“What” and “Where” in Auditory Sensory Processing: A High-Density Electrical Mapping Study of Distinct Neural Processes Underlying Sound Object Recognition and Sound Localization

Functionally distinct dorsal and ventral auditory pathways for sound localization (WHERE) and sound object recognition (WHAT) have been described in non-human primates. A handful of studies have explored differential processing within these streams in humans, with highly inconsistent findings. Stimuli employed have included simple tones, noise bursts, and speech sounds, with simulated left–right spatial manipulations, and in some cases participants were not required to actively discriminate the stimuli. Our contention is that these paradigms were not well suited to dissociating processing within the two streams. Our aim here was to determine how early in processing we could find evidence for dissociable pathways using better titrated WHAT and WHERE task conditions. The use of more compelling tasks should allow us to amplify differential processing within the dorsal and ventral pathways. We employed high-density electrical mapping using a relatively large and environmentally realistic stimulus set (seven animal calls) delivered from seven free-field spatial locations; with stimulus configuration identical across the “WHERE” and “WHAT” tasks. Topographic analysis revealed distinct dorsal and ventral auditory processing networks during the WHERE and WHAT tasks with the earliest point of divergence seen during the N1 component of the auditory evoked response, beginning at approximately 100 ms. While this difference occurred during the N1 timeframe, it was not a simple modulation of N1 amplitude as it displayed a wholly different topographic distribution to that of the N1. Global dissimilarity measures using topographic modulation analysis confirmed that this difference between tasks was driven by a shift in the underlying generator configuration. Minimum-norm source reconstruction revealed distinct activations that corresponded well with activity within putative dorsal and ventral auditory structures

Early, Low-Level Auditory-Somatosensory Multisensory Interactions Impact Reaction Time Speed

Several lines of research have documented early-latency non-linear response interactions between audition and touch in humans and non-human primates. That these effects have been obtained under anesthesia, passive stimulation, as well as speeded reaction time tasks would suggest that some multisensory effects are not directly influencing behavioral outcome. We investigated whether the initial non-linear neural response interactions have a direct bearing on the speed of reaction times. Electrical neuroimaging analyses were applied to event-related potentials in response to auditory, somatosensory, or simultaneous auditory–somatosensory multisensory stimulation that were in turn averaged according to trials leading to fast and slow reaction times (using a median split of individual subject data for each experimental condition). Responses to multisensory stimulus pairs were contrasted with each unisensory response as well as summed responses from the constituent unisensory conditions. Behavioral analyses indicated that neural response interactions were only implicated in the case of trials producing fast reaction times, as evidenced by facilitation in excess of probability summation. In agreement, supra-additive non-linear neural response interactions between multisensory and the sum of the constituent unisensory stimuli were evident over the 40–84 ms post-stimulus period only when reaction times were fast, whereas subsequent effects (86–128 ms) were observed independently of reaction time speed. Distributed source estimations further revealed that these earlier effects followed from supra-additive modulation of activity within posterior superior temporal cortices. These results indicate the behavioral relevance of early multisensory phenomena

Brief Monocular Deprivation as an Assay of Short-Term Visual Sensory Plasticity in Schizophrenia - The Binocular Effect

Background: Visual sensory processing deficits are consistently observed in schizophrenia, with clear amplitude reduction of the visual evoked potential (VEP) during the initial 50-150 of processing. Similar deficits are seen in unaffected first-degree relatives and drug-naïve first-episode patients, pointing to these deficits as potential endophenotypic markers. Schizophrenia is also associated with deficits in neural plasticity, implicating dysfunction of both glutamatergic and GABAergic systems. Here, we sought to understand the intersection of these two domains, asking whether short-term plasticity during early visual processing is specifically affected in schizophrenia. Methods: Brief periods of monocular deprivation (MD) induce relatively rapid changes in the amplitude of the early VEP - i.e., short-term plasticity. Twenty patients and 20 non-psychiatric controls participated. VEPs were recorded during binocular viewing, and were compared to the sum of VEP responses during brief monocular viewing periods (i.e., Left-eye + Right-eye viewing). Results: Under monocular conditions, neurotypical controls exhibited an effect that patients failed to demonstrate. That is, the amplitude of the summed monocular VEPs was robustly greater than the amplitude elicited binocularly during the initial sensory processing period. In patients, this binocular effect was absent. Limitations: Patients were all medicated. Ideally, this study would also include first-episode unmedicated patients. Conclusion: These results suggest that short-term compensatory mechanisms that allow healthy individuals to generate robust VEPs in the context of MD are not effectively activated in patients with schizophrenia. This simple assay may provide a useful biomarker of short-term plasticity in the psychotic disorders and a target endophenotype for therapeutic interventions

Village proposal for mixed use reappropriation of the industrial landscape

Thesis: S.B. in Art and Design, Massachusetts Institute of Technology, Department of Architecture, 2003.Cataloged from PDF version of thesis. Vita.Includes bibliographical references (pages 78-81).This urban design thesis addresses the transformation of single-use industrial space to mixed-use public and private space, linking pedestrian and vehicular paths within the village of Sussex, WI. The industrial revolution often reinforced the separation of functions (residential, commercial, industrial, civic) into separate buildings and often separate districts. In the midst of the built landscape, former places of industrial work and production are now large tracts of underused land. The reappropriation of urban and suburban industrial space provides the opportunity to create mixed-use, vital spaces relating well to pedestrian and vehicular traffic. Such reappropriation deals with the site not only visually, but also in terms of the way its history and natural processes are transformed. The reappropriation is essential on the urban scale of a village, and I choose to explore it at the site of the former quarry and canning factory in Sussex, WI. As a central link between Main Street and the pedestrian Bugline trail, the six acre urban landscape design (in several phases) includes over 100,000 indoor square feet of residential, commercial, and public spaces. This thesis examines issues of ownership, financing, phasing, landscaping, and architecture as they apply in the village. Through an urban design analysis and a series of schemes in drawings and models, the process shows the role of natural processes and public sector involvement in the site development, along with creative solutions to address these relationships on the site. It uses the prominent scale and location of former industrial land and spaces as a point of departure for improving a location's sense of local character, its local economy, its neighborhoods, and its public space.by David M. Foxe.S.B. in Art and Desig

