29/10/2009 by admin.

ScienceDaily has an item on research by A. Graybiel, ‘Neural representation of time in corticobasal ganglia circuits’. ( here )

“Keeping track of time is one of the brain’s most important tasks. As the brain processes the flood of sights and sounds it encounters, it must also remember when each event occurred. But how does that happen? … For decades, neuroscientists have theorized that the brain “time stamps” events as they happen, allowing us to keep track of where we are in time and when past events occurred. However, they couldn’t find any evidence that such time stamps really existed — until now … The research team trained two macaque monkeys to perform a simple eye-movement task. After receiving the “go” signal, the monkeys were free to perform the task at their own speed. The researchers found neurons that consistently fired at specific times — 100 milliseconds, 110 milliseconds, 150 milliseconds and so on — after the “go” signal … The neurons are located in the prefrontal cortex and the striatum, both of which play important roles in learning, movement and thought control. … We have sensory receptors for light, sound, touch, hot and cold, and smell, but we don’t have sensory receptors for time. This is a sense constructed by the brain.”

It strikes me that this clock system would be one more or less dedicated to motor processes because: it measures very short durations; it is found in the prefrontal cortex/striatum system; and it is more accurate than flexible. The conscious feeling of the passage of time may be from another system derived from this one or even a completely separate system.

The New Scientist had an article on time perception (here) by D. Fox that reviews a number of experiments.

• R. VanRullen showed that vision is framed rather than continuous and the frame rate is about 13 per second. He found that the visual area of the right inferior parietal lobe generated a 13 Hertz wave. The question then was - is the framing global or independent for each preceived object? Visual illusions showed that framing is not global.

“This implies that there is not a single “film roll” in the brain, but many separate streams, each recording a separate piece of information. What’s more, this way of dealing with incoming information may not apply solely to motion perception. Other brain processes, such as object or sound recognition, might also be processed as discrete packets.”

• Using very weak stimuli he showed that there are windows of perception.

“… found that the likelihood of them noticing the light depended on the phase of another wave in the front of the brain, which rises and falls about 7 times per second. It turned out that subjects were more likely to detect the flash when the wave was near its trough, and miss it when the wave was near its peak. There’s a succession of ‘on’ periods and ‘off’ periods of perception. Attention is collecting information through snapshots … So it seems that each separate neural process that governs our perception might be recorded in its own stream of discrete frames. But how might all these streams fit together to give us a consistent picture of the world?”

• E. Poppel looked at this problem, proposed blocks of frames and found some experimental evidence for the blocks.

“… separate snapshots from the senses may feed into blocks of information in a higher processing stream. He calls these the “building blocks of consciousness” and reckons they underlie our perception of time. … It’s an appealing idea, since patching together a chronological order of events hitting our senses is no mean feat. Sounds tend to be processed faster than images, so without some sort of grouping system we might, say, hear a vase smashing before we see it happen. Pöppel’s building blocks of consciousness would neatly solve this problem: if two events fall into the same building block, they are perceived as simultaneous; if they fall into consecutive buildings blocks, they seem successive. Perception cannot be continuous because the limits of neural processing. …. A space of 30 to 50 milliseconds is necessary to bring together in one time-window the distributed activity in the neural system.”

There is also interesting discussion of whether our sense of time becoming slower or faster is a function of brain speed or of memory density. And finally exploration of the idea that some symptoms of schizophrenia may be due to faulty timekeeping.

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27/08/2009 by admin.

Look at the frequency of some events: the gamma waves that synchronize the thalamus and large parts of the cortex happen between 25 and 100 times per second but typically near 40; the saccadic eye vibrations happen between 30 and 70 times per second; the flicker rate of movie projectors that makes the picture stable is between 48 and 72 times per second. This makes one guess that there is a good probability that the discontinuous nature of the ‘frames’ from the eye, from a movie screen and from consciousness all have the same timing centered on about 50 Hz. A group has now shown that the focus of attention shifts about 18 to 34 times a second and averages about 25 Hz. It looks like two frames per focus.

This attention timing is reported by ScienceDaily (here) in an item on a paper by T. Buschman and E. Miller.

You’re meeting a friend in a crowded cafeteria. Do your eyes scan the room like a roving spotlight, moving from face to face, or do you take in the whole scene, hoping that your friend’s face will pop out at you? And what, for that matter, determines how fast you can scan the room?…. you are more likely to scan the room, jumping from face to face as you search for your friend. In addition, the timing of these jumps appears to be determined by waves of activity in the brain that act as a clock. …the study showed that brain waves act as a kind of built-in clock that provides a framework for shifting attention from one location to the next. … Buschman found that the spotlight of the mind’s eye shifted focus at 25 times a second and that this process of switching was regulated by brain waves. …the speed at which the animals searched was related to the speed of their brain waves. When the clock ticked faster, the animals “thought” faster.

