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1.
Mon-Williams M McIntosh RD Milner AD 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2001,139(2):137-142
It has been shown that a patient with visual form agnosia (DF) relies predominantly on vergence information when gauging
target distance in an open-loop pointing task. This finding suggested that the programming of prehension might be severely
disrupted if DF viewed target objects through ophthalmic prisms. An initial experiment showed that this prediction was not
upheld; DF was able to programme reasonably accurate movements to objects located on a tabletop despite large changes in vergence
angle. A second experiment, however, showed that placing the target objects at eye height whilst manipulating vergence angle
caused gross disruption to prehension, with DF mis-programming the reach component in a predictable manner. Notably, the evidence
for DF's reliance on vergence distance information was obtained in a task where the targets were viewed at eye height. These
experiments indicate that DF uses vertical gaze angle to gauge target distance in normal prehension and suggest that this
extra-retinal cue may be a useful source of distance information for the human nervous system, especially where pictorial
cues are impoverished.
Electronic Publication 相似文献
2.
Wann JP Mon-Williams M McIntosh RD Smyth M Milner AD 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2001,139(2):143-150
Reaching out to grasp an object requires information about the size of the object and the distance between the object and
the body. We used a virtual reality system with a control population and a patient with visual form agnosia (DF) in order
to explore the use of binocular information and size cues in prehension. The experiments consisted of a perceptual matching
task in addition to a prehension task. In the prehension task, control participants modified their reach distance in response
to step changes in vergence in the absence of any clear reference for relative disparity. Their reach distance was unaffected
by equivalent step changes in size, even though they used this information to modify grasp and showed a size bias in a distance
matching task. Notably, DF showed the same pattern of results as the controls but was far more sensitive to step changes in
vergence. This finding complements previous research suggesting that DF relies predominantly on vergence information when
gauging target distance. The results from the perceptual matching tasks confirmed previous findings suggesting that DF is
unable to make use of size information for perceptual matching, including distance comparisons. These data are discussed with
regard to the properties of the pathways subserving the two visual cortical processing streams.
Electronic Publication 相似文献
3.
Tresilian JR Mon-Williams M 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2000,132(3):362-368
Combining multiple sources of information allows the human nervous system to construct an approximately Euclidean representation of near (personal) space. Within this space, binocular vergence is an important source of egocentric distance information. We investigated how the nervous system determines the significance (weight) accorded to vergence information when other (retinal) distance cues are present. We found that weight decreases with (1) increasing discrepancy between vergence information and other cues and (2) reduced vergence demand. The results also provided evidence that the nervous system represents vergence related distance information in units of nearness (the reciprocal of distance). 相似文献
4.
Gardner PL Mon-Williams M 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2001,136(3):379-385
One possible source of information regarding the distance of a fixated target is provided by the height of the object within the visual scene. It is accepted that this cue can provide ordinal information, but generally it has been assumed that the nervous system cannot extract "absolute" information from height-in-scene. In order to use height-in-scene, the nervous system would need to be sensitive to ocular position with respect to the head and to head orientation with respect to the shoulders (i.e. vertical gaze angle or VGA). We used a perturbation technique to establish whether the nervous system uses vertical gaze angle as a distance cue. Vertical gaze angle was perturbed using ophthalmic prisms with the base oriented either up or down. In experiment 1, participants were required to carry out an open-loop pointing task whilst wearing: (1) no prisms; (2) a base-up prism; or (3) a base-down prism. In experiment 2, the participants reached to grasp an object under closed-loop viewing conditions whilst wearing: (1) no prisms; (2) a base-up prism; or (3) a base-down prism. Experiment 1 and 2 provided clear evidence that the human nervous system uses vertical gaze angle as a distance cue. It was found that the weighting attached to VGA decreased with increasing target distance. The weighting attached to VGA was also affected by the discrepancy between the height of the target, as specified by all other distance cues, and the height indicated by the initial estimate of the position of the supporting surface. We conclude by considering the use of height-in-scene information in the perception of surface slant and highlight some of the complexities that must be involved in the computation of environmental layout. 相似文献
5.
