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PubMed1995

The hierarchical nature of perceiving direction of motion in depth from optic flow.

Monocular adaptation to flow fields of optic expansion and contraction juxtaposed on either side of fixation influenced subsequently perceived rotation direction of a figure rotating in depth (kinetic depth effect) about its vertical axis with a normally ambiguous direction. This influence was shown to be asymmetric since adapting to optic expansion produced significantly more aftereffects of translation in depth than did adapting to perceived rotation in depth when viewing a neutral test stimulus. The results are evidence for a hierarchical processing model for the perception of motion in depth from optic flow. Serendipitously, we discovered a new aftereffect from viewing kinetic depth rotation with direction specified by proximity-luminance covariation (PLC). The results and other research are discussed in terms of neural network models with synergistic interactions between levels.

Adaptation, Physiological↗
PubMed1989

Preserved learning and memory in amnesia: intact adaptation-level effects and learning of stereoscopic depth.

Amnesic patients and control Ss performed similarly on 2 memory tests. In Experiments 1A and 1B, amnesic patients exhibited intact adaptation-level effects: An experience lifting and judging a group of weights influenced their judgments of a 2nd group of weights 20-25 min later. The effect did not depend on peripheral accommodation, because Ss used 1 hand during their 1st encounter with the weights and the opposite hand during their 2nd encounter. In Experiment 2, amnesic patients acquired at a normal rate the ability to perceive binocular depth using random-dot stereograms. In both experiments, amnesic patients benefited from recent experience, despite the fact that they could not remember their prior experience accurately. The preserved memory abilities demonstrated here appear to be examples of implicit, or nondeclarative, memory.

Adaptation, Psychological↗
PubMed1982

Simultaneous and successive contrast effects in the perception of depth from motion-parallax and stereoscopic information.

Prolonged inspection of a three-dimensional corrugated surface resulted in a successive contrast effect, or aftereffect, of depth, whereby a subsequently-viewed physically-flat test surface appeared to be corrugated in depth with the opposite phase to the adapting surface. The aftereffect occurred both when the depth was specified by motion parallax, in the absence of all other sources of depth information, and when it was specified solely by stereoscopic information. The depth aftereffect was measured by 'nulling' the apparent depth in the test surface with physical relative motion or binocular disparity until the test surface appeared flat. Up to 70% of the depth in the adapting surface was necessary to null the aftereffect. Simultaneous contrast effects in the perception of three-dimensional surfaces were used to investigate the spatial interactions that exist in the processing of motion-parallax and stereoscopic information. A physically vertical surface appeared to slope in depth in the opposite direction to the slope of a surrounding surface. In this case up to 50% of the slope of the inducing surface was necessary to null the contrast effect. Similar results were again obtained for motion-parallax and stereoscopic depth.

Adaptation, Ocular↗
PubMed1999

Perceptual depth synthesis in the visual system as revealed by selective adaptation.

Selective adaptations was used to determine the degree of interactions between channels processing relative depth from stereopsis, motion parallax, and texture. Monocular adaptations with motion parallax or binocular stationary adaptation caused test surfaces, viewed either stationary binocularly or monocularly with motion parallax, to appear to slant in the opposite direction compared with the slant initially adapted to. Monocular adaptations on frontoparallel surfaces covered with a pattern of texture gradients caused a subsequently viewed test surface, viewed either monocularly with motion parallax or stationary binocularly, to appear to slant in the opposite direction as the slant indicated by the texture in the adaptation condition. No aftereffect emerged in the monocular stationary test condition. A mechanism of independent channels for relative depth perception is dismissed in favor of a view of an asymmetrical interactive processing of different information sources. The results suggest asymmetrical inhibitory interactions among habituating slant detector units receiving inputs from static disparity, dynamic disparity, and texture gradients.

Adaptation, Physiological↗
PubMed2003

Paired and unpaired features can be equally effective in human depth perception.

The horizontal separation of the eyes results in the projection of slightly different images in each eye that are used to recover depth. One source of depth information is disparity, the relative position of paired features in the two eyes. Another source of depth information comes from features that are present in only one eye's view. These unpaired features arise from occlusion and by definition cannot generate a conventional disparity signal. Here we compare the depth signals generated by paired and unpaired features using stimuli that differ only in whether a given feature (a vertical gap) is paired or unpaired. Ecologically, both stimuli are consistent with two panels separated in depth at the gap, but only the paired gap provides a conventional disparity signal. We found strikingly that depth thresholds for the two gap conditions were the same and that there was perfect cross-adaptation of perceived depth from the unpaired to paired condition, strongly suggesting a common mechanism.

