Environmental modeling and recognition for an autonomous land vehicle

An architecture for object modeling and recognition for an autonomous land vehicle is presented. Examples of objects of interest include terrain features, fields, roads, horizon features, trees, etc. The architecture is organized around a set of data bases for generic object models and perceptual structures, temporary memory for the instantiation of object and relational hypotheses, and a long term memory for storing stable hypotheses that are affixed to the terrain representation. Multiple inference processes operate over these databases. Researchers describe these particular components: the perceptual structure database, the grouping processes that operate over this, schemas, and the long term terrain database. A processing example that matches predictions from the long term terrain model to imagery, extracts significant perceptual structures for consideration as potential landmarks, and extracts a relational structure to update the long term terrain database is given

Effects of an 8-week strength training intervention on tibiofemoral joint loading during landing: a cohort study

Objectives To use a musculoskeletal model of the lower limb to evaluate the effect of a strength training intervention on the muscle and joint contact forces experienced by untrained women during landing. Methods Sixteen untrained women between 18 and 28 years participated in this cohort study, split equally between intervention and control groups. The intervention group trained for 8 weeks targeting improvements in posterior leg strength. The mechanics of bilateral and unilateral drop landings from a 30 cm platform were recorded preintervention and postintervention, as was the isometric strength of the lower limb during a hip extension test. The internal muscle and joint contact forces were calculated using FreeBody, a musculoskeletal model. Results The strength of the intervention group increased by an average of 35% (P<0.05; pre: 133±36 n, post: 180±39 n), whereas the control group showed no change (pre: 152±36 n, post: 157±46 n). There were only small changes from pre-test to post-test in the kinematics and ground reaction forces during landing that were not statistically significant. Both groups exhibited a post-test increase in gluteal muscle force during landing and a lateral to medial shift in tibiofemoral joint loading in both landings. However, the magnitude of the increase in gluteal force and lateral to medial shift was significantly greater in the intervention group. Conclusion Strength training can promote a lateral to medial shift in tibiofemoral force (mediated by an increase in gluteal force) that is consistent with a reduction in valgus loading. This in turn could help prevent injuries that are due to abnormal knee loading such as anterior cruciate ligament ruptures,patellar dislocation and patellofemoral pain

Effects of an 8-week strength training intervention on tibiofemoral joint loading during landing: a cohort study.

Objectives: To use a musculoskeletal model of the lower limb to evaluate the effect of a strength training intervention on the muscle and joint contact forces experienced by untrained women during landing. Methods: Sixteen untrained women between 18 and 28 years participated in this cohort study, split equally between intervention and control groups. The intervention group trained for 8 weeks targeting improvements in posterior leg strength. The mechanics of bilateral and unilateral drop landings from a 30 cm platform were recorded preintervention and postintervention, as was the isometric strength of the lower limb during a hip extension test. The internal muscle and joint contact forces were calculated using FreeBody, a musculoskeletal model. Results: The strength of the intervention group increased by an average of 35% (P<0.05; pre: 133±36 n, post: 180±39 n), whereas the control group showed no change (pre: 152±36 n, post: 157±46 n). There were only small changes from pre-test to post-test in the kinematics and ground reaction forces during landing that were not statistically significant. Both groups exhibited a post-test increase in gluteal muscle force during landing and a lateral to medial shift in tibiofemoral joint loading in both landings. However, the magnitude of the increase in gluteal force and lateral to medial shift was significantly greater in the intervention group. Conclusion: Strength training can promote a lateral to medial shift in tibiofemoral force (mediated by an increase in gluteal force) that is consistent with a reduction in valgus loading. This in turn could help prevent injuries that are due to abnormal knee loading such as anterior cruciate ligament ruptures, patellar dislocation and patellofemoral pain

