Cue conflict between disparity change and looming in the perception of motion in depth

We hypothesized that it is the conflict between various cues to distance that have produced results purportedly showing that vergence eye movements induced by disparity change are not an effective cue for depth. Single and compound stimuli were used to examine the perceived motion in depth (MID) produced by simulated motion oscillations specified by disparity, relative disparity, and/or looming. Estimations of the extent of MID and binocularly recorded eye movements showed that the vergence induced by disparity change is indeed an effective cue for motion in depth in conditions where looming information does not conflict with it. When looming and disparity are in conflict, looming is the stronger cue.     

Usefulness influences visual appearance in motion transparency depth rivalry

Two sets of dots moving in opposite directions are usually seen as two transparent surfaces. Deciding which surface is in front of the other is bistable and observers exhibit strong biases to see one particular motion direction in front. Surprisingly, biases are dependent on stimulus orientation in a persistent, idiosyncratic, and irrelevant manner. We investigated here whether this preferred direction is arbitrarily fixed or can instead be updated from the context. Observers performed two tasks alternately. One task was to report the surface seen in front in a transparent motion stimulus. The other task was a visual search for a slow dot. Unknown to the observers, we systematically paired the target dot with one surface direction in an attempt to make that surface appear preferentially in front. This manipulation was sufficient to change the observer's preferred direction for the surface seen in front. Attentional explanations did not account for the results. Observers modified their idiosyncratic preference in motion transparency depth rivalry only because it was useful to perform well in an auxiliary task.     

Processing of first-order motion in marmoset visual cortex is influenced by second-order motion

We measured the responses of single neurons in marmoset visual cortex (V1, V2, and the third visual complex) to moving first-order stimuli and to combined first- and second-order stimuli in order to determine whether first-order motion processing was influenced by second-order motion. Beat stimuli were made by summing two gratings of similar spatial frequency, one of which was static and the other was moving. The beat is the product of a moving sinusoidal carrier (first-order motion) and a moving low-frequency contrast envelope (second-order motion). We compared responses to moving first-order gratings alone with responses to beat patterns with first-order and second-order motion in the same direction as each other, or in opposite directions to each other in order to distinguish first-order and second-order direction-selective responses. In the majority (72%, 67/93) of cells (V1 73%, 45/62; V2 70%, 16/23; third visual complex 75%, 6/8), responses to first-order motion were significantly influenced by the addition of a second-order signal. The second-order envelope was more influential when moving in the opposite direction to the first-order stimulus, reducing first-order direction sensitivity in V1, V2, and the third visual complex. We interpret these results as showing that first-order motion processing through early visual cortex is not separate from second-order motion processing; suggesting that both motion signals are processed by the same system.     

The motion/pursuit law for visual depth perception from motion parallax

One of vision’s most important functions is specification of the layout of objects in the 3D world. While the static optical geometry of retinal disparity explains the perception of depth from binocular stereopsis, we propose a new formula to link the pertinent dynamic geometry to the computation of depth from motion parallax. Mathematically, the ratio of retinal image motion (motion) and smooth pursuit of the eye (pursuit) provides the necessary information for the computation of relative depth from motion parallax. We show that this could have been obtained with the approaches of Nakayama and Loomis [Nakayama, K., & Loomis, J. M. (1974). Optical velocity patterns, velocity-sensitive neurons, and space perception: A hypothesis. Perception, 3, 63-80] or Longuet-Higgens and Prazdny [Longuet-Higgens, H. C., & Prazdny, K. (1980). The interpretation of a moving retinal image. Proceedings of the Royal Society of London Series B, 208, 385-397] by adding pursuit to their treatments. Results of a psychophysical experiment show that changes in the motion/pursuit ratio have a much better relationship to changes in the perception of depth from motion parallax than do changes in motion or pursuit alone. The theoretical framework provided by the motion/pursuit law provides the quantitative foundation necessary to study this fundamental visual depth perception ability.     

Poor visibility of motion in depth is due to early motion averaging

Under a variety of conditions, motion in depth from binocular cues is harder to detect than lateral motion in the frontoparallel plane. This is surprising, as the nasal-temporal motion in the left eye associated with motion in depth is easily detectable, as is the nasal-temporal motion in the right eye. It is only when the two motions are combined in binocular viewing that detection can become difficult. We previously suggested that the visibility of motion-in-depth is low because early stereomotion detectors average left and right retinal motions. For motion in depth, a neural averaging process would produce a motion signal close to zero. Here we tested the averaging hypothesis further. Specifically we asked, could the reduced visibility observed in previous experiments be associated with depth and layout in the stimuli, rather than motion averaging? We used anti-correlated random dot stereograms to show that, despite no depth being perceived, it is still harder to detect motion when it is presented in opposite directions in the two eyes than when motion is presented in the same direction in the two eyes. This suggests that the motion in depth signal is lost due to early motion averaging, rather than due to the presence of noise from the perceived depth patterns in the stimulus.     

