bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical study of turbulent magnetohydrodynamic channel flow
Authors: BOECK THOMAS , KRASNOV DMITRY , ZIENICKE EGBERT
Published: January 2007

Mean flow properties of turbulent magnetohydrodynamic channel flow with electrically insulating channel walls are studied using high-resolution direct numerical simulations. The Lorentz force due to the homogeneous wall-normal magnetic field is computed in the quasi-static approximation. For strong magnetic fields, the mean velocity profile shows a clear three-layer structure consisting of a viscous region near each wall and a plateau in the middle connected by logarithmic layers. This structure reflects the significance of viscous, turbulent, and electromagnetic stresses in the streamwise momentum balance dominating the viscous, logarithmic, and plateau regions, respectively. The width of the logarithmic layers changes with the ratio of Reynolds- and Hartmann numbers. Turbulent stresses typically decay more rapidly away from the walls than predicted by mixing-length models.
Diagnosing pure-electron plasmas with internal particle flux probes
Authors: Kremer J. P. , Pedersen T. Sunn , Marksteiner Q. , Lefrancois R. G. , Hahn M.
Published: January 2007

Techniques for measuring local plasma potential, density, and temperature of pure-electron plasmas using emissive and Langmuir probes are described. The plasma potential is measured as the least negative potential at which a hot tungsten filament emits electrons. Temperature is measured, as is commonly done in quasineutral plasmas, through the interpretation of a Langmuir probe current-voltage characteristic. Due to the lack of ion-saturation current, the density must also be measured through the interpretation of this characteristic thereby greatly complicating the measurement. Measurements are further complicated by low densities, low cross field transport rates, and large flows typical of pure-electron plasmas. This article describes the use of these techniques on pure-electron plasmas in the Columbia Non-neutral Torus (CNT) stellarator. Measured values for present baseline experimental parameters in CNT are ϕp=−200±2 V, Te=4±1 eV, and ne on the order of 1012 m−3 in the interior.
Micro-Raman spectroscopy of a single freestanding GaN nanorod grown by molecular beam epitaxy
Authors: Hsiao Ching-Lien , Tu Li-Wei , Chi Tung-Wei , Chen Min , Young Tai-Fa , Chia Chih-Ta , Chang Yu-Ming
Published: January 2007

Micro-Raman spectra were measured on a single freestanding GaN nanorod, which was grown by molecular beam epitaxy. A sharp linewidth of E2(high) mode of 2.1cm−1 measured in the x(y,y)x¯ configuration indicates the high crystalline quality of the nanorod. The angle-dependent Raman spectroscopy shows that the integrated intensities of these first-order Raman modes follow the theoretical sinusoidal functions. The forbidden E1(LO) mode that appeared in the x(z,z)x¯ scattering configurations is assigned to the quasi-LO phonon mode. Power-dependent Raman spectroscopy shows redshift with increasing laser power density due to sample heating which is confirmed by Stokes and anti-Stokes measurements. The broadband centered at 708.5cm−1 is ascribed to the surface mode of the nanostructure.
Emergence of superhydrophobic behavior on vertically aligned nanocone arrays
Authors: D’Urso B. , Simpson J. T. , Kalyanaraman M.
Published: January 2007

The authors investigate the properties of water drops on uniform arrays of vertically aligned nanocones. A simple model predicts a variety of behaviors depending on the nanocone aspect ratio. At low aspect ratios, surface tension pulls the water into the nanocone array, resulting in a wetted drop with high contact angle hysteresis. At high aspect ratios, the effect of the surface tension is reversed, resulting in little liquid-solid contact and drops which easily slide off the surface. Experiments show that the transition occurs as a gradual change in drop contact angles, but an abrupt change in sliding angles.
Anharmonic decay of subterahertz coherent acoustic phonons in GaN
Authors: Liu Tzu-Ming , Sun Shih-Ze , Chang Chieh-Feng , Pan Chang-Chi , Chen Guan-Ting , Chyi Jen-Inn , Gusev Vitalyi , Sun Chi-Kuang
Published: January 2007

This letter examines the anharmonic decay in GaN of subthermal (ℏω⪡kBT) coherent longitudinal acoustic (LA) phonons with a frequency in the subterahertz range. In a collisionless regime (ωτ>1), the anharmonic decay rate of subterahertz coherent LA phonons in GaN shows square dependence on the phonon frequency and cubic dependence on the crystal temperature. As confirmed by the authors experiments, this behavior agrees with a model based on Herring scattering, indicating its importance for the estimation of acoustic attenuation in the subterahertz range.
The Orientation Anisotropy and Orientation Constancy: A Visual Evoked Potential Study
Authors: Frost Barrie J , Kaminer Jehuda J
Published: January 2007

