Degrees Of Visual Angle Research Articles

Depth Cues Changes Circle Size Judgment Measured by Psychophysical Scaling

The aim of our study was to investigate whether different circle sizes, in conditions of pure size judgment and in a simple contextual judgment with an interfering depth suggesting background, produce different size perceptions. We used the magnitude estimation to obtain the apparent size of circles under two different experimental conditions: with a neutral black background and with a convergent gradient to generate an artificial horizon to evoke depth cues. Twenty-two subjects with normal or corrected-to-normal visual acuity (mean age = 21.3 yrs; SD = 1.6) were tested. The procedure consisted of two gray circles at luminance of 40 cd/m2, separated 10 degrees of visual angle apart from each other. On the left side was always present the reference circle (visual angle of 1.1 degree) in which was assigned an arbitrary value of 50 was assigned. The subjects' task was to judge the size of the circles appearing in the right side of the monitor screen assigning a number proportional to the perceived altered size, relative to the reference circle. Seven different sizes (0.6, 0.8, 1.0, 1.1, 1.3, 1.4, 1.5 degrees) were presented in each condition. Our results have shown a high correlation for circle size and depth conditions (R = 0.987 and R = 0.997) between the logs of the stimuli and the subjective magnitude estimated values. The exponents obtained by the Power Law were 0.79 and 1.09, respectively to each condition. Additionally, a gender effect was observed in which males had showed an expansive perception of size with no dependence on the background. We concluded that in the induced depth condition, the perception of the circle sizes were judged subjectively closer to their respective physical size than in the condition of free visual cues. Our data reinforces the integrative manner of perceptual system when working with the sensory information

The effect of parametric stimulus size variation on individual face discrimination indexed by fast periodic visual stimulation.

BackgroundThe human brain is frequently exposed to individual faces across a wide range of different apparent sizes, often seen simultaneously (e.g., when facing a crowd). Here we used a sensitive and objective fast periodic visual stimulation approach while recording scalp electroencephalogram (EEG) to test the effect of size variation on neural responses reflecting individual face discrimination.MethodsEEG was recorded in ten observers presented with the same face identity at a fixed rate (5.88 Hz, frequency F) and different oddball face identities appearing every five faces (F/5, i.e., 1.18 Hz). Stimulus size was either constant (6.5 × 4 degrees of visual angle) or changed randomly at each stimulation cycle, by 2:1 ratio increasing values from 10% to 80% size variation in four conditions. Absolute stimulus size remained constant across conditions.ResultsThe base rate 5.88 Hz EEG response increased with image size variation, particularly over the right occipito-temporal cortex. In contrast, size variation decreased the oddball response marking individual face discrimination over the right occipito-temporal cortex. At constant stimulus size, the F/5 change of identity generated an early (about 100 ms) oddball response reflecting individual face discrimination based on image-based cues. This early component disappeared with a relatively small size variation (i.e., 20%), leaving a robust high-level index of individual face discrimination.ConclusionsStimulus size variation is an important manipulation to isolate the contribution of high-level visual processes to individual face discrimination. Nevertheless, even for relatively small stimuli, high-level individual face discrimination processes in the right occipito-temporal cortex remain sensitive to stimulus size variation.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2202-15-87) contains supplementary material, which is available to authorized users.

Acute effect of alcohol intake on sine-wave Cartesian and polar contrast sensitivity functions

The aim of this study was to assess contrast sensitivity for angular frequency stimuli as well as for sine-wave gratings in adults under the effect of acute ingestion of alcohol. We measured the contrast sensitivity function (CSF) for gratings of 0.25, 1.25, 2.5, 4, 10, and 20 cycles per degree of visual angle (cpd) as well as for angular frequency stimuli of 1, 2, 4, 24, 48, and 96 cycles/360°. Twenty adults free of ocular diseases, with normal or corrected-to-normal visual acuity, and no history of alcoholism were enrolled in two experimental groups: 1) no alcohol intake (control group) and 2) alcohol ingestion (experimental group). The average concentration of alcohol in the experimental group was set to about 0.08%. We used a paradigm involving a forced-choice method. Maximum sensitivity to contrast for sine-wave gratings in the two groups occurred at 4 cpd sine-wave gratings and at 24 and 48 cycles/360° for angular frequency stimuli. Significant changes in contrast sensitivity were observed after alcohol intake compared with the control condition at spatial frequency of 4 cpd and 1, 24, and 48 cycles/360° for angular frequency stimuli. Alcohol intake seems to affect the processing of sine-wave gratings at maximum sensitivity and at the low and high frequency ends for angular frequency stimuli, both under photopic luminance conditions.

