Hemispheric asymmetries in meaning selection: Evidence from the disambiguation of homophonic vs. heterophonic homographs

Research investigating hemispheric asymmetries in meaning selection using homophonic homographs (e.g., bank), suggests that the left hemisphere (LH) quickly selects contextually relevant meanings, whereas the right hemisphere (RH) maintains a broader spectrum of meanings including those that are contextually irrelevant (e.g., Faust & Chiarello, 1998). The present study investigated cerebral asymmetries in maintaining the multiple meanings of two types of Hebrew homographs: homophonic homographs and heterophonic homographs (e.g., tear). Participants read homographs preceded by a biasing, or a non-biasing sentential context, and performed a lexical decision task on targets presented laterally, 1000 ms after the onset of the sentence-final ambiguous prime. Targets were related to either the dominant or the subordinate meaning of the preceding homograph, or unrelated to it. When targets were presented in the LVF/RH, dominant and subordinate meanings, of both types of homographs, were retained only when they were supported by context. In a non-biasing context, only dominant meanings of homophonic homographs were retained. Alternatively, when targets were presented in the RVF/LH, priming effects for homophonic homographs were only evident when meanings were supported by both context and frequency (i.e., when context favored the dominant meaning). In contrast, heterophonic homographs resulted in activation of dominant meanings, in all contexts, and activation of subordinate meanings, only in subordinate-biasing contexts. The results challenge the view that a broader spectrum of meanings is maintained in the right than in the left hemisphere and suggest that hemispheric differences in the time course of meaning selection (or decay) may be modulated by phonology.     

Prose Reading in Neglect

Prose reading has been shown to be a very sensitive measure of Unilateral Spatial Neglect. However, little is known about the relationship between prose reading and other measures of neglect and its severity, or between prose reading and single word reading. Thirty participants with a first stroke in the right hemisphere and clear symptoms of spatial neglect in everyday life were assessed with tests of prose reading (text in one column book-like, and in two columns magazine-like), single words reading, and a battery of 13 tests investigating neglect. Seventy percent of these participants omitted words at the beginning of the text (left end), showing Prose Reading Neglect (PRN). The participants showing PRN differed from those not showing PRN only for the overall severity of neglect, and had a lesion centred on the insula, putamen and superior temporal gyrus. Double dissociations emerged between PRN and single word reading neglect, suggesting different cognitive requirements between the two tests: parallel processing in single word reading vs. serial analysis in text reading. Notably, the pattern of neglected text varied dramatically across participants presenting with PRN, including dissociations between reading performance of one and two columns text. Prose reading proved a complex and unique task which should be directly investigated to predict the effects of unilateral neglect. The outcome of this study should also inform clinical assessment and advises given to patients and care-givers.     

The neuropsychological profile of vascular cognitive impairment not demented: A meta‐analysis

The most common cause of vascular cognitive impairment not demented (VCIND) is cerebral small vessel disease leading to diffuse subcortical white matter lesions. While many studies indicate that the core cognitive features of VCIND are executive dysfunction and impaired processing speed, this finding is not always consistent, and may be partially dependent on the comparison group applied. Hence, we undertook two systematic meta‐analytic reviews on neuropsychological test performance across eight cognitive domains: between VCIND and healthy controls (data from 27 studies), and between VCIND and non‐vascular mild cognitive impairment (nv‐MCI; data from 20 studies). Our quantitative synthesis of the research literature demonstrates that individuals with VCIND show weaknesses across all cognitive domains relative to healthy controls, with the greatest impairment in the domain of processing speed (Md = ?1.36), and the least affected being working memory (Md = ?.48) and visuospatial construction (Md = ?.63). When compared directly with nv‐MCI, individuals with VCIND had significantly greater deficits in processing speed (Md = ?.55) and executive functioning (Md = ?.40), while those with nv‐MCI exhibited a greater relative deficit in delayed memory (Md = .41). Our analyses indicate that disruption to subcortical white matter tracts impairs more cognitive processes than is typically thought to be directly related to the fronto‐subcortical network. The data also suggest that differing brain aetiologies can be responsible for similar cognitive profiles. Although the findings do not evince diagnostic value, they allude to the interconnectivity of disparate cognitive processes and call for further research on the behavioural outcome of network disruption.     