Contrast Sensitivity↗
PubMed1997

Changes in perceived speed following adaptation to first-order and second-order motion.

To investigate whether or not adaptation to second-order motion can cause changes in perceived speed, measurements of perceived speed were obtained for two varieties of motion: (i) contrast-modulated two-dimensional static noise (second-order motion); and (ii) luminance-modulated noise (first-order motion). The test stimulus (either first-order or second-order) was presented to one side of a central fixation spot and a comparison stimulus (always first-order) was simultaneously presented on the opposite side. The observer's task was to indicate which of the two motion stimuli appeared to drift faster. The perceived speed of the test stimulus was measured with and without prior adaptation to motion on one side of the fixation spot only (that of the test stimulus). The modulation depth of the adaptation stimulus was always half that of the test stimulus and all test patterns were equated for visibility. The pattern of results for second-order motion was similar to that for first-order motion. Typically, adaptation reduced perceived speed, particularly when the adaptation speed was faster than the test speed. However, when the adaptation speed was low relative to the test speed, increases in perceived speed were found. Cross-over adaptation effects between first-order and second-order motion were also observed. Robust velocity aftereffects were found for second-order motion when the noise was dynamic or was high-pass filtered, suggesting that first-order (luminance) artifacts were not responsible for the velocity aftereffects observed. We conclude that the perceived speeds of first-order and second-order motion appear to be encoded in human vision using similar computational principles (but not necessarily utilizing the same mechanism), since the same pattern of results was found for the two varieties of motion.

Adaptation, Physiological↗
PubMed2003

Analysis of continuous-wave obturation using a single-cone and hybrid technique.

This study analyzed the adaptation of gutta-percha to prepared root canal walls using two obturation techniques and determined the influence of the System-B plugger depth on filling adaptation. Fifty-six extracted human mandibular molars were instrumented using Profile NiTi rotary instruments, stratified based on curvature, then randomly distributed into two groups. Group 1 was obturated using the single-cone continuous-wave technique. Group 2 was obturated with a hybrid technique: lateral condensation followed by a continuous-wave down-pack. Based on System-B plugger penetration, teeth were divided into three subgroups: (a) < 3.5 mm, (b) 3.5 to 4.5 mm, and (c) > 4.5 mm. Roots were horizontally sectioned at 1 mm and 3 mm coronal to the apical foramen, stained, and photographed. Four evaluators scored the adaptation of gutta-percha to the prepared canal walls. In 100% (n = 56) of the samples, no statistically significant difference existed between the two obturation methods at 1-mm (x = 1.80, SD +/- 0.69) or 3-mm (x = 1.804, SD +/- 0.69) sections. Best results were obtained with a plugger depth 3.5 to 4.5 mm from the working length.

Gutta-Percha↗
PubMed1993

Asymmetries in the sensitivity to motion in depth: a centripetal bias.

It is reasonable to ask whether observers are more sensitive to the pattern of image motion caused by forward locomotion through the environment than to the pattern caused by backward locomotion. The distribution of sensitivities of cells in MT does show such a bias, although this bias is minimal at small eccentricities. Additionally, both locomotion-induced stimulation and the sensitivities of MT cells suggest greater sensitivity should be obtained in the lower visual field. Previous research on this issue has usually employed frontoparallel motion in patterns presented to one side of the fixation point. Both centrifugal and centripetal biases have been obtained. In this study the stimuli present motion signals that travel radially from (or towards) the fixation point. These stimuli, which produce a strong percept of motion in depth, are an adaptation of the global-dot-motion stimulus employed by Newsome and Pare. With these stimuli we find that sensitivity to motion in depth is greater in the lower visual field than in the upper visual field, and that sensitivity is greater to centripetal motion than to either centrifugal or frontoparallel motion. This centrifugal bias in sensitivity decreases with eccentricity. The last two findings contradict the notion that the bias is produced by the visual experience induced by normal forward locomotion and also that the detection of motion in depth is subserved by MT.

Adult↗
PubMed1971

Stereoscopic depth aftereffect produced without monocular cues.

Random-dot stereograms when used as adaptation stimuli can influence the perceived depth of similar test stimuli. Adaptation for 1 minute is sufficient to evoke this three-dimensional aftereffect for several seconds. This aftereffect must occur after stereopsis because prior to stereopsis no relevant monocular cues exist in these adaptation and test stimuli.

Adaptation, Ocular↗
PubMed2003

Representation of the perceived 3-D object shape in the human lateral occipital complex.