Auditory modulation of visual apparent motion with short spatial and temporal intervals

Recently, E. Freeman and J. Driver (2008) reported a cross-modal temporal interaction in which brief sounds drive the perceived direction of visual apparent-motion, an effect they attributed to "temporal capture" of the visual stimuli by the sounds (S. Morein-Zamir, S. Soto-Faraco, & A. Kingstone, 2003). Freeman and Driver used "long-range" visual motion stimuli, which travel over long spatial and temporal intervals and engage high-order cortical areas (K. G. Claeys, D. T. Lindsey, E. De Schutter, & G. A. Orban, 2003; Y. Zhuo et al., 2003). We asked whether Freeman and Driver's temporal effects extended to the short-range apparent-motion stimuli that engage cortical area MT, a lower-order area with well-established spatiotemporal selectivity for visual motion (e.g. A. Mikami, 1991, 1992; A. Mikami, W. T. Newsome, & R. H. Wurtz, 1986a, 1986b; W. T. Newsome, A. Mikami, & R. H. Wurtz, 1986). Consistent with a temporal-capture account, we found that static sounds bias the perception of both the direction (Experiment 1) and the speed (Experiment 2) of short-range motion. Our results suggest that auditory timing may interact with visual spatiotemporal processing as early as cortical area MT. Examination of the neuronal responses of this well-studied area to the stimuli used in this study would provide a test and might provide insight into the neuronal representation of time.     

Perceived speed of motion in depth is reduced in the periphery

The perceived speed of motion in depth (MID) for a monocularly visible target was measured in central and peripheral vision using a 2AFC speed discrimination task. Only binocular cues to MID were available: changing disparity and interocular velocity difference (IOVD). Perceived speed for monocular lateral motion and perceived depth for static disparity were also assessed, again in both central and peripheral vision. The purpose of the experiment was to assess the relative contributions of changing disparity and IOVD cues to the perceived speed of stereomotion. Although peripheral stimuli appeared to lie at approximately the same depth as their central counterparts, their apparent speed was reduced. Monocular/lateral and binocular/MID speeds were reduced to a similar extent. It seems that reduced apparent monocular speed leads to reduced perceived MID speed, despite the fact that the disparity system appears to be unaffected. These results suggest that the IOVD cue makes a significant contribution to MID speed perception.     

Comparing motion induction in lateral motion and motion in depth

Induced motion, the apparent motion of an object when a nearby object moves, has been shown to occur in a variety of different conditions, including motion in depth. Here we explore whether similar patterns of induced motion result from induction in a lateral direction (frontoparallel motion) or induction in depth. We measured the magnitude of induced motion in a stationary target for: (a) binocularly viewed lateral motion of a pair of inducers, where the angular motion is in the same direction for the two eyes, and (b) binocularly viewed motion in depth of inducers, where the angular motions in the two eyes are opposite to each other, but the same magnitude as for the lateral motion. We found that induced motion is of similar magnitude for the two viewing conditions. This suggests a common mechanism for motion induction by both lateral motion and motion in depth, and is consistent with the idea that the visual signals responsible for induced motion are established before angular information is scaled to obtain metric motion in depth.     

Auditory event-related signals in mouse ERG recordings

Purpose

In murine disease models, particularly in cases when retinal electrical activity is reduced, an event-related component becomes apparent that does not change with the stimulus intensity in electroretinogram (ERG) recordings. In this work, we show that this electric component is evoked by the sound of the flash discharge rather than the light flash itself.

Methods

Wild-type mice (C57BL/6), mice with rod function only (Cnga3 ^?/?), mice lacking any photoreceptor function (Cnga3 ^?/? rho ^?/?), and mice with no auditory function (Cdh23 ^vAlb/vAlb ) were examined with Xenon flash ERG systems. An acoustic noise generator was used to mask discharge sounds.

Results

ERG recording modalities were identified where usually no discernible response can be elicited. These include photopic conditions in Cnga3 ^?/? mice, photopic conditions together with very low stimulus intensities in C57BL/6 mice, and both scotopic and photopic conditions in Cnga3 ^?/? rho ^?/? mice. However, in all of these cases, small signals, featuring an initial a-wave like deflection at about 20 ms and a subsequent b-wave like deflection peaking at about 40 ms after the flash, were detected. In contrast, such signals could not be detected in deaf Cdh23 ^vAlb/vAlb mice. Furthermore, masking the Xenon discharge sound by continuous acoustic noise led to a loss of the event-related signals in a reversible manner.