Two experiments were conducted on the orientation anisotropy in which averaged visual evoked potentials (VEPs) were recorded from the occipital scalp. The first experiment confirmed the findings of Maffei and Campbell (1970) that obliquely oriented gratings alternated back and forth produced smaller-amplitude VEPs than when the gratings were oriented horizontally or vertically. Since no asymmetry was found in VEPs produced by a Julesz figure presented under identical conditions, it was concluded that direction of displacement could not have been contributing to the effect. In a second experiment head tilt of the subject was manipulated together with grating orientation and the results indicated that the orientation anisotropy is retinally rather than gravitationally referenced. It was concluded that the site of orientation constancy is located either at higher levels of the primary visual system or in the second visual system.
Depth Perception in the Rat (Rattus Norvegicus): Prepotency of Three-Dimensional over Two-Dimensional Surfaces
Authors: Schiffman Harvey R , Lore Richard
Published: January 2007

The descent behavior to two- and three-dimensional surfaces in a depth situation was measured and compared for 45–50-days-old hooded rats. When depth differences between surfaces were controlled, significantly more descents were made to three-dimensional than to the two-dimensional surface. The results suggest that a three-dimensional surface—more representative of an animal's natural terrain—provides a more informative environment for motion parallax than does a two-dimensional one.
Drawing and Tracing in Three Dimensions—Stereoscribe
Authors: Gregory Richard L
Published: January 2007

A device has been designed and built for drawing in three dimensions. Drawing may be free-hand; or three-dimensional structures or stereograms (such as stereo x-ray pictures) may be traced in three dimensions. The device produces coordinate data, which may be fed to a plotter to produce permanent stereo pairs, and may be fed to a computer for storage and analysis. Stereoscribe can also be used to plot the ‘subjective space’ of observers, to record perceptual knowledge.
Integration and Interruption in the Masking of Form by Form
Authors: Bachmann Talis , Allik Jüri
Published: January 2007

Pairs of geometric forms of equal area were presented, one form after another, with interstimulus intervals t ranging from 0 to 250 ms. The subject's task in experiment 1 was to recognise both stimuli. Identification of the form presented first (backward masking) across all values of t was of a nonmonotonic nature, with greatest impairment at values of t from 30 to 60 ms. Identification of the second form presented (forward masking) increased monotonically with increasing t. Different forms were recognised with different effectiveness across all values of t where masking took place. The results are interpreted on the basis of a multiple-stage processing model which assumes interaction between stimuli at different levels at different values of t. In experiment 2 the subject's task was to detect the presence or absence of a predesignated form. This condition yielded monotonic functions for both backward and forward masking. An explanation in terms of attention-dependent masking is given.
The Dependence of the Visual Numerosity Limit on Orientation, Colour, and Grouping in the Stimulus
Authors: Atkinson Janette , Francis Marcus R , Campbell Fergus W
Published: January 2007

Visual numerosity judgements were made for tachistoscopically presented arrays of dots. The arrangement within the arrays was either linear or such that dots could be easily perceptually subdivided into two groups. Subdivision was either in terms of an orientation difference, a colour difference, or a spacing difference in the centre of the array. For a large difference in orientation between the two ‘arms’ of the array (90°), or a large central space (three times the interdot interval) up to 8 dots were accurately perceived. This numerosity limit was twice that found for equivalent linear arrays, with no grouping. Although in terms of accuracy it seems that in these conditions the two groups within each array can be counted independently, there is no evidence for independent processing in terms of response times. From the results of a subsidiary experiment it seems likely that the slow response times in the subgrouping conditions are due to the necessity of processes other than counting (such as judgements of symmetry). For arrays where subgrouping was in terms of a colour difference, or an orientation difference of between approximately 45° and 90°, or a small central space of twice the interdot interval, there was an improvement in accuracy compared to equivalent linear arrays, but no evidence of independent processing, up to a limit of 4, in each of the subgroups. From these preliminary results, tentative proposals concerning ‘numerosity’ units and their properties are made.
On the Structure of Texture
Authors: Zucker Steven W
Published: January 2007

This paper examines the structure underlying textural patterns. To this end, aspects of a model for texture are developed on the basis of both perceptual processes of the observer and structural properties of the patterns. Local constructs called primitives serve as generators for globally perfect, but unobservable, ideal textures. Study of the graph representation of these ideal textures reveals the basic regularity underlying visual textures. These perfect patterns are then transformed into observable textures by transformations which must not violate psychophysically based restrictions. Interpretively ambiguous textural patterns are used to demonstrate the influence that local primitives have on the formation of global pattern organizations.
Psychophysical ‘measurement’ of Cortical Colour Mechanisms: Reply to Meyer
Authors: Virsu Veijo , Haapasalo Seija
Published: January 2007

