bluuebunny/crossref_metadata_2025 huggingface dataset:
Absorption and Transit of Lutein and β-Carotene Supplements in the Mongolian Gerbil (Meriones unguiculatus)
Authors: Escaron  , Tanumihardjo
Published: January 2007

Based on a previous carotenoid bioavailability study in Mongolian gerbils (Meriones unguiculatus), we hypothesized that gerbils preferentially accumulate β-carotene over lutein in the liver and lipoproteins. To monitor transit times of these carotenoids through the gastrointestinal tract and concentrations in various tissues and tissue contents, 0.1 μmol each of β-carotene and lutein were given separately as well as in combination to gerbils (n = 30). Contents of stomach, intestines, and ceca were collected at 1.5, 3, and 6 hours following the dose and analyzed for β-carotene and lutein. Mucosal scrapings, liver, and serum were also collected. When β-carotene and lutein were given in combination, 41 ± 11% (mean ± SD) β-carotene versus 20 ± 4.0% lutein were recovered in total from all tissues and tissue contents. At 3 hours, 45 ± 19% and 55 ± 2.8% of the β-carotene and lutein supplements, respectively, were recovered in the cecum when given separately. When given in combination, 59 ± 32% and 55 ± 25% of the β-carotene and lutein, respectively, were recovered in the cecum. Beta-carotene was up to 45-fold higher than lutein liver concentrations 6 hours after dosing. Gerbils are a useful model for β-carotene bioavailability studies as they absorb and store β-carotene. More studies are needed to determine whether significant extra-hepatic lutein storage occurs in gerbils.
Effects of Antioxidant Supplementation and Exercise Training on Erythrocyte Antioxidant Enzymes
Authors: Marsh  , Laursen  , Coombes
Published: January 2007

Erythrocytes transport oxygen to tissues and exercise-induced oxidative stress increases erythrocyte damage and turnover. Increased use of antioxidant supplements may alter protective erythrocyte antioxidant mechanisms during training. Aim of study: To examine the effects of antioxidant supplementation (α-lipoic acid and α-tocopherol) and/or endurance training on the antioxidant defenses of erythrocytes. Methods: Young male Wistar rats were assigned to (1) sedentary; (2) sedentary and antioxidant-supplemented; (3) endurance-trained; or (4) endurance-trained and antioxidant-supplemented groups for 14 weeks. Erythrocyte superoxide dismutase (SOD), glutathione peroxidase (GPX), and catalase (CAT) activities, and plasma malondialdehyde (MDA) were then measured. Results: Antioxidant supplementation had no significant effect (p > 0.05) on activities of antioxidant enzymes in sedentary animals. Similarly, endurance training alone also had no effect (p > 0.05). GPX (125.9 ± 2.8 vs. 121.5 ± 3.0 U.gHb–1, p < 0.05) and CAT (6.1 ± 0.2 vs. 5.6 ± 0.2 U.mgHb–1, p < 0.05) activities were increased in supplemented trained animals compared to non-supplemented sedentary animals whereas SOD (61.8 ± 4.3 vs. 52.0 ± 5.2 U.mgHb–1, p < 0.05) activity was decreased. Plasma MDA was not different among groups (p > 0.05). Conclusions: In a rat model, the combination of exercise training and antioxidant supplementation increased antioxidant enzyme activities (GPX, CAT) compared with each individual intervention.
Control of magma flow in dykes on cyclic lava dome extrusion
Authors: Costa A. , Melnik O. , Sparks R. S. J. , Voight B.
Published: January 2007

Lava dome eruptions are commonly characterized by large fluctuations in discharge rate with cyclic behaviour on time‐scales ranging from hours to decades. Examples include Bezymianny volcano (Russia), Merapi (Java), Santiaguito (Guatemala), Mt St Helens (USA), Mt Unzen (Japan), and Soufrière Hills volcano (Montserrat). Previous models have assumed simple cylindrical conduits for magma transport, but extrusions are mainly fed by dykes, with cylindrical geometries developing only at shallow levels. The widths of dykes embedded in an elastic medium are influenced by local magma pressure, affecting flow rates and system dynamics strongly. We develop a model for magma flow in dykes, which predicts intense pulsations of magma extrusion for the case of a constant source pressure. The period time scale is determined by the elastic deformation of the dyke walls and the length‐to‐width ratio of the dyke. The dyke acts like a volumetric capacitor, storing magma as pressure increases and then releasing magma in a pulse of extrusion. For the Soufrière Hills volcano, cyclic extrusions with time‐scales of a few weeks are predicted for dykes 300–500 m long and 3–6 m wide, matching observations. The model explains the sharp onset of tilt pulsations and seismic swarms.
Large CO2 reductions via offshore wind power matched to inherent storage in energy end‐uses
Authors: Kempton Willett , Archer Cristina L. , Dhanju Amardeep , Garvine Richard W. , Jacobson Mark Z.
Published: January 2007

