This week's article focuses on primary research entitled, "Irrational choices in hummingbird foraging behavior" by Melissa Bateson, Susan Healy & Andrew Hurly. This research focuses on hummingbird decisions and preferences between competing choices. This is an important area of research because it gives us insight into how animals think and make decisions, especially in the wild, when foraging for food. The entire research is based on presenting hummingbirds with two choices -- a target and a competitor -- and seeing their preference. The target and competitor were two artificial flower types that differed in the volume of nectar and the sucrose concentration. The two flowers were designed to give an equal rate of energy intake, however. The material used was a Plexiglass plate with 18 wells drilled into it, arranged with flowers. Birds visited the flowers every 10 minutes throughout the day and were allowed to feed from as many wells as they wanted to. The preferences the birds made were calculated based on the final 100 choices they made for each treatment condition. The first choices were discarded, because it took at least 30 flower visits for birds to begin showing preferences. This procedure was followed by presenting three choices - a target, competitor and decoy flower - and seeing how the birds' preferences changed. In the trinary condition (three flowers) the decoy was adjusted to have the lowest rate of energy intake, by a wide margin. This was done because (in human literature) it is known that the effect of the decoy is strongest when the target and competitor are initially similar, and the decoy is noticeably different from the rest.
What I found strange about this study is that in the trinary condition (three flowers) they adjusted the target to have a lower rate of energy intake than the competitor, because they were hoping for the birds to show a preference for the Competitor in the Binary treatment, but switch to preferring the Target in the Trinary treatment. If the energy intake is lower in the target flower, then why would they prefer that one over the competitor in the trinary treatment?
The results showed that in the binary treatment (two flowers), birds chose the Competitor flower significantly more than the Target flower. In the trinary treatment, the birds chose the competitor more than the target, and the target more than the Decoy. The real interesting thing about this, however, is that the choice of Target flower dropped off more in the trinary condition than the drop off for the competitor, meaning that the preference for the Competitor over the Target was higher in the Trinary condition than in the Binary condition, which violates the principle of irrelevant alternatives. This principle states that, by introducing a third choice [X] that is irrelevant to the first choices [A and B], then the preferences for A and B should not be changed. In other words, even though the preferences for A and B may come down (as was seen with the hummingbirds), the ratios and relationships should stay relatively constant. So what they saw in these hummingbirds (as is often seen in humans as well) is that an irrational choice was made because the inclusion of a third, irrelevant variable changed the preferences. The hummingbirds ended up decreasing their preference for the treatment condition more than expected.
One explanation for these results is that the hummingbirds did not use an "absolute currency" to evaluate the options. In other words, the weight in preference they had for each option depended on the circumstance, and they didn't assign an absolute value to each option, regardless of other choices available. What I think was going on here is that since the hummingbirds already weren't that attached to the target flower, they were more likely to make choices of the third option, "just to test it out". But, they were pretty happy with the competitor flower, and so their preference for it hardly declined... they were loyal supporters of that flower. With humans, it has been found that a Decoy actually has the opposite effect, where it increases preference for the Target. The target is defined as the option which dominates the decoy in two dimensions (in this case the target had more volume and concentration than the decoy). The Competitor, on the other hand, had a lot more volume than the Decoy, but slightly less concentration, therefore it dominated the decoy in one dimension. The hummingbirds actually continued preferring this competitor, so maybe they were able to distinguish between concentration and volume, and they preferred volume.
Another explanation is that the Decoy option in this example is most similar to the Target on the volume dimension, and therefore, takes choices disproportionately from the Target option than the Competitor option in the Trinary Treatment. If two options are very similar, then they are more likely to flip-flop between the two, and only show a slight preference for one of the two. This does not fall in-line with the rational choice theory, which is interpreted as wanting more, not less of a good thing. In this case, the hummingbirds are taking less of the good thing (The Target option), in exchange for the Decoy.
As the researchers also admit, further experiments need to be conducted to see what exactly is causing this irrational choice in hummingbird behavior. There is one characteristic of the study that sticks out, that is, the variance in concentration between the three options. In order to adjust for rate of energy intake, the volume of the competitor option is three or four times the target and decoy options, respectively, while having a lower concentration %. Maybe the birds are detecting upon this variance and making choices based solely on the volume characteristic. Another field to investigate is the idea that maybe comparative evaluation may be more efficient than absolute evaluation mechanisms, and would, therefore, be favored by natural selection. Comparative evaluation would be what we saw in this example, birds are making judgments between options and sticking to what they prefer, while decreasing their preference for the other option disproportionately. To investigate these, further information would be needed about the fitness benefits of these choices.
Bateson, Melissa, Susan D. Healy, and T. Andrew Hurly. "Irrational choices in hummingbird foraging behaviour." Animal Behaviour 63.3 (2002): 587-596.
Saturday, November 24, 2012
Thursday, November 22, 2012
Sponger Dolphins in East Bay Australia
There's an interesting topic open for discussion this week about tool-use in Shark Bay bottlenose dolphins. What's interesting about these dolphins, found in the East and West gulfs of Shark Bay in Australia, is that they use marine sponges as a hunting tool to catch fish. The bottlenose dolphins basically wear a sponge on their beak while searching the seafloor for food in deep channels of water. These dolphins, called spongers, are unique in that they pass on the trait through vertical social transmission, from mother-to-daughter or from mother-to-son. Just to clarify, vertical transmission is the passing on of a trait (or disease) from the female of the species to the offspring. Vertical social transmission would mean that the mother is teaching a certain behavior to her offspring and not necessarily passing the trait through genetics or teaching it to other adults. Studies conducted by Kopps and Sherwin (2012) showed that horizontal transmission was not the method of transfer. Horizontal transmission involves the transfer of a trait between members of the same species that are not in a parent-child relationship. Horizontal social transmission was ruled out in this case because members of the same species are not teaching the behavior to each other, but rather mothers are teaching the behaviors to their offspring. Although males learn the trait and use it as well, males do not teach the behavior to their children. As of now, it is not fully understood why male dolphins do not teach the behavior, but it would be interesting to speculate, and this is why I have a blog.
