Hierarchical Brain

Attention

Attention is one of the major facets of consciousness. It feels to me like a spotlight that I can move between things that I want to examine more closely, and the focussing of my conscious thoughts on one thing at a time, applying to perception, memory and action. Research has shown, however, that attention is actually the selection of certain signals over others, driven by a multi-level competition involving relative signal strengths (which are bottom-up, or afferent, influences) and predictions (which are top-down, or efferent, influences). So there is a large explanatory gap between my experience and reality.

The explanation for this gap is that my personal experience of attention is based solely on my brain’s internal model of attention, which is built and maintained by exactly the same hierarchical afferent processing that is used to process sense data. The processing of sense data results in the creation and update of symbol schemas that represent things in the world or in my body; the processing of data related to my internal brain processes (which I call cognoception), in this case the process of attention, results in the creation and update of a symbol schema or model in my self symbol schema that represents the process of attention, and it is only this model that I can be aware of.

Attention is a high-level brain function at level 6 in my seven hierarchical levels of description because it depends on the existence of symbol schemas.

My personal experiences of attention

• This is quite a long list of my personal experience of aspects of attention with details of what each feels like to me; I suspect you will agree with most of these:
  1. It is like a single narrow spotlight that can focus on only one thing at a time, but which can move quite rapidly (many times a second) from one thing to another. There are no noticeable gaps, so there seems to be a continuous flow of my attention.
  2. This spotlight, which seems to originate from my inner self, can either point at something I want to concentrate on outside my brain (external attention), or at a memory or thought inside my brain (internal attention).
  3. Attention is always “on”, at least until I “lose consciousness” either by falling asleep, become comatose because of a large dose of a drug or serious illness, or die. (I fall asleep at least once a day, but the other reasons don’t happen so often!)
  4. Attention returns quite quickly after I wake up but it normally takes a few seconds, so there is not just an “on” and an “off”, there is a fuzzy boundary between the two. There are other times when attention is difficult, or limited in its duration and depth, such as when I am very tired, or ill, particularly with a fever, or under the influence of a relatively small dose of a drug (including alcohol).
  5. It feels as though I choose what to swing the spotlight onto, except that my attention is automatically diverted to an unexpected external event, such as a loud noise or flash of light.
  6. Although I describe it as being like a spotlight, the same process of attention seems to apply to all senses, not just vision; although for some senses, such as taste and smell, the sensations are much more fleeting than for sight or hearing.
  7. I can narrow the beam in order to concentrate on one small external thing, which seems to then include data from only one sense. For example, while I am concentrating on threading a needle, I find that all other sensory data such as music playing in the background is totally ignored. I feel I can also widen the beam it to get a broader view within one scenario and take in data from more than one sense, although I think that this might be enabled simply by more rapid movements of the spotlight.
  8. I can turn the spotlight on some bodily things such as my breathing, or a pain in my toe, or an itch in the middle of my back, but there are a lot of internal things that I cannot shine any light on, such as my blood pressure, my liver functions, or the state of some particular neurons in my brain. Even concentrating on my heartbeat is quite difficult, although it can be done with practice.
  9. I can direct attention to “a space”, where I expect something to happen in the near future, such as the toast to pop out of the toaster, or a bus to appear at the end of the road. This feels similar to when I am searching for something, such as my lost keys or a particular book on the shelf.
  10. When illuminating internally (internal attention), I can reenvisage scenes, replay memories, rehearse scenarios, plan actions etc., and these thoughts are easily remembered. However, this process can sometimes slip into day-dreaming, which seems different because it is not often remembered, just as dreams during sleep are not often remembered. While engaged in internal attention, external attention is not possible; an expected external stimulus will usually “break in” and disturb my thoughts, although this is less likely during day-dreaming. For all these reasons, internal attention seems very much like a continuation of external attention, but day-dreaming is not attention, although the boundary between the two is often not clear cut.
  11. I can only remember things or events when I pay attention to them. If I am doing some well-practised habitual task, such as getting dressed, I can be thinking about something entirely different such as a future meeting, and then later realise that I cannot remember what I was doing at all. This should perhaps be more worrying if it happens while I am driving a car, but it does sometimes happen, and I don’t crash, although I suspect my reactions times would not be as good as they should be¹.
  12. There is a time lag with attention that I notice sometimes. If a loud unexpected noise disturbs me while I am concentrating on something else, it takes perhaps half a second to realise what it is, or might be. Similarly, if I glance at the digital display of seconds on a clock, or the second hand on an analogue clock, it can sometimes seem to not move for about a second-and-a-half. This indicates to me that my attention actually runs about half a second behind reality, but my brain seems to do a good job in catering for this.
  13. Probably for similar reasons, I cannot do anything very fast, such as catching or hitting a fast-moving ball, or playing a fast set of notes on the piano, purely using attention; such a task has to be learnt so that it becomes largely unconscious. Once I have learnt a task like this, if I try to focus attention on it later, the learnt action can actually be disrupted; I have to try to not think about it, which is not easy to do.
  14. It is not possible for me pay attention to nothing. If I try to do this, I always find I am thinking about something else (for example, I am thinking about why it is not possible to think of nothing!).
  15. Attention has limits in terms of the number of things I can do at once, which seems to be to do with how quickly I can switch between one thing and another. It feels like attention is a limited resource, both in terms of how much at once, and how much over a specific period. Attention is tiring!
  16. It is not easy to describe the difference between seeing a frisbee, and imagining seeing a frisbee. The two seem very similar, but they feel different from each other in a way that is difficult to describe.
• It is clear from this list that my experience of attention is very wide-ranging with many aspects, but it is also a crucial part of me.
  • It is an extremely important part of my moment-to-moment existence and seems to be the basis of my what I call my consciousness.
  • It is also the basis of my free will, because my choices of what I say, what I do, and even what I think, are all driven solely by what I pay attention to, or at least that is what it seems like to me.

