Depth Discrimination Task Research Articles

Employment of time-varying sensory evidence to test the mechanisms underlying flexible decision-making.

To make flexible decisions in dynamic environments, the brain must integrate behaviorally relevant information while simultaneously discarding irrelevant information. This study aimed to investigate the mechanisms responsible for discarding irrelevant information during context-dependent decision-making. We trained two macaque monkeys to switch between direction and depth discrimination tasks in successive trials. During decision-making, the strength of the motion or depth signal changes transiently at various times, introducing a brief pulse. We assessed the effects of pulse on behavioral choices. Consistent with previous findings, early relevant pulses, such as motion pulses during direction discrimination, had a significantly larger effect compared to late pulses. Critically, the effects of irrelevant pulses, such as motion pulses during depth discrimination, exhibited an initial minimal effect, followed by an increase and subsequent decrease as a function of pulse timing. Gating mechanisms alone, aimed at discarding irrelevant information, did not account for the observed time course of pulse effects. Instead, the observed increase in the effects of irrelevant pulses with time suggested the involvement of a leaky integration mechanism. The results suggested that the brain controls the amount of disposal in accumulating sensory evidence during flexible decision-making.

The NMDA receptor antagonist ketamine impairs and delays context-dependent decision making in the parietal cortex

Flexible decision making is an indispensable ability for humans. A subanesthetic dose of ketamine, an N-methyl-D-aspartate receptor antagonist, impairs this flexibility in a manner that is similar to patients with schizophrenia; however how it affects neural processes related to decision making remains unclear. Here, we report that ketamine administration impairs neural processing related to context-dependent decision making, and delays the onset of decision making. We recorded single unit activity in the lateral intraparietal area (LIP) while monkeys switched between a direction-discrimination task and a depth-discrimination task. Ketamine impaired choice accuracy for incongruent stimuli that required different decisions depending on the task, for the direction-discrimination task. Neural sensitivity to irrelevant depth information increased with ketamine during direction discrimination in LIP, indicating impaired processing of irrelevant information. Furthermore, the onset of decision-related neural activity was delayed in conjunction with an increased reaction time irrespective of task and stimulus congruency. Neural sensitivity and response onset of the middle temporal area (MT) were not modulated by ketamine, indicating that ketamine worked on neural decision processes downstream of MT. These results suggest that ketamine administration may impair what information to process and when to process it for the purpose of achieving flexible decision making.

Shape judgments in natural scenes: Convexity biases versus stereopsis

Determining the relief of upcoming terrain is critical to locomotion over rough or uneven ground. Given the significant contribution of stereopsis to perceived surface shape, it should play a crucial role in determining the shape of ground surfaces. The aim of this series of experiments was to evaluate the relative contribution of monocular and binocular depth cues to judgments of ground relief. To accomplish this goal, we simulated a depth discrimination task using naturalistic imagery. Stimuli consisted of a stereoscopically rendered grassy terrain with a central mound or a dip with varying height. We measured thresholds for discrimination of the direction of the depth offset. To determine the relationship between relief discrimination and measures of stereopsis, we used two stereoacuity tasks performed under the same viewing conditions. To assess the impact of ambiguous two-dimensional shading cues on depth judgments in our terrain task, we manipulated the intensity of the shading (low and high). Our results show that observers reliably discriminated ground reliefs as small as 20 cm at a viewing distance of 9.1 m. As the shading was intensified, a large proportion of observers (30%) exhibited a strong convexity bias, even when stereopsis indicated a concave depression. This finding suggests that there are significant individual differences in the reliance on assumptions of surface curvature that must be considered in experimental conditions. In impoverished viewing environments with limiting depth cues, these convexity biases could persist in judgments of ground relief, especially when shading cues are highly salient.

Task-specific employment of sensory signals underlies rapid task switching.

Much of our flexible behavior is dependent on responding efficiently to relevant information while discarding irrelevant information. Little is known, however, about how neural pathways governing sensory-motor associations can rapidly switch to accomplish such flexibility. Here, we addressed this question by electrically microstimulating middle temporal (MT) neurons selective for both motion direction and binocular disparity in monkeys switching between direction and depth discrimination tasks. Surprisingly, we frequently found that the observed psychophysical bias precipitated by delivering microstimulation to neurons whose preferred direction and depth were related to opposite choices in the two tasks was substantially shifted toward a specific movement. Furthermore, these effects correlated with behavioral switching performance. Our findings suggest that the outputs of sensory signals are task specific and that irrelevant sensory-motor pathways are gated depending on task demand so as to accomplish rapid attentional switching.

