Actual Human Subjects Research Articles

The perception of 3-dimensional affine structure from minimal apparent motion sequences

The research described in the present article was designed to identify the minimal conditions for the visual perception of 3-dimensional structure from motion by comparing the theoretical limitations of ideal observers with the perceptual performance of actual human subjects on a variety of psychophysical tasks. The research began with a mathematical analysis, which showed that 2-frame apparent motion sequences are theoretically sufficient to distinguish between rigid and nonrigid motion and to identify structural properties of an object that remain invariant under affine transformations, but that 3 or more distinct frames are theoretically necessary to adequately specify properties of euclidean structure such as the relative 3-dimensional lengths or angles between nonparallel line segments. A series of four experiments was then performed to verify the psychological validity of this analysis. The results demonstrated that the determination of structure from motion in actual human observers may be restricted to the use of first order temporal relations, which are available within 2-frame apparent motion sequences. That is to say, the accuracy of observers' judgments did not improve in any of these experiments as the number of distinct frames in an apparent motion sequence was increased from 2 to 8, and performance on tasks involving affine structure was of an order of magnitude greater than performance on similar tasks involving euclidean structure.

Wounding Characteristics of .38 Caliber Revolver Cartridges

Abstract Injury patterns in both artificial media and animal tissues were analyzed, and the results were then correlated with autopsy findings in subjects who died from gunshot wounds to determine the wounding characteristics of bullets from two standard .38 caliber revolver cartridges. The 150-grain round nose bullet, in comparison with a 110-grain semi-jacketed controlled-expansion round (hollowpoint bullet), was found to have greater penetration and a greater tendency to deviate from its flight path. The controlled expansion round was found to produce a wider bullet track with greater deformation and bullet fragmentation than the round nose ammunition in artificial media and animal tissue. Autopsy study of shooting victims indicated more through-and-through wounds with round nose bullets than with hollowpoint rounds, and overall survival in shooting victims was greater with roundnose bullets, but was modified by site of injury and availability of prompt medical treatment. Neither round appeared to differ in inherent “knockdown” power. Though distinct differences in wounding patterns can be demonstrated in artificial and animal media, the differences between round nose and controlled expansion round bullets are not marked in actual human subjects with gunshot wounds.

Plutonium lung monitor using a thin NaI(T1) crystal of large area.

For the assessment of plutonium(Pu) amount in human lungs, a very efficient detector for low energy photons is necessary because of the low energy of emitted X-rays (17 keV on the average) and the small value of maximum permissible lung burden of 239Pu, 16 nCi. As such a detector, we have constructed a Pu lung monitor employing a combination of a large thin NaI(Tl) crystal and a photomultiplier of large photocathode. Size of the crystal is 8 in. diameter by 5 mm thickness in order to cover a large portion of the lungs, and the photomultiplier used (VMP/11/170) possesses a photocathode of 7 in. dia. that has been chosen for the best uniformity in photocathode sensitivity among five identical tubes. The whole detector was set in a shielding chamber of 20 cm thick iron plus 3 mm thick lead which is being used for the whole body monitor. Extraction of the optimum performance from the detector was attempted first by improving the energy resolution with insertion of light guide (made of Lucite) between the optical window of the crystal and the photocathode. An optimum thickness of the light guide was found to be 2 cm for the present detector. Then, background counts of the detector in the shielding chamber were analyzed and it was found that about 40% of the total background between 16 and 100 keV originated from y-activities in the optical window and the glass envelope of the photomultiplier. Noise of the photomultiplier was dominant below 13 keV when no light guide was used, but interfered with the detection of 17 keV X-rays when light guide was inserted. Consequently, it was decided that no light guide be employed in the final form of the detector with a slight sacrifice in energy resolution. Counting efficiency for 239Pu in the lungs was determined using a phantom that was made of Lucite plates. The detector was placed in a similar geometry to that in measurement of actual human subjects. The counting efficiency was found to be 1.34 × 10−2 counts/sec/nCi of 239Pu. The minimum detectable amount defined as 3 times the standard deviation of background counts is 6.2 nCi of 239Pu for a counting time of 100 min. The background counts include those from degraded gamma-rays of 137Cs and K in a normal subject and correction was made on the counting efficiency due to absorption of X-ray photons by rib bones. The values obtained above are rather tentative ones in view of uncertainties in the method of calibration, but it is well below the maximum permissibie lung burden of 239Pu. Finally, some improvements in the future are discussed.