The Orthogonal Orientation Shift and Spatial Filtering

Perception ◽  
1995 ◽  
Vol 24 (5) ◽  
pp. 513-524 ◽  
Author(s):  
Michael J Morgan ◽  
Andrew Medford ◽  
Philip Newsome
Keyword(s):  
Spatial Filtering ◽  
Line Length ◽  
End Points ◽  
Gray Background ◽  
Short Line ◽  
Apparent Length ◽  
Single Mechanism ◽  
Band Pass ◽  
Orthogonal Orientation ◽  
Opposite Contrast

A line abutting two tilted flanks is apparently shifted towards the orientation orthogonal to the flanks and at the same time is reduced in its apparent length. It has been suggested that both effects are caused by band-pass spatial filtering, followed by location of the end points of the line at the peaks in the filtered image. Here implications of the filtering explanation of these effects are explored further. In the first experiment, it was predicted that orientation thresholds (as opposed to biases) would be increased for short line lengths, and would be further increased by abutting bars. The predictions were confirmed. It was shown in experiment 2 that the orientation shift was reduced by a small (4 min arc) gap between target lines and orthogonal flanks. In experiment 3 the threshold elevations and the orientation shift produced by orthogonal and tilted flanks were compared. Last, in experiment 4, the threshold elevations and orientation shift produced by orthogonal and tilted flanks, at different retinal eccentricities varying from 0 to 3.2 deg were compared, and the prediction that the magnitude of the orientation shift would decrease with line length and increase with eccentricity was confirmed. The connection is explored between the orientation shift and the Zöllner illusion, and demonstrations are presented of the Zöllner effect in which target and inducing lines are of opposite contrast on a gray background. It is concluded that the Judd and Zöllner illusions do not depend upon a single mechanism.

scholarly journals Glass Patterns: Some Contrast Effects Re-Evaluated

Perception ◽  
1997 ◽  
Vol 26 (3) ◽  
pp. 253-268 ◽  
Author(s):  
Steven C Dakin
Keyword(s):  
Spatial Filtering ◽  
Contrast Effects ◽  
Visual Grouping ◽  
Relative Contrast ◽  
Low Pass ◽  
Band Pass ◽  
Opposite Contrast ◽  
Low Pass Filters ◽  
Glass Patterns ◽  
High Pass

The relative contrast of features is known to be important in determining if they can be grouped. Two manipulations of feature contrast have previously been used to criticise models of visual grouping based on spatial filtering: high-pass filtering and reversal of contrast polarity. The effects of these manipulations are considered in the context of the perception of Glass patterns. It is shown that high-pass filtering elements, whilst destroying structure in the output of low-pass filters, do not significantly disrupt the output of locally band-pass filters. The finding that subjects can perceive structure in Glass patterns composed of high-pass features therefore offers no evidence against such spatial filtering mechanisms. Band-pass filtering models are shown to explain the rotation of perceived structure in Glass patterns composed of opposite contrast features. However, structure is correctly perceived in patterns composed of two ‘interleaved’ opposite contrast patterns, which is problematic for oriented filtering mechanisms. Two possible explanations are considered: nonlinear contrast transduction prior to filtering, and integration of local orientation estimates from first-order and second-order mechanisms.

Spatial Filtering and the Zöllner—Judd Geometrical Illusion: Further Studies

Perception ◽  
1995 ◽  
Vol 24 (12) ◽  
pp. 1397-1406 ◽  
Author(s):  
David C Earle ◽  
Stephen J Maskell
Keyword(s):  
Spatial Filtering ◽  
Dual Process ◽  
Illusory Effect ◽  
Geometrical Illusion ◽  
Geometrical Figure ◽  
Difference Of Gaussians ◽  
Filter Output ◽  
Single Process ◽  
Band Pass ◽  
Opposite Contrast

In a geometrical figure in which long vertical lines are each crossed by a series of short oblique lines, an illusory effect is obtained such that the orientations of the long lines are perceived as nonvertical and shifted away from the orientation of the oblique lines (the Zöllner illusion). In addition, the vertical separation between the crossing (oblique) lines is perceived as less than that if the crossing lines are horizontal (the Judd illusion). It has previously been shown that these two effects are closely related, and a single-process account has been proposed in which both effects are explained by a computational model involving band-pass spatial filtering of the figure by means of difference-of-Gaussians (DOG) filters. Two arguments are presented against the latter account. First, in an opposite-contrast-polarity figure with, for example, white vertical lines and black crossing lines on a mid-grey background, the peaks in the DOG filter output are such as to predict the reversal of the Zöllner—Judd effects. It is shown by demonstration that this prediction is disconfirmed, and that the normal effects are obtained. Second, it is shown that the normal Zöllner—Judd effects are obtained in the absence of the long vertical lines, and in the presence of anomalous contours. The latter effects are also in contradiction to the band-pass-filtering model. These findings are discussed in relation to a dual-process account of the Zöllner—Judd effects.

