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PubMed1993

Effects of target distance and pupil size on letter contrast sensitivity with simultaneous vision bifocal contact lenses.

Using simulated presbyopia we measured the effects of target vergence and pupil size on letter contrast sensitivity while subjects wore accurately centered simultaneous vision bifocal contact lenses. These experiments examined the increase in depth of focus provided by two bifocal contact lenses, and the effects of pupil size on near and distance vision. Monocular contrast sensitivity was assessed with three different designs of soft contact lenses. First, as a single vision control, we measured contrast sensitivity with a Bausch & Lomb, Optima 38 lens corrected for distance. We then measured contrast sensitivity with an Allergan Optical, Hydron Echelon, which is a diffractive simultaneous bifocal and a CIBA Vision, Spectrum, which is a concentric design, center-near, two-zone simultaneous vision bifocal. In general both bifocal contact lenses improved contrast sensitivity at near but decreased contrast sensitivity at distance (when compared to the single vision lens). With a fixed 3.5-mm artificial pupil, the Echelon lens had two clear peaks of sensitivity, one at distance (0.00 D) and one at near (-2.00 D), but the Spectrum lens had no clear peaks. Performance of the Spectrum lens depended on its center zone size. Near (-2.00 D) and distance (0.00 D) contrast sensitivity was measured with pupil sizes that ranged from 1 to 6 mm. The results showed that visual performance with a diffractive lens was almost independent of pupil diameter up to 3 to 4 mm but, as predicted, performance with the two-zone lens depended critically on pupil size.

Contact Lenses, Hydrophilic↗
PubMed1978

Development of sensitivity to information provided by cast shadows in pictures.

The shadow cast by an object in a two-dimensional picture can specify for the observer the spatial relations between that object and its surroundings, and also the shape and size of the object itself. Some sensitivity to this information is present even in three-year-old children. Experiment 1 provided evidence that three- and four-year-old children can rely on the shape of the shadow cast by an object to judge the shape of the object. In experiment 2, with adults and three- and four-year-old children, the location of the shadow cast by an object influenced the perceived depth and height off the ground plane of the object. Although even the three-year-old children were sensitive to the location of the cast shadows, there was evidence of improvement with age in judging the distance and size of the object. The three-year-olds were not able to judge the object's size when the location of the cast shadow provided the only differential information for size. In contrast, they were significantly better in judging size when the location of the object, rather than the location of the shadow, was varied.

Adult↗
PubMed1990

Adaptation to optically-increased interocular separation under naturalistic viewing conditions.

Mirror spectacles which enhance binocular disparity by optically doubling the normal separation between the eyes were used to create conditions of combined perceptual and oculomotor conflict. Apparent depth and distance, as well as tonic accommodation, tonic vergence, and accommodative-vergence gain (response AC/A ratio), were assessed immediately before and after a 30 min exposure period of naturalistic viewing with the spectacles. Wearing the spectacles produced an increase in tonic vergence, and perceptual aftereffects consisting of increased apparent distance and depth. The results indicate that oculomotor conflict associated with enhanced interocular separation may be resolved through adaptation of tonic vergence, rather than through alteration of accommodative-vergence gain. The results also demonstrate that perceptual conflict between disparity and multiple veridical depth cues does not necessarily produce adaptive modification of the relationship between binocular disparity and apparent depth.

Accommodation, Ocular↗
PubMed1979

Information used in judging impending collision.

Many subhuman species and human infants, children, and adults can use two-dimensional information of relative rate of angular-size change to anticipate collisions between the self and approaching objects or surfaces. But extant studies have not determined what information is used when subjects view simulated approach events providing two-dimensional information and three-dimensional information (distance and distance change), as well as lower-order visual information contained in real approach events. Three experiments suggest that, given these several possibilities, adults' judgments of collision time are best predicted by two-dimensional spatiotemporal values which are invariant over object sizes, distances traversed, approach velocities, and several lower-order variables such as absolute angular size. However, collision time is substantially underestimated, with absolute amount of underestimation increasing as a function of actual time-to-collision. Large constant errors and loss of judgment linearity beyond about 10 s to contact time suggest that current models of human performances based on use of time-to-collision information require modified assumptions of operator efficiency.

Depth Perception↗
PubMed1994

Apparent motion determined by surface layout not by disparity or three-dimensional distance.

