Gibbon calls

There is some interesting news on gibbons. But first, what are gibbons? They are apes, called lesser apes but definitely in our group with chimps, gorillas, and orangs and not with monkeys. The Chinese used to call them “gentlemen of the forest” to separate them from troublesome monkeys. Our lineage split from theirs about 18 million years ago. For context, the separation with orangs was 14, gorillas 7, and chimps 5 mya.

They are the fastest travelers through forest canopy, clocked at 55 km/hr, swinging from branch to branch. They have ball and socket wrists on their long and powerful arms. When they are forced to the ground they walk upright (more upright than chimps can manage). Gibbons are social, territorial and pair bond for life. And they sing with very powerful voices due to reverberating throat sacs. They sing duets, and family choir performances. But they also whisper or “hoo”. There have been some studies of their song but the Clarke paper (citation below) is the first study of the softer hoos.

This is important to the inquiry into the history of human language. There are two approaches to looking at our language: one is to look at what is unique and separates us from our nearest cousins; the other is to look a what is similar and forms a continuum with our relatives. We can read many articles on the uniqueness but only recently have there been articles on the similarities.

Although language is a uniquely human behaviour, it is likely to have evolved from precursors in the primate lineage, some of which may still be detectable in the vocal behaviour of extant primates. One important candidate for such a precursor is the ability to produce context-specific calls, a prerequisite to referential communication during which an actor refers a recipient’s attention to an external event. … More recently, functionally referential calling behaviour also has been described for other species of monkeys, apes, dogs, dolphins, and birds such as fowl, jays and chickadees.

Overall, context-specific calling behaviour appears to be widespread in animal communication, presumably because the selection pressure to attend to and understand context-specific calls is very strong, especially in evolutionarily urgent situations. In addition, there is good evidence for call comprehension between different species of primates, between primates and birds and between primates and other mammals, suggesting that such phenomena are driven by a generalised cognitive mechanism that is widely available to animals. Whether or not such abilities are relevant for understanding language evolution has triggered much debate with no real consensus. Nevertheless, the comparative study of animal communication, especially across non-human primates, is one of the most useful tools to make progress and address open questions about human language evolution.

Although gibbon hoos sound much the same to human observers, when they are recorded and analyzed for highest pitch, lowest pitch, pitch delta, duration, volume, interval between calls, it is possible to see the difference between hoo calls in different situations. The distinct situations noted included: tiger, leopard, raptor, encounter with another group, feeding, and introduction to duet song.

This communication based calling, that is fairly common in non-solitary animals, differs from human language to the extent that the calls are relatively fixed to particular situations and are small in number for most animals (dolphins and whales may have a surprising number and it is not known whether they are fixed). Some would say that animal calls are automatic and do not involve any decision to call; it is difficult to measure this and in any case does not seem to apply to the more intelligent animals. The exchange of information is clearly involved in animal communication – communication and exchange of information are almost synonymous. The idea that our communication is based on affecting one another’s attention, metaphorically pointing at concepts, objects, actions etc. fits nicely with animal referential communication.

Here is the paper’s abstract:

Background: Close range calls are produced by many animals during intra-specific interactions, such as during home range defence, playing, begging for food, and directing others. In this study, we investigated the most common close range vocalisation of lar gibbons (Hylobates lar), the ‘hoo’ call. Gibbons and siamangs (family Hylobatidae) are known for their conspicuous and elaborate songs, while quieter, close range vocalisations have received almost no empirical attention, perhaps due to the difficult observation conditions in their natural forest habitats.

Results: We found that ‘hoo’ calls were emitted by both sexes in a variety of contexts, including feeding, separation from group members, encountering predators, interacting with neighbours, or as part of duet songs by the mated pair. Acoustic analyses revealed that ‘hoo’ calls varied in a number of spectral parameters as a function of the different contexts. Males’ and females’ ‘hoo’ calls showed similar variation in these context-specific parameter differences, although there were also consistent sex differences in frequency across contexts.