Exposure Duration and Line Length: An Analogy to the Broca-Sulzer Effect in Perception of Extent?

1980 ◽  
Vol 51 (3) ◽  
pp. 945-946 ◽  
Author(s):  
Ted Jaeger ◽  
Charles Kraemer
Keyword(s):  
Exposure Duration ◽  
Line Length ◽  
Apparent Length

For 30 undergraduates, brief exposures were shown to increase the apparent length of a line. This enhancement of length diminished as duration of exposure increased, creating an illusion of line length that resembles the Broca-Sulzer brightness anomaly.

The Stereokinetic Phenomenon from Two or Three Points

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 209-209 ◽  
Author(s):  
H Komatsu
Keyword(s):  
Visual System ◽  
Relative Velocity ◽  
Frontoparallel Plane ◽  
End Points ◽  
Apparent Position ◽  
Apparent Length ◽  
Straight Line ◽  
The Absolute ◽  
Centre Of Rotation

The stereokinetic phenomenon occurs when certain 2-D patterns are rotated in the frontoparallel plane. Zanforlin explained this phenomenon by the hypothesis of the minimisation of velocity differences. Our visual system minimises relative velocity differences between the various points of the pattern, which determines the apparent height of the stereokinetic cone. Zanforlin and Vallortigara applied the hypothesis to a rotating straight line or the two end-points of a straight line. They showed that the apparent length of the line does not depend on the absolute physical velocities of the end-points but rather on the relative velocities, and the absolute physical velocities merely affect the apparent position of the line with respect to the plane of the disk. In the present experiments with two points, the apparent length indeed depended on the relative velocities, but the absolute velocities did not affect the apparent position. The apparent position of the line with respect to the plane of the disk depended on whether or not the centre of rotation was between the two end-points. Adding one more point gave a triangle that appeared slanted into 3-D space. The shape composed of three points was held constant, even when rotated and slanted. The height of the apparent triangle also depended on the relative velocities.

A Novel Approach for Responsive Neural Stimulator Implantation With Infraclavicular Placement of the Internal Pulse Generator

2018 ◽  
Vol 15 (6) ◽  
pp. 711-719
Author(s):  
Lucas R Philipp ◽  
Mark R Witcher ◽  
Robert E Gross
Keyword(s):  
Pulse Generator ◽  
Therapeutic Option ◽  
Line Length ◽  
Seizure Freedom ◽  
Salvage Procedure ◽  
Peripheral Nerve Stimulator ◽  
Detection Rates ◽  
Novel Approach ◽  
Band Pass ◽  
Internal Pulse Generator

Abstract INTRODUCTION The Responsive Neurostimulation System (RNS, Neuropace, Mountain View, California) has been proven to be effective at reducing seizures in patients with partial-onset epilepsy. The system incorporates a skull-mounted neurostimulator that requires a cranial incision for replacement. Although integral to the functioning of the system, in some circumstances, such as in the setting of infection, this can be disadvantageous. At present, there are no alternatives to cranial implantation of the RNS System. METHODS We describe a novel procedure enabling implantation of the neurostimulator within the chest wall, using components from a peripheral nerve stimulator. In a patient who achieved complete seizure freedom with the use of the RNS System, distant site implantation provided a viable means of continuing therapy in a setting where device explantation would have otherwise been inevitable as a result of cranial infection. We present continuous electrocorticographic data recorded from the device documenting the performance of the system with the subclavicular neurostimulator. RESULTS Band pass detection rates increased by 50%, while line length detection rates decreased by 50%. The number of detections decreased from 1046 to 846, with a resultant decrease in stimulations. Although there was some compromise of function due to the elevated noise floor, more than 2 yr following the procedure the patient remains free of seizures and infection. CONCLUSION The salvage procedure we describe offered an alternative therapeutic option in a patient with a complicated cranial wound issue, using heterogeneous components with marginal compromises in device functionality and no sacrifice in patient outcome.

scholarly journals Poetic effects and visuospatial form: a relevance-theoretic perspective

2019 ◽  
Author(s):  
◽  
Daniel William Pinder
Keyword(s):  
Line Length ◽  
Great Depth ◽  
Linguistic Feature ◽  
Short Line ◽  
Syntactic Form ◽  
Poetic Text ◽  
Complex Forms ◽  
Poetic Texts ◽  
The Mind ◽  
Inferential Processing

