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At least 1,225 records · Page 68Linked to original sources
PubMed1995

A corpus of 714 full-color images of depth-rotated objects.

A set of full-color images of objects is described for use in experiments investigating the effects of in-depth rotation on the identification of three-dimensional objects. The corpus contains up to 11 perspective views of 70 nameable objects. We also provide ratings of the "goodness" of each view, based on Thurstonian scaling of subjects' preferences in a paired-comparison experiment. An exploratory cluster analysis on the scaling solutions indicates that the amount of information available in a given view generally is the major determinant of the goodness of the view. For instance, objects with an elongated front-back axis tend to cluster together, and the front and back views of these objects, which do not reveal the object's major surfaces and features, are evaluated as the worst views.

Color Perception↗
PubMed2002

Influence of chromaticity on vernier and stereo acuity.

Vernier offset thresholds for targets modulated in luminance or isoluminantly along the L-M axis were confirmed to be equal for targets whose contrasts were equal multiples of those required for detection. On the other hand, stereoscopic depth thresholds were elevated by a factor of 10 or more for isoluminantly modulated targets. Thresholds for vernier targets are 2 or 3 times larger with a gap of 20 arcmin than for a gap of 1 arcmin for both isoluminant and luminance targets. On the other hand, stereo thresholds decrease by a factor of 2 to 3 for both classes of target over the same range. We consider our results in the light of recent electrophysiological and psychophysical evidence and conclude that our results are consistent with the notion that stereo thresholds are mediated by a single class of mechanism for targets modulated in luminance or isoluminantly. We test and reject the hypothesis that stereopsis is subserved by independent chromatic and luminance mechanisms.

Color Perception↗
PubMed2000

[Statistical efficiency of depth discrimination in stereoscopically overlapped and step-edge patterns].

We compared observers' statistical efficiencies of depth discrimination for two stereoscopic patterns: an overlapped pattern where two planes are overlapped at different depths, and a step-edge pattern where two planes are arranged side by side. In both patterns, elements in one plane were differentiated from those in the other plane by color (red vs. green) or orientation (45 deg vs. -45 deg). In the experiment, subjects were required to determine which plane was in front when Gaussian disparity noise was added to both of the elements' disparity values. The results showed that efficiencies were the same level for both patterns when the elements were differentiated by color. On the other hand, efficiencies were lower for the overlapped pattern than the step-edge pattern when the elements were differentiated by orientation regardless of the set size of elements. The patterns which we used were so sparse that the differences between the color and orientation conditions should arise from the process after matching.

Color Perception↗
PubMed2005

Activation in visual cortex correlates with the awareness of stereoscopic depth.

Using event-related functional magnetic resonance imaging, we studied the activation correlating with the awareness of stereoscopic depth using a bistable slanted surface (slant rivalry). Bistability resulted from incongruence between two slant-defining cues: binocular disparity and monocular perspective. The stimulus was perceived as alternating between the perspective-dominated percept (monocular depth) and the disparity-dominated percept (stereopsis), while sensory input remained constant, enabling us to study changes in awareness of depth associated with either cue. Transient activation relating to perceptual alternations was found bilaterally in the caudal part of the intraparietal sulcus, in the right-hemispheric anterior intraparietal sulcus, within visual area V4d-topo, and inferior to area MT+. Transient activation correlating specifically with alternations toward the disparity-dominated percept was found in a number of visual areas, including dorsal visual areas V3A, V7, and V4d-topo and visual areas MT+ and lateral occipital complex. No activation was found for alternations toward the perspective-dominated percept. Our results show that of all visual areas responsive to disparity-defined depth, V4d-topo shows the most robust signal changes correlating with the instigation of stereoscopic depth awareness (stereopsis).

Awareness↗
PubMed1994

The effects of visual scene composition on the latency of saccadic eye movements of the rhesus monkey.

