Cognitive Daily reports nearly every day on fascinating peer-reviewed developments in cognition from the most respected scientists in the field.
Greta Munger is Associate Professor of Psychology at Davidson College whose works include The History of Psychology: Fundamental Questions. Dave Munger is a writer whose works include Researching Online and The Pocket Reader. And yes, he is married to Greta.
We've discussed implicit attitudes on Cognitive Daily before, but never in the context of food. The standard implicit attitude task asks you to identify items belonging to two different categories. Consider the following lists. Use your mouse to click on items which are either pleasant or related to Genetically Modified foods (GM foods). (Clicking won't actually do anything, it's just a way of self-monitoring your progress)
Horrible
Good
Transgenic
Nasty
Crops
Wonderful
dislike
GE livestock
Now with this next list, do the same task, only click on items which are either unpleasant or related to GM foods.
Recent research suggests that one of the reasons that as many as 97 percent of women and 68 percent of men experience food cravings is because of visual representations of food. When we picture food in our minds, our desire for the food increases. So why not just distract the visual system? One research team attempted just that, tempting volunteers with pictures of chocolate, and then distracting them with either a randomly changing visual image or an auditory task. The participants who watched the visual image experienced fewer food cravings.
I've attempted to reproduce the type of display these researchers suggest may distract you from your cravings (click on the image to start the animation).
The original research, however, didn't take into account whether participants were hungry. Perhaps if you're already hungry, the visual distraction won't help.
When I was a kid, school lunches didn't offer choice. I paid $1.10, and I was given four plops of foodlike substance. The entrees had names like "salisbury steak," "lasagne," or "beef stroganoff," but they all tasted about the same. Our "vegetable" was usually overcooked peas or green beans. There was a "starch," like mashed potatoes or a roll, and a dessert -- Jell-O or a cupcake -- typically the only edible item on the tray. If our lunch money wasn't stolen on the way to school, we were at least in theory presented with a balanced meal.
By the time my kids were in school, cafeteria philosophy had changed. Instead of serving up glop that no one ate, kids were given "healthy choices." They had charge accounts (no more stealing lunch money), and could select whatever they wanted to eat from a variety of options. What I don't understand is how the school nutritionists didn't realize that most kids were going to take three Jell-O's, two chocolate milks, and skip everything else. Jim regularly racked up charges of almost $10 a day. Needless to say, it didn't take long before we started resorting to homemade lunches.
I've finally found a study that addresses my concerns about putting children in charge of their own nutrition. A team led by Leonard H. Epstein gave 10- to 12-year-olds "budgets" to buy food in a laboratory setting. Then they varied the price of the foods to see if kids would modify their behavior: If we make junk food more expensive than healthy food, will kids substitute healthier foods?
Taste is a notoriously difficult sense to study. My son Jim can't stand baked potatoes, but I can't get enough of them. I don't like watermelon, but the rest of my family gobbles it up. Even more perplexingly, I do like watermelon candy. With all the individual differences in taste, how can scientists learn anything specific about how the sense works?
The difficulties in taste study are compounded by the fact that taste is intimately associated with the sense of smell. Every kid knows to plug his nose when trying a food he or she doesn't like. Researchers must be constantly aware that differences in taste may also be due to smell. So when they want to answer a question like "how does the texture of a food impact its taste?", they know it will not be a simple matter to explore.
A group of scientists led by David Cook wanted to examine just that question. Initially, the problem seems simple enough: just cook up a bunch of food with different textures but the same amount of flavoring, and see how people perceive the taste. But then the problems come in: how do you vary texture? Will the texturing agents themselves change the food's flavor? What about individual differences between tasters? Do foods with different textures smell different?
The team started by trying two different flavors: sugar and iso-amyl acetate—a banana flavoring. They diluted each flavor in water, and then progressively varied the viscosity of each solution by mixing with three different tasteless thickening agents: guar gum, carageenan, and hydroxypropylmethyl cellulose (HPMC). (Now you know what about half the ingredients listed on your Hostess Twinkie are for!)
First they controlled for smell having taster smell and taste each sample and then place their nostrils on a device that physically measured the concentration of odorant that remained in their breath. In this way, they could determine how much odorant was present while the samples were being consumed, instead of relying on the tasters' perception of smell. They found no systematic difference in odor across the range of samples.