Hibbard PB Bradshaw MF 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2003,148(2):196-201
Although, in principle, binocular cues provide veridical information about the three-dimensional shape of objects, our perception
on the basis of these cues is distorted systematically. The consequences of these distortions may be less serious than they
first appear, however, since in everyday life we rarely are required to judge the absolute shape, size or distance of objects.
An important exception to this is in the control of prehension, where veridical information about an object to be grasped
is required to plan the transport of the hand and to select the most appropriate grip. Here we investigate whether binocular
cues provide accurate depth information for the control of prehension using disparity-defined, virtual objects and report
that whilst binocular disparity can support prehensile movements, the kinematic indices, which reflect distance-reached and
perceived size, show clear biases. These results suggest that accurate metric depth information for the control of prehension
is not available from binocular cues in isolation.
Electronic Publication 相似文献
6.
Mon-Williams M Tresilian JR McIntosh RD Milner AD 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2001,139(2):127-136
The human nervous system constructs a Euclidean representation of near (personal) space by combining multiple sources of
information (cues). We investigated the cues used for the representation of personal space in a patient with visual form agnosia
(DF). Our results indicated that DF relies predominantly on binocular vergence information when determining the distance of
a target despite the presence of other (retinal) cues. Notably, DF was able to construct an Euclidean representation of personal
space from vergence alone. This finding supports previous assertions that vergence provides the nervous system with veridical
information for the construction of personal space. The results from the current study, together with those of others, suggest
that: (i) the ventral stream is responsible for extracting depth and distance information from "monocular" retinal cues (i.e.
from shading, texture, perspective) and (ii) the dorsal stream has access to binocular information (from horizontal image
disparities and vergence). These results also indicate that DF was not able to use size information to gauge target distance,
suggesting that intact temporal cortex is necessary for "learned size" to influence distance processing. Our findings further
suggest that in neurologically intact humans, object information extracted in the ventral pathway is combined with the products
of dorsal stream processing for guiding prehension. Finally, we studied the "size-distance paradox" in visual form agnosia
in order to explore the cognitive use of size information. The results of this experiment were consistent with a previous
suggestion that the paradox is a cognitive phenomenon.
Electronic Publication 相似文献
7.
Frank T. J. M. Zaal R. J. Bootsma Piet C. W. van Wieringen 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1998,119(4):427-435
Prehension involves the coordination of a reaching and a grasping movement, such that the hand opens and closes in tune with
the transport of the hand to the object to be grasped. To investigate this coordination, we focused on the transition from
hand opening to hand closing in the grasping component of prehension. Earlier research has suggested that the time taken to
close the hand remains constant over varying reaching amplitudes. In the present experiment, in which subjects reached for
objects at six different distances and for objects that moved away from them at three different, constant speeds, hand-closure
time was found to vary as a function of experimental conditions. Moreover, initiation of hand closure did not occur at a constant
value of the (perceptually available) first-order time remaining until contact with the object. However, the variations observed,
occurring as a function of initial hand-object distance and object speed, could be accounted for by an abstract dynamical
model of perceptually driven postural changes.
Received: 25 July 1996 / Accepted: 9 October 1997 相似文献
8.
Howard IP Fang X Allison RS Zacher JE 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2000,130(2):124-132
We measured the gain and phase of horizontal and vertical vergences of five subjects as a function of stimulus area and position.
Vergence eye movements were recorded by the scleral search coil method as subjects observed dichoptic displays oscillating
in antiphase either from side to side or up and down with a peak-to-peak magnitude of 0.5° at either 0.1 Hz or 1.0 Hz. The
stimulus was a central textured disc with diameter ranging from 0.75° to 65°, or a peripheral annulus with outer diameter
65° and inner diameter ranging from 5° to 45°. The remaining field was black. For horizontal vergence at both stimulus frequencies,
gain and the phase lag were about the same for a 0.75° stimulus as for a 65° central stimulus. For vertical vergence, mean
gain increased and mean phase lag decreased with increasing diameter of the central stimulus up to approximately 20°. Thus,
the stimulus integration area is much smaller for horizontal vergence than for vertical vergence. The integration area for
vertical vergence is similar to that for cyclovergence, as revealed in a previous study. For both types of vergence, response
gains were higher and phase lags smaller at 0.1 Hz than at 1.0 Hz. Also, gain decreased and phase lag increased with increasing
occlusion of the central region of the stimulus. Vergence gain was significantly higher for a 45° central disc than for a
peripheral annulus with the same area. Thus, the central retina has more power to evoke horizontal or vertical vergence than
the same area in the periphery. We compare the results with similar data for cyclovergence and discuss their ecological implications.
