Person: Serrano Pedraza, Ignacio
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First Name
Ignacio
Last Name
Serrano Pedraza
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Psicología
Department
Psicología Experimental, Procesos Cognitivos y Logopedia
Area
Psicología Básica
Identifiers
4 results
Search Results
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Item Visual suppression in intermittent exotropia during binocular alignment.(Investigative ophthalmology & visual science, 2011) Serrano Pedraza, Ignacio; Manjunath, Vina; Osunkunle, Olaoluwakitan; Clarke, Michael P; Read, Jenny C APURPOSE To investigate the cortical mechanisms that prevent diplopia in intermittent exotropia (X(T)) during binocular alignment (orthotropia). METHODS The authors studied 12 X(T) patients aged 5 to 22 years. Seventy-five percent had functional stereo vision with stereoacuity similar to that of 12 age-matched controls (0.2-3.7 min arc). Identical face images were presented to the two eyes for 400 ms. In one eye, the face was presented at the fovea; in the other, offset along the horizontal axis with up to 12° eccentricity. The task was to indicate whether one or two faces were perceived. RESULTS All X(T) patients showed normal diplopia when the nonfoveal face was presented to nasal hemiretina, though with a slightly larger fusional range than age-matched controls. However, 10 of 12 patients never experienced diplopia when the nonfoveal face was presented to temporal hemiretina (i.e., when the stimulus simulated exodeviation). Patients showed considerable variability when the single image was perceived. Some patients suppressed the temporal stimulus regardless of which eye viewed it, whereas others suppressed a particular eye even when it viewed the foveal stimulus. In two patients, the simulated exodeviation might have triggered a shift from normal to anomalous retinal correspondence. CONCLUSIONS Antidiplopic mechanisms in X(T) can be reliably triggered by purely retinal information during orthotropia, but the nature of these mechanisms varies between patients.Item Multiple channels for horizontal, but only one for vertical corrugations? A new look at the stereo anisotropy.(Journal of vision, 2010) Serrano Pedraza, Ignacio; Read, Jenny C AStereo vision displays a well-known anisotropy: disparity-defined slant is easier to detect for rotations about a horizontal axis than about a vertical axis, and low-frequency sinusoidal depth corrugations are easier to detect when the corrugations are horizontal than when they are vertical. Here, we determined disparity thresholds for vertically and horizontally oriented depth corrugations with both sinusoidal and square-wave profiles. We found that the orientation anisotropy for square waves is much weaker than for sine waves and is almost independent of frequency. This weaker anisotropy for square waves can be explained by considering the Fourier harmonics present in the stimulus. Using linear models imported from the luminance and texture perception domain, the disparity thresholds for square waves can be very well predicted from those for sine waves, for both horizontally and vertically oriented corrugations. For horizontally oriented corrugations, models based on the root mean square of the output of a single linear channel or the output of multiple linear channels worked equally well. This is consistent with previous evidence suggesting that stereo vision has multiple channels tuned to different spatial frequencies of horizontally oriented disparity modulations. However, for vertically oriented corrugations, only the root mean squared output of a single linear channel explained the data. We suggest that the stereo anisotropy may arise because the stereo system possesses multiple spatial frequency channels for detecting horizontally oriented modulations in horizontal disparity, but only one for vertically oriented modulations.Item Spatial non-homogeneity of the antagonistic surround in motion perception.(Journal of vision, 2011) Serrano Pedraza, Ignacio; Hogg, Ellen L; Read, Jenny C AAt high contrast, duration thresholds for motion direction discrimination deteriorate with increasing stimulus size. This counterintuitive result has been explained by the center-surround antagonism present in the neurons of visual area MT. Conversely, at very low contrast, direction discrimination improves with increasing size, a result that has been explained by spatial summation. In this investigation, we study the effects of stimulus shape and contrast on center-surround antagonism. Using adaptive Bayesian staircases, we measured duration thresholds of 5 subjects for vertically oriented Gabor patches of 1 cycle/deg with two types of oval Gaussian windows, one vertically elongated (Sx = 0.35, Sy = 2.5 deg) and other horizontally elongated (Sx = 2.5, Sy = 0.35 deg) moving rightward or leftward at a speed of 2 deg/s. We found that at high contrast (92%) duration thresholds were lower for vertically than horizontally elongated windows. However, at low contrast (2.8%), we found that duration thresholds were lower for horizontally than vertically elongated windows. These asymmetric results mirror the spatial non-homogeneity of the antagonistic surround found in MT neurons and suggest that the underlying center-surround antagonism is stronger along the direction of motion.Item Independent mechanisms for bright and dark image features in a stereo correspondence task(Journal of vision, 2011) Read, Jenny C A; Vaz, Xavier A; Serrano Pedraza, IgnacioA pioneering study by J. M. Harris and A. J. Parker (1995) found that disparity judgments using random-dot stereograms were better for stimuli composed of mixed bright and dark dots than when the dots were all bright or all dark. They attribute this to an improvement in stereo correspondence. This result is hard to explain within current models of how stereo correspondence is achieved. However, their experiment varied task difficulty by adding disparity noise. We wondered if this might challenge mechanisms subsequent to the solution of the correspondence problem rather than mechanisms that solve the correspondence problem itself. If so, this would avoid the need to modify current models of stereo correspondence. We therefore repeated Harris and Parker's experiment using interocular decorrelation to vary task difficulty. This technique is believed to probe stereo correspondence more specifically. We observed the efficiency increase reported by Harris and Parker for mixed-polarity dots both using their original technique of disparity noise and using interocular decorrelation. We show that this effect cannot be accounted for by the stereo energy or by simple modifications of it. Our results confirm Harris and Parker's original conclusion that mixed-polarity dots specifically benefit stereo correspondence and point up the challenge to current models of this process.