A training methodology for spatial orientation in spacecraft

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2006.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 41).This thesis investigates a way to use virtual reality techniques to teach space vehicle inhabitants about the configuration of their craft so that their performance in orientation and spatial memory tasks is improved. An "adjacency training" method was developed that taught connections between landmarks in two joined modules with inconsistent visual verticals by emphasizing functional relationships among adjacent surfaces within and between modules. An experiment was performed (n = 17) that compared this training with a control treatment that emphasized the rotational relationship between the two modules as a whole rather than connections between individual surfaces. On average, adjacency training was not effective in decreasing the total time to respond or increasing the accuracy in placement and orientation of module walls between the two modules. Adjacency trained subjects were significantly better in responding to a novel perspective. All subjects responded to an orienting cue surface more quickly when visually upright, suggesting their spatial knowledge of both groups remained orientation dependent.(cont.) However, within each group, subjects who used a "consistent visualization" as determined by a post training questionnaire, performed 5 seconds faster (F(1,9)=7.41, p= 0.02) than the subjects who did not. Visualization consistency was determined by asking the subjects to describe which direction they considered one module to be when viewed from the other module and then the reverse. Consistent responses indicated that the subjects were able to combine/concatenate their cognitive mental maps of each of the modules and make correct, consistent judgments in a single allocentric coordinate frame. Subjects who reported consistent visualization were distributed evenly among both training groups, so the training manipulation had no clear effect on the consistency of visualization achieved. The adjacency training method did help subjects remember the relationship between objects on which they had been specifically trained, as determined by a subsequent post-training questionnaire.by Daniel Aaron Buckland.S.M

Maps and memories of space in the human brain

Mammalian navigation is mostly studied in rodents and humans. Due to ethical and methodological constraints, rodent research so far primarily targeted the neurophysiological mechanisms of navigation, while navigation studies in humans predominantly focused on navigational behavior and the cognitive processes involved in it. Although basic mechanisms of navigation seem well preserved across rodents and humans in general, human and rodent navigation also differ substantially in several aspects and it is not obvious how particular findings translate across both species. As a consequence, for many aspects of navigation, we do not know how processes on the cognitive level can be attributed to those on the cellular level, and, eventually, how particular navigation behavior can be causally related to neural activity. This knowledge gap is addressed in this thesis with two studies that extend our understanding of how findings from rodents and humans translate across both species. To this end, a framework was developed that combines human navigation in landmark-sparse virtual environments that resemble the open-field setups typically used to study spatially tuned neurons in rodents. Applying this framework, the first study presented in this thesis separates passive and active components during navigation, and investigates how varying navigational and spatial memory demands impact participants' brain activity. The results suggest that, first, certain brain regions primarily known for perception of static scenes are recruited during passive navigation, and also contribute information processing specifically relevant for active navigation; and that, second, the anterior medial hippocampus provides a coherent spatial representation of the current environment that is dependent on spatial memory. Using a similar setup, the second study investigates participants' spatial representation in more detail. The results show that, first, a model inspired by electrophysiological findings in rodents that explains location memory as a function of proximity to the environment's boundaries generally matches participants' behavior in a similar open-field environment; that, second, the model's explanatory power may be further improved when, in addition to the precision, also the accuracy of participants' location memory is considered; and that, finally, in a quadratic open-field environment, the diagonals also impact participant's spatial orientation and location memory. The findings reported in this thesis demonstrate that the framework applied in both studies allows for a detailed investigation of human navigation behavior, and the cognitive processes associated with it. It furthermore increases comparability of findings between human and rodent navigation, and may eventually help to better understand how neurophysiological processes are transformed into navigation behavior

When Do Objects Become Landmarks? A VR Study of the Effect of Task Relevance on Spatial Memory

We investigated how objects come to serve as landmarks in spatial memory, and more specifically how they form part of an allocentric cognitive map. Participants performing a virtual driving task incidentally learned the layout of a virtual town and locations of objects in that town. They were subsequently tested on their spatial and recognition memory for the objects. To assess whether the objects were encoded allocentrically we examined pointing consistency across tested viewpoints. In three experiments, we found that spatial memory for objects at navigationally relevant locations was more consistent across tested viewpoints, particularly when participants had more limited experience of the environment. When participants’ attention was focused on the appearance of objects, the navigational relevance effect was eliminated, whereas when their attention was focused on objects’ locations, this effect was enhanced, supporting the hypothesis that when objects are processed in the service of navigation, rather than merely being viewed as objects, they engage qualitatively distinct attentional systems and are incorporated into an allocentric spatial representation. The results are consistent with evidence from the neuroimaging literature that when objects are relevant to navigation, they not only engage the ventral “object processing stream”, but also the dorsal stream and medial temporal lobe memory system classically associated with allocentric spatial memory

