2,261 research outputs found
Chemical based communication and its role in decision making within the social insects
This thesis investigates chemical communication and decision making in a stingless bee (Tetragonisca angustula) and two species of ants (Lasius flavus and L. niger). Complex
chemical signalling and seemingly elaborate behavioural patterns based upon decisions made by individuals of a colony have facilitated the evolution of social living in these insects. This thesis investigates two important features of social living that involve these features: nest mate recognition and navigation. The first part of this thesis (Chapter 3 and Appendix 3) investigates nestmate recognition and nest defence in the Neotropical stingless bee T. angustula. In Chapter 3, two mechanisms are investigated which could potentially facilitate the extremely efficient nest mate recognition system, previously demonstrated in this bee species. Both are found to play no role which will enable further work to focus on the few remaining possibilities.
The second part of this thesis (chapters 4-6) focuses on navigational decision making in two common British ant species with contrasting ecologies. Chapter 4 investigates how L. niger foragers adapt to foraging at night when the visual cues, so important to these ants for diurnal foraging, are unavailable. This study showed that nocturnal foraging is achieved in these ants by increasing trail pheromone deposition while concomitantly switching to a greater reliance on these cues to navigate. Chapter 5 contrasts the navigational strategies and capabilities of L. niger with another Lasius ant species, L. flavus, and demonstrates how these species can flexibly switch dependency between available navigational cues to cope with foraging within a fluxional ecological environment. Finally, Chapter 6 focuses on the glandular components and trail pheromone of L. flavus by measuring behavioural responses to glandular constituents and identifying the glandular source of the trail pheromone. The aim was to also identify the trail pheromone(s) but due to time constraints this was not possible. However, a new methodology that simplifies the process of identifying trail pheromone components was developed and is described. Furthermore, this study has laid the foundations for further work to establish if the compound prevalent in the Dufour glands’ of L. flavus does indeed serve as an antibacterial agent within the humid nest environment
Short and medium range navigation and its relationship to cognitive mapping and associative learning
Varied levels of fructose consumption induce physiological, cognitive, and mitochondrial alterations in aged female rats
Since the 1970s, fructose consumption has dramatically increased within the United States, as well as the world. While adolescents tend to be the largest consumer of fructose, mostly seen in the form of sugary beverages, the consequences of a high fructose diet started in adulthood can also have severe implications on physiological parameters as well as cognition. Several studies have linked fructose consumption to metabolic syndrome, a clustering of symptoms related to overall health, with particular emphasis placed on obesity, type II diabetes, and the relationship with Alzheimer’s Disease. These findings largely stem from the outcomes of studies on cognition, both in humans and rats, assessing the extent to which fructose consumption alters cognitive flexibility. Aging alone is a factor in cognitive decline, yet the extent to which age interacts with diet is largely unknown. Additionally, more emphasis has been placed on uncovering the relationship between diet and mitochondrial respiration as a possible explanation for sex-specific and age-related differences seen in relation to metabolic stress. Mitochondria are particularly vulnerable to metabolic disturbances, and as such, synaptosomal mitochondria in the hippocampus and prefrontal cortex were analyzed in this study. Surmountable evidence can conclude the effects of a fructose-rich diet on the cognition, behavior, and mitochondrial respiration of male rats, yet females are often neglected from studies. Males and females are equally susceptible to the deleterious effects of fructose, but the manifestation of these outcomes differ significantly between the sexes, according to research from our group. Several theories illuminate estrogen as a neuroprotective hormone that allows females to resist the deleterious effects on cognition, which can explain the negative implications of a high fructose diet being displayed in post-menopausal women only. However, females do seem to be more susceptible to physiological perturbations, and as such remains a point of interest. I therefore determined the extent to which a high fructose diet (55% fructose – 55FD) and a medium fructose diet (18% fructose – 18FD) differentially impacted the physiological parameters, cognition, and mitochondrial respiration of 12-month-old (aged) female rats. Additionally, I examined the potential of estrogen as a neuroprotective factor by administering a high fructose diet to ovariectomized and non-ovariectomized 6-month-old female rats. In the first experimental group, the 18FD group showed significantly higher body weights than their counterparts, while amount consumed and caloric efficiency was not significantly distinct. Additionally, all diet groups showed cognitive rigidity, and the 18FD group displayed increased levels of OCR in the hippocampus. In the second experimental group, there were no implications that estrogen/estradiol played a significant role in protecting non-ovariectomized females from the deleterious effects of a high fructose diet.
