Function Of Target Size Research Articles

Determinants of Maximum Magnetic Anomaly Detection Distance.

The maximum detection distance is usually the primary concern of magnetic anomaly detection (MAD). Intuition tells us that larger object size, stronger magnetization and finer measurement resolution guarantee a further detectable distance. However, the quantitative relationship between detection distance and the above determinants is seldom studied. In this work, unmanned aerial vehicle-based MAD field experiments are conducted on cargo vessels and NdFeB magnets as typical magnetic objects to give a set of visualized magnetic field flux density images. Isometric finite element models are established, calibrated and analyzed according to the experiment configuration. A maximum detectable distance map as a function of target size and measurement resolution is then obtained from parametric sweeping on an experimentally calibrated finite element analysis model. We find that the logarithm of detectable distance is positively proportional to the logarithm of object size while negatively proportional to the logarithm of resolution, within the ranges of 1 m~500 m and 1 pT~1 μT, respectively. A three-parameter empirical formula (namely distance-size-resolution logarithmic relationship) is firstly developed to determine the most economic sensor configuration for a given detection task, to estimate the maximum detection distance for a given magnetic sensor and object, or to evaluate minimum detectable object size at a given magnetic anomaly detection scenario.

GPU-accelerated calculation of proton microdosimetric spectra as a function of target size, proton energy, and bounding volume size

Objective. Shortcomings of dose-averaged linear energy transfer (LETD), the quantity which is most commonly used to quantify proton relative biological effectiveness, have long been recognized. Microdosimetric spectra may overcome the limitations of LETD but are extremely computationally demanding to calculate. A systematic library of lineal energy spectra for monoenergetic protons could enable rapid determination of microdosimetric spectra in a clinical environment. The objective of this work was to calculate and validate such a library of lineal energy spectra. Approach. SuperTrack, a GPU-accelerated CUDA/C++ based application, was developed to superimpose tracks calculated using Geant4 onto targets of interest and to compute microdosimetric spectra. Lineal energy spectra of protons with energies from 0.1 to 100 MeV were determined in spherical targets of diameters from 1 nm to 10 μm and in bounding voxels with side lengths of 5 μm and 3 mm. Main results. Compared to an analogous Geant4-based application, SuperTrack is up to 3500 times more computationally efficient if each track is resampled 1000 times. Dose spectra of lineal energy and dose-mean lineal energy calculated with SuperTrack were consistent with values published in the literature and with comparison to a Geant4 simulation. Using SuperTrack, we developed the largest known library of proton microdosimetric spectra as a function of primary proton energy, target size, and bounding volume size. Significance. SuperTrack greatly increases the computational efficiency of the calculation of microdosimetric spectra. The elevated lineal energy observed in a 3 mm side length bounding volume suggests that lineal energy spectra determined experimentally or computed in small bounding volumes may not be representative of the lineal energy spectra in voxels of a dose calculation grid. The library of lineal energy spectra calculated in this work could be integrated with a treatment planning system for rapid determination of lineal energy spectra in patient geometries.

On the Feasibility of Stereotactic Radiosurgery With 5.0 and 10.0 mm MLC Leaves as a Function of Target Size and Shape.

Introduction: This study explores the feasibility of SRS/SRT treatment with MLC leaves wider than 2.5 mm at isocenter by inter-comparing treatment plans produced with 2.5, 5.0, and 10.0 mm leaves for various target sizes and shapes.Materials and methods: Forty previously treated patients were re-planned using 2.5, 5.0, and 10.0 mm wide MLC leaves. For each patient, all three plans were evaluated and contrasted between them in terms of five metrics: target dose homogeneity, conformity index, organs at risk dose, dose fall off outside the target, and dose to normal tissues. A regularity index RI was introduced that quantified the degree of target shape irregularity. The effect of target size and shape irregularity on feasibility of 5.0 and 10.0 mm leaves was analyzed.Results: Consistent plan degradation was observed for 10.0 mm (sometimes for 5.0 mm) compared to 2.5 mm MLC in terms of the above five plan metrics, but this degradation was small to clinically insignificant. As an exception, when target (PTV) size was smaller than about 1 cm diameter, clinically significant differences were found between 2.5, 5.0, and 10.0 mm MLC.Conclusion: 5.0 and 10.0 mm MLC can be used in SRS/SRT for targets (PTV) diameter larger than 1 cm. For smaller targets, 2.5 mm MLC is clinically superior, 5.0 is acceptable and 10.0 mm MLC is discouraged in terms of PTV dose conformity.

