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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Now showing 1 - 10 of 12

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 A
PURPOSE 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.
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 A
Stereo 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.
Testing the horizontal-vertical stereo anisotropy with the critical-band masking paradigm
(Journal of vision, 2013) Serrano Pedraza, Ignacio; Brash, Claire; Read, Jenny C A
Stereo vision has a well-known anisotropy: At low frequencies, horizontally oriented sinusoidal depth corrugations are easier to detect than vertically oriented corrugations (both defined by horizontal disparities). Previously, Serrano-Pedraza and Read (2010) suggested that this stereo anisotropy may arise because the stereo system uses multiple spatial-frequency disparity channels for detecting horizontally oriented modulations but only one for vertically oriented modulations. Here, we tested this hypothesis using the critical-band masking paradigm. In the first experiment, we measured disparity thresholds for horizontal and vertical sinusoids near the peak of the disparity sensitivity function (0.4 cycles/°), in the presence of either broadband or notched noise. We fitted the power-masking model to our results assuming a channel centered on 0.4 cycles/°. The estimated channel bandwidths were 2.95 octaves for horizontal and 2.62 octaves for vertical corrugations. In our second experiment we measured disparity thresholds for horizontal and vertical sinusoids of 0.1 cycles/° in the presence of band-pass noise centered on 0.4 cycles/° with a bandwidth of 0.5 octaves. This mask had only a small effect on the disparity thresholds, for either horizontal or vertical corrugations. We simulated the detection thresholds using the power-masking model with the parameters obtained in the first experiment and assuming either single-channel and multiple-channel detection. The multiple-channel model predicted the thresholds much better for both horizontal and vertical corrugations. We conclude that the human stereo system must contain multiple independent disparity channels for detecting horizontally oriented and vertically oriented depth modulations.
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.
Moderate acute alcohol intoxication has minimal effect on surround suppression measured with a motion direction discrimination task.
(Journal of vision, 2015) Read, Jenny C A; Georgiou, Renos; Brash, Claire; Yazdani, Partow; Whittaker, Roger; Trevelyan, Andrew J; Serrano Pedraza, Ignacio
A well-studied paradox of motion perception is that, in order to correctly judge direction in high-contrast stimuli, subjects need to observe motion for longer in large stimuli than in small stimuli. This effect is one of several perceptual effects known generally as "surround suppression." It is usually attributed to center-surround antagonism between neurons in visual cortex, believed to be mediated by GABA-ergic inhibition. Accordingly, several studies have reported that this index of surround suppression is reduced in groups known to have reduced GABA-ergic inhibition, including older people and people with schizophrenia and major depressive disorder. In this study, we examined the effect on this index of moderate amounts of ethanol alcohol. Among its many effects on the nervous system, alcohol potentiates GABA-ergic transmission. We therefore hypothesized that it should further impair the perception of motion in large stimuli, resulting in a stronger surround-suppression index. This prediction was not borne out. Alcohol consumption slightly worsened duration thresholds for both large and small stimuli, but their ratio did not change significantly.
Stereoscopic vision in the absence of the lateral occipital cortex.
(PloS one, 2010) Read, Jenny C A; Phillipson, Graeme P; Serrano Pedraza, Ignacio; Milner, A David; Parker, Andrew J
Both dorsal and ventral cortical visual streams contain neurons sensitive to binocular disparities, but the two streams may underlie different aspects of stereoscopic vision. Here we investigate stereopsis in the neurological patient D.F., whose ventral stream, specifically lateral occipital cortex, has been damaged bilaterally, causing profound visual form agnosia. Despite her severe damage to cortical visual areas, we report that DF's stereo vision is strikingly unimpaired. She is better than many control observers at using binocular disparity to judge whether an isolated object appears near or far, and to resolve ambiguous structure-from-motion. DF is, however, poor at using relative disparity between features at different locations across the visual field. This may stem from a difficulty in identifying the surface boundaries where relative disparity is available. We suggest that the ventral processing stream may play a critical role in enabling healthy observers to extract fine depth information from relative disparities within one surface or between surfaces located in different parts of the visual field.