Conclusions: Our study provides evidence that lar gibbons are able to generate significant, context-dependent acoustic variation within their main social call, which potentially allows recipients to make inferences about the external events experienced by the caller. Communicating about different events by producing subtle acoustic variation within some call types appears to be a general feature of primate communication, which can increase the expressive power of vocal signals within the constraints of limited vocal tract flexibility that is typical for all non-human primates. In this sense, this study is of direct relevance for the on-going debate about the nature and origins of vocally-based referential communication and the evolution of human speech.”

Clarke, E., Reichard, U., & Zuberbühler, K. (2015). Context-specific close-range “hoo” calls in wild gibbons (Hylobates lar) BMC Evolutionary Biology, 15 (1) DOI: 10.1186/s12862-015-0332-2

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A new way to parse language

For many years I have followed EB Bolles’ blog Babel’s Dawn (here) while he discussed the origin of human language. He has convinced me of many things about the history and nature of language. And they fit with how I thought of language. Now he has written a chapter in a book, “Attention and Meaning: The Attentional Basis of Meaning”. In his chapter, “Attentional-Based Syntax” (here), Bolles re-writes the mechanics of parsing phrases and sentences. He uses new entities, not nouns and verbs etc., and very different rules.

The reason I like this approach so much is the same reasons that I cannot accept Chomsky’s view of language. I see language from a biological point of view, a product of genetic and cultural evolution, and continuous with the communication of other animals. It is a type of biological communication. I imagine (rightly or wrongly) that Chomsky finds biology and especially animals distasteful and that he also has no feel for the way evolution works. I on the other hand, find a study of language that seems to only deal with complete written sentences on a white board, not of much interest. Instead of a form of biological communication, Chomsky gives us a form of logical thought.

Bolles summarizes his chapter like this. “The commonsense understanding of meaning as reference has dominated grammatical thought for thousands of years, producing many paradoxes while leaving many mysteries about language’s nature. The paradoxes wane if we assume that meaning comes by directing attention from one phenomenon to another. This transfer of meaning from objective reality to subjective experience breaks with the objective grammatical accounts produced by many philosophers, lexicographers, and teachers through the ages. The bulk of this paper introduces a formal system for parsing sentences according to an attention- based syntax. The effort proves surprisingly fruitful and is capable of parsing many sentences without reference to predicates, nouns or verbs. It might seem a futile endeavor, producing an alternative to a system used by every educated person in the world, but the approach explains many observations left unexplained by classical syntax. It also suggests a promising approach to teaching language usage. ”

The key change of concept is that words do not have meanings, nor do they carry meaning from a speaker to a listener – instead, they pilot attention within the brain. Or in other words they work by forcing items into working memory and therefore attention (or attention and therefore working memory). This makes very good sense. Take a simple word like ‘tree': speaker says ‘tree’, listener hears ‘tree’ and memory automatically brings to the surface memories associated with ‘tree’. The word ‘tree’ is held in working memory and as long as it is there, the brain has recall or near recall of tree-ish concepts/ images/ ideas. The meaning of tree is found within the listener’s brain. No one thing, word or single element of memory has meaning; the meaning is formed when multiple things form a connection. It is the connections that gives meaning. I like this because I have thought for years that single words are without meaning. But words form a network of connections in any culture and a word’s connections in the network is what defines the word. Because we share cultural networks including a language, we can communicate. I also like this starting point because it explains why language is associated with consciousness (an oddity because very little else to do with thinking is so closely tied to consciousness). Consciousness is associated with working memory and attention, and the content of consciousness seems to be (or come from) the focus of attention in working memory.

Bolles uses a particular vocabulary in his parsing method: phenomenon is any conscious experience, sensation is a minimal awareness like a hue or tone, percept is a group of sensations like a loud noise, bound perception is a group of percepts that form a unified experience. We could also say phenomenon is another word for subjective consciousness. Then we have the process of perception. Perception starts with primary sensory input, memory and predictions. It proceeds to bind elements together to form a moment of perception, then serial momentary perceptions are bound into events. It matters little what words are used, the process is fairly well accepted. But what is more, it is not confined to how language is processed – it is how everything that passes through working memory and into the content of consciousness is processed. No magic here! No mutation required! Language uses what the brain more-or-less does naturally.