In this thesis, I will outline current literature on fructose, how it is metabolized, and the associated outcomes of consuming fructose-rich diets. In addition, I describe the experimental set-up and the assessments performed in order to demonstrate the effects of fructose on physiological, cognitive, and mitochondrial function in female Wistar rats. I then describe the results and finally discuss the interpretation of these results as well as highlight potential future directions for this research. This thesis should aid in further illuminating the consequences of consuming fructose in adult females, the extent to which cognition and associated diseases are affected by mitochondrial dysfunction, and the role estrogen plays in sheltering this effect
Engineering evolutionary control for real-world robotic systems
Evolutionary Robotics (ER) is the field of study concerned with the application
of evolutionary computation to the design of robotic systems. Two main
issues have prevented ER from being applied to real-world tasks, namely scaling to
complex tasks and the transfer of control to real-robot systems. Finding solutions
to complex tasks is challenging for evolutionary approaches due to the bootstrap
problem and deception. When the task goal is too difficult, the evolutionary process
will drift in regions of the search space with equally low levels of performance
and therefore fail to bootstrap. Furthermore, the search space tends to get rugged
(deceptive) as task complexity increases, which can lead to premature convergence.
Another prominent issue in ER is the reality gap. Behavioral control is typically
evolved in simulation and then only transferred to the real robotic hardware when
a good solution has been found. Since simulation is an abstraction of the real
world, the accuracy of the robot model and its interactions with the environment
is limited. As a result, control evolved in a simulator tends to display a lower
performance in reality than in simulation.
In this thesis, we present a hierarchical control synthesis approach that enables
the use of ER techniques for complex tasks in real robotic hardware by mitigating
the bootstrap problem, deception, and the reality gap. We recursively decompose
a task into sub-tasks, and synthesize control for each sub-task. The individual
behaviors are then composed hierarchically. The possibility of incrementally
transferring control as the controller is composed allows transferability issues to
be addressed locally in the controller hierarchy. Our approach features hybridity,
allowing different control synthesis techniques to be combined. We demonstrate
our approach in a series of tasks that go beyond the complexity of tasks where ER
has been successfully applied. We further show that hierarchical control can be applied
in single-robot systems and in multirobot systems. Given our long-term goal
of enabling the application of ER techniques to real-world tasks, we systematically
validate our approach in real robotic hardware. For one of the demonstrations in
this thesis, we have designed and built a swarm robotic platform, and we show the
first successful transfer of evolved and hierarchical control to a swarm of robots
outside of controlled laboratory conditions.A Robótica Evolutiva (RE) é a área de investigação que estuda a aplicação de
computação evolutiva na conceção de sistemas robóticos. Dois principais desafios
têm impedido a aplicação da RE em tarefas do mundo real: a dificuldade em solucionar
tarefas complexas e a transferência de controladores evoluídos para sistemas
robóticos reais. Encontrar soluções para tarefas complexas é desafiante para as
técnicas evolutivas devido ao bootstrap problem e à deception. Quando o objetivo
é demasiado difícil, o processo evolutivo tende a permanecer em regiões do espaço
de procura com níveis de desempenho igualmente baixos, e consequentemente não
consegue inicializar. Por outro lado, o espaço de procura tende a enrugar à medida
que a complexidade da tarefa aumenta, o que pode resultar numa convergência
prematura. Outro desafio na RE é a reality gap. O controlo robótico é tipicamente
evoluído em simulação, e só é transferido para o sistema robótico real quando uma
boa solução tiver sido encontrada. Como a simulação é uma abstração da realidade,
a precisão do modelo do robô e das suas interações com o ambiente é limitada,
podendo resultar em controladores com um menor desempenho no mundo real.
Nesta tese, apresentamos uma abordagem de síntese de controlo hierárquica
que permite o uso de técnicas de RE em tarefas complexas com hardware robótico
real, mitigando o bootstrap problem, a deception e a reality gap. Decompomos
recursivamente uma tarefa em sub-tarefas, e sintetizamos controlo para cada subtarefa.
Os comportamentos individuais são então compostos hierarquicamente.
A possibilidade de transferir o controlo incrementalmente à medida que o controlador
é composto permite que problemas de transferibilidade possam ser endereçados
localmente na hierarquia do controlador. A nossa abordagem permite
o uso de diferentes técnicas de síntese de controlo, resultando em controladores
híbridos. Demonstramos a nossa abordagem em várias tarefas que vão para além
da complexidade das tarefas onde a RE foi aplicada. Também mostramos que o
controlo hierárquico pode ser aplicado em sistemas de um robô ou sistemas multirobô.