We develop methods for assessing offshore wind resources, using a model of the vertical structure of the planetary boundary layer (PBL) over water and a wind‐electric technology analysis linking turbine and tower limitations to bathymetry and continental shelf geology. These methods are tested by matching the winds of the Middle‐Atlantic Bight (MAB) to energy demand in the adjacent states (Massachusetts through North Carolina, U.S.A.). We find that the MAB wind resource can produce 330 GW average electrical power, a resource exceeding the region's current summed demand for 73 GW of electricity, 29 GW of light vehicle fuels (now gasoline), and 83 GW of building fuels (now distillate fuel oil and natural gas). Supplying these end‐uses with MAB wind power would reduce by 68% the region's CO2 emissions, and reduce by 57% its greenhouse gas forcing. These percentages are in the range of the global reductions needed to stabilize climate.
Mass and electron densities in the inner magnetosphere during a prolonged disturbed interval
Authors: Grew R. S. , Menk F. W. , Clilverd M. A. , Sandel B. R.
Published: January 2007

The equatorial plasma density and composition at L = 2.5 were studied during an extended disturbed interval using field line resonance measurements (yielding plasma mass density), naturally and artificially stimulated VLF whistlers (electron number density) and IMAGE EUV observations (plasmapause position and line‐of‐sight He+ intensity). During the storm the plasmapause moved to L < 2.5 and at least one density notch and drainage plume formed. These features were evident in all the data sets for some days. One notch extended from 2.4–4.5 RE and spanned <4 hours in MLT. Plume mass and electron densities were enhanced by a factor of about 3. In the plasmasphere and plasmatrough the H+: He+: O+ composition by number was ∼82:15:3. However, just outside the plasmapause the O+ concentration exceeded 50%, suggesting the presence of an oxygen torus.
Quasiseparation of variables in the Schrödinger equation with a magnetic field
Authors: Charest F. , Hudon C. , Winternitz P.
Published: January 2007

We consider a two-dimensional integrable Hamiltonian system with a vector and scalar potential in quantum mechanics. Contrary to the case of a pure scalar potential, the existence of a second order integral of motion does not guarantee the separation of variables in the Schrödinger equation. We introduce the concept of “quasiseparation of variables” and show that in many cases it allows us to reduce the calculation of the energy spectrum and wave functions to linear algebra.
New developments for an electron impact (e,2e)∕(e,3e) spectrometer with multiangle collection and multicoincidence detection
Authors: Catoire F. , Staicu-Casagrande E. M. , Lahmam-Bennani A. , Duguet A. , Naja A. , Ren X. G. , Lohmann B. , Avaldi L.
Published: January 2007

We describe new developments aimed to extend the capabilities and the sensitivity of the (e,2e)∕(e,3e) multicoincidence spectrometer at Orsay University [Duguet et al., Rev. Sci. Instrum. 69, 3524 (1998)]. The spectrometer has been improved by the addition of a third multiangle detection channel for the fast “scattered” electron. The present system is unique in that it is the only system which combines three toroidal analyzers all equipped with position sensitive detectors, thus allowing the triple coincidence detection of the three electrons present in the final state of an electron impact double ionization process. The setup allows measurement of the angular and energy distributions of the ejected electrons over almost the totality of the collision plane as well as that of the scattered electron over a large range of scattering angles in the forward direction. The resulting gain in sensitivity (∼25) has rendered feasible a whole class of experiments which could not be otherwise envisaged. The setup is described with a special emphasis on the new toroidal analyzer, data acquisition hardware, and data analysis procedures. The performances are illustrated by selected results of (e,2e) and (e,3e) experiments on the rare gases.
Manipulating exciton fine structure in quantum dots with a lateral electric field
Authors: Gerardot B. D. , Seidl S. , Dalgarno P. A. , Warburton R. J. , Granados D. , Garcia J. M. , Kowalik K. , Krebs O. , Karrai K. , Badolato A. , Petroff P. M.
Published: January 2007

The fine structure of the neutral exciton in a single self-assembled InGaAs quantum dot is investigated under the effect of a lateral electric field. Stark shifts up to 1.5meV, an increase in linewidth, and a decrease in photoluminescence intensity were observed due to the electric field. The authors show that the lateral electric field strongly affects the exciton fine-structure splitting due to active manipulation of the single particle wave functions. Remarkably, the splitting can be tuned over large values and through zero.
Magnetic resonances in metallic double split rings: Lower frequency limit and bianisotropy
Authors: Zhou Lei , Chui S. T.
Published: January 2007

The authors employ a rigorous theory to study the electromagnetic resonances in double split rings of circular cross sections. The inter-ring interactions split each single-ring mode to two modes with different symmetries, and the bianisotropy of each mode is suppressed as two rings approach. They obtain analytical expressions to estimate the frequency of the fundamental (magnetic) mode, which facilitate the design of structures with the lowest possible resonance frequencies. Numerical calculations based on the present theory are supported by finite-difference-time-domain simulations on realistic structures and experimental data published previously.
Nonlinear electrical conducting behavior of carbon nanotube networks in silicone elastomer
Authors: Liu C. H. , Fan S. S.
Published: January 2007

