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PubMed1997

The TINS Lecture. The parietal association cortex in depth perception and visual control of hand action.

Recent neurophysiological studies in alert monkeys have revealed that the parietal association cortex plays a crucial role in depth perception and visually guided hand movement. The following five classes of parietal neurons covering various aspects of these functions have been identified: (1) depth-selective visual-fixation (VF) neurons of the inferior parietal lobule (IPL), representing egocentric distance; (2) depth-movement sensitive (DMS) neurons of V5A and the ventral intraparietal (VIP) area representing direction of linear movement in 3-D space; (3) depth-rotation-sensitive (RS) neurons of V5A and the posterior parietal (PP) area representing direction of rotary movement in space; (4) visually responsive manipulation-related neurons (visual-dominant or visual-and-motor type) of the anterior intraparietal (AIP) area, representing 3-D shape or orientation (or both) of objects for manipulation; and (5) axis-orientation-selective (AOS) and surface-orientation-selective (SOS) neurons in the caudal intraparietal sulcus (cIPS) sensitive to binocular disparity and representing the 3-D orientation of the longitudinal axes and flat surfaces, respectively. Some AOS and SOS neurons are selective in both orientation and shape. Thus the dorsal visual pathway is divided into at least two subsystems, V5A, PP and VIP areas for motion vision and V6, LIP and cIPS areas for coding position and 3-D features. The cIPS sends the signals of 3-D features of objects to the AIP area, which is reciprocally connected to the ventral premotor (F5) area and plays an essential role in matching hand orientation and shaping with 3-D objects for manipulation.

Animals↗
PubMed2000

Stereomammography: evaluation of depth perception using a virtual 3D cursor.

We are evaluating the usefulness of stereomammography in improving breast cancer diagnosis. One area that we are investigating is whether the improved depth perception associated with stereomammography might be significantly enhanced with the use of a virtual 3D cursor. A study was performed to evaluate the accuracy of absolute depth measurements made in stereomammograms with such a cursor. A biopsy unit was used to produce digital stereo images of a phantom containing 50 low contrast fibrils (0.5 mm diam monofilaments) at depths ranging from 1 to 11 mm, with a minimum spacing of 2 mm. Half of the fibrils were oriented perpendicular (vertical) and half parallel (horizontal) to the stereo shift direction. The depth and orientation of each fibril were randomized, and the horizontal and vertical fibrils crossed, simulating overlapping structures in a breast image. Left and right eye images were generated by shifting the x-ray tube from +2.5 degrees to -2.5 degrees relative to the image receptor. Three observers viewed these images on a computer display with stereo glasses and adjusted the position of a cross-shaped virtual cursor to best match the perceived location of each fibril. The x, y, and z positions of the cursor were indicated on the display. The z (depth) coordinate was separately calibrated using known positions of fibrils in the phantom. The observers analyzed images of two configurations of the phantom. Thus, each observer made 50 vertical filament depth measurements and 50 horizontal filament depth measurements. These measurements were compared with the true depths. The correlation coefficients between the measured and true depths of the vertically oriented fibrils for the three observers were 0.99, 0.97, and 0.89 with standard errors of the estimates of 0.39 mm, 0.83 mm, and 1.33 mm, respectively. Corresponding values for the horizontally oriented fibrils were 0.91, 0.28, and 0.08, and 1.87 mm, 4.19 mm, and 3.13 mm. All observers could estimate the absolute depths of vertically oriented objects fairly accurately in digital stereomammograms; however, only one observer was able to accurately estimate the depths of horizontally oriented objects. This may relate to different aptitudes for stereoscopic visualization. The orientations of most objects in actual mammograms are combinations of horizontal and vertical. Further studies are planned to evaluate absolute depth measurements of fibrils oriented at various intermediate angles and of objects of different shapes. The effects of the shape and contrast of the virtual cursor and the stereo shift angle on the accuracy of the depth measurements will also be investigated.

Biophysical Phenomena↗
PubMed1993

Precision of stereoscopic depth perception from double images.