Received: 30 January 1999 / Accepted: 25 June 1999 相似文献
9.
H. C. Dijkerman A. David Milner 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1998,118(3):408-414
Normal human subjects were tested for their ability to discriminate the orientation of a square plaque tilted in depth, using
two different tasks: a grasping task and a perceptual matching task. Both tasks were given under separate monocular and binocular
conditions. Accuracy of performance was measured by use of an opto-electronic motion analysis system, which computed the hand
orientation (specifically, a line joining the tips of the thumb and index finger) as the hand either approached the target
during grasping or was used to match the target. In all cases there was a very strong statistical coupling between hand orientation
and target orientation, irrespective of viewing conditions. However, the matching data differed from the grasping data in
showing a consistent curvature in the hand-target relationship, whereby the rate of change of hand orientation as a function
of object orientation was smaller for oblique orientations than for those near the horizontal or vertical. The results are
interpreted as reflecting the operation of two different mechanisms for analysing orientation in depth: a visuomotor system
(assumed to be located primarily in the dorsal cortical visual stream) and a perceptual system (assumed to be located in the
ventral stream). It may be that the requirements of visuomotor control dictate a primary need for absolute orientation coding,
whereas those of perception dictate a need for more categorical coding.
Received: 13 June 1997 / Accepted: 14 October 1997 相似文献
10.
Attention in action or obstruction of movement? A kinematic analysis of avoidance behavior in prehension 总被引:5,自引:5,他引:0
James R. Tresilian 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1998,120(3):352-368
Obstacle avoidance strategies are of two basic but interrelated types: moving around an obstacle to that body parts do not
come too close, and slowing down. In reaching-to-grasp, avoidance may involve the transport component, the grasp formation
component, or both. There has been little research that has directly examined obstacle avoidance strategies during reaches-to-grasp.
Several recent reports describe experiments in which reaches-to-grasp were made when nontarget objects were present in the
workspace. The effects of these nontargets were interpreted as being due to their distracting effects rather than their obstructing
effects. The results of these studies are reinterpreted as being due to the non-target’s obstructing effects. The obstacle
interpretation is more parsimonious and better predicts the pattern of results than the distractor interpretation. Predictions
of the obstacle interpretation were examined in an experiment in which participants were required to reach to grasp a target
in the presence of another object in various locations. The results were exactly in line with the interpretation of the object
as an obstacle and the data show how grasp and transport movements are subtly adjusted so as to avoid potential obstacles.
It is proposed that people move so as not to bring body parts within a minimum preferred distance from nontarget objects within
the workspace. What constitutes the preferred distance in a particular context appears to depend upon the speed of movement
and a variety of psychological factors related to the cost that a person attaches to a collision.
Received: 5 September 1997 / Accepted: 10 January 1998 相似文献
11.
M. Mon-Williams James R. Tresilian Anna Plooy John P. Wann Jack Broerse 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1997,117(3):501-506
A retinal afterimage of the hand changes size when the same unseen hand is moved backwards and forwards in darkness. We demonstrate that arm movements per se are not sufficient to cause a
size change and that vergence eye movements are a necessary and sufficient condition for the presence of the illusory size
change. We review previous literature to illustrate that changing limb position in the dark alters vergence angle and we explain
the illusion via this mechanism. A discussion is provided on why altering limb position causes a change in vergence and we
speculate on the underlying mechanisms.
Received: 6 May 1997 / Accepted: 16 July 1997 相似文献
12.
