Illusory auditory continuity despite neural evidence to the contrary

Dorsal Anterior Cingulate Cortex Coordinates Contextual Mental Imagery for Single-Beat Manipulation during Rhythmic Sensorimotor Synchronization

Flexible pulse-by-pulse regulation of sensorimotor synchronization is crucial for voluntarily showing rhythmic behaviors synchronously with external cueing; however, the underpinning neurophysiological mechanisms remain unclear. We hypothesized that the dorsal anterior cingulate cortex (dACC) plays a key role by coordinating both proactive and reactive motor outcomes based on contextual mental imagery. To test our hypothesis, a missing-oddball task in finger-tapping paradigms was conducted in 33 healthy young volunteers. The dynamic properties of the dACC were evaluated by event-related deep-brain activity (ER-DBA), supported by event-related potential (ERP) analysis and behavioral evaluation based on signal detection theory. We found that ER-DBA activation/deactivation reflected a strategic choice of motor control modality in accordance with mental imagery. Reverse ERP traces, as omission responses, confirmed that the imagery was contextual. We found that mental imagery was updated only by environmental changes via perceptual evidence and response-based abductive reasoning. Moreover, stable on-pulse tapping was achievable by maintaining proactive control while creating an imagery of syncopated rhythms from simple beat trains, whereas accuracy was degraded with frequent erroneous tapping for missing pulses. We conclude that the dACC voluntarily regulates rhythmic sensorimotor synchronization by utilizing contextual mental imagery based on experience and by creating novel rhythms.

Noise occlusion in discrete tone sequences as a tool towards auditory predictive processing?

The notion of predictive coding is a common feature of many theories of auditory information processing. Experimental demonstrations of predictive auditory processing often rest on omitting predictable input in order to uncover the prediction made by the brain. Findings show that auditory cortical activity elicited by the omission of a predictable tone resembles the activity elicited by the actual tone. Here we attempted to extend this approach towards using noises instead of omissions in order to capture a more prevalent case of degraded sensory input. By applying a subtraction approach to remove ERP effects of the noise itself, auditory cortical activity elicited "behind" the noise was uncovered. We hypothesized that ERPs elicited behind noise stimuli covering predictable tones should be more similar to ERPs elicited by the actual tones than when the same comparison is made for unpredictable tones. ERP results during passive listening partly confirm this hypothesis, but also point towards some methodological caveats in this particular approach towards studying neural correlates of predictive auditory processing due to contributions from predictability-unrelated factors. A follow-up active listening condition indicated that participants were not more likely to perceive the tone sequence as continuous when a predictable tone was covered with noise than when this pertained to an unpredictable tone. Overall, the noise-based paradigm in its present form was not shown to be successful in revealing predictive processing in perceptual judgments or early neural correlates of sound processing. We discuss these findings in the contexts of predictive processing and illusory auditory continuity. This article is part of a Special Issue entitled SI: Prediction and Attention.