The paper’s summary is below:

Attention regulates the flood of sensory information into a manageable stream, and so understanding how attention is controlled is central to understanding cognition. Competing theories suggest visual search involves serial and/or parallel allocation of attention, but there is little direct, neural evidence for either mechanism. Two monkeys were trained to covertly search an array for a target stimulus under visual search (endogenous) and pop-out (exogenous) conditions. Here, we present neural evidence in the frontal eye fields (FEF) for serial, covert shifts of attention during search but not pop-out. Furthermore, attention shifts reflected in FEF spiking activity were correlated with 18–34 Hz oscillations in the local field potential, suggesting a “clocking” signal. This provides direct neural evidence that primates can spontaneously adopt a serial search strategy and that these serial covert shifts of attention are directed by the FEF. It also suggests that neuron population oscillations may regulate the timing of cognitive processing.

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06/03/2009 by admin.

A week or so back there was an item in ScienceDaily, How we think before we speak: making sense of sentences. (here) I was reminded of it when I encountered an ‘up the garden path’ remark.

Linguists have a method of diagramming a sentence to make its grammar clear. If the sentence can be successfully diagrammed then it is grammatical and each word is given its function in the sentence. Diagramming works well with written language. But with spoken language or very difficult written language, it is possible to be misled at the beginning of a sentence so that the sentence is parsed in a way that makes no sense by the end of the sentence. It has to be re-parsed to make it understandable. This is a sentence that leads one ‘up the garden path’. With my bias to consider spoken language as real language and written language as somewhat artificial, I think of garden path sentences as ungrammatical even if, when the whole sentence is available, it can be diagrammed successfully. Wikipedia supplied these examples:

“The old man the boat.”

(The elderly are the crew of the boat)

“The man whistling tunes pianos.”

(The man who is whistling also tunes pianos)

“The cotton clothing is made of grows in Mississippi.”

(The cotton that clothing is made of is grown in Mississippi)

Back to the article – it shows how the listener predicts what the speaker is going to say next.

In … Current Directions in Psychological Science Jos J.A. Van Berkum …describes recent experiments using brain waves to understand how we are able to make sense of sentences. (They) examined Event Related Potentials (or ERPs) as people read or heard critical sentences as part of a longer text, or placed in some other type of context. ERPs are changes in brain activity that occur when we hear a certain stimulus, such as a tone or a word. Due to their speed, ERPs are useful for detecting the incredibly fast processes involved in understanding language…listeners only need a fraction of a second to determine that a word is out of place, given what the wider story is about. As soon as listeners hear an unexpected word, their brain generates a specific ERP, the N400 effect (so named because it is a negative deflection peaking around 400 milliseconds). And even more interesting, this ERP will usually occur before the word is even finished being spoken…Van Berkum speculates that “the linguistic brain seems much more ‘messy’ and opportunistic than originally believed, taking any partial cue that seems to bear on interpretation into account as soon as it can.”

But how does the language brain act so fast? Recent findings suggest that, as we read or have a conversation, our brains are continuously trying to predict upcoming information. Van Berkum suggests that this anticipation is a combination of a detailed analysis about what has been said before with taking ‘quick-and-dirty’ shortcuts to figure out what, most likely, the next bit of information will be.

One important element in keeping up with a conversation is knowing what or whom speakers are actually referring to. For example, when we hear the statement, “David praised Linda because. . .,” we expect to find out more about Linda, not David. Van Berkum and colleagues showed that when listeners heard “David praised Linda because he. . .,” there was a very strong ERP effect occurring with the word “he,” of the type that is also elicited by grammatical errors. Although the pronoun is grammatically correct in this statement, the ERP occurred because the brain was just not expecting it. This suggests that the brain will sometimes ignore the rules of grammar when trying to comprehend sentences.

These findings reveal that, as we make sense of an unfolding sentence, our brains very rapidly draw upon a wide range of information, including what was stated previously and who the speaker is, in helping us understand what is being said to us. Sentence understanding is not just about diligently combining stored word meanings. The brain rapidly throws in everything it knows, and it is always looking ahead.