Effects of Various Local Lighting Conditions and Visual Function on Performance of Depth Discrimination Task

Effects of Various Local Lighting Conditions and Visual Function on Performance of Depth Discrimination Task

Natural binocular depth discrimination behavior in mice explained by visual cortical activity

In mice and other mammals, forebrain neurons integrate right and left eye information to generate a three-dimensional representation of the visual environment. Neurons in the visual cortex of mice are sensitive to binocular disparity,1-3 yet it is unclear whether that sensitivity is linked to the perception of depth.4-8 We developed a natural task based on the classic visual cliff and pole descent tasks to estimate the psychophysical range of mouse depth discrimination.5,9 Mice with binocular vision descended to a near (shallow) surface more often when surrounding far (deep) surfaces were progressively more distant. Occlusion of one eye severely impaired their ability to target the near surface. We quantified the distance at which animals make their decisions to estimate the binocular image displacement of the checkerboard pattern on the near and far surfaces. Then, we assayed the disparity sensitivity of large populations of binocular neurons in primary visual cortex (V1) using two-photon microscopy2 and quantitatively compared this information available in V1 to their behavioral sensitivity. Disparity information in V1 matches the behavioral performance over the range of depths examined and was resistant to changes in binocular alignment. These findings reveal that mice naturally use stereoscopic cues to guide their behavior and indicate a neural basis for this depth discrimination task.

Monovision: Consequences for depth perception from large disparities

Recent studies have confirmed that monovision treatment degrades stereopsis but it is not clear if these effects are limited to fine disparity processing, or how they are affected by viewing distance or age. Given the link between stereopsis and postural stability, it is important that we have full understanding of the impact of monovision on binocular function. In this study we assessed the short-term effects of optically induced monovision on a depth-discrimination task for young and older (presbyopic) adults. In separate sessions, the upper limits of stereopsis were assessed with participants' best optical correction and with monovision (-1D and +1D lenses in front of the dominant and non-dominant eyes respectively), at both near (62 cm) and far (300 cm) viewing distances. Monovision viewing resulted in significant reductions in the upper limit of stereopsis or more generally in discrimination performance at large disparities, in both age groups at a viewing distance of 300 cm. Dynamic photorefraction performed on a sample of four young observers revealed that they tended to accommodate to minimize blur in one eye at the expense of blur in the other. Older participants would have experienced roughly equivalent blur in the two eyes. Despite this difference, both groups displayed similar detrimental effects of monovision. In addition, we find that discrimination accuracy was worse with monovision at the 3 m viewing distance which involves fixation distances that are typical during walking. These data suggest that stability during locomotion may be compromised, a factor that is of concern for our older participants.

Context-Dependent Accumulation of Sensory Evidence in the Parietal Cortex Underlies Flexible Task Switching.

Flexible behavior depending on context is a hallmark of human cognition. During flexible behavior, the frontal and parietal cortices have complex representations that hinder efforts to conceptualize their underlying computations. We now provide evidence that neurons in the lateral intraparietal area accumulate relevant information preferentially depending on context. We suggest that behavioral flexibility is implemented in the form of temporal integration gain control in the parietal cortex.

Stereopsis after anterior temporal lobectomy

Brain areas critical for stereopsis have been investigated in non-human primates but are largely unknown in the human brain. Microelectrode recordings and functional MRI (fMRI) studies in monkeys have shown that in monkeys the inferior temporal cortex is critically involved in 3D shape categorization. Furthermore, some human fMRI studies similarly suggest an involvement of visual areas in the temporal lobe in depth perception.We aimed to investigate the role of the human anterior temporal neocortex in stereopsis by assessing stereoscopic depth perception before and after anterior temporal lobectomy. Eighteen epilepsy surgery patients were tested, pre- and postoperatively, in 3 different depth discrimination tasks. Sensitivity for local and global disparity was tested in a near-far discrimination task and sensitivity for 3D curvature was assessed in a convex-concave discrimination task, where 3D shapes were presented at different positions in depth.We found no evidence that temporal lobe epilepsy surgery has a significant effect on stereopsis. In contrast with earlier findings, we conclude that local as well as global stereopsis is maintained after unilateral resection of the temporal pole in epilepsy surgery patients. Our findings, together with previous studies, suggest that in humans more posterior visual regions underlie depth perception.

