Dynamic Random-dot Stereograms Research Articles

Infants perceive two-dimensional shape from horizontal disparity

Previous studies observed that responsiveness to horizontal disparity as such emerges at approximately 2 months of age. Moreover, 3- to 4-month-old infants utilize stereoscopic information to perceive object variations in depth. The present study investigated infants’ ability to respond to crossed horizontal disparity information that defines two-dimensional shape. Infants 4 and 5 months of age were habituated to either a cross or the outline of a square. During the posthabituation period, they were presented with both shapes. The stimuli were dynamic random dot stereograms shown on an autostereoscopic monitor. The participants 5 but not 4 months of age displayed significant novelty preferences for the unfamiliar shape during the posthabituation period. Five-month-old infants are hence sensitive to horizontal disparity information that specifies shape.

On-State Voltage Measurement of Fast Switching Power Semiconductors

The on-state resistance R ds,on is a key characteristic of unipolar power semiconductors and its value depends on the operating conditions, e.g. junction temperature, conducted current and applied gate voltage. Hence, the exact determination of the R ds,on value cannot rely on datasheet information and requires the measurement of current and on-state voltage during operation. Besides the determination of the conduction losses, the on-state voltage measurement enables dynamic R ds,on analysis, device temperature estimation, condition monitoring and consequently time-to-failure prediction. However, in contrast to a switch current measurement, several challenges arise in the design of an on-state voltage measurement circuit (OVMC), i.e. high measurement accuracy (mV-range) during on-state, high blocking voltage capability (kV-range) during off-state and fast dynamic response (ns-range) during switching transitions are demanded. Different OVMC concepts are known from IGBT applications, however, the more severe requirements introduced from the high switching frequency and low OV characterizing the operation of fast switching power semiconductors, prevent their usage. Off-the-shelf products hardly satisfy the mentioned specifications, whereas the performance of state-of-the-art OVM research prototypes require further investigations and/or improvements. With this aim, an innovative OVMC concept is designed, analyzed, calibrated and tested in this paper. Furthermore, the conduction losses of different power semiconductors are measured as function of their operating conditions to validate the performance and highlight the potential of the proposed OVMC.

Simple reaction times to cyclopean stimuli reveal that the binocular system is tuned to react faster to near than to far objects.

Binocular depth perception is an important mechanism to segregate the visual scene for mapping relevant objects in our environment. Convergent evidence from psychophysical and neurophysiological studies have revealed asymmetries between the processing of near (crossed) and far (uncrossed) binocular disparities. The aim of the present study was to test if near or far objects are processed faster and with higher contrast sensitivity in the visual system. We therefore measured the relationship between binocular disparity and simple reaction time (RT) as well as contrast gain based on the contrast-RT function in young healthy adults. RTs were measured to suddenly appearing cyclopean target stimuli, which were checkerboard patterns encoded by depth in dynamic random dot stereograms (DRDS). The DRDS technique allowed us to selectively study the stereoscopic processing system by eliminating all monocular cues. The results showed that disparity and contrast had significant effects on RTs. RTs as a function of disparity followed a U-shaped tuning curve indicating an optimum at around 15 arc min, where RTs were minimal. Surprisingly, the disparity tuning of RT was much less pronounced for far disparities. At the optimal disparity, we measured advantages of about 80 ms and 30 ms for near disparities at low (10%) and high (90%) contrasts, respectively. High contrast always reduced RTs as well as the disparity dependent differences. Furthermore, RT-based contrast gains were higher for near disparities in the range of disparities where RTs were the shortest. These results show that the sensitivity of the human visual system is biased for near versus far disparities and near stimuli can result in faster motor responses, probably because they bear higher biological relevance.

Assessment of Cyclofusion Capabilities of Normal Subjects with 3D Dynamic Random-Dot Stereograms

Evaluation of a new method for cyclofusion measurement. The maximal incyclofusion and excyclofusion tolerated of 20 normal subjects (15 females, mean age 36 ± 9.9 years) were measured by computer-generated dynamic random-dot stereograms (DRDS). Subjects had to detect the orientation of only binocularly visible Landolt C stimuli randomly presented with a 3-D monitor. Both eyes were separately stimulated with shutter glasses. The DRDS-pattern projected to the left and right eye were rotated in the opposite direction in 0.5° steps. In 10 subjects, cyclofusion measurements were repeated. Incylofusional amplitudes were between 2.5° and 6°, excyclofusional amplitudes measured between 3° and 5.5°. Mean incyclofusion was 3.71° (SD 0.82) and mean excyclofusion measured 4.24° (SD 0.73). Repeated measurements of incyclofusion and excyclofusion in the same subject demonstrated a difference of about 0.5° (0.55° for incyclofusion, 0.45° for excyclofusion). The DRDS Landolt C method provided a reliable assessment with good reproducibility of cyclofusion in healthy subjects with only binocularly perceivable objects. Our cyclofusional capabilities were slightly higher than those received with dissociating 2D measurements.