Before speculating on this behavior, let's cover some background knowledge. Tool use is found very infrequently in wildlife (the most famous examples include primates), and this example of sponging is the first example in cetaceans. Cetaceans are the order of mammals including whales, dolphins, and porpoises. As of 2011, 55 dolphins had been documented as spongers in the Eastern Bay, with fewer being found in the Western Bay.
The implications of two articles will be discussed this week, one of which investigates the question of whether the sponger dolphins have a tendency to more closely associate with similar others or not (Mann, Stanton, Patterson, Bienenstock & Singh, 2012). This was mostly observational research being conducted and multiple maps and graphs of interactions between dolphins were formed. The researchers studied a 300 square kilometer area in the eastern gulf of Shark Bay, Australia. Researchers conducted "surveys" which are sightings of dolphins during five minute intervals. A dolphin was identified by marking its body and fins. Association between two dolphins was determined if dolphins were within 10 meters of each other. Researchers also recorded ecological, reproductive and demographic data. The research lasted from 1989 to 2010 with over 14,000 of these surveys taking place. The survey sample included dolphins that were sighted more than 11 times across three or more years.
In most taxa, individuals develop behaviors as part of a group, but it is interesting to see that these spongers actually form a subgroup because of the unique behavior that they undergo. By studying graphs of the sponger vs non-sponger centroids (center of masses), it was found that spongers associated with each other more-so than with non-spongers. On the other hand, since non-spongers outnumber spongers in any given area, there is inevitably going to be overlap and interactions between the two groups, but spongers do exhibit strong homophily. Homophily is the tendency of individuals to associate and bond with similar others. Results showed that spongers were more likely to form a clique and had stronger bonds with spongers than with non-spongers.
A more recent experiment conducted by Kopps and Sherwin (2012) actually implemented a computer model to determine when the cultural trait developed in bottlenose dolphins. The computer model was based on a diploid (having two complete sets of chromosomes, one from mother and father), sexually reproducing dolphin population. This experiment ran studies based on 41 possibly observed spongers. The computer model would run simulations for how many spongers should be expected during given time periods. Knowing that there has been sponging going on for at least 30 years, they tried to figure out how long ago sponging actually emerged. Without going into the complicated details, it was basically concluded that horizontal transmission was not a possibility, based on the number of spongers that were found; vertical transmission was the likely method. Also, they determined that the emergence of sponging should have been sometime around 120-180 years ago, ultimately they decided that ~180 years is a reasonable estimate. This is based on the idea that sponging emerged as a single innovation event (it emerged one time). If the event had emerged twice in separate places, then we should have seen a lot more spongers in the bay. It is always possible that sponging was innovated more than once, but lost in some areas. The model showed that the trait is passed on from a single parent through a vertical transmission. The trait would become stable over time through fitness benefits and learning fidelity. Learning fidelity is supposed to mean that learning is reliable from generation to generation and that virtually all daughters are going to learn the sponging behavior from their mothers. Sponging is not, however, a genetic trait (as defined in the typical Mendelian sense of genes being passed on if they confer a reproductive advantage), because the proportion of spongers would be expected to increase. The proportion of spongers has not ballooned rapidly, as would be expected with a behavior that gives a fitness advantage.
An important finding from the model simulations to keep in mind is that sponging could have been innovated more than once, but lost in some cases. When we think of cultural drift (similar to genetic drift) we realize that traits may be lost over time through random variation and chance. In a real event, this would mean that a mother does not have any female offspring who would learn the behavior and pass it on, and so they reach a dead-end in the lineage with male offspring. With this realistic possibility, it is better explained that the behavior was innovated more than once.
There is still an uncertainty surrounding what causes the males not to teach their children the behavior, while females teach the behavior to both the male and female children. In addition, since the male dolphins usually identify with and interact with their male parent more than the female, males in general have lower rates of tool use than females. If the tool use conferred such a great reproductive advantage, then you would expect the behavior to be taught and used a lot more frequently. Further investigation needs to be conducted in order to deduce the peculiar behavior of male spongers. Is it something genetic that leads them to not teach the behavior? Is there any evidence of males teaching their offspring other behaviors, perhaps foraging without a sponge or other swimming techniques, etc.? It may just be the case that males don't teach their offspring anything, and just leave it up to the females. It is possible that adult female dolphins spend more time with their young, and so they are more likely to teach the behavior before males ever get a chance to. We simply don't know exactly why. The door is left open for investigators to step in and uncover the mystery.
Kopps, Anna M., and William B. Sherwin. "Modeling the emergence and stability of a vertically transmitted
cultural trait in bottlenose dolphins." Animal Behaviour 1.16 (2012): n. pag. Sciencedirect.com.
Web. 22 Nov. 2012. <http://www.sciencedirect.com/science/article/pii/S0000347212003806>.
Mann, Janet, et al. "Social networks reveal cultural behaviour in tool-using dolphins." Nature
Communications 3 (2012): 980.
Before speculating on this behavior, let's cover some background knowledge. Tool use is found very infrequently in wildlife (the most famous examples include primates), and this example of sponging is the first example in cetaceans. Cetaceans are the order of mammals including whales, dolphins, and porpoises. As of 2011, 55 dolphins had been documented as spongers in the Eastern Bay, with fewer being found in the Western Bay.
The implications of two articles will be discussed this week, one of which investigates the question of whether the sponger dolphins have a tendency to more closely associate with similar others or not (Mann, Stanton, Patterson, Bienenstock & Singh, 2012). This was mostly observational research being conducted and multiple maps and graphs of interactions between dolphins were formed. The researchers studied a 300 square kilometer area in the eastern gulf of Shark Bay, Australia. Researchers conducted "surveys" which are sightings of dolphins during five minute intervals. A dolphin was identified by marking its body and fins. Association between two dolphins was determined if dolphins were within 10 meters of each other. Researchers also recorded ecological, reproductive and demographic data. The research lasted from 1989 to 2010 with over 14,000 of these surveys taking place. The survey sample included dolphins that were sighted more than 11 times across three or more years.