The increment depth discrimination function was originally described by Ogle [(1953) Journal of the Optical Society of America, 43, 906-913] as a single exponential function. In contrast, recent studies have suggested that a two-component function better describes increment depth discrimination. To determine the relative effects of stereoscopic and non-stereoscopic width cues on the form of the function, we measured increment depth discrimination under conditions where both stereoscopic and dichoptic width cues were available. We found that increment depth discrimination data were well described by two-segment functions if both stereoscopic and dichoptic width cues were available. However, when dichoptic width cues were eliminated, by randomizing the pedestal disparity (crossed or uncrossed disparity) between trials, the increment depth discrimination function was better described by a single exponential function. This result has important implications for models of stereoscopic depth processing because it shows that stereoscopic depth discrimination thresholds progressively increase as a function of distance from the horopter.

Depth Perception↗
PubMed1997

Depth perception during diplopia is direct.

Although depth is experienced with targets at large disparities when they are seen as double or diplopic, whether that depth is as direct as with fused targets has been a matter of considerable uncertainty. Researchers have often claimed that judgments of the depth of diplopic targets during simple near/far tasks rely upon indirect associations with eye-muscle proprioception or a copy of the vergence drive signal. We designed a four-alternative task that could not be performed without a direct appreciation of depth. Observers judged the depths of each of two Gabor stereo pairs presented simultaneously. Disparities were always above each observer's measured diplopia threshold. The signs of the disparities were varied independently and observers reported the perceived depth near and far for each target. Our results demonstrate conclusively that depth during diplopia requires neither proprioception nor an efferent copy but is direct.

Depth Perception↗
PubMed1992

Clinical measurement of depth perception by means of motion parallax: a case report.

An automated 2-rod stereoacuity test was modified to permit lateral head movement during testing so that depth perception by means of motion parallax could be assessed. The patient, a 48-year-old truck driver with one blind eye, found the test easy to perform. In 24 presentations of a 40 sec arc disparity he was 96% correct. With the same number of presentations at 20 sec arc he was 83% correct. In the latter case, the probability of success by chance alone was p = 0.0004.

Depth Perception↗
PubMed1996

How is motion disparity integrated with binocular disparity in depth perception?

Two experiments presented motion disparity conflicting with binocular disparity to examine how these cues determined apparent depth order (convex, concave) and depth magnitude. In each experiment, 8 subjects estimated the depth order and depth magnitude. The first experiment showed the following. (1) The visual system used one of these cues exclusively in selecting a depth order for each display. (2) The visual system integrated the depth magnitude information from these cues by a weighted additive fashion if it selected the binocular disparity in depth order perception and if the depth magnitude specified by motion disparity was small relative to that specified by binocular disparity. (3) The visual system ignored the depth magnitude information of binocular disparity if it selected the motion disparity in depth order perception. The second experiment showed that these three points were consistent whether the subject's head movement or object movement generated motion disparity.

Adult↗
PubMed2005

Depth perception by the active observer.

The connection between perception and action has classically been studied in one direction only: the effect of perception on subsequent action. Although our actions can modify our perceptions externally, by modifying the world or our view of it, it has recently become clear that even without this external feedback the preparation and execution of a variety of motor actions can have an effect on three-dimensional perceptual processes. Here, we review the ways in which an observer's motor actions--locomotion, head and eye movements, and object manipulation--affect his or her perception and representation of three-dimensional objects and space. Allowing observers to act can drastically change the way they perceive the third dimension, as well as how scientists view depth perception.

Depth Perception↗
PubMed1964

DEPTH PERCEPTION IN SHEEP: EFFECTS OF INTERRUPTING THE MOTHER-NEONATE BOND.

Twin lambs were divided into two groups: an unmothered group consisting of one of each pair of twins separated from its mother at birth, and a mothered group consisting of the other member of each pair reared by its mother. Lambs in both groups were placed individually on a "visual cliff" once every hour. In all instances lambs in the mothered group exhibited "cliff avoidance" behavior before those in the unmothered group. In another experiment, mothered lambs were fitted with translucent goggles for half the time required by unmothered lambs, matched on the basis of sex and birth weight, to acquire depth perception. Again, in all instances the mothered, goggled lambs avoided the cliff before the unmothered lambs.

Animals↗
PubMed1983

Depth perception in Pandora's box and size illusion: evolution with age.