This study examined how variations in the visual scene affect the generation of bimodal saccadic latency distributions, the first mode of which is called the population of "express saccades". The surface media used to make stimuli visible and the composition of the background were varied to determine the conditions under which express saccades can be generated in rhesus monkeys. The results show that express saccades to singly presented targets can readily be elicited when the stimuli are made visible by virtue of either luminance contrast, color contrast or motion cues. Express saccades are rarely obtained when stimuli are made visible by virtue of only stereoscopic depth or texture cues. Express saccades can, however, be elicited using random-dot stereograms or textures when luminance or chrominance information is added to the target. When single target stimuli are presented simultaneously with a set of non-target stimuli, express saccades are for the most part prevented unless either the non-target stimuli are near threshold or their numerosity is very high, in which case they form a texture-like array. However, when the non-target stimuli are continuously present in the display, express saccades reemerge. These findings suggest that express saccades are not unique to experimental situations in which only a single stimulus appears on an otherwise homogeneous surface; they can readily be generated as long as the target stimulus is made visible by virtue of luminance, chrominance, motion or a combination of more than one surface medium and as long as the target does not appear concurrently with a salient group of other non-target stimuli.

Animals↗
PubMed2005

Dynamic aspects of the continuity illusion: perception of level and of the depth, rate, and phase of modulation.

The perception of modulation of a tone interrupted by a noise burst was investigated. The tone and its modulation were perceived as continuing through the noise. In experiment 1, subjects rated the similarity of an uninterrupted tone and a tone interrupted by noise, in terms of the perceived level and modulation depth of the sinusoidal carrier. The values of these parameters in the central portion of the uninterrupted tone were systematically varied. Both amplitude and frequency modulation (AM and FM) were used. The results indicated that the perceived level and modulation depth of the carrier did not change greatly during the noise burst. When the modulation rate differed before and after the noise burst, the modulation-rate transition was perceived to occur near the end of the noise burst for the FM stimuli. Hence, for these stimuli, the continuity illusion appears to be dominated by the portion of the tone before, rather than after, the interruption. Results for the AM stimuli showed a non-significant trend in the same direction. Experiment 2 used forced-choice tasks to evaluate the ability to detect a change in the ongoing phase of AM and FM following interruption by a noise burst. The results confirmed earlier findings for FM tones, and extended them to AM tones, showing that listeners lost track of the phase of the modulation, even though the modulation was perceived as continuous.

Acoustic Stimulation↗
PubMedDate not supplied

Effects of insertion depth of cochlear implant electrodes upon speech perception.

OBJECTIVE: To investigate whether the insertion depth of a cochlear implant array affects postoperative speech perception. DESIGN: The subjects were 48 postlingually deaf adults who received either the Nucleus 22 or the Nucleus 24 cochlear implant with a straight array. A postoperative radiograph of the cochlear electrode was used to estimate insertion depth, as either the angle of the electrode tip (angle) or the intracochlear length of the electrode (length). Other estimates of insertion depth included the numbers of active electrodes and channels used by the speech processor. Electrode depth, together with the duration of deafness, hearing aid usage, pre-operative speech perception score and pre-operative pure-tone averages were independent variables in a forward stepwise multiple regression analysis, where the dependent variables were postoperative CNC words and CNC phonemes. RESULTS: Duration of deafness and insertion depth (angle, insertion length or active electrodes) were the predictive variables for CNC words or CNC phonemes. Angle was the best 'depth-related' predictor of postoperative speech perception. An even clearer relationship was found between CUNY sentences in noise and angle, in a subset of 26 patients. CONCLUSION: Depth of electrode insertion affects postoperative speech perception.

Adult↗
PubMed1982

Is the binocular rivalry mechanism tritanopic?

Binocular rivalry for a series of colored targets was measured in three trichomats and two red-green dichromats by cumulating those times when ony one target or the other was perceived (exclusive visibility time). Targets were black and colored 3 c/deg square-wave gratings, 1 degree in diameter. For trichromats, exclusive visibility time increased as a function of color difference between the targets, but for dichromats there was no effect of color on binocular rivalry. Taken together, these data indicate that the binocular rivalry mechanism is tritanopic: it is responsive to color signals only from the medium- and long-wave-sensitive cones.

