Weird Science: The complex cues behind 'hangryness'

Becoming "hangry" involves much more than low blood-sugar levels, scientists say. Photo / 123RF

We've all been there: you're spoiling for a spat, but all you really need is a sandwich.

Now scientists have shed a bit more light on what makes us go from being hungry to full-on "hangry".

And it's not just a simple drop in blood sugar, but a complicated emotional response involving an interplay of biology, personality and environmental cues.

"We all know that hunger can sometimes affect our emotions and perceptions of the world around us, but it's only recently that the expression 'hangry', meaning bad-tempered or irritable because of hunger, was accepted by the Oxford Dictionary," said Jennifer MacCormack, a University of North Carolina researcher and lead author of a new study.

"The purpose of our research is to better understand the psychological mechanisms of hunger-induced emotional states - in this case, how someone becomes hangry."

When someone is hungry, there are two key things that determine if that hunger will contribute to negative emotions or not: context and self-awareness.

"You don't just become hungry and start lashing out at the universe," study co-author Assistant Professor Kristen Lindquist said.

"We've all felt hungry, recognised the unpleasantness as hunger, had a sandwich and felt better.

"We find that feeling hangry happens when you feel unpleasantness due to hunger but interpret those feelings as strong emotions about other people or the situation you're in."

The researchers first conducted two online experiments involving more than 400 individuals from the United States.

Depending on the experiment, participants were shown an image designed to induce positive, neutral or negative feelings.

They were then shown an ambiguous image, a Chinese pictograph, and asked to rate the pictograph on a seven-point scale from pleasant to unpleasant. Participants were also asked to report how hungry they felt.

The researchers found the hungrier participants were more likely to rate ambiguous Chinese pictographs as negative, but only after first being primed with a negative image.

There was no effect for neutral or positive images.

"The idea here is that the negative images provided a context for people to interpret their hunger feelings as meaning the pictographs were unpleasant," MacCormack said.

"So there seems to be something special about unpleasant situations that makes people draw on their hunger feelings more than, say, in pleasant or neutral situations."

Furthermore, people who were more aware their hunger was manifesting as an emotion were less likely to become hangry.

"Our bodies play a powerful role in shaping our moment-to-moment experiences, perceptions and behaviours - whether we are hungry versus full, tired versus rested or sick versus healthy," she said.

"This means that it's important to take care of our bodies, to pay attention to those bodily signals and not discount them, because they matter not just for our long-term mental health, but also for the day-to-day quality of our psychological experiences, social relationships and work performance."

What makes us crave junk food?

Scientists believe our past experience with the nutritive properties of carbohydrates releases dopamine in the brain through an as-yet-unknown metabolic signal. Photo / 123RF

In more intriguing science about food and the brain, another new study has pin-pointed just why it is we crave foods that are both fatty and carb-loaded over those that are either.

"The biological process that regulates the association of foods with their nutritional value evolved to carefully define the value of a food so that organisms can make adaptive decisions," Yale University's Dana Small explained.

For example, she said, a mouse should not risk running into the open and exposing itself to a predator if a food provides little energy.

"Surprisingly, foods containing fats and carbohydrates appear to signal their potential caloric loads to the brain via distinct mechanisms."

Participants of a study Small led turned out to be very accurate at estimating calories from fat and very poor at estimating calories from carbohydrate.

"Our study shows that when both nutrients are combined, the brain seems to overestimate the energetic value of the food."

In work that could help explain brain-body mechanisms underlying the genetic predisposition for obesity, eating in the absence of hunger, and difficulty losing or keeping off excess weight, Small and colleagues looked at the neural response to food cues.

Test subjects underwent brain scans while being shown photographs of familiar snacks containing mostly fat, mostly sugar, and a combination of fat and carbs.

Allocated a limited amount of money to bid on their first-choice foods, subjects were willing to pay more for foods that combined fat and carbohydrates.

What's more, the fat-carb combo lit up neural circuits in the reward centre of the brain more than a favourite food, a potentially sweeter or more energy-dense food, or a larger portion size.

Our hunter-gatherer ancestors ate mostly woody plants and animal meat, the researchers noted.

"In nature, foods high in fat and carbohydrate are very rare and tend to have fibre, which slows metabolism," Small said.

"By contrast, it is very common for processed foods to have high fat and high carbohydrate loads."

After the domestication of plants and animals and the development of grain and dairy production about 12,000 years ago, opportunities to consume fat and carbohydrates together increased, but processed foods like doughnuts, which could contain 11g of fat and 17g of carbohydrate, have only been around for 150 years, not long enough for us to evolve a new brain response to them.

