Archive for the ‘memory’ Category

030826 – Parallel processing in the mind

Tuesday, August 26th, 2003

030826 – Parallel processing in the mind

I don’t know if it originated with Grossberg, but I like the concept of complementary processing streams.  Actually, he talks about it as if it always involves a dichotomy.  Could it not also be multiple (any number) parallel streams?  Certainly, the convergence of inputs from a large number of brain areas on the amygdala indicates that it’s not just dichotomous streams.

Grossberg writes as if he is describing exactly what happens—especially with his neural circuit diagrams, but the more I read, the more they seem fanciful.  Certainly there’s something missing when the diagrams only show neurons in layers 2/3, 4, and 6.

In also seems that there’s something missing from the analysis of the visual “what” pathway.  Edge and Surface processing seem very closely tied throughout.  In visual area V1, the “blob” neurons are surrounded by “interblob” neurons and in visual area V2, the “thin stripe” the neurons alternate with the “interstripe” neurons.  Surely there is some crosstalk between (among) the channels.

Grossberg uses the term “catastrophic forgetting”.  He also talks about complementary channels of processing in the brain.  And he, among others, and talks about a “where” channel to the parietal lobe and a “what” channel to the temporal lobe.  Things then get a little confused.  Part of the point of “catastrophic forgetting” is, in effect that certain memories need to get overwritten, e.g., memories of where a particular movable object is located.  In contrast other memories should not be easily forgotten.

It is not clear that the categories “easily over writable” and “not easily over writable” (or should it be “things that change often” and “things that don’t often change”?) are the same as “where” and “what”.  It’s certainly possible from an evolutionary standpoint that what and where are sufficiently essential aspects of the environment that they should be per se ensconced in genetically determined neural structures.  Nonetheless, is reasonable to ask whether what evolution has provided is also being used in ways unrelated to its evolutionarily determined functionality.

Or alternatively, given that evolution has cobbled together mechanisms capable of recording information with differing degrees of environmental permanence, it seems reasonable to suppose that the same mechanism could show up in different places; although, I am well aware that the essentially opportunistic functioning of evolution leaves open the possibility that the same function is performed in many different ways.  Still, in our environment and the environment of our animal ancestors some things change rapidly and some things don’t.

030819 – Emotion and incentive

Tuesday, August 19th, 2003

030819 – Emotion and incentive

I really don’t like Joseph LeDoux’s (2002) use of the words emotion and incentive.  He uses emotion to mean just about anything that can affect synaptic plasticity, that is, he defines the term backwards.  That doesn’t work because we don’t know what can affect synaptic plasticity, but we do have a good idea of what we think emotion means.

Similarly, incentive.  To my mind an incentive is a conditional promise of reward in the future.  It takes the form, “if you do this you’ll get that.”  The term is a bit confusing in ordinary speech.  Management announces an incentive program whereby workers who overfill their quotas will receive a significant bonus.  The announcement serves as the incentive for employees to work harder.
Hans-Lukas Teuber (Chair of the M.I.T. Psychology Department while I was getting my Ph.D there) liked to tell the  story of the monkey and the “consolation prize.”  The monkey works to get a piece of banana, but when the monkey gets the piece of banana, he doesn’t eat it, he just sticks it in his mouth and holds it in his cheek.  When the monkey makes a mistake and doesn’t get a piece of banana, he eats some of the banana he was holding in his cheek.  So the monkey “rewards” himself for making a mistake.  Teuber called it a “consolation prize.”

So the (implicit) promise of “a piece of banana if you do this correctly” is the incentive (I actually would have said motivation here—LeDoux can’t because he uses motivation to mean something else).  What’s the banana then?  A reward?  Maybe, but in the context of the situation, the banana is the confirmation that the incentive was correctly understood, and that, in itself is (arguably) rewarding.

It should be rewarding, in any case, by the following argument.  It is clearly adaptive for an organism to be able to reliably predict the way the future will unfold, particularly with respect to possible events that have (can have, may have) some kind of significance to the organism.  It is even more important for an organism to be able to reliably predict the effects of a possible action

“I’ll bet that if I figure out what to do here, I’ll get a piece of banana.  Hmmm.  This looks right.  I’ll do it.  Banana!  Yes!  I was right!”