The Fine-Scale Functional Correlation of Striate Cortex in Sighted and Blind People

To what extent are spontaneous neural signals within striate cortex organized by vision? We examined the fine-scale pattern of striate cortex correlations within and between hemispheres in rest-state BOLD fMRI data from sighted and blind people. In the sighted, we find that corticocortico correlation is well modeled as a Gaussian point-spread function across millimeters of striate cortical surface, rather than degrees of visual angle. Blindness produces a subtle change in the pattern of fine-scale striate correlations between hemispheres. Across participants blind before the age of 18, the degree of pattern alteration covaries with the strength of long-range correlation between left striate cortex and Broca's area. This suggests that early blindness exchanges local, vision-driven pattern synchrony of the striate cortices for long-range functional correlations potentially related to cross-modal representation.

How do the S-, M- and L-cones contribute to motion luminance assessed using minimum motion?

Purpose: To measure the relative contribution of short (S-), middle (M-), and long (L-) wavelength sensitive cones to luminance as gauged with a minimum motion task. Methods: For a given achromatic intensity I, an annular, rotary motion display (subtending the central two degrees of visual angle) was used to find colored lights that were equiluminant to I. The motion display was designed so that, in the context of this display and using a high temporal frequency, a given light would yield ambiguous first-order motion if and only if it was equiluminant to I. Each of ten (4 female) observers was tested using lights of 20 different hues saturated to the maximum extent afforded by our monitor and varying in intensity. For each hue, a 1-up-1-down staircase was used to concentrate observations in the neighborhood of the light that was equiluminant to I. Results: For each observer, the 20 lights estimated to be equiluminant to I projected within measurement error to a plane in the space spanned by the (Stockman-Sharpe) S-, M- and L-cone fundamentals. The axis perpendicular to this equiluminant plane was taken to be the motion luminance axis. This motion luminance axis was then expressed as a linear combination of the (normalized) S-, M- and L-cone sensitivity functions. For three of our observers (all male), the S-cone contribution to motion luminance was negative (as reported by Ripamonti et al., 2009 for flicker luminance) but small. However, for the other seven observers, the S-cone contribution to motion luminance was positive. Wide variations were seen across observers in the relative contributions to motion luminance of the S-, M- and L-cones, from (0.1 : 0.01 : 9.8) to (0.2 : 2.3 : 7.3), in the most extreme cases for a particular I, but in all cases the L-cone contribution was dominant. Meeting abstract presented at VSS 2013

The flash grab effect.

When an object moves back and forth, its trajectory appears significantly shorter than it actually is. The object appears to stop and reverse well before its actual reversal point, as if there is some averaging of location within a window of about 100 ms (Sinico et al., 2009). Surprisingly, if a bar is flashed at the physical end point of the trajectory, right on top of the object, just as it reverses direction, the flash is also shifted - grabbed by the object - and is seen at the perceived endpoint of the trajectory rather than the physical endpoint. This can shift the perceived location of the flash by as much as 2 or 3 times its physical size and by up to several degrees of visual angle. We first show that the position shift of the flash is generated by the trajectory shortening, as the same shift is seen with or without the flash. The flash itself is only grabbed if it is presented within a small spatiotemporal attraction zone around the physical end point of the trajectory. Any flash falling in that zone is pulled toward the perceived endpoint. The effect scales linearly with speed, up to a maximum, and is independent of the contrast of the moving stimulus once it is above 5%. Finally, we demonstrate that this position shift requires attention. These results reveal a new "flash grab" effect in the family of motion-induced position shifts. Although it most resembles the flash drag effect, it differs from this in the following ways: (1) it has a different temporal profile, (2) it requires attention, (3) it is about 10 times larger.

