Mark Wallace

Mark Wallace, Ph.D Laboratory Director

Director, Vanderbilt
Brain Institute

Overview

Development

Plasticity

Receptive Field Organization

Framework for Dyslexia

Multisensory Processes in Autism

Relevant Videos

Current Wallace Lab Projects

 

Circuit and Network Relations in Multisensory Cortex

Project Lead: Juliane Krueger-Fister

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My primary research interests focus on how the brain copes with sensory loss, particularly deafness, and the subsequent restoration of hearing, i.e. cochlear implants (CIs). Furthermore, I am interested what role multisensory networks may play during hearing loss and reinstatement. I postulate that other modalities may help overcome auditory deprivation and that subsequent to CI placement existing senses aid in instructing the newly arriving auditory signals. To investigate this, I am currently utilizing neurophysiological recording and neuroanatomical tract tracing techniques in order to characterize multisensory network properties in the normal brain with emphasis on corticocortical and thalamocortical loops. In the future, I would like to expand upon this work in the deaf brain. Here, I believe that identifying neurogenetic markers and physiological changes in network activity and comparing those findings to data from the normal brain would be of great value.

 

The neural underpinnings of multisensory behavior

Project Lead: Aaron Nidiffer

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My research project is aimed at understanding how multisensory neurons in the superior colliculus contribute to behavior. Non-human primates are trained to report the detection of auditory stimulus via manual response while being presented auditory, visual, and combined audiovisual stimuli. Behavioral responses are simultaneously recorded with neuronal activity so that a direct link between brain activity and behavior can be explored. Additionally, my research seeks to understand how stimulus factors such as intensity and the spatial and temporal relationships between the unisensory components of a multisensory stimulus affect behavior and the neuronal mechanisms responsible for that behavioral change.

 

Multisensory Integration in Clinical Populations

Project Lead: Justin Siemann

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Multisensory integration can be described as the merging and transformation of information from the different senses. Autism spectrum disorders (ASD) are complex neurodevelopmental disorders characterized by impairments in communication and social behavior as well as the presence of repetitive and restrictive behaviors. In addition to the classic domains impacted in autism, sensory abnormalities are also highly prevalent in ASD with the new DSM-V now including sensory disturbances as a criterion for diagnosis. Based on the wealth of evidence highlighting disturbances across multiple sensory systems, there has been increased focus on better characterizing how the integration of information across the different sensory modalities is impacted in autism. My project is focused on psychophysical, behavioral and systems based questions to gain a further understanding of the underlying mechanisms of multisensory processing as it relates to neurodevelopmental disorders such as autism with the ultimate goal of developing more effective remediation tools.

 

Multisensory Training in Anesthesia Practice

Project Lead: Joseph J. Schlesinger, M. D.

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In reference to the above figures, the pulse oximeter is a critical monitor in anesthesia practice designed to improve patient safety. Here, we present an approach to improve the ability of anesthesiologists to monitor arterial oxygen saturation via pulse oximetry through an audiovisual training process. Fifteen residents’ abilities to detect auditory changes in pulse oximetry were measured before and after perceptual training. Training resulted in a 9% (95% confidence interval, 4%–14%, P = 0.0004, t166 = 3.60) increase in detection accuracy, and a 72-millisecond (95% confidence interval, 40–103 milliseconds, P < 0.0001, t166 = −4.52) speeding of response times in attentionally demanding and noisy conditions that were designed to simulate an operating room. This study illustrates the benefits of multisensory training and sets the stage for further work to better define the role of perceptual training in clinical anesthesiology.

In acute care settings, the detection and response to clinical signals is critical to safe patient care. The design of audible and visual alarms has proven problematic in this regard; undue sensitivity or priority leads to excessive false alarms (and alarm fatigue) while, with insufficiently salient or sensitive alarms, critical events are missed. Studies suggest that clinical alarm design can be significantly improved by considering auditory and visual signals together as an integrated multisensory signal. I have created a unique experimental model to study the effects of the combined use of auditory and visual alarms on clinician detection and decision-making. I will use this model to study the dynamic responses of critical care clinicians performing multiple stimulus-response trials. The stimulus is an acute change in a visually presented vital sign and its associated audible alarm signal, presented on realistic ICU background sounds. Performance variables are response time and accuracy of a treatment decision. A secondary auditory task modulates attentional workload. I will examine the stimulus-response curves with: 1) Varying auditory signal-to-noise ratios and clinical scenario complexity and 2) Developing novel multisensory alarms to improve response time and accuracy to recognizing clinical deterioration and instituting therapeutic intervention. The results will inform recommendations for ICU alarm design to maximize performance while minimizing alarm fatigue.

 

Serotonergic Influences on Multisensory Processing

Project Lead: LeAnne Kurela

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The integration of information across the senses is vital for our everyday interaction with the world. The superior colliculus (SC) is a critical brain region for these integrative processes. While much is known about how this process develops and how it occurs, less is understood about the neuromodulatory systems involved in the tuning of multisensory integration. I am interested in understanding the role of the serotonin (5-HT) system in the multisensory processing occurring within the SC. I utilize the methods of in vivo electrophysiology and pressure-injection of serotonergic compounds during single-unit recordings to determine the part the 5-HT system plays in shaping multisensory integration.