Effects of Long-Term Exposure on Sensitivity and Comfort with Stereoscopic Displays

Stereoscopic 3D media has recently increased in appreciation and availability. This popularity has led to concerns over the health effects of habitual viewing of stereoscopic 3D content; concerns that are largely hypothetical. Here we examine the effects of repeated, long-term exposure to stereoscopic 3D in the workplace on several measures of stereoscopic sensitivity (discrimination, depth matching, and fusion limits) along with reported negative symptoms associated with viewing stereoscopic 3D. We recruited a group of adult stereoscopic 3D industry experts and compared their performance with observers who were (i) inexperienced with stereoscopic 3D, (ii) researchers who study stereopsis, and (iii) vision researchers with little or no experimental stereoscopic experience. Unexpectedly, we found very little difference between the four groups on all but the depth discrimination task, and the differences that did occur appear to reflect task-specific training or experience. Thus, we found no positive or negative consequences of repeated and extended exposure to stereoscopic 3D in these populations.

자극과 배경의 대비, 배경 텍스쳐 밀도, 자극의 화면 시차가 크로스톡 지각에 미치는 영향

3D 영상을 시청하면서 느끼는 고유한 피로를 입체 시각 피로라고 부른다. 이 현상을 유발시키는 주된 요인으로 꼽히는 것은 화면시차, 상 흐림, 크로스톡 (crosstalk)의 세 가지 요인으로 알려져 있다. 이 중 화면 시차와 상 흐림은 영상 콘텐츠에 의하여 결정되며, 사용하는 디스플레이 종류에 관계없이 직접 조작할 수 있다. 그러나 크로스톡 요인은 다른 요인과는 다르게 3D 디스플레이의 물리적인 특성에 의하여 결정되는 요인이며 따라서 손쉽게 감소시키거나 제거하는 것이 불가능하다. 그러나 크로스톡이 입체 시각 피로에 미치는 영향은 자극 특성에 의하여 달라지며, 이러한 자극 특성은 조작 가능하다. 따라서 크로스톡이 입체 시각 피로에 미치는 영향을 확인하려면 크로스톡 지각에 영향을 미치는 자극 특성의 효과를 확인하여야 한다. 이런 목적을 달성하기 위하여 상대적 깊이 판단 과제를 사용하여 자극 특성 (자극과 배경의 대비, 배경 텍스쳐 밀도, 자극의 화면 시차)이 크로스톡 지각에 미치는 영향을 확인하였다. 그 결과 영상에 배경이 존재하고 자극의 화면시차가 적을 때 지각되는 크로스톡이 감소함을 시사하는 결과를 얻었다. 3D contents could cause unique 3D visual fatigue. Screen disparity, image blurring, and crosstalk are known to be the three major factors responsible for the fatigue. Among these, screen disparity and image blurring are content factors, that is, one can directly manipulate contents themselves to handle visual fatigue caused by these two factors. On the other hand, because crosstalk is closely tied to physical characteristics of 3D display, it is difficult or even impossible to reduce crosstalk-driven visual fatigue unless one replaces 3D display itself (for example, from active to passive display). However, the effects of crosstalk on 3D visual fatigue depends on visual stimulus features (that is, contents), and thus it is possible to manipulate stimulus features in order to handle visual fatigue caused by crosstalk. Hence, this research tested the effects of visual stimulus features on crosstalk (which then causes 3D visual fatigue). Using relative depth discrimination task, we tested the effects of stimulus-background contrast, background texture density, and screen disparity on the degree of perceived crosstalk. The results showed that crosstalk decreases with presence of background texture and with less degree of screen disparity.

Change in Choice-Related Response Modulation in Area MT during Learning of a Depth-Discrimination Task is Consistent with Task Learning

