Learning Linear, Sparse, Factorial Codes

In previous work (Olshausen & Field 1996), an algorithm was described for learning linear sparse codes which, when trained on natural images, produces a set of basis functions that are spatially localized, oriented, and bandpass (i.e., wavelet-like). This note shows how the algorithm may be interpreted within a maximum-likelihood framework. Several useful insights emerge from this connection: it makes explicit the relation to statistical independence (i.e., factorial coding), it shows a formal relationship to the algorithm of Bell and Sejnowski (1995), and it suggests how to adapt parameters that were previously fixed.

Factorial Hidden Markov Models

We present a framework for learning in hidden Markov models with distributed state representations. Within this framework, we derive a learning algorithm based on the Expectation--Maximization (EM) procedure for maximum likelihood estimation. Analogous to the standard Baum-Welch update rules, the M-step of our algorithm is exact and can be solved analytically. However, due to the combinatorial nature of the hidden state representation, the exact E-step is intractable. A simple and tractable mean field approximation is derived. Empirical results on a set of problems suggest that both the mean field approximation and Gibbs sampling are viable alternatives to the computationally expensive exact algorithm.

Translation Invariance in Object Recognition, and Its Relation to Other Visual Transformations

Human object recognition is generally considered to tolerate changes of the stimulus position in the visual field. A number of recent studies, however, have cast doubt on the completeness of translation invariance. In a new series of experiments we tried to investigate whether positional specificity of short-term memory is a general property of visual perception. We tested same/different discrimination of computer graphics models that were displayed at the same or at different locations of the visual field, and found complete translation invariance, regardless of the similarity of the animals and irrespective of direction and size of the displacement (Exp. 1 and 2). Decisions were strongly biased towards same decisions if stimuli appeared at a constant location, while after translation subjects displayed a tendency towards different decisions. Even if the spatial order of animal limbs was randomized ("scrambled animals"), no deteriorating effect of shifts in the field of view could be detected (Exp. 3). However, if the influence of single features was reduced (Exp. 4 and 5) small but significant effects of translation could be obtained. Under conditions that do not reveal an influence of translation, rotation in depth strongly interferes with recognition (Exp. 6). Changes of stimulus size did not reduce performance (Exp. 7). Tolerance to these object transformations seems to rely on different brain mechanisms, with translation and scale invariance being achieved in principle, while rotation invariance is not.

Composición factorial de la versión española de la Spence Children Anxiety Scale (SCAS).

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An??lisis de la estructura factorial de las puntuaciones de la 'Preschool and Kindergarten Behavior Scale' en poblaci??n espa??ola

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Uso de R y GRASS para la obtención de mapas de disponibilidad de hábitat mediante análisis factorial de nicho

It is possible to obtain habitat suitability maps using several applications like "Biomapper" v. 3.1.5 (http://www2.unil.ch/biomapper) or the "adehabitat" library v. 1.2.1, developed to be used within R program (http//www.R-project.org)

Estructura factorial de la adaptaci??n espa??ola de la Escala de Identificaci??n Grupal de Tarrant

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El an??lisis factorial de datos ipsativos : un estudio de simulaci??n

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Evaluación de la equivalencia factorial y métrica de la Sexual Assertiveness Scale (SAS) por sexo.

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Desarrollo del cuestionario de agresividad proactiva-reactiva para profesores : estructura factorial y propiedades psicom??tricas

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Adaptaci??n al castellano y estructura factorial del Denison Organizational Culture Survey

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Procedimientos gr??ficos para evaluar la consistencia intra-individual en el an??lisis factorial de ??tems

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An??lisis factorial confirmatorio del ??ndice de Sensibilidad a la Ansiedad para Ni??os

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Liderazgo transformacional y liderazgo transaccional : un an??lisis de la estructura factorial del Multifactor Leadership Questionnaire (MLQ) en una muestra espa??ola

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Estructura factorial y consistencia interna de la versi??n espa??ola del Parenting Stress Index-Short Form

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