N. Kudoh Midori Hattori Nakaho Numata Kinya Maruyama 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1997,117(3):457-464
Human prehension movements have been studied with regard to the parallel processing of motor control and sensorimotor coordination.
Temporal aspects of the movement (e.g., onset time and duration) have been studied extensively, while spatial aspects have
not been studied systematically. Thus, the purpose of this study was to examine spatiotemporal variability of the transport
(wrist trajectory) and grasp (grip aperture between the index finger and the thumb) components. In this experiment, the extrinsic
(e.g., distance) and intrinsic object properties (e.g., object size) were manipulated. Subjects were required to pick up an
aluminum cylinder as quickly and accurately as possible using the index finger and the thumb. It was found that object size
significantly affected both transport and grasp components. Distance mainly affected the transport component. These kinematic
results were consistent with the findings of earlier studies. Furthermore, the distribution of mean within-subject variability
across normalized movement time for the transport component was not the same as that of the grasp component, suggesting that
the different motor control processes exist. The peak amplitudes in variability of the wrist trajectory and the grip aperture
were obtained at similar points throughout movement time. Furthermore, the peak of wrist variability depended on distance
not object size, while that of aperture variability depended on both distance and object size. These results strongly support
the hypothesis that the grasp component is adjusted using dynamic information provided from the transport component as the
wrist moves toward the object. We also found that wrist variability converged to the target point, while aperture variability
was biphasic: it converged, at least, around the point of maximum aperture in the first phase and then remained constant in
the second phase. This result suggests that the two components are under different control processes. We hypothesize that
the transport component can be modeled as a single feedforward system, while the grasp component can be divided into two separate
mechanisms.
Received: 4 March 1996 / Accepted: 29 January 1997 相似文献
13.
Allison RS Howard IP Fang X 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2004,156(3):305-313
Over what region of space are horizontal disparities integrated to form the stimulus for vergence? The vergence system might be expected to respond to disparities within a small area of interest to bring them into the range of precise stereoscopic processing. However, the literature suggests that disparities are integrated over a fairly large parafoveal area. We report the results of six experiments designed to explore the spatial characteristics of the stimulus for vergence. Binocular eye movements were recorded using magnetic search coils. Each dichoptic display consisted of a central target stimulus that the subject attempted to fuse, and a competing stimulus with conflicting disparity. In some conditions the target was stationary, providing a fixation stimulus. In other conditions, the disparity of the target changed to provide a vergence-tracking stimulus. The target and competing stimulus were combined in a variety of conditions including those in which (1) a transparent textured-disc target was superimposed on a competing textured background, (2) a textured-disc target filled the centre of a competing annular background, and (3) a small target was presented within the centre of a competing annular background of various inner diameters. In some conditions the target and competing stimulus were separated in stereoscopic depth. The results are consistent with a disparity integration area with a diameter of about 5°. Stimuli beyond this integration area can drive vergence in their own right, but they do not appear to be summed or averaged with a central stimulus to form a combined disparity signal. A competing stimulus had less effect on vergence when separated from the target by a disparity pedestal. As a result, we propose that it may be more useful to think in terms of an integration volume for vergence rather than a two-dimensional retinal integration area. 相似文献
14.
M. K. Watson L. S. Jakobson 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1997,117(2):273-280
In the present study, a kinematic analysis was made of unconstrained, natural prehension movements directed toward an object
approaching the observer on a conveyor belt at one of three constant velocities, from one of three different directions (head-on
or along the fronto-parallel plane coming either from the subject′s left or right). Subjects were required to grasp the object
when it reached a target located 20 cm directly in front of the hand′s start position. The kinematic analysis revealed that
both the transport and grasp components of the movement changed in response to the experimental manipulations, but did so
in a manner that guaranteed that, for objects approaching from a given direction, hand closure would begin at a constant time
prior to object contact (regardless of the object’s approach speed). The kinematic analysis also revealed, however, that the
onset of hand closure began earlier with objects approaching from the right than from other directions – an effect which would
not be predicted if time to contact was the key variable controlling the onset of hand closure. These results, then, lend
only partial support to the theory that temporal coordination between the transport and grasp components of prehension is
ensured through their common dependence on time to contact information.
