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Active inference, sensory attenuation and illusions.

Brown H, Adams RA, Parees I, Edwards M, Friston K - Cogn Process (2013)

Bottom Line: Furthermore, it explains the force-matching illusion and reproduces empirical results almost exactly.This is important, given the negative correlation between sensory attenuation and delusional beliefs in normal subjects--and the reduction in the magnitude of the illusion in schizophrenia.It also provides a functional account of deficits in syndromes characterised by false inference and impaired movement--like schizophrenia and Parkinsonism--syndromes that implicate abnormal modulatory neurotransmission.

View Article: PubMed Central - PubMed

Affiliation: Institute of Neurology, The Wellcome Trust Centre for Neuroimaging, UCL, 12 Queen Square, London, WC1N 3BG, UK, harriet.brown.09@ucl.ac.uk.

ABSTRACT
Active inference provides a simple and neurobiologically plausible account of how action and perception are coupled in producing (Bayes) optimal behaviour. This can be seen most easily as minimising prediction error: we can either change our predictions to explain sensory input through perception. Alternatively, we can actively change sensory input to fulfil our predictions. In active inference, this action is mediated by classical reflex arcs that minimise proprioceptive prediction error created by descending proprioceptive predictions. However, this creates a conflict between action and perception; in that, self-generated movements require predictions to override the sensory evidence that one is not actually moving. However, ignoring sensory evidence means that externally generated sensations will not be perceived. Conversely, attending to (proprioceptive and somatosensory) sensations enables the detection of externally generated events but precludes generation of actions. This conflict can be resolved by attenuating the precision of sensory evidence during movement or, equivalently, attending away from the consequences of self-made acts. We propose that this Bayes optimal withdrawal of precise sensory evidence during movement is the cause of psychophysical sensory attenuation. Furthermore, it explains the force-matching illusion and reproduces empirical results almost exactly. Finally, if attenuation is removed, the force-matching illusion disappears and false (delusional) inferences about agency emerge. This is important, given the negative correlation between sensory attenuation and delusional beliefs in normal subjects--and the reduction in the magnitude of the illusion in schizophrenia. Active inference therefore links the neuromodulatory optimisation of precision to sensory attenuation and illusory phenomena during the attribution of agency in normal subjects. It also provides a functional account of deficits in syndromes characterised by false inference and impaired movement--like schizophrenia and Parkinsonism--syndromes that implicate abnormal modulatory neurotransmission.

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Pathology of sensory attenuation. To simulate the force-matching results seen in schizophrenia, sensory attenuation was reduced and precision at non-sensory levels of the hierarchy increased to allow movement. This results in a precise and accurate perception of internally and externally generated sensations (upper left panel). However, the causes of sensory data are not accurately inferred: an illusory cause (circled response in the lower left panel) is perceived during internally generated movement that is antagonistic to the movement. This is because the proprioceptive prediction errors driving action are rendered overly precise, meaning higher levels of the hierarchy must be harnessed to explain them, resulting in a ‘delusion’
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Fig8: Pathology of sensory attenuation. To simulate the force-matching results seen in schizophrenia, sensory attenuation was reduced and precision at non-sensory levels of the hierarchy increased to allow movement. This results in a precise and accurate perception of internally and externally generated sensations (upper left panel). However, the causes of sensory data are not accurately inferred: an illusory cause (circled response in the lower left panel) is perceived during internally generated movement that is antagonistic to the movement. This is because the proprioceptive prediction errors driving action are rendered overly precise, meaning higher levels of the hierarchy must be harnessed to explain them, resulting in a ‘delusion’

Mentions: The answer is evident in Fig. 8, which shows the results of a simulation with low sensory attenuation and augmented precisions at non-sensory levels of the generative model. Here, there is an almost perfect and precise inference about internally and externally generated sensations. However, there is a failure of inference about their hidden causes. This can be seen on the lower left, where the subject has falsely inferred an antagonistic external hidden cause that mirrors the internal hidden causes: that is, it believes that when it presses its finger on its hand, something also pushes its hand against its finger. Note that this false inference does not occur during normal sensory attenuation (see previous figures), where the true external hidden cause always lies within the 90 % confidence intervals. The reason for this false inference or delusion is relatively simple: action is driven by proprioceptive prediction errors that always report less force than that predicted (if they did not, the reflex would not be engaged). However, when sensory precision increases, somatosensory prediction errors become very precise and need to be explained—and can only be explained by falsely inferring an opposing exogenous force. In more general terms, to reconcile a mismatch between the predicted consequences of action and the state of the world that precedes action, external forces are falsely invoked. This only occurs when both the predictions and their consequences are deemed to be very precise. This false inference could be interpreted as a delusion in the same sense that the sensory attenuation is an illusion. Having said this, it should be noted that—from the point of view of the subject—its inferences are Bayes optimal. It is only our attribution of the inference as false that gives it an illusory or delusionary aspect. In the context of these simulations, the only difference between an illusion and a delusion is the level of the supposed failure of inference. Here, we have associated false inference at the perceptual level of hidden states with illusions and false inference at the conceptual level of hidden causes with delusions.Fig. 8


Active inference, sensory attenuation and illusions.

