Binocular vision

Spatial scale of stereomotion speed processing

by Kevin Brooks

Brooks, K. R. & Stone L. S. (2006). Spatial scale of stereomotion speed processing. Journal of Vision, 6, 1257-1266, http://journalofvision.org/6/11/9, doi:10.1167/6.11.9

To examine the spatial scale of the mechanisms supporting the perception of motion in depth defined by binocular cues,... more To examine the spatial scale of the mechanisms supporting the perception of motion in depth defined by binocular cues, we measured stereomotion speed discrimination thresholds as a function of stimulus size using a two-interval speed comparison task. Stimuli were either random dot stereogram (RDS) bars featuring both the changing disparity (CD) and the interocular velocity difference (IOVD) cues to motion in depth or dynamic random dot stereogram (DRDS) bars featuring the CD cue alone. Monocular speed discrimination performance was also assessed, using half-images of the RDS stimulus. In addition, subjects’ stereoacuity for stationary versions of the binocular stimuli was measured. Stimuli ranged in vertical extent from 1.25 to 40 min. Sensitivity to speed differences was strongly related to stimulus height for DRDS stimuli. Performance decreased rapidly as stimulus size was reduced, becoming nearly random for heights below 5 min. However, for RDS stimuli, speed discrimination performance declined with reductions in stimulus size at a far slower rate, providing superior performance at every stimulus size used. Monocular performance was superior still for the majority of subjects, yet showed a similar rate of decline to binocular RDS stimuli. We conclude that the spatial resolution of the CD mechanism and its static disparity inputs is, on average, nearly nine times more coarse than the IOVD system and its monocular motion inputs. Static stereoacuity controls show that this finding cannot be explained by differences in the disparity signals available in our RDS and DRDS stimuli.

Stereomotion suppression and the perception of speed: accuracy and precision as a function of 3D trajectory

by Kevin Brooks

Brooks, K. R. & Stone L. S. (2006). Stereomotion suppression and the perception of speed: accuracy and precision as a function of 3D trajectory. Journal of Vision, 6, 1214-1223, http://journalofvision.org/6/11/6, doi:10.1167/6.11.6

The precision and accuracy of speed discrimination performance for stereomotion stimuli were assessed for several... more The precision and accuracy of speed discrimination performance for stereomotion stimuli were assessed for several receding 3D trajectories confined to the horizontal meridian. It has previously been demonstrated in a variety of tasks that detection thresholds are substantially higher when subjects observe a stereomotion stimulus than when simply viewing one of its component monocular half-imagesVa phenomenon known as stereomotion suppression (C. W. Tyler, 1971). Using monocularly visible motion in depth targets, we found mean speed discrimination thresholds to be higher for stereomotion,
compared with monocular lateral speed discrimination thresholds for equivalent stimuli, demonstrating a disadvantage for binocular viewing in the case of speed discrimination as well. Furthermore, speed discrimination thresholds for motion in depth were not systematically affected by trajectory angle; hence, the disadvantage of binocular viewing persists even when there are concurrent changes in binocular visual direction. Lastly, there was a tendency for oblique trajectories of stereomotion to be perceived as faster than equally rapid motion receding directly away from the subject along the midline. Our data, in addition to earlier stereomotion suppression observations, are consistent with a stereomotion system that takes a noisy, weighted difference of the stimulus velocities in the two eyes to compute motion in depth.

The swinging doors of perception: Stereomotion without binocular matching

by Kevin Brooks

Brooks, K. R. & Gillam, B. J. (2006). The swinging doors of perception: stereomotion without binocular matching. Journal of Vision, 6, 685-695, http://journalofvision.org/6/7/2, doi:10.1167/6.7.2

Until recently, it was considered necessary for features in the two eyes to be matched before the evaluation of... more Until recently, it was considered necessary for features in the two eyes to be matched before the evaluation of differences in their locations (binocular disparities) could reveal depth information. Motion in depth can also be perceived binocularly from related changes in the locations of matched binocular features. However, unmatched features can arise when a binocular object occludes more distant features in one eye but not the other. The presence and extent of such features can provide quantitative depth information, although perceived depth relative to geometrical predictions may vary from one such arrangement to another. The ability of humans to perceive motion in depth from unmatched stimuli has not previously been explored. Here, we use B. Gillam, S. Blackburn, and K. Nakayama’s (1999) ‘‘monocular gap’’ stimuli to investigate perception of motion in depth simulated by a change in the extent of a monocularly occluded feature in a binocular display. Settings of a motion in depth probe revealed that the magnitude of perceived motion in depth is generally as large as that for a stimulus containing matchable binocular features. We show that our stimuli provide disambiguating information not present in similar static stimuli. We conclude that in the computation of motion in depth, a binocular match is not required. A new cue--dynamic half-occlusion--can be used to reach an accurate percept.