In a paper recently published in this journal, Meyer criticised our study on relationships between channels for colour and spatial frequency for not being able to demonstrate a size aftereffect not specific to colour, a McCollough effect not specific to size, or the functions of cortical colour mechanisms. In fact, our study attempted none of these demonstrations in the sense suggested by Meyer because the first would have been impossible for empirical reasons, the second for conceptual reasons, and the third for methodological reasons. Instead, our study yielded evidence that at least three different types of perceptual channel underlie our capacity to perceive the size and colour of objects.
What is the Child's Own View in a Spatial Task?: A Spatial by Temporal Interaction Affecting Errors in Perceptual Reports
Authors: Freeman Norman H
Published: January 2007

Children are sometimes called ‘egocentric’ on the basis of their performance on Piagetian spatial-inference tasks. They often inappropriately substitute their own perceptual report for another observer's. Little is known about what responses are activated in giving perceptual reports. An experiment is presented which tightly controls spatial and temporal stimulus ordering. One condition elicted reports of that aspect of the display which children could not see instead of what they could see. Explanations are considered on the basis of relational coding and temporal responsiveness.
Orientation Masking and the Tilt Illusion with Subjective Contours
Authors: Smith Andrew T , Over Ray
Published: January 2007

Exposure to one edge renders another edge less visible as a function of relative orientation. Experiment 1 showed that orientation-selective masking occurs between phenomenal edges located at sites where the visual display is homogeneous (subjective contours) as well as between edges defined in terms of luminance discontinuity (real edges). In addition, real contours can be masked by subjective contours, and vice versa. In experiment 2 it was found that the tilt illusion (apparent expansion of the angle formed by intersecting lines) can be induced with subjective as well as with real contours. These results suggest that it is inappropriate to attribute the perception of real and subjective contours to fundamentally different processes.
A Simple On-Line Device for Scanning Photographs
Authors: Brown Christopher R
Published: January 2007

A cheap scanner, based on an x-y plotter, is described which has a resolution of 128 elements × 128 elements minimum. Digitisings obtained suggest that, at most, 20 grey levels can be resolved.
Field Dependence and the Role of Visual Frameworks in the Perception of Size
Authors: Sigman Eric , Oltman Philip K
Published: January 2007

The extent to which apparent size is relationally determined has been studied by Rock and Ebenholtz and by Wenderoth, who came to widely differing conclusions as to the magnitude of this phenomenon. In both studies, a large range of individual differences was observed. In the present study, an attempt was made to account for variations in the influence of visual contexts on the perception of size by relating them to the cognitive style dimension of field dependence/independence. In two situations, relatively field-dependent observers made size judgments which were influenced by a frame surrounding the target figure, while relatively field-independent observers tended to be less influenced by the frame, making their judgments approximate the retinal size of the target. The results suggest that assessment of the magnitude of the relational determination of apparent size must consider the cognitive style of the observers as well as situational variations.
On the Capacity of Directionally Selective Mechanisms to Encode Different Dimensions of Moving Stimuli
Authors: Pantle Allan , Lehmkuhle Steve , Caudill Michael
Published: January 2007

Direction-specific losses of contrast sensitivity for sinusoidal test gratings as a function of the contrast of a sinusoidal adapting grating were found to be similar to those measured previously with square-wave gratings. Furthermore, both relationships were similar to that between motion aftereffect duration and the contrast of sinusoidal adapting gratings, and all three sets of data can be fit by a single function. The function shows that the magnitude of direction-specific adaptation effects increases linearly with the logarithm of adapting contrast in the low contrast region, but is essentially independent of contrast once the contrast exceeds threshold by more than a factor of five—six. In addition, it was found that direction-specific losses of contrast sensitivity are restricted to limited ranges of spatial frequency.
The Effect of Refractive Error on Size Constancy and Shape Constancy
Authors: Leibowitz Herschel W , Wilcox Stephen B , Post Robert B
Published: January 2007

The effect of refractive error was determined for both size constancy and shape constancy. Although an error of 1·5 diopters reduces shape constancy, 3·0 diopters of blur had no effect on size constancy. The results are discussed in terms of the multiple mechanisms subserving the perceptual constancies. The importance of cues from the peripheral visual fields for size constancy and the role of foveally mediated texture and stereopsis cues for shape constancy are emphasized.
Two Dimensionality of the Correspondence Process in Apparent Motion
Authors: Ullman Shimon
Published: January 2007

A fundamental process underlying motion perception is the matching of corresponding elements in different views. In this correspondence process spatial separation between elements plays a major role. The relevant separation is shown by the current study to be the two-dimensional, uninterpreted distance, a finding that has an implication to the level at which the correspondence process is carried out. The current findings are compared with earlier results concerning ‘optimality’ of apparent motion to conclude that optimality cannot serve as a measure for the correspondence strength.
A Perceptual Phenomenon and its Neurophysiological Correlate
Authors: Maffei Lamberto , Morrone Concetta , Pirchio Mario , Sandini Giulio
Published: January 2007