In this work the authors investigated the electrical conducting properties of multiwalled carbon nanotube (MWNT) networks in the flexible polydimethylsiloxane rubber as a function of applied voltages. The results indicated that the I-V curves showed nonlinear relationships, which can be fitted to quadratic functions. The electrical resistance of the samples varies with the voltages more sharply in lower range. The nonlinear mechanism was related to the materials system including both the MWNTs and the matrix material. Furthermore, the I-V characteristic of the MWNT network/ZnO nanocomposite layer junction has shown a well rectified behavior at low voltages.
Detection of coherent acoustic oscillations in a quantum electromechanical resonator
Authors: Beil Florian W. , Blick Robert H. , Wixforth Achim , Wegscheider Werner , Schuh Dieter , Bichler Max
Published: January 2007

Coherent control of occupation numbers in quantum mechanical multilevel systems is widely studied driven by its application in lasers and its prospects for quantum computational elements. Here the authors present a nanoelectromechanical resonator equivalent to the coherent control of a quantum mechanical two level system. The distinct eigenmodes of a nanomechanical beam resonator represent the two levels whose amplitude mode occupation numbers are controlled by a frequency matched acoustic excitation, mediated by a pulsed surface acoustic wave. They show that similar to quantum mechanical systems it is possible to transfer occupation numbers from one mode to another by matched acoustic pulses.
Second harmonic generation and ferroelectric phase transitions in thick and ultrathin Pb0.35Sr0.65TiO3 films on (001) MgO substrates
Authors: Liu S. W. , Chakhalian J. , Xiao Min , Chen C. L.
Published: January 2007

Second harmonic generation of a 16-nm-thick ultrathin Pb0.35Sr0.65TiO3 film and a 243-nm-thick Pb0.35Sr0.65TiO3 film grown on (001) MgO substrates by pulsed laser deposition is investigated. It is concluded that in the ultrathin film the ferroelectric phase is still present and the diffuse phase transition is absent. In contrast, the thick film exhibits a pronounced diffuse phase transition. Theoretical analysis based on the polarization diagrams shows that the compensated c-domain fraction is dominant in both films whereas the nonlinear susceptibility of the ultrathin film has a different tensor property from the thick film.
Search Time as a Function of Context Letter Frequency
Authors: Latimer C R
Published: January 2007

Neisser (1967) posits the operation of purely feature analytic processes in the scanning of context letters in search lists. This contention was tested by varying the relative frequency of occurrence in English of the context letters in alphanumeric search lists, while holding their feature content constant. It was hypothesized that faster search time on lists of high-frequency context letters would indicate letter-level processing. Equality of search time would indicate the purely feature-level processing required by Neisser's theory.

Context letters were segregated into high- and low-frequency sets and their features defined and held constant according to two feature analyses. This yielded a 2 × 2 design with 22 subjects per condition. Attention was given to the control of feature frequency, size of the context-letter set, and approximation of English at the level of bigram, trigram, and word. Results supported a letter level or template model of processing but were shown also to be explainable in terms of some feature-testing models of pattern recognition. Apparatus which allowed for the removal of reaction time in search lists is described.
Individual Differences in Noise and Associated Perceptual Indices of Performance
Authors: Nettelbeck T
Published: January 2007

Vickers et al. (1972) proposed that three main determinants of perceptual organization are the inspection time λ governing the rate of accumulation of sensory data, the noise in the visual system sD, and the degree of caution adopted for responding. The mean overall latency of judgments in a simple psychophysical discrimination task L was suggested to provide a satisfactory indirect index of caution. Differences between individuals in these three behavioural descriptors, together with an index of the use made of immediate memory δ, were compared with personality measured by the Manifest Anxiety Scale and the Eysenck Personality Inventory. Results from two experiments confirmed the independence of λ, sD, L, and δ as indicators of individual differences. The relationships between these measures and scores on the personality scales were clear, but not always straightforward. They are examined in terms of interactions between the processes underlying the measures.
The Effects of Temporal Modulation on the Orientation Channels of the Human Visual System
Authors: Sharpe C R , Tolhurst D J
Published: January 2007

The orientation specificity of spatial adaptation was quantified by using an equivalent-contrast transformation. The half-width at half-amplitude of the adaptation effect was 6·5° when the sinusoidal gratings were stationary, but was increased to 11° when the gratings drifted laterally. Another type of temporal modulation, flashing the gratings on and off repetitively, also increased the half-width, but only at low spatial frequencies where these stimuli actually appeared to be flickering back and forth at threshold. At higher spatial frequencies the flashing stimuli appeared to be stationary at threshold and the half-width was as small as that for truly stationary gratings. It is suggested that there are two types of channel in the visual system: they differ in their orientation specificities, in their temporal properties, and in their roles in the analysis of a spatiotemporal stimulus.
Luminance Thresholds for Motion Contingent on Colour
Authors: Mayhew J E W
Published: January 2007

Sekuler and Ganz (1963) called the difference in luminance threshold for movement in the same direction versus movement in the opposite direction to the adapting motion ‘direction-specific adaptation’ (DSA). The experiments reported here investigate colour-contingent DSA.