This also makes the evolution of language easier to visualize. The basic mechanism existed in the way that attention, working memory and consciousness works. It was harnessed by a communication function and that function drove the evolution of language: both biological evolution and a great deal of cultural evolution. This evolution could be slow and steady over a long period of time and does not have to be the result of a recent (only 50-150 thousand years ago) all powerful single mutation.

So – the new method of parsing is essentially to formulate the rules that English uses to bind focuses of attention together to make a meaningful event (or bound perception). Each language would have its own syntax rules. The old syntax rules and the new ones are similar because they are both describing English. But… it is not arbitrary rules any more but understandable rules in the context of working memory and attention. Gone is the feeling of memorizing rules to parse sentences on a white board. Instead is an understanding of English as it is used.

I have to stick in a little rant here about peeves. If someone can understand without effort or mistake what someone else has said then what is the problem? Why are arbitrary rules important if breaking them does not interfere at all with communication? With the new parsing method, it is easy to see what is good communication and what isn’t; it is clear what will hinder communication. The method can be used to improve perfectly good English into even better English. Another advantage is that the method can be used for narratives longer than a sentence.

I hope that this approach to syntax will be taken up by others.


A video on self

Thomas Metzinger is a favorite philosopher of mine. Deric Bownds has a post that includes a video of Metzinger talking about the self (here). Have a look. He deals with consciousness, the self model, transparency, identification and some experimental illusions. It’s great.

How do morals work?

There is a way to study morality with little scenarios, little hypothetical questions, given to people, who then answer that they would do X or Y as a moral action in that situation. The scenarios have always struck me as simplistic and not believable, even sometimes impossible. And the answers people give do not have credibility – people are not always truthful and besides, in the the split second they would have to make a decision if the situation was really happening, with hardly any time for thought, they may do anything. The context is arbitrary and does not widen to include the society or the future beyond perhaps a day at most. This scenario method seems useless and misleading.

One of these scenarios goes like this. If you could time travel to Austria when Hitler was a small boy, would you try to kill him? Well, first of all this is not a believable story so the answerers will not actually take it really seriously. Secondly, we know what Hitler did but we have no idea what would have happened if there had been no Hitler. It could have been wonderful. Or for example, if no Hitler, then there may have been some other tyrant but a bit later on the scene. A war in the 50’s rather than the 40’s would be the future. This could have been after the invention of the nuclear bomb, so that instead of only 2, enough bombs were dropped to wipe out civilization.

Another question has been in the news lately. If you have a person who had hidden a bomb and that bomb was going to go off in a short time and kill many people, would you torture the person to get the location of the bomb? This again is not a believable scenario, although possible. This particular combination of knowing some things for absolutely, positively sure but not knowing the location at all is unlikely. No one has come up with a case like this having happened and it is unlikely to happen very often – maybe once in a few hundred years. If you were in this situation you would probably act without thinking and justify your action or inaction later. Again this scenario leaves out the future – over the course of future years you may cause many more deaths by opening a door to torture than you save by finding the bomb. It also leaves out a wider context by not including the fact that torture is not a very successful way to get correct information (you can do the torture and get nothing in return). In such a situation I want to think I would not torture but I am not sure. If someone says they would torture, I am not sure that they actually would. How people answer the question is next to meaningless.

A popular question (or questions really) is the trolley car that is going to kill 1 person or 5, where you can take action resulting in the death of the 1 or not take action and allow the 5 to die. Again the scenarios are not very believable and some not even credible. Here is one: you are on a bridge over the trolley line and you see 5 people tied to the track. A trolley car is coming and will hit the 5 if it is not stopped. Beside you is a fat man, weighing enough to stop the trolley if he is dropped on the track. Would you push him over the bridge onto the track? If you say you would then it is assumed that you are a utilitarian and decide moral questions by what gives the most total good or the least total bad. If you say no you would not, it is assumed that you follow moral rules and therefore will not participate in murder. In all the different models of this set-up there is no look at the future. What if the 1 that dies to save the 5, is about to find the cure for some fatal disease or something like that, saving thousands of lives? To a certain extent it is important that people do not think that someone may murder them for no other reason thean they were a convenient weight to save some other people. Societies need an amount of trust.

