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Biomedical subjects

Mark T Wallace

Publications and source records attributed to Mark T Wallace.

14 recordsLinked to original sources
PubMed2006

Auditory enhancement of visual temporal order judgment.

Although numerous studies have shown that response times can be speeded by the presentation of multisensory stimuli, here we show that such speeding can be seen even when the second sensory channel fails to provide any task-relevant (i.e. redundant) information, and where cueing appears an unlikely explanation. Study participants performed a visual temporal order judgment task in the presence of task uninformative auditory cues, with the latter sound delayed relative to the latter visual cue. Responses were maximally speeded when the auditory stimulus was delayed by a short time (i.e. 100 ms) relative to the second visual target. These results illustrate a unique form of temporal benefit underlying a multisensory interaction, and form the basis for a novel explanation of these perceptual enhancements.

Acoustic Stimulation↗
PubMed2005

Enhanced multisensory integration in older adults.

Information from the different senses is seamlessly integrated by the brain in order to modify our behaviors and enrich our perceptions. It is only through the appropriate binding and integration of information from the different senses that a meaningful and accurate perceptual gestalt can be generated. Although a great deal is known about how such cross-modal interactions influence behavior and perception in the adult, there is little knowledge as to the impact of aging on these multisensory processes. In the current study, we examined the speed of discrimination responses of aged and young individuals to the presentation of visual, auditory or combined visual-auditory stimuli. Although the presentation of multisensory stimuli speeded response times in both groups, the performance gain was significantly greater in the aged. Most strikingly, multisensory stimuli restored response times in the aged to those seen in young subjects to the faster of the two unisensory stimuli (i.e., visual). The current results suggest that despite the decline in sensory processing that accompanies aging, the use of multiple sensory channels may represent an effective compensatory strategy to overcome these unisensory deficits.

Adaptation, Physiological↗
PubMed2005

Altered temporal profile of visual-auditory multisensory interactions in dyslexia.

Recent studies have demonstrated that dyslexia is associated with deficits in the temporal encoding of sensory information. While most previous studies have focused on information processing within a single sensory modality, it is clear that the deficits seen in dyslexia span multiple sensory systems. Surprisingly, although the development of linguistic proficiency involves the rapid and accurate integration of auditory and visual cues, the capacity of dyslexic individuals to integrate information between the different senses has not been systematically examined. To test this, we studied the effects of task-irrelevant auditory information on the performance of a visual temporal-order-judgment (TOJ) task. Dyslexic subjects' performance differed significantly from that of control subjects, specifically in that they integrated the auditory and visual information over longer temporal intervals. Such a result suggests an extended temporal "window" for binding visual and auditory cues in dyslexic individuals. The potential deleterious effects of this finding for rapid multisensory processes such as reading are discussed.

Acoustic Stimulation↗
PubMed2005

On the use of superadditivity as a metric for characterizing multisensory integration in functional neuroimaging studies.

A growing number of brain imaging studies are being undertaken in order to better understand the contributions of multisensory processes to human behavior and perception. Many of these studies are designed on the basis of the physiological findings from single neurons in animal models, which have shown that multisensory neurons have the capacity for integrating their different sensory inputs and give rise to a product that differs significantly from either of the unisensory responses. At certain points these multisensory interactions can be superadditive, resulting in a neural response that exceeds the sum of the unisensory responses. Because of the difficulties inherent in interpreting the results of imaging large neuronal populations, superadditivity has been put forth as a stringent criterion for identifying potential sites of multisensory integration. In the present manuscript we discuss issues related to using the superadditive model in human brain imaging studies, focusing on population responses to multisensory stimuli and the relationship between single neuron measures and functional brain imaging measures. We suggest that the results of brain imaging studies be interpreted with caution in regards to multisensory integration. Future directions for imaging multisensory integration are discussed in light of the ideas presented.

Animals↗
PubMed2005

Superior colliculus neurons use distinct operational modes in the integration of multisensory stimuli.