Event-related cerebral hemodynamics reveal target-specific resource allocation for both “go” and “no-go” response-based vigilance tasks

Transcranial Doppler sonography was used to measure cerebral blood flow velocity (CBFV) in the right and left cerebral hemispheres during the performance of a 50-min visual vigilance session. Observers monitored a simulated flight of unmanned aerial vehicles for cases in which one of the vehicles was flying in an inappropriate direction relative to its cohorts. Two types of vigilance tasks were employed: a traditional task in which observers made button press (“go”) responses to critical signals, and a modification of the traditional task called the Sustained Attention to Response Task (SART) in which “go” responses acknowledged nonsignal events and response withholding (“no-go”) signified signal detection. Signal detections and global CBFV scores declined over time. In addition, fine-grained event-related analyses revealed that the detection of signals was accompanied by an elevation of CBFV that was not present with missed signals. As was the case with the global scores, the magnitude of the transient CBFV increments associated with signal detection also declined over time, and these findings were independent of task type. The results support the view of CBFV as an index of the cognitive evaluation of stimulus significance, and a resource model of vigilance in which the need for continuous attention produces a depletion of information-processing assets that are not replenished as the task progresses. Further, temporal declines in the magnitude of event-related CBFV in response to critical signals only is evidence that the decrement function in vigilance is due to attentional processing and not specific task elements such as the required response format.     

Hemispheric asymmetries in processing L1 and L2 idioms: effects of salience and context

This study investigates the contribution of the left and right hemispheres to the comprehension of bilingual figurative language and the joint effects of salience and context on the differential cerebral involvement in idiom processing. The divided visual field and the lexical decision priming paradigms were employed to examine the activation of salient and nonsalient ambiguous idiom interpretations (i.e., literal vs. non-literal) in the two hemispheres. Literally plausible ambiguous idioms, L1 (Polish) and L2 (English), were embedded in unconstraining ambiguous (e.g., I knew he kept an ace up his sleeve) or constraining unambiguous context clearly favoring their conventional idiomatic interpretation (e.g., The debating president kept an ace up his sleeve). Idioms were presented centrally, followed by laterally presented targets related to the figurative (e.g., GAIN) or literal (e.g., SHIRT) meaning of the idiom and displayed at Interstimulus Intervals (ISIs) of 0 ms (Experiment 1), 300 ms (Experiment 2), and 800 ms (Experiment 3). Results indicate that context and salience effects are significantly modulated by the language (native vs. nonnative) of the stimulus materials being presented to each hemisphere. Literal facilitation was found for L2 idioms in all three ISI conditions, which supports the notion of the special status that literal meanings of L2 idioms enjoy in the course of their processing by nonnative language users. No significant differences were found between the right and left hemispheres in regards to their sensitivity to contextual constraints. Results are discussed in terms of the Graded Salience Hypothesis and the Fine/Coarse Coding Theory.     

Approximate entropy used to assess sitting postural sway of infants with developmental delay

Infant sitting postural sway provides a window into motor development at an early age. The approximate entropy, a measure of randomness, in the postural sway was used to assess developmental delay, as occurs in cerebral palsy. Parameters used for the calculation of approximate entropy were investigated, and approximate entropy of postural sway in early sitting was found to be lower for infants with developmental delay in the anterior-posterior axis, but not in the medial-lateral axis. Spectral analysis showed higher frequency features in the postural sway of early sitting of infants with typical development, suggesting a faster control mechanism is active in infants with typical development as compared to infants with delayed development, perhaps activated by near-fall events.     

