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How the human brain combines the certainty of prior expectations and the clarity of sensory input during speech perception

Periodic Reporting for period 1 - EXPECTBRAIN (How the human brain combines the certainty of prior expectations and the clarity of sensory input during speech perception)

Período documentado: 2017-01-01 hasta 2018-12-31

• What is the problem/issue being addressed?
Our ability to successfully communicate with other people is an essential skill in everyday life. Speech recognition depends on both the clarity of the acoustic input and on what we expect to. For example, in noisy listening conditions, listeners of the identical speech input can differ in their perception of what was said. Similarly, for face recognition, brain responses to faces depend on expectations and do not simply reflect the presented facial features. However, it is still unclear how the human brain weights and combines prior expectations with sensory information.
• Why is it important for society?
Prior expectations can improve speech perception, but also lead to misperception. Misperceiving spoken words is an everyday experience, with outcomes that range from shared amusement to serious miscommunication. For hearing-impaired individuals, frequent misperception can lead to social withdrawal and isolation, with severe consequences for wellbeing. Understanding the neural mechanism by which the human brain combines prior expectations with sensory information might have important clinical implications.
• What are the overall objectives?
The aim of the current project was to understand how the human brain weights and combines prior expectations with sensory input.
As the first result of this project, we specified the neural mechanisms by which prior expectations, which are so often helpful for perception, can lead to misperception of degraded sensory signals. Most descriptive theories of illusory perception explain misperception as arising from a clear sensory representation of features or sounds that are in common between prior expectations and sensory input. Our work instead provides support for a complementary proposal: that misperception occurs when there is an insufficient sensory representation of the deviation between expectations and sensory signals. The work was disseminated in a paper (Blank, H., et al. (2018). Speech Perception or Deception? Neural Representations of Prediction Error Determine Perceptual Outcomes for Degraded Speech. The Journal of Neuroscience. 38 (27) 6076-6089) and at a conference (Symposium talk at the Tagung experimentell arbeitender Psychologen (TeaP). Dresden, Germany).

As the second result of this project, we investigated how the human brain represents the strength of expectations. Entering your office, you have relatively strong predictions about which faces you are going to see. These priors might help you to quickly recognize your office mate, even if she has new glasses and a new haircut. Usually, we have several expectations in parallel, which we can weight according to their probability, e.g. a student regularly entering the office will be expected with a higher precision than a shy colleague you rarely meet. How does the brain represent and weight multiple prior expectations?
Prior strength could be represented with prior content itself in sensory regions. Alternatively, there could be distinct, specialized brain regions that represent expectation strength separately from the content of the prior. We observed that during face anticipation, representations of expected face identity increased with prior strength in the face-sensitive anterior temporal lobe. In contrast, during face presentation, representations of face identity increased with surprise in the insula. Our findings suggest that strength of face expectations is represented in higher-level face areas. These priors seem to influence additional brain regions which signal surprise to unexpected stimuli. The work was disseminated via conference contributions (at the Cognitive Computational Neuroscience (CCN), Berlin, Germany and the 25th Annual Meeting of the Organization for Human Brain Mapping (HBM), Rome, Italy).
The results might have important implications (i) for treatments in several clinical areas, e.g. hearing impairments and neuropsychiatric conditions, which are accompanied by unusual perceptual experiences due to the dysfunctional use of prior expectations such as autism or schizophrenia and (ii) for neurally inspired engineering developments in machine speech recognition.
Expectations improve perception of degraded speech