What science shows that attention really is

• There has been a huge amount of research, in particular since around 1950, to try to pin down exactly what attention really is and how it works, and a lot of progress has been made^{2, 3}. This section is a very brief summary of the aspects of this history that are relevant to my proposals.
  • Research in this area has nearly always involved tests on real people, and assumptions always have to be made about how the volunteers will react and how attention is used by people.
    • Psychological research has usually involved specially designed tests performed on volunteers to investigate specific aspects of attention.
    • Neurological research has usually involved gathering data from various types of brain scans that are carried out while specially designed tasks are done by volunteers.
    • Much of the research into attention has been done on vision and hearing, but it is generally accepted now that the same principles apply to all sense data.
  • The ideas on what attention actually is have varied a lot over the years, and have also varied across the different scientific fields.
    • Psychologists have for many years referred to attention as if it were a resource⁴, something that is applied to brain processes, is limited in supply and scope⁵, and that overuse can lead to attention fatigue.
    • We now know that attention depends on arousal, the technical name for wakefulness, which in turn largely depends on the levels of various chemicals in the brain known as neuromodulators, in this case primarily one called dopamine (see also under the heading ADHD below).
    • A recent scientific review says that attention is an evolved brain process that is required for adaptive and effective selection of behavior⁶.
    • Another important point that is not often made is that attention evolved to ensure that the body as a whole makes only one decision to act at a time. To avoid the paradox of Buridan’s donkey, the brain must have a mechanism to choose one option and stick to it, at least in the short term.
    So rather than being a limited resource itself, attention evolved in order to manage the limited resources that the brain has at its disposal, as well as to manage the limited resources and opportunities available to the body that the brain serves.
  • Many models for attention have been proposed over the years, often to fit the evidence that has been gathered in relation to one particular aspect of attention³.
    • Some examples are Broadbent’s filter model of attention (1958), Feature integration theory (1980) and Perceptual load theory (1994).
    • Models have then sometimes had to be extended to explain evidence in other areas⁷, but other evidence does not always fit within a particular model.
    • Research publications have sometimes tangled their explanations of attention with working memory, perception, self-awareness or consciousness.
  • From the 1990s, models started to emerge that took into account neurological findings related to the multi-level nature of attention processing.
    • The first well-known one, called Biased Competition Theory, proposed bottom-up (that I call afferent) and top-down (that I efferent) competitive influences in visual processing⁸.
      • These influences have been extensively investigated in the human brain, but only in respect of visual processing^{2, 9}.
      • This paper was the first that I have found to suggest that attention is an emergent property⁸.
    • The concept of biased competition has been refined since then, with two recent papers suggesting new definitions of attention as “a multi-level system of weights and balances”¹⁰, and “dynamically weighted prioritization”⁷.
    • The main points from these latest models are as follows:
      • There is a hierarchy of multiple levels of processing - each level takes as input the output of the previous level and passes on its output to the next level, but the data goes in both directions, both up and down the hierarchy, or, in my terminology, in both afferent and efferent directions.
      • Each level therefore has an effect on the levels both above and below it.
      • Competition occurs both within and across all levels of processing, from the very bottom to the very top.
      • The bottom-up (afferent) influences are the strengths of the signals and the connections involved, which reflect the salience or important of the stimulus.
      • The top-down (efferent) influences are assumed to be voluntary, or goal-directed actions¹¹, but these theories do not give any information on how these come about.
  • A very different approach has been taken in recent years by a theory called Predictive Processing or Predictive Coding, which, as its name suggests, concentrates on predictive processes as the top-down aspects of influence.
    • More details on this theory is given on the pages relating to afferent processing and prediction, and it is also relevant to perception and action.
    • According to this theory¹²:
      • A model of the world is built by extracting patterns or statistical regularities from incoming signals.
      • At each level of the hierarchy, the model is compared to incoming information. A mis-match generates a prediction error, which updates the model on the level above (prediction error is also called surprise, or surprisal, or free energy)¹³.
      • A perception only happens when the prediction errors are minimised, which means the model fits the incoming data.
      • There is also a concept of precision weighting or expectation, which is a measure of how accurate a prediction might be, and depends on the details or circumstances of the sensing.
      • Attention then is the minimisation of prediction errors by selecting the signal most likely to fit the model¹⁴.
  • Two of these recent theories, the Biased Competition Theory and Predictive Processing, which at first sight seem very different, have been shown to be mathematically equivalent¹⁵.
    • This is not surprising; the predictive processing theory is just a different way of looking at the same thing.
    • The biased competition theories examine the competition at all levels; the predictive processing theories look at the same processes, but from the top-down viewpoint.
  • Many modern text books on neuroscience include large amounts of information about attention, about what happens when it fails to work correctly because of damage or trauma, and about the results of brain scans of varying precision during relevant tasks related to attention, and therefore there is often a lot of detail about the exact areas of the brain involved.