Conclusions

We could identify an auditory event-related component, presumably resembling auditory evoked potentials, as a major source of ERG signals of non-visual origin in mice. This finding may be of particular importance for the analysis and interpretation of ERG data in mice with reduced visual responses.     

Infant visual acuity is underestimated because near threshold gratings are not preferentially fixated

Grating acuity thresholds obtained by the looking preference procedure have been based on the assumption that infants always prefer to look at visible patterns over blank fields. Consequently, it has been assumed that the infant's preference for gratings, when compared to blank fields, would decline monotonically from 100 to 50% as the gratings increased in spatial frequency from above-threshold gratings to below-threshold gratings. Contrary to that assumption, we now find that the preference function falls significantly below 50% only to rise again at higher spatial frequencies. If preference for the grating drops significantly below 50% then the infant must be preferentially fixating the blank field which, in turn, implies discrimination of the grating. Consequently, grating acuity must exceed that based only on preferences for the grating greater than 50%.     

Object-based anisotropic mislocalization by retinotopic motion signals

The relative visual positions of briefly flashed stimuli are systematically modified in the presence of motion signals. We have recently shown that the perceived position of a spatially extended flash stimulus is anisotropically shifted toward a single convergent point back along the trajectory of a moving object without a significant change in the perceived shape of the flash [Watanabe, K., & Yokoi, K. (2006). Object-based anisotropies in the flash-lag effect. Psychological Science, 17, 728-735]. In the previous experiment, the moving stimulus moved in both retinotopic and environmental coordinates. In the present study, we examined whether the anisotropic mislocalization depends on retinotopic or object motion signals. When the retinal image of a moving stimulus was rendered stationary by smooth pursuit, the anisotropic pattern of mislocalization was not observed. In contrast, when the retinal image of a stationary stimulus was moved by eye movements, anisotropic mislocalization was observed, with the magnitude of the mislocalization comparable to that in the previous study. In both cases, there was little indication of shape distortion of the flash stimulus. These results demonstrate a clear case of object-based mislocalization by retinotopic motion signals; retinotopic--not object--motion signals distort the perceived positions of visual objects after the shape representations are established.     

Disparity-energy signals in perceived stereoscopic depth

Stereopsis, the ability to sense the world in three dimensions (3D) from pairs of retinal images, functions when both images have corresponding elements. When observers view stereograms lacking a global match, they do not perceive 3D structure, whereas several cortical areas encode stereoscopic depth in the disparity energy. Whether these neural representations are exploited or ignored in perceptual decisions remains elusive. By combining contrast-reversal and delay between stereo images, we found that disparity-energy signals mediate the reversal of stereoscopic depth judgments. A crisp, adjacent plane of reference was crucial for the signal to be used in the judgments. Disparity discrimination relies on the disparity-energy signal when the stimulus has no global binocular match and is accompanied by a fixed surface of reference.     

Motor signals in visual localization

We demonstrate a strong sensory-motor coupling in visual localization in which experimental modification of the control of saccadic eye movements leads to an associated change in the perceived location of objects. Amplitudes of saccades to peripheral targets were altered by saccadic adaptation, induced by an artificial step of the saccade target during the eye movement, which leads the oculomotor system to recalibrate saccade parameters. Increasing saccade amplitudes induced concurrent shifts in perceived location of visual objects. The magnitude of perceptual shift depended on the size and persistence of errors between intended and actual saccade amplitudes. This tight agreement between the change of eye movement control and the change of localization shows that perceptual space is shaped by motor knowledge rather than simply constructed from visual input.     

Integrating space and time in visual search: How the preview benefit is modulated by stereoscopic depth

We examined visual search for letters that were distributed across both 3 dimensional space, and time. In Experiment 1, when participants had foreknowledge of the depth plane and time interval where targets could appear, search was more efficient if the items could be segmented either by depth or by time (with a 1000 ms preview), and there were increased benefits when the two cues (depth and time) were combined. In Experiments 2 and 3 the target depth plane was always unknown to the participant. In this case, depth cues alone did not facilitate search, though they continued to increase the preview benefit. In Experiment 4 new items in preview search could fall at the same depth as preview items or a new depth. There was a substantial cost to search if the target appeared at a previewed depth. Experiment 5 showed that this cost remained even when participants knew the target would appear at the old depth on 75% of trials. The results indicate that spatial (depth) and temporal cues combine to enhance visual segmentation and selection, and this is accomplished by inhibition of distractors in irrelevant depth planes.     