Boundary completion is automatic and dissociable from shape discrimination

Normal visual perception readily overcomes suboptimal or degraded viewing conditions through perceptual filling-in processes, enhancing object recognition and discrimination abilities. This study used visual evoked potential (VEP) recordings in conjunction with electrical neuroimaging analyses to determine the spatiotemporal brain dynamics of boundary completion and shape discrimination processes in healthy humans performing the so-called "thin/fat" discrimination task (Ringach and Shapley, 1996) with stimuli producing illusory contours. First, results suggest that boundary completion processes occur independent of subjects' accuracy on the discrimination task. Modulation of the VEP to the presence versus absence of illusory contours [the IC effect (Murray et al., 2002)] was indistinguishable in terms of response magnitude and scalp topography over the 124-186 ms poststimulus period, regardless of whether task performance was correct. This suggests that failure on this discrimination task is not primarily a consequence of failed boundary completion. Second, the electrophysiological correlates of thin/fat shape discrimination processes are temporally dissociable from those of boundary completion, occurring during a substantially later phase of processing (approximately 330-406 ms). The earlier IC effect was unaffected by whether the perceived contour produced a thin or fat shape. In contrast, later time periods of the VEP modulated according to perceived shape only in the case of stimuli producing illusory contours, but not for control stimuli for which performance was at near-chance levels. Collectively, these data provide further support for a multistage model of object processing under degraded viewing conditions

Structuring beyond architecture

Thesis (M. Arch.)--Massachusetts Institute of Technology, Dept. of Architecture, 2006.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Vita.Includes bibliographical references (p. 170-179).This thesis explores the layering and negotiation of structural devices in urban settings. Its point of departure is a series of patterns of how structural design and urban design interact and overlap, from which are developed design strategies that encourage differentiation and the ability to accommodate change in the future. Therefore, the thesis traces an approach for growth rather than simply specifying a particular isolated solution to a single local set of conditions: a machine rather than a spare part. The overarching structural challenge which I have investigated as a vehicle for this approach is for foundation systems spanning over shallowly buried subway and highway tunnels at a site adjacent to the Fort Point Channel neighborhood in South Boston. This challenge, facing many cities around the world, provokes the problem of designing and creating the structure of support in these areas to enable more - rather than less - creative spatial possibilities above the ground. The subsequent proposal details a system of linear bundles - high-performance concrete beams rooted down to bedrock, along with utilities, walkways, plantings, open spaces, loading conditions, property rights, and implementation strategies bundled together -(cont.) as well as the bridges, piers, and canopies which articulate the termination conditions at the bundles' ends. This thesis asserts that architecture as a discipline and as a creation can negotiate urban conditions and grade separations with structural gestures, shaping the spaces and volumes immediately above and below the constructed ground, and thus addressing both pedestrian and vehicular movement in urban environments. The project leaps between the scales of internal structure and the external urban realm, and situates architecture at this boundary. This exploration integrates relationships with historical precedents of Technological Modernism as well as connections to biological metaphors, to fiction and imagination, to music and harmony, and to broader principles and qualities for shaping and implementing structures in urban spaces. This thesis is the final component for the author's completion of the Master of Architecture degree as well as the interdepartmental Urban Design Certificate.by David M. Foxe.M.Arch

Predicting success: patterns of cortical activation and deactivation prior to response inhibition

The present study investigated the relationships between attention and other preparatory processes prior to a response inhibition task and the processes involved in the inhibition itself. To achieve this, a mixed fMRI design was employed to identify the functional areas activated during both inhibition decision events and the block of trials following a visual cue introduced 2 to 7 sec prior (cue period). Preparing for successful performance produced increases in activation for both the cue period and the inhibition itself in the frontoparietal cortical network. Furthermore, preparation produced activation decreases in midline areas (insula and medial prefrontal) argued to be responsible for monitoring internal emotional states, and these cue period deactivations alone predicted subsequent success or failure. The results suggest that when cues are provided to signify the imminent requirement for behavioral control, successful performance results from a coordinated pattern of preparatory activation in task-relevant areas and deactivation of task-irrelevant ones

Operation of a 1-Liter-Volume Gaseous Argon Scintillation Counter

We have built a gas-phase argon ionization detector to measure small nuclear recoil energies (< 10 keVee). In this paper, we describe the detector response to X-ray and gamma calibration sources, including analysis of pulse shapes, software triggers, optimization of gas content, and energy- and position-dependence of the signal. We compare our experimental results against simulation using a 5.9-keV X-ray source, as well as higher-energy gamma sources up to 1332 keV. We conclude with a description of the detector, DAQ, and software settings optimized for a measurement of the low-energy nuclear quenching factor in gaseous argon. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory in part under Contract W-7405-Eng-48 and in part under Contract DE-AC52-07NA27344. Funded by Lab-wide LDRD. LLNL-JRNL-415990-DRAFT.Comment: 29 pages, single-column, double-spaced, 21 figure