A square-wave grating from which the fundamental harmonic has been subtracted (missing fundamental grating) when viewed from a suitable distance appears similar to another grating of periodicity three times higher. The neurons of the visual cortex of the cat, in a given range of spatial frequencies characteristic of each cell, give similar responses to the two gratings.
Angle-Matching Illusions and Perceived Line Orientation
Authors: Wenderoth Peter , White Dennis
Published: January 2007

Spatial illusions which occur in angle-matching tasks were examined in six experiments, using two different kinds of display. In experiments 1 and 2, illusory errors generally were in the direction predicted by Lennie's hypothesis which states that angle arms are attracted perceptually towards the oblique axes of space, although the display used in these experiments differed from Lennie's. However, experiment 3 showed that these errors might equally be explained by the addition of interactive effects between angle arms (tilt illusions). Parametric investigation of Lennie's figures (experiments 4 and 5) showed that the largest angular illusion occurred with the largest angle used (45°) and an intermediate line length (2 deg 7 min). These angular illusions were not explicable by the addition of tilt illusions (experiment 6), suggesting that different judgmental processes may underlie orientation and angle estimations.
Recognition of Upright and Inverted Faces: A Correlational Study
Authors: Phillips Richard J , Rawles Richard E
Published: January 2007

An investigation of ninety-five university admission candidates failed to replicate the finding by Yin of a negative correlation between the ability to recognise upright and inverted faces. A zero correlation was obtained when unknown faces were both learned and recognised upside down, but when well-known faces were presented normally and upside down for identification, a significant positive correlation appeared. Rock has suggested that inverted faces are difficult to recognise because they overtax a mechanism for correcting disoriented stimuli. This explanation satisfactorily accounts for the data with the proviso that, when inverted faces are to be remembered, the best strategy is not to attempt to correct their orientation, but to learn isolated features of the face. This describes the data more parsimoniously than Yin's face-specific mechanism.
The Nonequivalence of Abrupt and Diffuse Illusory Contours
Authors: Richardson Barry L
Published: January 2007

A distinction is drawn between diffuse regions of apparent brightness and illusory, but abrupt, brightness gradients. Differences between the two phenomena are sufficient to disqualify conclusions about one based on observations about the other. It is suggested that diffuse contours may be attributable to peripheral mechanisms while sharp contours may be central or cognitive in origin.
Colour and Brightness Preferences in the Lizard Anolis Carolinensis
Authors: Hodgkinson P E , Still A W
Published: January 2007

Lizards of the species Anolis carolinensis were tested for colour and brightness preferences by using the phototaxic response. A choice was given between two alleys leading to frosted Perspex panels back-projected with light varying in hue and brightness, the variation being controlled by Munsell colour and neutral-density filters. Five colours were combined with several levels of brightness in a series of tests from which estimates could be made of relative preferences. The assumptions that the effects of hue and brightness combine additively to determine preference, and that relative preferences are independent of pairing, were tested by attempting to fit an appropriate linear model to the data. Choice proportions for any comparison were plotted on a normal probability scale against filter density, and it was found, to a reasonably close fit, that the preference for any particular colour increased linearly with filter density on the comparison colour. The rate of increase was approximately the same for all comparisons, and it was possible to use the y intercepts of the regression lines of preference against filter density as a measure of the scale values of the preferences for each colour. Scale values remained invariant over comparisons, with one exception: the preference for red over yellow was greater than predicted from the comparisons of these two colours with others. This may be a contrast effect.
Perception of Surface Slant and Edge Labels from Optical Flow: A Computational Approach
Authors: Clocksin William F
Published: January 2007

I present here two results from investigations of a computational theory of how the human visual system may obtain information about the physical environment directly from optically sensed velocity fields (optical flow). Previous work has shown how optical flow arises when an observer moves through the static environment. The inverse problem is investigated here: how to recover intrinsic characteristics of the environment from optical flow patterns. The first result is a method for computing the local slant of surfaces relative to the moving observer. The second result is a method for detecting and discriminating among the five types of edges that form the boundaries of surfaces. The results have been formalised as mathematical equations, a physiological model, and a computer program. Properties and predictions resulting from these formal models are discussed with regard to experimental findings in psychophysics.
An Analysis of Perceptual and Cognitive Factors in Radiographic Interpretation
Authors: Carmody Dennis P , Nodine Calvin F , Kundel Harold L
Published: January 2007

Detection of small tumors in chest x-ray films was studied under tachistoscopic viewing conditions designed to simulate single fixations varying in dwell time, found in free search. Two questions were asked: How much dwell time is required to detect a nodule (experiment 1)?

