seebs

I spent a few weeks thinking I couldn't taste "sour".

I was discussing food flavors with a friend, and we discovered that my perception of certain foods was not the same as his. For instance, having agreed that lemon juice is "sour", I did not agree that grapefruit juice is "sour". Grapefruit juice, to me, tastes strongly bitter and faintly sweet.

So, we started experimenting. My friend and his wife find standard white vinegar VERY VERY strong. I think it has a bit of a tingle to it.

Mostly, though, most things that I know to be "sour" don't taste at all to me like the part of the taste of lemon that I thought was "sour".

Now... How can I tell whether or not I can detect this flavor? Is what I experience when I describe lemon juice as "sour" even SIMILAR to what other people experience?

I have no idea.

And I don't think there's much we can do to compare the actual experience. We can look at neurons, but we don't have any clear way, yet, of understanding what it is like for the conscious mind to *experience* those sensations.

scigirl

Hmm I'll have to think about this one. Empirically, there should be some "objectivity" to some aspects of sensory perception. For instance, the sweet/salty/bitter/sour/umami (MSG - the 5th taste) are in a sense digital experiences encoded by genes and expressed as specific receptors. But of course - some people have better sensation than others, despite having all the right receptors.

Yeah - it's a tough one. How do you explain to someone who is colorblind what "red" and "green" look like? You can't, really. Yet red and green are definable wavelengths.

This is one reason I still toy with specializing in neurology. What a fascinating field - so many questions, so few answers to date. Even as an atheist, there was something "spiritual" about holding a human brain in my hands during anatomy class. Somehow, in some way, this convoluted mass of neurons and glial cells held someone's beliefs, someone's loves, someone's passions. How??

Of course as a scientist, I think we can get closer to answering these questions. But will we ever truly understand how sensory experiences are coded? I don't think so.

scigirl

seebs

Exactly. You can tell me by analysis that what I am experiencing at a given moment is "the flavor called sour", but there's no way to compare my *experience* to anyone else's.

I wonder about this. I simply can't figure out how we could ever be *sure* that what we measured was what someone *really* experienced.

My favorite thought experiment is to imagine what it would be like to reverse the red/green distinction in your brain, so that suddenly, stop signs appeared a vivid green, and healthy grass were about fire-engine red.

Now... Here's the fun part. How do you know this hasn't already happened?

Daleth

scigirl, Ewww! Just ewww. Doctors! (Well, ok, it doesn't squick me, but it seemed the thing to say.)

On topic, I always wondered this as a kid, and never really grew out of it. I'm glad I'm not the only one. For me it was colors. When I was very young people would point to a color and tell me it was blue, so of course I still identify the color that I saw then as blue. But how do I know that my perception of blue is like anyone else's?

Sour: green apple gobstopper. Yum.

tribalbeeyatch

Qualia anybody? Sounds like a philosophy topic to me.

Daleth

I think qualia is what seebs was asking for... whether science can provide any. If not, it's not philosophy, just a dead end question.

tribalbeeyatch

It seems to me that seebs' question is perhaps a problem of language as much as it is one of biology. The simplest answer is that he and his friend don't share the same concept of the words 'sour' and 'bitter' and so their descriptions of different foods are inharmonious. Perhaps there is a biological explanation for his lack of sour perception, like mutant/absent sour chemoreceptors or CNS dysfunction, but not necessarily. As to whether science can crack the qualia nut, why couldn't it? Cognitive neuroscience is relatively new on the scene and has already made huge strides. Give it time.

[edited to add]
I'm with you on the grapefruit, seebs; it's bitter and sweet, not sour. But I'm not surprised that he would make that mistake; I've spent a lot of time consciously trying to develop my palate, and I'm often shocked by how crude and inaccurate other people's taste perceptions can be -- particularly when it comes to sour/bitter.

seebs

YES!

Well, here's the thing.

To the best of my knowledge, "sour" is just "hydrogen ions".

But, for instance, I think that lemons are VERY sour, but distilled white vinegar is just a bit tangy. Hmm. According to a web site I found, vinegar's pH should be around 2.4-3.4, but lemon juice should be around 2.2, so it should be more-sour... but I get no puckering reaction AT ALL to vinegar.

Anyway, I was always told "sour is what lemons taste like". But obviously, the thing I taste in lemons isn't the thing I taste in vinegar.

Interesting. I wonder if this is a biological distinction. Grapefruit SHOULD be sour; it's acidic.

Do you taste the horrible bitter taste in, e.g., green peppers? Apparently that's biological; only some people have the receptor for it.

seebs

I love green apple stuff, but I would never have identified that flavor as "sour" if I hadn't gotten into a discussion of what flavors are with a friend once.

Baloo

I don't think low pH and 'sour' are causally linked (just correlated in that the most common sour foods happen to be citrus fruits which happen to be acidic). Go to a candy store, by some "tear-jerkers" (or whatever they call tremendously sour candy these days), pop 3 or 4 in your mouth, and then decide if you can sense sourness or not (the mere thought of this makes me pucker). Another interesting test: go to a high school chemistry lab, ask to borrow a couple of litmus strips, drop the sour candy into a glass of water, wait 10 minutes, and test the water for acidity. I'd be interested to see if it was at all acidic...

Finally, a digression: the 2.4 - 3.4 pH of vinegar is less acidic than 2.2 pH of lemons... so if acidity was the source of sourness, the vinegar would be less sour than the lemon.