After exposure of subjects to clockwise motion of a red pattern alternating with counterclockwise motion of a green pattern, their threshold for clockwise motion was found to be greater than for counterclockwise motion when the illumination was red, but lower when the illumination was green.
Orientation Specificity and Spatial Selectivity in Human Vision
Authors: Movshon J A , Blakemore C
Published: January 2007

An adaptation method is used to determine the orientation specificity of channels sensitive to different spatial frequencies in the human visual system. Comparison between different frequencies is made possible by a data transformation in which orientational effects are expressed in terms of equivalent contrast (the contrast of a vertical grating producing the same adaptational effect as a high-contrast grating of a given orientation). It is shown that, despite great variances in the range of orientations affected by adaptation at different spatial frequencies (±10° to ±50°), the half-width at half-amplitude of the orientation channels does not vary systematically as a function of spatial frequency over the range tested (2·5 to 20 cycles deg−1). Two subjects were used and they showed significantly different orientation tuning across the range of spatial frequencies. The results are discussed with reference to previous determinations of orientation specificity, and to related psychophysical and neurophysiological phenomena.
Relation between the Magnitude of Flicker Sensation and Evoked Potential Amplitude in Man
Authors: Regan D , Beverley K I
Published: January 2007

Estimates of the subjective magnitudes of flicker sensations correlate poorly with the amplitudes of electrical brain responses (evoked potentials). A power function of exponent between 0·9 and 1·5 describes the relation between stimulus and subjective sensory magnitude. On the other hand, the relation between stimulus and objective measure varies with electrode position, is different for different frequency components of the evoked potential, and may not be a power function at all.

As a rough generalisation, correlations between evoked potentials and perception are poorer when spatially-unpatterned stimuli are used than when the stimulus is spatially patterned.
Untersuchungen zur Lokalisierung von Wahrnehmungsprozessen: Figurale Nachwirkungen bei binokularen Wettstreit-Bedingungen
Authors: Crabus H , Stadler M
Published: January 2007

Figural aftereffects were measured under binocular-rivalry conditions, the suppressed part of the binocular-rivalry situation being used as an inspection figure. The results show that figural aftereffects are reduced in a partly suppressed configuration and disappear completely when the inspection figure is fully suppressed. This indicates that the figural aftereffect process is localized at a higher level in the visual system than area 17.
Real and Apparent Visual Movement: Evidence for a Unitary Mechanism
Authors: Clatworthy J L , Frisby J P
Published: January 2007

Two experiments are described which investigated the effect of adaptation to real movement on the perception of subsequent apparent movement. A marked adaptation carry-over effect was observed for which no explanation could be found other than that the same movement-detecting mechanism mediates both real and apparent movement phenomena.
A New Experimental Paradigm for the Investigation of the Secondary System of Human Visual Motion Perception
Authors: Lamontagne C
Published: January 2007

An experimental paradigm is derived from a computational model of visual motion perception. The new family of phenomena that support this paradigm is presented in the context of the model. The basic phenomenon can be considered as being the apparent motion and the sustained eyetracking of a physically still object (relative to the subject) in the absence of any other object moving relative to the subject.
Pursuing Stationary Dots: Smooth Eye Movements and Apparent Movement
Authors: Heywood S
Published: January 2007

An apparent movement of a row of stationary simultaneously-presented dots lit with stroboscopic light is perceived if a smooth eye movement is made along the row. Such an apparent movement can itself act as a stimulus for sustained smooth eye movements in the absence of any objective external information about movement. Not only dot rows but also continuous lines may be tracked in this way. The effects of interdot distance and flash rate upon parameters of smooth eye movements and upon saccadic behaviour are examined.
A Velocity Analogue of Brightness Contrast
Authors: Loomis J M , Nakayama K
Published: January 2007

A velocity illusion is reported which is analogous to results obtained in the case of brightness contrast. When two targets move with the same velocity against a background of smaller moving dots which have a velocity gradient, the target which is moving faster than its immediate surround appears to move faster than the target which is moving slower than its immediate surround. Apparent velocity of a target therefore depends strongly on its velocity in relation to its immediate surround; we interpret this in terms of motion-sensitive cells which have center–surround antagonisms analogous to the physiological interpretation of brightness contrast.
Curvature Detectors in Human Vision?
Authors: Blakemore C , Over R
Published: January 2007

Observers were required to judge apparent straightness following exposure to curved lines. A curvature aftereffect was found when subjects had maintained steady fixation or made continuous eye movements at right angles to the chord of the arc during inspection, but no aftereffect was obtained when eye movements had been made in the direction of the chord. It is proposed that curved contours are processed in the visual system by reference to the orientation of local straight line approximations within an arc, rather than through global analysis of the extent and direction of curvature. The loss in aftereffect with eye movements in the direction of the chord is attributed to nonselective adaptation of orientation detectors.
Stroboscopic Movement Based on Perceptual Intelligence
Authors: Sigman E , Rock I
Published: January 2007

