Person: Sierra Vázquez, Vicente
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First Name
Vicente
Last Name
Sierra Vázquez
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Psicología
Department
Area
Psicología Básica
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Item Single-band amplitude demodulation of Müller-Lyer illusion images(The Spanish journal of psychology, 2007) Sierra Vázquez, Vicente; Serrano Pedraza, IgnacioThe perception of the Müller-Lyer illusion has previously been explained as a result of visual low band-pass spatial filtering, although, in fact, the illusion persists in band-pass and high-pass filtered images without visible low-spatial frequencies. A new theoretical framework suggests that our perceptual experience about the global spatial structure of an image corresponds to the amplitude modulation (AM) component (or its magnitude, also called envelope) of its AM-FM (alternatively, AM-PM) decomposition. Because demodulation is an ill-posed problem with a non-unique solution, two different AM-FM demodulation algorithms were applied here to estimate the envelope of images of Müller-Lyer illusion: the global and exact Daugman and Downing (1995) AMPM algorithm and the local and quasi-invertible Maragos and Bovik (1995) DESA. The images used in our analysis include the classic configuration of illusion in a variety of spatial and spatial frequency content conditions. In all cases, including those of images for which visual low-pass spatial filtering would be ineffective, the envelope estimated by single-band amplitude demodulation has physical distortions in the direction of perceived illusion. It is not plausible that either algorithm could be implemented by the human visual system. It is shown that the proposed second order visual model of pre-attentive segregation of textures (or "back-pocket" model) could recover the image envelope and, thus, explain the perception of this illusion even in Müller-Lyer images lacking low spatial frequencies.Item The effect of white-noise mask level on sinewave contrast detection thresholds and the critical-band-masking model(The Spanish journal of psychology, 2006) Serrano Pedraza, Ignacio; Sierra Vázquez, VicenteIt is known that visual noise added to sinusoidal gratings changes the typical U-shaped threshold curve which becomes flat in log-log scale for frequencies below 10c/deg when gratings are masked with white noise of high power spectral density level. These results have been explained using the critical-band-masking (CBM) model by supposing a visual filter-bank of constant relative bandwidth. However, some psychophysical and biological data support the idea of variable octave bandwidth. The CBM model has been used here to explain the progressive change of threshold curves with the noise mask level and to estimate the bandwidth of visual filters. Bayesian staircases were used in a 2IFC paradigm to measure contrast thresholds of horizontal sinusoidal gratings (0.25-8 c/deg) within a fixed Gaussian window and masked with one-dimensional, static, broadband white noise with each of five power density levels. Raw data showed that the contrast threshold curve progressively shifts upward and flattens out as the mask noise level increases. Theoretical thresholds from the CBM model were fitted simultaneously to the data at all five noise levels using visual filters with log-Gaussian gain functions. If we assume a fixed-channel detection model, the best fit was obtained when the octave bandwidth of visual filters decreases as a function of peak spatial frequency.Item Obtención de datos experimentales sobre imágenes con contenido emocional en el campus virtual UCM(II Jornada Campus Virtual UCM: cómo integrar investigación y docencia en el CV-UCM, 2005) Campos Bueno, José Javier; Serrano, Ignacio; Alorda, Tina; Sierra Vázquez, Vicente; Montoya, Pedro; Fernández-Valmayor Crespo, Alfredo; Fernández-Pampillón Cesteros, Ana María; Merino Granizo, JorgeLa realización de experimentos psicológicos on line es una práctica cada vez más frecuente en muchos laboratorios por las indudables ventajas que proporciona. El presente trabajo presenta un procedimiento que permite obtener datos experimentales sobre la evaluación de imágenes filtradas del International Affective Picture System en las dimensiones de valencia y afecto. Se ha utilizado la herramienta que proporciona WebCT (versión 4.1.) para construir exámenes y cuestionarios, describiendo los problemas y las estrategias seguidas.Item Low spatial frequency filtering modulates early brain processing of affective complex pictures(Neuropsychologia, 2007) Alorda, Catalina; Serrano Pedraza, Ignacio; Campos Bueno, José Javier; Sierra Vázquez, Vicente; Montoya, PedroRecent research on affective processing has suggested that low spatial frequency information of fearful faces provide rapid emotional cues to the amygdala, whereas high spatial frequencies convey fine-grained information to the fusiform gyrus, regardless of emotional expression. In the present experiment, we examined the effects of low (LSF, <15 cycles/image width) and high spatial frequency filtering (HSF, >25 cycles/image width) on brain processing of complex pictures depicting pleasant, unpleasant, and neutral scenes. Event-related potentials (ERP), percentage of recognized stimuli and response times were recorded in 19 healthy volunteers. Behavioral results indicated faster reaction times in response to unpleasant LSF than to unpleasant HSF pictures. Unpleasant LSF pictures and pleasant unfiltered pictures also elicited significant enhancements of P1 amplitudes at occipital electrodes as compared to neutral LSF and unfiltered pictures, respectively; whereas no significant effects of affective modulation were found for HSF pictures. Moreover, mean ERP amplitudes in the time between 200 and 500ms post-stimulus were significantly greater for affective (pleasant and unpleasant) than for neutral unfiltered pictures; whereas no significant affective modulation was found for HSF or LSF pictures at those latencies. The fact that affective LSF pictures elicited an enhancement of brain responses at early, but not at later latencies, suggests the existence of a rapid and preattentive neural mechanism for the processing of motivationally relevant stimuli, which could be driven by LSF cues. Our findings confirm thus previous results showing differences on brain processing of affective LSF and HSF faces, and extend these results to more complex and social affective pictures.