Many neurons in the superior colliculus (SC) integrate sensory information from multiple modalities, giving rise to significant response enhancements. Although enhanced multisensory responses have been shown to depend on the spatial and temporal relationships of the stimuli as well as on their relative effectiveness, these factors alone do not appear sufficient to account for the substantial heterogeneity in the magnitude of the multisensory products that have been observed. Toward this end, the present experiments have revealed that there are substantial differences in the operations used by different multisensory SC neurons to integrate their cross-modal inputs, suggesting that intrinsic differences in these neurons may also play an important deterministic role in multisensory integration. In addition, the integrative operation employed by a given neuron was found to be well correlated with the neuron's dynamic range. In total, four categories of SC neurons were identified based on how their multisensory responses changed relative to the predicted addition of the two unisensory inputs as stimulus effectiveness was altered. Despite the presence of these categories, a general rule was that the most robust multisensory enhancements were seen with combinations of the least effective unisensory stimuli. Together, these results provide a better quantitative picture of the integrative operations performed by multisensory SC neurons and suggest mechanistic differences in the way in which these neurons synthesize cross-modal information.

Acoustic Stimulation↗
PubMed2004

Visual experience is necessary for the development of multisensory integration.

Multisensory neurons and their ability to integrate multisensory cues develop gradually in the midbrain [i.e., superior colliculus (SC)]. To examine the possibility that early sensory experiences might play a critical role in these maturational processes, animals were raised in the absence of visual cues. As adults, the SC of these animals were found to contain many multisensory neurons, the large majority of which were visually responsive. Although these neurons responded robustly to each of their cross-modal inputs when presented individually, they were incapable of synthesizing this information. These observations suggest that visual experiences are critical for the SC to develop the ability to integrate multisensory information and lead to the prediction that, in the absence of such experience, animals will be compromised in their sensitivity to cross-modal events.

Animals↗
PubMed2004

Semantic congruence is a critical factor in multisensory behavioral performance.

It has repeatedly been demonstrated that the presence of multiple cues in different sensory modalities can enhance behavioral performance by speeding responses, increasing accuracy, and/or improving stimulus detection. Despite an extensive knowledge base as to how the spatial, temporal, and physical (eg., intensity) characteristics of multisensory stimuli influence such enhancements, little is known about the role of semantic or contextual congruence. Our hypothesis was that semantically congruent multisensory stimuli would result in enhanced behavioral performance, and that semantically incongruent multisensory stimuli would result in either no enhancement or a decrement in behavioral performance. The results from a redundant cue feature discrimination task clearly demonstrate that congruent cross-modal stimulation improves behavioral performance. This effect is specific to the multisensory stimuli, as no improvements are seen in the presence of redundant unimodal stimulus pairs. In contrast, incongruent stimulus pairs result in behavioral decrements for both multisensory and paired unimodal stimuli. These results highlight that in addition to such simple stimulus features as space, time and relative effectiveness, the semantic content of a multisensory stimulus plays a critical role in determining how it is processed by the nervous system.

Acoustic Stimulation↗
PubMed2004

A revised view of sensory cortical parcellation.

Traditional cortical parcellation schemes have emphasized the presence of sharply defined visual, auditory, and somatosensory domains populated exclusively by modality-specific neurons (i.e., neurons responsive to sensory stimuli from a single sensory modality). However, the modality-exclusivity of this scheme has recently been challenged. Observations in a variety of species suggest that each of these domains is subject to influences from other senses. Using the cerebral cortex of the rat as a model, the present study systematically examined the capability of individual neurons in visual, auditory, and somatosensory cortex to be activated by stimuli from other senses. Within the major modality-specific domains, the incidence of inappropriate (i.e., nonmatching) and/or multisensory neurons was very low. However, at the borders between each of these domains a concentration of multisensory neurons was found whose modality profile matched the representations in neighboring cortices and that were able to integrate their cross-modal inputs to give rise to enhanced and/or depressed responses. The results of these studies are consistent with some features of both the traditional and challenging views of cortical organization, and they suggest a parcellation scheme in which modality-specific cortical domains are separated from one another by transitional multisensory zones.

Animals↗
PubMed2003

Multisensory enhancement of localization under conditions of induced myopia.

Enhanced behavioral performance mediated by multisensory stimuli has been shown using a variety of measures, including response times, orientation behaviors, and even simple stimulus detection. However, there has been little evidence for a multisensory-mediated improvement in stimulus localization. We suggest that this lack of effect may be a result of the high acuity of the visual system. To examine whether normal visual acuity may be masking any potential multisensory benefit for stimulus localization, we examined the ability of human subjects to localize visual, auditory and combined visual-auditory targets under conditions of normal and degraded vision. Under conditions of normal vision, localization precision (i.e., variability) was equivalent for visual and multisensory targets, and was significantly worse for auditory targets. In contrast, under conditions of induced myopia, visual localization performance was degraded by an average of 25%, while auditory localization performance was unaffected. However, during induced myopia, multisensory (i.e., visual-auditory) localization performance was significantly improved relative to visual performance. These results show a multisensory-mediated enhancement in human localization ability, and illustrate the cross-modal benefits that can be obtained when spatial information in one sense is compromised or ambiguous.