Pulse visibility factor and its impact on infrared search and track systems

The performance of an infrared search and track (IRST) sensor depends on a large number of variables that are important for determining systems performance. One of the variables is the pulse visibility factor (PVF). The PVF is linearly related to IRST performance metrics, such as signal-to-noise ratio (SNR) or signal-to-clutter ratio (SCR). Maximizing the performance of an IRST through a smart design of the sensor requires understanding and optimizing the PVF. The resulting peak, average, or worst case PVF may cause large variations in the sensor SNR or SCR as the target position varies in the sensor field of view (FOV) and corresponding position on the focal plane. As a result, the characteristics of the PVF are not straightforward. The definitions and characteristics for the PVF to include ensquared energy (best case PVF), worst case PVF, and average PVF are provided as a function of F * Lambda / d cc ( d cc is the center-to-center distance between pixels, i.e., pixel pitch). F * Lambda / d cc is a generalized figure of merit that permits broad analysis of the PVF. We show the PVF trends when the target has a finite size but is still unresolved on the focal plane [smaller than an instantaneous field of view (IFOV)]. The target size was constrained to be no less than 2% of the IFOV but also no greater than 100 % to study the effects on the PVF as a function of target size. Finally, we describe the characteristics of the PVF when optical degradations, such as aberrations, are inherent in the sensor transfer function. The results have illustrated that small F * Lambda / d cc with large fill factor maximized the PVF at the expense of greater variability. Larger F * Lambda / d cc can reduce the PVF variations but results in a decreased PVF. Finite target sizes and additional optical degradation decreased the PVF compared to diffraction-limited systems.

Ricco's law and absolute threshold for foveal detection of black holes.

Visual detection of small black objects surrounded by a light background depends on background luminance, pupil size, optical blur, and object size. Holding pupil and optics fixed, we measured the minimum background luminance needed for foveal detection of small black targets as a function of target size. For all three observers, absolute threshold varied inversely with target area when disk diameter subtended less than 10' of visual angle. For target diameter ≥10', threshold remained constant at about 0.3Td, which was also the absolute threshold for detecting light spots 10' or larger in diameter on a black background. These results are consistent with Ricco's law of spatial summation: a "black hole" is just detectable when the background luminance is sufficiently high for its absence inside the Ricco area to reduce 555nm photon flux by 7500photons/s, which is the same change needed to detect light spots on a black surround. These results can be accounted for by a differential pair of Ricco detectors, each about the size of the receptive field center of magocellular retinal ganglion cells when projected into object space through the eye's weakly aberrated optical system. Statistical analysis of the model suggests the quantum fluctuations due to internal, biological noise (i.e., "scotons") are a greater handicap than the photon fluctuations inherent in the light stimulus at absolute foveal threshold.

SU‐E‐T‐80: A Study of the Effect of Dose Grid Resolution On Stereotactic Plan Evaluation as a Function of Target Size