What are the neural mechanisms underlying improvement in perceptual performance due to learning? A recent study using motion-direction discrimination suggested that perceptual learning is due to improvements in the "readout" of sensory signals in sensory-motor cortex and not to improvements in neural sensitivity of the sensory cortex. To test the generality of this hypothesis, we examined this in a similar but different task. We recorded from isolated neurons in the middle temporal (MT) area while monkeys were trained in a depth-discrimination task. Consistent with earlier reports using direction discrimination, we found no long-term improvement in MT neuron sensitivity to depth, although monkey performance improved over months with extensive training, even when taking out the effect of behavioral biases. We further addressed improvement in the readout of sensory signals by focusing on choice-related response modulation [choice probability (CP)]. CP increased with training, suggesting an improvement in the readout of sensory signals from MT. CP, however, correlated more strongly with lapse rate than psychophysical threshold, suggesting that changes in readout may be restricted to early phases of learning. To test how behavioral learning, as well as the magnitude of CP, transferred across visual fields, we measured CP variation in one hemifield after training monkeys on the depth-discrimination task in the opposite hemifield. CP was large from the beginning of training in the untrained hemifield, even though a small but significant improvement in sensitivity was observed behaviorally. Overall, our findings are consistent with the idea that increases in CP reflect task learning.

The effect of ecologically relevant variations in light level on the performance of Mongolian gerbils on two visual tasks

Tests of rodent visual capacities are typically performed under standard laboratory illumination. However, light level can have subtle and complex effects on behavior in rodents. We tested Mongolian gerbils (Meriones unguiculatus) - a species that shows individual differences in activity pattern - on visual tasks at three ecologically relevant levels of ambient illuminance: approximating moonlight (1 lx), dawn or dusk (10 lx), and low daylight (100 lx). A jumping task and a grating discrimination quantified depth perception and grating acuity, respectively. Illuminance variations had important effects on behavior. Gerbils jumped faster in lower light on the depth discrimination task, but were also less accurate than in bright light. Daytime activity levels (possibly reflecting variations in activity pattern) mediated these effects, with animals that were awake during a lower proportion of daytime hours exhibiting a trend toward jumping faster with lower light level as compared to more day-active gerbils. Moreover, while illuminance did not affect acuity overall, it interacted with activity levels in a complex way: in both the darkest and lowest light levels, animals that were awake during a greater proportion of daytime hours showed higher acuity levels than animals that were less active during the day. These results indicate that gerbils show behavioral profiles in vision tasks that represent an interaction between visual ability and illuminance-sensitive motivational or emotional actors, perhaps including chronotype. Thus, the most ecologically relevant assessments of the visual performance of rodents will likely be achieved by testing at species-specific preferred light levels.

Transfer of choice-related response modulation across visual fields during learning of a depth-discrimination task

Transfer of choice-related response modulation across visual fields during learning of a depth-discrimination task

Binocular depth discrimination and estimation beyond interaction space

The benefits of binocular vision have been debated throughout the history of vision science yet few studies have considered its contribution beyond a viewing distance of a few metres. What benefit, if any, does binocular vision confer for distance vision? Elementary texts commonly assert that stereopsis is ineffective beyond modest distances despite theoretical analysis suggesting a much larger effective range. We compared monocular and binocular performance on depth interval estimation and discrimination tasks at and beyond 4.5m. Stimuli consisted of a combination of: 1) the reference stimulus, a smoothly finished wooden architectural panel, mounted upright, and facing the subject, 2) the test stimulus, a thin rod that could be precisely moved in depth and 3) a homogeneous background. An aperture prevented view of the top and bottom of the stimuli. Subjects made verbal, signed estimates in cm of the depth between the test and reference stimuli. On each trial, the depth was set between ±100cm. Observers viewed the displays either monocularly or binocularly from 4.5, 9.0 or 18.0m. Depth discrimination at 9.0 m was also evaluated using adaptive staircase procedures. Regression analysis provided measures of the scaling between perceived depth and actual depth (the ‘gain’) and the precision. Under monocular conditions, perceived depth was significantly compressed. Binocular depth estimates were much nearer to veridical although also compressed. Both raw precision measures and those normalized by the gain were much smaller for binocular compared to monocular conditions (ratios between 2.1 and 48). We confirm that stereopsis supports reliable depth discriminations beyond typical laboratory distances. Furthermore, binocular vision can significantly improve both the accuracy and precision of depth estimation to at least 18m. We will discuss additional experiments to extend these results to larger viewing distances and to evaluate the contribution of stereopsis under rich cue conditions.