“I’ll bet that if I figure out what to do here, I’ll get a piece of banana.  Hmmm.  This looks right.  I’ll do it.  No banana?  Bummer!  I didn’t get it right.  I’m gonna eat a piece of banana.”

So, back to the question: what is the banana?  In evolutionary terms, at one level, the banana is nourishment and valuable as such; in this context, however, the banana is real-world confirmation of correct understanding of (at least one aspect) of the real world.

But notice the subtlety here.  Setting aside our knowledge that correlation is not causality (which we seem to do a lot), the banana confirms the existence of a pattern: In the context of this recognizable situation it is to be expected that a problem will be presented and if I correctly figure out what the situation requires and do it, I will get some banana and if I don’t figure out what the situation requires, I won’t get any banana.

If no banana is forthcoming, what is the correct conclusion in this situation?  There are several: 1) I got it wrong (everything else is unchanged); 2) I got it right, but there are no more bananas at the moment (everything else is unchanged); 3) The pattern is incorrect: there are no bananas to be had here.  This is clearly not an exhaustive list of all the alternatives, but it does indicate that the conclusion to be drawn in the situation is by no means obvious.  This is borne out by the well-known fact that behavior patterns established by a random reinforcement pattern are more resistant to extinguishment than patterns established by a 100 percent reliable reinforcement pattern.

Again let’s look from an evolutionary standpoint: Which is more important?  Obtaining a piece of banana or knowing how to obtain a piece of banana?  If I give a man a fish, I have fed him for a day; if I teach a man to fish, I have fed him for life.

An important question for an organism is: Where is food?  The obvious next question is: How do I get there? Once these questions are answered, the next question is: Once I get there, how do I get it?  I have a feeling that in the brain these questions, or rather the answers to these questions, are intimately related.  Ultimately, an organism needs a procedural answer: What steps need to be taken in order to arrive at the desired goal?  The organism needs a sequential plan.  It makes me wonder if the parietal lobe in addition to its involvement with the representation of physical space also is involved with the representation of conceptual space.

Maybe not.  Physical space has obvious nearness relationships that conceptual space does not necessarily have.  On the other hand, George Lakoff’s arguments about the way in which meanings are derived from physical relationships may suggest that parietal lobe involvement (or, more precisely, involvement of whenever part of the brain is responsible for keeping track of the physical organization of the universe with respect to the organism) in the organization of concepts is in fact plausible.

Correlation is not causality, but from an evolutionary standpoint an organism cannot in general afford to do the necessary research to establish reliable causality.  Interestingly, human beings have acquired the ability to reason systematically and have managed in some cases to determine causality.  What is more significant, and many have remarked upon this, is that humans can transmit patterns verbally to other humans.  Not only that, patterns thus transmitted can be used by the receiver almost as if they had been directly precedent or intuited or whatever the appropriate word is to describe the way we acquire patterns.  I say “almost” because I think there must be some difference between patterns established by word-of-mouth and patterns established by other means.

I don’t think, however, that the difference is as simple as the difference between declarative and non declarative memory.  And by the way am not real happy with the use of the word declarative.  And I guess part of the reason for that is that I think some if not much of things that enter “declaratively” ends up stored “non declaratively”.  Which, I suppose, is simply to say that we don’t always consciously examine the implications of things that we hear, but those implications may end up being stored.  Perhaps this is just a matter of “stimulus generalization”, but whatever it is, it feels like a hard and fast distinction between declarative and non declarative memory is ultimately misguided.  And, in fact, studies of “priming” and in individuals whose declarative memory system is damaged in some way seem to me to imply that non declarative priming (whatever that means) also occurs in those whose declarative memory system is intact.

I suppose the argument is simply that there are two kinds of memory, but things start to feel a little too glib when people start to discuss the pathways by which information enters one memory system or the other as if in the intact organism there is no (and can be no) “crosstalk” between the two.  Maybe it’s just that in the course of reviewing the literature of the past thirty years I have concluded that where there are dichotomies it is important, even essential, not to accept them literally, for fear of missing overlooked clues to the functioning of the system.