Purpose:To investigate and quantify the impact of dose‐calculation grid‐size on dose volume histogram (DVH) for small targets, such as those in stereotactic radiosurgery (SRS).Methods:A cohort of ten patients with multiple metastasis was used in this planning study. All patients were treated with SRS and had target volumes ranging from 0.1 to 4.3cc. The Varian eclipse planning system was used for planning using a mono‐isocentric VMAT technique with four arcs. Each plan was calculated twice using a 1×1×1 mm3 and 3×3×3 mm3 dose grid respectively. Moreover, we used an open source DICOM‐RT viewer to read the raw‐RDose data (1×1×1 mm3 resolution) and were subsequently rescaled by linear interpolation to dose grids of 1.5×1.5×1.5, 2×2×2, 2.5×2.5×2.5 and 3×3×3 mm3. DVHs for all targets were recalculated and inter‐compared for the native and post‐processed resolutions to quantify the effect on DVH of dose grid resolution and correlate that with the PTV volume size.Results:DVHs shape and numerical values have a significant dependence on dose grid size resulting to a reduced Dmean, Dmax and Dmin with volume averaging effect being the main reason for these changes. Moreover, the magnitude of the DVH alteration is inversely proportional to tumor volume size. As the dose grid increases from 1×1×1 to 3×3×3 mm3, the DVH‐derived Dmean value is underestimated by ∼4, ∼7 and ∼10 % for tumors with volume sizes of 1.3, 0.5 and 0.1 cc respectively.Conclusion:The dose grid size that is used for the final dose calculation is affecting significantly the DVHs of small PTVs. The higher the dose grid size, the more noticeable is the DVH alteration, especially for tumors with a volume less than 1cc. For SRS planning, a dose grid of 1×1×1 mm3 should be used, especially for tumors with a volume < 1cc, to avoid erroneous DVHs.UTHSCSA, division of medical physics, has a research grant with Brainlab

The Effect of Varying Target Sizes and Spaces between Target and Non-target Elements on Goal-directed Hand Movement Times while Driving

Expressed by Fitts in 1954, there is an inverse relationship between movement time and target size and/or the distance between the participant and a target; smaller and further away targets require longer movement times than larger, closer targets. Here, the applicability of Fitts’ law to an in-vehicle, dual-task setting is under investigation. In the current experiment, different target sizes and spaces between target and non-target elements (target-element space), were investigated in simulated driving and non-driving scenarios in two age groups (18 – 35 and 45 – 65 years old). The aim of this experiment was to investigate whether target size and target-element space (i.e., the space between targets and non-targets) would have an effect on the mean movement times of younger and older participants for driving and non-driving conditions. Participants pointed to and touched targets on a smartphone touch screen in a vehicle mock-up. Movement times were recorded while concurrently performing a simulated driving task (dual-task condition) and while performing just the pointing task (single task condition). Errors were defined and are presented. Mean movement times in the dual-task condition were significantly faster than in the single task condition. Additionally, in line with Fitts’ law, in-vehicle movement time decreased as a function of target size. Elements that had the most target-element space were moved to most quickly, however, the medium and small spaces did not differ. Differences between the two age groups were not found.

The influence of luminance, observation duration and procedure on the recognition of pedestrians’ faces

Past studies carried out to determine whether the spectral power distribution of a light source affects facial recognition have led to mixed results. One reason for this could be that different studies presented different levels of task difficulty, this being a function of target size, observation duration and type of procedure. This paper presents two facial recognition experiments carried out using matching and identification procedures to explore task difficulty as defined by observation duration and target luminance. It was confirmed that identification is more difficult than matching. A relationship between task difficulty (luminance and duration) and recognition probability was found and this allows the luminance to be determined for a given probability.

SU-E-T-702: Performance of Multiple Conformity, Homogeneity and Dose Gradient Indices in SRS and SBRT Treatment Planning of the Spinal, Pelvic and Lung Lesions

