Individual differences in interhemispheric transfer time (IHTT) as measured by event related potentials.

The present study examined possible gender differences in interhemisperic transfer time (IHTT), as measured by event related potentials (ERPs). Using visual half-field presentations of letter pairs in a match/no-match paradigm, N1 latency was measured for each visual half-field and hemisphere. IHTTs were determined by subtracting the "direct" (i.e., contralateral or non-callosal) pathway N1 latency from the "indirect" (i.e., callosal) pathway N1 latency. Based on studies showing gender differences in corpus callosum size and function, we hypothesized that females would show more symmetric and faster overall transfer times than males. Results showed faster right-to-left IHTT across all participants, but females had more symmetric IHTT and shorter overall IHTT--primarily due to significantly shorter left-to-right times compared to males. Little support was found for the influence of hemisphere (i.e., "direct" pathway) response, or potential lateralization of function, on the length of IHTT in either direction.

Glass-fiber self-mixing intra-arterial laser Doppler velocimetry: signal stability and feedback analysis.

We have developed a blood velocimeter based on the principle of self-mixing in a semiconductor laser diode through an optical fiber. The intensity of the light is modulated by feedback from moving scattering particles that contain the Doppler-shift frequency. Upon feedback the characteristics of the laser diode change. The threshold current decreases, and an instable region may become present above the new threshold. The amplitude of the Doppler signal turns out to be related to the difference in intensity between situations with and without feedback. This amplitude is highest just above feedback. The suppression of reflection from the glass-fiber facets is of paramount importance in the obtaining of a higher signal-to-noise ratio. Using an optical stabilization of the feedback, we optimized the performance of the laser-fiber system and the Doppler modulation depth and clarified its behavior with a suitable physical model. We also investigated the effect of the finite coherence length of the laser. We tested the efficiency of the self-mixing velocimeter in vivo with the optical glass fiber inserted in the artery with endoscopic catheters, both in upstream and in downstream blood flow conditions. For the latter we used a special side-reflecting device solution for the fiber facet to allow downstream measurements.