Next, a set of tasters who were trained and had two or more years' experience tasting food tried each sample, cleansing their palate with crackers and water between tastings, and rating them separately for "banana flavor" and "sweetness." As previous research had indicated, perception of flavor decreased as the solutions thickened. But why? Earlier studies had suggested that flavor diminished in proportion to the concentration of the thickening agent. While Cook et al.'s data confirmed this, they obtained different results for each thickener:
As the concentration of thickener increased, the perceived sweetness of solutions thickened with carrageenan decreased less than the other solutions. Perhaps concentration of thickener was not the best way model the impact of a thickener. So the team turned to the model of Jozef Kokini, who in the 1970s and 1980s developed a mathematical representation of how the mouth determines the viscosity of a substance. There's no reason to believe humans have detectors for carrageenan concentration in their mouths, but we do have nerves that can detect the sensation of touch. Perhaps we approximate viscosity by pressing food against the roof of our mouths with our tongues. Kokini developed a complex mathematical formula to model this method of determining "oral shear stress," or the amount of force it takes us to compress a thick liquid in our mouths. Cook et al. then applied this formula to their solutions and compared it to perceived sweetness:
Now, the results for each thickener follow a nearly identical path. Similar results were obtained for the banana flavoring.
Cook et al. conclude that we not only consider information from our taste buds and sensory organs in our noses, but also the feeling of the food in our mouths to determine flavor. While this research doesn't explain why Jim doesn't like potatoes, it does get us closer to understanding the many processes involved in the sensation of taste.
Cook, D. J., Hollowood, T. A., Linford, R., & Taylor, A. J. (2003). Oral shear stress predicts flavour perception in viscous solutions. Chemical Senses, 28, 11-23.
Baby rats, only 5 days old and still very much reliant on their mothers for food, can be artificially dehydrated by injecting them with a saline hypertonic solution. If a source of water is placed very close to the rat's snout, it will drink. But 21-day-old rats who have just been weaned from their mothers and who readily eat and drink on their own can be injected with the same saline hypertonic and won't drink any more than non-dehydrated rats the same age. The difference is that the older rats still have to decide to drink—the water is available in their cages, but they still must actively seek it in order to consume it. It's the difference between consummatory and appetitive behavior—to have an appetite, we must seek out food and water, not just consume it when it's placed in front of us. By the age of 35 days, rats have learned to drink when dehydrated:
W.G. Hall, H. Moore Arnold, and Keven P. Myers, in a study in Psychological Science, systematically tested rats by injecting half them with the saline hypertonic and removing the water from their cages for 60 minutes. When the water was returned, the dehydrated 21-day-old rats drank at the same rate as non-dehydrated rats their same age. But dehydrated 35-day-olds quickly consumed over four percent of their body weight in water. Clearly, in the two extra weeks following weaning, somehow the 35-day-olds had learned to detect when they were dehydrated. But how? Both 35-day-olds and 21-day-olds readily consume both dry food and water without assistance. Why don't 21-day-olds know when they're thirsty?
Hall and his colleagues suspected that 21-day-olds know to drink water under normal circumstances because their mouths feel dry after eating rat chow. When they are artificially dehydrated, they have no way of knowing they're thirsty, because they've only ever had to use dry mouth as a cue to thirst. They devised a clever experiment to test this theory. They raised rats from the time of weaning to the age of 35 days on a liquid-only diet and repeated their experiment, this time comparing 35-day-old chow-reared and liquid-reared rats. Here are their results:
Now dehydrated 35-day-old rats who had been raised on a liquid-only diet didn't drink significantly more than rats who weren't dehydrated. So the dry mouth associated with eating chow must have been the cue for rats to drink. When they never had that cue, they never learned to drink when they were dehydrated.
Interestingly, if the same rats were dehydrated artificially again after this experiment, they drank as much as the chow-reared rats. It only takes one experience with dehydration for rats to figure out what to do about it.
This study offers additional support for the study we discussed earlier about how amnesia patients don't realize they are full. Clearly building up an appetite involves more than sensing how much food and water is in our bodies—memory also plays a crucial role.
W.G. Hall, H. Moore Arnold, and Kevin P. Myers (2000). The acquisition of an appetite. Psychological Science 11(2), 101-105.
There's been a great deal of research on appetite and satiation, both on animals and humans. For humans, of course, the motivation is often focused on how we can lose weight. Almost everyone believes they would look better if they could just lose a few pounds. Most of the research has focused on the taste of food and the physical sensation of fullness, and the results—as you might have suspected—have been inconclusive.
There is some evidence that if you leave the remnants of a meal around (used candy wrappers, for example), then people will eat less than if the evidence of the food is discarded immediately. A study on a single amnesic patient ("H.M.") mentions that he ate a second full dinner only one minute after finishing the first one.