Quantitative perceived depth from sequential monocular decamouflage

by Kevin Brooks

Brooks, K. R. & Gillam, B. J. (2006). Quantitative perceived depth from sequential monocular decamouflage. Vision Research, 46, 605-613. doi:10.1016/j.visres.2005.06.015

We present a novel binocular stimulus without conventional disparity cues whose presence and depth are revealed by... more We present a novel binocular stimulus without conventional disparity cues whose presence and depth are revealed by sequential monocular stimulation (delay P 80 ms). Vertical white lines were occluded as they passed behind an otherwise camouflaged black rectangular target. The location (and instant) of the occlusion event, decamouflaging the target
s edges, differed in the two eyes. Probe settings to match the depth of the black rectangular target showed a monotonic increase with simulated depth. Control tests discounted the possibility of subjects integrating retinal disparities over an extended temporal window or using temporal disparity. Sequential monocular decamouflage was found to be as precise and accurate as conventional simultaneous stereopsis with equivalent depths and exposure durations.

Monocular Transparency and unpaired stereopsis

by Kevin Brooks

Grove, P. M., Brooks, K. R., Anderson, B. L. & Gillam, B. J. (2006). Monocular transparency and unpaired stereopsis. Vision Research, 46, 3041-3053. doi:10.1016/j.visres.2006.05.003

Howard and Duke [Howard, I.P., & Duke, P.A. (2003). Monocular transparency generates quantitative depth. Vision... more Howard and Duke [Howard, I.P., & Duke, P.A. (2003). Monocular transparency generates quantitative depth. Vision Research, 43, 2615–2621] recently proposed a new source of binocular information they claim is used to recover depth in stereoscopic displays. They argued that these displays lack conventional disparity and that the metrical depth experienced results from transparency rather than occlusion relations. Using a variety of modified versions of their stimuli, we show here that the conditions for transparency are not required to elicit the depth experienced in their stereograms. We demonstrated that quantitative and precise depth depended not on the presence of transparency but on the presence of horizontal contours of the same contrast polarity. Depth was attenuated, particularly at larger target offsets, when horizontal contours had opposite contrast polarity for at least a portion of their length. We also show that a demonstration Howard and Duke used to control for the role of horizontal contours can be understood as an example of Gillam et al.’s Gillam, B.J., Blackburn, S., & Nakayama, K. (1999). Stereopsis based on monocular gaps: metrical coding of depth and slant without matching contours. Vision Research, 39, 493–502 monocular gap stereopsis; a form of binocular occlusion. In summary the findings reported by Howard and Duke can be understood by known processes for the computation of binocular disparity and binocular occlusion.

Monocular motion adaptation affects the perceived trajectory of stereomotion

by Kevin Brooks

Brooks, K. R. (2002b). Monocular motion adaptation affects the perceived trajectory of stereomotion. Journal of Experimental Psychology: Human Perception and Performance, 28, 1470-1482.

Perceived stereomotion trajectory was measured before and after adaptation to lateral motion in the dominant or... more Perceived stereomotion trajectory was measured before and after adaptation to lateral motion in the dominant or nondominant eye to assess the relative contributions of 2 cues: changing disparity and interocular velocity difference. Perceived speed for monocular lateral motion and perceived binocular visual direction (BVD) was also assessed. Unlike stereomotion trajectory perception, the BVD of static targets showed an ocular dominance bias, even without adaptation. Adaptation caused equivalent biases in perceived trajectory and monocular motion speed, without significantly affecting perceived BVD. Predictions from monocular motion data closely match trajectory perception data, unlike those from BVD sources. The results suggest that the interocular velocity differences make a significant contribution to stereomotion trajectory perception.

Hinge versus twist: the effects of “reference surface” and discontinuities on stereoscopic slant perception

by Kevin Brooks

Gillam, B. J., Blackburn, S. & Brooks, K. R. (2007). Hinge versus twist: the effects of “reference surface” and discontinuities on stereoscopic slant perception. Perception, 36, 596-616, doi: 10.1068/p5535

Stereoscopic slant perception around a vertical axis (horizontal slant) is often found to be strongly attenuated... more Stereoscopic slant perception around a vertical axis (horizontal slant) is often found to be strongly attenuated relative to geometric prediction. Stereo slant is much greater, however,
when an adjacent surface, stereoscopically in the frontal plane, is added. This slant enhancement is often attributed to the presence of a `reference surface' or to a spatial change in the disparity gradient (introducing second and higher derivatives of disparity). Gillam, Chambers, and Russo (1988 Journal of Experimental Psychology: Human Perception and Performance 14 163-175) questioned the role of these factors in that placement of the frontal-plane surface in a direction collinear with the slant axis (twist configuration) sharply reduced latency for perceiving slant whereas placing the same surface in a direction orthogonal to the slant axis (hinge configuration) had little effect.We here confirm these findings for slant magnitude, showing a striking advantage for twist over hinge configurations.We also examined contrast slant measured on the frontal-plane surface in the hinge and twist configurations. Under conditions where test and inducer surfaces have centres at the same depth for twist and hinge, we found that twist configurations produced strong negative slant contrast, while hinge configurations produced significant positive contrast or slant assimilation.We conclude that stereo slant and contrast effects for neighbouring surfaces can only be understood from the patterns and gradients of step disparities present. It is not adequate to consider the second surface merely as a reference slant for the first or as having its effect via a spatial change in the disparity gradient.

