Parallel Independent Encoding of Orientation, Spatial Frequency, and Contrast

Perception ◽  
1995 ◽  
Vol 24 (5) ◽  
pp. 491-499 ◽  
Author(s):  
Alex Vincent ◽  
David Regan
Keyword(s):  
Spatial Frequency ◽  
Random Order ◽  
Frequency Discrimination ◽  
Discrimination Threshold ◽  
Orientation Discrimination ◽  
Stimulus Set ◽  
Response Set ◽  
Opponent Processing ◽  
The Mean ◽  
Contrast Discrimination

Subjects were presented with a set of 216 test gratings in random order. Each had a different combination of orientation, spatial frequency, and contrast. For each test grating, subjects were instructed to judge whether or not orientation was clockwise of the mean of the stimulus set, whether or not spatial frequency was higher than the mean of the stimulus set, and whether or not contrast was higher than the mean of the stimulus set. Each of the three sets of button presses was analyzed with respect to each of the three parameters, giving nine psychometric functions from one response set. It is concluded that, for gratings of high visibility, changes of orientation, spatial frequency, and contrast are encoded independently and in parallel, at least for small changes in these three visual parameters. In another experiment only one of the three parameters was varied at a time. Neither orientation-discrimination threshold, nor spatial-frequency-discrimination threshold, nor contrast-discrimination threshold was appreciably, if at all, lower than when all three parameters were varied simultaneously. It is concluded that interactions between the processing of small changes in orientation, spatial frequency, and contrast are negligible when all three are processed simultaneously. It is proposed that trial-to-trial variations of orientation, spatial frequency, and contrast are unconfounded by opponent processing within a population of neurons, each of which confounds the three variables.

The effects of contrast on visual orientation and spatial frequency discrimination: a comparison of single cells and behavior

1987 ◽  
Vol 57 (3) ◽  
pp. 773-786 ◽  
Author(s):  
B. C. Skottun ◽  
A. Bradley ◽  
G. Sclar ◽  
I. Ohzawa ◽  
R. D. Freeman
Keyword(s):  
Spatial Frequency ◽  
Striate Cortex ◽  
Frequency Tuning ◽  
Single Cells ◽  
Frequency Discrimination ◽  
Frequency Selectivity ◽  
Response Amplitude ◽  
Visual Orientation ◽  
Characteristic Analysis ◽  
Response Variance

We have compared the effects of contrast on human psychophysical orientation and spatial frequency discrimination thresholds and on the responses of individual neurons in the cat's striate cortex. Contrast has similar effects on orientation and spatial frequency discrimination: as contrast is increased above detection threshold, orientation and spatial frequency discrimination performance improves but reaches maximum levels at quite low contrasts. Further increases in contrast produce no further improvements in discrimination. We measured the effects of contrast on response amplitude, orientation and spatial frequency selectivity, and response variance of neurons in the cat's striate cortex. Orientation and spatial frequency selectivity vary little with contrast. Also, the ratio of response variance to response mean is unaffected by contrast. Although, in many cells, response amplitude increases approximately linearly with log contrast over most of the visible range, some cells show complete or partial saturation of response amplitude at medium contrasts. Therefore, some cells show a clear increase in slope of the orientation and spatial frequency tuning functions with increasing contrast, whereas in others the slopes reach maximum values at medium contrasts. Using receiver operating characteristic analysis, we estimated the minimum orientation and spatial frequency differences that can be signaled reliably as a response change by an individual cell. This analysis shows that, on average, the discrimination of orientation or spatial frequency improves with contrast at low contrasts more than at higher contrasts. Using the optimal stimulus for each cell, we estimated the contrast threshold of 48 neurons. Most cells had contrast thresholds below 5%. Thresholds were only slightly higher for nonoptimal stimuli. Therefore, increasing the contrast of sinusoidal gratings above approximately 10% will not produce large increases in the number of responding cells. The observed effects of contrast on the response characteristics of nonsaturating cortical cells do not appear consistent with the psychophysical results. Cells that reach their maximum response at low-to-medium contrasts may account for the contrast independence of psychophysical orientation and spatial frequency discrimination thresholds at medium and high contrasts.

Effect of Realistic Test Conditions on Spectral and Temporal Processing in Normal-Hearing Listeners

2021 ◽  
Vol 30 (1) ◽  
pp. 160-169
Author(s):  
Yang-Soo Yoon ◽  
Callie Michelle Boren ◽  
Brianna Diaz
Keyword(s):  
Temporal Processing ◽  
Detection Threshold ◽  
Frequency Discrimination ◽  
Normal Hearing ◽  
Discrimination Threshold ◽  
Test Environment ◽  
Test Conditions ◽  
Significant Difference ◽  
Test Order ◽  
Pure Tones

Purpose To measure the effect of testing conditions (in the soundproof booth vs. quiet room), test order, and number of test sessions on spectral and temporal processing in normal-hearing (NH) listeners. Method Thirty-two adult NH listeners participated in the three experiments. For all three experiments, the stimuli were presented to the left ear at the subjects' most comfortable level through headphones. All tests were administered in an adaptive three-alternative forced-choice paradigm. Experiment 1 was designed to compare the effect of soundproof booth and quiet room test conditions on amplitude modulation detection threshold and modulation frequency discrimination threshold with each of the five modulation frequencies. Experiment 2 was designed to compare the effect of two test orders on the frequency discrimination thresholds under the quiet room test conditions. The thresholds were first measured in the ascending and descending order of four pure tones, and then with counterbalanced order. For Experiment 3, the amplitude discrimination threshold under the quiet room testing condition was assessed 3 times to determine the effect of the number of test sessions. Then the thresholds were compared over the sessions. Results Results showed no significant effect of test environment. The test order is an important variable for frequency discrimination, particularly between piano tunes and pure tones. Results also show no significant difference across test sessions. Conclusions These results suggest that a controlled test environment may not be required in spectral and temporal assessment for NH listeners. Under the quiet test environment, a single outcome measure is sufficient, but test orders should be counterbalanced.

