Discrimination between Plaids: Do Oriented Filters Combine Dichoptically?

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 299-299
Author(s):  
L A Olzak ◽  
R L Wong
Keyword(s):  
Spatial Frequency ◽  
Opposite Sign ◽  
Pattern Discrimination ◽  
The Other ◽  
Frequency Content ◽  
Low Contrast ◽  
Combination Process ◽  
Test Conditions ◽  
Sinusoidal Gratings ◽  
Confidence Scale

Two oblique gratings combine perceptually to form a chequerboard appearance under monoptic presentation but not under dichoptic presentation (Georgeson and Meese, 1996 Perception25 Supplement, 121), suggesting an early combination process. Combining processes that operate over orthogonal orientations are also observed in complex pattern discrimination tasks (Olzak and Thomas, 1991 Vision Research31 1885 – 1898). We ask here whether the interactions observed in discrimination tasks occur before or beyond the site of binocular interaction. Observers discriminated between two patterns that differed slightly in their spatial-frequency content. On each trial, one of the two patterns was presented. Observers judged which stimulus had been presented on a 1 – 6 confidence scale. In control conditions, the stimuli were single sinusoidal gratings near 3 cycles deg−1, and were always presented monoptically. In test conditions, a second component was added to the first in each stimulus. The second component was either presented to the same eye as the first component (monoptic presentation), or to the other eye (dichoptic presentation). The second component was either a mask of exactly 3 cycles deg−1, or varied to give a second cue to discrimination. Second cues either varied with the first (both components lower frequency or both higher) or varied in opposite sign (high with low). Rivalry was eliminated by using low contrast (10 × threshold) and small (1.2 deg) patterns. Our results suggest that the combination processes we observe occur beyond the site of binocular combination and differ from those mediating the percept.

Temporal-Discontinuity Detection with Contrast-Modulated Gratings

Perception ◽  
1995 ◽  
Vol 24 (11) ◽  
pp. 1257-1264
Author(s):  
Shigeru Ichihara ◽  
Kenji Susami
Keyword(s):  
Spatial Frequency ◽  
Modulation Frequency ◽  
Sinusoidal Grating ◽  
Local Contrast ◽  
Staircase Method ◽  
Low Contrast ◽  
Discontinuity Detection ◽  
Temporal Discontinuity ◽  
Sinusoidal Gratings ◽  
The Subject

Three experiments on temporal-discontinuity detection were carried out. In experiment 1, temporal-discontinuity thresholds were measured for sinusoidal gratings by the use of the double-staircase method. A sinusoidal grating was presented twice successively. The subject judged whether or not an interval was present. The temporal-discontinuity threshold increased as the spatial frequency of the grating increased, but decreased as the contrast of the grating increased. In experiment 2, contrast-modulated gratings were used instead of the sinusoidal grating. The temporal-discontinuity threshold increased as the carrier frequency increased, and the threshold for each contrast-modulated grating was similar to that for the no-modulation (sinusoidal) grating whose contrast was the same as the maximum local contrast of the contrast-modulated grating. In experiment 3, temporal-discontinuity thresholds were measured for low-contrast (3%) sinusoidal gratings. The thresholds were very low, even for such low-contrast gratings. These results suggest that the low-spatial-frequency channels are not involved in detecting the modulation frequency of the contrast-modulated grating. Rather, the local contrast seems to be the determinant of the detection of the contrast-modulated grating itself.

The Effect of Spatial Frequency and Contrast on Visual Persistence

Perception ◽  
1979 ◽  
Vol 8 (5) ◽  
pp. 529-539 ◽  
Author(s):  
Alison Bowling ◽  
William Lovegrove ◽  
Barry Mapperson
Keyword(s):  
Spatial Frequency ◽  
Visual Persistence ◽  
Published Data ◽  
High Contrast ◽  
Low Contrast ◽  
Spatial Frequencies ◽  
Sinusoidal Gratings

The visual persistence of sinusoidal gratings of varying spatial frequency and contrast was measured. It was found that the persistence of low-contrast gratings was longer than that of high-contrast stimuli for all spatial frequencies investigated. At higher contrast levels of 1 and 4 cycles deg−1 gratings, a tendency for persistence to be independent of contrast was observed. For 12 cycles deg−1 gratings, however, persistence continued to decrease with increasing contrast. These results are compared with recently published data on other temporal responses, and are discussed in terms of the different properties of sustained and transient channels.

