What does the spike of a sensory neuron mean? This is a fundamental question in computational neuroscience. Conventional approaches provide an answer based on correlation between spike pattern and the stimulus that caused it. However, these approaches do not satisfactorily explain how the brain, which does not have direct knowledge of the world or the stimuli, can achieve this task. This thesis frames the problem in terms of a task for a simulated agent and provides a solution based on an approach which regards action as necessary for acquiring the meaning of neural spikes. This approach differs from some others in that it proposes a new criterion called the sensory invariance criterion, which can be used to associate meaning to spike patterns in terms of action sequences the agent generates. This criterion forms the basis of the Sensory Invariance Driven Action (SIDA) framework presented in this thesis. This framework is implemented in a reinforcement learning agent and the results indicate that the agent can successfully learn to associate meaning to the sensor activity in terms of specific actions which reflect the properties of the stimulus. Further behavioral experiments on the agent show that this framework allows the agent to learn the meaning of complex (spatiotemporal) spike patterns. The successful learning exhibited by the agent raises hopes that SIDA can be used to build agents with natural semantics.

Zernike moments are sets of mathematical quantities that uniquely characterize an image. It is known that they are invariant under rotation and reflection and robust to noise. In this thesis several other algorithms have been used to calculate these moments. The intent of this thesis is: 1. to use the classical method and the algorithms to reconstruct an image using Zernike moments and study their accuracy and 2. to examine if the invariance and noise insensitivity property of the calculated Zernike moments are upheld by these procedures. It is found that the constructed images using these algorithms do not resemble the original image. This prevents us from carrying out further study of these algorithms. The classical method has been successfully used to reconstruct an image when the height and width are equal. The classical method is also shown to be invariant under rotation and reflection and robust to Poisson noise. xxxvii

Zernike moments are sets of mathematical quantities that uniquely characterize an image. It is known that they are invariant under rotation and reflection and robust to noise. In this thesis several other algorithms have been used to calculate these moments. The intent of this thesis is: 1. to use the classical method and the algorithms to reconstruct an image using Zernike moments and study their accuracy and 2. to examine if the invariance and noise insensitivity property of the calculated Zernike moments are upheld by these procedures. It is found that the constructed images using these algorithms do not resemble the original image. This prevents us from carrying out further study of these algorithms. The classical method has been successfully used to reconstruct an image when the height and width are equal. The classical method is also shown to be invariant under rotation and reflection and robust to Poisson noise. xxxvii

[Truncated abstract] This thesis presents the design, construction and operation of a new rotating mod- ern Michelson-Morley test of Lorentz invariance. The experiment measures the isotropy of the speed of light by comparing the frequencies of two orthogonally ori- ented cryogenic sapphire whispering gallery mode resonators. Putative violations of Lorentz invariance will manifest as periodic variations in the difference frequency between the two resonators, related to the changing orientation of the experiment with respect to a preferred cosmological frame. Actively rotating the experiment is advantageous for three reasons. Firstly, by careful selection of the rotation frequency in the laboratory we are able to sample the isotropy of the speed of light at a rate that coincides with the optimal frequency instabilities of the oscillators (18 seconds). Secondly, the statistics of this exper- iment are improved with respect to non-rotating (stationary) experiments, which rely on the motion of the Earth to sample the isotropy of the speed of light. This results from integrating over more periods of rotation per unit of time, compared to the sidereal rotation experienced by stationary experiments. ... Many noise sources and systematic disturbances have been characterized and the operation of the experiment optimized. Two frequencies are generated at 10 GHz with 226 kHz separation, exhibiting a fractional frequency instability of less than 2x10-14 from 5 to 500 seconds. Furthermore, the work includes a detailed analysis of the experiment within the Standard Model Extension and Robertson, Mansouri and Sexl frameworks. The sensitivity of the experiment to violations of Lorentz invariance has been derived in each of these frameworks, for both short data set and the complete full year analysis. The data has been analysed using two separate data analysis techniques, which were optimised for noise present in the data. We have operated the experiment over the course of more than one year, collect- ing data more than 30 percent of the time. By analysing over 1 year of data we were able to set the first independent limits on 8 parameters in the photon sector of the Standard Model Extension as low as 10-16 for Ke- and 10-12 for Ko+ parameters, improving upon previous non-rotating experiments by up to an order of magnitude. We have also set new a new limit on the isotropy parameter PMM = 9.4(8.1)x10-11 of the Robertson, Mansouri and Sexl framework, which is a factor of 25 improvement.

Bibliography: leaves 237-246. / The concept of invariance in hypothesis testing is discussed for purposes of target detection. Invariant tests are proposed and analysed in two contexts. The first involves the use of cyclic permutation invariance as a solution to detecting targets with unknown location in noise. An invariance condition is used to eliminate the target location parameter, and a uniformly most powerful test developed for the reduced data. The test is compared with conventional solutions, and shown to be more powerfu. The difference however is slight, justifying the simpler formulations. This conclusion continues to hold even when additional unknown noise parameters are introduced.

