Low Spatial Frequencies Dominate Apparent Motion

Perception ◽  
1983 ◽  
Vol 12 (4) ◽  
pp. 457-461 ◽  
Author(s):  
Vilayanur S Ramachandran ◽  
Arthur P Ginsburg ◽  
Stuart M Anstis
Keyword(s):  
Apparent Motion ◽  
Central Figure ◽  
Spatial Frequencies ◽  
Low Pass ◽  
High Pass

Experiments are reported which have been designed to establish what features of a pair of figures can be used as an input for apparent motion. The display consisted of a central figure, A, which appeared briefly and was followed immediately afterwards by two figures, B and C, which appeared on either side of the original location of A. Figure A can thus move towards either B or C. When A was a low-pass filtered square it moved towards C (a low-pass filtered square that was similar to A but ‘rotated’ by 45°) rather than towards B (a high-pass filtered square identical to A in orientation and size). When A was an unfiltered square it moved towards C (a low-pass filtered square of identical orientation) rather than towards B (a high-pass filtered square of identical orientation). Lastly, when A was a ‘solid’ square it moved towards C (a solid circle) rather than towards B (an outline square). All three experiments suggest that the direction of perceived movement is determined exclusively by low spatial frequencies rather than by similarity of oriented edges, especially when speed of alternation is rapid.

The Importance of High Spatial Frequencies for Exogenous Consciousness. Evidence from the Attentional Blink Paradigm.

2019 ◽  
Author(s):  
Mickaël Jean Rémi Perrier ◽  
Louise Kauffmann ◽  
Carole Peyrin ◽  
Nicolas Vermeulen ◽  
Frederic Dutheil ◽  
...  
Keyword(s):  
Spatial Frequency ◽  
Visual System ◽  
Attentional Blink ◽  
Crucial Role ◽  
Conscious Perception ◽  
Frequency Content ◽  
Spatial Frequencies ◽  
Low Pass ◽  
Visual Consciousness ◽  
High Pass

We attempted to highlight the respective importance of low spatial frequencies (LSFs) and high spatial frequencies (HSFs) in the emergence of visual consciousness by using an attentional blink paradigm in order to manipulate the conscious report of visual stimuli. Thirty-eight participants were asked to identify and report two targets (happy faces) embedded in a rapid stream of distractors (angry faces). Conscious perception of the second target (T2) usually improved as the lag between the targets increased. The distractors between T1 and T2 were either non-filtered (broad spatial frequencies, BSF), low-pass filtered (LSF), or high-pass filtered (HSF). The spatial frequency content of the distractors resulted in a greater disturbance of T2 reporting in the HSF than in the LSF condition. We argue that this could support the idea of HSF information playing a crucial role in the emergence of exogenous consciousness in the visual system. Other interpretations are also discussed.

The Role of High Spatial Frequencies in Face Perception

Perception ◽  
1983 ◽  
Vol 12 (2) ◽  
pp. 195-201 ◽  
Author(s):  
Adriana Fiorentini ◽  
Lamberto Maffei ◽  
Giulio Sandini
Keyword(s):  
Spatial Frequency ◽  
Face Perception ◽  
Energy Content ◽  
High Spatial Frequency ◽  
Face Width ◽  
Spatial Frequencies ◽  
Low Pass ◽  
High Pass ◽  
Spatial Frequency Domain

The relevance of low and high spatial-frequency information for the recognition of photographs of faces has been investigated by testing recognition of faces that have been either low-pass (LP) or high-pass (HP) filtered in the spatial-frequency domain. The highest resolvable spatial frequency was set at 15 cycles per face width (cycles fw−1). Recognition was much less accurate for images that contained only the low spatial frequencies (up to 5 cycles fw−1) than for images that contained only spatial frequencies higher than 5 cycles fw−1. For faces HP filtered above 8 cycles fw−1, recognition was almost as accurate as for faces LP filtered below 8 cycles fw−1, although the energy content of the latter greatly exceeded that of the former. These findings show that information conveyed by the higher spatial frequencies is not redundant. Rather, it is sufficient by itself to ensure recognition.

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.