Inspired by this evidence, a team of researchers led by Paul Rozin suspected that perhaps memory is the key (Paul Rozin and Sara Dow, University of Pennsylvania; Morris Moscovitch, University of Toronto; and Suparna Rajaram, SUNY-Stony Brook, "What Causes Humans to Begin and End a Meal? A Role for Memory for What Has Been Eaten, As Evidenced by a Study of Multiple Meal Eating in Amnesic Patients," Psychological Science, 1998).
The experiment they devised to explore the role of memory was simple. They found two severely amnesic patients who were otherwise normal. "R.H." was an intelligent man who managed to live alone with his condition for 20 years. Yet without reminders, he could not remember any new information for more than about a minute. After over 12 hours with the experimenters, he was unable to recognize them. "B.R." was a man of average intelligence who was hospitalized by his amnesia after it occurred in 1992. Even after spending a year in the hospital, he was completely unfamiliar with its environment, and like R.H., could not remember the experimenters after working with them for many hours.
The experimenters began the session as if they were merely interviewing the patient. Then, without any fanfare, they presented a meal that they knew the patient liked and said "here's lunch." B.R. ate the entire meal and R.H. consumed part of his. After the meal, patients were asked to rate their hunger level on a scale of 1 (extremely full) to 9 (extremely hungry). Ten minutes later, each patient was offered another meal, and each patient proceeded to eat exactly as before. B.R. finally rejected his third meal, but R.H. consumed that as well. There were no differences in R.H.'s hunger ratings for the duration of the experiment, which was repeated on three separate occasions. While B.R., a small man weighing only 120 pounds, did report becoming slightly more full, he did not reject the second meal, and on two occasions he began his third meal before being stopped by the experimenter.
For comparison, the experiment was repeated with two people who were not amnesic. Not surprisingly, both participants reported being completely full after one meal, and rejected offers for a second meal.
The obvious conclusion is that memory of what we've eaten actually accounts for a significant portion of our hunger. Rather than being solely a physical sensation, being "full" is largely a matter of recalling that we've eaten a meal appropriate for the occasion. Rozin et al. point out that most people are very reluctant to eat dinner foods like spaghetti or lamb chops for breakfast. The reason we feel full after meals may be similar: it's what we expect to happen.
One potential objection to the study's conclusion is that the same condition that led to the three patients' amnesia may have also impaired their ability to detect fullness. Rozin and his colleagues reason that this is highly unlikely, because each patient had a different condition, each of which affected slightly different areas of the brain. The only brain area which had suffered damage in all patients was the amygdala, which has been shown in animals not to be related to hunger/satiety.
If hunger and satiety are predominantly social phenomena, then this explains why some of the tricks dieters use are sometimes successful. For example, a common piece of dieting advice is to use small plates to "fool" yourself into believing you've eaten a lot. Given the results of Rozin et al.'s study, it's easy to see why this strategy could work.
Heinz's green ketchup nothwithstanding, we generally like our foods to be predictable colors: milk, white; bananas, yellow; oranges—well, you get the idea. But when foods are the "right" color, do they actually taste any different? We all know that food coloring is tasteless, so what happens when we dye foods different colors?
The results so far have been difficult to pin down. A study in 1960 found that green pear nectar tasted less sweet than colorless pear nectar. A study in 1962 found no such result. A 1982 study revealed red dye made strawberry juice sweeter; a 1989 study found it did not. Studies have found that brown liquids are refreshing, but brown beers are not. Perhaps the impact of color depends on the specific flavor being tested. Perhaps color matters for some people but not others, depending on their likes and dislikes.
It was in this foggy terrain that Debra Zellner of Montclair State and Paula Durlach of Army Research Institute devised a new experiment to see if they could find some order in the chaos of taste/color research ("Effect of Color on Expected and Experienced Refreshment, Intensity, and Liking of Beverages," American Journal of Psychology, 2003). Their experiment presented people with glasses of liquid in eight different colors (clear, red, blue, green, yellow, orange, purple, and brown). Each set of participants tried only one flavor of liquid: lemon, vanilla, or mint. They were asked to rate each drink they sampled on a scale of refreshing—not refreshing, intensity of flavor, and like—dislike. A separate group was told the flavor of the liquids but was not allowed to taste them, and then rated each glass of liquid based on how they thought it would taste.