As it happens, I think I would not push the fat man but there are other trolley scenarios where I might sacrifice the 1. And again I am not sure that I know what I would do in some of the trolley questions. But – I am quite sure that I am not a utilitarian all the time or none of the time; ditto, with following rules. Sometimes I do and sometimes I don’t. I am not concerned with being consistent to a philosophical opinion of what should be labeled moral.

The reason we even have moral questions is that we are social beings and the health of our societies is important to our survival. Because we are social, there can be choices we have to make that have no absolutely right answer. We have to choose between two good things or which of two bad things to avoid. The problems are not clear cut nor do we have all the information needed to ‘solve’ them. We can use our intellect and find logical answers but these may not be the best answers because they don’t take into consideration the statistics of unknown repercussions. We can follow the rules of society but these may not be the best answers for us in certain situations. We can follow our emotional feelings but they are also not always the best route. In the real world, out brains sort this out using cognition, learned values and emotions. This can be done quickly or more slowly depending on the time available. We end up with an action plan and a justification, should we need it, but with practically no idea of how the action plan was arrived at. We can trust, for what it’s worth, that the brain used a mechanism that has withstood the test of our ancestors/societies survival. There is no guarantee that evolution will have provided us with a way to always be morally right just likely that it will be probabilistically better than alternatives. Children seem to come with a rudimentary moral sense which they improve with experience and learning from their culture – still no guarantee!

If we want to understand how the brain makes these difficult choices, we will have to use more realistic questions (whether in a scanner or on a questionnaire). Morality is unlikely to be understandable in terms of utility or rule, logic or emotion, or self-interest verses societal-interest.

Curious sponge behaviour

In a little tidy-up of old files, I ran across a paper on sneezing sponges. This is not an April Fool’s joke – today is the 2nd of April. When we sneeze, we fill our lungs and then hold the air in while increasing the pressure on the lung. When we open up and let the air out, it rushes out, moving particles, mucous and irritants as it rushes. Sponges take in water all over their surface but the water exits through one hole. In order to rid themselves of particles and irritants, they close that single hole while continuing to take in water. When the exit is opened, the water inside comes out with some force.

Sponges are such primitive animals that they have no muscles and no nervous system. Until recently it was believed that they also lacked sense organs. But they do have a sense organ and that is how they are able to organize a sneeze. The exit hole (osculum) is lined with cells that have little hairs (cilia) protruding into the water stream. These cilia can sense grit and changes in flow. The cilia are of a type called ‘primary'; they cannot move but can sense being moved. Primary cilia are found in a number of sensory organs in other animals; for example, in our ears and the lateral line of fishes. The general molecular structure of primary cilia is more or less conserved over multicellular animals.

In the same way that the molecules needed for neurons and synapses are seen in organisms that have no nervous systems, this is another component of our nervous system that has a very ancient lineage.

Here is the abstract of the paper ( D. Ludeman, N. Farrar, A. Riesgo, J. Paps, S. Leys; Evolutionary origins of sensation in metazoans: functional evidence for a new sensory organ in sponges. BMC Evolutionary Biology, 2014; 14 (1): 3 ):

Background: One of the hallmarks of multicellular organisms is the ability of their cells to trigger responses to the environment in a coordinated manner. In recent years primary cilia have been shown to be present as ‘antennae’ on almost all animal cells, and are involved in cell-to-cell signaling in development and tissue homeostasis; how this sophisticated sensory system arose has been little-studied and its evolution is key to understanding how sensation arose in the Animal Kingdom. Sponges (Porifera), one of the earliest evolving phyla, lack conventional muscles and nerves and yet sense and respond to changes in their fluid environment. Here we demonstrate the presence of non-motile cilia in sponges and studied their role as flow sensors.

