Biomedical subjects

S M Wuerger

Publications and source records attributed to S M Wuerger.

8 recordsLinked to original sources

PubMed2004

Catching audiovisual mice: predicting the arrival time of auditory-visual motion signals.

We investigated the extent to which auditory and visual motion signals are combined when observers are asked to predict the location of a virtually moving target. In Condition 1, the unimodal and bimodal signals were noisy, but the target object was continuously visible and audible; in Condition 2, the virtually moving object was hidden (invisible and inaudible) for a short period prior to its arrival at the target location. Our main finding was that the facilitation due to simultaneous visual and auditory input is very different for the two conditions. When the target is continuously visible and audible (Condition 1), the bimodal performance is twice as good as the unimodal performances, thus suggesting a very effective integration mechanism. On the other hand, if the object is hidden for a short period (Condition 2) and the task therefore requires the extrapolation of motion speed over a temporal and spatial period, the facilitation due to both sensory inputs is almost absent, and the bimodal performance is limited by the visual performance.

Adolescent↗

PubMed2003

The integration of auditory and visual motion signals at threshold.

To interpret our environment, we integrate information from all our senses. For moving objects, auditory and visual motion signals are correlated and provide information about the speed and the direction of the moving object. We investigated at what level the auditory and the visual modalities interact and whether the human brain integrates only motion signals that are ecologically valid. We found that the sensitivity for identifying motion was improved when motion signals were provided in both modalities. This improvement in sensitivity can be explained by probability summation. That is, auditory and visual stimuli are combined at a decision level, after the stimuli have been processed independently in the auditory and the visual pathways. Furthermore, this integration is direction blind and is not restricted to ecologically valid motion signals.

Attention↗

PubMed2001

Cross-modal integration of auditory and visual motion signals.

Real-world moving objects are usually defined by correlated information in multiple sensory modalities such as vision and hearing. The aim of our study was to assess whether simultaneous auditory supra-threshold motion introduces a bias or affects the sensitivity in a visual motion detection task. We demonstrate a bias in the perceived direction of visual motion that is consistent with the direction of the auditory motion (audio-visual motion capture). This bias effect is robust and occurs even if the auditory and visual motion signals come from different locations or move at different speeds. We also show that visual motion detection thresholds are higher for consistent auditory motion than for inconsistent motion, provided the stimuli move at the same speed and are co-localised.

Acoustic Stimulation↗

PubMed2001

Blur tolerance for luminance and chromatic stimuli.

We investigated the blur tolerance of human observers for stimuli modulated along the isoluminant red-green, the isoluminant yellow-blue, and the luminance (black-white) direction in color space. We report the following results: (i) Blur difference thresholds for red-green and luminance stimuli (of equal cone contrast) are very similar and as low as 0.5 min of visual angle; for yellow-blue the lowest blur thresholds are much higher (1.5 min of visual angle). (ii) The smallest blur thresholds are found for slightly blurred square waves (reference blur of 1 arc min) and not for sharp edges. (iii) Blur thresholds for red-green and black-white follow a Weber law for reference (pedestal) blurs greater than the optimum blur. (iv) Using the model proposed by Watt and Morgan [Vision Res. 24, 1387 (1984)] we estimated the internal blur of the visual system for the black-white and the red-green color directions and arrived at the following estimates: 1.2 arc min for black-white stimuli at 10% contrast and 0.9 arc min for red-green stimuli at 10% cone contrast. Blur tolerance for yellow-blue is independent of external blur and cannot be predicted by the model. (v) The contrast dependence of blur sensitivity is similar for red-green and luminance modulations (slopes of -0.15 and -0.16 in log-log coordinates, respectively) and slightly stronger for yellow-blue (slope = -0.75). Blur discrimination thresholds are not predicted by the contrast sensitivity function of the visual system. Our findings are useful for predicting blur tolerance for complex images and provide a spatial frequency cutoff point when Gaussian low-pass filters are used for noise removal in colored images. They are also useful as a baseline for the study of visual disorders such as amblyopia.

Color↗

PubMed2000

The spatio-chromatic sensitivity of the human visual system.

