Effects of sleep on Remembering to Remember

Prospective memory is a class of memory that is unique in that it involves the future rather than the present or the past. Various examples of prospective memory include remembering to buy a pet monkey, or remembering to break up with your girlfriend or remembering to do that blasted thesis that you have been putting off for the umpteenth time. Hence, some researchers have called it the act of "remembering to remember" (Winograd, 1988). Although prospective memory is quite important for daily functioning and goal fulfilment, research on it has been quite sparse in comparison to other forms of memory. One big question remains: how do we remember to remember? Do we devote some resources to maintain this intention? Or is it maintained without anything being devoted to it?

You know you want it.

One theory of prospective memory suggests that prospective memory can be both effortful and automatic. One way in which prospective memory can be automatic is when cues in our environment alert us to something we have to do. Kvavilashvili and Fisher (2007) has found that individuals often encounter cues related to a goal (eg, seeing a monkey in the magazine, receiving a text message from the girlfriend) and these cues spontaneously remind participants of their goal. Another way in which prospective memory is maintained is through conscious retrieval. Other researchers have also found that prospective memory surprisingly is better after 15 minutes than 3 minutes, one interpretation being that participants consciously retrieve and rehearse the goal prior to and up to the point when they are going to execute it (Hicks, Marsh & Cook, 2005).

One question that arises from these findings is that, what happens when we sleep on something? During sleep it appears that both automatic and effortful mechanisms are absent; we don't consciously retrieve and rehearse goals, and we aren't exposed to cues from the external environment. In such a case we might expect that prospective memory would weaken. However, given that a huge amount of literature has also shown that sleep improves memory, we might expect that sleep would improve prospective memory. These contradictory hypotheses form the basis for Scullin and McDaniel's study, "Remembering to execute a Goal: Sleep on it!" (2010)

The researchers had participants do a series of tasks (too lengthy to cover), while remembering to do a particular action at a particular time ("press the Q key when you see the word table or horse"). In one set of participants, this target came after a short delay (20 minutes) while in the long delay condition, participants were told to come back after 12 hours for another series of experiments and the target came there. The other crucial manipulation was time of day, the experiment for one set of participants was started in the morning, and the other set at night. The study was between groups, so participants were spread out across 4 conditions.

1. Short Morning Delay

2. Short Evening Delay

3. Wake Delay (from morning to night, during which time the participant was awake)

4. Sleep Delay (from night to morning, during which time the participant was sleeping)

What the researchers found was that sleeping improved the ability to remember to do something, as compared to being awake. In some of the tests, the performance was almost as good as if one was tested after 20 minutes. One important possible confound in this experiment was that the sleep and awake conditions also differed not just in amount of sleep but also when the experiment was conducted. The authors eliminated this confound by comparing performance for prospective memory during the day and night after a short delay and found that time of day had little effect.

So the results are inconsistent with the idea that sleep might undermine prospective memory by preventing conscious retrieval or exposure to environmental stimuli. It seems like prospective memory might not rely heavily on these 2 processes, as suggested by some proponents of the theory above. The implication being that if you need to remember to do something, you might as well sleep on it.

But how does sleep improve prospective memory? The authors suggest that sleep increases associative binding and that it amplifies weak goals or links. In this case, it seems like prospective memory might not be very much different from other types of memory. However the authors find that sleep improves prospective memory for only certain types of tasks, thus raising new avenues for research into different kinds of prospective memory and how they are affected by different variables.

One problem which I found in this paper was that the participants were engaging in quite an unnatural prospective memory task, in which case environmental cues present during the awake phase would not help the participant in remembering to do the task. On the other hand, in the real world, such environmental cues would be present and abundant (like seeing your thesis supervisor). So in that sense, the authors can't make the claim that sleeping improves prospective memory more than staying awake and being exposed to constant pictures of monkeys.