The hierarchical explanation

• My personal experiences of attention listed above seem to bear very little relationship to what attention has been shown to be in the brain (see immediately above), there is a very large explanatory gap.
  • I have no knowledge (by introspection) of the multi-level competition that apparently goes on prior to any object or concept coming to my attention.
  • I am sometimes aware that there might be things that impinge on my senses that I never become consciously aware of, but the number or volume of things that remain unconscious is clearly many times higher than I can know.
  • The amount of influence “I” actually have over what I pay attention to is clearly different from what I believe.
  • I have to conclude that many, if not all, of my experiences listed above are illusions, which means that my views above on consciousness and free will are also not correct.
• My answer to this problem is to propose that what I am aware from introspection about my own attention is in fact knowledge solely from a symbol schema that is a model of my process of attention that has been built in my brain, by my brain.
  • Like all symbol schemas, this model is not fully complete or accurate, it is a compressed, abstracted and generalised version of the real thing, so my awareness of my attention is neither accurate nor complete.
  • The model has been built in exactly the same way as all other symbol schemas are built, by afferent processing of data, but in this case not of sense data, but of data from the attention process within the brain. Drawing a parallel with perception, I call this process cognoception.
  • As discussed in cognoception - further details, my model of all internal brain processes, including that of attention, can only be of the part of the process that is conscious, in other words the part that my self symbol schema is aware of. This is why I am totally unaware of the process of the multi-level competition, and only aware of what actually wins the competition and arrives in my conscious awareness.
  • For the same reason, I can only be aware of my initiation of a change to what I am paying attention to if it succeeds, I will not be aware of failed attempts.
  • This also means that my view of my free will is not fully correct, I do not have full control over my choices, but I do have an influence via attention.
• Attention is a high-level feature that emerges from four separate layers of lower levels of description.
  1. Level 2 in my hierarchy of 7 levels describes memory-enhanced coincidence detection and lateral inhibition, and the third of these three functions, lateral inhibition, is the lowest level of attention.
     • This is the inhibiting of the firing of one or more neurons by the firing of one or more other neurons where the inhibition is lateral, or sideways, between sets of neurons that are fulfilling similar functions.
     • This is a form of competition where only the most important or strongest afferent signals in any one area make it through to the higher levels of processing.
  2. Level 3 in my hierarchy describes abstraction and prediction-enhanced selection, and the third of these three functions, selection, is the next level up in the creation of attention.
     • Many levels of the competition created by lateral inhibition means that certain signals are selected over others, depending on the importance and strength of these afferent signals.
     • However, in addition at this level, there is efferent influence from prediction, using what is, in effect, a memory of previous encounters.
     • These memories are stored as efferent connections that are created by afferent processing.
  3. Level 4 in my hierarchy describes symbol schemas, networks of neurons and the connections between them that are representative symbols. A symbol schema is activated when sufficient neurons in the network fire at the same time.
     • A given symbol schema is activated or not by the processes of attention depending on the multi-level competition that results from the processing in the lower levels of the hierarchy in levels 2 and 3.
     • These afferent influences depend on the importance (salience) of the signals, but there are also efferent competing influences from predictions as well as lateral competing influences between individual symbol schemas.
     
