Resolving Semantic Ambiguities in Sentences: Cognitive Processes and Brain Mechanisms

fMRI studies of how the brain processes sentences containing semantically ambiguous words have consistently implicated (i) the left inferior frontal gyrus (LIFG) and (ii) posterior regions of the left temporal lobe in processing high-ambiguity sentences. This article reviews recent findings on this topic and relates them to (i) psycholinguistic theories about the underlying cognitive processes and (ii) general neuro-cognitive accounts of the relevant brain regions. We suggest that the LIFG plays a general role in the cognitive control process that are necessary to select contextually relevant meanings and to reinterpret sentences that were initially misunderstood, but it is currently unclear whether these control processes should best be characterised in terms of specific processes such as conflict resolution and controlled retrieval that are required for high-ambiguity sentences, or whether its function is better characterised in terms of a more general set of ‘unification’ processes. In contrast to the relatively rapid progress that has been made in understanding the function of the LIFG, we suggest that the contribution of the posterior temporal lobe is less well understood and future work is needed to clarify its role in sentence comprehension

Cognitive and Neural Mechanisms Underlying Semantic Ambiguity Resolution

The ultimate goal of language comprehension is to obtain meaning. However, this is difficult because many words are semantically ambiguous, mapping onto multiple meanings. Semantic ambiguity resolution has proven a useful tool to investigate language processing in general. However, the majority of research has focused on the initial encounter of an ambiguous word. Less work has investigated the processes occurring after an ambiguous word is encountered, when the initially understood meaning needs to be reinterpreted in light of subsequent inconsistent information. The first part of this thesis investigated the cognitive processes underlying semantic reinterpretation, examining how successful listeners are at this process as well as assessing the time course of suppressing and integrating the contextually inappropriate and appropriate meanings respectively. A semantic relatedness task was employed in which participants listened to ambiguous and unambiguous sentences and decided whether a following visual probe word was related or unrelated to the sentence. The results revealed that listeners are highly effective at reinterpretation but that suppression of the inappropriate meaning is delayed relative to integration of the appropriate meaning. The rest of the thesis examined the neural responses to these sentences by using functional magnetic resonance imaging (fMRI) and Transcranial magnetic stimulation (TMS). The fMRI study demonstrated ambiguity-elevated responses in left inferior frontal gyrus (LIFG) and posterior temporal cortex. These responses were modulated by the frequency of the ambiguous word’s meanings, such that activation was greater for sentences with a higher likelihood of reinterpretation. The final study developed a TMS paradigm to examine whether LIFG is necessary for this process, demonstrating evidence that this region may be important for sentence processing more generally. Together, this thesis has advanced understanding into the cognitive and neural processes underlying semantic reinterpretation that have various implications for models of ambiguity resolution and language comprehension in general

Transcranial Magnetic Stimulation for Investigating Causal Brain-behavioral Relationships and their Time Course

Transcranial magnetic stimulation (TMS) is a safe, non-invasive brain stimulation technique that uses a strong electromagnet in order to temporarily disrupt information processing in a brain region, generating a short-lived “virtual lesion.” Stimulation that interferes with task performance indicates that the affected brain region is necessary to perform the task normally. In other words, unlike neuroimaging methods such as functional magnetic resonance imaging (fMRI) that indicate correlations between brain and behavior, TMS can be used to demonstrate causal brain-behavior relations. Furthermore, by varying the duration and onset of the virtual lesion, TMS can also reveal the time course of normal processing. As a result, TMS has become an important tool in cognitive neuroscience. Advantages of the technique over lesion-deficit studies include better spatial-temporal precision of the disruption effect, the ability to use participants as their own control subjects, and the accessibility of participants. Limitations include concurrent auditory and somatosensory stimulation that may influence task performance, limited access to structures more than a few centimeters from the surface of the scalp, and the relatively large space of free parameters that need to be optimized in order for the experiment to work. Experimental designs that give careful consideration to appropriate control conditions help to address these concerns. This article illustrates these issues with TMS results that investigate the spatial and temporal contributions of the left supramarginal gyrus (SMG) to reading

VisIVOWeb: A WWW Environment for Large-Scale Astrophysical Visualization

This article presents a newly developed Web portal called VisIVOWeb that aims to provide the astrophysical community with powerful visualization tools for large-scale data sets in the context of Web 2.0. VisIVOWeb can effectively handle modern numerical simulations and real-world observations. Our open-source software is based on established visualization toolkits offering high-quality rendering algorithms. The underlying data management is discussed with the supported visualization interfaces and movie-making functionality. We introduce VisIVOWeb Network, a robust network of customized Web portals for visual discovery, and VisIVOWeb Connect, a lightweight and efficient solution for seamlessly connecting to existing astrophysical archives. A significant effort has been devoted for ensuring interoperability with existing tools by adhering to IVOA standards. We conclude with a summary of our work and a discussion on future developments

Modular Middleware for Gestural Data and Devices Management

In the last few years, the use of gestural data has become a key enabler for human-computer interaction (HCI) applications. The growing diffusion of low-cost acquisition devices has thus led to the development of a class of middleware aimed at ensuring a fast and easy integration of such devices within the actual HCI applications. The purpose of this paper is to present a modular middleware for gestural data and devices management. First, we describe a brief review of the state of the art of similar middleware. Then, we discuss the proposed architecture and the motivation behind its design choices. Finally, we present a use case aimed at demonstrating the potential uses as well as the limitations of our middleware

A Novel Technique for Fingerprint Classification based on Fuzzy C-Means and Naive Bayes Classifier

Fingerprint classification is a key issue in automatic fingerprint identification systems. One of the main goals is to reduce the item search time within the fingerprint database without affecting the accuracy rate. In this paper, a novel technique, based on topological information, for efficient fingerprint classification is described. The proposed system is composed of two independent modules: the former module, based on Fuzzy C-Means, extracts the best set of training images; the latter module, based on Fuzzy C-Means and Naive Bayes classifier, assigns a class to each processed fingerprint using only directional image information. The proposed approach does not require any image enhancement phase. Experimental trials, conducted on a subset of the free downloadable PolyU database, show a classification rate of 91% over a 100 images test database using only 12 training examples

Transcranial Magnetic Stimulation for Investigating Causal Brain-behavioral Relationships and their Time Course.