Stroboscopic movement perception can be viewed as the solution on the part of the perceptual system of the problem posed by the alternating appearance and disappearance of the stimulus objects. Under typical conditions there is no information provided which could account for such inexplicable stimulus change, so that movement is the most ‘plausible’ solution. If, however, such information is provided, other solutions may be preferred, and motion will not be perceived. In several experiments it is demonstrated that, when an object alternately covers and uncovers two dots, movement is not perceived, provided (a) the object is in the location in front of where a dot had just appeared rather than to the side of this location, and (b) the object appears to be solid or opaque rather than outline. Under such conditions the dots appear to be permanently present entities undergoing covering and uncovering. This effect does not require that a physical object with edges progressively occlude and disocclude the dots, since a moving phenomenal square based on subjective contours only and a stroboscopically moving square also eliminate or minimize perceived movement of the dots. Control experiments employing the same spatial and temporal intervals show that, without the information supporting the covering—uncovering solution, movement typically is perceived. These findings are interpreted as supporting the theory that perception results from a process analogous to intelligent problem solving.
A New Illusion of Movement Dependent on Eye Movement during Head Rotations
Authors: Mack Arien , Fendrich R , Fisher Celia B
Published: January 2007

A previously undocumented illusion of movement is reported which occurs when an observer, in an otherwise dark room, attempts to maintain fixation on a stationary light point located straight ahead of him while rotating his head from left to right. The light appears essentially stationary during head rotations up to about 25°, but with more extreme rotations the point suddenly appears to sail off in the direction opposite to the head turn. This illusion was investigated and data are reported which indicate that it results from unmonitored movements of the eye (i.e. eye movements which are not efferently controlled and about which there is no proprioceptive information), in the direction of the head turn, which occur when the eye is no longer able to maintain fixation by counterrotating.
Optical Velocity Patterns, Velocity-Sensitive Neurons, and Space Perception: A Hypothesis
Authors: Nakayama K , Loomis J M
Published: January 2007

A hypothesis is put forward of how global patterns of optical flow, as discussed by Gibson, Johansson, and others, could be processed by relatively simple physiological mechanisms. It is suggested that there may exist motion-sensitive cells in the visual system which operate on the optical flow over the retina, and, in so doing, structure the visual field in terms of distinct surfaces that move and/or lie at varying distances from the observer. First, concepts of static and dynamic perspective relative to a sphere centered about the eye are developed, partly on the basis of the work of Gordon. It is pointed out that the velocity flow pattern has a very simple form making it amenable to analysis by relatively low-level mechanisms. Next a higher-order variable of optical flow, the ‘convexity’, is defined; under the assumption of a rigid environment, convexity is shown to be related to relative depth. It is then postulated that velocity-sensitive cells having center—surround organization could be linked in such a way as to define a higher-order cell, the convexity cell, having functional properties that make it sensitive to the convexity function. The response profile of a layer of such cells would provide an efficient structuring of the visual field in terms of distinct optical surfaces. Relevant evidence is briefly discussed. Lastly, the optical flow patterns corresponding to rotations of the observer are considered. It is shown that the convexity cell is insensitive to rotations and in consequence responds in an invariant fashion to aspects of the optical flow which are related to the surrounding environment.
Inductive Inference, Coding, Perception, and Language
Authors: Barlow H B
Published: January 2007

The sensory system of animals, the words and language that connect the thoughts of one individual with those of another, and man-made communication systems, are all greatly influenced by the way information is coded. It is suggested that the role of inductive reasoning is to improve the efficiency of linguistic communication by changing the code, and its effectiveness in performing this function explains its survival value—the reason why this habit of mind is biologically successful and persists. The principles of coding are best understood in a limited, well-defined situation, but inductive reasoning should be viewed in a broad context, which must include the physiological and psychological mechanisms that form perceptions from physical stimuli and attach words to perceptions.
The Detectability of an Unsharp Edge in an Additive Noisy Background
Authors: Orhaug T , Johansson R
Published: January 2007

The detectability of one part of an illuminated field which has a straight edge as the border to the remaining part of the field was studied experimentally while the illumination of the total field had an irregular contrast based on a gaussian-noise spatial structure. The two parts of the field had different average illuminations. The detectability of the edge was studied for various illumination differences, field areas, edge lengths, and sharpnesses. The results are discussed in terms of the characteristics of the background noise and the visual system. The observations are interpreted in terms of a model that assumes spatial differentiation and spatial integration.
Some Effects of Exposure to Optical Disarrangement on Adaptation to Optical Rearrangement
Authors: Uhlarik J
Published: January 2007

Although optical rearrangement has been extensively investigated, disarrangement has received far less attention. It is quite possible that the response of the perceptual system to the latter state, which entails a decorrelation of the normal relationship between vision and motor behavior, will lead to a better understanding of the nature of visual spatial localization.