In most taxa, individuals develop behaviors as part of a group, but it is interesting to see that these spongers actually form a subgroup because of the unique behavior that they undergo. By studying graphs of the sponger vs non-sponger centroids (center of masses), it was found that spongers associated with each other more-so than with non-spongers. On the other hand, since non-spongers outnumber spongers in any given area, there is inevitably going to be overlap and interactions between the two groups, but spongers do exhibit strong homophily. Homophily is the tendency of individuals to associate and bond with similar others. Results showed that spongers were more likely to form a clique and had stronger bonds with spongers than with non-spongers.
A more recent experiment conducted by Kopps and Sherwin (2012) actually implemented a computer model to determine when the cultural trait developed in bottlenose dolphins. The computer model was based on a diploid (having two complete sets of chromosomes, one from mother and father), sexually reproducing dolphin population. This experiment ran studies based on 41 possibly observed spongers. The computer model would run simulations for how many spongers should be expected during given time periods. Knowing that there has been sponging going on for at least 30 years, they tried to figure out how long ago sponging actually emerged. Without going into the complicated details, it was basically concluded that horizontal transmission was not a possibility, based on the number of spongers that were found; vertical transmission was the likely method. Also, they determined that the emergence of sponging should have been sometime around 120-180 years ago, ultimately they decided that ~180 years is a reasonable estimate. This is based on the idea that sponging emerged as a single innovation event (it emerged one time). If the event had emerged twice in separate places, then we should have seen a lot more spongers in the bay. It is always possible that sponging was innovated more than once, but lost in some areas. The model showed that the trait is passed on from a single parent through a vertical transmission. The trait would become stable over time through fitness benefits and learning fidelity. Learning fidelity is supposed to mean that learning is reliable from generation to generation and that virtually all daughters are going to learn the sponging behavior from their mothers. Sponging is not, however, a genetic trait (as defined in the typical Mendelian sense of genes being passed on if they confer a reproductive advantage), because the proportion of spongers would be expected to increase. The proportion of spongers has not ballooned rapidly, as would be expected with a behavior that gives a fitness advantage.
An important finding from the model simulations to keep in mind is that sponging could have been innovated more than once, but lost in some cases. When we think of cultural drift (similar to genetic drift) we realize that traits may be lost over time through random variation and chance. In a real event, this would mean that a mother does not have any female offspring who would learn the behavior and pass it on, and so they reach a dead-end in the lineage with male offspring. With this realistic possibility, it is better explained that the behavior was innovated more than once.
There is still an uncertainty surrounding what causes the males not to teach their children the behavior, while females teach the behavior to both the male and female children. In addition, since the male dolphins usually identify with and interact with their male parent more than the female, males in general have lower rates of tool use than females. If the tool use conferred such a great reproductive advantage, then you would expect the behavior to be taught and used a lot more frequently. Further investigation needs to be conducted in order to deduce the peculiar behavior of male spongers. Is it something genetic that leads them to not teach the behavior? Is there any evidence of males teaching their offspring other behaviors, perhaps foraging without a sponge or other swimming techniques, etc.? It may just be the case that males don't teach their offspring anything, and just leave it up to the females. It is possible that adult female dolphins spend more time with their young, and so they are more likely to teach the behavior before males ever get a chance to. We simply don't know exactly why. The door is left open for investigators to step in and uncover the mystery.
Kopps, Anna M., and William B. Sherwin. "Modeling the emergence and stability of a vertically transmitted
cultural trait in bottlenose dolphins." Animal Behaviour 1.16 (2012): n. pag. Sciencedirect.com.
Web. 22 Nov. 2012. <http://www.sciencedirect.com/science/article/pii/S0000347212003806>.
Mann, Janet, et al. "Social networks reveal cultural behaviour in tool-using dolphins." Nature
Communications 3 (2012): 980.
Wednesday, November 14, 2012
Social Spatial Working Memory in Rats
This week's blog post is going to focus on an interesting research experiment conducted by Mike Brown (not the ex-Lakers coach) who studied social spatial working memory in rats. In laymen's term, he was studying to see if rats would remember the locations that other rats had visited and foraged, so that they would not revisit those locations after food sources had been exhausted. As a quick introduction, it is important to remember that many animals, including rats, are social creatures that forage in groups. Foraging in groups provides numerous costs and benefits. On the one hand, animals that forage together are usually more successful in finding new sources of food, utilizing those sources, and protecting each other from predators. On the other hand, these animals may be competing with each other for the same resources, thus limiting the total quantity of food that they may have been able to secure had they gone foraging alone. Think of humans, for example, if we are set to roam freely in the forest with a rifle and hunting equipment, I would imagine most people to travel in packs and search for food together. One the one hand, they may be able to combine their navigating abilities and resources in order to search the forest, most efficiently, for food. On the other hand, if they hunt a deer, then they would have to share their prize between the group. No one will go hungry, but everyone will receive a smaller portion (it's like a Democracy). Another interesting idea about foraging strategies is that of the producer-scrounger model. This model makes the claim that animals can be one of two types: producers, who find and procure food, and scroungers, who find other animals that have procured food. The model predicts that animals distribute themselves between these two behaviors, depending on the availability of food in an environment and the number of competitors around. Connecting this to last week's post... success in foraging for food also depends on social learning through observation and imitation. If one species is better able to discover a way of foraging for food and teach their friends and relatives, then they may have more success and eventually fitness in an environment. This also goes to show that long-term memory is at work in food foraging. Michael Brown and his team were interested in working-memory as a participant in foraging.
The basis for this research comes from a previous experiment done with a pole box maze. In this maze, pairs of rats search for sucrose pellets hidden on top of vertical poles. The finding in this study was that during the early trials, rats preferred to visit the poles that the other rat had already visited, or was recently foraging in. In later trials, however, the rats learned that no food was found during a revisit to those locations, so they began to visit new locations. This suggests that rats are learning and that memory is at play, but critics of these results suggested that some form of local enhancement was at play. Reviewing from last week, local enhancement in this situation would mean that the mere presence of a rat next to a pole would draw the attention of the other rat to that location and cause it to start exploring and foraging by that pole. The presence of the other rat, therefore, and not memory, may be controlling behavior.
