Distributed source analysis of the pattern onset visual evoked magnetic response

Distributed source analyses of half-field pattern onset visual evoked magnetic responses (VEMR) were carried out by the authors with a view to locating the source of the largest of the components, the CIIm. The analyses were performed using a series of realistic source spaces taking into account the anatomy of the visual cortex. Accuracy was enhanced by constraining the source distributions to lie within the visual cortex only. Further constraints on the source space yielded reliable, but possibly less meaningful, solutions.

Hemispherical differences in the pattern onset visual evoked magnetic response

Recently, hemispherical asymmetries have been demonstrated for primary visual processing suggesting that basic spatiotemporal features of the stimulus may play a role in the lateralisation effects that have been observed in the human brain. However, to our knowledge no studies have reported hemispheric differences using magnetoencephalography (MEG). Hence, the objective of this study was to determine whether MEG could detect hemispherical asymmetry to the onset of a checkerboard pattern.

Neuro-electromagnetic imaging of the human visual cortex

Methods of solving the neuro-electromagnetic inverse problem are examined and developed, with specific reference to the human visual cortex. The anatomy, physiology and function of the human visual system are first reviewed. Mechanisms by which the visual cortex gives rise to external electric and magnetic fields are then discussed, and the forward problem is described mathematically for the case of an isotropic, piecewise homogeneous volume conductor, and then for an anisotropic, concentric, spherical volume conductor. Methods of solving the inverse problem are reviewed, before a new technique is presented. This technique combines prior anatomical information gained from stereotaxic studies, with a probabilistic distributed-source algorithm to yield accurate, realistic inverse solutions. The solution accuracy is enhanced by using both visual evoked electric and magnetic responses simultaneously. The numerical algorithm is then modified to perform equivalent current dipole fitting and minimum norm estimation, and these three techniques are implemented on a transputer array for fast computation. Due to the linear nature of the techniques, they can be executed on up to 22 transputers with close to linear speedup. The latter part of the thesis describes the application of the inverse methods to the analysis of visual evoked electric and magnetic responses. The CIIm peak of the pattern onset evoked magnetic response is deduced to be a product of current flowing away from the surface areas 17, 18 and 19, while the pattern reversal P100m response originates in the same areas, but from oppositely directed current. Cortical retinotopy is examined using sectorial stimuli, the CI and CIm ;peaks of the pattern onset electric and magnetic responses are found to originate from areas V1 and V2 simultaneously, and they therefore do not conform to a simple cruciform model of primary visual cortex.

Are guanxi-type supervisor-subordinate relationships culture-general? An eight-nation test of measurement invariance

Three dimensions of subordinate-supervisor relations (affective attachment, deference to supervisor, and personal-life inclusion) that had been found by Y. Chen, Friedman, Yu, Fang, and Lu to be characteristic of a guanxi relationship between subordinates and their supervisors in China were surveyed in Taiwan, Singapore, and six non-Chinese cultural contexts. The Affective Attachment and Deference subscales demonstrated full metric invariance whereas the Personal-Life Inclusion subscale was found to have partial metric invariance across all eight samples. Structural equation modeling revealed that the affective attachment dimension had a cross-nationally invariant positive relationship to affective organizational commitment and a negative relationship to turnover intention. The deference to the supervisor dimension had invariant positive relationships with both affective and normative organizational commitment. The personal-life inclusion dimension was unrelated to all outcomes. These results indicate the relevance of aspects of guanxi to superior-subordinate relations in non-Chinese cultures. Studies of indigenous concepts can contribute to a broader understanding of organizational behavior. © The Author(s) 2014.