Brown H, Adams RA, Parees I, Edwards M, Friston K - Cogn Process (2013)

Pathology of sensory attenuation. To simulate the force-matching results seen in schizophrenia, sensory attenuation was reduced and precision at non-sensory levels of the hierarchy increased to allow movement. This results in a precise and accurate perception of internally and externally generated sensations (upper left panel). However, the causes of sensory data are not accurately inferred: an illusory cause (circled response in the lower left panel) is perceived during internally generated movement that is antagonistic to the movement. This is because the proprioceptive prediction errors driving action are rendered overly precise, meaning higher levels of the hierarchy must be harnessed to explain them, resulting in a ‘delusion’
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3824582&req=5

Fig8: Pathology of sensory attenuation. To simulate the force-matching results seen in schizophrenia, sensory attenuation was reduced and precision at non-sensory levels of the hierarchy increased to allow movement. This results in a precise and accurate perception of internally and externally generated sensations (upper left panel). However, the causes of sensory data are not accurately inferred: an illusory cause (circled response in the lower left panel) is perceived during internally generated movement that is antagonistic to the movement. This is because the proprioceptive prediction errors driving action are rendered overly precise, meaning higher levels of the hierarchy must be harnessed to explain them, resulting in a ‘delusion’
Mentions: The answer is evident in Fig. 8, which shows the results of a simulation with low sensory attenuation and augmented precisions at non-sensory levels of the generative model. Here, there is an almost perfect and precise inference about internally and externally generated sensations. However, there is a failure of inference about their hidden causes. This can be seen on the lower left, where the subject has falsely inferred an antagonistic external hidden cause that mirrors the internal hidden causes: that is, it believes that when it presses its finger on its hand, something also pushes its hand against its finger. Note that this false inference does not occur during normal sensory attenuation (see previous figures), where the true external hidden cause always lies within the 90 % confidence intervals. The reason for this false inference or delusion is relatively simple: action is driven by proprioceptive prediction errors that always report less force than that predicted (if they did not, the reflex would not be engaged). However, when sensory precision increases, somatosensory prediction errors become very precise and need to be explained—and can only be explained by falsely inferring an opposing exogenous force. In more general terms, to reconcile a mismatch between the predicted consequences of action and the state of the world that precedes action, external forces are falsely invoked. This only occurs when both the predictions and their consequences are deemed to be very precise. This false inference could be interpreted as a delusion in the same sense that the sensory attenuation is an illusion. Having said this, it should be noted that—from the point of view of the subject—its inferences are Bayes optimal. It is only our attribution of the inference as false that gives it an illusory or delusionary aspect. In the context of these simulations, the only difference between an illusion and a delusion is the level of the supposed failure of inference. Here, we have associated false inference at the perceptual level of hidden states with illusions and false inference at the conceptual level of hidden causes with delusions.Fig. 8

Bottom Line: Furthermore, it explains the force-matching illusion and reproduces empirical results almost exactly.This is important, given the negative correlation between sensory attenuation and delusional beliefs in normal subjects--and the reduction in the magnitude of the illusion in schizophrenia.It also provides a functional account of deficits in syndromes characterised by false inference and impaired movement--like schizophrenia and Parkinsonism--syndromes that implicate abnormal modulatory neurotransmission.

View Article: PubMed Central - PubMed

Affiliation: Institute of Neurology, The Wellcome Trust Centre for Neuroimaging, UCL, 12 Queen Square, London, WC1N 3BG, UK, harriet.brown.09@ucl.ac.uk.

ABSTRACT
Active inference provides a simple and neurobiologically plausible account of how action and perception are coupled in producing (Bayes) optimal behaviour. This can be seen most easily as minimising prediction error: we can either change our predictions to explain sensory input through perception. Alternatively, we can actively change sensory input to fulfil our predictions. In active inference, this action is mediated by classical reflex arcs that minimise proprioceptive prediction error created by descending proprioceptive predictions. However, this creates a conflict between action and perception; in that, self-generated movements require predictions to override the sensory evidence that one is not actually moving. However, ignoring sensory evidence means that externally generated sensations will not be perceived. Conversely, attending to (proprioceptive and somatosensory) sensations enables the detection of externally generated events but precludes generation of actions. This conflict can be resolved by attenuating the precision of sensory evidence during movement or, equivalently, attending away from the consequences of self-made acts. We propose that this Bayes optimal withdrawal of precise sensory evidence during movement is the cause of psychophysical sensory attenuation. Furthermore, it explains the force-matching illusion and reproduces empirical results almost exactly. Finally, if attenuation is removed, the force-matching illusion disappears and false (delusional) inferences about agency emerge. This is important, given the negative correlation between sensory attenuation and delusional beliefs in normal subjects--and the reduction in the magnitude of the illusion in schizophrenia. Active inference therefore links the neuromodulatory optimisation of precision to sensory attenuation and illusory phenomena during the attribution of agency in normal subjects. It also provides a functional account of deficits in syndromes characterised by false inference and impaired movement--like schizophrenia and Parkinsonism--syndromes that implicate abnormal modulatory neurotransmission.

Show MeSH
Related in: MedlinePlus