scholarly journals The influence of kihap on the impact of Dolio-chagui kicks in taekwondo

2014 ◽  
Vol 20 (1) ◽  
pp. 54-57
Author(s):  
Rodrigo Dias Martins ◽  
Debora Cantergi ◽  
Jefferson Fagundes Loss
Keyword(s):  
Martial Arts ◽  
Random Order ◽  
T Test ◽  
Real Effect ◽  
The Real ◽  
The Mean ◽  
The Difference ◽  
The Impact

The kihapis a technique used in several oriental martial arts. It is a yell used by practitioners with the ex pectation of enhancing the force of a hit. However, the real effect of using the kihapis unknown. Therefore, this study aims to compare the peak of acceleration of the Dolio-chaguikick in taekwondo performed with and without the use of kihap. Twenty two experienced taekwondo practitioners performed 30 kicks each against a punching bag, alternating in random order with and without kihap, while the acceleration of the punching bag was measured. A t-test was used to compare the difference between the mean acceleration in both conditions. Higher values were found with the use of kihap(7.8 ± 2.8 g) than without the use of kihap(7.1 ± 2.4 g), p< 0.01, r= 0.57. The results indicate that kihapenhances the impact of the kick.

Visual Field Differences in Spatial Frequency Discrimination

1999 ◽  
Vol 41 (3) ◽  
pp. 381-389 ◽  
Author(s):  
Christopher L. Niebauer ◽  
Stephen D. Christman
Keyword(s):  
Visual Field ◽  
Spatial Frequency ◽  
Frequency Discrimination

Comparison at a Distance

Perception ◽  
10.1068/p3393 ◽  
2003 ◽  
Vol 32 (4) ◽  
pp. 395-414 ◽  
Author(s):  
Marina V Danilova ◽  
John D Mollon
Keyword(s):  
Visual Field ◽  
Spatial Frequency ◽  
Visual System ◽  
Spatial Separation ◽  
Orientation Discrimination ◽  
Human Observer ◽  
Systematic Effect ◽  
Trained Subjects ◽  
Stimulus Attribute ◽  
The Subject

The visual system is known to contain hard-wired mechanisms that compare the values of a given stimulus attribute at adjacent positions in the visual field; but how are comparisons performed when the stimuli are not adjacent? We ask empirically how well a human observer can compare two stimuli that are separated in the visual field. For the stimulus attributes of spatial frequency, contrast, and orientation, we have measured discrimination thresholds as a function of the spatial separation of the discriminanda. The three attributes were studied in separate experiments, but in all cases the target stimuli were briefly presented Gabor patches. The Gabor patches lay on an imaginary circle, which was centred on the fixation point and had a radius of 5 deg of visual angle. Our psychophysical procedures were designed to ensure that the subject actively compared the two stimuli on each presentation, rather than referring just one stimulus to a stored template or criterion. For the cases of spatial frequency and contrast, there was no systematic effect of spatial separation up to 10 deg. We conclude that the subject's judgment does not depend on discontinuity detectors in the early visual system but on more central codes that represent the two stimuli individually. In the case of orientation discrimination, two naïve subjects performed as in the cases of spatial frequency and contrast; but two highly trained subjects showed a systematic increase of threshold with spatial separation, suggesting that they were exploiting a distal mechanism designed to detect the parallelism or non-parallelism of contours.

Measurement of tear production and establishment of reference values in guinea pigs (Cavia porcellus) using a modified Schirmer tear test

2019 ◽  
Vol 186 (10) ◽  
pp. 321-321
Author(s):  
Anna Linda Nogradi ◽  
Zsolt Szentgáli ◽  
Márton Battay ◽  
Iain Cope ◽  
János Gál ◽  
...  
Keyword(s):  
Reference Values ◽  
Guinea Pigs ◽  
Small Volume ◽  
Clinical Signs ◽  
Random Order ◽  
Cavia Porcellus ◽  
Tear Production ◽  
Schirmer Tear Test ◽  
The Mean ◽  
One Year

BackgroundPast studies have shown that 5-mm Schirmer tear tests (STTs) are difficult to interpret in guinea pigs. Modified 2.5-mm STT strips are more adequate for measuring the small volume of tear production in these animals. The aim of this study was to establish reference values for the modified 2.5-mm STT strips.MethodsModified STT measurements were performed in random order in both eyes of 50 guinea pig patients. The wetting of the strip was noted at 30 seconds and at 1 minute.ResultsThe mean±sd STT values for both eyes were 7.58±3.19 mm at 30 seconds and 10.42±3.92 mm at 60 seconds. The median was 8 mm at 30 seconds and 10 mm at 60 seconds for both eyes. Animals under one year of age had lower STT values. STT values at 30 and 60 seconds can both be used. Both eyes should be measured when possible.ConclusionThe authors recommend values above 8 mm at 30 seconds and 10 mm at 60 seconds to be considered normal when using a 2.5-mm STT strip. There are ambiguous areas at 5–8 mm and 6–10 mm. If in these ranges the results should be combined with clinical signs and judgement.

Sign in / Sign up

Export Citation Format

Share Document