Color↗
PubMed1991

Binocular visual impairment in glaucoma.

Monocular and binocular vision was assessed in patients with glaucoma (n = 21), in patients with ocular hypertension (n = 20), and in age-matched visual control subjects (n = 20) using three tests: color vision with the Lanthony Desaturated D-15 test, low spatial frequency contrast sensitivity with the Pelli-Robson chart, and stereoacuity with the RANDOT test. No significant differences were found among the groups in the severity or type of color vision loss. Monocular contrast sensitivity testing showed considerable overlap among groups but a significant loss of contrast sensitivity in the glaucoma patients relative to ocular hypertensives and control subjects. Binocular testing also showed a significant loss of contrast sensitivity in the glaucoma patients compared with both the ocular hypertensives and the control subjects. Stereoacuity also was significantly impaired in the glaucoma patients. These results indicate that two tests of binocular function, stereoacuity and binocular contrast sensitivity testing, may have utility in identifying early glaucomatous damage.

Aged↗
PubMed1992

[Evaluating visual function with visual display graphics on the Macintosh II computer].

A collection of programs has been developed on the Macintosh II computer to generate visual tests for an ophthalmological practice. The large number of available colours makes it possible to emulate most of the available tests and also to develop new ones. The system allows testing of the following visual functions: Visual acuity, Stereopsis, Aniseikonia, Phoria, Cyclophoria, Colour Vision and Contrast sensitivity.

Color Perception Tests↗
PubMed1981

A new class of visual defect. Spreading inhibition elicited by chromatic light stimuli.

This paper deals with a single male subject, M., who has a well-defined visual defect of a kind not previously described. The defect is associated with a potent inhibitory response to long-wavelength stimuli, which spreads for up to 12 deg from the area of stimulation, suppressing M.'s detection of other high contrast stimuli. The effect can also be observed, weakly, with certain other coloured stimuli, but not with yellows or whites. Detailed psychophysical data are given for threshold sensitivity, colour matching, two-colour increment thresholds and visual acuity, all of which are more or less abnormal, depending on the stimulus colour. No abnormal effects were, however, observed with white light stimuli. On the basis of M.'s ability to fuse red and green random dot stereogram pairs, we argue that the inhibition arises centrally in the visual pathways. and we examine the implications of M.'s response characteristics for the analysis of central visual processing.

Adult↗
PubMed1978

Operant conditioning and assessment of stereopsis in young children.

Stereposis was assessed in 94 children ages 2--5 yr using random-dot stereograms (RDSs) and operant conditioning. After five traditional screening tests of stereopsis, all children were trained to perform a match-to-sample discrimination task involving RDSs with and without lateral disparity. An added feature of the operant RDS task was the availability of monocular cue-fading for children who failed initial RDS testing. The operant RDS test facilitated stereopsis-based responding more than the traditional clinical tests did. This finding is interpreted as indicating the importance of such factors as attention, motivation, and language ability in the assessment of stereopsis in young children.

Child↗
PubMed1998

Biases in three-dimensional structure-from-motion arise from noise in the early visual system.

The projected pattern of retinal-image motion supplies the human visual system with valuable information about properties of the three-dimensional environment. How well three-dimensional properties can be recovered depends both on the accuracy with which the early motion system estimates retinal motion, and on the way later processes interpret this retinal motion. Here we combine both early and late stages of the computational process to account for the hitherto puzzling phenomenon of systematic biases in three-dimensional shape perception. We present data showing how the perceived depth of a hinged plane ('an open book') can be systematically biased by the extent over which it rotates. We then present a Bayesian model that combines early measurement noise with geometric reconstruction of the three-dimensional scene. Although this model has no in-built bias towards particular three-dimensional shapes, it accounts for the data well. Our analysis suggests that the biases stem largely from the geometric constraints imposed on what three-dimensional scenes are compatible with the (noisy) early motion measurements. Given these findings, we suggest that the visual system may act as an optimal estimator of three-dimensional structure-from-motion.