Two studies are described in which exposure (and adaptation) to prism-displaced vision is preceded by a period of exposure to disarrangement. In the first study, concurrent exposure with a target was used. No increase in localization variability resulted from preexposure to disarrangement. However, it was found that this experience retarded the subsequent adaptation to rearrangement, relative to a condition of preexposure to normal viewing. It is argued that this result supports the existence of a cross-correlator comparator mechanism in sensorimotor coordination.

The second study was similar to the first except that there was no target-error information available during disarrangement or rearrangement. The pattern of results for the second study was different from those of the first study; this suggests that there might be important differences in the manner in which information regarding intermodality discordance and target-error is processed by the comparator.
Three Processes Which Occur during Adaptation to Transformation of the Visual Field
Authors: Austin Margaret , Singer G , Wallace Meredith
Published: January 2007

Changes in visually guided responses, including spatial judgments of object or limb position, which result from optical transformation of visual input are usually referred to as adaptation. The purpose of this paper is to show that the response changes observed in adaptation can be conceptualized as resulting from at least three distinct components—behavioral compensation, sensory adaptation, and visual shift. Data from a series of experiments show the nature of the interaction of behavioral compensation and sensory adaptation. Implications of this latter finding for intermanual transfer are discussed.
The Possible Role of Eye-Muscle Potentiation in Several Forms of Prism Adaptation
Authors: Ebenholtz S M
Published: January 2007

It is possible to explain a number of observations of visual adaptation to optical rearrangement and other visual effects as examples of the ‘Kohnstamm phenomenon’. This is the tendency for a stressed muscle to remain innervated for a period of time after cessation of the voluntary signal to relax. When this phenomenon operates with respect to eye muscles, it may be referred to as ‘eye-muscle potentiation’. Several studies and their results are presented that demonstrate eye-muscle potentiation effects on apparent visual distance. The implications of these studies for prism adaptation are discussed.
Motor-Transformation Learning
Authors: Hay J C
Published: January 2007

Motor-transformation learning theory asserts that people learn through experience what stimulus transformations are under the control of their behavior. More specifically, it asserts that the parameter values of certain predetermined transformation groups are learned.

This theory was inferred, in the first place, from research on adaptation to optical rearrangement—in particular, from position-constancy adaptation in inverting-spectacles experiments, prism-displacement experiments, and in more recent computer-controlled feedback experiments. The detailed characteristics of position-constancy adaptation are found to be consistent with the theory.

Diverse consequences radiate from the theory for other human abilities, both in perception and in memory retrieval. These diverse implications are tested in studies of (a) learning to manipulate ‘objects’ in an artificial computer-controlled visual space; (b) learning to compute, in the absence of overt action, the consequences of such action; (c) learning how to access the features of prior stimuli by the execution of motor actions.
Apparent Motion and the Pulfrich Effect
Authors: Morgan Michael J , Thompson Peter
Published: January 2007

The Pulfrich pendulum effect, obtained by viewing a moving object with a filter over one eye, was examined with target stimuli in apparent, rather than continuous, motion. The filter-induced depth effect persisted until a certain degree of intermittency in the presentations of the target was reached, and then it broke down. The degree of intermittency that could be tolerated before the depth effect broke down increased with the density of the filter. It could be argued that the filter determined a shift in the pairing of successive inputs to the eyes, such that the target position in the unfiltered eye was fused with the preceding target position in the filtered eye. However, it appears that the shifted-pairing effect cannot account for the depth impression seen when the target intermittency is less than about 30 ms. Below this value of intermittency a filter can produce a depth effect even when the delay it introduces is small in comparison to the intermittency of the input. The depth effect seen with intermittencies less than 30 ms appears to be of the same magnitude as that obtained with stimuli in continuous motion. It is concluded that a filter can cause two different kinds of depth shift with apparently moving stimuli.
Monocular and Binocular Rivalry between Contours
Authors: Wade Nicholas J
Published: January 2007

The temporal characteristics of binocular and monocular rivalry between orthogonal gratings of the same or complementary colours were investigated. Rivalry was measured in terms of the dominance of either grating or the visibility of composites comprised of parts of both gratings. The total duration for which either grating was dominant was significantly longer in binocular rivalry between gratings of complementary colours. A comparison of binocular and monocular rivalry indicated considerable phenomenal differences between them. Dominance in binocular rivalry corresponds to the visibility of one grating alone; this occurs rarely in monocular rivalry, which is characterized by fluctuations in the distinctiveness of the gratings. The changes in distinctiveness are influenced by colour in a similar manner to that in binocular rivalry, and the frequencies of fluctuations are higher for gratings of complementary colours.
Independent Spatial-Frequency-Tuned Channels in Binocular Fusion and Rivalry
Authors: Julesz Bela , Miller Joan E
Published: January 2007