The large number of different colors and choices helped clear up the picture: the group that didn't taste the drinks had the strongest opinions, but both groups indicated that they did not like the brown mint and lemon drinks, and that they didn't think they would be refreshing. The brown vanilla drink, by contrast, was rated as good tasting. The same people who said the brown mint drink did not taste good believed the clear mint drink was fine—even though each drink contained the same amount of flavoring. This result makes sense, since vanilla extract and vanilla beans are brown, but nothing minty or lemony is. Oddly, green mint drink and yellow lemon drink weren't rated as any better-tasting than other colors.
So, sometimes, especially in the case of brown, color makes a difference. If color does make a difference in how things taste, we tend to prefer colors that are appropriate for the thing we're tasting. I'm still not sure what all this means for the sales of green ketchup, but I'd definitely suggest Heinz not try selling brown ketchup anytime soon!
Wine expert Robert Parker claims to be able to distinguish every wine he has ever tasted—10,000 different wines a year—by taste alone. Winemakers can use their sense of smell to detect slight imbalances early in the wine production process that might lead to a spoiled batch. Meanwhile, novices walk the aisles of the typical wine store in a daze, uncertain of which wine to select and unsure whether paying a premium for a "better" vintage is worth the cost. During the German occupation of France, when winemakers were forced to ship their best wines to Hitler's henchmen in Berlin, they poured thousands of gallons of plonk into fancy bottles, a ruse which went unnoticed until after the war.
True wine experts' superior recognition of the subtle differences between wines over even educated amateurs has often prompted the question perhaps best expressed by The Wizard of Oz's Cowardly Lion: "What do they got that I ain't got?"
Can wine expertise be learned through careful study? Some research suggests that an improved vocabulary to describe different wines (learning how to use terms like bouquet, terroir, and tannin) has helped novices learn to taste the differences. However, other studies have found that an increased tasting vocabulary simply masks weaknesses of the palate. Here's a sampling of what I found on my shelves, which doesn't seem to have helped me much:
If it isn't their superior understanding of wine terminology that helps experts recall the nuances of different wines, then perhaps they simply have superior senses: better noses and taste buds. Another possibility is that experts have superior "semantic memory"— verbal memory of wine terminology associated with a particular sensation. Wendy Parr and David Heatherbell of Lincoln University, and K. Geoffrey White of University of Ontego devised an experiment to determine exactly where the differences between experts and novices lie ("Demystifying Wine Expertise: Olfactory Threshold, Perceptual Skill and Semantic Memory in Expert and Novice Wine Judges," Chemical Senses, 2002 [full text]).
Parr and her colleagues tested 11 wine experts (wine makers, professional wine critics, or wine scientists) and and 11 "novices" (regular wine drinkers with little formal training—typically students with some experience in food science or wine—this group might be considered "intermediate" or even "expert" in some studies. If formal training includes knowing how to open a bottle of wine with a screwdriver and a pair of pliers, then I'd probably be a member of this group).
The first test was simply to determine each participant's odor-detecting ability, using a chemical not found in wine: butanol. Participants sniffed bottles containing tiny traces of the chemical. The proportion of butanol was gradually increased until the participant could reliably distinguish between its odor and that of pure water. On this test, no difference was found between the experts and the novices.
Next, they were asked to identify 11 of 28 possible odor-producing chemicals commonly found in wine, again using just their sense of smell. They were not required to give each compound's chemical name (terms like "ethyl anthranilate," or "5-ethyl-4-methyl-3-hydroxy furanone"), but just the common wine-taster's description of the aroma ("grape-like, foxy" or "caramel, maple"). Again—surprisingly—there was no difference between the expert and novice wine tasters. Each group accurately named each smell only about half the time—so their "semantic memory" appeared to be equal.
Finally, participants were given a set of 22 chemicals (from the original set of 28). They had smelled 11 of them before, but 11 were new, and in each case they were asked whether they had smelled the chemical previously. In this condition, the experts were indeed substantially better than the novices. They were both more accurate at indicating when they had encountered an odor before, and better at detecting a new scent.
Parr et al. suggest that the difference between the experts and novices may be due to the fact that smells are very difficult to describe. Novices may over-rely on linguistic descriptions of odors, which often don't readily correspond to the scents themselves. Experts, with their years of exposure to the aromas of wine, have developed perceptual memories that are able to overcome the deficiencies of language. This distinction might be similar to the way new doctors diagnose illness "by the book," while veterans tend to look at the overall health of the patient to come up with a treatment.
Another way of putting it is that all those verbose descriptions on the backs of wine bottles and in magazines and books may do little to explain the real differences in wines: it's better to simply taste the wines and experience the differences yourself. I'll drink to that!
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Cognitive Daily reports nearly every day on fascinating peer-reviewed developments in cognition from the most respected scientists in the field.
