M. Alex Meredith

Bio: M. Alex Meredith is an academic researcher from Virginia Commonwealth University. The author has contributed to research in topics: Sensory system & Auditory cortex. The author has an hindex of 31, co-authored 58 publications receiving 6088 citations. Previous affiliations of M. Alex Meredith include VCU Medical Center.

The Merging of the Senses

Abstract: Bringing together neural, perceptual, and behavioral studies, The Merging of the Senses provides the first detailed review of how the brain assembles information from different sensory systems in order to produce a coherent view of the external world. Stein and Meredith marshall evidence from a broad array of species to show that interactions among senses are the most ancient scheme of sensory organization, an integrative system reflecting a general plan that supersedes structure and species. Most importantly, they explore what is known about the neural processes by which interactions among the senses take place at the level of the single cell.The authors draw on their own experiments to illustrate how sensory inputs converge (from visual, auditory, and somatosensory modalities, for instance) on individual neurons in different areas of the brain, how these neurons integrate their inputs, the principles by which this integration occurs, and what this may mean for perception and behavior. Neurons in the superior colliculus and cortex are emphasized as models of multiple sensory integrators.Barry E. Stein is Professor of Physiology and M. Alex Meredith is Associate Professor of Anatomy, both at the Medical College of Virginia, Virginia Commonwealth University.

Cross-modal plasticity in specific auditory cortices underlies visual compensations in the deaf

Abstract: When the brain is deprived of input from one sensory modality, it often compensates with supranormal performance in one or more of the intact sensory systems. In the absence of acoustic input, it has been proposed that cross-modal reorganization of deaf auditory cortex may provide the neural substrate mediating compensatory visual function. We tested this hypothesis using a battery of visual psychophysical tasks and found that congenitally deaf cats, compared with hearing cats, have superior localization in the peripheral field and lower visual movement detection thresholds. In the deaf cats, reversible deactivation of posterior auditory cortex selectively eliminated superior visual localization abilities, whereas deactivation of the dorsal auditory cortex eliminated superior visual motion detection. Our results indicate that enhanced visual performance in the deaf is caused by cross-modal reorganization of deaf auditory cortex and it is possible to localize individual visual functions in discrete portions of reorganized auditory cortex.

Behavioral indices of multisensory integration: Orientation to visual cues is affected by auditory stimuli

Abstract: Physiological studies have demonstrated that inputs from different sensory modalities converge on, and are integrated by, individual superior colliculus neurons and that this integration is governed by specific spatial rules. The present experiments were an attempt to relate these neural processes to overt behavior by determining if behaviors believed to involve the circuitry of the superior colliculus would show similar multisensory dependencies and be subject to the same rules of integration. The neurophysiological-behavioral parallels proved to be striking. The effectiveness of a stimulus of one modality in eliciting attentive and orientation behaviors was dramatically affected by the presence of a stimulus from another modality in each of the three behavioral paradigms used here. Animals trained to approach a low intensity visual cue had their performance significantly enhanced when a brief, low intensity auditory stimulus was presented at the same location as the visual cue, but their performance was significantly depressed when the auditory stimulus was disparate to it. These effects were independent of the animals' experience with the modifying (i.e. auditory) stimulus and exceeded what might have been predicted statistically based on the animals' performance with each single-modality cue. The multiplicative nature of these multisensory interactions and their dependence on the relative positions and intensities of the two stimuli were all very similar to those observed physiologically for single cells. The few differences that were observed appeared to reflect the fact that understanding integration at the level of the single cell requires reference to the individual cell's multisensory receptive field properties, while at the behavioral level populations of receptive fields must be evaluated. These data illustrate that the rules governing multisensory integration at the level of the single cell also predict responses to these stimuli in the intact behaving organism.

Multisensory Integration in the Superior Colliculus of the Alert Cat

Abstract: Wallace, Mark T., M. Alex Meredith, and Barry E. Stein. Multisensory integration in the superior colliculus of the alert cat. J. Neurophysiol. 80: 1006–1010, 1998. The modality convergence patterns...

Being There: Putting Brain, Body, and World Together Again

Abstract: From the Publisher: The old opposition of matter versus mind stubbornly persists in the way we study mind and brain. In treating cognition as problem solving, Andy Clark suggests, we may often abstract too far from the very body and world in which our brains evolved to guide us. Whereas the mental has been treated as a realm that is distinct from the body and the world, Clark forcefully attests that a key to understanding brains is to see them as controllers of embodied activity. From this paradigm shift he advances the construction of a cognitive science of the embodied mind.

The Self-Organizing Map

Abstract: An overview of the self-organizing map algorithm, on which the papers in this issue are based, is presented in this article.