030718 – Self-Reporting

Friday, July 18th, 2003

030718 – Self-Reporting

Is there any advantage to an organism to be able to report its own internal state to another organism?  For that is one of the things that human beings are able to do.  Is there any advantage to an organism to be able to use language internally without actually producing an utterance?

Winograd’s SHRDLU program had the ability to answer questions about what it was doing.  Many expert system programs have the ability to answer questions about the way they reached their conclusions.  In both cases, the ability to answer questions is implemented separately from the part of the program that “does the work” so to speak.  However, in order to be able to answer questions about its own behavior, the question answering portion of the program must have access to the information required to answer the questions.  That is, the expertise required to perform the task is different from the expertise required to answer questions about the performance of the task.

In order to answer questions about a process that has been completed, there must be a record of, or a way to reconstruct, the steps in the process.  Actually, is not sufficient simply to be able to reconstruct the steps in the process.  At the very least, there must be some record that enables the organism to identify the process to be reconstructed.

Not all questions posed to SHRDLU require memory.  For example one can ask SHRDLU, “What is on the red block?”  To answer a question like this, SHRDLU need only observe the current state of its universe and report the requested information.  However, to answer at question like, “Why did you remove the pyramid from the red block?”  SHRDLU must examine the record of its recent actions and the “motivations” for its recent actions to come up with an answer such as, “In order to make room for the blue cylinder.”

Not all questions that require memory require information about motivation as, for example, “When was the blue cylinder placed on the red cube?”

Is SHRDLU self-aware?  I don’t think anyone would say so.  Is an expert system that can answer questions about its reasoning self-aware?  I don’t think anyone would say so.  Still, the fact remains that it is possible to perform a task without being able to answer questions about the way the task was performed.  Answering questions is an entirely different task.


Wednesday, July 9th, 2003


I think of the sensorium as being something like an extremely resonant bell.  Sensory inputs or rather the processed remnants of sensory inputs, that is to say the effects of sensory inputs, prime various patterns in the sensorium and alter the way that subsequent sensory inputs are processed.  This process manifests itself as what we call short-term memory, intermediate term memory, long-term memory, as well as some form of learning.  Because we think of memory as the acquisition of factual information and not the development in the sensorium of patterns or the recognition of patterns, we’re not accustomed to thinking of short-term memory as learning.

Assuming that there is some sort of automatic recirculating mechanism, I wonder if the fact that in short-term (and long-term) memory experiments there is a clear effect favoring recall of the first item of a list is simply an artifact that results because generally the first item of a list is preceded by silence or by some irrelevant stimulus.  I wonder if short-term memory is some kind of more or less fixed time constant.  One might think of an initial stage of processing in which inputs are recirculated after some time.  This raises the question of whether observed limits on the number of memory chunks that can be stored in short-term memory is a result of the amount of time it takes for each chunk to be entered.  No, it’s probably much more complicated than that.  There is already an interaction between sensory inputs and pre-existing patterns from the get go.  That’s why zillions of short-term memory experiments use nonsense syllables.

Rather than thinking of attention as adding processing power to particular sensory inputs it may make more sense to think of attention as a way of suppressing, or at least reducing, the strength of competing sensory inputs.  That of course makes more sense than thinking that the brain has excess processing capacity just lying around waiting to be called into action for the purpose of attention.

How long is “now”?  I don’t think the question really has an answer.  I think the hetero phenomenological experience of “now” depends on the contents of the recirculating short-term memory buffer.  When I talk about the recirculating short-term memory buffer I mean that at a certain point in the processing of incoming sensory inputs, the processed inputs are fed back to an earlier point in the processing and somehow combined with the current incoming sensory inputs.  At the same time, the processed inputs continue to be further processed.

As I think more about “now” I realized that there are a number of different now’s depending on the sensory modality.  Well even that’s not right.  We know from various tachistoscopic experiments that there is a short-term visual buffer with a very short time constant, which suggests that there is a very short visual “now”.  I can’t think of any good evolutionary reason why each modality’s “now” should have the same time constant.

I see that I’ve written “the” recirculating short-term memory buffer.  I certainly don’t know that there’s only one, and I don’t know that any of my conclusions depend on there being only one.  Indeed I think that patterns recirculate with differing time constants depending in some way on the nature (whatever that means) of each pattern.