Dado o nosso objetivo de longo prazo de permitir o uso de técnicas de
RE em tarefas no mundo real, concebemos e desenvolvemos uma plataforma de
robótica de enxame, e mostramos a primeira transferência de controlo evoluído e
hierárquico para um exame de robôs fora de condições controladas de laboratório.This work has been supported by the Portuguese Foundation for Science
and Technology (Fundação para a Ciência e Tecnologia) under the grants
SFRH/BD/76438/2011, EXPL/EEI-AUT/0329/2013, and by Instituto de Telecomunicações
under the grant UID/EEA/50008/2013
Creating proactive interference in immediate recall: building a dog from a dart, a mop and a fig
[Abstract]: Phonemic codes are accorded a privileged role in most current models of immediate serial recall, although their effects are apparent in short-term proactive interference (PI) effects as well. The current research looks at how assumptions concerning distributed representation and distributed storage involving both semantic and phonemic codes might be operationalized to produce PI in a short-term cued recall task. The four experiments reported here attempted to generate the phonemic characteristics of a non-rhyming, interfering foil from unrelated filler items in the same list. PI was observed when a rhyme of the foil was studied or when the three phonemes of the foil were distributed across three studied filler items. The results suggest that items in short-term memory are stored in terms of feature bundles and that all items are simultaneously available at retrieval
Exploring the relationship between spatial cognitive ability and movement ecology
Spatial cognitive ability is hypothesised to be a key determinant of animal movement patterns. However, empirical demonstrations linking intra-individual variations in spatial cognitive ability with movement ecology are rare. I reared ~200 simultaneously hatched pheasant chicks per year over three years in standardised conditions without parents, controlling for the confounding effects of experience, maternal influences and age. I tested the chicks on spatial cognitive tasks from three weeks old to obtain measures of inherent, early-life spatial cognitive ability. Each year, I released birds when 10 weeks old into an open-topped enclosure in woodland. Birds dispersed from this enclosure after about one-month. Importantly, all birds were released into the same, novel area simultaneously, thus their experiences and opportunities were standardised. I remotely tracked pheasant movement through either RFID antenna placed under 43 supplementary feeders situated throughout our field site (2016) or by using a novel reverse-GPS tracking system (2017-2018). Spatial cognitive ability, determined through binary spatial discrimination (2016) or a Barnes maze (2017), was related to the diversity of foraging sites an individual used (Chapter 2: 2016). Those with better spatial cognitive ability used a more diverse range of artificial feeders than poor performing counterparts, perhaps to retain a buffer of alternative foraging sites where resource profitability was known. I found no relationship between the timing of daily foraging onset between birds of differing cognitive ability (Chapter 3; 2016), which I had hypothesised to be a consequence of birds developing efficient routes between refuges and feeders. After establishing a reverse GPS system on our field site (Chapter 4: 2017), I collected more detailed information about pheasant movement and found that birds with higher accuracy scores on the cognition tasks initially moved between foraging and resting sites more slowly than inaccurate birds in novel environments, perhaps to gather more detailed information. Accurate birds increased their speed over one month to match the same speed as inaccurate birds. All birds increased the straightness of their routes at a similar rate. Lastly, I found intraspecific differences in the orientation strategy that birds used to solve a dual strategy maze task (Chapter 5: 2018). These differences predicted habitat use after release: birds that utilised landmarks (allocentric strategies) showed less aversion to urban habitats (farm buildings/yards) than egocentric/mixed strategy birds, which is potentially due to the presence of large, stable landmarks within these habitats. In this thesis, I provide several empirical links between spatial cognitive ability and movement ecology across a range of ecological contexts. I suggest that very specific cognitive processes may govern particular movement behaviours and that there is not one overarching general spatial ability.European Commissio
The Neural Basis of a Cognitive Map
It has been proposed that as animals explore their environment they build and maintain a cognitive map, an internal representation of their surroundings (Tolman, 1948). We tested this hypothesis using a task designed to assess the ability of rats to make a spatial inference (take a novel shortcut)(Roberts et al., 2007). Our findings suggest that rats are unable to make a spontaneous spatial inference. Furthermore, they bear similarities to experiments which have been similarly unable to replicate or support Tolman’s (1948) findings. An inability to take novel shortcuts suggests that rats do not possess a cognitive map (Bennett, 1996). However, we found evidence of alternative learning strategies, such as latent learning (Tolman & Honzik, 1930b) , which suggest that rats may still be building such a representation, although it does not appear they are able to utilise this information to make complex spatial computations.