Results: Demosponges excrete wastes from their body with a stereotypic series of whole-body contractions using a structure called the osculum to regulate the water-flow through the body. In this study we show that short cilia line the inner epithelium of the sponge osculum. Ultrastructure of the cilia shows an absence of a central pair of microtubules and high speed imaging shows they are non-motile, suggesting they are not involved in generating flow. In other animals non-motile, ‘primary’, cilia are involved in sensation. Here we show that molecules known to block cationic ion channels in primary cilia and which inhibit sensory function in other organisms reduce or eliminate sponge contractions. Removal of the cilia using chloral hydrate, or removal of the whole osculum, also stops the contractions; in all instances the effect is reversible, suggesting that the cilia are involved in sensation. An analysis of sponge transcriptomes shows the presence of several transient receptor potential (TRP) channels including PKD channels known to be involved in sensing changes in flow in other animals. Together these data suggest that cilia in sponge oscula are involved in flow sensation and coordination of simple behaviour.

Conclusions: This is the first evidence of arrays of non-motile cilia in sponge oscula. Our findings provide support for the hypothesis that the cilia are sensory, and if true, the osculum may be considered a sensory organ that is used to coordinate whole animal responses in sponges. Arrays of primary cilia like these could represent the first step in the evolution of sensory and coordination systems in metazoans. ”

Music affects on the brain

A recent paper identified genes that changed their expression as a result of music performance in trained musicians. (see citation below). There were a surprising number of affected genes, 51 genes had increased and 22 had decreased expression, compared to controls who were also trained musicians but were not involved in making or listening to music for the same time period. It is also impressive that this set of 73 genes has a very broad range of presumed functions and effects in the brain.

musictableAnother interesting aspect is the overlap of a number of these genes with some that have been identified in song birds. This implies that the music/sophisticated sound perception and production has been conserved from a common ancestor of birds and mammals.

It has been known for some time that musical training has a positive effect on intelligence and outlook – that it assists learning. Musical training changes the structure of the brain. Now scientists are starting to trace the biology of music’s effects. Isn’t it about time that education stopped treating music (and other arts for that matter) as unimportant frills? It should not be the first thing to go when money or teaching time is short.

Here is the Abstract:

Music performance by professional musicians involves a wide-spectrum of cognitive and multi-sensory motor skills, whose biological basis is unknown. Several neuroscientific studies have demonstrated that the brains of professional musicians and non-musicians differ structurally and functionally and that musical training enhances cognition. However, the molecules and molecular mechanisms involved in music performance remain largely unexplored. Here, we investigated the effect of music performance on the genome-wide peripheral blood transcriptome of professional musicians by analyzing the transcriptional responses after a 2-hr concert performance and after a ‘music-free’ control session. The up-regulated genes were found to affect dopaminergic neurotransmission, motor behavior, neuronal plasticity, and neurocognitive functions including learning and memory. Particularly, candidate genes such as SNCA, FOS and DUSP1 that are involved in song perception and production in songbirds, were identified, suggesting an evolutionary conservation in biological processes related to sound perception/production. Additionally, modulation of genes related to calcium ion homeostasis, iron ion homeostasis, glutathione metabolism, and several neuropsychiatric and neurodegenerative diseases implied that music performance may affect the biological pathways that are otherwise essential for the proper maintenance of neuronal function and survival. For the first time, this study provides evidence for the candidate genes and molecular mechanisms underlying music performance.”

Kanduri, C., Kuusi, T., Ahvenainen, M., Philips, A., Lähdesmäki, H., & Järvelä, I. (2015). The effect of music performance on the transcriptome of professional musicians Scientific Reports, 5 DOI: 10.1038/srep09506

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Recommended video

This link has a series of interviews with prominent neuroscientists (Haggard, Smith, Koch, Greenfield, Martin, Hameroff, Theise). “Does brain make mind” is a good watch.

Free Will has lost all meaning

A headline got me going and the summary got me laughing, “Even worms have free will.” ScienceDaily has the item (here) on a paper about reactions of a worm to odors (A. Gordus, N. Pokala, S. Levy, S. Flavell, C. Bargmann; Feedback from Network States Generates Variability in a Probabilistic Olfactory Circuit; Cell, 2015)

This is not just any worm that has free will, it is C. elegans, a microscopic worm whose brain is completely known, all 302 neurons and their few thousand connecting synapses. Each neuron has a name and has been individually studied. Most of the little networks in the tiny brain have been studied to some extent. What can they mean when they say that C.elegans has free will? “If offered a delicious smell, for example, a roundworm will usually stop its wandering to investigate the source, but sometimes it won’t. Just as with humans, the same stimulus does not always provoke the same response, even from the same individual.