Another interesting idea that this paper raises is the implication of sleep on prospective memory in old people. It has been found that prospective memory is one memory that is especially impaired and gets worse with old age (they keep forgetting to get the groceries for instance). Old people also get less sleep, especially sleep of the slow wave kind. Coincidence? :)


Scullin MK, & McDaniel MA (2010). Remembering to execute a goal: sleep on it! Psychological science : a journal of the American Psychological Society / APS, 21 (7), 1028-35 PMID: 20519489

Jealousy, Turning Saints into the Sea?

"Not so long ago jealousy was considered a pointless, archaic institution in need of reform. But like other denials of human nature from the 1960s, this bromide has not aged well. ... The rock musician who wrote 'If you love somebody set them free' also wrote 'Every breath you take, I'll be watching you.'"

- Steven Pinker, on David Buss's The Dangerous Passion


Have you ever felt threatened in the presence of others you perceive to be superior to you? I recall one time when I was a teaching assistant in an introductory psychology course and, in the middle of a discussion about how jealousy is experienced when your partner interacts with someone else who appears to have higher mate value than you, an eager student asked, “Professor, but how do you know if that person has a higher mate value than you?” To which the professor smiled and cheekily said, “Oh, you just know.”

To humour the bemused student, the professor gave some scenarios. If you’re a guy, just imagine this. Some other socially dominant male is talking to your girlfriend or wife, and he’s trying to make her laugh. Worse, she actually laughs along and looks like she’s having a very comfortable and enjoyable time. If you’re a lady, imagine the reverse – your boyfriend or husband has met a younger and physically attractive woman, and now he’s the one trying to make her laugh, and she’s playing along and being very reciprocative. That creeping feeling of alarm bells and jealousy becomes just a tad more resonant.

In the dating and mating game, what exactly are those social cues that get us to be on our guard, to experience inferiority and to feel threatened? Gutierres, Kenrick and Partch (1999), researchers looking at the issue through an evolutionary perspective, explored the oft-cited mating preferences of men for physical attractiveness and women for status and social dominance, and elucidated interesting sex differences in contrast effects.

The researchers gathered data from 91 undergraduate females and 99 undergraduate males and primed the men with either physically attractive men or socially dominant men while, on the other hand, priming the women with either physically attractive women or socially dominant women. Exposure to physically attractive men or women was done by showing participants photographs of people, while exposure to socially dominant men or women was done by getting participants to read a descriptive profile of a person with high dominance.

Interestingly, their study found that men’s self-assessments of desirability were adversely affected by exposure to highly socially dominant men and were relatively unaffected by exposure to physically attractive men. Conversely, women’s self-reports of their mate value were more affected by the physical attractiveness than by the social dominance of the women to whom they were exposed. This demonstrated that humans are sensitive to the selective mate preferences of the opposite gender. If we consistently fail to match up to the quality of our rivals, this can have an effect on how we perceive our own desirability!

More recently, another set of experiments conducted by Maner, Gailliot, Rouby and Miller (2007) also looked at how our state of mind affects the level of attention we give to stimulus objects in our environment.

A total of three studies were done on undergraduate students to explore how this interacts in the scene of human mating. It was found that when participants were primed with feelings of romantic and sexual arousal, a ‘mate-search’ psychological mechanism was activated which resulted in greater attentional adhesion* towards attractive members of the opposite sex. On the contrary, when participants were evoked with feelings of jealousy (imagining a scenario that perhaps closely resembles the one that the professor had painted), a ‘mate-guard’ state of mind was primed which led to greater attentional adhesion to attractive same-sex targets.

So is jealousy simply a manifestation of insecurity? Perhaps the answer is both yes and no. Yes, because it does seem apparent that the mind is designed to experience jealousy when the environment provides feedback on where you stand. If there are many people of the same sex as you in the room who are far more attractive, that’s good reason to feel insecure especially when being evaluated by members of the opposite sex. But jealousy isn’t only just a manifestation of insecurity because it serves an important adaptive function – to alert us to the potential dangers of losing your mate, telling us to be aware of snakes and wolves in the environment, and getting us to turn on our A-game where necessary. As David Buss writes in The Dangerous Passion, jealousy is as necessary as love and sex.