The first experiment conducted by Mike Brown and his team involves a radial-arm maze. This maze has a central hub and usually eight arms sticking out of it, each approximately 1-m long. A small amount of food, such as sucrose pellets, is placed at the end of each arm. The arms are constructed of PVC tubing, and they are wide enough for the rats to pass each other as they travel through the arms. In a preliminary training, pairs of rats were exposed to the maze and trained to obtain pellets from the end of the maze arms. If both rats entered a maze arm in one trial, then food was taken away the next day (less food was available for them in the central hub as a form of punishment), but if both members of a pair obtained pellets from the food cups at the end of the arm, then pellets were placed again in the food cup the following day. After this training, a free-choice test was conducted. The choice of a maze arm was defined as a rat having all four paws in the maze arm. A pair of rats were placed in the central hub and were allowed to make choices for six minutes. Then, finally a forced-choice test was conducted. Before each trial, four maze arms were randomly chosen to be closed off by putting plastic inserts into the maze arms. The rats were then placed in the central arena and were allowed to enter the other four maze arms (all of which had food pellets in them), until all four accessible maze arms had been chosen by at least one rat. Then, the rats were lifted and the maze arms were rotated... this was done to make sure that the next choices rats made were not done because of the odor cues left behind by rats. Rotating the arms was supposed to eliminate the possibility of odor as an explanation. The rats were then placed back in the central arena and were allowed to make choices again until all four locations, that were not visited prior to rotation, had been visited by at least one rat. This specifies that the location must be visited, even if a previously visited maze arm was in that location.
The results of this first experiment showed that rats made a higher-than-expected proportion of visits to locations not previously visited by their foraging partner, and they made a lower-than-expected number of visits to locations that had been previously visited by the other rat. This is the tendency that we would expect of rats to avoid revisiting locations, because it is quite likely that food would be depleted in that location. This experiment goes to show you that the choices made by one rat in a radial maze affect the choies made later in the trial by a second rat. There may be some local enhancement at play here, however, as there was a tendency for rats to choose to visit the location that had most recently been visited by another rat. In the free-choice trials, the other rat may still have been around near the maze arm that it had most recently visited, and so its presence there could have served as a trigger for the other rat to be interested and want to come check out the area. To control for this, and to control for the possibility of odor cues, they conduct the forced tests, which showed that rats were making choices based on memory, since it was impossible for them to make choices based on the presence of another rat (the rats were lifted from the arena, the maze was rotated and the rats were placed back into the arena to forage). In the forced choice tests, the rats were also more likely to visit locations that had previously not been visited before.
The researchers expanded upon this study with a second experiment with a larger sample size. They conducted a free-choice trial once again, as well as a forced-choice trial, but this time only allowing one of the two rats to make choices. In the forced-choice trial, one rat was allowed to make choices in the maze arms, while the other rat had to watch from a central observation hub. Then, the rat that had been watching was allowed to make choices, in the absence of the other rat. The free-choice test produced very similar results to experiment 1, even with the larger sample size (26 rats). In the observation test trials, since the observing rat was allowed to forage alone after watching, it was not affected by any position effects of a rat nearby. After observing and then foraging, these observing rats still chose to visit those locations that had previously not been visited by the first rat. This shows working memory at play. As rats are observing, they are learning and remembering where they should visit next to find food, and which places they should avoid because food must be depleted from there.
Finally, a third experiment was done to fill in some holes in the results and test new research parameters. The limitation to experiment 2 was that the maze was not rotated, so there is the possibility that the results may have been due to odor cues left behind by the previous rat that had visited. Experiment 3 involved rotating the maze between the first rat's run and the observing rat's run so that avoidance of a previously visited arm of the maze would be due to memory and not due to any odor cues. The main thing manipulated in experiment 3 was the same condition or different condition groups. For the same condition groups, after a stimulus rat went around and visited maze arms, the rat was then removed, and food was added to those arms that had been visited. This makes the study unusual, because normally you would not expect there to be food where a rat had previously visited. For the different condition groups, after a stimulus rat made its rounds through the maze arms, the maze arms that had not been visited were supplied with food. After food was placed in the same or different maze arms, the observer rats were allowed to roam. For observational training I, each pair of rats was randomly assigned to be in the same or different condition. Then, the rats were exposed to a free-choice trial, where they could visit any of the eight maze arms, all of which had food in them. Finally, the same rats were put in Observational Testing II, the rats were all put in the different condition. The same group defied the normal expectation, whereas the different group was expected to have no food where rats had previously visited. The results showed that there was no difference between where rats went in Observational Training I. When the rats finally came to the Observational Training II, evidence of social learning was apparent. Rats that had been in the same condition in observational training I stayed around baseline levels, but rats that were in the different condition visited maze arms that were different from where the stimulus rats had visited. This shows that working memory was taking place and that rats had learned to avoid those locations that were previously visited by rats. Also, since the maze was rotated in this case, any odor cues were ruled out as a cause.
The basis for this research comes from a previous experiment done with a pole box maze. In this maze, pairs of rats search for sucrose pellets hidden on top of vertical poles. The finding in this study was that during the early trials, rats preferred to visit the poles that the other rat had already visited, or was recently foraging in. In later trials, however, the rats learned that no food was found during a revisit to those locations, so they began to visit new locations. This suggests that rats are learning and that memory is at play, but critics of these results suggested that some form of local enhancement was at play. Reviewing from last week, local enhancement in this situation would mean that the mere presence of a rat next to a pole would draw the attention of the other rat to that location and cause it to start exploring and foraging by that pole. The presence of the other rat, therefore, and not memory, may be controlling behavior.