Improving spatial orientation in virtual reality with leaning-based interfaces

Advancement in technology has made Virtual Reality (VR) increasingly portable, affordable and accessible to a broad audience. However, large scale VR locomotion still faces major challenges in the form of spatial disorientation and motion sickness. While spatial updating is automatic and even obligatory in real world walking, using VR controllers to travel can cause disorientation. This dissertation presents two experiments that explore ways of improving spatial updating and spatial orientation in VR locomotion while minimizing cybersickness. In the first study, we compared a hand-held controller with HeadJoystick, a leaning-based interface, in a 3D navigational search task. The results showed that leaning-based interface helped participant spatially update more effectively than when using the controller. In the second study, we designed a "HyperJump" locomotion paradigm which allows to travel faster while limiting its optical flow. Not having any optical flow (as in traditional teleport paradigms) has been shown to help reduce cybersickness, but can also cause disorientation. By interlacing continuous locomotion with teleportation we showed that user can travel faster without compromising spatial updating

The Aha! Experience of Spatial Reorientation

The experience of spatial re-orientation is investigated as an instance of the wellknown phenomenon of the Aha! moment. The research question is: What are the visuospatial conditions that are most likely to trigger the spatial Aha! experience? The literature suggests that spatial re-orientation relies mainly on the geometry of the environment and a visibility graph analysis is used to quantify the visuospatial information. Theories from environmental psychology point towards two hypotheses. The Aha! experience may be triggered by a change in the amount of visual information, described by the isovist properties of area and revelation, or by a change in the complexity of the visual information associated with the isovist properties of clustering coefficient and visual control. Data from participants’ exploratory behaviour and EEG recordings are collected during wayfinding in virtual reality urban environments. Two types of events are of interest here: (a) sudden changes of the visuospatial information preceding subjects' response to investigate changes in EEG power; and (b) participants brain dynamics (Aha! effect) just before the response to examine differences in isovist values at this location. Research on insights, time-frequency analysis of the P3 component and findings from navigation and orientation studies suggest that the spatial Aha! experience may be reflected by: a parietal alpha power decrease associated with the switch of the representation and a frontocentral theta increase indexing spatial processing during decision-making. Single-trial time-frequency analysis is used to classify trials into two conditions based on the alpha/theta power differences between a 3s time-period before participants’ response and a time-period of equal duration before that. Behavioural results show that participants are more likely to respond at locations with low values of clustering coefficient and high values of visual control. The EEG analysis suggests that the alpha decrease/theta increase condition occurs at locations with significantly lower values of clustering coefficient and higher values of visual control. Small and large decreases in clustering coefficient, just before the response, are associated with significant differences in delta/theta power. The values of area and revelation do not show significant differences. Both behavioural and EEG results suggest that the Aha! experience of re-orientation is more likely to be triggered by a change in the complexity of the visual-spatial environment rather than a change in the amount, as measured by the relevant isovist properties

Mice learn multi-step routes by memorizing subgoal locations

The behavioral strategies that mammals use to learn multi-step routes are unknown. In this study, we investigated how mice navigate to shelter in response to threats when the direct path is blocked. Initially, they fled toward the shelter and negotiated obstacles using sensory cues. Within 20 min, they spontaneously adopted a subgoal strategy, initiating escapes by running directly to the obstacle’s edge. Mice continued to escape in this manner even after the obstacle had been removed, indicating use of spatial memory. However, standard models of spatial learning—habitual movement repetition and internal map building—did not explain how subgoal memories formed. Instead, mice used a hybrid approach: memorizing salient locations encountered during spontaneous ‘practice runs’ to the shelter. This strategy was also used during a geometrically identical food-seeking task. These results suggest that subgoal memorization is a fundamental strategy by which rodents learn efficient multi-step routes in new environments