* Attentional adhesion refers to how readily a person tends to a particular stimulus. In most documented cases, this is determined by measuring participants' reaction time taken to respond to stimulus.


Maner JK, Gailliot MT, Rouby DA, & Miller SL (2007). Can't take my eyes off you: Attentional adhesion to mates and rivals. Journal of personality and social psychology, 93 (3), 389-401 PMID: 17723055

Gutierres, S., Kenrick, D., & Partch, J. (1999). Beauty, Dominance, and the Mating Game: Contrast Effects in Self-Assessment Reflect Gender Differences in Mate Selection Personality and Social Psychology Bulletin, 25 (9), 1126-1134 DOI: 10.1177/01461672992512006

Buss, D. M. (2000). The Dangerous Passion: Why Jealousy Is As Necessary As Love and Sex. New York: Free Press.

Racial Differences in the Concept of Beauty

Are average composite faces the most attractive faces or are highly attractive faces markedly different from average faces? Rhee & Lee (2010) agrees with Perrett & Yoshikawa (1994) that the most attractive face is actually the average of attractive faces and that an average face; while attractive, is not the most attractive.

They also argue that previous concepts of beauty such as the divine proportion (golden ratio) are not a good measure of beauty across different races and should not be used as an overarching universal indicator of beauty. Between different races, there appears to be different characteristics that are deemed beautiful. They merged some of the most attractive female faces of African, Caucasian, Chinese and Japanese people respectively, to create the images below.

They also mentioned some of the defining characteristics of beauty for the different races.

• African: Narrow nose, smaller and more acute eyes, smaller upper lip, slender chin compared to the average African face.
• Caucasian: Somewhat masculine, narrow palpebral (eyelids) height, angulated and squared mandible (lower jaw), protruding cheek and fuller lips compared to the average Caucasian face.
• Chinese: Narrow cheek, slim and thin face, lantern jaw.
• Japanese: relatively longer face, slightly slanted eyes, sharp chin and chubby cheeks.
  

Unfortunately, they did not conduct any experimental study to compare attractiveness ratings of such faces versus other faces that are considered beautiful based on traditional morphometrics. It would also have been interesting to look at how the male composite faces would look like. 

Rhee SC, & Lee SH (2010). Attractive Composite Faces of Different Races. Aesthetic plastic surgery PMID: 20953953

Perrett DI, May KA, & Yoshikawa S (1994). Facial shape and judgements of female attractiveness. Nature, 368 (6468), 239-42 PMID: 8145822

The link between coffee and acute ischemic stroke onset

Do you drink coffee on a regular basis? I do. And what does drinking coffee have to do with acute ischemic stroke (caused by disruption of blood supply to part of the brain)? In a study published in Neurology, Mostofsky and colleagues investigated the relationship between drinking caffeinated coffee and the risk of acute ischemic stroke in the next hour.

Using a case-crossover design, each subject served as his/her own control. All the subjects were patients with a confirmed diagnosis of ischemic stroke. Coffee consumption information one hour before the onset of stroke symptoms was compared with their frequency of coffee consumption in the previous year.

They found that drinking coffee doubles your risk of ischemic stroke onset in the next hour compared to drinking other caffeinated drinks such as tea or cola; which may be due to lower concentrations of caffeine in those drinks.

When they looked at the frequency of caffeinated coffee intake in the previous week, they found that only people who were drinking ≤1 cup of coffee per day had increased risk for ischemic stroke in the following hour.

The take-home message?

• Drinking coffee temporarily increases one’s risk of ischemic stroke – especially so for infrequent drinkers (≤1 cup of coffee per day).

Well, I don’t think I’m willing to forsake my coffee just yet so I’m going to have 2 cups a day instead of my usual 1 a day.


Mostofsky E, Schlaug G, Mukamal KJ, Rosamond WD, & Mittleman MA (2010). Coffee and acute ischemic stroke onset: The Stroke Onset Study. Neurology PMID: 20881275

What the Presence of Attractive Young Women can do to Men

Much has been said about the female preference for resources and the male preference for physical attractiveness, but at the time of James R. Roney's (2003) writing little had been done to tease out cognitive mechanisms that underlie this adaptive preference.