So it appears that free will can be ascribed to anything that is not completely predictable. Until, that is, it is understood enough to be predictable. But no, it does not even have to be unpredictable. They appear to have an understanding of the little 3 neuron web that controls whether the worm stops at an odor. “We found that the collective state of the three neurons at the exact moment an odor arrives determines the likelihood that the worm will move toward the smell.” So it appears that anything that can do more than a single thing when triggered with a particular stimulation, has free will. I think that would include all living things and a good many inanimate things too. Weather seems to fit the bill.

I hate to be pedantic but why use the phrase ‘free will’ with a meaning that is not remotely related to its philosophical meaning or its legal meaning. It either means that a choice is made outside the brain in some spiritual mind or it means that a choice was made consciously and carries attached responsibility. It should not be reduced to a meaning like: a worm will stop for a smell or go on depending on the state of 3 of its neurons. If sensory information is going to have only one effect on motor action, we do not need a brain at all; the sensory neurons can connect directly with the motor neurons with no need for other neurons in between. C. elegans may have a very small brain but it is a brain and it’s function is to nuance behavior – not a surprise when it does.

Here is the abstract, unlike the press release, it is very reasonable and does not mention free will:

Variability is a prominent feature of behavior and is an active element of certain behavioral strategies. To understand how neuronal circuits control variability, we examined the propagation of sensory information in a chemotaxis circuit of C. elegans where discrete sensory inputs can drive a probabilistic behavioral response. Olfactory neurons respond to odor stimuli with rapid and reliable changes in activity, but downstream AIB interneurons respond with a probabilistic delay. The interneuron response to odor depends on the collective activity of multiple neurons—AIB, RIM, and AVA—when the odor stimulus arrives. Certain activity states of the network correlate with reliable responses to odor stimuli. Artificially generating these activity states by modifying neuronal activity increases the reliability of odor responses in interneurons and the reliability of the behavioral response to odor. The integration of sensory information with network states may represent a general mechanism for generating variability in behavior.


New method – BWAS

There is a report of a new method of analyzing fMRI scans – using enormous sets of data and giving very clear results. Brain-wide association analysis (BWAS for short) was used in a comparison of autistic and normal brains in a recent paper (citation below).

The scan data is divided into 47,636 small areas of the brain, voxels, and then these are analyzed in pairs, each voxel with all other voxels. This gives 1,134,570,430 data points for each brain. This sort of analysis has been done in the past but only for restricted areas of the brain and not the whole brain. The method was devised by J. Feng, University of Warwick, Computer Department.

This first paper featuring the method shows its strengths. Cheng and others used data from over 900 existing scans from various sources that had matched autistic and normal pairs. The results are in the abstract below. (This blog does not usually deal with information on autism and similar conditions but tries to keep to normal function; I am not a physician. So the results are not being discussed, just the new method.)

bwasA flow chart of the brain-wide association study [termed BWAS, in line with genome-wide association studies (GWAS)] is shown in Fig. 1. This ‘discovery’ approach tests for differences between patients and controls in the connectivity of every pair of brain voxels at a whole-brain level. Unlike previous seed-based or independent components-based approaches, this method has the advantage of being fully unbiased, in that the connectivity of all brain voxels can be compared, not just selected brain regions. Additionally, we investigated clinical associations between the identified abnormal circuitry and symptom severity; and we also investigated the extent to which the analysis can reliably discriminate between patients and controls using a pattern classification approach. Further, we confirmed that our findings were robust by split data cross-validations.” FC = functional connectivity; ROI = region of interest.

The results are very clear and have a very good statistical probability.