How effective are peripheral inputs in the detection of a nodule (experiment 2)? Our findings indicate that a dwell time of 300 ms was sufficient to detect 85% of the nodules when they were viewed directly. Detection accuracy was reduced by one-half when the tumor was located 5° from the axis of gaze. Taken together with data from eye movement experiments, these results provide useful estimates of perceptual and cognitive parameters of visual search.
The Influence of Visual Pattern on Perceived Speed
Authors: Denton Gordon G
Published: January 2007

The two experiments to be described are concerned with the instability of the relationship between objective and subjective speed as experienced by the driver of a motor vehicle. A number of factors that contribute to the instability are outlined, one of the most important of which is considered to be rectilinear speed adaptation. The hypothesis is made that by deliberately distorting the spatial geometry of the visual field it should be possible to counteract the effects of sensory adaptation. The first experiment tests the hypothesis on a motion simulator and confirms the possible value of such a technique. The second experiment describes a field study in which the proven technique is applied to a stretch of motorway at a site where the accident rate was exceptionally high owing to excessive speed. The observed reduction of relevant accidents at this and a number of other motorway sites where the system has been installed is discussed.
Learning to See the Impossible
Authors: Young Andrew W , Deregowski Jan B
Published: January 2007

Four experiments investigating children's ability to detect the impossibility of impossible figures are reported. In the first, children were required to identify the impossible figure from a pair of corresponding possible and impossible figures. Whilst seven-year-old children were able to detect the impossibility of certain impossible figures, their overall level of performance was lower than that of older children. Regardless of age, the impossibility of some types of figure was found to be relatively easy or difficult to detect. Experiment 2 confirmed this pattern of results using a task that required children to copy possible and impossible figures from memory. Experiment 3 showed that, when the impossibility of an impossible figure is not readily detected, this is not due to failure to understand the conventions used in that figure to represent depth and solidity. In experiment 4 predictions from different hypotheses concerning the principal factor responsible for the detection of impossibility were tested. Results support the view that the detection of impossibility requires the construction of a mental representation (internal model) of the interrelationships of the constituent parts of the depicted object. It is suggested that the construction of such internal models may be of general importance in picture perception.
Peripheral Movement, Induced Movement, and Aftereffects from Induced Movement
Authors: Reinhardt-Rutland Anthony H
Published: January 2007

Substantial rotatory induced movement and aftereffects associated with induced movement were observed in a large static patterned disc bounded at its periphery by a rotating patterned annulus. The area of the annulus was less than one tenth that of the disc, so its peripheral location seemed to be important in eliciting these phenomena. This was confirmed in two experiments comparing a peripheral annulus and a relatively central annulus in their ability to elicit induced movement and aftereffects in the same large static field. Aspects of the vection (induced self-movement) phenomenon may have been involved in generation of induced movement. This suggested that the motion-inducing properties of the peripheral annulus might have derived from: (i) its eccentric location in the perceiver's visual field; or (ii) its location with regard to the display itself. Two further experiments showed that (ii) was important for the elicitation of both induced movement and the aftereffects, and (i) was important for the elicitation of induced movement. Neurons responsive to relative movement in conjunction with lateral inhibition may provide a partial explanation for these effects. However, they do not explain why the visual system can assign considerable movement to a large static field under the conditions of these experiments.
Depth Perception in Linear and Inverse Perspective Pictures
Authors: Topper David R , Simpson William A
Published: January 2007

The range of pictorial depth perception was tested with four pictures from the repertoire of European art, rather than the customary line drawings or photographs. These pictures included those rendered in linear perspective and inverse perspective, as well as those with different degrees of depth. Using Pandora’ Box, the subjects were asked to place a lamp at the same apparent depth as objects in the pictures. The subjects did so without regard to the depiction technique. The results suggest that depth is seen in pictures both where the rules of linear perspective hold and where they have been violated.
Neonatal Localisation of a Sound in Visual Space
Authors: Castillo Marcela , Butterworth George
Published: January 2007

A tone was played to neonates in one of four conditions: in an unstructured visual field; spatially concordant with a single visual target; spatially discordant with a single visual target; or spatially concordant with one of two identical visual targets at different locations. Auditory–oculomotor spatial coordination, contingent on sound, was enhanced by the presence of a target in the visual field. Audition and vision are mutually supportive in auditory localisation from birth.
Effects of Tilt Adaptation on the Direction of Voluntary Saccades
Authors: Callan Judith , Ebenholtz Sheldon M
Published: January 2007

Records were taken of the horizontal and vertical amplitudes of eye movements of subjects instructed to move their eyes back and forth from 12 to 6 and from 9 to 3 o'clock without targets. These records were used to compute the angles of the eye-movement paths, and corresponding paths were compared before and after exposure in a hallway to a prism-induced clockwise tilt of 30°. Perceived orientation was also measured, by having the subjects set a luminous line in the dark to the orientations indicated above. Both tasks yielded significant preexposure—postexposure changes in the direction of tilt, such that after exposure the line was set at a tilt and eye movements were made at an angle clockwise with respect to the preexposure orientation. A control group exposed to 0° tilt showed no change on either task. Thus, tilt adaptation is capable of altering the direction of volitional eye movements.
A Note on the Masking of Pictures
Authors: Forster Peter M
Published: January 2007