Illusory motion reversal is caused by rivalry, not by perceptual snapshots of the visual field

In stroboscopic conditions--such as motion pictures--rotating objects may appear to rotate in the reverse direction due to under-sampling (aliasing). A seemingly similar phenomenon occurs in constant sunlight, which has been taken as evidence that the visual system processes discrete "snapshots" of the outside world. But if snapshots are indeed taken of the visual field, then when a rotating drum appears to transiently reverse direction, its mirror image should always appeared to reverse direction simultaneously. Contrary to this hypothesis, we found that when observers watched a rotating drum and its mirror image, almost all illusory motion reversals occurred for only one image at a time. This result indicates that the motion reversal illusion cannot be explained by snapshots of the visual field. The same result is found when the two images are presented within one visual hemifield, further ruling out the possibility that discrete sampling of the visual field occurs separately in each hemisphere. The frequency distribution of illusory reversal durations approximates a gamma distribution, suggesting perceptual rivalry as a better explanation for illusory motion reversal. After adaptation of motion detectors coding for the correct direction, the activity of motion-sensitive neurons coding for motion in the reverse direction may intermittently become dominant and drive the perception of motion.     

The perceived visual direction of monocular objects in random-dot stereograms is influenced by perceived depth and allelotropia

The proposed influence of objects that are visible to both eyes on the perceived direction of an object that is seen by only one eye is known as the “capture of binocular visual direction”. The purpose of this study was to evaluate whether stereoscopic depth perception is necessary for the “capture of binocular visual direction” to occur. In one pair of experiments, perceived alignment between two nearby monocular lines changed systematically with the magnitude and direction of horizontal but not vertical disparity. In four of the five observers, the effect of horizontal disparity on perceived alignment depended on which eye viewed the monocular lines. In additional experiments, the perceived alignment between the monocular lines changed systematically with the magnitude and direction of both horizontal and vertical disparities when the monocular line separation was increased from 1.1° to 3.3°. These results indicate that binocular capture depends on the perceived depth that results from horizontal retinal image disparity as well as allelotropia, or the averaging of local-sign information. Our data suggest that, during averaging, different weights are afforded to the local-sign information in the two eyes, depending on whether the separation between binocularly viewed targets is horizontal or vertical.     

Illusory motion in visual displays

The apparent motion of a change in the structure of a random check pattern is studied by spatially masking it with another noise pattern and it is compared with phi motion. A fundamental difference with phi motion is the insensitivity of second order correlators (Reichardt mechanisms) to this apparent motion. The following experimental characteristics distinguish this motion from phi motion: it induces no motion after-effect, it is not transparent to another simultaneous motion, it is strongly influenced by spatial masking and it does not evoke optokinetic nystagmus. A fourth order detector is introduced which is sensitive to this illusory motion as well as to phi motion. Simulation experiments with this detector together with the subjective reports of the observers lead us to the conclusion that human subjects inadvertently treat the coarsest spatial structures as signal and the finest as the disturbing noise.     

The integration of local chromatic motion signals is sensitive to contrast polarity

Global motion integration mechanisms can utilize signals defined by purely chromatic information. Is global motion integration sensitive to the polarity of such color signals? To answer this question, we employed isoluminant random dot kinematograms (RDKs) that contain a single chromatic contrast polarity or two different polarities. Single-polarity RDKs consisted of local motion signals with either a positive or a negative S or L-M component, while in the different-polarity RDKs, half the dots had a positive S or L-M component, and the other half had a negative S or L-M component. In all RDKs, the polarity and the motion direction of the local signals were uncorrelated. Observers discriminated between 50% coherent motion and random motion, and contrast thresholds were obtained for 81% correct responses. Contrast thresholds were obtained for three different dot densities (50, 100, and 200 dots). We report two main findings: (1) dependence on dot density is similar for both contrast polarities (+S vs. -S, +LM vs. -LM) but slightly steeper for S in comparison to LM and (2) thresholds for different-polarity RDKs are significantly higher than for single-polarity RDKs, which is inconsistent with a polarity-blind integration mechanism. We conclude that early motion integration mechanisms are sensitive to the polarity of the local motion signals and do not automatically integrate information across different polarities.     

Neurons in cat visual cortex tuned to the direction of motion in depth: Effect of positional disparity

We investigated sensitivity to the direction of stimulus motion in depth in neurons of cat visual cortex by using bar stimuli with different image velocities on the two retinae. These stimuli were presented at seven different retinal disparities (i.e. with different locations in depth). Approximately one-fourth of the neurons examined were sensitive to the direction of stimulus motion in depth. In general, the motion-in-depth tuning of these neurons was either unaffected by disparity or changed simply and systematically as a function of disparity, even when disparity was varied over the broad range of 12°. In their relative indifference to disparity, the motion-in-depth neurons contrast with the units that are very selective to disparity and that respond best to sideways motion. Human equivalents to these two classes of units might provide a physiological basis for the distinction between binocularlydriven channels for motion in depth and for disparity (i.e. relative position in depth) that have been proposed on psychophysical grounds.