Received: 20 September 1996 / Accepted: 16 June 1997 相似文献
15.
J. J. Marotta A. Kruyer M. A. Goodale 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1998,120(1):134-138
Binocular information has been shown to be important for the programming and control of reaching and grasping. But even without
binocular vision, people are still able to reach out and pick up objects accurately – albeit less efficiently. As part of
a continuing investigation into the role that monocular cues play in visuomotor control, we examined whether or not subjects
could use retinal motion information, derived from movements of the head, to help program and control reaching and grasping
movements when binocular vision is denied. Subjects reached out in the dark to an illuminated sphere presented at eye-level,
under both monocular and binocular viewing conditions with their head either free to move or restrained. When subjects viewed
the display monocularly, they showed fewer on-line corrections when they were allowed to move their head. No such difference
in performance was seen when subjects were allowed a full binocular view. This study, combined with previous work with neurological
patients, confirms that the visuomotor system “prefers” to use binocular vision but, when this information is not available,
can fall back on other monocular depth cues, such as information produced by motion of the object (and the scene) on the retina,
to help program and control manual prehension.
Received: 22 December 1997 / Accepted: 4 February 1998 相似文献
16.
Y. Paulignan V. G. Frak I. Toni M. Jeannerod 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1997,114(2):226-234
Prehension movements of the right hand were recorded in normal subjects using a computerized motion analyzer. The kinematics
and the spatial paths of markers placed at the wrist and at the tips of the index finger and thumb were measured. Cylindrical
objects of different diameters (3, 6, 9 cm) were used as targets. They were placed at six different positions in the workspace
along a circle centered on subject’s head axis. The positions were spaced by 10° starting from 10° on the left of the sagittal
axis, up to 40° on the right. Both the transport and the grasp components of prehension were influenced by the distance between
the resting hand position and the object position. Movement time, time to peak velocity of the wrist and time to maximum grip
aperture varied as a function of distance from the object, irrespective of its size. The variability of the spatial paths
of wrist and fingers sharply decreased during the phase of the movement prior to contact with the object. This indicates that
the final position of the thumb and the index finger is a controlled parameter of visuomotor transformation during prehension.
The orientation of the opposition axis (defined as the line connecting the tips of the thumb and the index finger at the end
of the movement) was measured. Several different frames of reference were used. When an object-centered frame was used, the
orientation of the opposition axis was found to change by about 10° from one object position to the next. By contrast, when
a body-centered frame was used (with the head or the forearm as a reference), this orientation was found to remain relatively
invariant for different object positions and sizes. The degree of wrist flexion was little affected by the position of the
object. This result, together with the invariant orientation of the opposition axis, shows that prehension movements aimed
at cylindrical objects are organized so as to minimize changes in posture of the lower arm.
Received: 2 July 1996 / Accepted: 5 October 1996 相似文献
17.
A. W. H. Minken J. A. M. Van Gisbergen 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1994,101(2):331-345
Earlier studies have shown that eye positions, recorded in subjects scanning a distant visual scene with the head in a stable position, have only two degrees of freedom (Listing's law). Due to cyclovergence, this law is modified in near-vision. Two previous quantitative studies have documented that the sign of the torsional vergence component depends systematically on elevation: when fixating a nearby target, the eyes show intorsion in up gaze, extorsion in down gaze and no cyclotorsion at some intermediate elevation level (to be denoted as the null elevation). Both studies found a linear cyclovergence/elevation relation, but disagreed on the amount of cyclotorsion. A further uncertainty is how this phenomenon develops dynamically when the binocular fixation point shifts from a far to a near position. Therefore, we have investigated the dynamic coupling between the horizontal and torsional components of vergence in human subjects who were instructed to refixate a light target after it stepped in depth. The target steps were presented at various vertical and horizontal directions relative to the straight-ahead axis of the cyclopean eye. We found that the quantitative relations among horizontal vergence, torsional vergence and elevation were intermediate between those found in the two earlier near-vision studies and that they correspond reasonably to the predictions of a model by Mok and co-workers. The cyclotorsion vergence component had about the same latency and dynamics as the horizontal component. When refixations were studied at different elevations, the torsional vergence component changed from incyclotorsion in up gaze to excyclotorsion in down gaze. In agreement with expectations derived from two quantiative models, the null elevation of cyclovergence was near the binocular primary position. Furthermore, we found no consistent additional dependence on the horizontal direction of the refixation trajectory relative to the midsaggital plane. Other experiments showed that the cyclotorsional changes accompanying convergence were not critically dependent upon the visual conditions. Quantitatively similar cyclotorsional components were found even in convergent refixations executed in full darkness towards the location of a remembered (flashed) near target. We conclude that visual feedback is unlikely to be very important in controlling cyclovergence in these various conditions. 相似文献
18.