Acoustic Stimulation↗
PubMed2003

Neuron-specific response characteristics predict the magnitude of multisensory integration.

Multisensory neurons in the superior colliculus (SC) typically respond to combinations of stimuli from multiple modalities with enhancements and/or depressions in their activity. Although such changes in response have been shown to follow a predictive set of integrative principles, these principles fail to completely account for the full range of interactions seen throughout the SC population. In an effort to better define this variability, we sought to determine if there were additional features of the neuronal response profile that were predictive of the magnitude of the multisensory interaction. To do this, we recorded from 109 visual-auditory SC neurons while systematically manipulating stimulus intensity. Along with the previously described roles of space, time, and stimulus effectiveness, two features of a neuron's response profile were found to offer predictive value as to the magnitude of the multisensory interaction: spontaneous activity and the level of sensory responsiveness. Multisensory neurons with little or no spontaneous activity and weak sensory responses had the capacity to exhibit large response enhancements. Conversely, neurons with modest spontaneous activity and robust sensory responses exhibited relatively small response enhancements. Together, these results provide a better view into multisensory integration, and suggest substantial heterogeneity in the integrative characteristics of the multisensory SC population.

Acoustic Stimulation↗
PubMed2003

Cross-modal sensory processing in the anterior cingulate and medial prefrontal cortices.

One of the principal functions of the nervous system is to synthesize information from multiple sensory channels into a coherent behavioral and perceptual gestalt. A critical feature of this multisensory synthesis is the sorting and coupling of information derived from the same event. One of the singular features of stimuli conveying such information is their contextual or semantic congruence. Illustrating this fact, subjects are typically faster and more accurate when performing tasks that include congruent compared to incongruent cross-modal stimuli. Using functional magnetic resonance imaging, we demonstrate that activity in select brain areas is sensitive to the contextual congruence among cross-modal cues and to task difficulty. The anterior cingulate gyrus and adjacent medial prefrontal cortices showed significantly greater activity when visual and auditory stimuli were contextually congruent (i.e., matching) than when they were nonmatching. Although activity in these regions was also dependent on task difficulty, showing decreased activity with decreasing task difficulty, the activity changes associated with stimulus congruence predominated.

Acoustic Stimulation↗
PubMed2003

An irrelevant light enhances auditory detection in humans: a psychophysical analysis of multisensory integration in stimulus detection.

Physiological and behavioral studies in animal models have revealed that information from the different senses can be used synergistically to enhance the detection of objects and events. Although a great deal of evidence exists which demonstrates the synergistic use of multisensory cues in human behavior and perception, there is conflicting evidence about whether such interactions can be used to aid in stimulus detection. To examine this issue, we had volunteers indicate the presence or absence of a brief, low-intensity sound that was either presented alone or paired with a simultaneous light in a one-interval signal detection task. In the first experiment, the task-irrelevant light was found to enhance the detectability of the sound, but also to increase the subject's willingness to report the presence of a sound (i.e., response bias). In the second experiment, designed to eliminate this response bias, we found an improvement in stimulus detectability in the absence of any change in bias. These findings demonstrate the presence of a significant multisensory-mediated gain in stimulus detection in human subjects.

Acoustic Stimulation↗
PubMed2002

Deactivation of sensory-specific cortex by cross-modal stimuli.

Visual and auditory cortices traditionally have been considered to be "modality-specific." Thus, their activity has been thought to be unchanged by information in other sensory modalities. However, using functional magnetic resonance imaging (fMRI), the present experiments revealed that ongoing activity in the visual cortex could be modulated by auditory information and ongoing activity in the auditory cortex could be modulated by visual information. In both cases, this cross-modal modulation of activity took the form of deactivation. Yet, the deactivation response was not evident in either cortical area during the paired presentation of visual and auditory stimuli. These data suggest that cross-modal inhibitory processes operate within traditional modality-specific cortices and that these processes can be switched on or off in different circumstances.

Acoustic Stimulation↗