The first experiment conducted by Mike Brown and his team involves a radial-arm maze. This maze has a central hub and usually eight arms sticking out of it, each approximately 1-m long. A small amount of food, such as sucrose pellets, is placed at the end of each arm. The arms are constructed of PVC tubing, and they are wide enough for the rats to pass each other as they travel through the arms. In a preliminary training, pairs of rats were exposed to the maze and trained to obtain pellets from the end of the maze arms. If both rats entered a maze arm in one trial, then food was taken away the next day (less food was available for them in the central hub as a form of punishment), but if both members of a pair obtained pellets from the food cups at the end of the arm, then pellets were placed again in the food cup the following day. After this training, a free-choice test was conducted. The choice of a maze arm was defined as a rat having all four paws in the maze arm. A pair of rats were placed in the central hub and were allowed to make choices for six minutes. Then, finally a forced-choice test was conducted. Before each trial, four maze arms were randomly chosen to be closed off by putting plastic inserts into the maze arms. The rats were then placed in the central arena and were allowed to enter the other four maze arms (all of which had food pellets in them), until all four accessible maze arms had been chosen by at least one rat. Then, the rats were lifted and the maze arms were rotated... this was done to make sure that the next choices rats made were not done because of the odor cues left behind by rats. Rotating the arms was supposed to eliminate the possibility of odor as an explanation. The rats were then placed back in the central arena and were allowed to make choices again until all four locations, that were not visited prior to rotation, had been visited by at least one rat. This specifies that the location must be visited, even if a previously visited maze arm was in that location.
The results of this first experiment showed that rats made a higher-than-expected proportion of visits to locations not previously visited by their foraging partner, and they made a lower-than-expected number of visits to locations that had been previously visited by the other rat. This is the tendency that we would expect of rats to avoid revisiting locations, because it is quite likely that food would be depleted in that location. This experiment goes to show you that the choices made by one rat in a radial maze affect the choies made later in the trial by a second rat. There may be some local enhancement at play here, however, as there was a tendency for rats to choose to visit the location that had most recently been visited by another rat. In the free-choice trials, the other rat may still have been around near the maze arm that it had most recently visited, and so its presence there could have served as a trigger for the other rat to be interested and want to come check out the area. To control for this, and to control for the possibility of odor cues, they conduct the forced tests, which showed that rats were making choices based on memory, since it was impossible for them to make choices based on the presence of another rat (the rats were lifted from the arena, the maze was rotated and the rats were placed back into the arena to forage). In the forced choice tests, the rats were also more likely to visit locations that had previously not been visited before.
The researchers expanded upon this study with a second experiment with a larger sample size. They conducted a free-choice trial once again, as well as a forced-choice trial, but this time only allowing one of the two rats to make choices. In the forced-choice trial, one rat was allowed to make choices in the maze arms, while the other rat had to watch from a central observation hub. Then, the rat that had been watching was allowed to make choices, in the absence of the other rat. The free-choice test produced very similar results to experiment 1, even with the larger sample size (26 rats). In the observation test trials, since the observing rat was allowed to forage alone after watching, it was not affected by any position effects of a rat nearby. After observing and then foraging, these observing rats still chose to visit those locations that had previously not been visited by the first rat. This shows working memory at play. As rats are observing, they are learning and remembering where they should visit next to find food, and which places they should avoid because food must be depleted from there.
Finally, a third experiment was done to fill in some holes in the results and test new research parameters. The limitation to experiment 2 was that the maze was not rotated, so there is the possibility that the results may have been due to odor cues left behind by the previous rat that had visited. Experiment 3 involved rotating the maze between the first rat's run and the observing rat's run so that avoidance of a previously visited arm of the maze would be due to memory and not due to any odor cues. The main thing manipulated in experiment 3 was the same condition or different condition groups. For the same condition groups, after a stimulus rat went around and visited maze arms, the rat was then removed, and food was added to those arms that had been visited. This makes the study unusual, because normally you would not expect there to be food where a rat had previously visited. For the different condition groups, after a stimulus rat made its rounds through the maze arms, the maze arms that had not been visited were supplied with food. After food was placed in the same or different maze arms, the observer rats were allowed to roam. For observational training I, each pair of rats was randomly assigned to be in the same or different condition. Then, the rats were exposed to a free-choice trial, where they could visit any of the eight maze arms, all of which had food in them. Finally, the same rats were put in Observational Testing II, the rats were all put in the different condition. The same group defied the normal expectation, whereas the different group was expected to have no food where rats had previously visited. The results showed that there was no difference between where rats went in Observational Training I. When the rats finally came to the Observational Training II, evidence of social learning was apparent. Rats that had been in the same condition in observational training I stayed around baseline levels, but rats that were in the different condition visited maze arms that were different from where the stimulus rats had visited. This shows that working memory was taking place and that rats had learned to avoid those locations that were previously visited by rats. Also, since the maze was rotated in this case, any odor cues were ruled out as a cause.
In conclusion, social spatial working memory apparently plays a big role in rats foraging for food. These experiments go to show you that it is not necessarily odor cues that are causing a rat to avoid a certain area where another rat has visited, but it is actually learning and working memory that causes a rat not to revisit. The results confirm initial predictions that rats will avoid those locations that other rats have previously visited, because it is more than likely that the first rat to attend an arm of the maze will eat the food that is available there. If we think about this in real life, we can imagine competition in a parking garage. If there are a very limited number of spots available, and you see someone make a left at the end of the row, you are more likely to turn the opposite way from that car, rather than follow behind it. This is because you expect that person to take the last available spot in an area, and it will be a waste of time for you to follow that car and compete for a limited number of spaces. It is more logical for you to search in an area that has not been visited. The same principal is at work with these rats. They are making a mental map of where the initial rat has visited and they are trying to avoid those locations. It is adaptively significant for rats to exhibit this behavior, because it leads to more food procured and greater reproductive success. This definitely shows that rats are more complex and intelligent than initially thought.
Brown, M.F., Farley, R. F., & Lorek, E. J. (2007). Remembrance of places you passed: Social spatial working memory in rats. Journal of Experimental Psychology: Animal Behavior Processes, 33(3), 213-224. doi: http://dx.doi.org/10.1037/0097-7403.33.3.213
Brown, M.F., Farley, R. F., & Lorek, E. J. (2007). Remembrance of places you passed: Social spatial working memory in rats. Journal of Experimental Psychology: Animal Behavior Processes, 33(3), 213-224. doi: http://dx.doi.org/10.1037/0097-7403.33.3.213
Wednesday, November 7, 2012
Zentall paper on imitation
This week's blog is going to focus on an online chapter titled, "Imitation in Animals: Evidence, Function, and Mechanisms" by Tom Zentall and Chana Akins. It is primarily a review article discussing various topics and research studies about imitation. Imitation is a rather complex and advanced form of learning which can only be determined after simpler forms of learning mechanisms have been ruled out as the explanation for a behavior.