  4. The final, and highest, layer of processing required for an activated symbol schema to become the subject of conscious attention is for connections to become activated between it and the self symbol schema (see diagram and afferent processing example 7).
     • This is yet another layer of competition, this time between symbol schemas, driven by both afferent and efferent influences.
     • Once an activated symbol schema is connected to the self symbol schema, it can remain dominant and be self-perpetuating for a time (many seconds) because of a large circuit of looping signals from the self symbol schema to the symbol schema in question and then via reinstatement to sensory neurons.
  • In summary, the process of attention emerges from a multi-level competitive hierarchy with upwards, downwards and lateral influences at all levels.
    • Lower levels of the hierarchy tend to be more dominated by afferent influences; these reflect the strength of the signals and connections.
    • Higher levels of the hierarchy tend to be more dominated by efferent influences; these are predictions based on memories of previous encounters.
    • At a higher level of description, the bottom-up (afferent) influences are the importance or salience of the signals; the top-down (efferent) influences are downward causations or actions.
    So what I think of as my attention is actually my perception of the model of my attention in my brain, just as my perception is my awareness of symbol schemas, not the real world.
• This explanation seems to fill the explanatory gap and answer a number of other questions.
  • It fits well with the latest descriptions of attention outlined above.
  • It explains why and how my experiences of attention are very different from the known neurological findings about attention.
  • My experiences of attention are exactly what one might expect if my self symbol schema is only aware of a model of attention.
  • This fits very well with my higher-level conclusion that I am my self symbol schema.

Differences in attention

• Research has shown that some aspects of attention can vary between people depending on a combination of genetics, environment and also possibly learning.
  • There are two areas of evidence to support this:
    1. Research has found that there are some differences in attention between different cultures, which could be due to any of these three factors¹⁶.
    2. Research into the causes of Attention Deficit Hyperactivity Disorder (ADHD) has shown that it is largely due to genetics, but there are also environmental and societal factors that could affect learning.
  • The main reason for variations in attention (including in ADHD) are likely to be related to the neuromodulator called dopamine, specifically the mesocortical pathway.
    • This neuromodulator is known to affect general executive functions in the brain, including attention, and controls arousal.
    • It is probably what I am deficient in when I am feeling so tired that I cannot concentrate on anything.
  • This supports the proposal that, to a certain extent, attention is a learnt skill and therefore could potentially be learnt in different ways.
  • It also shows that a certain level of the dopamine neuromodulator is a prerequisite for the proper working of attention, and so the lack of this is one reason for sleep.
• Attention, as described above, is a multi-level competition with afferent, efferent, and lateral influences at all levels. It is finely-balanced process that could be unbalanced or impeded by issues at any level, issues with the influences from any direction, issues with any of the neurons and synapses involved, or issues with the neuromodulation chemicals that are required for the correct functioning of attention. When the process of attention becomes unbalanced or goes wrong in any way, many problems can arise.
  • Attention does make heavy use of inhibition in the multi-level competition process; overall there is more inhibition that excitation, because a single symbol schema has to win the competition against many others.
  • Heavy use of the inhibitory links means that many of them will increase in strength.
  • It is known that a balance is maintained in the brain between excitation and inhibition (see model of my world - chaos) in order to maintain the criticality of the chaotic state of the brain.
  • If this starts to become unbalanced because of heavy use of attention, it will become harder to concentrate and to change attention from one thing to another, so attention is more difficult and becomes more tiring, which feels like a lack of willpower (see free will).
  • Sleep is known to reset this balance.

