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At least 1,585 records · Page 88Linked to original sources
PubMed2003

The effect of perceived surface orientation on perceived surface albedo in binocularly viewed scenes.

We examined how observers discount perceived surface orientation in estimating perceived albedo (lightness). Observers viewed complex rendered scenes binocularly. The orientation of a test patch was defined by depth cues of binocular disparity and linear perspective. On each trial, observers first estimated the orientation of the test patch in the scene by means of a gradient probe and then matched its perceived albedo to a reference scale. We found that observers' perception of orientation was nearly veridical and that they substantially discounted perceived orientation in estimating perceived albedo.

Cues↗
PubMed2007

Sex differences in judging self-orientation: the morphological horizon and body pitch.

BACKGROUND: Sex differences exist for many spatial tasks. This is true for circular vection, field dependence, and perception of veridical vertical with body tilt. However, explanations for these sex differences is lacking in the literature. In this study, we investigated the nature of individual differences in the perception of self-orientation in humans. Male and female participants were asked to identify their Morphological Horizon (i.e., line perpendicular to saggital plane at eye-level) in different body orientations relative to gravity (i.e., 45 deg and 135 deg body pitch) with and without prior whole body rotation. RESULTS: Sex explained the observed differences in the perception of self-orientation only when blood distribution was least altered (i.e., 45 deg body pitch) and without prior whole body rotation. Specifically, females presented a more footward bias than males in these conditions. CONCLUSION: These results add to the literature on sex differences for spatial orientation tasks. As the differences were only observed with static conditions and when blood distribution was least affected, we concluded that sex differences in the perception of self-orientation are associated with gravireceptors (e.g., otoliths).

Adult↗
PubMed2004

Navigation and seasonal migratory orientation in juvenile sea turtles.

Juvenile loggerhead and green turtles that inhabit inshore waters of North Carolina, USA undertake long seasonal migrations, after which they often return to specific feeding areas. In addition, juvenile turtles are capable of homing to specific sites after being displaced. As a first step towards investigating the navigational mechanisms that underlie these movements, juvenile turtles were captured in coastal waters of North Carolina and displaced 30-167 km along circuitous routes while deprived of visual cues. At the testing location, turtles were tethered in a circular arena and permitted to swim while their orientation was monitored. Between May and September, when juvenile loggerhead and green turtles inhabit feeding areas along the North Carolina coast, turtles oriented in directions that corresponded closely with the most direct route back to their capture locations. During October and November, however, both loggerhead and green turtles oriented southward, a direction consistent with the migratory paths of turtles beginning their autumn migration. The results demonstrate for the first time that both homing and migratory orientation can be elicited in juvenile turtles under laboratory conditions in which orientation cues can be readily manipulated. In addition, the results provide evidence that juvenile loggerheads can assess their position relative to a goal using local cues available at the test site and are therefore capable of map-based navigation.

Animal Migration↗
PubMed2004

Sound localization in a small passerine bird: discrimination of azimuth as a function of head orientation and sound frequency.

Sound localization is critical to communication when signalers are distributed widely in space and when reverberations that accumulate over distance might otherwise degrade temporal patterns in vocalizations. We readdress the accuracy with which a small passerine bird, the eastern towhee, Pipilo erythrophthalmus L., is able to resolve azimuth in the field. We then report results from two-alternative forced-choice (2AFC) experiments in which three of four subjects were able to discriminate an estimated speaker separation angle of approximately 7 degrees . Subjects oriented laterally when discriminating azimuth in the 2AFC task and each subject preferred a different head orientation. Side biases occurred as a function of head orientation and, as a consequence, we conducted a second 2AFC experiment in which subjects were required to discriminate between two closely spaced lights. Subjects oriented similarly in this visual task, however, side biases did not occur as a function of head orientation. Despite side biases in the auditory task, performance generally declined when subjects were played tones with frequencies near approximately 3 kHz.

Animal Communication↗
PubMed1987

Laboratory studies of homing orientation in the eastern red-spotted newt, Notophthalmus viridescens.

