Orientation during short-range feeding in the crab Dotilla wichmanni

The ocypodid crab Dotilla wichmanni is a common inhabitant of tropical sandy shores, where it feeds at low tide by sorting the material deposited by the ebbing tide. Feeding occurs in the immediate vicinity of the burrow by means of systematically sampling the sand surface. While feeding, the crabs move along trenches radiating from the burrow and produce pseudofaecal pellets which are amassed over the already excavated area. When disturbed, the crabs rapidly vanish into the burrow, where they remain hidden for a while. Upon re-emerging, they recommence feeding moving along the same trench as before retreat. The crabs, however, were found to assume the same feeding direction held before retreating even if any sign that could be derived from their previous activity was removed experimentally. To uncover the orientation cues used in this behaviour, the area near the burrow was manipulated in particular ways. The crabs were found to rely mainly on the skylight polarization pattern, while visual landmarks near the feeding area may play a role when astronomic cues provide no useful information, such as under overcast skies. Both cues were used by the crabs as references to assume the same feeding direction as that used before retreat. Accepted: 9 June 1997     

Analysis of pelvic strain in different gait configurations in a validated cohort of computed tomography based finite element models

The pelvis functions to transmit upper body loads to the lower limbs and is critical in human locomotion. Semi-automated, landmark-based finite element (FE) morphing and mapping techniques eliminate the need for segmentation and have shown to accelerate the generation of multiple specimen-specific pelvic FE models to enable the study of pelvic mechanical behaviour. The purpose of this research was to produce an experimentally validated cohort of specimen-specific FE models of the human pelvis and to use this cohort to analyze pelvic strain patterns during gait. Using an initially segmented specimen-specific pelvic FE model as a source model, four more specimen-specific pelvic FE models were generated from target clinical CT scans using landmark-based morphing and mapping techniques. FE strains from the five models were compared to the experimental strains obtained from cadaveric testing via linear regression analysis, (R² values ranging from 0.70 to 0.93). Inter-specimen variability in FE strain distributions was seen among the five specimen-specific pelvic FE models. The validated cohort of specimen-specific pelvic FE models was utilized to examine pelvic strains at different phases of the gait cycle. Each validated specimen-specific FE model was reconfigured into gait cycle phases representing heel-strike/heel-off and midstance/midswing. No significant difference was found in the double-leg stance and heel-strike/heel-off models (p = 0.40). A trend was observed between double-leg stance and midstance/midswing models (p = 0.07), and a significant difference was found between heel-strike/heel-off models and midstance/midswing models (p = 0.02). Significant differences were also found in comparing right vs. left models (heel-strike/heel-off p = 0.14, midstance/midswing p = 0.04).     

Variability,agreement and reliability of MRI knee landmarks

Surface mesh reconstructions of bones are often required to define landmark-based coordinate systems, regions of interest and morphological features when studying the soft tissues of the knee from MRI scans. This study reports the variability, agreement and reliability of osseous landmarks to better understand their downstream effects. Fifteen landmarks were defined on the distal femur and twelve on the proximal tibia. Surface meshes were created from twenty right knee MRI scans with a mean subject age of 30.9 years. A single observer identified landmarks on all twenty knees, while three observers repeated the observations three times on a subset of eight knees. All observations were aligned to the Procrustes mean shapes. Principal component analysis was used to study inter-subject variability and two-way ANOVA for inter- and intra-observer agreement and reliability. Inter-subject landmark variation ranged from 0.6 to 5.26 mm, while inter- and intra-observer agreement were at most 5.1 and 5.69 mm respectively. Between-observer reliability ranged from 0.07 to 0.98 while within-observer values were between 0.51 and 0.98. Landmarks derived from fitted spheres or circles often performed well, while most others had their poorest agreement or greatest variation limited to only one or two cardinal directions.     

地标对犬蝠空间记忆的影响

为了研究地标（landmarks）是否影响犬蝠（Cynopterus sphinx）的空间记忆,我们通过室内模拟试验研究犬蝠和地标在觅食过程中空间记忆形成的关系。实验组按照每天地标数分别为0、2、4、8、0的数目连续进行5天实验,对照组不设地标进行相同条件的实验。结果显示,两组犬蝠第一次取食所用的时间与实验天数之间极显著相关（Pearson Correlations: 实验组r=-0.593, P<0.01;对照组r=-0.581, P<0.01）;实验组取食成功率与实验天数之间无明显相关性（Pearson Correlations: r=0.177, P>0.05）;对照组取食成功率与实验天数之间显著相关（Pearson Correlations: r=0.445, P<0.05）。实验组与对照组犬蝠第一次取食的时间差异不显著（GLM: F_0.05,1=4.703, P>0.05）,两组间取食的成功率差异也不显著（GLM: F_0.05,1=0.849, P>0.05）。这些结果说明了随着时间增加,犬蝠对取食地的空间记忆逐渐形成,放置地标在犬蝠对取食地空间记忆形成的过程中无显著影响。     