Additional points

• The following important points concern attention in general and are not necessarily dependent on my explanation, but in some cases are easier to understand in the context of my explanation.
• Attention is not the same as consciousness.
  • Attention is one of the major facets of consciousness, the others being self-awareness, memory and feelings and emotions.
  • Attention is certainly the feature of consciousness that I am most aware of moment-by-moment, but self-awareness is a more basic requirement for consciousness than attention.
    • If I had no self-awareness, I could not be aware of my attention or what I was paying attention to.
    • If I had no self-awareness, I could not be aware of any memories and could not have any feelings.
  • So I regard attention, memory, and feelings and emotions as being subsidiary to self-awareness, but all are part of consciousness.
• Attention cannot happen without efferent connections, and these are created and/or strengthened by afferent processing as symbol schemas are created or updated.
  • I cannot have attention on a thing if I have no symbol schema for it, and I cannot have any conscious attention on a thing if there are no efferent connections from my self symbol schema to the symbol schema of the thing in question.
  • The process of attention does not apply to all afferent processing within the brain, because there are many things that I am not able to focus my attention on.
    • I am not able to pay attention to data from brain processes and how they work.
    • I am not aware of data from many internal organs that is processed autonomously.
    The reason is presumably because the required efferent connections do not exist in these areas.
  • There are many well-known examples where attention on an object would be expected, but does not happen, for various reasons. They are generally classed as examples of inattentional blindness, and includes the famous gorilla-on-the-basketball-court experiment.
• Attention evolved before self-awareness evolved, for two important reasons:
  1. So that the brain could prioritise important signals over unimportant ones by allocating more resource to important signals that to unimportant ones. This is necessary to be efficient, but also because it would impossible for the brain to fully process all data that it receives or generates.
  2. To allow only one action to be taken by the whole body in response to a stimulus (more on this in the next paragraph).
  As detailed above, self-awareness then came about by the requirement to model the process of attention.
• Conscious attention is single-threaded, i.e. only one thing is conscious at any one time, because the body as a whole must make only one decision at a time^{17, 18}.
  • If I was able to have attention on more than one thing at once, it is possible that one of those things might require my legs to go in one direction and my arms in another. This would not be a good thing!
  • Certainly in circumstances of do-or-die, or freeze-or-flight, my whole body has to make one decision to take one action.
  • This is why, although some people, or even cultures, may be better at concentrating on more than one thing at a time, ultimately this is still a rapid switching technique, and not literally two things at once.
  • This, I think, is a much more practical reason for attention than minimisation of an emergent quantity (such as free energy, surprise, or prediction error).
  • However, the two could be broadly equivalent.
• In attention research, there is often talk of working memory, as if there is some part of the brain that is capable of storing information about any possible object or concept that has been moved from elsewhere in the brain, or has been perceived in the real world, and from where it can be moved to somewhere else in the brain.
  • If the brain were a computer, and the object or concept in question was somehow encoded as a series of bits, then this is possible, but of course the brain is not a computer, and it does not have any rules for how the representation of objects or concepts can be encoded in bits or decoded again.
  • However, if by working memory is meant short-term memory, then the concept is possible, providing it is acknowledged that it is not one area of the brain that is storing different information.
  • A short-term memory is held using short-term changes in synapses or neurons, longer-term memories are held using long-term changes.
• In everyday speech, when someone says that they are conscious of something, they generally mean either that they are paying attention to an external object, or that they are aware of a particular internal thought or concept.
  • You might think that the use of the verb “pay” when referring to attention implies that some resource is being expended, and most people would agree that paying attention requires more effort than day-dreaming or sleeping.
  • However, the word “pay” is used in this sense to mean “give” or “bestow”, as also used in the phrases “to pay someone a visit” or “to pay someone a compliment”.
  • What is actually meant is to give attention to the external here-and-now (what is supposed to be concentrated on) - after all, you might be giving all your attention to an internal discomfort, an unsolved past problem, or a future concern.
• According to the normal scientific definition of attention, any selection or prioritisation of incoming signals is a form or attention, whether or not the selected signals reach or update a symbol schema, or reach the self symbol schema and become consciously available.
  • Conscious attention forms a much larger circuit that is self-perpetuating and long-lived compared to unconscious processing.
  • While the connection from a symbol schema to the self symbol schema is maintained, the attention is a conscious process and we are aware of what we are doing, and also remember it later.
  • If there is no connection to the self symbol schema the events recorded by the incoming signals are not remembered, although if the symbol schema in question is updated, there could be change to future behaviour. This is how unconscious learning can take place.
  • Attention is closely related to a number of other functions such as memory, perception, reinstatement and thought and imagination, as well as action and free will.