The most meaningful events ecologically, including the motion of objects, occur in relation to or on surfaces. We run along the ground, cars travel on roads, balls roll across lawns, and so on. Even though there are other motions, such as flying of birds, it is likely that motion along surfaces is more frequent and more significant biologically. To examine whether events occurring in relation to surfaces have a preferred status in terms of visual representation, we asked whether the phenomenon of apparent motion would show a preference for motion attached to surfaces. We used a competitive three-dimensional motion paradigm and found that there is a preference to see motion between tokens placed within the same disparity as opposed to different planes. Supporting our surface-layout hypothesis, the effect of disparity was eliminated either by slanting the tokens so that they were all seen within the same surface plane or by inserting a single slanted background surface upon which the tokens could rest. Additionally, a highly curved stereoscopic surface led to the perception of a more circuitous motion path defined by that surface, instead of the shortest path in three-dimensional space.

Depth Perception↗
PubMed1992

[Evaluation of the image quality of bi- and multifocal intraocular lenses with a new optical system].

By means of a new optical device developed by Reiner, an "optical implantation" of 6 different bi- and multifocal intraocular lenses (MIOLs) was performed in 20 young healthy subjects, and results were compared with those of a monofocal reference IOL. The following parameters were investigated: distance and near visual acuity, depth of focus and contrast sensitivity. The median of distance visual acuity was 1.0 in all IOLs with the exception of a 7-zone refractive MIOL (0.75). Near acuity without near addition was 1.0 in all MIOL models; through focus curves of all MIOLs showed an increase in depth of focus with a typical two peak course. Contrast sensitivity at high contrasts was reduced for the 7-zone-model, but contrast sensitivity at low contrasts was significantly reduced for all MIOLs, except the 2- and 3-zone refractive models.

Adult↗
PubMed1995

Wayfinding, displacements, and mental maps: velocity fields are not typically used to determine one's aimpoint.

When an individual moves through a cluttered environment, he or she often fixates an object relatively near his or her path in the middle distance and uses pursuit eye movements to follow it while moving forward. On the basis of previous evidence, either motion fields or displacement fields around the fixated object--two alternative representations of the same information--could be used to determine one's direction of self-movement, sometimes called heading or aimpoint. In a series of 5 experiments, the relationship between these representations was explored and it was found that the displacements of identifiable objects, not their motions, are most likely the direct inputs for wayfinding. It may be that these inputs are used in conjunction with a mental map to determine one's aimpoint. A mathematical framework for this process is proposed.

Acceleration↗
PubMed1989

[Comparison of the Kolling distance vision stereo-test with current stereo-test procedures].

A new type of stereotest for distant vision (after Kolling) is compared with established stereotests for distant (different types of Zeiss Polatest) and near vision (Titmus, TNO, Lang tests) in a total of 203 patients. The Kolling test is based on the three-rod method in accordance with Helmholtz. The apparatus does not require separation of the visual input of the two eyes. This new stereotest is practice-oriented, quick, easy to understand and gives reliable and reproducible results. The test cannot be completed successfully with monocular viewing, if the head is fixed. The results show a good correspondence between the Kolling test and the Zeiss Polatest using disparate outlined figures. The Zeiss Polatest using random-dot patterns turned out to have the strictest criteria for this purpose of all stereotests. Interestingly enough, subjects performed much better in stereotests for near vision (Titmus, TNO tests) than in those for distant vision (Kolling test, different types of Zeiss Polatest). The widespread use of stereotests of near vision in driving tests is therefore problematic.

Adolescent↗
PubMed1980

[Effect of acoustic stimulation parameters on human appreciation of changes in distance from a sound source].

Minimal time necessary for appearance of sensation of approaching or withdrawing of the amplitude-impulse-modulated sound was 0.3--0.4 sec at changing the intensity from minimal to maximal within the range of 30--60 dB over the threshold of rhythmic series determination (10--50 Hz). The number of short lengths of tones or noises in the series within this time epoch should be not less than three. The effect of the value of carrying frequency of the series lengths upon the sensation of approaching or withdrawing is only evident within the range of those temporal parameters of the signal which accompanied change of criterion of estimation of the sound quality. Further shortening of the signal leads to substitution of the criterion for estimation of stimulus position for the criterion of sound accentuation at a tonal carrier and for the criterion of consonant-likeness at a noise carrier. The downward frequency modulation from the initial frequency at a growing amplitude enhances the sensation of "approaching", the upward modulation enhances the sensation of source "withdrawing", as compared with the constant frequency or the frequency modulation of opposite sign.

Adult↗
PubMed1996

The effect of display size on disparity scaling from differential perspective and vergence cues.

