Invariant Target Research Articles

Left Hand Advantage for Prey Capture in the Galago (<em>Galago Moholi</em>)

Efficiency of hand use in nonhuman primates is often difficult to assess because of the relatively small number of responses made with a nonpreferred hand. The present study compared measures of reach efficiency in 8 galagos ( Galago moholi ), 4 left-hand preferent and 4 right-hand preferent subjects, tested in a reach apparatusdesigned to elicit equal numbers of responses by the left and right hands. The effect of variant or invariant target placement within sessions was also assessed by the use of both blocked and randomized trials. Efficiency was defined in terms of the percentage of successful reaches and the average duration of time required for reach execution. There was no effect of target variance on strength of hand preference or on either measure of performance efficiency. Preferred and nonpreferred hands did not differ with respect to these two measures. There was also no difference in the percentage of successful reaches between the left and right hands. However, for 7 of 8 subjects the left hand generated faster reach times than did the right hand, regardless of hand preference. The greater execufion speed with the left arm/hand is interpreted as exemplifying a lateralized neural advantage for the execution of ballistic reaching in galago species. The highly consistent timing of this prey capture behavior in the galago supports the view that this arm/hand movement is ballistic in type.

Temporal and spatial patterns in vegetation and atmospheric properties from AVIRIS

Little research has focused on the use o f intaging spectrometry for change detection. In this paper, we apply Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data to the monitoring of seasonal changes in atinospheric water vapor, liquid water, and surface cover in the vicinity of the Jasper Ridge, CA, for three dates in 1992. Apparent surface reflectance was retrieved and water vapor and liquid water mapped by using a radiativetransfer-based inversion that accounts for spatially variable atmospheres. Spectral mixture analysis (SMA) was used to model reflectance data as mixtures of green vegetation (GV), nonphotosynthetic vegetation (NPV), .soil, and shade. Temporal and spatial patterns in endineinber fractions and liquid water were compared to the normalized difference vegetation index (NDVI). The reflectance retrieval algorithm was tested by using a temporally invariant target. Atmospheric analysis showed a strongly negative linear relation between water vapor and elevation with significant seasonal variation in water vapor. Comparison of AVIRIS estimates of specific humidity to ground-based measures showed good correspondence for all three dates. Analysis of .surface properties showed that GV, NDVI, and liquid water varied in. response to green vegetation and were highly correlated. However, whereas the NDVI peaked between 0.7 and 0.85 in forests, liquid water continued to vary by as much as a factor of two. Seasonal patterns included senescence in herbaceous and nonconiferous vegetation, potential leaf growth in cortiferous forests, and a general increase in shadows. This resulted in seasonal declines in NDVI, GV, and liquid water for non forested vegetation and increases in NPV. Nonconiferous forests showed similar declines in liquid water rend GV and increases in shade and NPV, but they showed an. increase in NDVI. In coniferouns forests, liquid water and NDVI increased seasonally, matching an interpretation of continued growth, but GV decreased owing to increased .shade. The combination of retrieved surface reflectance, atmospheric modeling, and mapping of liquid water demonstrates the utility of imaging spectrometry for change detection. SMA with the use of reference endmembers is an c effective method for monitoring surficial changes. Temporal patterns in NDVI that contradict trends of GV and liquid water in nonconiferous forests raise additional questions about the NDVI. Liquid water may be more appropriate for analysis of high-leaf-area, shadowed forests because it overcomes the problem of saturation with NDVI.

Calibrating long-term AVHRR-derived NDVI imagery

Several studies have confirmed that the radiometric calibration of AVHRR instruments changes following launch, and drifts over time. These changes cause spurious trends to appear in NDVI data that confound the reliable detection of vegetation change. It has previously been established that approximate additive corrections can be applied to an entire NDVI image, if the postlaunch calibration coefficients are known. However, the results of postlaunch calibration studies published in the literature vary, leading to different NDVI corrections depending on which coefficients are used. We acquired ten years (1981–1991) of monthly NDVI images covering Western Australia (Latitude 13°S to 36°S) in which the NDVI had been derived using prelaunch calibration coefficients. To address the calibration issue, we have computed theoretical corrections to the NDVI based on the prelaunch coefficients used to compute the NDVI in our data set, and postlaunch calibration coefficients reported by Che and Price (1992) and Kaufman and Holben (1993). Large differences were found in the NDVI corrections, depending on which set of postlaunch calibrations was adopted. To resolve the differences, we assumed that the entire image was a seasonally invariant target, and that the trend in the mean NDVI time series was solely due to changes in sensor calibration. The results obtained using this “time series” approach agreed with those computed in theoretical simulations using the calibration coefficients of Kaufman and Holben (1993). It is concluded that the time series technique described in this article can be used to remove sensor-induced trends from a time series of NDVI data without any knowledge of the postlaunch calibration coefficients. To apply the time series calibration technique, the dates of any changes in the sensor prelaunch calibration coefficients (including changes in the satellite platform) must be known. No other information is necessary, offering a significant advantage over existing methods for users of NDVI time series image data.

All‐optical invariant target recognition based on intensity‐to‐phase coding

We have experimentally demonstrated the feasibility of a scale, rotation, and translation invariant all-optical processor for automatic target recognition. This simple processor consists of a single Fourier lens and uses a phase-coded input image of the target obtained by the recording of the original image onto a phase-only material through a Ronchi-type grating. A logarithmic distance measure is introduced to separate two classes of targets under the experiment. A real-time implementation of the processor is suggested utilizing a specially designed spatial light modulator.

Three- and four-year-olds' perceptual confusions for spoken words.