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References For information on references, see structure of this website - references

1. ^ ^ Impact of Distracted Driving on Safety and Traffic Flow - Stavrinos et al. 2013
   doi: 10.1016/j.aap.2013.02.003 downloadable here or see GoogleScholar.
   Page 2, beginning of first paragraph: “With advancing technology, the number of distractions to which motor vehicle drivers are exposed continues to increase. This increase in availability of distractions has most likely attributed to the 30% increase in the number of motor vehicle collisions (MVCs) in the United States from 2005 to 2008 related to distraction. One of the most common distractions in which motor vehicle drivers engage is using a cell phone.”
   Page 4, end of first paragraph: “drivers who are distracted navigate at slower speeds, leave larger intervals between their own vehicle and the vehicle in front of them, and have reduced reaction times.”
2. ^ ^ The attention schema theory: a mechanistic account of subjective awareness - Webb and Graziano 2015
   doi:10.3389/fpsyg.2015.00500 downloadable here or see GoogleScholar.
   Pages 3-4 under the heading “Attention”: “Because the amount of information with which our senses are bombarded is typically far too vast to deeply process in its entirety, some mechanism must exist to determine or 'select' which information to process deeply. Much work in cognitive psychology and neuroscience over the past half century has focused on which factors determine this 'selection' process and how the brain accomplishes such an operation.
   An influential theory put forward by Desimone and Duncan, the 'biased competition' theory, characterizes attention as a signal competition within the brain. Signals compete in order to be more deeply processed and ultimately to influence and guide behavior. This signal competition emerges at the earliest stages of processing in the nervous system and is present at every stage. ...Different factors can influence or 'bias' the outcome of this competition. One such factor has to do with the saliency of the stimulus. Especially intense or salient stimuli can 'grab' attention in a bottom-up, stimulus-driven manner.
   As signals progress through the nervous system, they are increasingly subject to the influence of top-down, biasing signals. By this method, attention can be internally directed, slanting the outcome of this signal competition in a goal-directed manner based on the demands of the current task. Signals that correspond to current goals can be boosted and irrelevant signals can be suppressed.”
3. ^ ^ A selective review of selective attention research from the past century - Driver 2010
   doi: 10.1348/000712601162103 downloadable here or see GoogleScholar.
   This useful review focuses on work from the 1950s onwards, mostly cognitive neuroscience in Britain.
   Page 72, under the heading “Future attention research”: “I hope that this rather idiosyncratic review has illustrated the tremendous progress made in selective attention research in the second half of the 20th century, and also the substantial contribution from British psychology.”
4. ^ Is Attentional Resource Allocation Across Sensory Modalities Task-Dependent - Wahn and Konig 2017
   doi: 10.5709/acp-0209-2 downloadable here or see GoogleScholar.
   Beginning of abstract, page 83: “Human information processing is limited by attentional resources. That is, via attentional mechanisms, humans select a limited amount of sensory input to process while other sensory input is neglected.”
5. ^ Working memory and attention - a conceptual analysis and review - Oberauer 2019
   doi: 10.5334/joc.58 downloadable here or see GoogleScholar.
   Page 3, under the heading “Attention as a Resource”: “The idea of attention as a resource is that the cognitive system has a limited resource that can be used for carrying out so-called attention-demanding processes. The resource is assumed to be a continuous quantity that can be split arbitrarily and allotted to different processes, depending on task demands.”
6. ^ What is attention? - Krauzlis, Wang, Yu and Katz 2021
   doi: 10.1002/wcs.1570 download not available, but see GoogleScholar.
   This starts with the most general definition of attention. Beginning of abstract, page 1: “We define attention as 'the set of evolved brain processes that leads to adaptive and effective behavioral selection.'”
   It goes on to make some useful points. Second paragraph of introduction, page 1: “... we hold attention to be synonymous with a particular set of brain processes. This might seem obvious, but it is not unusual to see attention described as though it were some sort of agent acting on the brain (e.g., 'attention increases the firing rates of neurons'), rather than a set of processes within the brain.”