Monocular masking studies show that the visibility of a one-dimensional sinusoidal grating remains unchanged in the presence of masking noise filtered so as to contain spectral components that are at least two octaves away from the spatial frequency of the grating (Stromeyer and Julesz 1972). In the present study, random-dot stereograms were bandpass filtered in the two-dimensional Fourier domain, and masking noise of various spatial frequency bands was added to the filtered stereograms. Masking noise bands containing equally effective noise energy were selected such that their bands were either overlapping with the stereoscopic image spectrum or were two octaves distant. The first case resulted in binocular rivalry; however, in the second case stereoscopic fusion could be maintained in the presence of strong binocular rivalry owing to the masking noise. This finding indicates that spatial-frequency-tuned channels are not restricted to one-dimensional gratings but operate on two-dimensional patterns as well. Furthermore, these frequency channels are utilized in stereopsis and work independently from each other, since some of these channels can be in binocular rivalry while at the same time other channels yield fusion. The main binocular experiments are demonstrated.
The Role of Monocularly Conspicuous Features in Facilitating Stereopsis from Random-Dot Stereograms
Authors: Saye Ann , Frisby John P
Published: January 2007

Two experiments are reported which investigated the effects on stereopsis perception times of including monocularly conspicuous features in random-dot stereograms. It was found that such features facilitated stereopsis in large-disparity but not in small-disparity stereograms, perception times for the latter being relatively short with or without monocular features. Facilitation in the large-disparity stimuli came about both from features which delineated the shape of the whole disparate area and from features which merely happened to lie in the same depth plane as the disparate area, but which did not give any shape cues. It is argued that these various results can be well accounted for by a ‘vergence hypothesis’, which supposes that the long perception times often found with random-dot stereograms are due in part to the absence of stimulus features which can guide the vergence movements necessary for fusing the display.
Stereoscopic Tilt and Size Aftereffects
Authors: Tyler Christopher W
Published: January 2007

Adaptation to a random-dot stereograting with no monocularly visible contours produces a tilt aftereffect in a briefly-viewed test stereograting. The effect is maximal for adapting orientation at ±20–30° from the test orientation. Similarly, the perceived spatial frequency of a stereograting is altered by adaptation to a stereograting of adjacent spatial frequencies.
The Complication Experiment Uncomplicated
Authors: Cairney Peter T
Published: January 2007

Early work on the complication experiment, which involved the subject judging the position of a moving pointer at the onset of an auditory signal, is reviewed. The traditional explanation in terms of the earlier processing of input in one modality (the prior entry hypothesis) is critically discussed and rejected. Two experiments are reported in which constant error is shown to vary as a function of the position at which the auditory signal was delivered and the direction of rotation of the pointer. A third experiment found that auditory signals of different intensities gave rise to errors of similar magnitude. Unlike other recent complication experiments, all three gave rise to predominantly anticlockwise constant error. This disagreement was resolved by a fourth experiment in which predominantly clockwise error was obtained by presenting the auditory signal on only one revolution per trial. An explanation, developed from models of absolute judgement tasks, is put forward to account for the present and earlier results in terms of subjects’ judgement strategy.
The Effect of Stationary Patterns on Adaptation for Movement: Evidence for Inhibitory Interaction
Authors: Mayhew John E W
Published: January 2007

Contingent movement aftereffects (CMAEs) can be demonstrated by adapting to a red pattern rotating clockwise (cw) alternating with a green pattern rotating counterclockwise (ccw). After 5 min subjects typically report stationary test patterns as apparently rotating clockwise when they are green and counterclockwise when they are red. Also, luminance thresholds for motion now depend on both the colour and direction of the moving pattern. The thresholds for red—cw and green—ccw motion will be relatively greater than for the opposite colour motion pairings. This is called contingent threshold elevation.

When stationary dots the same colour as the moving patterns are added to the adapting stimuli, subjects report weak CMAEs but no contingent threshold elevation can be demonstrated.

When stationary dots opposite in colour to the moving patterns are added to the adapting stimuli, neither CMAEs nor contingent threshold elevation can be demonstrated. And yet colour specific adaptation does occur, and can be demonstrated in the colour specificity of the simple movement aftereffect. When stationary dots are added to the adapting pattern, the simple movement aftereffect though reduced, is greatest on a test pattern of the same colour as the moving dots. These findings suggest that the CMAE, contingent threshold elevation, and the colour specificity of the movement aftereffect involves neural processes differentially sensitive to the presence of stationary patterns.
Illusory Shifts in Spatial Frequency Caused by Temporal Modulation
Authors: Tolhurst David J
Published: January 2007

It is known that temporal modulation of a sinusoidal grating of low spatial frequency causes an increase in the apparent spatial frequency of the grating. A possible explanation for the illusion is proposed. Temporal modulation would favour channels which respond only transiently to prolonged presentation of a grating. These channels may be the human analogues of Y-cells found in the cat retina. Y-cells respond nonlinearly to gratings, and the nonlinearity may be the root of the apparent spatial-frequency illusions.
Pattern Recognition in Humans: Correlations Which Cannot be Perceived
Authors: Glass Leon , Switkes Eugene
Published: January 2007

