Power spectrum model of visual masking: simulations and empirical data

In the study of the spatial characteristics of the visual channels, the power spectrum model of visual masking is one of the most widely used. When the task is to detect a signal masked by visual noise, this classical model assumes that the signal and the noise are previously processed by a bank of linear channels and that the power of the signal at threshold is proportional to the power of the noise passing through the visual channel that mediates detection. The model also assumes that this visual channel will have the highest ratio of signal power to noise power at its output. According to this, there are masking conditions where the highest signal-to-noise ratio (SNR) occurs in a channel centered in a spatial frequency different from the spatial frequency of the signal (off-frequency looking). Under these conditions the channel mediating detection could vary with the type of noise used in the masking experiment and this could affect the estimation of the shape and the bandwidth of the visual channels. It is generally believed that notched noise, white noise and double bandpass noise prevent off-frequency looking, and high-pass, low-pass and bandpass noises can promote it independently of the channel's shape. In this study, by means of a procedure that finds the channel that maximizes the SNR at its output, we performed numerical simulations using the power spectrum model to study the characteristics of masking caused by six types of one-dimensional noise (white, high-pass, low-pass, bandpass, notched, and double bandpass) for two types of channel's shape (symmetric and asymmetric). Our simulations confirm that (1) high-pass, low-pass, and bandpass noises do not prevent the off-frequency looking, (2) white noise satisfactorily prevents the off-frequency looking independently of the shape and bandwidth of the visual channel, and interestingly we proved for the first time that (3) notched and double bandpass noises prevent off-frequency looking only when the noise cutoffs around the spatial frequency of the signal match the shape of the visual channel (symmetric or asymmetric) involved in the detection. In order to test the explanatory power of the model with empirical data, we performed six visual masking experiments. We show that this model, with only two free parameters, fits the empirical masking data with high precision. Finally, we provide equations of the power spectrum model for six masking noises used in the simulations and in the experiments.

Phenomenological model of visual acuity

We propose in this work a model for describing visual acuity (VV) as a function of defocus and pupil diameter. Although the model is mainly based on geometrical optics, it also incorporates nongeometrical effects phenomenologically. Compared to similar visual acuity models, the proposed one considers the effect of astigmatism and the variability of best corrected VV among individuals; it also takes into account the accommodation and the “tolerance to defocus,” the latter through a phenomenological parameter. We have fitted the model to the VV data provided in the works of Holladay et al. and Peters, showing the ability of this model to accurately describe the variation of VV against blur and pupil diameter. We have also performed a comparison between the proposed model and others previously published in the literature. The model is mainly intended for use in the design of ophthalmic compensations, but it can also be useful in other fields such as visual ergonomics, design of visual tests, and optical instrumentation.

Tener hambre de luz y devorar una estrella: la poesía de J.E. Eielson

The present Doctoral Thesis is framed within the study of the poetry of the great Peruvian artist Jorge Eduardo Eielson (April 13, 1924 – March 8, 2006). In general terms, it focuses on the symbols that articulate both his literary productions and his work in the field of visual arts. Throughout this project, I used the principles of the modern semiotics as well the myth criticism theory developed by Gilbert Durand in his work The Anthropological Structures of the Imaginary as the basis. Following the assumption of considering Eielsońs work as an indivisible whole, in contrast to many studies that often attempted to analyse part of his creative work by privileging one medium over the others, I analyzed each symbol in all its forms, looked at its presence and relevance in his entire work and sought the archetypal level of each term. For this task, the works of Joseph Campbell and Mircea Eliade provided valuable guidances. At the beginning of this study I present a short author's biography, in order to help to understand the circumstances under which his poems were composed. (Let us remember that most of his books were published many years after their conception). Throughout this chapter, I have carefully considered the Lima period, his relationship with his first mentor, the anthropologist and writer José María Arguedas who introduced him to the knowledge of the ancient civilizations of Peru, his link with the literary circles of Lima and his first acknowledgments: the National Poetry Award (1944) and the National Drama Award (1948)...