Computer Simulation↗
PubMed1997

Restorative certainty and varying perceptions of dental caries depth among dentists.

OBJECTIVE: The question of whether dentists who most frequently identify tooth surfaces for definite restoration perceive dental caries as significantly deeper than other dentists is assessed. METHODS: One group of 20 dentists independently examined 145 unrestored approximal tooth surfaces on 16 bitewing radiographs and recorded their restorative and depth decisions. Another group of 15 dentists similarly scored 304 unrestored surfaces on 30 bitewing radiographs. Each group of dentists was later divided into four subgroups according to the number of surfaces designated for definite restoration by each dentist. RESULTS: As the number of tooth surfaces designated for definite restoration increased, mean caries depth (P < .05 for the high vs low subgroups) and the percent of dentinally carious surfaces increased, while the percent of surfaces assessed as sound decreased. Dentists with the lower numbers of surfaces designated for definite restoration came closest to the true histologic mean caries depth of the examined tooth surfaces. CONCLUSIONS: Dentists who designated high numbers of approximal tooth surfaces for definite restoration assessed caries as deeper than other dentists, and deeper than was proven histologically.

Analysis of Variance↗
PubMed1978

Central representation of colour vision deduced from studies on a subject with a central colour vision defect.

M.W.'s grossly defective responses to red light stimuli are caused by an abnormality of central vision which is highly specific in its action. The abnormal activity does not affect stereoscopic function and only partially modifies the parametric characteristics of the contrast threshold elevation effect. These experimental observations lend support to the concept of parallel processing of different attributes of the visual stimulus, possibly by different cortical areas. We suggest that understanding of central visual processes could be facilitated by further studies on subjects with malfunction of the visual cortex.

Adult↗
PubMed1997

Vision profile of the athletes of the 1995 Special Olympics World Summer Games.

BACKGROUND: Special Olympics were organized in 1968 by Eunice Shriver as a program of physical fitness for individuals with mental handicaps. Numerous epidemiologic studies report an increase in visual problems in this population. METHODS: A comprehensive vision screening was conducted at the 1995 Special Olympic World Summer Games to identify the prevalence of visual anomalies in this select group. Testing included visual acuity, refractive error, ocular motor skills, stereopsis, color vision, contrast sensitivity, eye-hand coordination, eye-foot coordination, and an ocular health evaluation. RESULTS: Nine hundred five special athletes, ranging in age from 8 to 58 years, participated in the screening. More than 65% of the participants had not received eye care for more than 3 years. The most commonly reported symptom was difficulty in seeing. Other ocular health problems included refractive errors, poor distance monocular acuity, and strabismus. CONCLUSION: The results of the study indicate that Special Olympians have a high prevalence of vision anomalies that may go undetected. This population demonstrates a high prevalence of refractive errors, decreased visual acuity, ocular health problems, and strabismus. In addition, based on the number of individuals who have not received eye care within the last year, there is a need to increase the availability of vision care to these and other people with mental retardation.

Adolescent↗
PubMed1976

Development of ability to perceive and produce pictorial depth cue of overlapping.

The perception of the pictorial depth cue of overlapping was studied in children 3, 5, and 7 yr. old. Both a sequential and a simultaneous picture/object-matching task were used to test sensitivity. All age groups successfully perceived the depth relation information provided by pictorial overlapping. Height on the picture plane, which projectively covaries with overlapping, was not consistently used as a depth cue by any age group. Children's drawings were also analyzed for the presence of distance information. The drawings of the 3- and 5-yr. old children contained no overlapping cues and indicated a general lack of understanding of the third demension behind the picture plane. Seven-yr.-old children showed the beginnings of this understanding through their use of size perspective and height on the picture plane as depth cues. For all ages the production of the overlapping cue lags behind its perception.

Age Factors↗