Sperber and Wilson (1995:222) posit the term poetic effect for the peculiar effect of an utterance which achieves most of its relevance through a wide array of weak implicatures. Crucially, the input to pragmatic processing, which prompts the derivation of a poetic effect, is achieved via some stylistically pronounced linguistic feature: for example, a repeated lexical item, a peculiar syntactic form, a piece of alliteration, and so on. However, what has never been considered to any great depth from a relevancetheoretic perspective is how unusual elements of visuospatial form might also impact upon the reader’s basic understanding and wider interpretation of a given poetic text in ways that result in the derivation of specialised poetic effects. Therefore, the thesis posits a relevance-theoretic account of the cognitive-pragmatic effects of short linelength and line divisions, when employed and interpreted within complex forms of poetry. The account is split into two hypotheses relating to short line-length and line divisions respectively. Hypothesis 1 states that the use of short line-length leads to the majority of the text’s lexical material being perceived in a much slower, and therefore intense fashion, which consequently causes the lexical and encyclopaedic entries that such material links to within the mind to remain active for relatively longer periods of time. During such extended periods of lexical and encyclopaedic activation, literary readers are encouraged to inferentially process the text’s explicit-propositional content in relation to a range of further items of encyclopaedic-contextual material, which can give rise to arrays of additional contextual effects of a weakly implicit and therefore poetic nature. Hypothesis 2 states that line divisions are often intentionally utilised in poetic texts by writers in order to visuospatially separate integral syntactic units upon the page. This can encourage readers to pause and briefly consider, upon an anticipatoryhypothetical basis, the various possible pragmatic extensions of the text’s momentarily incomplete logical and propositional status, pre-line division as it were. The various pragmatic extensions may be formulated as arrays of weak explicatures, which for some readers may achieve poetic effects (in the specialised relevance-theoretic sense of the term). The process effectively constitutes the visuospatial equivalent of a deliberate ‘pause for effect’, which triggers a considerable degree of further inferential processing, and provides a distinct communicational ‘reward’ primarily at an explicit-propositional level.

scholarly journals Single-Band Amplitude Demodulation of Müller-Lyer Illusion Images

2007 ◽  
Vol 10 (1) ◽  
pp. 3-19 ◽  
Author(s):  
Vicente Sierra-Vázquez ◽  
Ignacio Serrano-Pedraza
Keyword(s):  
Spatial Filtering ◽  
Single Band ◽  
Frequency Content ◽  
Visual Model ◽  
Lyer Illusion ◽  
Spatial Frequencies ◽  
Low Pass ◽  
Ill Posed ◽  
Band Pass ◽  
High Pass

The perception of the Müller-Lyer illusion has previously been explained as a result of visual low band-pass spatial filtering, although, in fact, the illusion persists in band-pass and high-pass filtered images without visible low-spatial frequencies. A new theoretical framework suggests that our perceptual experience about the global spatial structure of an image corresponds to the amplitude modulation (AM) component (or its magnitude, also called envelope) of its AM-FM (alternatively, AM-PM) decomposition. Because demodulation is an ill-posed problem with a non-unique solution, two different AM-FM demodulation algorithms were applied here to estimate the envelope of images of Müller-Lyer illusion: the global and exact Daugman and Downing (1995) AMPM algorithm and the local and quasi-invertible Maragos and Bovik (1995) DESA. The images used in our analysis include the classic configuration of illusion in a variety of spatial and spatial frequency content conditions. In all cases, including those of images for which visual low-pass spatial filtering would be ineffective, the envelope estimated by single-band amplitude demodulation has physical distortions in the direction of perceived illusion. It is not plausible that either algorithm could be implemented by the human visual system. It is shown that the proposed second order visual model of pre-attentive segregation of textures (or “back-pocket” model) could recover the image envelope and, thus, explain the perception of this illusion even in Müller-Lyer images lacking low spatial frequencies.

The structure of membranes and membrane proteins embedded in amorphous ice

1992 ◽  
Vol 50 (1) ◽  
pp. 432-433
Author(s):  
Uwe Lücken ◽  
Joachim Jäger
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Membrane Proteins ◽  
Phase Transition Temperature ◽  
Lipid Vesicles ◽  
Freezing Stress ◽  
Amorphous Ice ◽  
Different Temperatures ◽  
Band Pass ◽  
Lipid Polymorphism

TEM imaging of frozen-hydrated lipid vesicles has been done by several groups Thermotrophic and lyotrophic polymorphism has been reported. By using image processing, computer simulation and tilt experiments, we tried to learn about the influence of freezing-stress and defocus artifacts on the lipid polymorphism and fine structure of the bilayer profile. We show integrated membrane proteins do modulate the bilayer structure and the morphology of the vesicles.Phase transitions of DMPC vesicles were visualized after freezing under equilibrium conditions at different temperatures in a controlled-environment vitrification system. Below the main phase transition temperature of 24°C (Fig. 1), vesicles show a facetted appearance due to the quasicrystalline areas. A gradual increase in temperature leads to melting processes with different morphology in the bilayer profile. Far above the phase transition temperature the bilayer profile is still present. In the band-pass-filtered images (Fig. 2) no significant change in the width of the bilayer profile is visible.

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