Cardiac Conduction System: Delineation of Anatomic Landmarks With Multidetector CT

Major components of the cardiac conduction system including the sinoatrial node (SAN), atrioventricular node (AVN), the His Bundle, and the right and left bundle branches are too small to be directly visualized by multidetector CT (MDCT) given the limited spatial resolution of current scanners. However, the related anatomic landmarks and variants of this system a well as the areas with special interest to electrophysiologists can be reliably demonstrated by MDCT. Some of these structures and landmarks include the right SAN artery, right atrial cavotricuspid isthmus, Koch triangle, AVN artery, interatrial muscle bundles, and pulmonary veins. In addition, MDCT has an imperative role in demarcating potential arrhythmogenic structures. The aim of this review will be to assess the extent at which MDCT can outline the described anatomic landmarks and therefore provide crucial information used in clinical practice.     

Highly resistant regression and object matching

In many disciplines, it is of great importance to match objects. Procrustes analysis is a popular method for comparing labeled point configurations based on a least squares criterion. We consider alternative procedures that are highly resistant to outlier points, and we describe an application in electrophoretic gel matching. We consider procedures based on S estimators, least median of squares, and least quartile difference estimators. Practical implementation issues are discussed, including random subset selection and intelligent subset selection (where subsets with small size or near collinear subsets are ignored). The relative performances of the resistant and Procrustes methods are examined in a simulation study.     

Cognitive performance in rhesus monkeys varies by sex and prenatal androgen exposure

Men and women differ on performance and strategy on several spatial tasks. Rodents display similar sex differences, and manipulations of early hormone exposure alter the direction of these differences. However, most cognitive testing of nonhuman primates has utilized sample sizes too small to investigate sexually differentiated behaviors. This study presents an investigation of sex differences and the effects of prenatal androgen on spatial memory and strategy use in rhesus monkeys. Monkeys prenatally exposed to vehicle, testosterone, or the androgen receptor blocker flutamide performed a search task in which 5 of 12 goal boxes contained food rewards. Spatial consistency and the presence of local landmarks were varied. Performance when both spatial and marker cues were available did not differ by sex or prenatal treatment. Contrary to predictions, females easily solved the task when local markers were removed, and their performance outscored males. Although eliminating spatial consistency and requiring subjects to use local markers impaired performance by all monkeys, females continued to locate correct goal boxes at higher than chance levels and scored better than males. Blocking prenatal androgen exposure in males improved use of local markers. These findings suggest that the tendency to attend to landmarks and to use them in solving spatial problems is typical of females across many species, including rodents, humans, and rhesus monkeys. In rhesus monkeys and rodents, developmental androgen eliminates this specialization. However, these results are the only known example of better performance of females than males when salient markers are removed.     

Visual landmarks and route following in desert ants

Summary Little is known about the way in which animals far from home use familiar landmarks to guide their homeward path. Desert ants, Cataglyphis spp., which forage individually over long distances are beginning to provide some answers. We find that ants running 30 m from a feeding place to their nest memorise the visual characteristics of prominent landmarks which lie close to their path. Although remembered visual features are used for identifying a landmark and for deciding whether to go to its left or right, they are not responsible for the detailed steering of an ant's path. The form of the trajectory as an ant approaches and detours around a landmark seems to be controlled by the latter's immediate retinal size; the larger it is, the greater the ant's turning velocity away from the landmark.     

Responses of toad's tectal neurons to in-phase and anti-phase movements of object and textured background

Summary Pigeons (Columba livia) were trained to find hidden food in a sunken well within a square box. After learning the location, they were tested occasionally with the well and food absent. The resulting search distributions were symmetric about the peak, implying a linear scale of measurement for distance. The spread of the distribution was a constant proportion of the distance to the nearest landmark, supporting Weber's Law. As well, in one test in which a landmark was shifted in a diagonal direction, the pigeons shifted their peak place of search both in the direction of landmark shift and in the direction orthogonal to the direction of landmark shift. This contradicted a pattern found earlier: For landmark shifts along the principal axes of the square box, pigeons only shifted their peak place of search in the direction of landmark shift, not in the orthogonal direction. The vector sum model, which predicts shifts of the peak place of search only in the direction of landmark shift, is disconfirmed and must be revised.     

What is geometric information and how do animals use it?

Unlike investigations of animals’ use of spatial cues such as landmarks, studies of sensitivity to the geometry of surfaces in an enclosure have proceeded mostly as an attempt to explain a laboratory finding with few direct tests of how animals use such a cue in nature. In this brief review, I discuss the current debate over whether global or local information from the enclosure drives the typical rotational error pattern in such studies. A consideration of the form and function of geometric cues in natural settings suggests that the natural boundaries for which arena walls are considered analogous might better be thought as landmarks. With a clearer picture of what geometric information is and how it might be used in nature, the generality of findings from laboratory studies of geometry enclosure can be better assessed.