Imitation is generally defined as any influence that an organism may have on another that results in a similarity of behavior or appearance between the two. Therefore, imitation may be used as a defensive mechanism when the viceroy butterfly mimics the appearance of the monarch butterfly. The viceroy is normally hunted and eaten, but the monarch butterfly is considered unpalatable, so the viceroy mimics the monarch butterfly in order to confuse predators. Another form of imitation, that we actually talked about in our Psych 118 class, is that of the killdeer. This species of birds builds their nest on the ground, and, therefore, have developed unique ways of protecting their eggs and growing chicks. Whenever a predator approaches, the mother killdeer will try to distract predators by flying away from the nest, but acting as if its wing is broken and that it has difficulty flying away. This serves as an enticing catch for predators, and will pull them away from the nest to chase the killdeer. The killdeer is essentially putting its own life at risk, in order to save its children. In this way, the female bird is mimicking the pattern of flight shown by a bird with a broken wing. As we will see, imitation can take on many forms, involving defense mechanisms, as well as, food foraging.
It is important to remember that all behaviors are done only when there is motivation to do so. Research is being conducted as to whether the presence of a member of the same species (a conspecific) near a rat that is being tested, serves to facilitate or hurt the motivation of a behavior. One test was done surrounding a bar-press demonstrator and an observer. This type of test involves two rats in a box, where one is trained to demonstrate a behavior, and the other must observe. The observer rat is tested to see if it has learned a behavior. Whenever the demonstrator rat got fed as a reward for his behavior, the observers were also more likely to learn the specific association and press the bars more as well. In typical research cases, food reward serves as a good incentive to motivate behavior or a type of shock avoidance. Food is also used in typical Pavlovian, or classical conditioning tasks because it is an enticing US that participants want. The chapter actually says that social learning may be more likely to occur under conditions of fear motivation because of its evolutionary value. I would agree with this because even though food is essential to survival, someone's first priority in life is to protect themselves so that they will be able to reproduce and pass on genes, before they go after food. By introducing this topic, the point I am trying to get at is that in order to determine that imitation is happening, one must control for motivational effects that would arise by the food reward (consequence) for the behavior of the demonstrator.
Another process that must be ruled out in order to determine imitation is local enhancement or stimulus enhancement. Local enhancement means that an observer is drawn to an area because some other individual, usually a member of their own species (conspecific) is in that area. Local enhancement is something that must be controlled for if imitation is to be explained as the true learning process. Local enhancement can be used to explain how birds of the great tit species learn how to peck through the top of a milk bottle to get to the milk. If one bird is pecking at the top of a bottle, then other members of its species may learn to do the same behavior. This may be considered observation in some instances, but it can also be explained by local enhancement. Simply the fact that another bird is in the area and showing interest to the bottle, may cause other birds to be intrigued as well and try pecking or experimenting with the bottle to try and get it open. In that way then, local enhancement may bring another bird closer to a bottle and then it may learn to get to the milk inside through trial-and-error. To clarify this, let me give an example with humans that is more relatable. Let's say you are naive to the idea of using a dimmer switch to dim the lights in a room, but you walk into a room and see that there is someone next to the light switch playing around with it. Simply the fact that someone is by the light switch draws your attention to that area, and you walk over there as well. When you get to the light switch you may end up pushing the button, pulling it, tapping it, until you finally realize you have to move the dial clockwise or counterclockwise to dim the lights. This may be misconstrued as learning through observation, but if you broke it down into simpler elements, you may see that local enhancement was at play, as well as trial-and-error learning. It is important not to confuse imitation with these simpler learning mechanisms.
If you have studied psychology in any form, then you must have encountered the example of Konrad Lorenz and the imprinting ducks. Imprinting is a term used to describe learning that occurs rapidly at a particular stage in life, such as early in life (infancy). The infamous study showed that ducks that had just hatched would "imprint" on the first moving stimulus that they encountered, during what was called a "critical period". Upon hatching, these ducks would follow the object that they saw moving, their mother, and follow its movements, walking in a similar style and pace. In nature it is beneficial for ducks to imprint their mother in order to be protected and learn from her, but experimenters have also made ducks imprint to a human, as well as a soccer ball. The distinction must be made here that imprinting is a form of social learning, but is not true imitation, although it appears that the ducks are imitating their mother. It may be a form of classical conditioning, with the reduction of fear serving as reinforcement. If you watch a video on the ducks imprinting their mother, you will notice that the ducks walk just like the mother and follow her every movement. When the mother stops, however, the ducks may walk forward a little bit out of formation, thus exploring the area around them, but always in close proximity to the mother. They are clearly fearful of their surroundings, because they never venture off too far alone, but they are reinforced for walking like the mother and staying close to her, because their fear is alleviated.
The primary research done by Akins and Zentall focuses on training quail to learn how to acquire food by either pecking at a treadle or stepping on a treadle. Imagine a quail inside a training box, there is a hole where food is delivered and a light that signals that food is coming. Think of the treadle as a pedal or a lever which the quail can peck at or press down on, in order to turn on the light and deliver food. Akins and Zentall discovered that in an experiment involving an observer and demonstrator, the quail would learn how to respond to the treadle with the same body part as their demonstrator. For example if their demonstrator was pecking at a treadle, the quail would learn to peck as well; if the demonstrator was stepping on the treadle, the quail would step as well. One explanation for this may be local enhancement, as it may be assumed that a quail may be drawn to a certain light (stimulus enhancement) or drawn to a demonstrator (local enhancement) and then may mess around with the manipulanda in the area until it figures out what it takes to deliver a reinforcement. This learning was a form of imitation, however, that could not be explained by trial-and-error learning; the observers were imitating and copying the same behavior that their demonstrator was performing. Behaviors never occur within a bubble, as there are multiple factors at play leading up to a behavior. First of all, it is important that food is actually delivered as a reinforcement for pecking or stepping on the treadle. This is essential for the observer to establish the contingency between performing a behavior and the expected reward outcome. If the observer does not see a food reinforcement arrive, then it will have no motivation to learn a behavior itself. In this way, reinforcement may be serving as the catalyst to bring about imitation. Akins and Zentall also found that hungry quail were more likely to imitate a demonstrator's behavior if they observed while hungry, than while satiated. To further prove that imitation was taking place, Zentall showed an example of deferred imitation. Critics of this type of research have said that if imitation is happening immediately after the observer watches a demonstrator, then it may just be a reflexive response that is genetically predisposed and doesn't involve much cognition. To disprove this idea, Zentall conducted his experiment with hungry quail and allowed them to observe either the treadle pecking or stepping. He then tested these quail with a half-hour delay and saw that the quail were able to imitate the demonstrator's behavior, thus they had learned the behavior and had cognitively processed the learning, as opposed to simply performing a reflex.