J. P. Kuhtz-Buschbeck H. Stolze K. Jöhnk A. Boczek-Funcke M. Illert 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1998,122(4):424-432
To evaluate the normal development of functional hand motor skill, the kinematics of prehension movements were analyzed in
54 healthy children (age 4–12 years). The subjects repeatedly reached out for cylindrical target objects and grasped them
with a precision grip of their dominant hand. The trajectory of the reaching hand and the finger aperture were monitored by
optoelectronic motion analysis. To obtain comparable conditions for the different age groups, the experimental setup was scaled
according to the individual body proportions of each subject. Within the investigated age range, neither the movement duration
nor the normalized (according to body proportions) peak spatial velocity of the reaching hand changed significantly. However,
the hand trajectory straightened and the coordination between hand transport and grip formation improved, resulting in smooth
and stereotyped kinematic profiles at the age of 12 years. The younger children opened their grip relatively wider than the
older ones, thus grasping with a higher safety margin. The dependence on visual control of the movement declined during motor
development. Only the oldest childen were able to scale the grip aperture adequately, according to various sizes of the target
objects, when visual control of the movement was lacking. The results suggest that the development of prehensile skills during
childhood lasts until the end of the first decade of life. This functional maturation is discussed in relation to the development
of neuronal pathways.
Received: 20 November 1997 / Accepted: 4 July 1998 相似文献
19.
R. L. Boltz O.D. Ph.D. R. S. Harwerth 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1979,37(1):87-91
Summary Fusional vergence ranges were behaviorally determined for two rhesus monkeys and two human subjects using random dot stereograms as stimuli. The subject performed a two-alternative forced choice form discrimination of discretely presented stimuli and the fusional vergence stimulus was changed during the intertrial intervals. The fusional vergence measurements for the monkey were similar to those for the human subjects. 相似文献
20.
The removal of binocular cues disrupts the calibration of grasping in patients with visual form agnosia 总被引:2,自引:0,他引:2
J. J. Marotta M. Behrmann M. A. Goodale 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1997,116(1):113-121
The present study tested the idea that the visuomotor systems mediating prehension do not have independent access to pictorial
cues processed by perceptual mechanisms. Individuals with visual form agnosia, whose perceptual systems are compromised but
who have intact visuomotor control, were examined to determine whether they could use pictorial scene cues to calibrate manual
prehension when binocular information was removed. The removal of binocular cues produced considerable disruptions in size-constancy
of grip aperture, which, combined with earlier observations in normal subjects, suggests that binocular cues are of primary
importance in calibration of grasping. In the absence of binocular vision, normal subjects can use pictorial information,
information that is severely compromised in individuals with visual form agnosia, to compute the distance (and thus the size)
of the goal object. Thus, individuals with visual form agnosia must rely on a retinal image that remains uncalibrated, leading
to inaccurate calibrations of grip aperture. The fact that these individuals scaled their grasp much less accurately under
the monocular viewing condition, despite showing normal binocular grasping, suggests that pictorial cues to depth, which are
presumably processed by mechanisms mediating our perception of objects and events in the world, can be accessed by visuomotor
mechanisms only indirectly. These results, together with others, suggest that the visuomotor system ’prefers’ to use binocular
information and uses pictorial cues only as a last resort.
Received: 10 September 1996 / Accepted: 25 February 1997 相似文献