Scientists believe our past experience with the nutritive properties of carbohydrates releases dopamine in the brain through an as-yet-unknown metabolic signal.

These kinds of signals seem to help regulate what and how much we eat.

The researchers theorise that the simultaneous activation of fat and carbohydrate signalling pathways launches an effect that human physiology has not evolved to handle.

Consistent with this suggestion, rodents given access to fat alone or carbohydrate alone regulate their total daily caloric intake and body weight.

But given unrestricted access to fat and carbohydrates, they quickly gained weight.

Inside the 'speech to song illusion'

The so-called "speech-to-song illusion" has the potential to greatly increase our fundamental understanding of speech and music perception. Photo / 123RF

The great Laurel-or-Yanny debate of 2018 was so fun because it shined a light on the often-illusory nature of auditory perception.

What you hear may not be the same as what somebody else hears.

Or, perhaps what you hear could change over time.

What surely was "Yanny" to some people at first sounded a lot more like "Laurel" upon their 27th listening.

Now US researchers have explored these ideas further by investigating the "speech-to-song illusion" where a spoken phrase is repeated and begins to sound as if it were being sung.

"There's this neat auditory illusion called the speech-to-song illusion that musicians in the 60s knew about and used to artistic effect - but scientists didn't start investigating it until the 90s," explained Professor Michael Vitevitch, of the University of Kansas.

"The illusion occurs when a spoken phrase is repeated - but after it's repeated several times it begins to sound like it's being sung instead of spoken."

Previous studies have already looked at characteristics of phrases that contribute to the illusion and have elicited the phenomenon in speakers of English, German and Mandarin.

Further studies have shown brain regions that process speech to be active when a phrase is perceived as speech while brain regions that process music fire when the phrase is heard as song.

"But nobody had a good explanation about how this illusion was coming about in the first place," Vitevitch said.

"A lot of the researchers who looked at this were music-perception scientists, but there weren't a lot of people coming at it from the speech-and-language side.

"I'm one of the few speech people that started looking at this. I brought some of these models of how language processing works to see if that might explain what's going on with this illusion."

Vitevitch and colleagues designed six studies to test if a model of language processing known as Node Structure Theory that accounts for other aspects of language processing might also be responsible for the speech-to-song illusion.

Under the theory, word nodes and syllable nodes act as "detectors" when people hear syllables, words and phrases.

"You've got word detectors and syllable detectors and, like with lots of things in life, as you use them they're going to get worn out - like your muscles," he said.

"As you use them, they get tired. Like with muscles, you have a type of muscle for short bursts of sprinting and also muscles for endurance, like running a marathon.

"Word nodes are like sprinting muscles, and syllable nodes are like endurance muscles."

The results of six experiments suggest word detectors initially are activated, giving one the perception of speech, but they fatigue as the phrase is repeated.

The continued presentation of a phrase still activates syllable detectors, which do not fatigue as quickly as the word detectors.

Because syllables carry the rhythmic information of language, the continued stimulation of the syllable detectors - but not the word detectors - shifts perception to a songlike state.

"We tried to test the different parts of the model," he said.

"We looked at the word nodes and singled out phrases that had a lot of similar-sounding words.

"We looked at different characteristics, like is it the word that matters or the number of syllables?"

The team even created random lists of words to prevent the inherent intonation in everyday speech from influencing the subjects' perception of musicality.

"Because we do have intonation, we wanted to have the strongest-possible test of the mechanism of these detectors," Vitevitch said.

"We tried to strip musicality away by randomly putting words together without intonation shifts, so it didn't sound musical at all to begin with.

"When people hear it once, they said it didn't sound musical at all.

"The fact that we could get people to shift perception to something musical after several repetitions gives us confidence that we're on the right track with the mechanism explaining the effect."

While the illusion could be seen as a mere novelty, like the Laurel-or-Yanny meme, Vitevitch said the phenomenon has the potential to greatly increase our fundamental understanding of speech and music perception.

"All scientists are trying to look inside of a black box to understand what's going on inside," he said.

"We're all trying to understand the universe or the brain or how atoms work.

"So, any opportunity to get a crack in the black box where you can look inside, you need to take.

"Things like illusions are often dismissed, but they're unique opportunities to get another angle on what's going on.

"Yes, they're kind of fun and interesting and goofy and they get attention - but really they're another opportunity to see what's going on inside the black box."