli slightly differently, but because we learned to name them the same it doesn't matter--and there's no way to know for sure.

- How do I prove that we have similar experience in smell?

You can't.  We do not have the tools to address this scientifically.

- Is it possible for sensor to feel the same thing? like size,surface and temperature? is our perception the same?

The answer here is the same:  It is possible that there is individual variation in perception.  But it is nearly impossible to test this.  We do know that different humans can be more or less sensitive to certain smells, that some smells are pleasant to one individual and noxious to others.  And there is a difference between individuals' capacity to detect subtle differences in color shades (this can be measured with a interference filters that change the wavelength of a stimulus one nanometer at a time, and asking the subject to tell the investigator when s/he can first detect a color change).

But that's about it.  We really cannot get inside each other's heads to know the specifics of *how* different our perception experiences are.

-Do we perceive the same sound?

Same answers as above.  Different people have different *sensitivity* to sounds.  But there is no way to know if we perceive sounds the same way or differently.  Personal preferences for different types of music may be more determined by environment and upbringing than by the wiring of the receptors and the brain.  That would be hard to test, since you'd have to use human subjects raised for the purpose of the experiment!

-How can I prove that I have the same experience as other?

You can't.  Not with the tools we now have.

Hope that helps!

Dana

---------- FOLLOW-UP ----------

QUESTION: Hi, I still some question that is more toward philsophy side

-What is colour? Is colour just a perception of the mind? Do colour really exist? How do colour come about?
-Is there a standard for normal human vision? how do we define "normal human vision"? What is the "normal sense" of taste or colour vision like? How to define it?
-How can I prove that my visual system is working normally like everyone else?
-.How about taste? how can we find out our taste receptor and tastebud is tasting normally?
-How can I prove that my sense of taste is working normally like everyone else? in a scienficially way?

As you say we are NOT ABLE to find out how other people has perceive the world, do you think it is still normal if our sense perceive the world differently? In your opinion, How do we know we are the same?
for instance, we are all human, in what way are we the same? how do we know what is normal? how do we know what are we like?

Basically is our body receptor and sensor work the same?

Answer
Dear Rambo,

My answers are going to start sounding very similar, because the questions you are asking are also very similar.

-What is colour? Is colour just a perception of the mind? Do colour really exist? How do colour come about?

This is far to complicated to explain in a single email.  But essentially, "colors" are the psychological perception we have of a physical phenomenon:  photons of different wavelengths exciting the three different types of color photoreceptors (blue, green, and red cones) in different proportions.  "Color" cannot really be said to exist outside the brain.  And again, we cannot know whether all humans see color the same way.

There are certainly humans with abnormal color vision who lack one or more cone pigments, so they are "blind" to the difference between red and green, between yellow and blue, or they cannot perceive color at all.  But in normal, trichromatic humans, color perception may vary a bit, because the opsin (protein) portion of the receptor pigments vary as much as our DNA does.

-Is there a standard for normal human vision? how do we define "normal human vision"? What is the "normal sense" of taste or colour vision like? How to define it?

We define "normal" as that which is exhibited by the majority of humans.  Most humans have trichromatic color vision (i.e., conferred by three different types of cone photoreceptor).  "20:20" vision is defined as the ability to see clearly at a distance of 20 feet what *most* humans with normal eye anatomy can see at 20 feet.  All such standards are based on averages and the majority.

-How can I prove that my visual system is working normally like everyone else?

An ophthalmologist can run standard tests on you to check your visual acuity and your color perception.  But these measurements will tell you only how you compare to the average human.  There is some variation among individuals that's normal and not a problem.

-.How about taste? how can we find out our taste receptor and tastebud is tasting normally?

Same thing as above.  I've already addressed this.  Taste and smell are essentially very similar senses.

-How can I prove that my sense of taste is working normally like everyone else? in a scienficially way?

A physician may be able to direct you to a specialist who can test your ability to taste and smell various substances.  But again, the results will be as compared to an "average" human.  Some variation is normal.

> do you think it is still normal if our sense perceive the world
> differently?

Yes.

> In your opinion, How do we know we are the same?
> for instance, we are all human, in what way are we the same? how do
> we know what is normal? how do we know what are we like?

We define normal as what is present in the majority of the population. There is some variation among individuals that's to be expected, but as long as our perceptions allow us to communicate with each other clearly enough to share our experiences, then this variation is probably not a disadvantage for anyone.

> Basically is our body receptor and sensor work the same?
 
As same as any members of the same species can be.  Maybe not exactly the same, but close enough for us to be able to communicate about similar experiences.

And that's really about all I can say on this matter.  If you need further information, I'd suggest you check a good library for books on vertebrate vision and sensory systems.  Until you understand a bit more about the anatomy and physiology of these systems, your understanding won't be as clear as it might be once you do learn these things.  

Good luck!

Dana