We must not think that imitative learning is the ultimate end on an evolutionary scale. In other words, it is not an inevitability that species living in social groups will develop such behaviors. Trial and error learning is a very necessary way to acquire new traits, especially in order to have the flexibility to figure out what is good to eat or not and adapt to a changing environment. For example, pandas like to eat bamboo, but if their forests are depleted or destroyed, then imitative learning may not help them discover new sources of food, but rather trial and error learning will. Think of imitation as a quick and efficient way of distributing a learned practice to observers, but will not necessarily help species discover new methods of food foraging. Trial and error may lead to success in terms of flexibility, but it also has negative consequences if it leads to food poisoning, or in terms of practicality, it may be a time-consuming and inefficient practice that does not work in all situations. The reasons I say these things is because imitation is found in apes and humans, as well as parrots and dolphins, but is not found in monkeys and some bird species, although they live socially in groups. From a biological perspective, ultimately, whichever strategy that leads to greater fitness, in terms of being able to successfully reproduce and have multiple progeny will be passed on to subsequent generations. Imitation is not always the behavior leading to that success.
Imitation can be explained in terms of psychological and biological mechanisms. Psychologically, imitation may simply be a form of instrumental learning. A clear-cut example stems from verbal behavior and imitation. An eager and excited family that repeatedly says "daddy" around a baby, may eventually get the child to imitate that behavior and say "dadda" or "daddy", simply because it is being reinforced for that behavior through food and attention. This explanation may work for individual cases, but not all imitation is clear associative learning. The alternative explanation for such behaviors is an inborn, genetic drive. Experiments are being conducted on whether newborns can actually imitate, because this would rule out any cognitive explanation and align more closely with a biological explanation. There is data that suggests that infants have an innate ability to observe and analyze the behaviors and movements around them, and match them up with their own movements in space, which would suggest an innate ability to imitate those around them. This is clearly an interesting finding that could require some more time and investigation. It is only in the context of both psychological and biological mechanisms that we may understand true imitation. But as mentioned before, true imitation is a higher level of learning that must be distinguished from simpler forms of learning and enhancement.
Zentall, T., & Akins, C. (n.d.). Imitation in Animals: Evidence, Function, and Mechanisms. In Avian
Visual Cognition. Retrieved from http://www.pigeon.psy.tufts.edu/avc/zentall/default.htm
Imitation is generally defined as any influence that an organism may have on another that results in a similarity of behavior or appearance between the two. Therefore, imitation may be used as a defensive mechanism when the viceroy butterfly mimics the appearance of the monarch butterfly. The viceroy is normally hunted and eaten, but the monarch butterfly is considered unpalatable, so the viceroy mimics the monarch butterfly in order to confuse predators. Another form of imitation, that we actually talked about in our Psych 118 class, is that of the killdeer. This species of birds builds their nest on the ground, and, therefore, have developed unique ways of protecting their eggs and growing chicks. Whenever a predator approaches, the mother killdeer will try to distract predators by flying away from the nest, but acting as if its wing is broken and that it has difficulty flying away. This serves as an enticing catch for predators, and will pull them away from the nest to chase the killdeer. The killdeer is essentially putting its own life at risk, in order to save its children. In this way, the female bird is mimicking the pattern of flight shown by a bird with a broken wing. As we will see, imitation can take on many forms, involving defense mechanisms, as well as, food foraging.
It is important to remember that all behaviors are done only when there is motivation to do so. Research is being conducted as to whether the presence of a member of the same species (a conspecific) near a rat that is being tested, serves to facilitate or hurt the motivation of a behavior. One test was done surrounding a bar-press demonstrator and an observer. This type of test involves two rats in a box, where one is trained to demonstrate a behavior, and the other must observe. The observer rat is tested to see if it has learned a behavior. Whenever the demonstrator rat got fed as a reward for his behavior, the observers were also more likely to learn the specific association and press the bars more as well. In typical research cases, food reward serves as a good incentive to motivate behavior or a type of shock avoidance. Food is also used in typical Pavlovian, or classical conditioning tasks because it is an enticing US that participants want. The chapter actually says that social learning may be more likely to occur under conditions of fear motivation because of its evolutionary value. I would agree with this because even though food is essential to survival, someone's first priority in life is to protect themselves so that they will be able to reproduce and pass on genes, before they go after food. By introducing this topic, the point I am trying to get at is that in order to determine that imitation is happening, one must control for motivational effects that would arise by the food reward (consequence) for the behavior of the demonstrator.
Another process that must be ruled out in order to determine imitation is local enhancement or stimulus enhancement. Local enhancement means that an observer is drawn to an area because some other individual, usually a member of their own species (conspecific) is in that area. Local enhancement is something that must be controlled for if imitation is to be explained as the true learning process. Local enhancement can be used to explain how birds of the great tit species learn how to peck through the top of a milk bottle to get to the milk. If one bird is pecking at the top of a bottle, then other members of its species may learn to do the same behavior. This may be considered observation in some instances, but it can also be explained by local enhancement. Simply the fact that another bird is in the area and showing interest to the bottle, may cause other birds to be intrigued as well and try pecking or experimenting with the bottle to try and get it open. In that way then, local enhancement may bring another bird closer to a bottle and then it may learn to get to the milk inside through trial-and-error. To clarify this, let me give an example with humans that is more relatable. Let's say you are naive to the idea of using a dimmer switch to dim the lights in a room, but you walk into a room and see that there is someone next to the light switch playing around with it. Simply the fact that someone is by the light switch draws your attention to that area, and you walk over there as well. When you get to the light switch you may end up pushing the button, pulling it, tapping it, until you finally realize you have to move the dial clockwise or counterclockwise to dim the lights. This may be misconstrued as learning through observation, but if you broke it down into simpler elements, you may see that local enhancement was at play, as well as trial-and-error learning. It is important not to confuse imitation with these simpler learning mechanisms.