Stereomotion perception for a monocularly camouflaged stimulus

by Kevin Brooks

Brooks, K. R. & Gillam, B. J. (2007). Stereomotion perception for a monocularly camouflaged stimulus. Journal of Vision, 7, 1-14, http://journalofvision.org/7/13/1, doi:10.1167/7.13.1

Under usual circumstances, motion in depth is associated with conventional stereomotion cues: a change in disparity... more Under usual circumstances, motion in depth is associated with conventional stereomotion cues: a change in disparity and differences between object velocities in each monocular image. However, occasionally these cues are unavailable due to the fact that in one eye the object may be occluded by, or camouflaged against appropriately positioned binocular objects. We report two experiments concerned with stereomotion perception under conditions of monocular camouflage. In Experiment 1, the visible half-image of a monocularly camouflaged object translated laterally. In this binocular context, percepts of lateral motion and motion in depth were equally consistent with the stimulus. Subjects perceived an oblique trajectory of 3D motion, compared to the more direct 3D trajectory experienced for binocularly matched stimuli. In Experiment 2, the perceived velocity of stereomotion was assessed. Again, for the stimulus used in Experiment 1, perceived stereomotion speed was lower than that for matched stimuli. However, when additional background objects were present, tightening the ecological constraints, perceived stereomotion velocity was often equivalent to that for matched stimuli. These results demonstrate for the first time that the motion of a monocularly camouflaged object can result in the perception of stereomotion, and that the perceived trajectory and speed are influenced by the ecological constraints of binocular geometry.

Breaking camouflage: Binocular disparity reduces contrast masking in natural images

by Kevin Brooks

Wardle, S., Cass, J., Brooks, K.R. & Alais, D. (2010). Breaking camouflage: Binocular disparity reduces contrast masking in natural images. Journal of Vision, 10, 38, 1-12, http://www.journalofvision.org/content/10/14/38, doi:10.1167/10.14.38.

Visual overlay masking is typically studied with a mask and target located at the same depth plane. Masking is reduced... more Visual overlay masking is typically studied with a mask and target located at the same depth plane. Masking is reduced when binocular disparity separates the target from the mask (G. Moraglia & B. Schneider, 1990). We replicate this finding for a broadband target masked by natural images and find the greatest masking (threshold elevation) when target and mask occupy the same depth plane. Masking was reduced equally whether the target appeared at a crossed or an uncrossed disparity. We measure the tuning of masking and determine the extent of the benefit afforded by disparity. Threshold elevation decreases monotonically with increasing disparity until +/-8 arcmin. Two underlying components to the masking are evident; one accounts for around two-thirds of the masking and is independent of disparity. The second component is disparity-dependent and results in additional masking when there is zero disparity. Importantly, the reduction in masking with disparity cannot be explained by interocular decorrelation; we use a single-interval orientation discrimination task to exclude this possibility. We conclude that when the target and mask are presented at different depths they activate distinct populations of disparity-tuned neurons, resulting in less masking of the target.

Interocular velocity difference contributes to stereomotion speed perception

by Kevin Brooks

Brooks, K. R. (2002a). Interocular velocity difference contributes to stereomotion speed perception. Journal of Vision, 2, 218-231, http://journalofvision.org/2/3/2/, doi:10.1167/2.3.2.

