Context is everything: How context shapes modulations of responses to unattended sound.

The concept of perceptual inferences taking place over multiple timescales simultaneously raises questions about how the brain can balance the demands of remaining sensitive to local rarity while utilising more global longer-term predictability to modulate cortical responses. In the present study auditory evoked potentials to four presentations of the same sound sequence containing predictable structure on a local (milliseconds to seconds) and more global (many minutes) timescales were recorded. The results from 33 participants are used to demonstrate that predictions about both local (internal predictive models) and global (meta-models that define expected precisions associated with familiar internal model states) regularities are formed. The study exposes more local context-based modulations of the P1 but more global order-based modulations of the auditory evoked N2 components. The results are discussed in terms of theoretical links advocating that uncertainty at multiple timescales could lead to differential component modulations, and the importance of considering the broader learning context in auditory evoked potential studies.

Setting precedent: Initial feature variability affects the subsequent precision of regularly varying sound contexts.

The task of making sense of the world around us is supported by brain processes that simplify the environment. For example, repetitive patterns of sensory input help us to predict future events. This study builds on work, suggesting that sensory predictions are heavily influenced by first impressions. We presented healthy adults with a sequence comprising three sounds each differing from the other two on three dimensions; for simplicity A, B and C. These three sounds were arranged in blocks where two were equally common and one was rare, and the probabilities rotated creating three different block types (i.e., probabilities, A < B = C, B < A = C, C < A = B). Sequences included two of each block type with three versions-one starting with A < B = C, one with B < A = C and one with C < A = B. The common tone evoked responses in any given block were highly suppressed consistent with the auditory system predicting regular events, while the rare tone in each block elicited a larger response signaling a prediction error. However, results indicated that the auditory system assessed the configurations in which the two common tones were adjacent in space (within the three locations used) as less volatile compared to when they were highly separate. When the more volatile environment was encountered at the beginning of the sequence, all deviance-related responses were significantly lower in amplitude. Results suggest that the representation of a stimulus configuration is affected by the estimate drawn from the initial context, expanding our notion of the nature of primacy bias to include powerful effects of initial feature variance.

The cognitive resource and foreknowledge dependence of auditory perceptual inference.

Auditory perceptual inference engages learning of complex statistical information about the environment. Inferences assist us to simplify perception highlighting what can be predicted on the basis of prior learning (through the formation of internal "prediction" models) and what might be new, potentially necessitating an investment of resources to remodel predictions. In the present study, we tested the hypothesis that sound sequences with multiple levels of predictability may rely on cognitive resources and be cognitively penetrable to a greater extent than was previously shown by studies presenting simpler sound sequences. Auditory-evoked potentials (AEPs) were recorded from 117 participants. All participants heard the exact same sound sequence but under different conditions: 51 while watching a DVD movie and 66 while performing a cognitively demanding task. Participants were asked to ignore the sounds and focus their attention on the movie/task. However, prior to commencing the experiment we manipulated what participants knew about the sound sequence by providing explicit sequence information to 15 and 34 of the participants in the DVD and cognitive-task conditions, respectively, and no information to the others. The results demonstrated that although local pattern violations elicited distinctive AEP responses (namely, mismatch negativity), the way the amplitude of this response was modulated by sequence learning over time was dependent upon both task and explicit sequence knowledge. The implications are discussed with reference to how the division of available attention resources between the primary task and concurrent sound impacts what is learned.

Effects of immune activation during early or late gestation on schizophrenia-related behaviour in adult rat offspring.

Maternal exposure to infectious agents during gestation has been identified as a significant risk factor for schizophrenia. Using a mouse model, past work has demonstrated that the gestational timing of the immune-activating event can impact the behavioural phenotype and expression of dopaminergic and glutamatergic neurotransmission markers in the offspring. In order to determine the inter-species generality of this effect to rats, another commonly used model species, the current study investigated the impact of a viral mimetic Poly (I:C) at either an early (gestational day 10) or late (gestational day 19) time-point on schizophrenia-related behaviour and neurotransmitter receptor expression in rat offspring. Exposure to Poly (I:C) in late, but not early, gestation resulted in transient impairments in working memory. In addition, male rats exposed to maternal immune activation (MIA) in either early or late gestation exhibited sensorimotor gating deficits. Conversely, neither early nor late MIA exposure altered locomotor responses to MK-801 or amphetamine. In addition, increased dopamine 1 receptor mRNA levels were found in the nucleus accumbens of male rats exposed to early gestational MIA. The findings from this study diverge somewhat from previous findings in mice with MIA exposure, which were often found to exhibit a more comprehensive spectrum of schizophrenia-like phenotypes in both males and females, indicating potential differences in the neurodevelopmental vulnerability to MIA exposure in the rat with regards to schizophrenia related changes.

Surprising sequential effects on MMN.

The mismatch negativity (MMN) is conceptualized as a confidence-weighted error signal elicited when a deviation violates the predicted next-state based on regularity. The mechanisms underpinning its generation remain contentious. Smaller MMN response is a robust finding in schizophrenia and reduced amplitude may implicate impairment in prediction-error signalling. An enriched understanding of factors that influence MMN size in healthy people is a prerequisite for translating the relevance of reduced MMN in schizophrenia. This paper features two studies designed to explore factors that impact MMN in healthy individuals. Study 1 confirms that MMN amplitude does not faithfully reflect transition statistics and is susceptible to order-driven bias. In study 2, we demonstrate that an order-driven bias remains despite repeated encounters with sound sequences. These data demonstrate that factors that impact on MMN size in non-clinical groups are not fully understood and that some mechanisms driving relevance filtering are likely influenced by 'top-down' expectations.