Auditory rhythms are systemically associated with spatial-frequency and density information in visual scenes

A variety of perceptual correspondences between auditory and visual features have been reported, but few studies have investigated how rhythm, an auditory feature defined purely by dynamics relevant to speech and music, interacts with visual features. Here, we demonstrate a novel crossmodal association between auditory rhythm and visual clutter. Participants were shown a variety of visual scenes from diverse categories and asked to report the auditory rhythm that perceptually matched each scene by adjusting the rate of amplitude modulation (AM) of a sound. Participants matched each scene to a specific AM rate with surprising consistency. A spatial-frequency analysis showed that scenes with greater contrast energy in midrange spatial frequencies were matched to faster AM rates. Bandpass-filtering the scenes indicated that greater contrast energy in this spatial-frequency range was associated with an abundance of object boundaries and contours, suggesting that participants matched more cluttered scenes to faster AM rates. Consistent with this hypothesis, AM-rate matches were strongly correlated with perceived clutter. Additional results indicated that both AM-rate matches and perceived clutter depend on object-based (cycles per object) rather than retinal (cycles per degree of visual angle) spatial frequency. Taken together, these results suggest a systematic crossmodal association between auditory rhythm, representing density in the temporal domain, and visual clutter, representing object-based density in the spatial domain. This association may allow for the use of auditory rhythm to influence how visual clutter is perceived and attended.

Sharpness of vision of pilots in air force of Serbia after +Gz acceleration in human centrifuge

The high speeds achieved during the take-off, flight, and landing of modern aircraft present limitations for the visual system. The importance of maintaining visual function during these intervals has been recognized since the earliest stages of aviation development. Because of the great practical importance of air combat, research on visual stress during flight is of great importance receives much attention. Vision is the most important sensory function in terms of both flight safety and the quality performance of flight duties. Visual acuity of 12 Air Force pilots was investigated before and after exposure to + Gz acceleration in a human centrifuge. This centrifuge is a combination gravity and altitude apparatus, capable of reaching accelerations of up to 20 G and simulating altitudes of up to 30,000 m. Each pilot had individual centrifuge training, and individual skills were first stated measured at the first time of exposure to G acceleration, and again in a one week. The training level that corresponds corresponding to the improvement of individual skills during submission to Gz acceleration was applied. Exposure to +Gz acceleration provokes significant reactions and fluctuations in the eye. Immediately after exposure to + Gz acceleration, there was a transient decrease in visual acuity at a distance of 0.02 ± 0.04 degrees of visual angle. Pupil diameter increased from 3.5 ± 0.6 to 5.6 ± 0.5 mm. This dilation continued for 15 min following exposure to acceleration. Changes on the eye bottom were not noted. Previous work has shown that exposure to + Gz acceleration results in an increase in the depth of the eye chamber. Energy reserves in retinal tissue and the central nervous system allow continued operation of brain and visual systems to continue for a few seconds following interruption of blood supply to the head. This enables rapid tolerance to high G loads for a short period of time, usually approximately 5 seconds. At high initial rates of acceleration, significant changes in visual function can occur. However, the importance of maintaining visual acuity is increasing due to the application of novel functional displays for rapid orientation of the pilot in space, the configuration of the area field, aircraft opponents, and weapon systems. Therefore, it is necessary to continue studies that will provide accurate indicators of visual acuity in the context of real Gz acceleration and spatial disorientation.

The Flash Grab Effect

Abstract When an object moves back and forth, its trajectory appears significantly shorter than it actually is. The object appears to stop and reverse well before its actual reversal point, as if there is some averaging of location within a window of about 100 ms ( Sinico et al., 2009 ). Surprisingly, if a bar is flashed at the physical end point of the trajectory, right on top of the object, just as it reverses direction, the flash is also shifted – grabbed by the object – and is seen at the perceived endpoint of the trajectory rather than the physical endpoint. This can shift the perceived location of the flash by as much as 2 or 3 times its physical size and by up to several degrees of visual angle. We first show that the position shift of the flash is generated by the trajectory shortening, as the same shift is seen with or without the flash. The flash itself is only grabbed if it is presented within a small spatiotemporal attraction zone around the physical end point of the trajectory. Any flash falling in that zone is pulled toward the perceived endpoint. The effect scales linearly with speed, up to a maximum, and is independent of the contrast of the moving stimulus once it is above 5%. Finally, we demonstrate that this position shift requires attention. These results reveal a new “flash grab” effect in the family of motion-induced position shifts. Although it most resembles the flash drag effect, it differs from this in the following ways: (1) it has a different temporal profile, (2) it requires attention, (3) it is about 10 times larger.