Roney thus set out to ascertain the ability of ecological cues to prime and activate psychological constructs related to mate attraction and establish linkages between human mating and social cognition.

In his first study, participants - young students from the 10th and 12th grades of a Midwestern high school - were made to answer three large booklets of surveys. However, the manipulation of the environment within which the surveys were answered was as follows: in the first condition, all participants were male; in the second condition, all participants were female; in the last condition, males and females were present during the study. Without knowing what the experimenter was up to, participants answered questions in the surveys, and nested in those surveys were questions related to one's attitudes towards wealth and resources.

The results fascinatingly appear to support evolutionary theories about human mating. Male students in the mixed-sex environment reported higher valuations of material wealth than did male students in the same-sex environment.


The young men in the mixed-sex condition also reported higher ratings of having an active dating life. These findings suggest that the presence of females may have primed implicit mate attraction goals and, subsequently, the activation of cognitive attitudes associated with mating objectives (detailed manipulation checks were conducted via cleverly placed questions on items such as current relationship status and mate preferences, reducing the possibility of confounding variables).

Now that the first experiment appears to be consistent with evolutionary theory predictions, Roney sought to find out if other mating goal-related attributes in men can be primed. In his second study, male participants were exposed to advertisements featuring either younger female models or older female models, after which they filled out a questionnaire.

The results again confirm evolutionary theory hypotheses - men in the younger models condition reported higher valuations of wealth (replicating the findings of the first study), had a greater desire to display/showcase talent and, interestingly, listed self-descriptive traits that increase men's odds of attracting women (this was confirmed through separate ratings of the male participants' self-descriptive traits by women), such as ambitiousness and aggressiveness.

Roney's study thus brings evolutionary psychology one step further by utilizing ecologically realistic stimuli, in the process demonstrating powerful but previously unknown psychological effects. Specific to this study, visual exposure to young women caused significant changes in the attitudes and personality trait descriptions of the young male participants. In particular, young men who were exposed to young women reported far more favourable attitudes towards material wealth than did men exposed to either other men or older women.

This makes sense because if securing a mate was an important task in ensuring the survival of one's lineage (without which those of us alive today wouldn't be here), then there should be psychological mechanisms present to facilitate the achievement of such goals, and men should thus be sensitive to cues that relate to both potential mates and resources. Using an adaptive basis for understanding psychology can also prove useful, because without this evolutionary context of mating, such stable behavioural changes demonstrated in Roney's study can, at best, only appear random and lead to invalid conclusions.


Roney, J. (2003). Effects of Visual Exposure to the Opposite Sex: Cognitive Aspects of Mate Attraction in Human Males Personality and Social Psychology Bulletin, 29 (3), 393-404 DOI: 10.1177/0146167202250221

Is eating 6 meals a day instead of 3 a better weight loss strategy?

I’ve come across a significant number of non-peer reviewed articles on the internet about weight loss, body building etc. that advocates eating 6 meals a day (just Google "3 meals or 6 meals" to see what I mean). Reasons given for doing so includes less fluctuation in blood glucose and lower fat storage among others. But is eating 6 meals instead of 3 a day really beneficial for someone trying to cut some flab? Some researchers think not.

In an article published in Obesity, Leidy and colleagues (2010) investigated how differing amount of dietary protein and eating frequency influences our perceived appetite and satiety levels during weight loss. 

In a 12 week experiment, 27 obese men were randomized into either the high protein or normal protein group and were required to engaged in a weight-loss diet that is 750kcal/day lower than their daily needs. Beginning on the 7^th week, all participants alternated between 3 meals a day or 6 meals a day, each lasting for 3 days. Information on their perception of daily hunger, desire to eat and thinking about food were recorded and compared.