Neurons found in the hippocampus show remarkable spatial modulation of their firing rate and have been suggested as a possible neural substrate for a cognitive map (O'Keefe & Nadel, 1978). However, the firing of these place cells often appears to be modulated by features of an animal’s behaviour (Ainge, Tamosiunaite, et al., 2007; Wood, Dudchenko, Robitsek, & Eichenbaum, 2000). For instance, previous experiments have demonstrated that the firing rate of place fields in the start box of some mazes are predictive of the animal’s final destination (Ainge, Tamosiunaite, et al., 2007; Ferbinteanu & Shapiro, 2003). We sought to understand whether this prospective firing is in fact related to the goal the rat is planning to navigate to or the route the rat is planning to take. Our results provide strong evidence for the latter, suggesting that rats may not be aware of the location of specific goals and may not be aware of their environment in the form of a contiguous map. However, we also found behavioural evidence that rats are aware of specific goal locations, suggesting that place cells in the hippocampus may not be responsible for this representation and that it may reside elsewhere (Hok, Chah, Save, & Poucet, 2013).
Unlike their typical activity in an open field, place cells often have multiple place fields in geometrically similar areas of a multicompartment environment (Derdikman et al., 2009; Spiers et al., 2013). For example, Spiers et al. (2013) found that in an environment composed of four parallel compartments, place cells often fired similarly in multiple compartments, despite the active movement of the rat between them. We were able to replicate this phenomenon, furthermore, we were also able to show that if the compartments are arranged in a radial configuration this repetitive firing does not occur as frequently. We suggest that this place field repetition is driven by inputs from Boundary Vector Cells (BVCs) in neighbouring brain regions which are in turn greatly modulated by inputs from the head direction system. This is supported by a novel BVC model of place cell firing which predicts our observed results accurately.
If place cells form the neural basis of a cognitive map one would predict spatial learning to be difficult in an environment where repetitive firing is observed frequently (Spiers et al., 2013). We tested this hypothesis by training animals on an odour discrimination task in the maze environments described above. We found that rats trained in the parallel version of the task were significantly impaired when compared to the radial version. These results support the hypothesis that place cells form the neural basis of a cognitive map; in environments where it is difficult to discriminate compartments based on the firing of place cells, rats find it similarly difficult to discriminate these compartments as shown by their behaviour.
The experiments reported here are discussed in terms of a cognitive map, the likelihood that such a construct exists and the possibility that place cells form the neural basis of such a representation. Although the results of our experiments could be interpreted as evidence that animals do not possess a cognitive map, ultimately they suggest that animals do have a cognitive map and that place cells form a more than adequate substrate for this representation
Algorithms for Robot Coverage Under Movement and Sensing Constraints
This thesis explores the problem of generating coverage paths—that is, paths that pass within some sensor footprint of every point in an environment—for mobile robots. It both considers models for which navigation is a solved problem but motions are constrained, as well for models in which navigation must be considered along with coverage planning because of the robot’s unreliable sensing and movements.
The motion constraint we adopt for the former is a common constraint, that of a Dubins vehicle. We extend previous work that solves this coverage problem as a traveling salesman problem (TSP) by introducing a practical heuristic algorithm to reduce runtime while maintaining near-optimal path length. Furthermore, we show that generating an optimal coverage path is NP-hard by reducing from the Exact Cover problem, which provides justification for our algorithm’s conversion of Dubins coverage instances to TSP instances. Extensive experiments demonstrate that the algorithm does indeed produce path lengths comparable to optimal in significantly less time.
In the second model, we consider the problem of coverage planning for a particular type of very simple mobile robot. The robot must be able to translate in a commanded direction (specified in a global reference frame), with bounded error on the motion direction, until reaching the environment boundary.
The objective, for a given environment map, is to generate a sequence of motions that is guaranteed to cover as large a portion of that environment as possible, in spite of the severe limits on the robot’s sensing and actuation abilities.
We show how to model the knowledge available to this kind of robot about its own position within the environment, show how to compute the region whose coverage can be guaranteed for a given plan, and characterize regions whose coverage cannot be guaranteed by any plan. We also describe an algorithm that generates coverage plans for this robot, based on a search across a specially-constructed graph. Simulation results demonstrate the effectiveness of the approach
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