Low-Frequency Sound Pressure and Transtympanic Endoscopy of the Middle Ear in Assessment of “Spontaneous” Perilymphatic Fistula

This study was designed to verify an eventual perilymphatic fistula (PLF) in 264 patients with sensorineural hearing loss (SNHL) and/or vertigo. The patients were exposed to a low-frequency sound stimulation (LFS) on posturography to objectively test Tullio's phenomenon and Hennebert's sign. Endoscopes with 5 degree and 25 degree of visual angle and an outer diameter of 1.7 mm were used. The round window niche, with its foldings, oval window with stapes superstructure, a part of the facial recess and the area in the fissula ante fenestram were examined and video recorded. In one patient, we endoscopically verified a fistula in the round window membrane (resulting from a diving accident) that was covered with a fibrinous layer. In 4 cases, there was abnormal mucosal shining in the round window but without PLF. In 7 cases, the tympanic cavity could not be visualized because of the adhesive middle ear process, the abnormal anatomy, or the prominent exostoses of the ear canal prohibited vision. In 34 patients, LFS provoked unsteadiness on posturography without PLF. In 6 cases, a postoperative middle ear infection was recorded. No permanent tympanic membrane perforation occurred. It is unlikely that disease entity of “spontaneous PLF” exists. Tympanoscopy should be regarded as the first choice when a PLF is suspected.

A visual code book-structured probability distributions in natural scenes

Natural visual scenes consist of objects of various physical properties that are arranged in three-dimensional (3D) space in a variety of ways. When projected onto the retina, visual scenes entail highly structured statistics, occurring over the full range of natural variations in the world. To deal efficiently with this full range of natural variations, the visual system may have to generate percepts according to the probability distributions (PDs) of visual variables underlying any stimulus [1-5]. What, then, are these PDs in natural scenes? In this work, we proposed that these PDs are the components of the grand joint PD of the physical world and the images on the retina (GPDWI). Thus, our approach is to decompose GPDWI into a large set of PDs without information reduction. We call these PDs a visual code book. To examine this visual code book, we first sampled a large number of scene patches (~2 degrees of visual angle) from a database of high-resolution 3D natural scenes and fitted a concatenation of 8th order polynomial functions to the 2D and 3D data in the patches. Using the fitted polynomial functions, we classified all the natural scene patches into a large set of 2D-3D natural scene structures that have distinctive distributions of ranges and/or luminance. Finally, we developed a PD for each of the 2D-3D natural scene structures. Since any joint 2D-3D natural scene patch is a combination of the samples of these PDs, they form a faithful representation of GPDWI and can be used a visual code book. We used these PDs to estimate 3D scenes from 2D images and to categorize 2D-3D natural scenes. Our results showed that accurate 3D vision from a single monocular view is achievable in many situations and that near-human performance can be achieved on categorizing 2D-3D natural scenes. We thus conclude that the visual code book obtained here captures faithfully the extraordinarily complex 2D-3D natural scene statistics and supports a range of tasks of natural vision.

Pacientes com depressão maior têm menor sensibilidade a contraste visual que indivíduos saudáveis

O objetivo foi medir a sensibilidade ao contraste, SC, visual de grades senoidais circulares concêntricas com frequências espaciais de 0,25; 4 e 8 cpg, ciclos por grau de ângulo visual, em adultos saudáveis e com depressão maior. Foram estimadas a SC de 20 participantes, 10 saudáveis e 10 participantes com depressão maior, utilizando o método psicofísico da escolha forçada e luminância média de 0,7 cd/m². Todos os participantes apresentavam acuidade visual normal ou corrigida e estavam livres de doenças identificáveis. Os resultados mostraram que a SC visual máxima ocorreu na faixa de 0,25 cpg para os dois grupos. Os resultados demonstraram ainda que a SC visual dos participantes com depressão maior foi mais baixa do que a dos participantes saudáveis (p < 0,05), pois os participantes com transtorno precisaram de mais contraste para detectar as frequências espaciais testadas. Estes resultados sugerem alterações na percepção visual relacionadas à depressão maior.

The Moving Eye is Easy to Spy: How Motion Improves Gaze Discrimination

The Moving Eye is Easy to Spy: How Motion Improves Gaze Discrimination Nicola Anderson University of British Columbia Evan Risko Arizona State University Alan Kingstone University of British Columbia Abstract: When people move their eyes, their change in eye direction carries a motion signal. However, most research using gaze direction as a stimulus either controls or excludes the motion of the eyes. Here, we directly examined the role of motion in the discrimination of eye movements. Participants were shown two images: a person looking straight ahead and then looking to the left or right at 1, 2 or 3 degrees visual angle from fixation. This resulted in the apparent motion of the eyes to the left or right. In the no motion condition, participants received the two images separated by a 200 ms blank display, eliminating the perception of motion. Participants were more accurate and more confident of their judgements in the condition that included eye motion, but were also highly accurate without motion. These data indicate that eye motion can contribute to the computation of another’s gaze direction.

