scholarly journals A Development Strategy for SHM Applications

2021 ◽  
pp. 1-17
Author(s):  
Peter Cawley
Keyword(s):  
Spatial Frequency ◽  
Development Strategy ◽  
Temporal Frequency ◽  
High Spatial Frequency ◽  
Operating Conditions ◽  
Damage Growth ◽  
Periodic Inspection ◽  
High Temporal Frequency ◽  
Industrial Use ◽  
Signal Changes

Abstract Permanently installed SHM systems are now a viable alternative to traditional periodic inspection (NDT). However, their industrial use is limited and this paper reviews the steps required in developing practical SHM systems. The transducers used in SHM are fixed in location, whereas in NDT they are generally scanned. The aim is to reach similar performance with high temporal frequency, low spatial frequency SHM data to that achievable with conventional high spatial frequency, low temporal frequency NDT inspections. It is shown that this can be done via change tracking algorithms such as the Generalized Likelihood Ratio (GLR) but this depends on the input data being normally distributed, which can only be achieved if signal changes due to variations in the operating conditions are satisfactorily compensated; there has been much recent progress on this topic and this is reviewed. Since SHM systems can generate large volumes of data, it is essential to convert the data to actionable information, and this step must be addressed in SHM system design. It is also essential to validate the performance of installed SHM systems, and a methodology analogous to the model assisted POD (MAPOD) scheme used in NDT has been proposed. This uses measurements obtained from the SHM system installed on a typical undamaged structure to capture signal changes due to environmental and other effects, and to superpose the signal due to damage growth obtained from finite element predictions. There is a substantial research agenda to support the wider adoption of SHM and this is discussed.

APB Selectively Reduces Visual Responses in Goldfish to High Spatiotemporal Frequencies

1989 ◽  
Vol 2 (1) ◽  
pp. 15-18 ◽  
Author(s):  
Paul J. DeMarco ◽  
Jonathan D. Nussdorf ◽  
Douglas A. Brockman ◽  
Maureen K. Powers
Keyword(s):  
Spatial Frequency ◽  
Optokinetic Nystagmus ◽  
Temporal Frequency ◽  
High Spatial Frequency ◽  
Visual Responses ◽  
High Temporal Frequency ◽  
Frequency Responses ◽  
Intraocular Injection ◽  
Before And After ◽  
High Doses

AbstractVisual responses of goldfish to rotating square-wave gratings were recorded before and after intraocular injection of 2-amino-4-phosphonobutyric acid (APB). High doses of APB reduced the rate of optokinetic nystagmus (OKN) to a relatively high spatial frequency grating moving at a high temporal frequency. Responses to a low spatial frequency grating were not altered, nor were responses to the higher spatial frequency when it rotated slowly. The effects of APB were transient and lasted no longer than 3 d. We conclude that APB reduces OKN to high spatiotemporal frequencies in goldfish.

Orientation Channels in the Peripheral Visual Field

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 362-362
Author(s):  
R J Snowden
Keyword(s):  
Spatial Frequency ◽  
Peripheral Vision ◽  
Frequency Tuning ◽  
Temporal Frequency ◽  
High Spatial Frequency ◽  
Selective Adaptation ◽  
Orientation Tuning ◽  
Peripheral Retina ◽  
Foveal Vision ◽  
Analysis Techniques

Peripheral vision has been modelled as a coarser version of foveal vision. Thus visual behaviour elicited by, say, a 2 cycles deg−1 grating imaged foveally would be reproduced in the periphery by a lower spatial frequency (say 1 cycle deg−1). Tuning for orientation is broader at a low than high spatial frequency (Snowden, 1992 Vision Research32 1965 – 1974). Taken together this leads to the surprising prediction that, given a particular spatial frequency, tuning for orientation is narrower for peripheral viewing! In this study it has also been found that orientation tuning broadens with increasing temporal frequency, but the opposite relationship has been reported for peripheral vision (Sharpe and Tolhurst, 1973 Vision Research13 2103 – 2112). Orientation bandwidths were measured by the method of selective adaptation following the procedures and analysis techniques described by Snowden (1991 Proceedings of the Royal Society of London, Series B246 53 – 59). The results show that orientation bandwidths did indeed narrow as a stimulus was imaged more peripherally, so that its bandwidth in the peripheral retina could be half that of the fovea. However, at a greater eccentricity, bandwidths broadened once more. The results were not influenced by the contrast of the adaptation pattern eliminating visibility as a possible explanation. Increasing temporal frequency broadened orientation bandwidth at all eccentricities.

