The overall aim of our research is to understand how the human brain combines expectations and sensory information to communicate. Our ability to successfully communicate with other people is an essential skill in everyday life. Therefore, unravelling how the human brain is able to derive meaning from acoustic speech signals and to recognize our communication partner based on seeing a face represents an important scientific endeavour.
Speech recognition depends on both the clarity of the acoustic input and on what we expect to hear. 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.
These findings for speech and face recognition are compatible with the more general view that perception is an active process in which incoming sensory information is interpreted with respect to expectations. The neural mechanisms supporting such integration of sensory signals and expectations, however, remain to be identified. Conflicting theoretical and computational models have been suggested for how, when, and where expectations and new sensory information are combined.
Prediction errors during speech perception
Perception inevitably depends on combining sensory input with prior expectations. This is particularly critical for identification of degraded input. However, the underlying neural mechanism by which expectations influence sensory processing is unclear. Recent theories of Predictive Coding suggest that the brain passes forward the unexpected part of the sensory input while expected properties are suppressed (Prediction Error). However, evidence to rule out the opposite and perhaps more intuitive mechanism, in which the expected part of the sensory input is enhanced or sharpened (Sharpening), has been lacking.Read more
Blank, H. & Davis, M. (2016). Prediction errors but not sharpened signals simulate multivoxel fMRI patterns during speech perception, PLOSBiology, 14(11) http://dx.doi.org/10.1371/journal.pbio.1002577
Slips of the Ear: When Knowledge Deceives Perception
The ability to draw on past experience is important to keep up with a conversation, especially in noisy environments where speech sounds are hard to hear. However, these prior expectations can sometimes mislead listeners; convincing them that they heard something that a speaker did not actually say.Read more
Using fMRI, we found that misperception was associated with reduced activity in the left superior temporal sulcus a brain region critical for processing speech sounds. Furthermore, when perception of speech was more successful, this brain region represented the difference between prior expectations and heard speech (like the initial k/p in kick-pick).
Blank, H., Spangenberg, M., & Davis, M. (2018). Neural Prediction Errors Distinguish Perception and Misperception of Speech. The Journal of Neuroscience, . 38 (27) 6076-6089.
Direct structural connections between face and voice ares
By combining fMRI with diffusion-weighted imaging we could show that the brain is equipped with direct structural connections between face- and voice-recognition areas to activate learned associations of faces and voices even in unimodal conditions to improve person-identity recognition.Read more
What kind of information is exchanged between these specialized areas during cross‐modal recognition of other individuals? To address this question, we used functional magnetic resonance imaging and a voice‐face priming design. In this design, familiar voices were followed by morphed faces that matched or mismatched with respect to identity or physical properties. The results showed that responses in face‐sensitive regions were modulated when face identity or physical properties did not match to the preceding voice. The strength of this mismatch signal depended on the level of certainty the participant had about the voice identity. This suggests that both identity and physical property information was provided by the voice to face areas.
Blank, H., Anwander, A., & von Kriegstein, K. (2011). Direct structural connections between voice- and face-recognition areas. The Journal of Neuroscience, 31(36), 12906-12915. https://doi.org/10.1523/JNEUROSCI.2091-11.2011
Blank, H., Kiebel, S. J. & von Kriegstein, K. (2015). How the human brain exchanges information across sensory modalities to recognize other people. Human Brain Mapping, 36(1), 324-39. http://dx.doi.org/10.1002/hbm.22631
Lipreading: How we “hear” with our eyes
In a noisy environment it is often very helpful to see the mouth of the person you are speaking to. When our brain is able to combine information from different sensory sources, for example during lip-reading, speech comprehension is improved.Read more
Blank, H. & von Kriegstein, K. (2013). Mechanisms of enhancing visual-speech recognition by prior auditory information. Neuroimage, 65, 109-118. http://dx.doi.org/10.1016/j.neuroimage.2012.09.047