An exploration of the spatial scale over which orientation-dependent surround effects affect contour detection

Contour detection is a crucial component of visual processing; however, performance on contour detection tasks can vary depending on the context of the visual scene. S. C. Dakin and N. J. Baruch (2009) showed that detection of a contour in an array of distracting elements depends on the orientation of flanking elements. Here, using a line of five collinear Gabor elements ("target contour") in a field of distractor Gabor elements, we systematically measured the effects of eccentricity, spacing, and spatial frequency on contour detection performance in three different contexts: randomly oriented distractors (control condition), flanking distractors (on either side of the collinear Gabors) aligned approximately parallel to the target contour, and flanking distractors aligned approximately orthogonal to the target contour. In the control condition, contour detection performance was best for larger Gabors (2 cpd) spaced farther apart (1.2°). Parallel flankers reduced performance for intermediate and large spacings and sizes compared to the control condition, while orthogonal flankers increased performance for the smallest spacing and size compared to the control condition. The results are fit by a model in which collinear facilitation, which is size-dependent but can persist for several degrees of visual angle, competes with orientation-dependent suppression from the flanking context when elements are separated by less than a degree of visual angle.

Visuomotor control of steering: the artefact of the matter

Previous behavioural research (Land and Horwood in Nature 377:339-340, 1995) indicates that surprisingly little visual information is required to effect smooth and accurate steering through a curving roadway. Based on results from a driving simulator study, Land and Horwood reported that viewing the roadway through two horizontal apertures, one degree of visual angle in height, can result in steering performance which is indistinguishable from that obtained with the whole scene visible. The position of the apertures in the visual field, they claimed, is crucial; higher up leads to less accurate but more stable steering responses, whilst lower down leads to jerky steering but more accurate lane-keeping. These findings are consistent with a two-stage model of steering control proposed by Donges in Human Factors 20:691-707 (1978). However, in a driving simulator, the temporal lag between the input signal received from a control device and the output presented on the display can have profound effects on steering behaviour. In two experiments, we show that the effect of aperture position on steering accuracy and stability is pronounced when a slow frame update rate is used (7.2 Hz, as used by Land and Horwood in Nature 377:339-340, 1995), but largely attenuated with a faster update rate (72 Hz). These results are consistent with the broader empirical literature dealing with temporal delays in manual tracking, and urge a critical reappraisal of the behavioural evidence for the two-stage steering model.

Visual contrast sensitivity in tonic-clonic epileptic patients.

We measured the effects of epilepsy on visual contrast sensitivity to linear and vertical sine-wave gratings. Sixteen female adults, aged 21 to 50 years, comprised the sample in this study, including eight adults with generalized tonic-clonic seizure-type epilepsy and eight age-matched controls without epilepsy. Contrast threshold was measured using a temporal two-alternative forced-choice binocular psychophysical method at a distance of 150 cm from the stimuli, with a mean luminance of 40.1 cd/m2. A one-way analysis of variance (ANOVA) applied to the linear contrast threshold showed significant differences between groups (F[3,188] = 14.829; p < .05). Adults with epilepsy had higher contrast thresholds (1.45, 1.04, and 1.18 times for frequencies of 0.25, 2.0, and 8.0 cycles per degree of visual angle, respectively). The Tukey Honestly Significant Difference post hoc test showed significant differences (p < .05) for all of the tested spatial frequencies. The largest difference between groups was in the lowest spatial frequency. Therefore, epilepsy may cause more damage to the neural pathways that process low spatial frequencies. However, epilepsy probably alters both the magnocellular visual pathway, which processes low spatial frequencies, and the parvocellular visual pathway, which processes high spatial frequencies. The experimental group had lower visual contrast sensitivity to all tested spatial frequencies.

