Person:
Serrano Pedraza, Ignacio

First Name

Ignacio

Last Name

Serrano Pedraza

URI

https://hdl.handle.net/20.500.14352/80226

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Psicología

Department

Psicología Experimental, Procesos Cognitivos y Logopedia

Area

Psicología Básica

Identifiers

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Search Results

Now showing 1 - 9 of 9

Evidence for reciprocal antagonism between motion sensors tuned to coarse and fine features
(Journal of vision, 2007) Serrano Pedraza, Ignacio; Goddard, Paul; Derrington, Andrew M
Early visual processing analyses fine and coarse image features separately. Here we show that motion signals derived from fine and coarse analyses are combined in rather a surprising way: Coarse and fine motion sensors representing the same direction of motion inhibit one another and an imbalance can reverse the motion perceived. Observers judged the direction of motion of patches of filtered two-dimensional noise, centered on 1 and 3 cycles/deg. When both sets of noise were present and only the 3 cycles/deg noise moved, judgments were reversed at short durations. When both sets of noise moved, judgments were correct but sensitivity was impaired. Reversals and impairments occurred both with isotropic noise and with orientation-filtered noise. The reversals and impairments could be simulated in a model of motion sensing by adding a stage in which the outputs of motion sensors tuned to 1 and 3 cycles/deg and the same direction of motion were subtracted from one another. The subtraction model predicted and we confirmed in experiments with orientation-filtered noise that if the 1 cycle/deg noise flickered and the 3 cycles/deg noise moved, the 1 cycle/deg noise appeared to move in the opposite direction to the 3 cycles/deg noise even at long durations.
Single-band amplitude demodulation of Müller-Lyer illusion images
(The Spanish journal of psychology, 2007) Sierra Vázquez, Vicente; Serrano Pedraza, Ignacio
The 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.
Stereo vision requires an explicit encoding of vertical disparity.
(Journal of vision, 2009) Serrano Pedraza, Ignacio; Read, Jenny C A
Vertical disparities influence the perception of 3D depth, but little is known about the neuronal mechanisms underlying this. One possibility is that these perceptual effects are mediated by an explicit encoding of two-dimensional disparity. Recently, J. C. A. Read and B. G. Cumming (2006) pointed out that current psychophysical and physiological evidence is consistent with a much more economical one-dimensional encoding. Almost all relevant information about vertical disparity could in theory be extracted from the activity of purely horizontal-disparity sensors. Read and Cumming demonstrated that such a 1D system would experience Ogle's induced effect, a famous illusion produced by vertical disparity. Here, we test whether the brain employs this 1D encoding, using a version of the induced effect stimulus that simulates the viewing geometry at infinity and thus removes the cues which are otherwise available to the 1D model. This condition was compared to the standard induced effect stimulus, presented on a frontoparallel screen at finite viewing distance. We show that the induced effects experienced under the two conditions are indistinguishable. This rules out the 1D model proposed by Read and Cumming and shows that vertical disparity, including sign, must be explicitly encoded across the visual field.
Symmetrical interaction of sex and expression in face classification tasks
(Attention, Perception, and Psychophysics, 2009) Aguado Aguilar, Luis; García Gutiérrez, Ana; Serrano Pedraza, Ignacio
Classification of faces as to their sex or their expression—with sex and expression varying orthogonally—was studied in three experiments. In Experiment 1, expression classification was influenced by sex, with angry male faces being classified faster than angry female faces. Complementarily, sex classification was faster for happy than for angry female faces. In Experiment 2, mutual interaction of sex and expression was also found when the participants were asked to classify top and bottom face segments. In Experiment 3, a face inversion effect was found for both sex and expression classification of whole faces. However, a symmetrical interaction between sex and expression was again found. The results are discussed in terms of configural versus feature processing in the perception of face sex and expression and of their relevance to face perception models that postulate independent processing of different facial features.
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, Pedro
Recent 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.
Saccades and microsaccades during visual fixation, exploration, and search: foundations for a common saccadic generator.