Purpose: Presently, various forms of quality indices (QI) are used to compare and evaluate stereotactic treatment plans with no single QI accepted as universal. In this work we evaluate and compare the performance of 11 previously reported QI: 5 conformity (CI), 5 homogeneity (HI), and 1 dose gradient (DGI) indices as a function of target size, site, and mode of treatment. A novel unified quality function (UQF) which combines conformity, homogeneity and dose gradient is presented and investigated. Methods: 27 spine SRS, 8 pelvic SBRT and 34 lung SBRT cases were analyzed using an in-house wxPython program which imports treatment plan data and calculates various quality indices, dose volume tables, displays 3D dose/CT images, cumulative and differential DVHs. Results: Mean spine, pelvis and lung coverages were 0.91, 0.93, 0.85 respectively. Mean maximum target dose was best for pelvis (108%), followed by the lung (115%) and the spine (118%). Mean minimum target dose was best for the lung (95%), followed by pelvis (94%) and spine (88%). Mean DGI were 4.6, 5.2 and 7.54 for the pelvis, spine and lung. UQF scores the best for pelvis (0.2), followed by spine (0.28) and the lung (0.42). IMRT spine plans had better mean coverages (0.94), and lower maximum target dose (114%), while VMAT plans had better minimum target dose (89%). Conclusion: Mean CI, HI and DGI show various sensitivities to the treatment site, size and the delivery type (VMAT or IMRT). All CI except coverage show large variations with volume < 130 cc while all 5 HI show little dependence on the PTV volume. DGI values fall sharply for the lung (from 15 to 6) and spine (from 10 to 5) as the PTV increases to about 100 cc, while pelvic DGI stays about 5 for all PTV sizes.

Seeing visual word forms: Spatial summation, eccentricity and spatial configuration

We investigated observers’ performance in detecting and discriminating visual word forms as a function of target size and retinal eccentricity. The contrast threshold of visual words was measured with a spatial two-alternative forced-choice paradigm and a PSI adaptive method. The observers were to indicate which of two sides contained a stimulus in the detection task, and which contained a real character (as opposed to a pseudo- or non-character) in the discrimination task. When the target size was sufficiently small, the detection threshold of a character decreased as its size increased, with a slope of −1/2 on log–log coordinates, up to a critical size at all eccentricities and for all stimulus types. The discrimination threshold decreased with target size with a slope of −1 up to a critical size that was dependent on stimulus type and eccentricity. Beyond that size, the threshold decreased with a slope of −1/2 on log–log coordinates before leveling out. The data was well fit by a spatial summation model that contains local receptive fields (RFs) and a summation across these filters within an attention window. Our result implies that detection is mediated by local RFs smaller than any tested stimuli and thus detection performance is dominated by summation across receptive fields. On the other hand, discrimination is dominated by a summation within a local RF in the fovea but a cross RF summation in the periphery.

Distinct Visual Thresholds for Egocentric and Allocentric Information Pick UP?

Unlike perceptual size judgments, actions—but not delayed actions—performed under full vision are relatively unaffected by the Müller-Lyer illusion. Controversy remains as to the source of these effects. We aimed to illuminate the problem by exploiting the possibility that vision for action and perception may have distinct thresholds. In Experiment 1 participants performed delayed pointing movements towards briefly presented (12 ms–masked) M-L targets of different sizes. While participants were unable to perceptually discriminate between targets, their movements were nevertheless a function of target size, but not of the illusion (de Wit, van der Kamp, & Masters, in press). This implies 1) that vision for action is functional even after a delay and/or 2) that distinct thresholds exists for egocentric and allocentric information pick up, possibly irrespective of whether a task is perceptual or motoric in nature. Experiment 2, in which participants manually matched the size of perceptually indiscriminable M-L targets, supports the latter option. These findings are reviewed in relation to recent discussions of the two-visual-systems model. de Wit, M.M., van der Kamp, J., & Masters, R.S.W. (in press). Delayed pointing movements to masked Müller-Lyer figures are affected by target size but not the illusion. Neuropsychologia.