This implies that we experience a prediction from just past information into the near future – so that our ‘present’ is approximately what should be happening ‘now’. This feed forward has been shown in vision by the nature of illusions and is now shown in hearing. It also appears to be true for motor movement.

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09/11/2008 by admin.

There was an interesting item in Discover site by Nina Bai on Oct 28. Apparently tennis refs are biased in the direction of their calls. They make many more mistaken ‘out’ calls than ‘in’ calls. This is the result of an illusion. The refs like everyone else anticipate the motion of an object. Dr. David Whitney had the idea of testing the calls while watching Wimbledon.

“The visual system is sluggish…It takes a hundred or more milliseconds for us to become aware of an image that strikes our retina. If the object is moving fast, the brain produces an illusion that the object has moved slightly further than it actually has in order to overcome this lag.”

This is another example of our consciousness predicting into the very near future.

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26/08/2008 by admin.

Brain Blogger (here) had a post on predicting the near future based on a paper (paper) by Changizi, Hsieh, Nijhawan, Kenai, and Shimojo called ‘Percieving the Present and a Systematization of Illusions’. The Abstract:

“Over the history of the study of visual perception there has been great success at discovering countless visual illusions. There has been less success in organizing the overwhelming variety of illusions into empirical generalizations (much less explaining them all via a unifying theory). Here, this article shows that it is possible to systematically organize more than 50 kinds of illusion into a 7 x 4 matrix of 28 classes. In particular, this article demonstrates that (1) smaller size, (2) slower speeds, (3) greater luminance contrast, (4) farther distance, (5) lower eccentricity, (6) greater proximity to the vanishing point, and (7) greater proximity to the focus of expansion all tend to have similar perceptual effects, namely, to (A) increase perceived size, (B) increase perceived speed, (C) decrease perceived luminance contrast, and (D) decrease perceived distance. The detection of these empirical regularities was motivated by a hypothesis, called ‘perceiving the present’, that the visual system possesses mechanisms for compensating neural delay during forward motion. This articles shows how this hypothesis predicts the empirical regularity.”

It takes about a tenth of a second for light on the retina to be processed to a conscious perception. A significant distance can be traveled in that time by a person or an object that a person wants to avoid or wants to catch. It is unlikely that we could walk down a crowded street without accident if we had a tenth of a second delay between our ‘now’ and the real ‘now’. By looking at the optic flow regularities of a moving observer going in the same direction as they are looking, it is possible to predict the scene changes in a tenth of a second. This appears to be what the brain does (whether or not we are moving forward). The logic would be that it everything is a little wrong because we are not moving forward, that is a safe mistake. But it would not be safe to have everything a little wrong if we are moving forward. One can do no harm and the other just might be lethal.

This adds more weight to the notion that we do live our lives in a projection into the near future. Also pointing in this direction are investigations of the flash-lag illusion (as described below by Chappell and Hine).

“The flash-lag effect occurs when an object is flashed adjacent to the path of a smoothly moving object, and abreast of the moving object. The flashed object appears to spatially lag the moving object in the direction of motion…”

In other words, the moving object is seen to be ahead of its position at the time of the flash. It has been projected into the future in our consciousness. This trick of foreseeing the probably future about a tenth of a second ahead is either a sophisticated calculation of the trajectories of objects depending on their bearing and speed or it is a collection of little ‘rule of thumb’ corrections that are ‘good enough’ for the purpose most of the time.

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19/07/2008 by admin.

As everyone knows, even little children, moving pictures do not move. They are a series of very still pictures. But we make a movie from them in our brain. The question is how.

Surprisingly, sometimes we don’t. Some people with migraines have periods of ‘cinematographic vision’. It is like a movie run too slow so that there is the effect of little jumps between frames. The sufferers are not making the normal movement-effect in their perception.

So – maybe we do the movie trick all the time. Maybe our visual perception is a series of still pictures that are then made into a movie for our consciousness. 

When I went looking for info on this subject I happened on a paper by Walter J Freeman, A Cinematographic Hypothesis of Cortical Dynamics in Perception, University of California, Postprints 2006. It is not an easy paper for someone outside that specialty to read.  (found here) . Using EEG methods and sophisticated analysis, he was able classify spatial and temporal patterns. The abstract is below.