Contrast adaptation in retinal and cortical evoked potentials: No adaptation to low spatial frequencies

2002 ◽  
Vol 19 (5) ◽  
pp. 645-650 ◽  
Author(s):  
THOMAS STEPHAN HEINRICH ◽  
MICHAEL BACH
Keyword(s):  
Spatial Frequency ◽  
Visual Evoked Potential ◽  
Evoked Potential ◽  
Opposite Effect ◽  
Pattern Electroretinogram ◽  
Low Contrast ◽  
Contrast Adaptation ◽  
Spatial Frequencies ◽  
Sinusoidal Gratings ◽  
Cross Adaptation

Contrast adaptation occurs in both the retina and the cortex. Defining its spatial dependence is crucial for understanding its potential roles. We thus asked to what degree contrast adaptation depends on spatial frequency, including cross-adaptation. Measuring the pattern electroretinogram (PERG) and the visual evoked potential (VEP) allowed separating retinal and cortical contributions. In ten subjects we recorded simultaneous PERGs and VEPs. Test stimuli were sinusoidal gratings of 98% contrast with spatial frequencies of 0.5 or 5.0 cpd, phase reversing at 17 reversals/s. Adaptation was controlled by prolonged presentation of these test stimuli or homogenous gray fields of the same luminance. When adaptation and test frequency were identical, we observed significant contrast adaptation only at 5 cpd: an amplitude reduction in the PERG (−22%) and VEP (−58%), and an effective reduction of latency in the PERG (−0.95 ms). When adapting at 5 cpd and testing at 0.5 cpd, the opposite effect was observed: enhancement of VEP amplitude by +26% and increase in effective PERG latency by +1.35 ms. When adapting at 0.5 cpd and testing at 5 cpd, there was no significant amplitude change in PERG and VEP, but a small effective PERG latency increase of +0.65 ms. The 0.5-cpd channel was not adapted by spatial frequencies of 0.5 cpd. The adaptability of the 5-cpd channel may mediate improved detail recognition after prolonged blur. The existence of both adaptable and nonadaptable mechanisms in the retina allows for the possibility that by comparing the adaptational state of spatial-frequency channels the retina can discern between overall low contrast and defocus in emmetropization control.

Up-Down Asymmetries in Speed Perception

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 6-6 ◽  
Author(s):  
P Thompson ◽  
L S Stone
Keyword(s):  
Spatial Frequency ◽  
Central Point ◽  
The Other ◽  
Upward Motion ◽  
Optokinetic Response ◽  
Downward Motion ◽  
Preliminary Results ◽  
Sinusoidal Gratings ◽  
Speed Perception

We compared speed matches for pairs of stimuli that moved in opposite directions (upward and downward). Stimuli were elliptical patches (2 deg horizontally by 1 deg vertically) of horizontal sinusoidal gratings of spatial frequency 2 cycles deg−1. Two sequential 380 ms foveal presentations were compared. One of each pair of gratings (the standard) moved at 4 Hz (2 deg s−1), the other (the test) moved at a rate determined by a simple up - down staircase. The point of subjectively equal speed was calculated from the average of the last eight reversals. The task was to fixate a central point and to determine which one of the pair appeared to move faster. Eight of ten observers perceived the upward drifting grating as moving faster than a grating moving downward but otherwise identical. On average (N = 10), when the standard moved downward, it was matched by a test moving upward at 94.7± 1.7(SE)% of the standard speed, and when the standard moved upward it was matched by a test moving downward at 105.1± 2.3(SE)% of the standard speed. On extending this paradigm over a range of spatial (1.5 to 13.5 cycles deg−1) and temporal (1.5 to 13.5 Hz) frequencies, preliminary results (N = 4) suggest that, under the conditions of our experiment, upward motion is seen as faster than downward motion for speeds greater than ∼1 deg s−1, but the effect appears to reverse at speeds below ∼1 deg s−1 with downward motion perceived as faster. Given that an up - down asymmetry has been observed by other investigators for the optokinetic response, both perceptual and oculomotor contributions to this phenomenon deserve exploration.