The present study compared the relative effectiveness of differential perspective and vergence angle manipulations in scaling depth from horizontal disparities. When differential perspective and vergence angle were manipulated together (to simulate a range of different viewing distances from 28 cm to infinity), approximately 35% of the scaling required for complete depth constancy was obtained. When manipulated separately the relative influence of each cue depended crucially on the size of the visual display. Differential perspective was only effective when the display size was sufficiently large (i.e., greater than 20 deg) whereas the influence of vergence angle, although evident at each display size, was greatest in the smaller displays. For each display size the independent effects of the two cues were approximately additive. Perceived size (and two-dimensional spacing of elements) was also affected by manipulations of differential perspective and vergence. These results confirm that both differential perspective and vergence are effective in scaling the perceived two-dimensional size of elements and the perceived depth from horizontal disparities. They also show that the effect of the two cues in combination is approximately equal to the sum of their individual effects.

Convergence, Ocular↗
PubMed1984

Effects of hierarchical organization on children's judgments of distance and direction.

The impact of the hierarchical organization of a space on judgments of direction and distance was assessed in two studies using two-dimensional models analogous to those used by A. Stevens and P. Coupe (1978, Cognitive Psychology, 10, 422-437). In each study the models contained two stars and were divided into two parts by a curved boundary line. In the Homogeneous condition the stars were located in the same subsection. In the Congruent condition the leftmost star was in the left subsection and the rightmost star was in the right subsection. In the Incongruent condition the rightmost star was in the left subsection and the leftmost star was in the right subsection. In Experiment 1 first graders, third graders, and college students were required to remember the location of the stars. Results indicated that the first and third graders tended to use the relationship between the subsections as a clue to the relationship between the sites within them, thus extending the results of Stevens and Coupe (1978) to children. In Experiment 2 preschoolers, first, and third graders were asked to judge with the materials directly in front of them, which of the two stars was closer to a site located in one of the subsections. Results indicated that the Incongruent condition led to errors among the preschoolers and first graders but not the third graders, thus indicating that these groups tended to judge as closer the site within the same subsection even though it was really farther away. The results of both studies are discussed as indicative of a tendency among young children to impose organization on information encoded in memory and in relation to increases in metric accuracy, decentration, and efficient scanning which enable them to more accurately evaluate when such organization is and is not appropriate. Implications for behavior in large-scale environments are also discussed, with particular reference to the effect of barriers on perceptions of distance and direction.

Age Factors↗
PubMed1995

Voluntary binocular gaze-shifts in the plane of regard: dynamics of version and vergence.

We studied the dynamics of voluntary, horizontal, binocular gaze-shifts between pairs of continuously visible, real three-dimensional targets. Subjects were stabilized on a biteboard to allow full control of target angles, which were made to differ only in distance (pure vergence), only in direction (pure version; conjugate saccades) or in both distance and direction (disjunctive saccades). A wide range of changes in vergence (0-25 deg) and version (0-65 deg) was recorded to study the dynamics of disjunctive saccades, described until now for limited ranges, throughout the horizontal oculomotor range within manual working space, and to study the velocity-duration-amplitude relations ("main sequence") of disjunctive vs conjugate saccades. Pure vergence was almost never observed; divergence, especially, was always associated with saccades. Likewise, horizontal saccades were never strictly conjugate, they always contained a transient divergence-convergence sequence. The amplitude and velocity of these transient components varied systematically with saccadic size. In combined version-vergence movements, vergence was, in general, accelerated and shortened as a function of increasing version. This effect was fairly uniform for divergence, which appeared to increase in velocity by about as much as the transient peak divergent velocity of the version saccade. The intrasaccadic fraction of divergence increased from about 50% to close to 100% as a function of increasing version. For convergence, saccades up to about 20 deg were also accelerating; in this case it appeared as if the transient peak convergent velocity of the version saccade was added to the basic convergence velocity. For larger saccades this effect was partly counteracted by the penetration of an initial divergence associated with the saccade. This initial divergence delayed and slowed down convergence. The intrasaccadic fraction of convergence varied between about 40% and 70%. In disjunctive saccades the individual eyes did not follow the main-sequence parameters of conjugate saccades of comparable sizes, except for the eye that moved with the combination "abduction and divergence". For all other combinations of vergence and version, disjunctive saccades had lower peak velocities and longer durations than conjugate saccades. As a consequence, disjunctive version was also slower than conjugate version. Thus, while version accelerates vergence, vergence slows down version: in the generalized case of three-dimensional gaze-shifts, peak velocities and durations are in between those of the limiting cases of pure version and pure vergence. We conclude that, within manual working space, binocular gaze-shifts are effected by the highly integrated action of conjugate and disjunctive mechanisms, both of which are expressed preferentially in fast, saccadic movements.

Adult↗