Motion-in-depth direction discrimination in dynamic random dot stereogram: The role of visual perceptual training

Motion-in-depth direction discrimination in dynamic random dot stereogram: The role of visual perceptual training

Binocular vision in infancy: Responsiveness to uncrossed horizontal disparity

This research explored the onset of stereopsis, the ability to perceive depth from the different views provided by the two eyes. In a longitudinal study, infants were tested weekly from 6 to 20 weeks of age. The primary goal of the study was to establish the onset and the early development of sensitivity to uncrossed horizontal disparity. The infant participants were shown dynamic random dot stereograms displaying two squares, one with uncrossed horizontal disparity (0.5°) and one with vertical disparity (0.5°). The stimuli were presented on an autostereoscopic monitor. We used two methods, the forced-choice preferential looking (FPL) method and the classical natural preference (CNP) method, to measure whether the infants preferred the uncrossed over the vertical disparity display. According to the FPL data, the mean relative preferences for horizontal over vertical disparity were significantly greater than chance probability (0.50) from 13 weeks of age onward. With the CNP method we found significant preferences for uncrossed horizontal disparity from 15 weeks onward. The FPL method was hence more sensitive than the CNP method as it indicated an earlier onset of responsiveness to stereoscopic information.

Using Functional Near Infrared Spectroscopy (fNIRS) to Study Dynamic Stereoscopic Depth Perception.

The parietal cortex has been widely implicated in the processing of depth perception by many neuroimaging studies, yet functional near infrared spectroscopy (fNIRS) has been an under-utilised tool to examine the relationship of oxy- ([HbO]) and de-oxyhaemoglobin ([HbR]) in perception. Here we examine the haemodynamic response (HDR) to the processing of induced depth stimulation using dynamic random-dot-stereograms (RDS). We used fNIRS to measure the HDR associated with depth perception in healthy young adults (n = 13, mean age 24). Using a blocked design, absolute values of [HbO] and [HbR] were recorded across parieto-occipital and occipital cortices, in response to dynamic RDS. Control and test images were identical except for the horizontal shift in pixels in the RDS that resulted in binocular disparity and induced the percept of a 3D sine wave that ‘popped out’ of the test stimulus. The control stimulus had zero disparity and induced a ‘flat’ percept. All participants had stereoacuity within normal clinical limits and successfully perceived the depth in the dynamic RDS. Results showed a significant effect of this complex visual stimulation in the right parieto-occipital cortex (p < 0.01, η2 = 0.54). The test stimulus elicited a significant increase in [HbO] during depth perception compared to the control image (p < 0.001, 99.99 % CI [0.008–0.294]). The similarity between the two stimuli may have resulted in the HDR of the occipital cortex showing no significant increase or decrease of cerebral oxygenation levels during depth stimulation. Cerebral oxygenation measures of [HbO] confirmed the strong association of the right parieto-occipital cortex with processing depth perception. Our study demonstrates the validity of fNIRS to investigate [HbO] and [HbR] during high-level visual processing of complex stimuli.Electronic supplementary materialThe online version of this article (doi:10.1007/s10548-016-0476-4) contains supplementary material, which is available to authorized users.

Investigations of dynamic performance in AlGaN/GaN HFETs with field plates by stressed C–V and dynamic on‐resistance measurements

Stressed C–V measurement was used to extract the trap profiles in AlGaN/GaN HFETs with field plates enduring high‐voltage off‐state stress. The C–V measurement results also correlated with the degradation in dynamic on‐resistance (RDS,on) after transistors were stressed with similar stress conditions. Based on the correlation between the trap profiles and dynamic RDS,on degradation, the location with high electric field that determines the major degradation is determined. Finally, a new source field plate is proposed and demonstrated to improve the dynamic performance degradation.

Dynamic on-resistance of normally-off recessed AlGaN/GaN-on-Si metal–oxide–semiconductor heterojunction field-effect transistor

In this study, we investigated the process-dependent dynamic on-resistance [RDS(on)] characteristics of recessed AlGaN/GaN-on-Si metal–oxide–semiconductor heterojunction field-effect transistors with a SiO2 gate oxide. In order to improve the dynamic RDS(on) characteristics, the processing technology was carefully optimized, including post-metallization annealing and field plate formation. A threshold voltage of 2.0 V was achieved with a breakdown voltage of 1070 V. The fabricated device exhibited a DC RDS(on) of 5.22 mΩ·cm2 with very stable dynamic RDS(on) characteristics, i.e., a less than 20% increase up to the drain voltage of 200 V.