   Page 5, 4th paragraph, under the heading “An evolutionary perspective”: “...attention emerged as a set of brain functions that helped match the flexibility and selectivity of the animal’s behavioral repertoire to the affordances of their ever-changing environment. These brain functions do not generate the behavior; instead, they help ensure that the appropriate information is ready at each moment to select and guide the next behavioral response. This perspective also provides an answer to the question 'why is there attention?'. Attention is often described as necessary for managing limited resources, but the arguments tend to focus on internal resources: energy consumption and computing capacity in the brain. We agree these internal limitations are important, but we suggest that attention evolved primarily to address a different limited resource that is external to the animal: the fleeting opportunities to extract value from the environment.”
7. ^ ^ Attention and platypuses - Shomstein, Zhang and Dubbelde - 2023
   doi: 10.1002/wcs.1600 downloadable here or see GoogleScholar.
   The reference to “platypuses” is an allusion to biological taxonomy where the platypus does not fit into either mammal or bird categories. This paper proposes a new model called “dynamically weighted prioritization”, which is based on, and similar to, the “multi-level system of weights and balances” in reference 10 below. It then gives examples of some phenomena that have been uncovered by attention research that do not fit neatly into other attentional models; these are what they refer to as platypuses. It does briefly cover prediction (without using the word) by referencing Karl Friston’s work on the free energy principle, and says a Bayesian framework is helpful.
8. ^ ^ Neural mechanisms of selective visual attention - Desimone and Duncan 1995
   doi: 10.1146/annurev.ne.18.030195.001205 downloadable here or see GoogleScholar.
   Page 194, first and second paragraphs: “At some point (or several points) between input and response, objects in the visual input compete for representation, analysis, or control. The competition is biased, however, towards information that is currently relevant to behavior. ... the model we develop is that attention is an emergent property of many neural mechanisms working to resolve competition for visual processing and control of behavior.”
9. ^ Top-down and bottom-up mechanisms in biasing competition in the human brain - Beck and Kastner 2009
   doi:10.1016/j.visres.2008.07.012 downloadable here or see GoogleScholar.
   Beginning of abstract: “The biased competition theory of selective attention has been an influential neural theory of attention, motivating numerous animal and human studies of visual attention and visual representation. There is now neural evidence in favor of all three of its most basic principles: that representation in the visual system is competitive; that both top-down and bottom-up biasing mechanisms influence the ongoing competition; and that competition is integrated across brain systems.”
   And from conclusions on page 11: “The first principle of competition now seems well established; multiple stimuli presented simultaneously in the visual field compete for representation in visual cortex by mutually suppressing neural responses. Moreover, evidence suggests that this competition is greatest at the level of the RF [Receptive Field]. There is also now an increasing body of evidence in favor of the second principle of control, suggesting that competition can be biased by both top-down and bottom-up factors. The finding that the stimulus-driven factor of stimulus similarity also affects competition is particularly interesting, as it opens a new avenue of investigation into influences on competition.”
10. ^ Attention as a multi-level system of weights and balances - Narhi-Martinez, Dube and Golomb 2022
    doi: 10.1002/wcs.1633 downloadable here or see GoogleScholar.
    This paper first tries to give a definition of attention. Second sentence of abstract, page 1: “Despite the word’s place in the common vernacular, a satisfying definition for 'attention' remains elusive. Part of the challenge is there exist many different types of attention, which may or may not share common mechanisms. Here we review this literature and offer an intuitive definition that draws from aspects of prior theories and models of attention but is broad enough to recognize the various types of attention and modalities it acts upon: attention as a multi-level system of weights and balances. While the specific mechanism(s) governing the weighting/balancing may vary across levels, the fundamental role of attention is to dynamically weigh and balance all signals - both externally-generated and internally-generated - such that the highest weighted signals are selected and enhanced. Top-down, bottom-up, and experience-driven factors dynamically impact this balancing, and competition occurs both within and across multiple levels of processing.”
    The introduction (pages 1-2) is an excellent summary of definitions of attention and previous research on “What is attention?”. However, this paper has no mention of the multiple levels being hierarchical, no mention of prediction as the major top-down influence, and also no mention of the difference (or explanatory gap) between the personal experience of attention and the neurological explanation of what it is.
11. ^ Cognitive Neuroscience: The Biology of the Mind - Gazzaniga, Ivry and Mangun, Fourth Edition 2014 Norton & Company USA
    Page 285, under the heading “Take-home messages” at the end of the section on “Models of attention”: “Attention involves both top-down (voluntary), goal-directed processes and bottom-up (reflexive), stimulus-driven mechanisms.”