Ongoing expansion of digital images requires new methods for sorting, browsing, and sear- ching through huge image databases. This is a domain of Content-Based Image Retrieval (CBIR) systems, which are database search engines for images. A user typically submit a query image or series of images and the CBIR system tries to find and to retrieve the most similar images from the database. Optimally, the retrieved images should not be sensitive to circumstances during their acquisition. Unfortunately, the appearance of natural objects and materials is highly illumination and viewpoint dependent. This work focuses on representation and retrieval of homogeneous images, called textu- res, under the circumstances with variable illumination and texture rotation. We propose a novel illumination invariant textural features based on Markovian modelling of spatial tex- ture relations. The texture is modelled by Causal Autoregressive Random field (CAR) or Gaussian Markov Random Field (GMRF) models, which allow a very efficient estimation of its parameters, without the demanding Monte Carlo minimisation. Subsequently, the estimated model parameters are transformed into the new illumination invariants, which represent the texture. We derived that our textural representation is invariant to changes of illumination intensity and...

Objective: Mindfulness or the full attention state is a factor that contributes to the successful process of aging. This study aims to evaluate the evidence of validity, on the basis of the internal structure, convergent and discriminant validity, reliability and factorial invariance across gender, for the five items Mindful Attention Awareness Scale (MAAS-5) within a sample of older adults. Methods: The participants were 323 Peruvian older adults, consisting of 160 women and 163 men, whose average ages were 68.58 (S.D = 7.23) and 68.91 years (S.D = 7.12), respectively. In addition to the MAAS-5, the Satisfaction with Life Scale and the Patient Health Questionnaire-2 were administered. Results: The Confirmatory Factor Analysis indicates that the one-factor structure of the MAAS-5 presents adequate fit for the total sample (χ2 = 11.24, df = 5, χ2/df = 2.25, CFI =.99, RMSEA =.06 [90%CI:.01,.11]; and SRMR =.025), as well as for the sub-samples of men and women. This one-factor solution presents adequate internal consistency (ω = 80 [95%CI:.76 -.82]) and it is invariant across gender. Regarding convergent validity, high scores in the MAAS are associated with a greater satisfaction with life (r =.88, p<.01 [95%CI:.85,.95]) and less depression (r = −.56, p<.01 [95%CI: −.48, −.77]) in older adults. Conclusions: The preliminary results back the use of the MAAS-5 as a self-report measure of mindfulness that has an adequate unifactorial structure that is reliable and invariant across gender for measuring the full attention state in elderly Peruvians.

Introduction: Owing to its importance in the development and evaluation of health policies in favor of the general population, there is currently a greater interest in the study of well-being. Therefore, a valid and reliable measurement of well-being is necessary. In this context, this study evaluated the evidence of validity based on the internal structure, reliability, and factor invariance by sex of the General Well-Being Index (who-5 wbi). Materials and Methods: A total of 499 university students (female = 271; male = 228) from the city of Trujillo, Peru, participated in the study. A confirmatory factor analysis, reliability by internal consistency, and factor invariance by sex were performed using a multigroup analysis. Results: The confirmatory factor analysis indicated that the 5-dimensional model with 5 correlated errors of items 1 and 4 presented a good fit (χ² = 9.667 [gl = 4], p > 0.05; χ²/gl = 2.416; cfi = 0.994; rmsea = 0.053 [ic90% 0.006–0.097]; srmr = 0.018). In addition, acceptable reliability (ω = 0.758) and factor invariance by sex were reported. Conclusion: The who-5 wbi demonstrated empirical evidence in favor of validity based on internal structure, reliability of scores, and factor invariance that allow for a useful and rapid instrument for measuring subjective well-being in university students.

The Interpersonal Theory of Suicide (ITS) has garnered much attention in the literature. Studies that have examined ITS among Black and other racially/ethnically diverse populations continue to be met with inconsistent results. This suggests the need to confirm measurement equivalence across populations to improve accuracy in identifying individuals who are at increased risk for suicide. This study examined measurement invariance of the Interpersonal Needs Questionnaire (INQ) and Acquired Capability for Suicide Scale (ACSS) across White and Black racial groups using two college student samples. Multigroup confirmatory factor analyses were conducted from Sample 1, a group of 1,019 (86.8% White) students from a midwestern university, and from Sample 2, a group of 1,664 (82.3% White) students from a southern university. The INQ demonstrated configural, metric, and scalar invariance for Sample 1, but did not demonstrate invariance at any measurement level for Sample 2. The ACSS did not meet configural, metric, or scalar invariance in Sample 1 or Sample 2. These results suggest the presence of systematic bias against Black respondents on both the INQ and ACSS. These results also indicate the need for more race-related and culture-specific measures of suicide risk.

Yes / Background: Human vision is vital in determining our interaction with the outside world. In this study we characterize our ability to judge changes in the direction of motion of objects-a common task which can allow us either to intercept moving objects, or else avoid them if they pose a threat. Methodology/Principal Findings: Observers were presented with objects which moved across a computer monitor on a linear path until the midline, at which point they changed their direction of motion, and observers were required to judge the direction of change. In keeping with the variety of objects we encounter in the real world, we varied characteristics of the moving stimuli such as velocity, extent of motion path and the object size. Furthermore, we compared performance for moving objects with the ability of observers to detect a deviation in a line which formed the static trace of the motion path, since it has been suggested that a form of static memory trace may form the basis for these types of judgment. The static line judgments were well described by a 'scale invariant' model in which any two stimuli which possess the same two-dimensional geometry (length/width) result in the same level of performance. Performance for the moving objects was entirely different. Irrespective of the path length, object size or velocity of motion, path deviation thresholds depended simply upon the duration of the motion path in seconds. Conclusions/Significance: Human vision has long been known to integrate information across space in order to solve spatial tasks such as judgment of orientation or position. Here we demonstrate an intriguing mechanism which integrates direction information across time in order to optimize the judgment of path deviation for moving objects. / Wellcome Trust, Leverhulme Trust, NIH