Nonlinearities of Near-Threshold Contrast Transduction

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 208-208
Author(s):  
L L Kontsevich ◽  
C W Tyler
Keyword(s):  
Spatial Frequency ◽  
Psychometric Function ◽  
High Frequency ◽  
Opposite Sign ◽  
The Other ◽  
Threshold Behaviour ◽  
Threshold Elevation ◽  
Difference Of Gaussians ◽  
Local Difference ◽  
Near Threshold

The existence of analytic threshold nonlinearities was probed with a variety of local and extended stimuli. Incremental thresholds were measured by the 2AFC procedure for same-sign and opposite-sign stationary pedestals. In contrast to the dipper effect for same-sign pedestals, subthreshold bumper effects were observed of threshold elevation (up to a factor of 4 in some conditions). The results for local difference of Gaussians (DoG) and 10 cycles deg−1 Gabors were consistent with accurate hard-threshold behaviour. The results for negative DoG (whose increment corresponds to the darkening of the central spot) and 2 cycles deg−1 Gabor profiles revealed a quadratic nonlinearity for one observer and linear transduction for the other. These results repudiate the uncertainty explanation for the steep psychometric function near threshold, and suggest that there are two different hard-wired nonlinearities: one for luminance increments and another for luminance decrements. According to our analysis, in low-spatial-frequency gratings, a contrast change is detected within those bars that become darker; in high-frequency gratings, transient changes are detected in the bars that become brighter.

Spatial Filter Combination in Human Pattern Vision: Channel Interactions Revealed by Adaptation

Perception ◽  
1996 ◽  
Vol 25 (3) ◽  
pp. 255-277 ◽  
Author(s):  
Tim S Meese ◽  
Mark A Georgeson
Keyword(s):  
Spatial Frequency ◽  
Spatial Filter ◽  
Selective Adaptation ◽  
Compound Structure ◽  
Spatial Filters ◽  
Linear Filters ◽  
Combination Process ◽  
Sinusoidal Gratings ◽  
Channel Interactions ◽  
Conventional Models

Above threshold, two superimposed sinusoidal gratings of the same spatial frequency (eg 1 cycle deg−1), of equal moderate contrast (eg C1 = C2 = 6%), and with orientations of ±45°, usually look like a compound structure containing vertical and horizontal edges (ie a blurred checkerboard). These feature orientations are very different from the dominant filter orientations in a wavelet-type (eg simple-cell) transform of the stimulus, and so present a serious challenge to conventional models of orientation coding based on labelled linear filters. Previous experiments on perceived structure in static plaids have led to the view that the outputs of tuned spatial filters are combined in a stimulus-dependent way, before features such as edges are extracted. Here an adaptation paradigm was used to investigate the cross-channel interactions that appear to underlie the spatial-filter-combination process. Reported are two aftereffects of selective adaptation: (i) adaptation to a 1 cycle deg−1 plaid whose component orientations are intermediate to those in a 1 cycle deg−1 test plaid ‘breaks’ perceptual combination of the components in the test plaid; (ii) adapting to a 3 cycles deg−1 plaid whose component orientations match those in a 1 cycle deg−1 test plaid facilitates perceptual combination of the components in the test plaid. The results are taken as evidence that spatial channels remote from those most responsive to a test plaid play a crucial role in determining whether the test plaid segments or coheres perceptually.

On the Variety of Percepts Associated with Dichoptic Viewing of Dissimilar Monocular Stimuli

Perception ◽  
1992 ◽  
Vol 21 (1) ◽  
pp. 47-62 ◽  
Author(s):  
Yuede Yang ◽  
David Rose ◽  
Randolph Blake
Keyword(s):  
Spatial Frequency ◽  
High Spatial Frequency ◽  
Frequency Difference ◽  
The Other ◽  
Frequency Content ◽  
High Transparency ◽  
Frequency Information ◽  
Dichoptic Viewing ◽  
Spatial Frequencies ◽  
Over Time

Upon dichoptic viewing of dissimilar patterns, several distinct perceptual states may be experienced over time. One state is exclusive monocular dominance, wherein the view of only one eye is seen in its entirety for some period of time. Another state is characterized by a mosaic-like collage consisting of portions of the view of each eye. Two other states involve simultaneous perception of both monocular images in their entirety. In one of these states, the two monocular stimuli appear to be superimposed without depth (a phenomenon we shall term ‘superimposition’). In the other state, the two monocular stimuli appear to be located at different depth planes (which we shall term ‘transparency’). This paper documents the stimulus conditions favoring these various perceptual states. Exclusive monocular dominance occurs most often when the two eyes view dissimilar patterns with the same spatial-frequency content, particularly when both patterns consist of low spatial frequencies. Superimposition also occurs most often when the two eyes view the same spatial frequencies, but predominantly when those spatial frequencies are high. Transparency is favored when the spatial-frequency difference between the eyes is great, particularly when the view of one eye consists of high spatial-frequency information.