Results

• The high protein group felt fuller, had lower desire to snack at night and thought less about food than the normal protein group.
• Eating 3 or 6 meals a day did not have any effect on hunger, fullness, desire to eat nor preoccupation with thoughts of food.

The take-home message? Getting on a high protein diet appears to be a viable weight loss strategy because it gives you better control over your appetite and satiety but switching to a 6 meals a day strategy appears not to be helpful in these areas.

Furthermore, some previous studies have found a relationship between higher meal frequency and higher colon cancer risk (eg. Shoff et al, 2000 (for women), Wei et al. 2004(for men)). So I were you, I'll think twice about adopting that 6 meals a day plan too readily. 

Leidy HJ, Tang M, Armstrong CL, Martin CB, & Campbell WW (2010). The Effects of Consuming Frequent, Higher Protein Meals on Appetite and Satiety During Weight Loss in Overweight/Obese Men. Obesity (Silver Spring, Md.) PMID: 20847729
Wei, J., Connelly, A., Satia, J., Martin, C., & Sandler, R. (2004). Eating Frequency and Colon Cancer Risk Nutrition and Cancer, 50 (1), 16-22 DOI: 10.1207/s15327914nc5001_3
Shoff, S., Newcomb, P., & Longnecker, M. (1997). Frequency of eating and risk of colorectal cancer in women Nutrition and Cancer, 27 (1), 22-25 DOI: 10.1080/01635589709514496
 

Spicy food and collectivism: How the brain shapes culture

We are used to thinking of culture as a social factor and not a biological factor. We attribute dispositions such as being individualistic or being collectivist to the country that one was brought up in, but no one has really looked into why certain cultures tend to be that way. An emerging field of research called cultural neuroscience says that cultural values can be shaped by the brain and genes.


For example, in one striking example I read about quite recently, one hypothesis put forth for the reason why Asian people like spicy food was because spices conferred natural bacteria killing properties that was especially important in a humid climate where food went bad. Over time, the hypothesis goes, people who liked spicy food more and ate more spicy food were less prone to stomach diseases that killed the others, thus passing on their genes for the next generation. A similar finding was found when examining lactose intolerance. Lactose intolerance is far more prevalent in certain regions of Asia where the rearing of lifestock for milk is less common. In Europe however, up to 95% are able to digest lactose, and this is reflected in their preference for milk products like cream and cheese.


In this review by Way and Lieberman, they sought to answer the question as to why certain cultures tend towards individualism and collectivism. They reason that because of evolution, genes that change brain function and influence the cultural norms we adopt and we institute are selected for between people born in different regions. For people brought up in one region that was say marked by famine, grouping together and helping one another might have brought about greater survival for the people, hence the genes that promote this thinking get passed on. In a separate part of the world, marked by conflict perhaps, survival would favor people who think for themselves and for their immediate family members. Over time, those different selective pressures would have promoted different social behaviors in different regions.


What mechanisms might have promoted these behaviors? They reviewed work from scientists studying the distribution of several genetic alleles. Previous work has shown that variation in the serotonin transporter gene, a very important neurotransmitter associated with emotion and reward, was associated with individual differences in social sensitivity. People with the short version show greater reaction to social events such as death or birth of children, regardless of whether it was positive or negative. When these scientists studied the distribution of these alleles in different cultures, surprise surprise! They found that the short version of this allele was much more prevalent in collectivist cultures than individualist cultures.



*higher score on individualism collectivism scale indicates higher individualism.


The authors hypothesize that since this allele makes people more sensitive to being socially excluded, it promotes individuals to tend and befriend, leading to a cultural trend of being more collectivist. There's more to read about other such alleles in the review, but seeing as to how this post is quite wordy already, I'll stop here :)




Sherman, P., & Billing, J. (1999). Darwinian Gastronomy: Why We Use Spices BioScience, 49 (6) DOI: 10.2307/1313553

Way, B., & Lieberman, M. (2010). Is there a genetic contribution to cultural differences? ... SCAN, 5 (2-3), 203-211 DOI: 10.1093/scan/nsq059