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Archive for the summary Category

Evidence for predictive awareness

Is seems generally accepted in neuroscientific circles that the brain predicts the results of motor action, constructs a prediction of sensory signals, compares the prediction with the outcome and uses the error to correct motor action and perceptual processes. It is also accepted that the prediction is singular and global in nature. Many assume it is Bayesian, at least in spirit. Below is some representative evidence for this predictive process being linked to the awareness that we experience. What we are aware of is the prediction.

(This was written to appear elsewhere and so I have avoided the use of the word consciousness in order to bypass fruitless discussion. But most neuroscientists do not avoid the word and in fact, many consider it the object of their investigations. If you find the wording awkward, then just substitute consciousness for awareness.)

  1. The failure of simultaneity between moving events and stationary objects: Nijhawan’s experiment had an object move across the visual field and pass a flashbulb on the way. The flashbulb flashed at exactly the moment that the object passed it. Subjects reported perceiving the object pass the bulb before the bulb flashed. The brain ’sees’ a split second into the future for moving objects but not individual stationary ones. Bai’s showed that there were more mistaken ‘out’ calls in tennis than ‘in’ calls because the officials perceive the ball is having moved further then it had.

  2. The systematic nature of some types of visual illusion: Changizi’s investigation of illusions mathematically predicts the extent that certain attributes of an object (smaller size, slower speeds, greater luminance contrast, farther distance, low eccentricity, greater proximity to the vanishing point, greater proximity to the focus of expansion) produce similar perceptual effects (increased perceived size, increased perceived speed, decreased perceived luminance contrast, deceased perceived distance). This shows that the visual system uses mechanisms for compensating for neural delay during forward motion in order to ‘perceive the present’.

  3. Problems with timing of normal sensory input and direct stimulation of the cortex: Libet’s experiment showed that stimulation of the skin reached awareness in a much shorter time then stimulation of the exposed surface of the cortex. This prompted him to propose a system of backward referrals of the timing of events. A much cleaner explanation is a predictive projection into the future occurs in normal awareness.

  4. Comprehension of language has a predictive nature: Berkum reported that event-related-potentials show the same pattern for unexpected words as for actual grammatical errors. This implies a ‘look ahead’ feature in language comprehension that produces surprise when predictions are wrong.

  5. There is an error registering system in the brain: Firth states that the brain is Bayesian, correcting its understanding on the basis of comparing prediction with current input. He states that the dopamine signal is a prediction error indicator. Dopamine neurons become more active if a good surprise happens, do not change their activity if there is no surprise and become less active if a negative surprise happens. Menon’s investigation of Go/NoGo experiments shows clear error-related activity (named ERN and ERP) in a wide network of cortical areas. Others have slightly different statements of the error registering system but all seem to agree that errors are identified and corrected. A prediction is needed in order to generate an error signal.

  6. Prediction is required for movement: Morsella has a theory that explains much about awareness. It postulates that it is used to meld together separate skeletomotor plans to avoid conflict. The conflict would only be apparent if our awareness predicted the course of the somewhat independent plans to see how they interacted with each other and the environment before the conflict actually happened. Llinas and Roy postulate that the main function of brain is a global one to implement intelligent motricity through prediction of the consequences of impending motion. They have outlined a thalamocortical system to do this that resembles the ‘neural correlates of consciousness’.

  7. Energy use by the sensory areas of the brain is higher for unexpected input: Alink’s investigation found that the response in V1 to unexpected signals was higher than for expected ones. This is thought to be the result of feedback from higher levels of predictive information.

  8. Reaching awareness takes time: Results of the bulk of experiments following the neural events leading up to awareness, it takes about 300msec from event to awareness of the event. There appears to be no evidence that we appear to live our lives a third of a second out of sync with the world. Predictive awareness eliminates this problem.

Summary May 24 2010

This blog has reached its second birthday and it is time for a little summary. I have made a list of general ideas/questions that I am trying to investigate, and then, for each heading, I list the posts that apply to that idea.

Purpose of the blog

The aim of this blog is to prepare people for the revolution that is going to happen now in neuroscience. The very first post (1 Jun 08 aims ) outlined the scope of the blog. The aims are enlarged on later in (10 Aug 08 scientific shocks). To give an indication of the type of material that was intended in the blog an early post gave a list (12 Jun 08 what do we know about consciousness) and another gave probable functions (2 Jul 08 does consciousness have a function). Putting consciousness in context was the purpose of (9 Oct 08 one way to look at consciousness).


A different way to look at consciousness

Some posts have been specifically written to help people come to grips with a different way of viewing their mental life. These posts hardly contain any quotes or links to scientific material. I have used some descriptions of my own way of seeing myself: (6 Jun 08 living without a conscious mind) (10 Jul 08 decisions) (15 Aug 08 who is watching) (18 Oct 08 why make problems) (15 Nov 08 metaphors for consciousness) (30 Nov 08 metaphor) (15 Dec 08 a few definitions) (18 Mar 09 Little thought experiment) (22 Feb 09 A framework) (23 Apr 09 History of the quest) (29 Sep 2009 mind maintenance) (11 Feb 10 definitions of consciousness) (21 Apr 10 mind maintenance 2)

Some posts look at more specific problems in understanding consciousness

Old ideas that get in the way

There are ways of thinking that interfere with understanding the brain. (12 Dec 08 a different angle) (25 Dec 09 folk knowledge)

Some ‘how’ hypotheses

There are some hypotheses that seem very convincing. So far we have taken a quick look at the following:

Methods and instrumentation concerns

(19 Jul 09 EEG questions) (5 Sep 09 fMRI scans astorcytes) (2 Oct 09 dead fish and voodoo) (14 Oct 09 effects of brain waves) (2 Feb 10 a decade of neuroscience) (25 Mar 10 materialism) (18 May 10 discounting science)

Miscellaneous bits and pieces

(23 Jul smell is different), (30 Aug 08 do grandmother cells fly?), (12 Oct 08 metaphor to embodiment), (27 Nov 08 not inside us), (11 Jan 09 Epistemology changes), (20 Jan 09 Proprioception), (16 Feb 09 Other definitions) (20 Apr 09 A kluge?) (8 May 09 Top down processing) (25 Jun 09 consciousness takes a lot of energy) (31 Jul 09 revisiting grandmother cells) (3 Aug 09 reading brain patterns) (30 Aug 09 innate categories) (11 Sep 09 wisdom) (23 Oct 09 fruits of introspection) (19 Nov 09 astrocytes) (22 Nov 09 a radio metaphor) (2 Dec 09 where are the concepts?) (19 Dec 09 the missing hierarchical level) (22 Dec 09 working in the missing hierarchical level) (9 Jan 10 the content of consciousness) (18 Jan 10 the big C) (25 Mar 10 a possible reason for consciousness) (27 Apr 10 the connection is important)