12. ^ YouTube video - “Ransom & Fazelpour’s Intro to 'Three Problems For Predictive Coding Theory Of Attention'” - Ransom and Fazelpour 2016
    The summary of Predictive Processing is taken partly from this video, which is an accompaniment to the online paper Three Problems for the Predictive Coding Theory of Attention - Ransom and Fazelpour 2015. The video contains a useful introduction to the theory, as well as a description of a possible problem with the theory, and the online paper has a number of thoughts and answers at the end.
    The following quote is from the a slide on the YouTube video at 4' 45": “Attention is the process of selecting the prediction error expected to be most precise and revising perceptual hypotheses on this basis.”
13. ^ Whatever next? Predictive brains, situated agents, and the future of cognitive science - Andy Clark 2013
    doi: 10.1017/S0140525X12000477 downloadable here or see GoogleScholar.
    Beginning of abstract: “Brains, it has recently been argued, are essentially prediction machines. They are bundles of cells that support perception and action by constantly attempting to match incoming sensory inputs with top-down expectations or predictions. This is achieved using a hierarchical generative model that aims to minimize prediction error within a bidirectional cascade of cortical processing. Such accounts offer a unifying model of perception and action, illuminate the functional role of attention, and may neatly capture the special contribution of cortical processing to adaptive success.”
14. ^ The free-energy principle: a rough guide to the brain? - Friston 2009
    doi: 10.1016/j.tics.2009.04.005 downloadable here or see GoogleScholar.
    Page 299, under the heading “Attention and precision”, second paragraph: “...attention is simply the process of optimising precision [of prediction errors] during hierarchical perceptual inference.”
15. ^ Reconciling predictive coding and biased competition models of cortical function - Spratling 2008
    doi: 10.3389/neuro.10.004.2008 downloadable here or see GoogleScholar.
    Beginning of conclusion on page 8: “At first sight the biased competition and predictive coding theories seem to be diametrically opposed: one requires cortical feedback to be excitatory while the other proposes that feedback is suppressive. The predictive coding and biased competition models have therefore been considered as distinct theories of cortical function. However, a simple variation on the conventional neural network implementation of the biased competition model has been shown to be identical to the linear predictive coding model. Hence, a particular implementation of the biased competition model, in which nodes compete via inhibition that targets the inputs to a cortical region, is mathematically equivalent to linear predictive coding. These previously distinct, rival, theories of cortical function can thus be united.”
16. ^ Cultural variation in management of attention by children and their caregivers - Chavajay and Rogoff 1999
    doi: 10.1037/0012-1649.35.4.1079 downloadable here or see GoogleScholar.
    Page 1089, last paragraph: “In conclusion, the findings of the present research provide insight into processes of human attention across communities. Our research suggests that simultaneous attention may be practiced in some cultural groups much more commonly than in others. This may relate to cultural expectations regarding what are considered appropriate and desirable ways to attend to others in social interactions rather than to variation in skill.”
17. ^ Principles of Neural Science Fifth edition - Kandel et al. McGraw-Hill US 2012
    Page 619, third paragraph, relating to attention: “Our sense that we identify multiple objects simultaneously is illusory. Instead, we serially process objects in rapid succession by shifting attention from one to the next.”
18. ^ The Emperor’s New Mind - Penrose Oxford University Press 1989, also see The Emperor’s New Mind
    Pages 514-5, in chapter 9 “Real brains and model brains”, under the heading “Parallel computers and the 'Oneness' of consciousness”: “A characteristic feature of conscious thought ... is its 'oneness' - as opposed to a great many independent activities going on at once. Utterances like 'How can you expect me to think of more than one thing at a time?' are commonplace. Is it possible at all to keep separate things going on in one’s consciousness simultaneously? Perhaps one can keep a few things going on at once, but this seems to be more like continual flitting backwards and forwards between the various topics than actually thinking about them simultaneously, consciously, and independently. If one were to think consciously about two things quite independently it would be more like having two separate consciousnesses, even if only for a temporary period, while what seems to be experienced (in a normal person, at least) is a single consciousness which may be vaguely aware of a number of things, but which is concentrated at any one time on only one particular thing. Of course, what we mean by 'one thing' here is not altogether clear.”

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