 

Plasticity of Multisensory Temporal Processing

Project Lead: Matt De Niear

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Autism Spectrum Disorder (ASD) is a developmental disorder diagnostically characterized by impairments of social communication and restricted interests and repetitive behaviors. Impaired sensory processing (including multisensory processing) has been identified as an additional element of the diagnostic criteria for ASD in the DSM-V and may represent an important and unappreciated factor contributing to the observed overall impairments in social communication. From a multisensory perspective, communication and social impairments in ASD might arise from an inability to perceive the temporal relationships between stimuli affecting different sensory modalities. For example, audiovisual speech comprehension, a process that relies heavily on the temporal relationships between component auditory and visual modalities, has been suggested to be affected in ASD by the impaired ability to perceptually integrate sensory information. My project seeks to identify the neural correlates that underlie deficits of multisensory temporal acuity in ASD and to determine if a perceptual learning paradigm previously observed to enhance temporal acuity for audiovisual in typically developed adults is capable of enhancing temporal acuity in those with ASD.

 

Behavioral and Neural Variability in Autism Spectrum Disorder

Project Lead: Sarah Baum, Ph D

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Sensory dysfunction is now recognized as a core symptom of Autism Spectrum Disorder (ASD), as well as restricted interests and repetitive behaviors, and deficits in social communication and interaction. In addition to atypical sensory response, performance on a number of sensory and motor tasks is not only worse, but also more inconsistent from trial to trial in individuals with ASD. A growing body of literature suggests that differences in behavioral variability, and its underlying neural correlates, may provide important clues about the encoding of sensory information and its transformation to behavioral output in ASD. Using both behavioral testing and neuroimaging with fMRI, the experiments carried out under the project aim to provide a thorough characterization of both behavioral and neural (i.e. BOLD) variability in ASD and TD children, and the associated effect of variability on speech processing abilities. Our second goal is to investigate the malleability of sensory processing through the use of a perceptual training paradigm with ASD individuals, aimed at decreasing variability and improving speech perception.

 

Audiovisual Processing in Patients with Cochlear Implants

Project Lead: Iliza Butera

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Cochlear implants allow those with profound hearing loss to experience sound, some of them for the first time. However, cochlear implant patients have difficulties with pitch discrimination and sound localization, even using modern implant processors. I’m interested in the mechanisms by which multiple senses are filtered and fused together in the brain, creating what we call spatial and temporal binding. Prior research suggests that perceptual binding may be shaped by experience and can be influenced by subsequent training. My work utilizes lab-based computer games and app-based mobile platforms to understand the development of multisensory integration and cortical plasticity. This research may help shape therapeutic interventions in the clinic as well as future cochlear implant technology.

 

EEG Investigation of Sensory Processing Networks

Project Lead: David Simon

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My research interest is using Electroencephalography (EEG) to explore differences in sensory processing and brain networks in individuals with autism spectrum disorder (ASD).  Sensory dysfunction is a recognized primary component of ASD, but there is still a great deal we do not know about how the neural mechanisms of sensory processing are altered in individuals with ASD and how this leads to behavioral impairment.  Specifically in the multisensory domain, we know that individuals with ASD have a wider temporal window for integration of unisensory components as well as decreased behavioral facilitation in terms of reaction times.  My work centers on using the high temporal resolution of EEG combined with psychophysical approaches to determine how differences in sensory system activity lead to altered perception in individuals with ASD.  Additionally, through application of graph theory approaches of network modelling to EEG data I am investigating how disruptions in overall network properties, such as long range connectivity and modularity, are associated with perception in both ASD and typical development. 

 

Spatio-temporal dynamics and oscillatory mechanisms of auditory-visual detection across space

Project Lead: Antonia Thelen, Ph D

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The goal of the study is to investigate the existence of preferential multisensory interactions across visual spatial representations and auditory cues. More specifically, the project will aim at revealing the spatio-temporal dynamics of the neuronal populations which underpin multisensory interactions in different spatial positions. To this end we will combine behavioral measures and EEG recordings. The methods at hand will reveal 1) selective perceptual enhancement at the behavioral level, and 2) the temporal dynamics and oscillatory activity implicated, as well as the underlying neuronal substrates.

Based on previous literature, significant stimulus detection enhancement upon multisensory trials as compared to unisensory trials in terms of shorter RTs and higher d’ measures should be observed. Further, RTs to eccentric stimuli have been shown to be shorter than to centrally presented stimuli (preliminary results, published abstract: Thelen, & Murray, 2012). Results should reflect preferential integration of high-frequency tones with centrally presented stimuli, while the inverse can be expected in the periphery (e.g. preference for low-frequency tone; (Spence, 2011; Guzman-Martinez, et al., 2012)). Additionally, the selective enhancement observed at the behavioral level should be reflected in the EEG analyses. 

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Past Projects

The Development of Multisensory Processes. Research in this area seeks to better characterize how multisensory circuits mature during early postnatal life. The approaches used for this work range from single neuron electrophysiology to psychophysics and event related potentials (ERPs) in children.

Experiential Plasticity in Developing and Adult Multisensory Circuits. Works seeks to better understand how early sensory experience shapes developing multisensory circuits, and the surprising degree of plasticity that can be enabled in adult representations.

Spatiotemporal Receptive Field Organization and Multisensory Integration. Ongoing research in the lab seeks to describe the complex receptive fields that characterize multisensory neurons in both cortical and subcortical structures, and to describe how this receptive field architecture influences the multisensory processing capabilities of these neurons.

A Multisensory Framework for Developmental Dyslexia. In prior work we have shown that alterations in multisensory temporal processes may be associated with the prevalent reading disability - developmental dyslexia. Current work seeks to extend this finding and better elucidate the affected brain circuits.

Altered Multisensory Processes in Autism Spectrum Disorder. New research in the lab seeks to better characterize sensory and multisensory processing in children with autism spectrum disorder.