Infants' discrimination of crossed and uncrossed horizontal disparity.

In a series of preferential-looking experiments, infants 5 to 6 months of age were tested for their responsiveness to crossed and uncrossed horizontal disparity. In Experiments 1 and 2, infants were presented with dynamic random dot stereograms displaying a square target defined by either a 0.5° crossed or a 0.5° uncrossed horizontal disparity and a square control target defined by a 0.5° vertical disparity. In Experiment 3, infants were presented with the crossed and the uncrossed horizontal disparity targets used in Experiments 1 and 2. According to the results, the participants looked more often at the crossed (Experiment 1), as well as the uncrossed (Experiment 2), horizontal disparity targets than at the vertical disparity target. These results suggest that the infants were sensitive to both crossed and uncrossed horizontal disparity information. Moreover, the participants exhibited a natural visual preference for the crossed over the uncrossed horizontal disparity (Experiment 3). Since prior research established natural looking and reaching preferences for the (apparently) nearer of two objects, this finding is consistent with the hypothesis that the infants were able to extract the depth relations specified by crossed (near) and uncrossed (far) horizontal disparity.

Influence of Buffer Carbon Doping on Pulse and AC Behavior of Insulated-Gate Field-Plated Power AlGaN/GaN HEMTs

Pulse behavior of insulated-gate double-field-plate power AlGaN/GaN HEMTs with C-doped buffers showing small current-collapse effects and dynamic RDS,on increase can accurately be reproduced by numerical device simulations that assume the CN-CGa autocompensation model as carbon doping mechanism. Current-collapse effects much larger than experimentally observed are instead predicted by simulations if C doping is accounted by dominant acceptor states. This suggests that buffer growth conditions favoring CN-CGa autocompensation can allow for the fabrication of power AlGaN/GaN HEMTs with reduced current-collapse effects. The drain-source capacitance of these devices is found to be a sensitive function of the C doping model, suggesting that its monitoring can be adopted as a fast technique to assess buffer compensation properties.

The onset of sensitivity to horizontal disparity in infancy: A short-term longitudinal study

In this short-term longitudinal study, infants were examined for their natural preference of a square defined by crossed horizontal disparity (either 1° or 0.5°) over a square defined by a vertical disparity (either 1° or 0.5°). The square targets were embedded in a dynamic random dot stereogram. The stimuli were presented on an autostereoscopic monitor equipped with a face-tracking device. The infants were tested weekly between 6 and 16 weeks of age. Four experiments were conducted. In two experiments, the infants were examined with the forced-choice preferential looking (FPL) method for their ability to perceive either 1° or 0.5° horizontal disparity. In the remaining two experiments, the classical natural preference (CNP) method (measurement of looking times) was applied. According to the results of the FPL experiments, mean relative preference for the horizontal disparity square became significant at 8 weeks of age. The CNP data indicated an onset of stereopsis at 12–15 weeks. The mean relative preferences for horizontal disparity indicated by the CNP method were smaller than those found in the FPL experiments. Thus, the FPL method was more sensitive than the CNP method in the measurement of infant responsiveness to crossed horizontal disparity.

Evidence for speed sensitivity to motion in depth from binocular cues

Motion in depth can be perceived from binocular cues alone, yet it is unclear whether these cues support speed sensitivity in the absence of the monocular cues that normally co-occur in natural viewing. We measure threshold contours in space-time for the discrimination of three-dimensional (3D) motion to determine whether observers use speed to discriminate a test 3D motion from two identical standards. We compare thresholds for random-dot stereograms (RDS) containing both binocular cues to 3D motion-interocular velocity difference and changing disparity over time-with performance for dynamic random-dot stereograms (DRDS), which contain only the second cue. Threshold contours are tilted along the axis of constant velocity in space-time for RDS stimuli at slow speeds (0.5 m/s), evidence for speed sensitivity. However, for higher speeds (1.5 m/s) and DRDS stimuli, observers rely on the component cues of duration and disparity. In a second experiment, noise of constant velocity is added to the standards to degrade the reliability of these separate components. Again there is evidence for speed tuning for RDS, but not for DRDS. Considerable variation is observed in the ability of individual observers to use the different cues in both experiments, however, in general the results emphasize the importance of interocular velocity difference as a critical cue for speed sensitivity to motion in depth, and suggest that speed sensitivity to stereomotion from binocular cues is restricted to relatively slow speeds.