Two experiments are presented assessing the contributions of the rate of change of disparity (CD) and interocular... more Two experiments are presented assessing the contributions of the rate of change of disparity (CD) and interocular velocity difference (IOVD) cues to stereomotion speed perception. Using a two-interval forced-choice paradigm, the perceived speed of directly approaching and receding stereomotion and of monocular lateral motion in random dot stereogram (RDS) targets was measured. Prior adaptation using dysjunctively moving random dot stimuli induced a velocity aftereffect (VAE). The degree of interocular correlation in the adapting images was manipulated to assess the effectiveness of each cue. While correlated adaptation involved a conventional RDS stimulus, containing both IOVD and CD cues, uncorrelated adaptation featured an independent dot array in each monocular half-image, and hence lacked a coherent disparity signal. Adaptation produced a larger VAE for stereomotion than for monocular lateral motion, implying effects at neural sites beyond that of binocular combination. For motion passing through the horopter, correlated and uncorrelated adaptation stimuli produced equivalent stereomotion VAEs. The possibility that these results were due to the adaptation of a CD mechanism through random matches in the uncorrelated stimulus was discounted in a control experiment. Here both simultaneous and sequential adaptation of left and right eyes produced similar stereomotion VAEs. Motion at uncrossed disparities was also affected by both correlated and uncorrelated adaptation stimuli, but showed a significantly greater VAE in response to the former. These results show that (1) there are two separate, specialised mechanisms for encoding stereomotion: one through IOVD, the other through CD; (2) the IOVD cue dominates the perception of stereomotion speed for stimuli passing through the horopter; and (3) at a disparity pedestal both the IOVD and the CD cues have a significant influence.

Stereomotion speed perception is contrast dependent

by Kevin Brooks

Brooks, K. (2001). Stereomotion speed perception is contrast dependent. Perception, 30, 725-731.

The effect of contrast on the perception of stimulus speed for stereomotion and monocular lateral motion was... more The effect of contrast on the perception of stimulus speed for stereomotion and monocular lateral motion was investigated for successive matches in random-dot stimuli. The familiar `Thompson effect' - that a reduction in contrast leads to a reduction in perceived speed - was found in similar proportions for both binocular images moving in depth, and for monocular images translating laterally. This result is consistent with the idea that the monocular motion system has a significant input to the stereomotion system, and dominates the speed percept for approaching motion.

Stereomotion suppression and the perception of speed: Accuracy and precision as a function of 3D trajectory

by Kevin Brooks

Brooks, K. R. & Stone L. S. (2006). Stereomotion suppression and the perception of speed: accuracy and precision as a function of 3D trajectory. Journal of Vision, 6, 1214-1223, http://journalofvision.org/6/11/6, doi:10.1167/6.11.6

The precision and accuracy of speed discrimination performance for stereomotion stimuli were assessed for several... more The precision and accuracy of speed discrimination performance for stereomotion stimuli were assessed for several receding 3D trajectories confined to the horizontal meridian. It has previously been demonstrated in a variety of tasks that detection thresholds are substantially higher when subjects observe a stereomotion stimulus than when simply viewing one of its component monocular half-imagesVa phenomenon known as stereomotion suppression (C. W. Tyler, 1971). Using monocularly visible motion in depth targets, we found mean speed discrimination thresholds to be higher for stereomotion,
compared with monocular lateral speed discrimination thresholds for equivalent stimuli, demonstrating a disadvantage for binocular viewing in the case of speed discrimination as well. Furthermore, speed discrimination thresholds for motion in depth were not systematically affected by trajectory angle; hence, the disadvantage of binocular viewing persists even when there are concurrent changes in binocular visual direction. Lastly, there was a tendency for oblique trajectories of stereomotion to be perceived as faster than equally rapid motion receding directly away from the subject along the midline. Our data, in addition to earlier stereomotion suppression observations, are consistent with a stereomotion system that takes a noisy, weighted difference of the stimulus velocities in the two eyes to compute motion in depth.

The effect of induced vertical divergence on horizontal fusional amplitudes

by Greg Richardson

Richardson GA and Firth AY. British and Irish Orthoptic Journal; 2009:6:71-74

Inter-facial relations: Binocular geometry when eyes meet

by Nick Wilkinson

Int. Conf. Morphological Computation Venice 2011

Infants are sensitive to eye contact and face like
stimuli from birth. We advance the novel hypothesis that... more Infants are sensitive to eye contact and face like
stimuli from birth. We advance the novel hypothesis that the
observed sensitivity of human neonates to eye contact may be
mediated in part by sensor distribution. The arrangement of the
observers eyes acts as a morphological template for eye-like feature
pairs in the world, providing certain geometric constraints
on stereo relations which may help to focus attention on eyelike
stimuli. We give a brief proof-of-concept demonstration and
discuss how this morphological mechanism could be exploited
by humans and humanoid robots to facilitate the establishment
and maintenance of eye contact. We advance three experimental
hypotheses which would help to distinguish this mechanism from
existing explanations.

Frontiers: Fear modulates visual awareness similarly for facial and bodily expressions

by Bernard Stienen

Hysteresis effects in stereopsis and binocular rivalry

by Athena Buckthought

Interaction between binocular rivalry and depth in plaid patterns

by Athena Buckthought

Bistable percepts in the brain: fMRI contrasts monocular pattern rivalry and binocular rivalry

by Athena Buckthought

A matched comparison of binocular rivalry and depth perception with fMRI

by Athena Buckthought

Stereoscopic depth discrimination with contrast windowed stimuli

by Athena Buckthought