An experiment is described in which photographs of everyday objects were masked by frequency-filtered random visual noise. The masking functions obtained were of the same type as those obtained by masking letters and words with random noise or a pattern mask. That is, the high-frequency mask produced a type A function while the low-frequency mask produced a type B function. This result is discussed in terms of the general applicability of models of visual information processing constructed on the basis of experiments with letter or word stimuli. It is suggested that spatial-frequency concepts may usefully be employed to describe the relevant features of different types of mask.
Aftereffects of Sustained Convergence: Some Implications of the Eye Muscle Potentiation Hypothesis
Authors: Heuer Herbert , Lüschow Ullrich
Published: January 2007

Aftereffects of sustained convergence are generally explained as the result of eye muscle potentiation (EMP). Three implications of this hypothesis for aftereffects in distance perception were tested: (i) According to the EMP hypothesis the aftereffects are based on oculomotor distance cues only. The addition of secondary cues during the test period should therefore reduce or eliminate the aftereffects. This expectation was confirmed. (ii) According to the EMP hypothesis the critical variable determining the aftereffect should be the distance of the inspection stimulus from the observer but not from the test stimulus. In confirmation of the expectation the aftereffects of certain inspection stimuli were of the same direction for test stimuli which bounded the range of inspection distances on both sides. (iii) When the aftereffects are based on oculomotor distance cues only, the effect of secondary cues during the test period should remain unchanged when they are present during the inspection period as well. Contrary to this expectation the aftereffects did not depend on the cues available during the test. This suggests that they are based on secondary cues, too, provided they are present during the inspection period.
Pattern Recognition in Kittens: Performance on Lie Patterns
Authors: Dodwell Peter C , Wilkinson Frances E , von Grünau Michael W
Published: January 2007

Despite a vast accumulation of knowledge about the anatomy and physiology of the cat's visual system in recent years, and about its early development, there has been very little experimental study of the development of visual behaviour in this species. This is especially true of the kitten's ability to recognize patterns. Two experiments are reported that aim to remedy some part of this deficiency, and that also serves to examine a particular hypothesis about the basis of pattern analysis in the young organism. This is Hoffman's hypothesis that the orbits of elementary Lie transformation groups (a species of continuous transformation group) represent the basis for coding pattern information.
Afterimages, Binocular Rivalry, and the Temporal Properties of Dominance and Suppression
Authors: Wolfe Jeremy M
Published: January 2007

When different contours are presented to the two eyes, an unstable percept, binocular rivalry, is the result. Parts of each set of contours may be seen but the two sets are not seen in the same place at the same time. The contours need not be physically present. Afterimages will produce binocular rivalry. Normal rivalry can be prevented if intermittent stimulation is used. Previous work has shown that orthogonal gratings, flashed for less than 150 ms and separated by more than 150 ms, will appear to fuse into a plaid or checkerboard pattern. In the present experiment this phenomenon is examined with afterimages used to produce rivalry. This abnormal ‘fusion’ is seen when negative afterimages are stroboscopically illuminated at less than 5 Hz. The results obtained with afterimages are predictable from the previous results obtained with stimuli external to the eye.
Triangles and Squares Look Smaller Than They are: Some New Illusions of Extent
Authors: Treisman Michel
Published: January 2007

Some new illusions of extent are described, and they are discussed in relation to the Müller-Lyer illusion and the constancy-scaling hypothesis. It is concluded that they support a minimal version of this hypothesis in which certain configurations of lines cause changes in local scale in certain directions, independently of whether or not these configurations are incorporated in larger patterns in a way which supports and receives a depth interpretation.
Modelling the Stages of the Identity Theory of Object-Concept Development in Infancy
Authors: Luger George F , Wishart Jennifer G , Bower T G R
Published: January 2007

A computational model is presented for the three stages of development of the object concept in infancy identified by Bower and Wishart in their research. The stages are described by sets of PROLOG clauses that interpret object structures representing the perceptual phenomena interpreted by the infants themselves. The infant's changes between developmental stages can be described by differences between the rules modelling each stage. Three experiments are presented and the behaviour of the PROLOG model is described for each stage of development. Motion, rest, and boundedness of objects constitute the theoretical underpinning of the running PROLOG model and are hypothesized as the invariant aspects of perception that explain the behaviour of the infant at each stage of development. A possible explanation for transitions between stages is offered and justified in part by the output of the model, which in turn is used to predict the behavioural outcome of an experiment.
Perturbing Line Pictures for Identification of Visual Features and Their Syntax
Authors: Eijkman Eg G J
Published: January 2007

Experiments are reported in which line pictures were perturbed by omission or displacement of a combination of single pixels, fragments of lines, contours, and whole figures. Different effects of perturbation were expected by selectively violating visual syntactic rules or by impeding the contribution of certain feature detectors.

