We have developed a pulsed optically pumped magnetometer (OPM) array for detecting magnetic field maps originated from an arbitrary current distribution. The presented magnetic source imaging (MSI) system features 24 OPM channels, has a data rate of 500 S/s, a sensitivity of 0.8 pT / Hz, and a dynamic range of 72 dB. We have employed our pulsed-OPM MSI system for measuring the magnetic field map of a test coil structure. The coils are moved across the array in an indexed fashion to measure the magnetic field over an area larger than the array. The captured magnetic field maps show excellent agreement with the simulation results. Assuming a 2D current distribution, we have solved the inverse problem, using the measured magnetic field maps, and the reconstructed current distribution image is compared to that of the simulation.
Auditory Evoked Magnetic Fields (EFs) to tonal stimuli were recorded at homotopic maxima over the left and right auditory areas in nine subjects. Recordings were made during two conditions, both involving simultaneous presentation of the probe tone stimuli and a set of tape-recorded verbal material. During the control condition subjects were instructed to attend to the tones and ignore the verbal material. In the phonological processing condition they were instructed to ignore the tones and attempt to identify a phonological target item which was embedded in the verbal material. EFs obtained during both conditions were characterized by an early N1m and a later P2m component corresponding to the N1 and P2 components of auditory evoked potentials (EPs). During the phonological condition, the amplitude of the N1m was significantly reduced in both hemispheres symmetrically whereas the amplitude of the P2m was attenuated to a significantly greater degree in the left hemisphere. These data are in agreement with previous EP evidence of greater interference of linguistic processing with processing of irrelevant probe stimuli in the left hemisphere, indicative of greater left hemisphere involvement in language tasks.
A machine vision system needing to remain vigilant within its environment must be able to quickly perceive both clearly identifiable objects as well as those that are deceptive or camouflaged (attempting to blend into the background). Humans accomplish this task early in the visual pathways, using five spatially defined forms of processing. These forms are Luminance-defined, Color-defined, Texture-defined, Motion-defined, and Disparity-defined. This paper discusses a visual sensor approach that combines a biological system's strategy to break down camouflage with simple image processing algorithms that may be implemented for real time video. Thermal imaging is added to increase sensing capability. Preliminary filters using MATLAB and operating on digital still images show somewhat encouraging results. Current efforts include implementing the sensor for real-time video processing.
A double Gaussian Model was used t o estimate dipole source contributions t o magnetoencephalograms. The method w a s tested using four 2mn length dipoles fixed in conductive material enclosed within the human s k u l l . simulated by Gaussian activation of one dipole with a mean latency of 100ms, and a second dipole a t 200ms. temporal bone and the occipital bone. Source contributions t o each resultant waveform were estimated as the amplitude parameters of a best f i t double Gaussian function. Canparing dipole inverse solutions frcm waveform paks with those frun estimated contributions revealed only a mall difference in localization accuracy. Source strength is s l i g h t l y better estimated using the component d e l method. The peak picking method overestimated strength when dipoles were aligned and underestimated when they were opposed. hroked responses were Simulations were performed over the l e f t 1NI"CTION cXlr laboratory measures auditory and visual A evoked responses t o study the behavior of cognitive components under various workload conditions. typical evoked f i e l d w i l l have several canponents occurring a f t e r stimulus onset. of various canpnents typically localize the neural source contributing t o the component a t a unique location (1,2,3). The localization of a 100 ms auditory component has a different location f r m that of a 160 ms (31, and thus can not be modeled simply as a generator reversing polarity. In t h i s paper, a Gaussian model is used t o simulate many closely packed neurons being activated with distributed latencies. 'Ihe model might be used t o estimate neural sources' contributions t o the canponents of the observed evoked response. Inverse solutions Four current dipoles were constructed frun 32 Pm; single conductor shielded wire. insulation and the shield were cut back t o give a 2nnn length between the exposed center conductor and The outer the shield. the ends of the dipole. conductor simulates intracellular currents of many closely packed c o r t i c a l neurons. The dipoles were positioned i n a s o f t sponge, wrapped in chamois cloth, and soaked i n a conductive electrode paste solution. material allowed the return currents t o better approximate extracellular volume currents. !&a dipoles were placed i n the l e f t tempxal region t o simulate auditory evoked responses (AEX) and the other two were placed i n the occipital region t o simulate visual evoked responses (VER).After enclosing the simulated brain within the s k u l l , x-ray images were used t o precisely locate the true dipole positions. An x-ray shot was taken parallel t o each axis of a designated "head reference" coordinate system. The x-axis passes through s k u l l l a d m a r k s j u s t above the external ear or i f ices, the y-axis passes between the nasd bones, and the z-axis is the cross product of x and y. Because the x-ray procedure w i l l produce an expanded image as a function of cbject position between the x-ray source and t h e film, a ccmputer program was written t o convert each...
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