The orientation behaviour of adult male eastern red-spotted newts (Notophthalmus viridescens) was studied in laboratory tests. Newts were collected from ponds located 10-30 km from the laboratory, and housed in water-filled, all-glass aquaria located in a greenhouse or outdoors adjacent to the laboratory building. The aquaria were aligned on the magnetic north-south axis. Newts were tested in a dry, enclosed arena in four magnetic fields: the ambient magnetic field (magnetic north at North) and three altered fields (magnetic north rotated to East, West or South). Newts tested during January-March exhibited weak bimodal magnetic orientation along the axis of the holding tank. However, during the spring migratory period (April until early May), the bimodal response shifted to coincide with the direction of the pond from which the newts had been collected. Much stronger unimodal orientation was elicited by elevating the water temperature to 33-34 degrees C immediately prior to testing. If newts were held in a training tank with an artificial shoreline at one end and exposed to elevation of water temperature after several days of stable water temperatures, they exhibited unimodal shoreward orientation and did not show the seasonal switch to homing behaviour observed in the earlier tests. If, however, the elevation of water temperature followed a period of fluctuating water temperature (over a 20 degrees C range), the newts exhibited strong unimodal orientation in the direction of the pond from which they had been collected. These results suggest that newts possess a navigational system that enables them to home from distances in excess of 20 km. Moreover, these experiments provide the first opportunity to examine the sensory basis of navigational ability in any animal under controlled laboratory conditions.

Animals↗
PubMed1991

Magnetic orientation by hatchling loggerhead sea turtles (Caretta caretta).

Laboratory experiments were conducted to test the ability of loggerhead sea turtle hatchlings (Caretta caretta L.) to orient using the magnetic field of the earth. Hatchlings were tethered to a rotatable lever-arm apparatus which tracked swimming orientation in complete darkness. Hatchlings tested in the earth's magnetic field were nonrandomly oriented with a mean angle of 42 degrees; those tested under an earth-strength field with a reversed horizontal component were also nonrandomly oriented, but with a mean angle of 196 degrees. The distributions under the two magnetic field conditions were significantly different, indicating that loggerhead sea turtle hatchlings can detect the magnetic field of the earth and use it as a cue in orientation.

Animals↗
PubMed2000

Simple mechanisms organise orientation of escape swimming in embryos and hatchling tadpoles of Xenopus laevis.

Many amphibian tadpoles hatch and swim before their inner ears and sense of spatial orientation differentiate. We describe upward and downward swimming responses in hatchling Xenopus laevis tadpoles from stages 32 to 37/38 in which the body rotates about its longitudinal axis. Tadpoles are heavier than water and, if touched while lying on the substratum, they reliably swim upwards, often in a tight spiral. This response has been observed using stroboscopic photography and high-speed video recordings. The sense of the spiral is not fixed for individual tadpoles. In 'more horizontal swimming' (i.e. in directions within +/-30 degrees of the horizontal), the tadpoles usually swim belly-down, but this position is not a prerequisite for subsequent upward spiral swimming. Newly hatched tadpoles spend 99 % of their time hanging tail-down from mucus secreted by a cement gland on the head. When suspended in mid-water by a mucus strand, tadpoles from stage 31 to 37/38 tend to swim spirally down when touched on the head and up when touched on the tail. The three-dimensional swimming paths of stage 33/34 tadpoles were plotted using simultaneous video images recorded from the side and from above. Tadpoles spiralled for 70 % of the swimming time, and the probability of spiralling increased to 1 as swim path angles became more vertical. Tadpoles were neutrally buoyant in Percoll/water mixtures at 1.05 g cm(-)(3), in which anaesthetised tadpoles floated belly-down and head-up at 30 degrees. In water, their centre of mass was ventral to the muscles in the yolk mass. A simple mathematical model suggests that the orientation of tadpoles during swimming is governed by the action of two torques, one of which raises the head (i.e. increases the pitch) and the other rotates (rolls) the body. Consequently, tadpoles (i) swim belly-down when the body is approximately horizontal because the body is ballasted by dense yolk, and (ii) swim spirally at more vertical orientations when the ballasting no longer stabilises orientation. Measurements in tethered tadpoles show that dorsal body flexion, which could produce a dorsal pitch torque, is present during swimming and increases with tailbeat frequency. We discuss how much of the tadpole's behaviour can be explained by our mathematical model and suggest that, at this stage of development, oriented swimming responses may depend on simple touch reflexes, the organisation of the muscles and physical features of the body, rather than on vestibular reflexes.