Abstract: “Whole-brain voxel-based unbiased resting state functional connectivity was analysed in 418 subjects with autism and 509 matched typically developing individuals. We identified a key system in the middle temporal gyrus/superior temporal sulcus region that has reduced cortical functional connectivity (and increased with the medial thalamus), which is implicated in face expression processing involved in social behaviour. This system has reduced functional connectivity with the ventromedial prefrontal cortex, which is implicated in emotion and social communication. The middle temporal gyrus system is also implicated in theory of mind processing. We also identified in autism a second key system in the precuneus/superior parietal lobule region with reduced functional connectivity, which is implicated in spatial functions including of oneself, and of the spatial environment. It is proposed that these two types of functionality, face expression-related, and of one’s self and the environment, are important components of the computations involved in theory of mind, whether of oneself or of others, and that reduced connectivity within and between these regions may make a major contribution to the symptoms of autism.

Cheng, W., Rolls, E., Gu, H., Zhang, J., & Feng, J. (2015). Autism: reduced connectivity between cortical areas involved in face expression, theory of mind, and the sense of self Brain DOI: 10.1093/brain/awv051

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Adaptive forgetting

We know that memories are changed by up-dating details, consolidating similar memories, and forgetting some altogether. In a recent paper, researchers have shown that forgetting a memory can be due to recall of other memories (citation and abstract below). Remembering a memory enhances that memory but can suppress similar memories that interfere with its recall. This ‘adaptive forgetting’ strengthens often recalled memories and causes forgetting of interfering memories.

The New York Times has a report on this paper (here) giving details of the method.

Wimber and others, using scans and pattern analysis were able to observe the activity of memories in the visual cortex. First the subjects were trained to associate words with unrelated pictures – each word was associated with two different pictures. Then they were given a word and asked to remember the first picture they were trained to associate with that word. The pattern analysis showed the extent of the pattern for the first picture and for the second picture. This trial was repeated several times amongst other trials. The pattern for the first picture grew stronger over the repeated trials and the pattern of the second picture grew weaker. To see what had happened to the second picture, the subjects were shown each picture along with a similar one and asked which picture they had been trained and tested on in each pair. They knew the correct first picture but not had more trouble identifying the correct second picture – in other words, the memory of the word and second picture association was being destroyed.

This has implications for witness testimony after repeated questioning – the questioning may have destroyed some memories by adaptive forgetting. It also weakens the theory that memories are not forgotten but overlaid and hidden by newer memories.

Here is the abstract of the paper (Wimber, Alink, Charest, Kriegeskorte, Anderson; Retrieval induces adaptive forgetting of competing memories via cortical pattern suppression. Nature Neuroscience, 2015) “Remembering a past experience can, surprisingly, cause forgetting. Forgetting arises when other competing traces interfere with retrieval and inhibitory control mechanisms are engaged to suppress the distraction they cause. This form of forgetting is considered to be adaptive because it reduces future interference. The effect of this proposed inhibition process on competing memories has, however, never been observed, as behavioral methods are ‘blind’ to retrieval dynamics and neuroimaging methods have not isolated retrieval of individual memories. We developed a canonical template tracking method to quantify the activation state of individual target memories and competitors during retrieval. This method revealed that repeatedly retrieving target memories suppressed cortical patterns unique to competitors. Pattern suppression was related to engagement of prefrontal regions that have been implicated in resolving retrieval competition and, critically, predicted later forgetting. Thus, our findings demonstrate a cortical pattern suppression mechanism through which remembering adaptively shapes which aspects of our past remain accessible.

Could this have anything to do with the urban myth about the professor who complained that every time he remembered a student’s name, he forgot the name of another fish?

The BBC report: “Dr Wimber told the BBC the implications of the new findings were not as simple as a “one in, one out” policy for memory storage. “It’s not that we’re pushing something out of our head every time we’re putting something new in. The brain seems to think that the things we use frequently are the things that are really valuable to us. So it’s trying to keep things clear – to make sure that we can access those important things really easily, and push out of the way those things that are competing or interfering.” The idea that frequently recalling something can cause us to forget closely related memories is not new; Dr Wimber explained that it had “been around since the 1990s“.

This probably is only be one of the ways we forget our memories.