Cortical Correlates of Fitts’ Law

Fitts’ law describes the fundamental trade-off between movement accuracy and speed: it states that the duration of reaching movements is a function of target size (TS) and distance. While Fitts’ law has been extensively studied in ergonomics and has guided the design of human–computer interfaces, there have been few studies on its neuronal correlates. To elucidate sensorimotor cortical activity underlying Fitts’ law, we implanted two monkeys with multielectrode arrays in the primary motor (M1) and primary somatosensory (S1) cortices. The monkeys performed reaches with a joystick-controlled cursor toward targets of different size. The reaction time (RT), movement time, and movement velocity changed with TS, and M1 and S1 activity reflected these changes. Moreover, modifications of cortical activity could not be explained by changes of movement parameters alone, but required TS as an additional parameter. Neuronal representation of TS was especially prominent during the early RT period where it influenced the slope of the firing rate rise preceding movement initiation. During the movement period, cortical activity was correlated with movement velocity. Neural decoders were applied to simultaneously decode TS and motor parameters from cortical modulations. We suggest that sensorimotor cortex activity reflects the characteristics of both the movement and the target. Classifiers that extract these parameters from cortical ensembles could improve neuroprosthetic control.

A kinematic analysis of visually-guided movement in Williams syndrome

Previous studies have reported that people with the neurodevelopmental disorder Williams syndrome exhibit difficulties with visuomotor control. In the current study, we examined the extent to which visuomotor deficits were associated with movement planning or feedback-based on-line control. We used a variant of the Fitts' reciprocal aiming task on a computerized touchscreen in adults with WS, IQ-matched individuals with Down syndrome (DS), and typically developing controls. By manipulating task difficulty both as a function of target size and amplitude, we were able to vary the requirements for accuracy to examine processes associated with dorsal visual stream and cerebellar functioning. Although a greater increase in movement time as a function of task difficulty was observed in the two clinical groups with WS and DS, greater magnitude in the late kinematic components of movement—specifically, time after peak velocity—was revealed in the WS group during increased demands for accuracy. In contrast, the DS group showed a greater speed-accuracy trade-off with significantly reduced and more variable endpoint accuracy, which may be associated with cerebellar deficits. In addition, the WS group spent more time stationary in the target when task-related features reflected a higher level of difficulty, suggestive of specific deficits in movement planning. Our results indicate that the visuomotor coordination deficits in WS may reflect known impairments of the dorsal stream, but may also indicate a role for the cerebellum in dynamic feed-forward motor control.

Preliminary clinical applications of a device-dedicated whole-body positron emission tomography reconstruction method: impact on standardized uptake values

¹⁸F-fluorodeoxyglucose positron emission tomography has proven relevance in oncological diagnosis, staging and follow-up. The standardized uptake value (SUV) is one of the most widely used semi-quantitative criteria in PET imaging. However, factors such as noise and image resolution affect the measurement of the SUV. We reported earlier that a device-dedicated projector [attenuation-weighted ordered-subsets expectation maximization detector response (AW-OSEM DR), based on point-source measurements] introduces less noise than a geometrical model (AW-OSEM). The aim of this study was to investigate the AW-OSEM DR method's impact on SUV measurements under clinical conditions. We first performed a bias analysis to assess the accuracy of the quantitation for the two reconstruction methods as a function of target size and the number of iterations, with 14 acquisitions of the NEMA IEC/2001 phantom. We then used each method to calculate the maximum and average SUVs, respectively for 32 lesions. For all spheres and all iterations, the bias was significantly lower with AW-OSEM DR than with AW-OSEM (P=0.012). Moreover, a paired Student's t-test showed significant intermethod differences for maximum SUV and average SUV (both P<0.001) in cancer patients. Conversely, the two methods did not differ significantly in terms of the mean SUV and signal-to-noise ratio calculated in the liver for each patient (P=0.5 and 0.08, respectively). Phantom and patient studies were performed to quantify the effects of AW-OSEM DR on PET images. The phantom study highlighted the fact that our method produces more accurate images in terms of the SUV, which is an essential quality for ensuring correct diagnosis, follow-up and treatment planning.

