Enhanced deviant responses in patterned relative to random sound sequences

Rosy Southwell,Maria Chait

doi:10.1016/j.cortex.2018.08.032

Abstract

The brain draws on knowledge of statistical structure in the environment to facilitate detection of new events. Understanding the nature of this representation is a key challenge in sensory neuroscience. Specifically, it is unknown whether real-time perception of rapidly-unfolding sensory signals is driven by a coarse or detailed representation of the proximal stimulus history. We recorded electroencephalography brain responses to frequency outliers in regularly-patterned (REG) versus random (RAND) tone-pip sequences which were generated anew on each trial. REG and RAND sequences were matched in frequency content and span, only differing in the specific order of the tone-pips. Stimuli were very rapid, limiting conscious reasoning in favour of automatic processing of regularity. Listeners were naïve and performed an incidental visual task. Outliers within REG evoked a larger response than matched outliers in RAND. These effects arose rapidly (within 80 msec) and were underpinned by distinct sources from those classically associated with frequency-based deviance detection. These findings are consistent with the notion that the brain continually maintains a detailed representation of ongoing sensory input and that this representation shapes the processing of incoming information. Predominantly auditory-cortical sources code for frequency deviance whilst frontal sources are associated with tracking more complex sequence structure.

Highlights

Detection of new events within a constantly fluctuating sensory input is a fundamental challenge to organisms in dynamic environments
The mean rating given for how distracting the sound sequences were overall was 2.2 out of 5, range 1e4; indicating that subjects were moderately distracted by the sound sequences on average, but with considerable variability
Our results reveal two main findings: Firstly, robust effects of context were observed despite the fact that patterns were never repeated and had to be discovered anew on each trial

Summary

Introduction

Detection of new events within a constantly fluctuating sensory input is a fundamental challenge to organisms in dynamic environments Hypothesized to underlie this process is a continually-refined internal model of the real-world causes of sensations, made possible by exploiting statistical structure in the sensory input (Dayan, Hinton, Neal, & Zemel, 1995; Friston & Kiebel, 2009; Rubin, Ulanovsky, Nelken, & Tishby, 2016; Winkler, Denham, & Nelken, 2009). Accumulating evidence suggests that at least part of the deviant response arises from neural processes associated with computing ‘surprise’ or detecting a mismatch between expected and actual sensory input (Daikhin & Ahissar, 2012; Khouri & Nelken, 2015; Parras et al, 2017; Taaseh, Yaron, & Nelken, 2011). The underlying network, consistently implicated in these processes, is comprised of bilateral auditory cortex (Heschl's Gyrus and superior temporal gyrus) and right inferior frontal gyrus (Barascud, Pearce, Griffiths, Friston, & Chait, 2016; Chennu et al, 2016; Garrido et al, 2009, 2008; Heilbron & Chait, 2017; Opitz, Rinne, Mecklinger, Cramon von, & Schro€ger, 2002)

Methods

Results

Conclusion