If you have studied psychology in any form, then you must have encountered the example of Konrad Lorenz and the imprinting ducks. Imprinting is a term used to describe learning that occurs rapidly at a particular stage in life, such as early in life (infancy). The infamous study showed that ducks that had just hatched would "imprint" on the first moving stimulus that they encountered, during what was called a "critical period". Upon hatching, these ducks would follow the object that they saw moving, their mother, and follow its movements, walking in a similar style and pace. In nature it is beneficial for ducks to imprint their mother in order to be protected and learn from her, but experimenters have also made ducks imprint to a human, as well as a soccer ball. The distinction must be made here that imprinting is a form of social learning, but is not true imitation, although it appears that the ducks are imitating their mother. It may be a form of classical conditioning, with the reduction of fear serving as reinforcement. If you watch a video on the ducks imprinting their mother, you will notice that the ducks walk just like the mother and follow her every movement. When the mother stops, however, the ducks may walk forward a little bit out of formation, thus exploring the area around them, but always in close proximity to the mother. They are clearly fearful of their surroundings, because they never venture off too far alone, but they are reinforced for walking like the mother and staying close to her, because their fear is alleviated.
The primary research done by Akins and Zentall focuses on training quail to learn how to acquire food by either pecking at a treadle or stepping on a treadle. Imagine a quail inside a training box, there is a hole where food is delivered and a light that signals that food is coming. Think of the treadle as a pedal or a lever which the quail can peck at or press down on, in order to turn on the light and deliver food. Akins and Zentall discovered that in an experiment involving an observer and demonstrator, the quail would learn how to respond to the treadle with the same body part as their demonstrator. For example if their demonstrator was pecking at a treadle, the quail would learn to peck as well; if the demonstrator was stepping on the treadle, the quail would step as well. One explanation for this may be local enhancement, as it may be assumed that a quail may be drawn to a certain light (stimulus enhancement) or drawn to a demonstrator (local enhancement) and then may mess around with the manipulanda in the area until it figures out what it takes to deliver a reinforcement. This learning was a form of imitation, however, that could not be explained by trial-and-error learning; the observers were imitating and copying the same behavior that their demonstrator was performing. Behaviors never occur within a bubble, as there are multiple factors at play leading up to a behavior. First of all, it is important that food is actually delivered as a reinforcement for pecking or stepping on the treadle. This is essential for the observer to establish the contingency between performing a behavior and the expected reward outcome. If the observer does not see a food reinforcement arrive, then it will have no motivation to learn a behavior itself. In this way, reinforcement may be serving as the catalyst to bring about imitation. Akins and Zentall also found that hungry quail were more likely to imitate a demonstrator's behavior if they observed while hungry, than while satiated. To further prove that imitation was taking place, Zentall showed an example of deferred imitation. Critics of this type of research have said that if imitation is happening immediately after the observer watches a demonstrator, then it may just be a reflexive response that is genetically predisposed and doesn't involve much cognition. To disprove this idea, Zentall conducted his experiment with hungry quail and allowed them to observe either the treadle pecking or stepping. He then tested these quail with a half-hour delay and saw that the quail were able to imitate the demonstrator's behavior, thus they had learned the behavior and had cognitively processed the learning, as opposed to simply performing a reflex.
We must not think that imitative learning is the ultimate end on an evolutionary scale. In other words, it is not an inevitability that species living in social groups will develop such behaviors. Trial and error learning is a very necessary way to acquire new traits, especially in order to have the flexibility to figure out what is good to eat or not and adapt to a changing environment. For example, pandas like to eat bamboo, but if their forests are depleted or destroyed, then imitative learning may not help them discover new sources of food, but rather trial and error learning will. Think of imitation as a quick and efficient way of distributing a learned practice to observers, but will not necessarily help species discover new methods of food foraging. Trial and error may lead to success in terms of flexibility, but it also has negative consequences if it leads to food poisoning, or in terms of practicality, it may be a time-consuming and inefficient practice that does not work in all situations. The reasons I say these things is because imitation is found in apes and humans, as well as parrots and dolphins, but is not found in monkeys and some bird species, although they live socially in groups. From a biological perspective, ultimately, whichever strategy that leads to greater fitness, in terms of being able to successfully reproduce and have multiple progeny will be passed on to subsequent generations. Imitation is not always the behavior leading to that success.
Imitation can be explained in terms of psychological and biological mechanisms. Psychologically, imitation may simply be a form of instrumental learning. A clear-cut example stems from verbal behavior and imitation. An eager and excited family that repeatedly says "daddy" around a baby, may eventually get the child to imitate that behavior and say "dadda" or "daddy", simply because it is being reinforced for that behavior through food and attention. This explanation may work for individual cases, but not all imitation is clear associative learning. The alternative explanation for such behaviors is an inborn, genetic drive. Experiments are being conducted on whether newborns can actually imitate, because this would rule out any cognitive explanation and align more closely with a biological explanation. There is data that suggests that infants have an innate ability to observe and analyze the behaviors and movements around them, and match them up with their own movements in space, which would suggest an innate ability to imitate those around them. This is clearly an interesting finding that could require some more time and investigation. It is only in the context of both psychological and biological mechanisms that we may understand true imitation. But as mentioned before, true imitation is a higher level of learning that must be distinguished from simpler forms of learning and enhancement.
Zentall, T., & Akins, C. (n.d.). Imitation in Animals: Evidence, Function, and Mechanisms. In Avian
Visual Cognition. Retrieved from http://www.pigeon.psy.tufts.edu/avc/zentall/default.htm
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