Spatial scale interactions in stereopsis for different types of band-limited stimuli

Stereo depth perception depends on computing the correspondence between image features in the two eyes. This computation is believed to occur in parallel at different spatial scales of the stimulus, and to yield independent estimates of disparity at each scale. In simple terms, the input image is filtered into spatial frequency bands and binocular disparities are computed separately for each band. In order to characterize these spatial-frequency selective computations, various studies have utilized band-limited stimuli such as Difference-of-Gaussian (DOG), Gabor and filtered noise patterns. Results have generally confirmed the importance of spatial scale in stereo depth perception, and have also identified interactions among spatial scales, but have yielded some puzzling inconsistencies. In particular, results have shown that factors other than spatial scale, such as the envelope or outline of the stimulus can play a role in reducing false matches in repetitive and high spatial frequency stimuli. Following this line of reasoning, our research compared how the spatial frequency of different types of band-limited stimuli affected performance in a depth discrimination task, where the pedestal disparity of the reference stimulus was varied. Our immediate goal was to explain why DOG stimuli used by Siderov and Harwerth (1993) revealed a minor effect of spatial frequency, whereas filtered noise used by Smallman and MacLeod (1997) revealed a very large effect. We confirmed that the differences found using DOG and filtered noise patterns were reliable. We also conducted an experiment measuring depth discrimination using filtered noise that was contrast modulated with a Gaussian envelope, thus bridging the effects observed with DOG and filtered noise stimuli. We explained the differences between the different stimuli using a model that was sensitive to the number of false matches in the stimulus.

MT neurons can account for behavioral performance in a depth discrimination task

MT neurons can account for behavioral performance in a depth discrimination task

Dynamic Readout of Behaviorally Relevant Signals from Area MT during Task Switching

The processes underlying dynamic changes in human behavior during real situations contain much irrelevant information and represent a key issue facing neuroscientists. Although the roles played by the frontal cortex in this switching behavior have been well documented, little is known regarding how neural pathways governing sensorimotor associations accomplish such a switch. We addressed this question by recording activities of middle temporal (MT) neurons in monkeys switching between direction versus depth discrimination tasks. Although the monkeys successfully switched between the tasks, neural sensitivity did not change as a function of task. More importantly, neurons that signaled the same motor output showed trial-to-trial covariation between neuronal responses and perceptual judgments during both tasks, whereas neurons that signaled the opposite motor output showed no covariation in either task. These results suggest that task switching is accomplished via communication from distinct populations of neurons when sensorimotor associations switch within a short time period.

Binocular depth discrimination and estimation beyond interaction space

The benefits of binocular vision have been debated throughout the history of vision science yet few studies have considered its contribution beyond a viewing distance of a few meters. In the first set of experiments, we compared monocular and binocular performance on depth interval estimation and discrimination tasks at 4.5, 9.0 or 18.0 m. Under monocular conditions, perceived depth was significantly compressed. Binocular depth estimates were much nearer to veridical although also compressed. Regression-based precision measures were much more precise for binocular compared to monocular conditions (ratios between 2.1 and 48). We confirm that stereopsis supports reliable depth discriminations beyond typical laboratory distances. Furthermore, binocular vision can significantly improve both the accuracy and precision of depth estimation to at least 18 m. In another experiment, we used a novel paradigm that allowed the presentation of real binocular disparity stimuli in the presence of rich environmental cues to distance but not interstimulus depth. We found that the presence of environmental cues to distance greatly enhanced stereoscopic depth constancy at distances of 4.5 and 9.0 m. We conclude that stereopsis is an effective cue for depth discrimination and estimation for distances beyond those traditionally assumed. In normal environments, distance information from other sources such as perspective can be effective in scaling depth from disparity.

Virtual reality hardware and graphic display options for brain–machine interfaces

Virtual reality hardware and graphic displays are reviewed here as a development environment for brain–machine interfaces (BMIs). Two desktop stereoscopic monitors and one 2D monitor were compared in a visual depth discrimination task and in a 3D target-matching task where able-bodied individuals used actual hand movements to match a virtual hand to different target hands. Three graphic representations of the hand were compared: a plain sphere, a sphere attached to the fingertip of a realistic hand and arm, and a stylized pacman-like hand. Several subjects had great difficulty using either stereo monitor for depth perception when perspective size cues were removed. A mismatch in stereo and size cues generated inappropriate depth illusions. This phenomenon has implications for choosing target and virtual hand sizes in BMI experiments. Target-matching accuracy was about as good with the 2D monitor as with either 3D monitor. However, users achieved this accuracy by exploring the boundaries of the hand in the target with carefully controlled movements. This method of determining relative depth may not be possible in BMI experiments if movement control is more limited. Intuitive depth cues, such as including a virtual arm, can significantly improve depth perception accuracy with or without stereo viewing.