We used human functional magnetic resonance imaging (fMRI) to test whether the human lateral occipital complex (LOC), an area known to be involved in the analysis of visual shape, represents the perceived 3-D shape of objects or simply their 2-D contours. We employed an fMRI adaptation paradigm, in which repeated presentation of a stimulus results in decreased responses compared to responses to different stimuli. We found adaptation in the LOC for images of objects with the same perceived 3-D shape structure but different 2-D contours that resulted from small rotations of the objects in the frontal plane or in depth. However, no adaptation was observed in the LOC for images of objects that had the same 2-D contours but differed in their perceived 3-D shape; namely, 2-D silhouettes versus 3-D shaded images of objects, or convex versus concave objects. Differences in the fMRI adaptation responses across subregions in the LOC suggest that different neural populations in the LOC may mediate different mechanisms for the processing of object features.

Depth Perception↗
PubMed1994

Stereopsis and positional acuity under dark adaptation.

Though experience tells us we can perceive depth in dim light, it is not so obvious that one of the chief mechanisms for depth perception, stereopsis, is possible under scotopic conditions. The only studies on human stereopsis in the dark adapted state seem to be those of Nagel [(1902) Zeitschrift für Psychologie, 27, 264-266] and Mueller and Lloyd [(1948) Proceedings of the National Academy of Science, U.S.A., 34, 223-227], both of which used real objects or line stereograms. We tested stereopsis using both random-dot and line stereograms and, in agreement with these studies, found that stereopsis is indeed possible in dark adaptation. We also measured stereo acuity and positional acuity (both of which are examples of hyperacuity) and compared these with grating acuity at several levels of light and dark adaptation. At all illumination levels tested, acuities for stereopsis and relative line position were both higher than for grating acuity. As light levels decreased, positional and grating acuity declined in parallel fashion, whereas stereoacuity declined more steeply.

Dark Adaptation↗
PubMedDate not supplied

Implementation of depth-dependent soil concentrations in multimedia mass balance models.

In standard multimedia mass balance models, the soil compartment is modeled as a box with uniform concentrations, which often does not correspond with actual field situations. Therefore, the theoretically expected decrease of soil concentrations with depth was implemented in the multimedia model SimpleBox 3.0. The effects of this implementation on the model outcomes were explored for nine compounds in four environmental compartments. For compounds with a low penetration depth, the new model predicts substantially higher or lower concentrations in the vegetation compartment than the old model. For those compounds, predicted concentrations in surface water and air were higher in the new model, but the deviations from the old model were smaller than in the vegetation compartment. For compounds with a large penetration depth, the model adaptations show little effect. No field study was carried out to validate the results of the model calculations, but we did collect measured data on concentrations in vertical soil profiles from literature. According to those data, we concluded that the implementation of depth dependent soil concentrations might be a useful extension for steady state multimedia mass balance models. More field study has to be carried out to validate the model outcomes.

Databases, Factual↗
PubMed2005

Frameless stereotactic placement of depth electrodes in epilepsy surgery.

OBJECT: Depth electrodes are useful in the identification of deep epileptogenic foci. Computerized tomography-magnetic resonance (CT/MR)- and angiography-guided frame-based techniques are safe and accurate but require four-point skull fixation that limits cranial access for the placement of additional grids and strips. The authors investigated the viability and accuracy of placing depth electrodes by using a commercially available frameless system. METHODS: A slotted, custom-designed adapter was built to interface with the StealthStation Guide Frame-DT and 960-525 StealthFighter. The Cranial Navigation software was used to plan the trajectory and entry site based on preoperative spoiled gradient MR imaging studies. Forty-one depth electrodes were placed in 51 targets in 20 patients. Thirty-one of these electrodes were inserted through the temporal neocortex following craniotomy and placement of subdural grids, whereas 10 were placed through burr holes. All electrodes had contact either within (71%) or touching (29%) the target, 50 of which (98%) provided adequate recordings. Although the mean distance of the distal electrode contact from the intended target was 3.1 +/- 0.5 mm, the mean distance to the edge of the anatomical structure was 0.4 +/- 0.9 mm. Placement via the laterotemporal approach was significantly (p < 0.001) more accurate than that via the occipitotemporal approach. No complication occurred. CONCLUSIONS: Depth electrodes can be placed safely and accurately by using a commercially available frameless stereotactic navigation system and a custom-made adapter. Depth electrode placement to record ictal onsets during epilepsy surgery only requires the contacts to touch rather than to reside within the intended structure. The laterotemporal approach is a more accurate method of placing electrodes than is the occipitotemporal one, likely due to the increased distance from the entry point to the target.

Adolescent↗