SU-FF-T-178: Optimization of Internal Target Margins for Dynamic IMRT and RapidARC

Purpose: To determine the optimal Internal Margin (IM) for targets undergoing respiratory motion during treatment with dynamic IMRT and RapidARC. Methods and Materials: Dynamic IMRT and RapidArc plans were created for two targets (3 cm and 5 cm diameter) in the exhale phase with 6 different IM expansions (0,2,4,6,8,10 mm). The plans were delivered to a stationary two‐dimensional ion chamber array (Matrixx, IBA) using a 0.2 second sampling rate. Breathing motions of sin, sin2, sin4, and sin6, with amplitudes of 0 to 4 cm, were simulated by shifting the dose frames by the respiration trace. The resulting simulated motion‐blurred dose planes were randomly sampled from ten starting breathing phases and summed for 30 fractions. The summed dose planes were then compared to the dose delivered to a stationary target with a 0 mm. The optimal IM was calculated as that which resulted in the Equivalent Uniform Dose (EUD) or minimum dose to 95% of the target (D95) closest to that of the stationary case. The optimal margins were fit to the following linear equation: IM = C1*Amp + C2 using a least‐squares fit. Results: The value of C1 ranged from 0.55 to 0.98, depending on the target size, type of target motion, and treatment plan. The optimal IM was ∼2mm larger for sin motion compared with sin6 motion. In all cases the optimal IM calculated using the two different criteria (EUD and D95) agreed within 1mm. Conclusion: Optimal Internal Margins are a function of target size and target motion. In many cases the IM is smaller than the peak‐to‐peak motion. We have developed formulae that correlate motion with the necessary IM.

Ionisation cluster-size formation by electrons: from macroscopic to nanometric target sizes

An indispensable prerequisite for a deeper understanding of specified physical, chemical or biological changes initiated in matter when being exposed to ionising radiation is a detailed knowledge of particle track structure. Here, the structure of electron tracks is of particular interest since electrons are set in motion in large numbers as secondary particles during the slow down of any kind of ionising radiation in matter. From the point of view of radiation induced early damage to genes and cells, which starts with the early damage to segments of the DNA molecule, the most effective secondary electrons are those at energies of a few hundred eV since the yield of double-strand breaks induced by such electrons in the DNA shows a maximum. This can be explained by the fact that in water cylinders, 2 nm in diameter and height (as a substitute to small segments of the DNA), the probability of the electron-induced formation of ionisation cluster sizes greater than or equal to two is highest also at initial electron energies of a few hundred eV. In view of this promising feature of ionisation cluster-size distributions formed by low-energy electrons in nanometric targets of liquid water for explaining particular radio-biological endpoints, it is the aim of the present work to investigate the properties of cluster-size formation by electrons as a function of target size. Here, main emphasis is laid on the behaviour of cluster-size distributions if the target size is reduced from macroscopic to nanometric volumes.

Dose uncertainty due to aperture effects in dynamic fields

Dosimetry of intensity modulated radiation therapy requires accurate modeling of the beamlets that comprise each treatment segment. Planning systems such as Varian Eclipse and Philips Pinnacle recommend measuring dose distributions and output factors for fields as small as possible, generally down to at least 2 x 2 cm2. Conventionally, we perform these measurements for regular fields, defined by the secondary collimators. In practice, it is the multileaf collimation system (MLC) that defines the intensity map and provides dynamic dose modulation in either a moving window or segmented step-and-shoot mode. For this review we have only considered the latter delivery mode. Using this method, we have studied aperture motion effects on the dynamic collimator scatter (S(c)), total scatter (S(c,p)), and phantom scatter (S(p)) factors for various combinations of collimator settings (4 x 4-14 x 40 cm2) and dynamically stepped leaf gaps (0.1 to 1.0 cm) in comparison with those for static field factors. For two different Varian linear accelerators, we found similar results in a systematic dependence of collimator scatter on gap width and collimator setting. As the gap increases from 0.1 to 1.0 cm the dynamic collimator scatter factors converge from a maximum difference of about 30% toward the static field values. At the same time, there is no measurable difference between dynamic field phantom scatter factors and those conventionally obtained for static fields. Second, we evaluated the two planning systems as to how well they account for collimator scatter by attempting to mimic the dynamic apertures used above by planning and measuring dose distributions to several small, cylindrical targets for a similar range of fixed collimator settings. We found that the ratio of measured-to-planned doses as a function of target size were similar to the measured, dynamic S(c) data for the Varian Eclipse planning system, indicating underestimation of dose for targets smaller than 1 cm diameter, but were close to unity for the Philips Pinnacle system, suggestive of the underlying differences in the dose calculation algorithms. We discuss the measurements and results and potential impact on the dosimetry of small clinical targets.