Animals↗
PubMed2001

The orienting response of Lake Michigan mottled sculpin is mediated by canal neuromasts.

Lake Michigan mottled sculpin, Cottus bairdi, exhibit a naturally occurring and unconditioned orienting response that can be triggered by both live prey and chemically inert vibrating spheres, even in blinded animals. CoCl(2)-induced reductions of the orienting response demonstrate that the lateral line is required for this behavior in the absence of non-mechanosensory cues (such as vision), but shed no light on the relative contributions of superficial and canal neuromasts to this behavior. To determine the relative roles of these two subsystems, we measured the frequency with which mottled sculpin oriented towards a small vibrating sphere before and after two treatments: (i) immersion of fish in a solution of gentamicin, an aminoglycoside antibiotic that damages hair cells in canal, but not superficial, neuromasts; and (ii) scraping the skin of the fish, which damages the superficial, but not the canal, neuromasts. To ensure that both superficial and canal neuromasts were adequately stimulated, we tested at different vibration frequencies (10 and 50 Hz) near or at the best frequency for each type of neuromast. At both test frequencies, response rates before treatment were greater than 70 % and were significantly greater than 'spontaneous' response frequencies measured in the absence of sphere vibration. Response rates fell to spontaneous levels after 1 day of gentamicin treatment and did not return to pre-treatment levels for 10-15 days. In contrast, response rates stayed approximately the same after superficial neuromasts had been damaged by skin abrasion. Scanning electron microscopy confirmed hair cell damage (loss of apical cilia) in canal, but not superficial, neuromasts of gentamicin-treated animals after as little as 24 h of treatment. The sensory epithelium of canal neuromasts gradually returned to normal, following a time course similar to behavioral loss and recovery of the orienting response, whereas that of superficial neuromasts appeared normal throughout the entire period. This study shows that the orienting response of the mottled sculpin is mediated by canal neuromasts.

Animals↗
PubMed2002

Magnetic compass orientation in European robins is dependent on both wavelength and intensity of light.

Magnetic compass orientation in birds has been shown to be light dependent. Results from behavioural studies indicate that magnetoreception capabilities are disrupted under light of peak wavelengths longer than 565 nm, and shifts in orientation have been observed at higher light intensities (43-44x10(15) quanta s(-1) m(-2)). To investigate further the function of the avian magnetic compass with respect to wavelength and intensity of light, we carried out orientation cage experiments with juvenile European robins, caught during their first autumn migration, exposed to light of 560.5 nm (green), 567.5 nm (green-yellow) and 617 nm (red) wavelengths at three different intensities (1 mW m(-2), 5 mW m(-2) and 10 mW m(-2)). We used monochromatic light of a narrow wavelength range (half bandwidth of 9-11 nm, compared with half bandwidths ranging between 30 nm and 70 nm used in other studies) and were thereby able to examine the magnetoreception mechanism in the expected transition zone between oriented and disoriented behaviour around 565 nm in more detail. We show (1) that European robins show seasonally appropriate migratory directions under 560.5 nm light, (2) that they are completely disoriented under 567.5 nm light under a broad range of intensities, (3) that they are able to orient under 617 nm light of lower intensities, although into a direction shifted relative to the expected migratory one, and (4) that magnetoreception is intensity dependent, leading to disorientation under higher intensities. Our results support the hypothesis that birds possess a light-dependent magnetoreception system based on magnetically sensitive, antagonistically interacting spectral mechanisms, with at least one high-sensitive short-wavelength mechanism and one low-sensitive long-wavelength mechanism.

Animals↗
PubMed2003

The effects of orientation on detection and identification of facial expressions of emotion.

Signal detection procedures were used to examine the ability of participants to detect and label facial expressions of emotion in an upright or inverted orientation when the faces were rapid videotaped presentations. The detection and identification of facial expressions were remarkably accurate. In the upright orientation, the A' measure of sensitivity was above.9 for detection and identification of all six facial expressions of emotion. Sensitivity to inverted expressions was diminished for all emotions; however, the extent of the decline in sensitivity depended upon the specific facial expression. If the expression was difficult to detect or label in the upright orientation, the sensitivity score was lower in the inverted orientation. An assessment of the errors made in the detection and labelling process allowed a demonstration of the specific facial expressions that were confused in either the upright or inverted orientation. The assessment of sensitivity and analysis of the errors suggests that the nature of perceptual processing of some, but not all, facial expressions is changed by inversion.