Contrast gain-control in stereo depth and cyclopean contrast perception

Although human observers can perceive depth from stereograms with considerable contrast difference between the images presented to the two eyes (Legge & Gu, 1989), how contrast gain control functions in stereo depth perception has not been systematically investigated. Recently, we developed a multipathway contrast gain-control model (MCM) for binocular phase and contrast perception (Huang, Zhou, Lu, & Zhou, 2011; Huang, Zhou, Zhou, & Lu, 2010) based on a contrast gain-control model of binocular phase combination (Ding & Sperling, 2006). To extend the MCM to simultaneously account for stereo depth and cyclopean contrast perception, we manipulated the contrasts (ranging from 0.08 to 0.4) of the dynamic random dot stereograms (RDS) presented to the left and right eyes independently and measured both disparity thresholds for depth perception and perceived contrasts of the cyclopean images. We found that both disparity threshold and perceived contrast depended strongly on the signal contrasts in the two eyes, exhibiting characteristic binocular contrast gain-control properties. The results were well accounted for by an extended MCM model, in which each eye exerts gain control on the other eye's signal in proportion to its own signal contrast energy and also gain control over the other eye's gain control; stereo strength is proportional to the product of the signal strengths in the two eyes after contrast gain control, and perceived contrast is computed by combining contrast energy from the two eyes. The new model provided an excellent account of our data (r(2) = 0.945), as well as some challenging results in the literature.

Synchronized Audio-Visual Transients Drive Efficient Visual Search for Motion-in-Depth

In natural audio-visual environments, a change in depth is usually correlated with a change in loudness. In the present study, we investigated whether correlating changes in disparity and loudness would provide a functional advantage in binding disparity and sound amplitude in a visual search paradigm. To test this hypothesis, we used a method similar to that used by van der Burg et al. to show that non-spatial transient (square-wave) modulations of loudness can drastically improve spatial visual search for a correlated luminance modulation. We used dynamic random-dot stereogram displays to produce pure disparity modulations. Target and distractors were small disparity-defined squares (either 6 or 10 in total). Each square moved back and forth in depth in front of the background plane at different phases. The target’s depth modulation was synchronized with an amplitude-modulated auditory tone. Visual and auditory modulations were always congruent (both sine-wave or square-wave). In a speeded search task, five observers were asked to identify the target as quickly as possible. Results show a significant improvement in visual search times in the square-wave condition compared to the sine condition, suggesting that transient auditory information can efficiently drive visual search in the disparity domain. In a second experiment, participants performed the same task in the absence of sound and showed a clear set-size effect in both modulation conditions. In a third experiment, we correlated the sound with a distractor instead of the target. This produced longer search times, indicating that the correlation is not easily ignored.

Neural Activity in Cortical Area V4 Underlies Fine Disparity Discrimination

Primates are capable of discriminating depth with remarkable precision using binocular disparity. Neurons in area V4 are selective for relative disparity, which is the crucial visual cue for discrimination of fine disparity. Here, we investigated the contribution of V4 neurons to fine disparity discrimination. Monkeys discriminated whether the center disk of a dynamic random-dot stereogram was in front of or behind its surrounding annulus. We first behaviorally tested the reference frame of the disparity representation used for performing this task. After learning the task with a set of surround disparities, the monkey generalized its responses to untrained surround disparities, indicating that the perceptual decisions were generated from a disparity representation in a relative frame of reference. We then recorded single-unit responses from V4 while the monkeys performed the task. On average, neuronal thresholds were higher than the behavioral thresholds. The most sensitive neurons reached thresholds as low as the psychophysical thresholds. For subthreshold disparities, the monkeys made frequent errors. The variable decisions were predictable from the fluctuation in the neuronal responses. The predictions were based on a decision model in which each V4 neuron transmits the evidence for the disparity it prefers. We finally altered the disparity representation artificially by means of microstimulation to V4. The decisions were systematically biased when microstimulation boosted the V4 responses. The bias was toward the direction predicted from the decision model. We suggest that disparity signals carried by V4 neurons underlie precise discrimination of fine stereoscopic depth.