The Stereoscopic Anisotropy Develops During Childhood
(Investigative ophthalmology & visual science, 2016) Serrano Pedraza, Ignacio; Herbert, William; Villa Laso, Laura; Widdall, Michael; Vancleef, Kathleen; Read, Jenny C A
PURPOSE Human vision has a puzzling stereoscopic anisotropy: horizontal depth corrugations are easier to detect than vertical depth corrugations. To date, little is known about the function or the underlying mechanism responsible for this anisotropy. Here, we aim to find out whether this anisotropy is independent of age. To answer this, we compare detection thresholds for horizontal and vertical depth corrugations as a function of age. METHODS The depth corrugations were defined solely by the horizontal disparity of random dot patterns. The disparities depicted a horizontal or vertical sinusoidal depth corrugation of spatial frequency 0.1 cyc/deg. Detection thresholds were obtained using Bayesian adaptive staircases from a total of 159 subjects aged from 3 to 73 years. For each participant we computed the anisotropy index, defined as the log10-ratio of the detection threshold for vertical corrugations divided by that for horizontal. RESULTS Anisotropy index was highly variable between individuals but was positive in 87% of the participants. There was a significant correlation between anisotropy index and log-age (r = 0.21, P = 0.008) mainly driven by a significant difference between children and adults. In 67 children aged 3 to 13 years, the mean anisotropy index was 0.34 ± 0.38 (mean ± SD, meaning that vertical thresholds were on average 2.2 times the horizontal ones), compared with 0.59 ± 0.55 in 84 adults aged 18 to 73 years (vertical 3.9 times horizontal). This was mainly driven by a decline in the sensitivity to vertical corrugations. Children had poorer stereoacuity than adults, but had similar sensitivity to adults for horizontal corrugations and were actually more sensitive than adults to vertical corrugations. CONCLUSIONS The fact that adults show stronger stereo anisotropy than children raises the possibility that visual experience plays a critical role in developing and strengthening the stereo anisotropy.
A specialization for vertical disparity discontinuities
(Journal of vision, 2010) Serrano Pedraza, Ignacio; Phillipson, Graeme P; Read, Jenny C A
Because our eyes are set apart horizontally in our head, most disparities between the retinal images are horizontal. However, vertical disparities also occur, and can influence depth perception. The classic example is Ogle's induced effect (K. N. Ogle, 1938), in which applying a uniform vertical magnification to one eye's image produces the illusion that the surface has been rotated around a vertical axis. This is thought to be because uniform vertical magnifications can be produced in natural viewing when the eyes are in eccentric gaze (J. E. Mayhew, 1982; J. E. Mayhew & H. C. Longuet-Higgins, 1982). Thus, vertical magnification is taken by the visual system as indicating that the viewed surface is slanted away from the line of sight. Here, we demonstrate that the induced effect becomes stronger when the sign of the magnification alternates across the visual field. That is, as one moves horizontally across the screen, the left eye's image is alternately stretched and squashed vertically relative to the right eye's image, producing the illusion of a surface folded into triangular corrugations (H. Kaneko & I. P. Howard, 1997). For most subjects, slant judgments in this folded surface have lower thresholds and greater reliability than the classic induced effect, where magnification is applied uniformly across the whole visual field. This is remarkable, given that the disparity pattern of the classic induced effect can be produced by real surfaces with the eyes in eccentric gaze, whereas it is not clear that stripes of alternating vertical disparity could be produced by any physically realizable situation. The analogous improvement for alternating horizontal magnification is attributed to neuronal mechanisms which detect the jumps in horizontal disparity that occur at object boundaries. Our results suggest that a similar, previously unreported system may exist for vertical disparity. Jumps in vertical disparity do occur at object boundaries, and we suggest that our surprising results may reflect the activation of neuronal mechanisms designed to detect these.
Spatial non-homogeneity of the antagonistic surround in motion perception.
(Journal of vision, 2011) Serrano Pedraza, Ignacio; Hogg, Ellen L; Read, Jenny C A
At 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.
Spatial frequency bandwidth of surround suppression tuning curves.
(Journal of vision, 2012) Serrano Pedraza, Ignacio; Grady, John P; Read, Jenny C A
The contrast detection threshold of a grating located in the periphery is increased if a surrounding grating of the same frequency and orientation is present. This inhibition between center and surround has been termed surround suppression. In this work we measured the spatial frequency bandwidth of surround suppression in the periphery for different spatial frequencies (0.5, 1.1, 3, and 5 cycles/deg) of a sinusoidal grating (target) surrounded by a grating with different spatial frequencies (surround). Using a Bayesian adaptive staircase, we measured contrast detection thresholds in an 8AFC detection task in which the target (grating with a 2.3-deg Butterworth window) could appear in one of eight possible positions at 4° eccentricity. The target was surrounded by a grating (with a 18° Butterworth window) with the same or an orthogonal orientation. In each session we fixed the spatial frequency of the target and changed the spatial frequency and the orientation of the surround. When the surround was orthogonal to the target, the thresholds were similar to those obtained without surround, independent of the surrounding spatial frequency. However, when the target and surround had the same orientation and spatial frequency, the contrast threshold was increased by a factor ranging from 3 to 6 across subjects. This suppression reduced rapidly as the spatial frequency of the surround moved away from that of the target. The bandwidth of the suppressive effect depended on spatial frequency, declining from 2.9 octaves at 0.5 c/deg to 1 octave for frequencies above 3 c/deg. This is consistent with the bandwidth of individual simple cells in visual cortex and of spatial frequency channels measured psychophysically, both of which decline with increasing spatial frequency. This suggests that surround suppression may be due to relatively precise inhibition by cells with the same tuning as the target.