Adolescent↗
PubMed1995

Spatial alignment across gaps: contributions of orientation and spatial scale.

To assess the contributions of orientation and spatial scale to the processing of relative-position information for broadband spatial targets, we measure misalignment thresholds for dots separated by as much as 6 deg, in the presence of one-dimensional spatial noise. For all the dot separations, thresholds for misalignment are raised most when the mask is oriented at approximately 20 deg to either side of true alignment. This bimodal orientation tuning function appears to be fundamental to the alignment judgment, including abutting vernier acuity for equally visible lines [Vision Res. 33, 1619 (1993)]. With increasing dot separation the spatial frequency at which peak masking occurs becomes progressively lower, a finding that suggests that the spatial mechanisms important for processing this information become larger. However, the rate of increase in size of these putative mechanisms is insufficient to account for the increase in relative-position thresholds for increasingly separated stimuli (i.e., Weber's law for alignment). In addition, oriented masks placed between two target lines lead to threshold elevation, revealing that the collection of positional information between target features may be important for optimal processing of misalignment thresholds. The findings of this study suggest that, although shifts in spatial scale of the underlying low-level oriented mechanisms may contribute to increased misalignment thresholds with increasing separation, additional factors, such as positional uncertainty associated with eccentricity per se, are limiting.

Contrast Sensitivity↗
PubMed2006

Mapping iso-orientation columns by contrast agent-enhanced functional magnetic resonance imaging: reproducibility, specificity, and evaluation by optical imaging of intrinsic signal.

Activation resembling ocular dominance or orientation columns has been mapped with high-resolution functional magnetic resonance imaging (fMRI). However, the neuronal interpretation of these functional maps is unclear because of the poor sensitivity of fMRI, unknown point spread function (PSF), and lack of comparison with independent techniques. Here we show that cerebral blood volume (CBV)-weighted fMRI with a blood plasma contrast agent (monocrystalline iron oxide nanoparticles), in combination with continuous temporally encoded stimulation, can map columnar neuronal activity in the cat primary visual cortex with high sensitivity, selectivity, and reproducibility. We examined hemodynamic response PSF by comparing these CBV-based signals with oxygen metabolism-based negative blood oxygenation level-dependent signals. A significant positive correlation exists between CBV- and metabolism-based iso-orientation maps, suggesting that the hemodynamic PSF is narrower than intercolumn distances. We also compared CBV-based fMRI with optical intrinsic signal (OIS) imaging, a technique that identifies sites of increased neuronal activity, to investigate neuronal correlation. Iso-orientation maps obtained by fMRI and OIS were well matched, indicating that areas of the highest orientation-selective CBV signals correspond to sites of increased neural activity. Using CBV-based fMRI, we successfully mapped orientation-selective functional architecture in the medial bank of the visual cortex, an area inaccessible to OIS imaging. Thus, we conclude that contrast agent-based fMRI, in combination with continuous temporally encoded stimulation, is a highly sensitive technique capable of mapping neural activity at the resolution of functional columns without depth limitation.

Animals↗
PubMed1976

Orienting responses as a function of age and task complexity.

Aged-related differences in the elicitation and habituation of orienting responses to the onset and offset of stimuli have been suggested by several authors. Electrodermal and cardiac orienting responses to the onset and offset of a visual stimulus were measured in three age groups (4 yr., 7 yr., and undergraduate). Each S made one of three judgments: non-signal (observe stimulus), content (color of stimulus), and duration (length of time stimulus presented). Few age differences were found in elicitation or habituation of orienting responses to stimulus onset or offset. There was a trend for elicitation of orienting responses to stimulus offset to be age-related, but the failure to find any other age-related changes made this difference somewhat questionable. Instructions as to the judgement to be made by S were the primary determinants of orienting responses to stimulus onset and offset across all age groups.

Adolescent↗
PubMed1979

Effects of left-right orientation and position reversals on spatial perspective taking in young children.