Synchronized audio-visual transients drive efficient visual search for motion-in-depth

In natural audio-visual environments, a change in depth is usually correlated with a change in loudness. In the present study, we investigated whether correlating disparity and loudness provides a functional advantage in binding disparity and sound amplitude in a visual search paradigm. To test this assumption, we used a method similar to that used by Van der Burg et al. (2008) to show that non-spatial modulations of loudness can drastically improve spatial visual search for a correlated luminance modulation. Subsequently (2010), they varied the shape of temporal modulation and demonstrated that transient events (square modulations) are required for this search efficiency, and that sinusoidal audiovisual modulations do not support efficient search. We used dynamic random-dot stereogram displays to produce pure disparity modulations. Target and distractors were 0.35 × 0.35 degrees disparity-defined squares (either 6 or 10 in total) presented on a ring at 2.5 deg eccentricity. Each square moved back and forth in depth from zero to +12 arcmin (crossed) disparity at different phases. The target's depth modulation was synchronized with an amplitude-modulated 500 Hz tone. Visual and auditory modulations were always congruent (both sinewave or squarewave). Four observers were asked to give speeded responses in a discrimination task on the target. Because binocular matching processes are known to favor smooth over abrupt changes of disparity across space and time, we expected the sine modulation condition to be at least as efficient as the square modulation in supporting efficient search. However, results show a significant improvement in visual search in the square condition compared to the sine condition, suggesting that transient auditory information can efficiently drive visual search in the disparity domain. In a second experiment, correlating sound with a distractor led to longer search times, indicating that the correlation is not easily ignored.

Recovery of stereopsis through perceptual learning in human adults with abnormal binocular vision

Stereopsis, the perception of depth based on the disparity of the images projected to the retinas of the two eyes, is an important process in our three-dimensional world; however, 3-5% of the population is stereoblind or has seriously impaired stereovision. Here we provide evidence for the recovery of stereopsis through perceptual learning, the repetitive practice of a demanding visual task, in human adults long deprived of normal binocular vision. We used a training paradigm that combines monocular cues that were correlated perfectly with the disparity cues. Following perceptual learning (thousands of trials) with stereoscopic gratings, five adults who initially were stereoblind or stereoanomalous showed substantial recovery of stereopsis, both on psychophysical tests with stimuli that contained no monocular cues and on clinical testing. They reported that depth "popped out" in daily life, and enjoyed 3D movies for the first time. After training, stereo tests with dynamic random-dot stereograms and band-pass noise revealed the properties of the recovered stereopsis: It has reduced resolution and precision, although it is based on perceiving depth by detecting binocular disparity. We conclude that some human adults deprived of normal binocular vision can recover stereopsis at least partially.

Accuracy of Stereomotion Speed Perception with Persisting and Dynamic Textures

It has been established that the motion in depth of stimuli visible to both eyes may be signalled binocularly either by a change of disparity over time or by the difference in the velocity of the images projected on each retina, known as an interocular velocity difference. A two-interval forced-choice stereomotion speed discrimination experiment was performed on four participants to ascertain the relative speed of a persistent random dot stereogram (RDS) and a dynamic RDS undergoing directly approaching or receding motion in depth. While the persistent RDS pattern involved identical dot patterns translating in opposite directions in each eye, and hence included both changing disparity and interocular velocity difference cues, the dynamic RDS pattern (which contains no coherent monocular motion signals) specified motion in depth through changing disparity, but no motion through interocular velocity difference. Despite an interocular velocity difference speed signal of zero motion in depth, the dynamic RDS stimulus appeared to move more rapidly. These observations are consistent with a scheme in which cues that rely on coherent monocular motion signals (such as looming and the interocular velocity difference cue) are less influential in dynamic stimuli due to their lack of reliability (i.e., increased noise). While dynamic RDS stimuli may be relatively unaffected by the contributions of such cues when they signal that the stimulus did not move in depth, the persistent RDS stimulus may retain a significant and conflicting contribution from the looming cue, resulting in a lower perceived speed.

Orientation preference and horizontal disparity sensitivity in the monkey visual cortex

Disparity sensitivity may be explained by interocular positional differences of the receptive fields (RF) of visual cortical cells or by interocular shifts of the On and Off RF subregions. Since this latter model assumes shifts are orthogonal to the orientation of the RF, cells with disparity sensitivity should be oriented. The objective of the present study is to test this assumption. Single unit recordings were performed in areas V1 and V2 of two Macaca mulatta. For assessing disparity sensitivity, we generated dynamic random dot stereograms. A stereofigure was flashed over the cell RF with different horizontal disparities. To assess orientation sensitivity we used a flashing bar with eight orientations, in several positions over the cell RF in a pseudorandom manner. We found no relationship between sensitivity to horizontal disparity and orientation preference in V1 and V2 cells. Our data indicate that horizontal disparity sensitivity and orientation preference are unrelated properties. This favors the notion that sensitivity to horizontal disparity is mostly based on RF interocular horizontal positional differences.