(Journal of vision, 2008) Otero Millan, Jorge; Troncoso, Xoana G; Macknik, Stephen L; Serrano Pedraza, Ignacio; Martinez Conde, Susana
Microsaccades are known to occur during prolonged visual fixation, but it is a matter of controversy whether they also happen during free-viewing. Here we set out to determine: 1) whether microsaccades occur during free visual exploration and visual search, 2) whether microsaccade dynamics vary as a function of visual stimulation and viewing task, and 3) whether saccades and microsaccades share characteristics that might argue in favor of a common saccade-microsaccade oculomotor generator. Human subjects viewed naturalistic stimuli while performing various viewing tasks, including visual exploration, visual search, and prolonged visual fixation. Their eye movements were simultaneously recorded with high precision. Our results show that microsaccades are produced during the fixation periods that occur during visual exploration and visual search. Microsaccade dynamics during free-viewing moreover varied as a function of visual stimulation and viewing task, with increasingly demanding tasks resulting in increased microsaccade production. Moreover, saccades and microsaccades had comparable spatiotemporal characteristics, including the presence of equivalent refractory periods between all pair-wise combinations of saccades and microsaccades. Thus our results indicate a microsaccade-saccade continuum and support the hypothesis of a common oculomotor generator for saccades and microsaccades.
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, Vicente
It 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.
Procesos visuales de demodulación espacial
(2006) Serrano Pedraza, Ignacio; Sierra Vázquez, Vicente
Esta Tesis estudia el mecanismo visual implicado en el procesamiento de imágenes cuyas características no son accesibles a los canales o filtros del mecanismo de primer orden propuestos por la teoría multicanal. Esas imágenes se han denominado estímulos de segundo orden y el mecanismo implicado en su procesamiento, mecanismo de segundo orden. Los estímulos de segundo orden utilizados aquí son imágenes de contraste modulado (CM) y el esquema propuesto para demodular su contraste es el denominado filtro-rectificación-filtro (FRF). El propósito de la Tesis es completar algunos aspectos de ese esquema. En primer lugar, se ha probado la linealidad del mecanismo de segundo orden. En segundo lugar, se caracterizaron los filtros de la primera etapa del esquema FRF utilizando el paradigma de enmascaramiento y dos modelos de detección: canal fijo y canal óptimo (que tiene en cuenta el efecto de off-frequency looking). Se confirmó que la forma de la FTM de los canales es asimétrica y que su anchura de banda en octavas decrece con su frecuencia de pico. En tercer lugar, generalizando el paradigma de enmascaramiento al dominio de la modulación en amplitud, se caracterizaron los filtros de la segunda etapa. Para ello, se midieron los umbrales de detección de estímulos CM en los que la modulación sinusoidal del contraste fue enmascarada por ruido modulador paso-banda. Los resultados obtenidos sugieren que la segunda etapa se compone de un banco de filtros lineales solapados, selectivos a la frecuencia de modulación, que descomponen la envolvente de la imagen en el rango de 1 a 15 c/gav y cuya anchura de banda en octavas decrece con la frecuencia de pico del filtro. Así, esa estructura parece replicar la arquitectura funcional conocida del mecanismo de primer orden. Con estos resultados, se diseñó un modelo computable de demodulación visual de la amplitud que explica resultados experimentales previos y fenómenos de la percepción visual de la forma, como el agrupamiento perceptivo y la percepción de ilusiones geométricas cuyo espectro de Fourier carece de bajas frecuencias espaciales.
Legado Luis Simarro (web 2002-2021) https://webs.ucm.es/info/simarro/
(2002) Campos Bueno, José Javier; Serrano Pedraza, Ignacio
Se recoge el contenido de antigua la Web de la Universidad Complutense de Madrid https://webs.ucm.es/info/simarro/ desarrollada y mantenida por J.Javier Campos Bueno e Ignacio Serrano Pedraza durante los años 2002 a 2021. Se informa del origen del Legado con una cronología del periodo histórico durante el que vivió el Dr. Luis Simarro, que ocupó la primera Cátedra de Psicología Experimental desde el año 1902 hasta su muerte en 1921. En año 2002, centenario de la obtención de la cátedra, la Universidad Complutense presentó en la Biblioteca Histórica Marqués de Valdecilla la exposición Luis Simarro y la Psicología Científica en España. La exposición fue comisariada por H. Carpintero, J. Campos-Bueno y J. Bandrés. También se da noticia en la web de Marina Romero, ahijada del Dr. Simarro, catedrática de Literatura Española en la Universidad de Rutgers y notable poeta de la generación del 27. Marina Romero en 1992 donó a la Universidad Complutense un retrato de su padrino pintado por Luis de Madrazo.