CURRENT-MODE ACTIVE-C FILTER EMPLOYING REDUCED NUMBER OF CCCII+s

2007 ◽  
Vol 16 (04) ◽  
pp. 507-516 ◽  
Author(s):  
SHAHRAM MINAEI ◽  
ERKAN YUCE
Keyword(s):  
Current Mode ◽  
Pass Band ◽  
Passive Component ◽  
Resistorless Filter ◽  
Low Pass ◽  
Component Matching ◽  
Band Pass ◽  
High Output Impedance ◽  
Quality Factor Q ◽  
High Pass

In this paper, a universal current-mode second-order active-C filter for simultaneously realizing low-pass, band-pass and high-pass responses is proposed. The presented filter employs only three plus-type second-generation current-controlled conveyors (CCCII+s). This filter needs no critical active and passive component matching conditions and no additional active and passive elements for realizing high output impedance low-pass, band-pass and high-pass characteristics. The angular resonance frequency (ω0) and quality factor (Q) of the proposed resistorless filter can be tuned electronically. To verify the theoretical analysis and to exhibit the performance of the proposed filter, it is simulated with SPICE program.

NOVEL VOLTAGE-MODE UNIVERSAL FILTER USING ONLY TWO CDBAs

2005 ◽  
Vol 14 (01) ◽  
pp. 159-164 ◽  
Author(s):  
SUDHANSHU MAHESHWARI ◽  
IQBAL A. KHAN
Keyword(s):  
Pass Band ◽  
Universal Filter ◽  
Input Selection ◽  
Voltage Mode ◽  
Single Output ◽  
Control Computer ◽  
Low Pass ◽  
Band Pass ◽  
Pass Through ◽  
High Pass

A novel voltage-mode universal filter employing only two current differencing buffered amplifiers (CDBAs) is proposed. The filter uses four inputs and single output to realize six responses, viz. low-pass, high-pass, inverting band-pass, noninverting band-pass, band-elimination, and all-pass through input selection with independent pole-Q control. Computer simulation results using SPICE are also given to verify the theory.

Coding of temporal parameters of complex sounds by frog auditory nerve fibers

1991 ◽  
Vol 65 (3) ◽  
pp. 424-445 ◽  
Author(s):  
A. S. Feng ◽  
J. C. Hall ◽  
S. Siddique
Keyword(s):  
Auditory Nerve ◽  
Transfer Functions ◽  
Nerve Fibers ◽  
Spike Count ◽  
Complex Sounds ◽  
Temporal Parameters ◽  
Low Pass ◽  
The Mean ◽  
Auditory Nerve Fibers ◽  
High Pass

1. Physiological recordings were made from single auditory fibers in the frog eighth nerve to determine quantitatively how the different behaviorally relevant temporal parameters (the signal rise-fall time, duration, and rate of amplitude modulation) of complex sounds are encoded in the auditory periphery. Individual temporal parameters were varied. Response functions (RFs) were constructed with respect to each of these parameters using each unit's best excitatory frequency (BF) as the carrier. 2. In response to a change in signal rise-fall time, auditory nerve fibers showed little change in the mean spike count or firing rate, i.e., all fibers displayed ALL-PASS RFrfts. But the transient components, particularly the early phasic component, of responses varied with rise-fall times; these components were more pronounced in the responses to stimuli with shorter rise-fall times. 3. In response to an increase in signal duration, auditory nerve fibers showed a corresponding increase in firing duration and thus in the mean spike count, giving rise to HIGH-PASS RFdurs. The shape of response curves differed among fibers; the difference appeared to be related to the fiber's temporal adaptation characteristic. When the firing rate was measured, all fibers displayed higher mean firing rates in response to shorter duration stimuli than they did to longer duration stimuli, thus giving rise to LOW-PASS response functions. 4. To determine the response transfer functions to modulation rate, pulsed (PAM) and sinusoidally (SAM) amplitude-modulated signals were used. These signals differed substantially in terms of their envelopes and how they varied with AM rate. Data were analyzed by 1) plotting spike counts against the AM rate to derive modulation transfer functions (MTFspks) and 2) plotting synchronization coefficients (SCs) against the AM rate to generate MTFscs. 5. In response to PAM stimuli, all fibers showed an increase in mean spike count with modulation frequency over the range examined, giving rise to HIGH-PASS MTFspks. 6. For SAM stimuli, the average energy and duty cycle are independent of AM rate. Most (79%) auditory fibers showed little selectivity for AM rate over a range of 5-400 Hz, giving rise to ALL-PASS MTFspks. The remaining auditory fibers displayed LOW-PASS MTFspks, i.e., there was a distinct decline in the mean spike count with increasing AM rate. 7. In response to PAM stimuli, most fibers showed good response synchrony at low AM rates but the SC declined with an increase in the AM rate (i.e., LOW-PASS MTFscs). The cut-off frequency was typically very high, averaging 90 pulses/s.(ABSTRACT TRUNCATED AT 400 WORDS)

