Opposing serial effects of stimulus and choice in speech perception scale with context variability

Here, we disentangled stimulus and choice history revealing opposing effects on perception: Choice history attracts and stimulus history repels current speech perception. The repulsive effect of stimulus history was only revealed once choice history was accounted for. On top of that, stability in the speaker context strengthens the repulsive effects of stimulus history.

Ufer, C., & Blank, H., (2024) Opposing serial effects of stimulus and choice in speech perception scale with context variability. iScience.

The pupil dilation response as an indicator of visual cue uncertainty and auditory outcome surprise

Expectations can be induced by cues that indicate the probability of following sensory events. The information provided by cues may differ and hence lead to different levels of uncertainty about which event will follow. In this experiment, we employed pupillometry to investigate whether the pupil dilation response to visual cues varies depending on the level of cue-associated uncertainty about a following auditory outcome.

Becker, J., Viertler, M., Korn, C., & Blank, H., (2024) The pupil dilation response as an indicator of visual cue uncertainty and auditory outcome surprise. European Journal of Neuroscience, 1-16.

Pupil diameter as an indicator of sound pair familiarity after statistically structured auditory sequence

Inspired by recent findings in the visual domain, we investigated whether the stimulus-evoked pupil dilation reflects temporal statistical regularities in sequences of auditory stimuli. Our findings suggest that pupil diameter may serve as an indicator of sound pair familiarity but does not invariably respond to task-irrelevant transition probabilities of auditory sequences.

Becker, J., Korn, C.W. & Blank, H. (2024) Pupil diameter as an indicator of sound pair familiarity after statistically structured auditory sequence. Scientific Reports, 14, 8739.

Multivariate analysis to unravel predictive processes in speech

Speech perception is heavily influenced by our expectations about what will be said. In this review, we discuss the potential of multivariate analysis as a tool to understand the neural mechanisms underlying predictive processes in speech perception.

Speech perception depends on speaker priors

When different speakers articulate identical words, the physical properties of the produced sounds can vary substantially. Fundamental frequency (F0) and formant frequencies (FF), the two main parameters that discriminate between voices, also influence vowel perception. 

Krumbiegel J, Ufer C, Blank H (2022) Influence of voice properties on vowel perception depends on speaker context. The Journal of the Acoustical Society of America 152:820–834.

Prediction errors during speech perception

Perception inevitably depends on combining sensory input with prior expectations, particularly for the identification of degraded input. However, the underlying neural mechanism by which expectations influence sensory processing is unclear. Predictive Coding suggests 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 (Sharpening), has been lacking.

Blank, H. & Davis, M. (2016). Prediction errors but not sharpened signals simulate multivoxel fMRI patterns during speech perception, PLOSBiology, 14(11) 

Slips of the Ear: When Knowledge Deceives Perception

The ability to draw on 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.
To investigate the neural underpinnings of speech misperception, we presented participants with pairs of written and degraded spoken words that were either identical, clearly different or similar-sounding. Reading and hearing similar-sounding words (like kick followed by pick), led to frequent misperception.

Blank, H., Spangenberg, M., & Davis, M. (2018). Neural Prediction Errors Distinguish Perception and Misperception of Speech. The Journal of Neuroscience,  38 (27) 6076-6089.

Prediction error processing and sharpening of expected information across the face-processing hierarchy

The perception and neural processing of sensory information are strongly influenced by prior expectations. The integration of prior and sensory information can manifest through distinct underlying mechanisms: focusing on unexpected input, denoted as prediction error (PE) processing, or amplifying anticipated information via sharpened representation. 

Garlichs, A., Blank, H. (2024). Prediction error processing and sharpening of expected information across the face-processing hierarchy. Nature Communications, 15, 3407.

Representations of face priors

In everyday life, we face our environment with several prior expectations about what we are going to encounter, for example, whom we are going to see most likely at a certain location. These expectations have to be weighted according to their probability, e.g., a student regularly entering our office will be expected with a higher probability than a shy colleague we rarely meet. 

Blank, H., Alink, A., & Büchel, C. (2023). Multivariate functional neuroimaging analyses reveal that strength-dependent face expectations are represented in higher-level face-identity areas. Communications Biology, 6, 135.

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 conncetions between face- and voice-recognition areas to activate learned associations of faces and voices even in unimodal conditions to improve person-identity recognition.

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 can combine information from different sensory sources, for example during lip-reading, speech comprehension is improved.

Blank, H. & von Kriegstein, K. (2013). Mechanisms of enhancing visual-speech recognition by prior auditory information. Neuroimage, 65, 109-118"