The deterioration of the perturbed picture was measured according to standard psychophysical methods by rating on a 5-point scale. Multivariate methods were used to single out the relative effects of perturbation by, respectively, a set of single pixels, line fragments, contours and whole figures.

Lines, as opposed to loose pixels, are clearly powerful descriptors of the pictures; contours or whole figures do not add significantly to what lines already describe. Different effects were observed if perturbations were dislocations rather than removals. Then contours and whole figures showed a typical disrupting effect compared to line fragments. These results have consequences for the development of a syntax of visual form perception. The perturbation method seems appropriate for identifying features or syntactic rules, although the results are dependent on a number of environmental and contextual factors.
The Perception of Control in Loud Noise
Authors: Fisher Shirley , Ledwith Margaret
Published: January 2007

Perception of control is known to affect performance under stress. Two experiments are reported the object of which was to find out how loud noise during a contingency assessment task influences perceived control. Subjects were required to choose one of two responses, note one of two results, and then provide an overall percentage estimation of the degree of contingency present after 40 trials. Subjects made these judgements for one of three levels of objective contingency (25%, 50%, 75%), either in quiet (55 dBA) or in loud noise (95 dBA) conditions. The first experiment involved a series of randomly chosen, preprogrammed outcomes for noncontingent trials. An unexpected effect of noise was that subjects improved their successes in predicting events, and could only have done so by finding sequential structure in the preprogrammed alternations. They also overestimated control relative to contingency data actually received, at the 25% objective contingency level, but the result could have been dependent on different base levels of data actually received. A second experiment, with a random generation of outcomes for noncontingent trials, resulted in no differences in success levels, but confirmed that noise is associated with the overestimation of contingency at the 25% objective contingency level and demonstrated the same effect for the 50% level. The results are discussed in the context of the ‘illusion of control’.
Tactual Perception of Embossed Morse Code and Braille: The Alliance of Vision and Touch
Authors: Heller Morton A
Published: January 2007

In three experiments observers made visual matches to tangible embossed patterns. Stained glass was used to blur vision and thus allow the effect of visual guidance of tactual exploration on the accuracy of symbol recognition to be evaluated. Stained glass rendered the embossed code invisible, but allowed sight of the hand. In the first experiment subjects identified patterns made up of dots and dashes drawn from Morse code; in the second and third experiments they studied braille. The results show that subjects are more accurate in ‘reading’ tangible codes when provided with visual guidance. Performance was higher for braille than for Morse code. Vision aided touch through the provision of a frame of reference and through sight of scanning movements. Naive sighted observers were able to identify invisible braille dots by watching other individuals touch the symbols, suggesting the importance of vision of kinesthetic patterns.
Some Tests of the Marr-Ullman Model of Movement Detection
Authors: Moulden Bernard , Begg Helena
Published: January 2007

Several psychophysical experiments are described which test and uphold predictions derived from the Marr–Ullman model of movement detection. First, we demonstrate the existence of adaptation which is specific not merely to the direction of movement of an edge, but also to its contrast polarity. Second, it is shown that adaptation to a spatially homogeneous field whose luminance is modulated according to a temporal sawtooth waveform produces predictable changes in sensitivity to the movement of an edge; these changes, too, are specific to particular conjunctions of direction and edge polarity. Third, similar changes in sensitivity are demonstrated to occur when the luminance of an edge is physically perturbed at the moment of its displacement. Finally, it is shown that, as predicted, the sudden onset of an edge can itself give rise to a momentary impression of movement, the apparent direction of which depends upon the change in luminance that accompanies the onset of the edge.
A Psychophysical Measure of Visual and Kinaesthetic Spatial Discriminative Abilities of Adults and Children
Authors: Manyam Victor J
Published: January 2007

Quantitative estimates of the spatial discriminative capacities of the visual and kinaesthetic systems in adults and children were obtained. Intersensory integration was investigated by including spatial discriminations based on congruent visual plus kinaesthetic reafference. The psychophysical method of adjustment was used with simultaneous comparisons of a fixed and a variable stimulus. The subject's task was to estimate when the variable stimulus (ellipse) was identical to the standard one (circle), under one of three modality conditions: vision, kinaesthesis, and vision plus kinaesthesis.