A semi-lumped microstrip UWB bandpass filter

2009 ◽  
Vol 1 (1) ◽  
pp. 57-64 ◽  
Author(s):  
Darine Kaddour ◽  
Jean-Daniel Arnould ◽  
Philippe Ferrari
Keyword(s):  
Group Delay ◽  
Bandpass Filter ◽  
Filter Design ◽  
Sensitivity Study ◽  
Critical Parameters ◽  
Center Frequency ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Low Pass ◽  
High Pass

In this paper, a miniaturized bandpass filter for ultra-wide-band applications is proposed. It is based on the embedding of high-pass structures in a low-pass filter. A semi-lumped technology combining surface-mounted capacitors and transmission lines has been used. The filter design rules have been carried out. Furthermore, two filters having a 3-dB fractional bandwidth of 142 and 150%, centered at 0.77 and 1 GHz, respectively, have been realized for a proof of concept. Measured characteristics, in good agreement with simulations, show attractive properties of return loss (|S11| <−18 dB), insertion loss (<0.3 dB), and a maximum group delay and group delay variation of 2 and 1.3 ns, respectively. A distributed filter based on the same low-pass/high-pass approach has been also realized and measured for comparison. The size reduction reaches 85% for the semi-lumped filter, and its selectivity is improved with a shape factor of 1.3:1 instead of 1.5:1. The semi-lumped filter's drawback is related to a smaller rejection bandwidth compared to the distributed one. To improve the high-frequency stopband, an original technique for spurious responses suppression based on capacitively loaded stubs has been proposed. Even if the performances do not reach that obtained for the distributed approach, with this technique spurious responses are pushed until eight times the center frequency. A sensitivity study vs. critical parameters has also been carried out, showing the robustness of the design.

Utilisation d'une ligne de microphotodiodes en spectroscopie dispersive : application à la détection du NO2

1983 ◽  
Vol 61 (2) ◽  
pp. 301-304 ◽  
Author(s):  
Jacques Bures ◽  
François Leonard ◽  
Jean-Pierre Monchalin
Keyword(s):  
Absorption Spectrum ◽  
Systematic Errors ◽  
Sufficient Information ◽  
Atmospheric Pollutant ◽  
Spatial Frequencies ◽  
Low Pass ◽  
On Line ◽  
Photodiode Array ◽  
Analysis System

A self-scanned photodiode array has been used as a multiplex sensor for laboratory detection and measurement, by dispersive spectroscopy, of trace quantities of the atmospheric pollutant NO2. The on-line data acquisition and numerical analysis system allows in particular to eliminate some systematic errors and drifts (Taylor filtering) and the noise associated with high spatial frequencies (low-pass filtering). We have then been able to show that an absorption spectrum, corresponding to low absorber concentrations, has a sufficient information content for the characterization of the pollutant and the measurement of its concentration (ppm m), even when noise and drifts are present. The proposed system can be favorably compared to the ones, based on a single photoelectric detector, which are commercially used.

scholarly journals Функциональные оптические элементы и устройства терагерцовой фотоники на основе метаповерхностей