Measurement of Noise inside the Compartment and Vibration on both Sides of Elastomeric Powertrain Mounts of Passenger Car

2013 ◽  
Vol 471 ◽  
pp. 59-63
Author(s):  
Mohd Noor Arib Rejab ◽  
Roslan Abd Rahman ◽  
Raja Ishak Raja Hamzah ◽  
Jawaid Iqbal Inayat Hussain ◽  
Nazirah Ahmad ◽  
...  
Keyword(s):  
Fast Response ◽  
Sound Level ◽  
Measurement Noise ◽  
The Other ◽  
Vibration Level ◽  
Test Conditions ◽  
Exhaust Noise ◽  
Run Up ◽  
Level Meter ◽  
High Level

This paper presents an evaluation on elastomeric mount used to isolate vibration from powertrain to chassis or structure vehicle. The assessments started with measurement of noise inside compartment, and exhaust noise. This is followed by the measurement of vibration on both sides of elastomeric mounts. The noise in the compartment and exhaust noise is measured according to BS 6086: 1981 and BS ISO 5130: 2007. The noise in the compartment and vibration is tested in three conditions. Firstly, engine is run-up with load (driving at second gear); secondly, without load; and thirdly, without load but hanging. A microphone is fixed at the ear of the mannequin. The fast response and A weighting sound level meter were used for measurement noise in the compartment and exhaust noise. The vibration is measured in terms of acceleration on both sides of each elastomeric powertrain mounts. Two accelerometer transducers are fixed on both sides of powertrain elastomeric mounts. One side was identified as a source of vibration and the other as receiver of vibrations. The results showed that the pattern of overall vibration level on source and receiver increased from 1050 RPM (idling) to 4000 RPM on all test conditions. Vibration transmitted to chassis or receiver structure was analyzed using transmissibility concept. By evaluating test condition of engine run-up without load, informed that the front and rear mounts showed a high level transmissibility contributing to structure-borne noise.

Adaptation in single units in visual cortex: The tuning of aftereffects in the spatial domain

1989 ◽  
Vol 2 (6) ◽  
pp. 593-607 ◽  
Author(s):  
A. B. Saul ◽  
M. S. Cynader
Keyword(s):  
Spatial Frequency ◽  
Cortical Neurons ◽  
Frequency Tuning ◽  
Cortical Cell ◽  
Selective Adaptation ◽  
Single Units ◽  
Spatial Frequency Tuning ◽  
Sinusoidal Gratings ◽  
A Cell ◽  
Drift Direction

AbstractCat striate cortical neurons were investigated using a new method of studying adaptation aftereffects. Stimuli were sinusoidal gratings of variable contrast, spatial frequency, and drift direction and rate. A series of alternating adapting and test trials was presented while recording from single units. Control trials were completely integrated with the adapted trials in these experiments.Every cortical cell tested showed selective adaptation aftereffects. Adapting at suprathreshold contrasts invariably reduced contrast sensitivity. Significant aftereffects could be observed even when adapting at low contrasts.The spatial-frequency tuning of aftereffects varied from cell to cell. Adapting at a given spatial frequency generally resulted in a broad response reduction at test frequencies above and below the adapting frequency. Many cells lost responses predominantly at frequencies lower than the adapting frequency.The tuning of aftereffects varied with the adapting frequency. In particular, the strongest aftereffects occurred near the adapting frequency. Adapting at frequencies just above the optimum for a cell often altered the spatial-frequency tuning by shifting the peak toward lower frequencies. The fact that the tuning of aftereffects did not simply match the tuning of the cell, but depended on the adapting stimulus, implies that extrinsic mechanisms are involved in adaptation effects.

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