Transcranial magnetic stimulation (TMS) is a safe, non-invasive brain stimulation technique that uses a strong electromagnet in order to temporarily disrupt information processing in a brain region, generating a short-lived "virtual lesion." Stimulation that interferes with task performance indicates that the affected brain region is necessary to perform the task normally. In other words, unlike neuroimaging methods such as functional magnetic resonance imaging (fMRI) that indicate correlations between brain and behavior, TMS can be used to demonstrate causal brain-behavior relations. Furthermore, by varying the duration and onset of the virtual lesion, TMS can also reveal the time course of normal processing. As a result, TMS has become an important tool in cognitive neuroscience. Advantages of the technique over lesion-deficit studies include better spatial-temporal precision of the disruption effect, the ability to use participants as their own control subjects, and the accessibility of participants. Limitations include concurrent auditory and somatosensory stimulation that may influence task performance, limited access to structures more than a few centimeters from the surface of the scalp, and the relatively large space of free parameters that need to be optimized in order for the experiment to work. Experimental designs that give careful consideration to appropriate control conditions help to address these concerns. This article illustrates these issues with TMS results that investigate the spatial and temporal contributions of the left supramarginal gyrus (SMG) to reading

pH dependence of cyanide and imidazole binding to the heme domains of \u3cem\u3eSinorhizobium meliloti\u3c/em\u3e and \u3cem\u3eBradyrhizobium japonicum\u3c/em\u3e FixL

Equilibrium and kinetic properties of cyanide and imidazole binding to the heme domains of Sinorhizobium meliloti and Bradyrhizobium japonicum FixL (SmFixLH and BjFixLH) have been investigated between pH 5 and 11. KD determinations were made at integral pH values, with the strongest binding at pH 9 for both ligands. KD for the cyanide complexes of BjFixLH and SmFixLH is 0.15 ± 0.09 and 0.50 ± 0.20 μM, respectively, and 0.70 ± 0.01 mM for imido-BjFixLH. The association rate constants are pH dependent with maximum values of 443 ± 8 and 252 ± 61 M−1 s−1 for cyano complexes of BjFixLH and SmFixLH and (5.0 ± 0.3) × 104 and (7.0±1.4) × 104M−1 s−1 for the imidazole complexes. The dissociation rate constants are essentially independent of pH above pH 5; (1.2 ± 0.3) × 10−4 and (1.7 ± 0.3) × 10−4 s−1 for the cyano complexes of BjFixLH and SmFixLH, and (73±19) and (77±14) s−1 for the imidazole complexes. Two ionizable groups in FixLH affect the rate of ligand binding. The more acidic group, identified as the heme 6 propionic acid, has a pKa of 7.6 ± 0.2 in BjFixLH and 6.8 ± 0.2 in SmFixLH. The second ionization is due to formation of hydroxy-FixLH with pKa values of 9.64± 0.05 for BjFixLH and 9.61 ± 0.05 for SmFixLH. Imidazole binding is limited by the rate of heme pocket opening with maximum observed values of 680 and 1270 s−1 for BjFixLH and SmFixLH, respectively

Localising semantic and syntactic processing in spoken and written language comprehension: an Activation Likelihood Estimation meta-analysis

We conducted an Activation Likelihood Estimation (ALE) meta-analysis to identify brain regions that are recruited by linguistic stimuli requiring relatively demanding semantic or syntactic processing. We included 54 functional MRI studies that explicitly varied the semantic or syntactic processing load, while holding constant demands on earlier stages of processing. We included studies that introduced a syntactic/semantic ambiguity or anomaly, used a priming manipulation that specifically reduced the load on semantic/syntactic processing, or varied the level of syntactic complexity. The results confirmed the critical role of the posterior left Inferior Frontal Gyrus (LIFG) in semantic and syntactic processing. These results challenge models of sentence comprehension highlighting the role of anterior LIFG for semantic processing. In addition, the results emphasise the posterior (but not anterior) temporal lobe for both semantic and syntactic processing

A double-negative (IgD CD27 ) B cell population is increased in the peripheral blood of elderly people

The T cell branch of the immune system has been extensively studied in the elderly and it is known that the elderly have impaired immune function, mainly due to the chronic antigenic load that ultimately causes shrinkage of the T cell repertoire and filling of the immunologic space with memory T cells. In the present paper,we describe the IgD CD27 double-negative B cell population which (aswe have recently described) is higher in the elderly. Most of these cells were IgG+. Evaluation of the telomere length and expression of the ABCB1 transporter and anti-apoptotic molecule, Bcl2, shows that they have the markers of memory B cells. We also show that these cells do not act as antigen presenting cells, as indicated by the low levels of CD80 and DR, nor do they express significant levels of the CD40 molecule necessary to interact with T lymphocytes through the ligand, CD154. Hence, we hypothesize that these expanded cells are late memory or exhausted cells that have down-modulated the expression of CD27 and filled the immunologic space in the elderly. These cells might be the age-related manifestation of time-enduring stimulation or dysregulation of the immune system