Pretectal Neurons Optimized for the Detection of Saccade-Like Movements of the Visual Image

2001 ◽  
Vol 85 (4) ◽  
pp. 1512-1521 ◽  
Author(s):  
N.S.C. Price ◽  
M. R. Ibbotson
Keyword(s):  
Spatial Frequency ◽  
Second Harmonic ◽  
Temporal Frequency ◽  
Receptive Fields ◽  
High Spatial Frequency ◽  
Sine Wave ◽  
Wide Field ◽  
Visual Response ◽  
High Contrast ◽  
Sine Wave Gratings

The visual response properties of nondirectional wide-field sensitive neurons in the wallaby pretectum are described. These neurons are called scintillation detectors (SD-neurons) because they respond vigorously to rapid, high contrast visual changes in any part of their receptive fields. SD-neurons are most densely located within a 1- to 2-mm radius from the nucleus of the optic tract, interspersed with direction-selective retinal slip cells. Receptive fields are monocular and cover large areas of the contralateral visual field (30–120°). Response sizes are equal for motion in all directions, and spontaneous activities are similar for all orientations of static sine-wave gratings. Response magnitude increases near linearly with increasing stimulus diameter and contrast. The mean response latency for wide-field, high-contrast motion stimulation was 43.4 ± 9.4 ms (mean ± SD, n = 28). The optimum visual stimuli for SD-neurons are wide-field, low spatial frequency (<0.2 cpd) scenes moving at high velocities (75–500°/s). These properties match the visual input during saccades, indicating optimal sensitivity to rapid eye movements. Cells respond to brightness increments and decrements, suggesting inputs from on and off channels. Stimulation with high-speed, low spatial frequency gratings produces oscillatory responses at the input temporal frequency. Conversely, high spatial frequency gratings give oscillations predominantly at the second harmonic of the temporal frequency. Contrast reversing sine-wave gratings elicit transient, phase-independent responses. These responses match the properties of Y retinal ganglion cells, suggesting that they provide inputs to SD-neurons. We discuss the possible role of SD-neurons in suppressing ocular following during saccades and in the blink or saccade-locked modulation of lateral geniculate nucleus activity to control retino-cortical information flow.

Role of the color-opponent and broad-band channels in vision

1990 ◽  
Vol 5 (04) ◽  
pp. 321-346 ◽  
Author(s):  
Peter H. Schiller ◽  
Nikos K. Logothetis ◽  
Eliot R. Charles
Keyword(s):  
Spatial Frequency ◽  
Temporal Frequency ◽  
Broad Band ◽  
High Spatial Frequency ◽  
Brightness Perception ◽  
Rods And Cones ◽  
Form Vision ◽  
Temporal Domain ◽  
Frequency Domains

AbstractThe functions of the primate color-opponent and broad-band channels were assessed by examining the visual capacities of rhesus monkeys following selective lesions of parvocellular and magnocellular lateral geniculate nucleus, which respectively relay these two channels to the cortex. Parvocellular lesions impaired color vision, high spatial-frequency form vision, and fine stereopsis. Magnocellular lesions impaired high temporal- frequency flicker and motion perception but produced no deficits in stereopsis. Low spatial-frequency form vision, stereopsis, and brightness perception were unaffected by either lesion. Much as the rods and cones of the retina can be thought of as extending the range of vision in the intensity domain, we propose that the color-opponent channel extends visual capacities in the wavelength and spatial-frequency domains whereas the broad-band channel extends them in the temporal domain.

Effect of repetitive visual stimuli on behaviour and plasma corticosterone of European starlings

2005 ◽  
Vol 55 (3) ◽  
pp. 245-258 ◽  
Author(s):  
◽  
◽  
◽  
Keyword(s):  
Spatial Frequency ◽  
High Frequency ◽  
Temporal Frequency ◽  
Low Frequency ◽  
High Spatial Frequency ◽  
Plasma Corticosterone ◽  
European Starlings ◽  
Fluorescent Lamps ◽  
Spatial Frequencies ◽  
Temporal And Spatial

AbstractFlickering light can cause adverse effects in some humans, as can rhythmic spatial patterns of particular frequencies. We investigated whether birds react to the temporal frequency of standard 100 Hz fluorescent lamps and the spatial frequency of the visual surround in the manner predicted by the human literature, by examining their effects on the preferences, behaviour and plasma corticosterone of European starlings (Sturnus vulgaris). We predicted that high frequency lighting (> 30 kHz) and a relatively low spatial frequency on the walls of their cages (0.1 cycle cm−1) would be less aversive than low frequency lighting (100 Hz) and a relatively high spatial frequency (2.5 cycle cm−1). Birds had strong preferences for both temporal and spatial frequencies. These preferences did not always fit with predictions, although there was evidence that 100 Hz was more stressful than 30 kHz lighting, as birds were less active and basal corticosterone levels were higher under 100 Hz lighting. Our chosen spatial frequencies had no overall significant effect on corticosterone levels. Although there are clearly effects of, and interactions between, the frequency of the light and the visual surround on the behaviour and physiology of birds, the pattern of results is not straightforward.