Gain and Target Size Effects on Cursor-Positioning Time with a Mouse

Movement time to align a cursor with targets on a computer screen a mouse was examined across settings of gain and target size. Empirical evidence was sought in light of previous suggestions that performance declines observed at higher gains can be explained by decreased effective cursor resolution, not gain per se. We tested this hypothesis by holding the effective cursor resolution constant while systematically varying gain and target size. Analysis of movement times showed a significant gain effect as a function of target size. Specifically, movement time increased with gain at the smallest target size (i.e. 1.5 mm) but decreased with gain at the largest target size (i.e. 12 mm). These results do not support the no-effect of gain hypothesis and suggest that target size is an important factor in determining the effects of gain on mouse movement performance.

Properties of receptive field on binocular fusion stimulation in the central visual field.

Visual information projected onto corresponding points on the right and left retinas converges on the binocular cells in the visual cortex. The aim of this study is to investigative the characteristics of the receptive field for binocular stimulation in the central visual field of normal-sighted human subjects. We investigated the receptive field for binocular stimulation under fusion conditions by combining the Octopus 201 with the space synoptophore. We measured binocular and monocular sensitivities while the fusion patterns were projected onto the Octopus 201 cupola, using the space synoptophore. We designed a new program to test 37 points in the central 6 degrees visual field. Six target sizes were tested: the white-spot targets of 0.054 degrees, 0.108 degrees, 0.216 degrees, 0.431 degrees, 0.862 degrees and 1.724 degrees projected diameters. The threshold energy necessary for binocular stimulation was lower than that for the monocular stimulation in all subjects. This difference was more obvious on the test points that were more distant from the fovea when target sizes of 0.054 degrees and 0.108 degrees were used. The amount of binocular summation ratio was highest for target size 0.054 degrees in each stimulus area in the central 6 degrees of the visual field. When we measured binocular summation using target sizes larger than 0.108 degrees, the result was the constant summation. The size of the receptive field for binocular stimulation is smaller than monocular stimulation under the same fusion condition. The amount of binocular summation varies as a function of target size.

Polarimetric characterization of debris and faults in the highway environment at millimeter-wave frequencies

In this paper, measurements and models for the polarimetric backscatter response of various paint targets on roads and road surface faults are presented. Of particular interest are debris and faults that could lead to fatal accidents and damage of property. A desired safety feature for automotive radar sensors is the capability of detecting such debris and faults. The detectability of a point target is evaluated by comparing its RCS value with the RCS threshold value defined by the backscatter response of the road surface. Extensive backscatter measurements at W-band were conducted to obtain the backscatter response of typical debris and faults on asphalt surfaces at near grazing incidence angles (76/spl deg/-86/spl deg/). On the other hand, theoretical models, based on diffraction from impedance wedges and scattering from impedance cylinders, respectively, as well as physical optics approximation, were developed to predict the backscatter response of road surface faults and targets with planar facets on road surfaces. Experimental results indicate that detectability in all cases is a function of target size, its azimuthal angle with respect to radar boresight, and the polarization state of the system. The measured backscatter response is used to verify the validity of the theoretical models. Angular polarimetric backscatter measurements of targets defining roadside boundaries such as a concrete curb, a guardrail, and a pebble surface are also presented. The results of these measurements could be used to alert fatigued drivers should their vehicles be heading sideward.