An inter-hemispheric imbalance in the psychopath’s brain

Psychopathy is associated with two extremities. On the one hand, psychopathic individuals lack any concern for social norms and they are severely poor in maintaining healthy social relationships. In addition, the ability of individuals with psychopathy to feel certain emotions such as empathy, guilt or fear is seriously compromised. In contrast to these deficits, some behaviors and tendencies are exaggerated in psychopathy. For instance, psychopathic individuals display higher than normal impulsivity, stimulation-seeking, aggression and risk-taking. There are indications in the literature that pro-social behavior, as well as the feelings of empathy, guilt and fear are mediated predominantly by regions within the right hemisphere (RH), whereas impulsivity, stimulation-seeking, aggression and risk-taking are linked primarily with left hemisphere (LH) activity. From a neurobiological perspective, it seems that psychopathy may be associated with an altered and imbalanced inter-hemispheric dynamics; a relatively hyperfunctioning LH and/or a hypofunctioning RH. Furthermore, within the psychopathic population, the RH hypofunctioning is more characteristic of primary psychopathy with its affective and interpersonal deficits, while the LH hyperfunctioning is most typical of the secondary psychopathy which is marked by impulsivity and antisocial style.     

Cerebral blood flow differences between long-term meditators and non-meditators

We have studied a number of long-term meditators in previous studies. The purpose of this study was to determine if there are differences in baseline brain function of experienced meditators compared to non-meditators. All subjects were recruited as part of an ongoing study of different meditation practices. We evaluated 12 advanced meditators and 14 non-meditators with cerebral blood flow (CBF) SPECT imaging at rest. Images were analyzed with both region of interest and statistical parametric mapping. The CBF of long-term meditators was significantly higher (p < .05) compared to non-meditators in the prefrontal cortex, parietal cortex, thalamus, putamen, caudate, and midbrain. There was also a significant difference in the thalamic laterality with long-term meditators having greater asymmetry. The observed changes associated with long-term meditation appear in structures that underlie the attention network and also those that relate to emotion and autonomic function.     

Cost minimization during simulated evolution of paired neural networks leads to asymmetries and specialization

Motivated by specialization (lateralization) that occurs in corresponding left and right regions of the cerebral cortex, several past computational models have studied conditions under which functional specialization can arise during learning due to underlying asymmetries in paired neural networks. However, these past studies have not addressed the basic issue of how such underlying asymmetries arise in the first place. As an initial step in addressing this issue, we investigated the hypothesis that underlying asymmetries will appear in paired neural networks during a simulated evolutionary process when fitness is based not only on maximizing performance, but also on minimizing various ‘costs’ such as energy consumption, neural connection weights, and response times. Simulated evolution under these conditions consistently produced networks with left–right asymmetries in region size, excitability and plasticity. These underlying asymmetries were often synergistic, leading to subsequent functional lateralization during network training. While our computational models are too simple for these results to be directly extrapolated to real nervous systems, they provide support for the hypothesis that brain asymmetries and lateralization in biological nervous systems may be a consequence of cost minimization present during evolution, and are the first computational demonstration of emergent population lateralization.     

Variability in infant motor behavior: A hallmark of the healthy nervous system

Application of the concepts of the Neuronal Group Selection Theory (NGST) may shed a new light on motor development. According to NGST, normal motor development is characterized by two phases of variability. Variation is not random, but determined by criteria set by genetic information. Development starts with the phase of primary variability, during which variation in motor behavior is not geared to external conditions. At function-specific ages secondary variability starts, during which motor performance can be adapted to specific situations. In both forms of variability selection on the basis of afferent information plays a significant role. From the NGST point of view, children with pre- or perinatally acquired brain damage suffer from stereotyped motor behavior produced by a limited repertoire of primary (sub)cortical neuronal networks. These children also have problems in selecting the most efficient neuronal activity due to deficits in the processing of sensory information.