2019 ◽  
pp. 84-84
Keyword(s):  
Low Pass ◽  
Band Pass ◽  
High Pass

Освоение диапазона терагерцовых (ТГц) частот электромагнитного спектра (0,1–10 ТГц) делает актуальными задачи разработки и изготовления эффективных оптических элементов для управления характеристиками пучков ТГц-излучения. С инструментальной точки зрения данный спектральный диапазон, соответствующий интервалу длин волн 30÷3000 мкм, удобно позиционирован между примыкающими к нему СВЧ и ИК областями, поскольку позволяет сочетать в терагерцовой аппаратуре инструментальные решения как оптической, так и микроволновой техники. Примером таких решений служат тонкие планарные метало-диэлектрические структуры субволновой топологии, известные в технологии метаматериалов как «метаповерхности» (МП). МП являются, как правило, резонансными электродинамическими структурами, которые эксплуатируются в режиме, когда их характерные резонансные частоты лежат значительно ниже точки возбуждения высших дифракционных гармоник, что отличает такие структуры от дифракционных решеток. Последнее достигается малостью периода расположения элементарных ячеек МП в ее латеральной плоскости в сравнении с рабочей длиной волны. Существенно, что амплитудные, фазовые и поляризационные характеристики МП в заданной полосе частот определяются дизайном ее ячеек, соответствующий выбор которого обеспечивает требуемые функциональные свойства МП-устройств. Последние выгодно сочетают малость толщины/веса и высокую эффективность, которая зачастую не может быть достигнута в рамках решений классической оптики. При этом в ТГц-диапазоне характерный размер элементов топологического рисунка МП в большинстве случаев составляет от нескольких единиц до сотен мкм, что позволяет применять для его производства сравнительно недорогие и хорошо отработанные литографические технологии. В настоящем докладе представлен обзор экспериментальных результатов по разработке оптических элементов и устройств на основе метаповерхностей традиционных и новых конфигураций, которые предназначены как для автономного применения, так и для интеграции с различными метрологическими системами, работающими в области частот от сотни ГГц до нескольких ТГц. Составляя неотъемлемую часть российской элементной базы радиофотоники, разработанные элементы в ряде случаев опережают по функциональным характеристикам отечественные и зарубежные аналоги. Обсуждаются вопросы электродинамического моделирования, технологического производства, спектральной характеризации, а также практического использования следующих типов терагерцовых МП-устройств и систем на их основе: 1) частотные фильтры различных видов: band-pass, low-pass, high-pass; дихроичные мультиплексоры пучков излучения; спектрорадиометрические системы на базе полосовых фильтров; 2) поляризаторы; преобразователи фазы и поляризации; 3) плоские фокусирующие элементы, включая голографические структуры; 4) ультратонкие резонансные поглотители и тепловые детекторы на их основе, включая многоканальные пироэлектрические линейки для спектральных и поляризационных измерений с пространственным разрешением; 5) перестраиваемые ЖК-устройства на основе высокоимпедансных поверхностей; 6) сенсоры тонкопленочных аналитов, включая SEIRA-структуры.

scholarly journals Redesigning a “Writing for Chemists” Course Using Specifications Grading

2020 ◽  
Author(s):  
Stephen Mang ◽  
Kate J. McKnelly ◽  
Michael Morris
Keyword(s):  
Student Learning ◽  
Learning Outcomes ◽  
Student Learning Outcomes ◽  
Graduation Requirement ◽  
School Year ◽  
Low Pass ◽  
The University ◽  
The Relationship ◽  
Writing Practice ◽  
High Pass

The Department of Chemistry at the University of California, Irvine (UCI) instituted an upper-division “Writing for Chemists” course in fall 2017 that fulfills part of UCI’s writing graduation requirement. During the 2019-2020 school year, we re-designed the course using a specifications grading system with the following goals: 1) to teach students how to develop their own writing practice, while mastering chemistry discipline-specific writing conventions, 2) to provide students with frequent and constructive instructor and teaching assistant (TA) feedback by providing ample revision opportunities, 3) to increase transparency in how students can achieve course SLOs, and 4) to provide students with consistent and clear assessment rubrics. This specifications grading approach uses a high-pass, low-pass, unsatisfactory system predicated on whether students meet a certain number of criteria for each assignment. Achievement of Student Learning Outcomes (SLOs) was assessed using criteria instead of points so that instructors and students could more objectively measure student learning. Standardized rubrics and a student grade tracker helped students understand the relationship between meeting criteria, achieving SLOs, and earning grades. Students completed surveys at the end of the course to determine if their writing habits and attitudes towards writing changed. After the course, students self-reported increased propensities to pre-write and edit, and several students mentioned that they appreciated the transparency of the specifications rubrics and the control the specifications system gave them over their grades.

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