“The aim of this study was to measure and classify spatial patterns in sensory cortical EEGs relating to conditioned stimuli (CSs) in order to test the hypothesis, based on clinical reports, that cortical dynamics is not continuous but operates in steps that resemble frames in a cinema. Recent advances in the application of the Hilbert Transform to intracranial recordings of the EEG in animals have revealed markers for repetitive phase transitions in neo-cortex at frame rates in the theta band…The impact of a CS on a sensory neo-cortex reorganized background EEG into two types of sequential patterns of coordinated activity, initially local and modality-specific, later global. The initial stage of phase transitions required 3-7ms. Large-scale cortical activity then reorganized itself repeatedly and reliably over relatively immense cortical distances within the cycle duration of the center frequency of oscillation. The size, texture, timing and duration of the amplitude modulation patterns support the hypothesis that these frames may provide the basis for multi-sensory percepts.”

The paper identifies a phase transition that is localized to the primary sensory area with a carrier frequency in the gamma band and recurrence rates in the theta band (gamma packets). The later phase transitions that involve many sensory areas have carrier frequencies in the beta band (beta packets) and recurrence rates in the theta band. The activity is not continuous but in demarcated discontinuous patterns.

Another report that caught my eye was Working Memory Has Limited ‘Slots’ Science Daily Apr 7 2008 reporting work by Luck and Zhang. (here) 

Humans rarely move their eyes smoothly. As our eyes flit from object to object, the visual system briefly shuts off to cut down visual “noise,” said Steven J. Luck, professor of psychology at the UC Davis Center for Mind and Brain. So the brain gets a series of snapshots of about a quarter-second, separated by brief gaps… The working memory system smooths out this jerky sequence of images by retaining memories from each snapshot so that they can be blended together. These memories typically last just a few seconds, Luck said.

If the memory of our consciousness is individual frames then it is not unreasonable that the original consciousness was too. It takes time to create a perceptual model and when it is complete, it is stored. The creation of the next iteration of the model can then start. There is a process that morphs one into the next to give an impression of continuous movement.

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02/07/2008 by admin.

Well, it seems to me to be a rule of thumb in biology: if something has significant costs then it has significant function. Usually function is fairly obvious in our bodies but not with consciousness.

Some options are:

1. It has no function whatsoever. It can safely be ignored and is not necessary for our thoughts and action to be understood. Just relax, enjoy the show but don’t take it seriously.
2. It is a product of the process of forming memories. Memory has a function but consciousness by itself does not.
3. It is a method of different parts/modules/processes in the brain to communicate with each other. This assumes that our brains are so compartmentalized that without consciousness there would be not unity in our actions.
4. It is a model of the world created from our senses, memories, knowledge and in-born a priori concepts. We live and act within this model and have no naive direct knowledge of the world.
5. It is a model of the world created as above but projected into the near future. We live and act within this model but it is not time lagged and can be used to monitor actions by comparing the error between previous projection and current perception.

I am tentatively working on the assumption that consciousness is a model of the world that is the raw material for our memory and also a way to live in the present through projection for the near past into the near future and furthermore a global view that all parts of the brain can access if they require a global view.   

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24/06/2008 by admin.

In seems that we are conscious of an event a fraction of a second after our brains start to process the perception of the event. This is not surprising – we are conscious of the ‘finished’ perception and ‘finishing’ the perception takes time. The surprise is that we live in the present and not a fraction of a second into the past. How is this done?

There seems to be three possibilities:

-         we live a fraction of a second into the past but never realize it.

-         we play very weird games with the perception of time and simultaneous events.

-         we do not live in the past but in a projection of the past into the future, giving an approximate present.

The last one seems the most useful to us and also may be a good reason to have consciousness. If the present is t0 and at that time the brain is constructing a model of the world as of t-x. This model is then run forward as a simulation through x duration of time so that it represents a simulation of t0. So we would be living in a simulation of the present. This gives a measure of error to prompt corrections of motor action and of perception. That would really be a cool system and well worth the effort of creating a single global model of the world accessible by all the systems of the brain.

It is not take much of a leap to go from thinking of a MPOFBL system (massively parallel overlapping feed-back loops) to thinking of a MPOFFL system (massively parallel overlapping feed-forward loops).

After writing the above but before posting it, I found a blog post on a NYTimes article. See article and blog. They discuss visual illusions that point to a projection into the near future. In particular the article talks about seeing an image before it actually happens.

“In an experiment originated by Dr. Nijhawan, people watch an object pass a flashbulb. The timing is exact: the bulb flashes precisely as the object passes. But people perceive that the object has moved past the bulb before it flashes. Scientists argue that the brain has evolved to see a split second into the future when it perceives motion. Because it takes the brain at least a tenth of a second to model visual information, it is working with old information. By modeling the future during movement, it is “seeing” the present.”

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