Predictions of U-Shaped Backward Pattern Masking from Considerations of the Spatio-Temporal Frequency Response

Perception ◽  
1975 ◽  
Vol 4 (3) ◽  
pp. 297-304 ◽  
Author(s):  
Bruno G Breitmeyer
Keyword(s):  
Spatial Frequency ◽  
Temporal Frequency ◽  
High Spatial Frequency ◽  
Stimulus Onset ◽  
Masking Effect ◽  
Time Interval ◽  
Sinusoidal Grating ◽  
Frequency Content ◽  
Pattern Masking ◽  
Spatio Temporal

The threshold detectability of a briefly presented target stimulus consisting of a vertical sinusoidal grating was affected not only by the spatial frequency content of an equally briefly presented, two-octave-wide masking noise, but also by the time interval separating the onsets of the target and its mask. Over a range of stimulus onset asynchronies, in which the mask onset either preceded, coincided with, or followed the target onset, a mask with a low spatial frequency content had its greatest masking effect on a high spatial frequency target grating when the mask followed the target by 120–180 ms. When the mask had a high spatial frequency content and the target was of low spatial frequency, or when the target was entered on the mask frequency band, optimal masking effects occurred when the onsets of the mask and target coincided. The results are discussed in relation to previous masking studies, particuarly those in which U-shaped backward pattern masking functions are obtained.

Organisation and Interrelationships of Functional Maps in Cat and Monkey Striate Cortex

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 356-356
Author(s):  
D Shoham ◽  
M Hübener ◽  
T Bonhoeffer ◽  
A Grinvald
Keyword(s):  
Spatial Frequency ◽  
Cytochrome Oxidase ◽  
Striate Cortex ◽  
Temporal Frequency ◽  
Activity Patterns ◽  
Ocular Dominance ◽  
High Spatial Frequency ◽  
Spatial Frequencies ◽  
Frequency Domains

Optical imaging of intrinsic signals allows mapping of the cortical functional architecture in vivo at high spatial resolution. The ability to image activity patterns evoked by many different stimuli in the same piece of cortex can provide information on the spatial relationships between different functional maps. Our findings on the organisation of multiple functional maps in cat and monkey striate cortex are reviewed. The main focus is on the recent finding in cat of two subsystems differing in their response to spatiotemporal aspects of the stimulus. We used grating stimuli of different spatial frequencies in an attempt to verify the existence of spatial frequency columns in cat area 17. Rather than observing a map of continuously changing spatial frequency across the cortical surface we found two distinct sets of domains, one preferring low and one preferring high spatial frequencies. By using different drift velocities we also found that the low-spatial-frequency domains preferred higher speeds than the high-spatial-frequency domains. Comparison of these spatiotemporal frequency domains with the cytochrome oxidase staining pattern revealed that the cytochrome oxidase blobs in cat striate cortex coincide with domains devoted to the processing of the low-spatial-frequency and high-temporal-frequency contents of the visual scene. Together with recent anatomical results these data suggest that spatiotemporal frequency domains are the manifestation of parallel streams in cat visual cortex with distinct patterns of thalamic inputs and extrastriate projections. In the same experiments we also imaged the orientation preference and ocular dominance maps. We investigated the relationships between these three columnar systems, and compared them to an earlier study of orientation, ocular dominance, and blobs in macaque striate cortex. We found systematic relationships between the three systems. While some of these relationships were much weaker than those found in monkey, the organisational principles are similar.

Evoked responses to sinusoidal gratings in the pigeon optic tectum

1989 ◽  
Vol 2 (2) ◽  
pp. 137-145 ◽  
Author(s):  
V. Porciatti ◽  
R. Alesci ◽  
P. Bagnoli
Keyword(s):  
Steady State ◽  
Spatial Frequency ◽  
Contrast Sensitivity ◽  
Second Harmonic ◽  
Temporal Frequency ◽  
Harmonic Component ◽  
High Spatial Frequency ◽  
Slow Potentials ◽  
Sinusoidal Gratings ◽  
Band Pass

AbstractTectal evoked potentials (TEPs) in response to sinusoidal gratings of different contrast, spatial and temporal frequency have been recorded from the tectal surface of the pigeon. Responses have been digitally filtered in order to isolate transient oscillatory (fast) potentials (50–150 Hz), transient slow potentials (1–50 Hz), and the steady-state second-harmonic component (16.6 Hz). Transient slow potentials, as well as the steady-state second-harmonic component, are band-pass spatially tuned with a maximum at 0.5 cycles/deg and attenuation at higher and lower spatial frequencies. The high spatial frequency cutoff is 4–5 cycles/deg. Both transient slow potentials and the steady-state second-harmonic component increase in amplitude as a function of log contrast and saturate at about 20% contrast. The contrast sensitivity, as determined by extrapolating TEP amplitude to 0 V is 0.1–0.2%. These characteristics of spatial-frequency selectivity and contrast sensitivity are similar to those reported for single tectal cells. Unlike slow potentials, oscillatory potentials are not band-pass spatially tuned. In addition, their contrast response function does not saturate at moderate contrast. These differences suggest that tectal evoked slow and fast potentials reflect the activity of different neuronal mechanisms.

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