Although infants have the ability to discriminate a variety of speech contrasts, young children cannot always use this ability in the service of spoken-word recognition. The research reported here asked whether the reason young children sometimes fail to discriminate minimal word pairs is that they are less efficient at word recognition than adults, or whether it is that they employ different lexical representations. In particular, the research evaluated the proposal that young children's lexical representations are more "holistic" than those of adults, and are based on overall acoustic-phonetic properties, as opposed to phonetic segments. Three- and four-year-olds were exposed initially to an invariant target word and were subsequently asked to determine whether a series of auditory stimuli matched or did not match the target. The critical test stimuli were nonwords that varied in their degree of phonetic featural overlap with the target, as well as in terms of the position(s) within the stimuli at which they differed from the target, and whether they differed from the target on one or two segments. Data from four experiments demonstrated that the frequency with which children mistook a nonword stimulus for the target was influenced by extent of featural overlap, but not by word position. The data also showed that, contrary to the predictions of the holistic hypothesis, stimuli differing from the target by two features on a single segment were confused with the target more often than were stimuli differing by a single feature on each of two segments. This finding suggests that children use both phonetic features and segments in accessing their mental lexicons, and that they are therefore much more similar to adults than is suggested by the holistic hypothesis.

Pattern recognition properties of various feature spaces for higher order neural networks

The authors explore alternatives that reduce the number of network weights while maintaining geometric invariant properties for recognizing patterns in real-time processing applications. This study is limited to translation and rotation invariance. The primary interest is in examining the properties of various feature spaces for higher-order neural networks (HONNs), in correlated and uncorrelated noise, such as the effect of various types of input features, feature size and number of feature pixels, and effect of scene size. The robustness of HONN training is considered in terms of target detectability. The experimental setup consists of a 15*20 pixel scene possibly containing a 3*10 target. Each trial used 500 training scenes plus 500 testing scenes. Results indicate that HONNs yield similar geometric invariant target recognition properties to classical template matching. However, the HONNs require an order of magnitude less computer processing time compared with template matching. Results also indicate that HONNs could be considered for real-time target recognition applications.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Polymerase chain reaction (PCR) mutagenesis enabling rapid non‐radioactive detection of common β‐thalassaemia mutations in Mediterraneans

The IVS-1-110 (G----A) and IVS-1-1 (G----A) mutations occur in approximately 33% and 9% respectively of beta-thalassaemia alleles in Mediterraneans (Kazazian & Boehm, 1988). They are generally detected in polymerase chain reaction (PCR)-amplified material by allele-specific oligonucleotide (ASO) hybridization patterns. In this study, artificial base substitutions in amplified material have been created to distinguish normal from mutant alleles on the basis of restriction enzyme digestion patterns. Invariant target sites provide an internal control for restriction enzyme activity. Mutagenesis was achieved by 3' base mismatches in primers selected to anneal immediately adjacent to target sites. Digestion of PCR products from normal and thalassaemic alleles with the restriction enzymes MboI (IVS-1-110) and HinfI (IVS-1-1) produced different fragments on electrophoresis. The above strategy was validated by allele-specific oligonucleotide probing. Identification of the three commonest mutations in this population (IVS-1-110, codon 39 and IVS-1-1), which account for approximately 69% of thalassaemic alleles (Kazazian & Boehm, 1988), was subsequently undertaken in seven chorion villus biopsies.

An adaptive neural model for mapping invariant target position.

We perceive a constant target in space as constant even though the registration of that target on our senses is continuously shifting. This article derives and stimulates a neural network model that represents visual spot targets, invariant with respect to any combination of egocentric target measures. The model represents space in terms of signals used to move in that space. The model learns and maintains precise sensory-motor calibrations starting with only loosely defined relations. It is adaptive to physical changes of the eye and muscles as well as internal system parameters. Its performance is noise and fault tolerant. Computer simulations show that the average error in target orientation after learning is about 1% of the total visual field extent. The model maintains good accuracy with many different parameter choices. Its performance is most related to the function of the posterior parietal cortex. Testable predictions are made for the columnar topography and learning in that brain structure.

An adaptive neural model for mapping invariant target position.

An adaptive neural model for mapping invariant target position.

Structure of the gene encoding the immunodominant surface antigen on the sporozoite of the human malaria parasite Plasmodium falciparum.

The gene for the circumsporozoite (CS) protein of Plasmodium falciparum has been cloned and its nucleotide sequence determined. The gene encodes a protein of 412 amino acids as deduced from the nucleotide sequence. The protein contains 41 tandem repeats of a tetrapeptide, 37 of which are Asn-Ala-Asn-Pro and four of which are Asn-Val-Asp-Pro. Monoclonal antibodies against the CS protein of Plasmodium falciparum were inhibited from binding to the protein by synthetic peptides of the repeat sequence. The CS protein of Plasmodium falciparum and the CS protein of a simian malaria parasite, Plasmodium knowlesi, have two regions of homology, one of which is present on either side of the repeat. One region contains 12 of 13 identical amino acids. Within the nucleotide sequence of this region, 25 of 27 nucleotides are conserved. The conservation of these regions in parasites widely separated in evolution suggests that they may have a function such as binding to liver cells and may represent an invariant target for immunity.

Manufacturing Repetition Effects— a Reply to Gentile and Nemetz (1978)

Under the guise of repetition effects, Gentile and Nemetz (1978) vociferously attack the explanatory power and utility of short-term motor memory research. Such a criticism is based on the belief that treatment effects are confounded with learning effects in experiments which require subjects to constantly reproduce invariant target positions. In this note a systematic critique of Gentile and Nemetz's logic and experimental evidence illuminates the questionable status of their position. It is argued that the Gentile and Nemetz findings actually oppose the existence of the procedural artifact they would have us consider. On the basis of methodological and logical arguments presented, it is concluded that a properly designed experiment need not be confounded by repetition effects. Finally, guidelines on both the manufacture and avoidance of repetition effects are suggested.