After a pilot study with adults, children (aged 8, 10, and 12 years) and adults were both tested. Subjects from each age group were randomly allocated to each of the three experimental conditions. Results show that the visual and kinaesthetic estimates of the 8- and 10-year-old subjects did not differ significantly, but the visual responses of the adults and 12 year olds were significantly more accurate than corresponding kinaesthetic estimates. Bisensory estimates were significantly more accurate than visual responses only for the 8- and 10-year-old age groups. Intramodal comparisons showed the kinaesthetic estimates of the 8, 10, and 12 year olds to be significantly more accurate than the corresponding adult performance. Adult visual estimates were significantly more accurate than those made by 8 year olds, but were not significantly different from the visual responses of 10 and 12 year olds. Estimates based on bisensory reafference did not differ from each other across the four age groups. It is concluded that modality adeptness and dominance are task dependent and empirically determined rather than being innate properties of sensory systems. The data indicate that intersensory differentiation rather than integration occurs with maturity.
Briefly Presented Stimuli Can Disrupt Constant Suppression and Binocular Rivalry Suppression
Authors: Wolfe Jeremy M
Published: January 2007

An earlier study has shown that the intermittent suppression of one monocular stimulus by another in binocular rivalry does not occur when normally rivalrous stimuli are briefly presented. Constant suppression of stimuli presented to one eye is a common consequence of esotropia during development. A study is reported which demonstrates that constant suppression does not occur when stimuli are briefly presented. The dependence of suppression on stimulus duration is similar in both forms of suppression.
Binocular Rivalry with Rotary and Radial Motions
Authors: Wade Nicholas J , De Weert Charles M M
Published: January 2007

Binocular rivalry between a radially sectored and a concentrically circular pattern was investigated in three experiments. Motion of the circular pattern was either cyclical expansion and contraction with corresponding changes in spatial frequency (experiment 1), or outward motion with a constant linear velocity (experiment 2). When both patterns were static the circular pattern was visible for longer than the radial one. Motion of either pattern alone resulted in an increase in the predominance duration and the mean period for which the pattern was visible. This is at variance with Levelt's model of rivalry. In the third experiment, rivalry was between a static circular pattern and a radial pattern that could be rotated at different angular velocities. Again it was found that an increase in stimulus strength, as measured by predominance, led to an increase in the mean periods of visibility of the rotating pattern.
Facilitatory Interactions between Flashed Lines
Authors: Smith Robert A , Cass Peter
Published: January 2007

The detectability of pairs of flashed lines was investigated as a joint function of their separation in both space and time. In contrast to previous studies of contrast interactions as a function of either spatial or temporal separation alone, the predominant interaction is not lateral inhibition, but a delayed facilitation. A quantitative model based on probability summation between lateral-inhibitory detectors does not appear able to account for these results. Two related explanations are suggested: either a motion detection system or the nonlinear ‘transient’ subsystem is being tapped.
Spatiotemporal Isosensitivity Fields in the Human Visual System
Authors: Jenkins Bill
Published: January 2007

The human visual system is capable of detecting correlations, manifested perceptually as global pattern, in mathematically constrained dynamic textures. This ability has given rise to speculation that correlative mechanisms in the human visual system exist and that they have a neural basis similar to the orientationally selective structures discovered in area 17 of the mammalian visual cortex. The limits to the detection of correlation were mapped, spatially and temporally, by means of a psychophysical technique. Evidence is presented that, at least in the spatial domain, the correlation mechanism may be served by a population of such neural units.
The Basis of Stroop Interference Involving the Multimodal Correlates of Auditory Pitch
Authors: Walker Peter , Smith Sylvia
Published: January 2007

A pure auditory tone has a range of multimodal qualities that are determined by its pitch. A reaction-time task was used to demonstrate that subjects respond immediately and automatically to these qualities. Subjects were required to press one of two keys depending on which word, from a limited set, appeared on a microcomputer screen. The words were antonyms that represented multimodal stimulus qualities, and they were assigned to alternative responses so that the two words that shared the same response were correlated in the same way with pitch. As an incidental stimulus, either a 50 Hz tone or a 5500 Hz tone accompanied the presentation of each word. Subjects were found to respond more slowly when the multimodal qualities of the tone were incongruent with the qualities represented by the test word. When the stimulus-response mapping rules were changed, however, the Stroop effect did not occur; suggesting that a polarised semantic code of the incidental tone, that embraces its multimodal features, accesses the same semantic register as the equivalent code for the test word itself.
Apparent Velocity of Motion Aftereffects in Central and Peripheral Vision
Authors: Wright Michael J
Published: January 2007

Adapting to a drifting grating (temporal frequency 4 Hz, contrast 0.4) in the periphery gave rise to a motion aftereffect (MAE) when the grating was stopped. A standard unadapted foveal grating was matched to the apparent velocity of the MAE, and the matching velocity was approximately constant regardless of the visual field position and spatial frequency of the adapting grating. On the other hand, when the MAE was measured by nulling with real motion of the test grating, nulling velocity was found to increase with eccentricity. The nulling velocity was constant when scaled to compensate for changes in the spatial ‘grain’ of the visual field. Thus apparent velocity of MAE is constant across the visual field, but requires a greater velocity of real motion to cancel it in the periphery. This confirms that the mechanism underlying MAE is spatially-scaled with eccentricity, but temporally homogeneous. A further indication of temporal homogeneity is that when MAE is tracked, by matching or by nulling, the time course of temporal decay of the aftereffect is similar for central and for peripheral stimuli.