The aim of the experiment was to study the evolution with age (6, 8, 11 and 14 years) of pictorial depth perception in Pandora's box and to compare it with the evolution of size illusion with the same subjects and the same pictorial backgrounds. In addition to familiar size and relative position, each pictorial stimulus contained one or more of the following depth cues: linear perspective, texture gradient, and interposition. The two kinds of measurements produced different results. Size illusions, although present, did not vary with age but increased with the number of cues. Estimates of distance in Pandora's box increased with age and varied according to the type of cue present: texture gradient seemed to be critical to the amount of depth perceived. The correlation between size adjustments and distance adjustments was significant only for the two oldest groups of subjects (11 and 14 years).

Adolescent↗
PubMed1997

Depth perception in simple line drawings.

Three-dimensional interpretation of simple line drawings, composed of two triangles with a common side, was studied through the quantitative measurement of perceived orientation of the surface indicated by a stimulus figure. In a single triangle, depth perception is ambiguous and is not stable even if perceived. In two triangles with a common side, however, depth is stably perceived. Depth effect, defined as the magnitude of the angle formed by the two perceived surfaces, increased linearly as the magnitude of an angle at a vertex facing the common side became larger. The depth effect did not vary significantly for the change of a triangular from when the magnitude of the angle at the vertex facing the common side was constant. These results suggest that the depth effect changes systematically with variation in the triangle's form.

Depth Perception↗
PubMed1983

Binocular depth perception in the meerkat (Suricata suricatta).

Although it has been widely assumed that mammals with frontally placed eyes have stereoscopic vision, there is actually a paucity of supporting evidence. We have measured monocular and binocular depth perception in the meerkat (Suricata suricatta), obtaining strong evidence for the presence of stereopsis. The data provide additional evidence for the generality of stereoscopic vision across many different species.

Animals↗
PubMed1962

Visual depth perception of a 10-month-old monocular human infant.

A monocular infant tested on the "visual cliff" crawled over glass which had a patterned surface just beneath it and would not cross glass which had the same pattern 40 inches below its surface. Since this infant, using only monocular visual cues, was able to discriminate depth, the experiment disproves a general belief in the primacy of binocular cues in depth perception.

Child↗
PubMed1998

Generation of depth-perception information in stereoscopic nuclear magnetic resonance imaging by non-linear magnetic field gradients.

Stereoscopic NMR images have been produced in the past. However, because of the gradients are linear, only isometric projections can be produced, i.e., they do not carry correct depth-perception information. The resulting stereoscopic image will not have correct relative sizes at different depths. This paper gives an analysis of what perception information is needed and shows that it can be produced by a non-linear magnetic field gradient. The concept is exemplified by simulations and its implementation is demonstrated successfully by experiments. The depth-encoding gradient can be generated by static steel pieces or by current loops. The procedure can be incorporated into any existing hardware and pulse sequences, and has potential application in surgery.

Depth Perception↗
PubMed2006

Depth perception in cerebellar and basal ganglia disease.

There is increasing evidence that the cerebellum and the basal ganglia serve not only a role in motor control but also in visual perception. Patients with Parkinson's disease (PD) as well as patients with cerebellar lesions exhibit impairments of vision that are not fully explained by ocular motor deficits. It is less clear to which extent these visual deficits contribute to an impaired control of visually guided movements. This study examined whether a dysfunction of the cerebellum or the basal ganglia induces impairments in depth perception, which affect action. We employed an illusionary display, the Ames trapezoidal window, to determine the ability of PD patients (n=10) and patients with spinocerebellar ataxia (SCA) (n=6) to process depth cues when estimating object slant. Participants either pointed to the edges of the window (motor judgement) or verbally indicated the perceived orientation of the display (verbal judgement). To control for ocular and limb motor deficits, participants judged the slant of a non-illusionary display in a second task. Slant estimation of the non-illusionary window was not impaired in either patient group when compared to control subjects (all P>0.2). In contrast, SCA as well as PD patients exhibited significantly greater slant estimation errors than controls when pointing to the illusionary window (P=0.005). In addition, both patient groups made larger errors than controls in their verbal judgements during binocular viewing of the illusion (P=0.005), but not during monocular viewing (P>0.2). In sum, the present findings point towards a role for both the basal ganglia and cerebellum for the processing of visual information about depth. Since the deficits were seen both in the context of action and perception and were only partially reconciled by the availability of binocular depth cues, we conclude that basal ganglia as well as cerebellar disease may affect the visual perception of depth.

Adult↗