Random-dot Moiré patterns are manipulated to destroy our ability to perceive the spatial correlations which remain present in the patterns.
Psychophysical Measurement of Cortical Color Mechanisms Not Sensitive to Spatial Frequency
Authors: Meyer Glenn
Published: January 2007

Virsu and Haapasalo report that the Blakemore and Sutton apparent spatial-frequency shift is not color specific. Also supposedly demonstrated is a McCollough effect that is not specific to spatial frequency. It is suggested that inadequate test procedures and a confusion between retinal and cortical adaptation negate these results.
Grouping of Multiple Ambiguous Contours: Towards an Understanding of Surface Perception
Authors: Gillam Barbara
Published: January 2007

Coplanar lines of different orientations rotating in depth and viewed in parallel projection may appear to rotate in different directions and reverse independently of each other, or they may appear coplanar and all reverse together. The frequency of the latter ‘grouped’ appearance for lines with an orientation range of 30° was a function of the number of lines in a given space. Grouping was greater for lines converging to an implicit vanishing point and for lines with collinear edges regardless of their orientations. Line length and, by inference, interline separation also had effects on the nature of the response.
Word Length and Visual-Noise Texture in Backward Masking
Authors: Zamansky Harold S , Corwin Thomas R
Published: January 2007

Visual-noise masks composed of randomly scattered letter fragments disrupt the recognition of briefly viewed letter arrays when the masks are presented immediately after these arrays. According to the feature-similarity assumption, maximal disruption should occur when the target letters and the letter fragments comprising the mask share a common stroke width. This assumption was disconfirmed in the present experiment. Two-, four-, and six-letter arrays, whose stroke width subtended a visual angle of 3·8′, were viewed tachistoscopically in conjunction with visual-noise masks whose letter fragments subtended visual angles of 1·2′, 1·9′, 3·8′, 6·6′, or 9·7′. The most effective mask for all three letter-array lengths was the one composed of letter fragments subtending 6·6′. The results, together with those of previous experiments, are accounted for in terms of a neural line-detecting mechanism.
Implicit Labelling and Readiness for Pronunciation during the Perceptual Process
Authors: Noizet Georges , Pynte Joël
Published: January 2007

The authors assume that during the visual perception of labelable objects there occurs an implicit labelling which gives rise to a readiness for pronunciation, and that the two phenomena are involved in stimulus processing.

In order to test these assumptions, the duration of eye fixation on drawings representing familiar objects was measured. The data show that on an average this duration was longer when the name for the object required four or five syllables to pronounce than when it required only one syllable. This syllable effect was observed in various experimental conditions where possible effects of other variables could be controlled. The effect was obtained irrespective of whether or not the subjects were allowed to see the drawings before the experiment, and of whether or not they were allowed to go through the list of names for the objects.
Influence of Selection Difficulty on the Time Required for Icon Formation
Authors: Solman Robert T
Published: January 2007

By increasing the number of display items and the physical similarity between the target and the irrelevant items it was possible to vary the difficulty of target selection in a visual-search task. The results showed that the accuracy with which the target was located declined as target selection became more difficult. On the other hand, estimates of the cumulative probability and the probability distributions of times necessary to form the icon indicated that these times were not influenced by changes in the difficulty of the task. The latter result supports Neisser's suggestion that the information processing carried out during the first stage of analysis can be attributed to the action of a distinct cognitive mechanism.
Away from a Unisex Psychology: Individual Differences in Visual Sensory and Perceptual Processes
Authors: McGuinness Diane
Published: January 2007

Four tests of visual perception were given to twenty-five men and twenty-five women. These were a test of acuity, threshold for four field positions, visual persistence, and a measure of comfortable brightness. Subjects also completed five personality questionnaires. In most measures, differences were found to be related to sex rather than to personality factors. In fact, the analyses performed suggest that personality tests do not measure equivalent processes in men and women. Correlational analysis showed all visual functions to be independent of one another with the exception of photopic acuity and scotopic threshold, which were highly correlated. Two new findings on the visual system emerged which have not been reported elsewhere: (i) Four distinct dark adaptation curves were produced, and have been labeled as exponential, flat-exponential, linear, and plateau. All subjects fell into one of these categories and showed a consistent trend to exhibit these curves for all field positions, (ii) Highly significant differences were found in sensitivity for the four visual fields, the upper field was superior, followed by the right, then left, with the lower visual field considerably poorer.
Model-Driven Interpretation in Intelligent Vision Systems
Authors: Mackworth Alan K
Published: January 2007

With a constructive knowledge-based theory of perception as its foundation, this paper starts with a review and critique of some artificial-intelligence programs that purport to see. It is then argued that these computer programs for scene analysis offer the hope of providing a more adequate account of human competence in interpreting line drawings as polyhedra than do the current psychological theories. This thesis has several aspects. The one emphasized here is that those programs have explored a variety of methods of incorporating a priori knowledge of objects through the use of models. After outlining the range of models used, presenting a set of criteria for evaluating the use of model information, and sketching some psychological theories, the various proposals are contrasted. This discussion leads to two new proposals for exploiting model information that involve elaborations of an existing program, POLY.