The response of the human visual system depends on a multitude of image features, such as the wavelength (colour) of the visual stimulus and its spatial frequency content. Hence we need to take into account the spatial and chromatic sensitivity as well as spatio-chromatic interactions to properly characterize visual sensitivity. In this paper we report two experiments that further characterize the spatio-chromatic sensitivity of the human visual system for stationary stimuli, namely the detection of small visual orientation differences and the detection of blur. In both cases we find that the visual system is equally sensitive to red-green and to black-white modulations for a wide range of spatial parameters. Furthermore, the contrast dependence for red green and black white modulations is identical, suggesting that the same mechanism mediates both types of stimulus. Our results are in accordance with the hypothesis that both tasks are mediated by the parvocellular as opposed to the magnocellular pathway.

Color Perception↗

PubMed1996

Color appearance changes resulting from iso-luminant chromatic adaptation.

By means of asymmetric color matching, the effects of steady-state chromatic adaptation on the color appearance of briefly presented chromatic flashes were investigated. The adapting and test lights were of equal luminance (35 cd/m2) and differed from the standard grey adapting light either along the L-2M (red and green), or along the S-(L+M) (yellow and violet) line. The red (green) adapting light results in 6% positive (negative) L cone contrast and 11% negative (positive) M cone contrast with respect to the grey adapting light. The violet (yellowish) adapting light yields a positive (negative) S cone contrast of 50% relative to the standard adapting light. The main findings are: (i) iso-luminant adapting lights that differ only in their L-2M signal (red and green) resulted in asymmetric matches that differ mainly in the L-2M coordinate; (ii) iso-luminant adapting lights that differ in their S cone excitation only (yellow and violet) result in asymmetric matches that differ mainly in their S cone coordinate; (iii) the largest difference between test and match coordinates is found in the S cone signal for violet adaptation; (iv) the luminance differences of the asymmetric matches are within 1% of the mean luminance and are mostly non-systematic; (v) adaptation to iso-luminant red and green lights yields adaptational changes mainly in the L cones and not in the M cones; (vi) substantial quantitative deviations from a von Kries law are observed for L cone signals for red and green adaptation and for S cone decrements under yellow adaptation; (vii) S cone-isolating adapting lights results in small additive shifts in the S cone matches; adapting lights differing only in the L and M cone signal from the standard grey adapting light yield additive shifts only in the L and M cone matches.

Adaptation, Ocular↗

PubMed1995

Proximity judgments in color space: tests of a Euclidean color geometry.

We describe two tests of the hypothesis that human judgments of the proximity of colors are consistent with a Euclidean geometry on color matching space. The first test uses proximity judgments to measure the angle between any two intersecting lines in color space. Pairwise estimates of the angles between three lines in a plane were made in order to test the additivity of angles. Three different color proximity tasks were considered. Additivity failed for each of the three proximity tasks. Secondly, we tested a prediction concerning the growth of the variability of judgments of similarity with the distance between the test and reference stimuli. The Euclidean hypothesis was also rejected by this test. The results concerning the growth of variability are consistent with the assumption that observers use a city-block metric when judging the proximity of colored lights.

Color Perception↗

PubMed1993

Role of chromatic and luminance contrast in inferring structure from motion.

We measured the ability to infer structure from motion (SFM) in several directions in three-dimensional color space. Only motion cues are useful to subjects in performing this three-dimensional shape-identification task. We report the following results: (1) SFM performance is at chance for equiluminant stimuli that isolate short-wavelength-sensitive cones. Hence the short-wavelength-sensitive-cone input to SFM is negligible. (2) SFM performance increases with the magnitude of delta L - delta M signal when delta L + delta M = 0 (i.e., only chromatic and no luminance contrast is available). We reject the hypothesis that SFM obtains input from a single chromatic mechanism combining the long- and medium-wavelength-sensitive cones linearly. Our data are compatible with SFM that uses the output of two mechanisms, one taking the difference between the long- and medium-wavelength-sensitive-cone signals and the other taking the respective sum. We reject the particular hypothesis that SFM utilizes only the magnitude and not the sign of the long- and medium-wavelength-sensitive-cone signal. (3) We compare SFM performance with threshold performance for velocity and motion discrimination. Stimuli with luminance contrast yield SFM performance that is superior to stimuli without luminance contrast when they are expressed as multiples of velocity discrimination threshold. This superiority is even greater when SFM performance is compared with motion-direction discrimination thresholds.

Color Perception↗