Acute inhalation of 2,2,4-trimethylpentane alters visual evoked potentials and signal detection behavior in rats

The volatile organic compound 2,2,4-trimethylpentane (TMP, “isooctane”) is a constituent of gasoline for which the current health effects data are insufficient to permit the US Environmental Protection Agency to conduct a risk assessment. The potential neurological impairment from acute inhalation exposure to TMP was evaluated in adult male Long–Evans rats using both electrophysiological and behavioral assessments. Visual evoked potentials (VEPs) were recorded from rats viewing modulated visual patterns (0.16 cycles per degree visual angle (cpd), 60% contrast, 4.55 Hz appear/disappear). Rats ( n = 7–10/dose) were exposed to TMP vapors in concentrations of 0, 500, or 1000 ppm for 60-min. A VEP was recorded before exposure and at 10 min intervals during exposure and also for 60 min after exposure terminated. The spectral amplitude of the frequency-double component (F2) was significantly reduced after exposure to TMP. In behavioral assessments, rats ( n = 14) performed an appetitively motivated visual signal detection task while breathing 0, 500, 1500, 1000, 2000, or 2500 ppm TMP for 62 min. Slight reductions in accuracy of performance were observed at the 2500 ppm concentration. Concentrations of TMP in the brain were estimated using a physiologically based pharmacokinetic (PBPK) model to be less than 0.2 mM after 62 min at 2500 ppm. Together these data demonstrate that TMP, like other volatile organic substances, impairs neurological function during acute inhalation exposure and that the small magnitude of the observed effects is consistent with the low concentrations of this hydrocarbon that were estimated to reach the CNS.

Study of clinical application of aberration-free aspheric intraocular lens

To compare spherical aberration, visual quality and apparent accommodation between pseudophakic patients with an aberration-free aspheric intraocular lens (IOL) and patients with a spherical IOL. A prospective study of 130 consecutive cases (132 eyes) was conducted. All cataract patients underwent phacoemulsification were randomized to receive an aberration-free aspheric IOL (Akreos AO, Bausch & Lomb) or a spherical IOL (KS-1, Cannon Staar). Spherical aberration of total eye, best corrected visual acuity (BCVA), near visual acuity (NVA), contrast sensitivity, glare sensitivity and apparent accommodation were measured. Data were analyzed using chi-square test and independent t-test. The mean spherical aberration in eyes with a Tecnis IOL [(0.141 +/- 0.070) microm] was significantly lower than that of eyes with a spherical IOL [(0.210 +/- 0.108) microm; t = 4.365, P = 0.000]. In addition, Akreos AO IOL provided a better contrast sensitivity at 2.5 degrees visual angle (30.62 +/- 12.50 vs. 25.92 +/- 7.36; t = 2.606, P = 0.010), and improved glare sensitivity at 4.0 degrees (31.25 +/- 8.65 vs. 26.70 +/- 7.98; t = 3.116, P = 0.002), 2.5 degrees (26.35 +/- 8.72 vs. 22.43 +/- 7.35; t = 2.772, P = 0.006) and 1.6 degrees (12.35 +/- 4.01 vs. 9.82 +/- 4.12; t = 3.553, P = 0.001) visual angles. The difference of BCVA, NVA and apparent accommodation between these two groups was not statistically significant. The present results demonstrated that an aberration-free aspheric IOL, Akreos AO, may reduce the spherical aberration and improve visual performance of pseudophakic eyes and without negative influence on apparent accommodation as compare to conventional spherical IOL.

Masking produced by mach bands

The detectability of narrow target or signal bars perturbing a stimulus that produces Mach bands is difficult to measure in the vicinity of either dark or bright Mach bands because the targets affect the shape of the bands. An incremental signal makes the dark Mach band shallower and wider and a decremental signal makes the dark Mach band narrower and deeper; the converse occurs in the bright Mach bands. Signals in, but not centred on, either band make the bands asymmetric (Henning, Millar & Hill, 2000). To prevent observers using such cues, we randomized the polarity of the signals on each trial. We used a two-alternative forced-choice experiment in which each trial comprised two 400-msec observation intervals separated by a 600-msec pause. A Mach-band stimulus was presented in both intervals with the narrow target on any trial presented with equal probability in only one of the two observation intervals. Further, on any given trial, the target was randomly chosen to be an increment or a decrement. The psychometric functions relating the percentage of correct responses to the logarithm of the signal luminance were parallel, and the “thresholds” indicate that both dark and bright Mach bands make detection difficult. Separation of the results into those produced by increments and those produced by decrements reveal oscillations in detectability at about 5 cycles per degree of visual angle. The oscillations observed with increments are 180° out-of-phase with those observed with decrements. HenningG. BMillarR. W.HillN. J.(2000). “Detection of incremental and decremental bars at different locations across Mach bands and related stimuli,” J. Opt. Soc. Am., A 17, 1147– 1159.

Highly selective processing of temporal information from attended stimuli in macaque’s visual area V4

Highly selective processing of temporal information from attended stimuli in macaque’s visual area V4