50 boys and 50 girls, from Grades K through 4, were presented with 180 degrees perspective-taking tasks that varied arrays in terms of the number of front-back and left-right orientation reversals and left-right position reversals. Results confirmed existing evidence that left-right orientation reversals are more difficult than front-back orientation reversals in arrays of one object. However, with arrays of two objects, left-right orientation reversals appear easier than front-back orientation reversals, apparently because of the relationship between the objects.

Child↗
PubMed1995

Effect of orientation in haptic reproduction of line length.

We investigated the accuracy of haptic reproduction of line length and whether accuracy is influenced by line orientation. 13 blindfolded subjects felt along different line lengths at various orientations in the horizontal plane, then reproduced the line lengths in the same orientation as that felt. Efforts were made to equate learning and reproductive scanning movements. Reproductions of line lengths were a nonveridical power function of their true lengths, but the power function exponents did not differ across spatial orientations. It was concluded that people can encode line lengths across spatial orientations by a common power function if care is taken to equate proprioceptive information across learning and reproduction.

Adult↗
PubMed1983

Orientational anisotropy in the human visual system: an evoked potential and psychophysical study.

Orientational anisotropy in the human visual system was investigated using electrophysiological and psychophysical techniques. Grating patterns of various orientations were presented and contrast detection thresholds were measured using a two alternative forced choice procedure. Using the same observers, visual evoked cortical potentials (VECPs) were elicited by identical gratings set at various contrasts ranging from subthreshold to high levels. Plots of contrast sensitivity versus grating orientation were derived using the amplitude of a negative wave of the VECP for low contrast data and the amplitude of a positive wave for moderate to high contrast data. These plots were compared with plots obtained during the psychophysical experiment. The results indicate that the low contrast VECP functions exhibit an orientational anisotropy that is qualitatively and quantitatively similar to that observed in the psychophysical data. The high contrast VECP functions, however, exhibit an orientational effect that is qualitatively similar but greater in magnitude than that found in the low contrast VECP or psychophysical experiments. These findings suggest that the amplitudes of VECPs elicited by low contrast stimuli are highly correlated with psychophysical detection performance, and that an additional physiological mechanism is reflected in the VECPs elicited by moderate to high contrast stimuli.

Cerebral Cortex↗
PubMed2001

Reference frames and haptic perception of orientation: body and head tilt effects on the oblique effect.

The aim of this study was to examine the effect of body and head tilts on the haptic oblique effect. This effect reflects the more accurate processing of vertical and horizontal orientations, relative to oblique orientations. Body or head tilts lead to a mismatch between egocentric and gravitational axes and indicate whether the haptic oblique effect is defined in an egocentric or a gravitational reference frame. The ability to reproduce principal (vertical and horizontal) and oblique orientations was studied in upright and tilted postures. Moreover, by controlling the deviation of the haptic subjective vertical provoked by postural tilt, the possible role of a subjective gravitational reference frame was tested. Results showed that the haptic reproduction of orientations was strongly affected by both the position of the body (Experiment 1) and the position of the head (Experiment 2). In particular, the classical haptic oblique effect observed in the upright posture disappeared in tilted conditions, mainly because of a decrease in the accuracy of the vertical and horizontal settings. The subjective vertical appeared to be the orientation reproduced the most accurately. These results suggest that the haptic oblique effect is not purely gravitationally or egocentrically defined but, rather, depends on a subjective gravitational reference frame that is tilted in a direction opposite to that of the head in tilted postures (Experiment 3).

Defense Mechanisms↗
PubMed2004

Active navigation and orientation-free spatial representations.

In this study, we examined the orientation dependency of spatial representations following various learning conditions. We assessed the spatial representations of human participants after they had learned a complex spatial layout via map learning, via navigating within a real environment, or via navigating through a virtual simulation of that environment. Performances were compared between conditions involving (1) multiple- versus single-body orientation, (2) active versus passive learning, and (3) high versus low levels of proprioceptive information. Following learning, the participants were required to produce directional judgments to target landmarks. Results showed that the participants developed orientation-specific spatial representations following map learning and passive learning, as indicated by better performance when tested from the initial learning orientation. These results suggest that neither the number of vantage points nor the level of proprioceptive information experienced are determining factors; rather, it is the active aspect of direct navigation that leads to the development of orientation-free representations.

Adolescent↗