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Biomedical subjects

M W Cannon

Publications and source records attributed to M W Cannon.

17 recordsLinked to original sources
PubMed1999

Target detection against narrow band noise backgrounds.

We studied the detectability of narrow band random noise targets embedded in narrow band random noise backgrounds as a function of differences in center frequency, spatial frequency bandwidth and orientation bandwidth between target and the immediately adjacent background. Unlike most target detection experiments the targets were not added to the background; they replaced the underlying background texture. Simulations showed that target detection probabilities could be accounted for by a simple transformation on the summed outputs of a two layer filter model similar to the complex channels model proposed by Graham, Beck and Sutter (Graham, N., Beck, J., & Sutter, A. (1992). Vision Research, 32, 719-743). Subsequently, the model was tested on the detection of camouflaged vehicle targets with encouraging results.

Contrast Sensitivity↗
PubMed1996

A model for inhibitory lateral interaction effects in perceived contrast.

The apparent contrast of a centrally viewed Gabor target patch was measured by contrast matching in the presence of Gabor flanking patches positioned on a ring of radius r from the center of the target patch. Central patch apparent contrast was determined as a function of the number of flanking patches, the radius r of the ring, and the contrasts of both central and flanking patches. The apparent contrast of the central patch was reduced by the presence of the flanking patches for all experimental conditions. A two layer non-linear model for contrast perception accounts quite well for the data. The first layer performs a power function transformation on the contrast signals from the patches. The second layer takes the outputs from the first layer and divides them by one plus the square root of spatially weighted responses of nearby first layer mechanisms.

Contrast Sensitivity↗
PubMed1993

Spatial interactions in apparent contrast: individual differences in enhancement and suppression effects.

The apparent contrast of a small grating patch embedded in the center of an annular grating filled surround was studied as a function of the surround to central patch contrast ratio, the width of the annulus, and the contrast level of the central patch. Data from ten observers show large individual differences in apparent contrast, but these differences can be interpreted in terms of the relative strength of two interacting mechanisms. One mechanism mediates enhancement of the central patch. The other mediates suppression.

Contrast Sensitivity↗
PubMed1993

Multiple myeloma in a 25-year-old woman.

A 25-year-old woman with acute knee pain and a lytic area in the proximal femur was diagnosed as having multiple myeloma (MM). This case is one of only eight in patients younger than aged 30 years to meet modern diagnostic criteria for MM. Failure to consider MM in young individuals precludes early diagnosis and valuable time for treatment.

Adult↗
PubMed1992

The battalion medical platoon: a flawed scalpel.

This article discusses the current organization and doctrine for a medical platoon in an armour-heavy task force in light of experience gained in Operations Desert Shield and Desert Storm. The organization of and doctrine for the use of the platoon is covered first. This is followed by a discussion of how doctrine was modified based on field exercises, and projected, and actual, combat operations. It concludes with a presentation of lessons learned and recommendations for changes.

Humans↗
PubMed1991

Spatial interactions in apparent contrast: inhibitory effects among grating patterns of different spatial frequencies, spatial positions and orientations.

Suppression of the apparent contrast of a small 4 cycle wide suprathreshold sine wave grating patch by a high contrast sine wave grating surround pattern was studied as a function of the spatial frequency, orientation and spatial extent of the surround. The data are consistent with the existence of a complex network of inhibitory interconnections among mechanisms that mediate contrast perception. These connections must extend over spatial distances equivalent to more than 12 cycles of the central grating patch.

Adaptation, Physiological↗
PubMed1991

A transducer model for contrast perception.

Multiple channel models of visual function proposed to date have been either threshold models or suprathreshold models. The transition between detection and perception of contrast which involves the gradual disappearance of spatial response pooling has not been addressed. We propose a model that allows us to simulate contrast detection, contrast perception and the gradual disappearance of spatial response pooling with contrast. The model successfully predicts thresholds and perceived contrast functions for several multiple component stimuli.

Calibration↗
PubMed1988

Perceived contrast and stimulus size: experiment and simulation.

Perceived contrast functions were determined for three different Gabor patch sizes using magnitude estimation and verified by contrast matching. While thresholds show a significant decrease with decreasing patch size, perceived contrasts are equal and independent of patch size for contrasts above 0.06. Contrast matching was also used to study the apparent contrast of two other spatially limited stimuli; the sum of two orthogonal 4 c/deg sine waves multiplied by a gaussian envelope and the sum of spatially adjacent positive and negative gaussians. Models of contrast perception, based on tuned Gabor spatial filters, were formulated and tested for agreement with our experimental data. A model that pools filter responses across spatial frequencies and orientations was found to be more in agreement with our data than a model that simply uses the response of a single, maximally excited, mechanism to mediate contrast perception. Optimum filter bandwidth was found to be about 1.1 octaves.

Contrast Sensitivity↗
PubMed1985

Perceived contrast in the fovea and periphery.

Subjects estimated the perceived contrast of 2 degrees-diameter sine-wave grating patches for spatial frequencies of 2, 4, 8, and 16 cycles/deg, at eccentricities from 0 degrees to 40 degrees and contrasts up to 0.8. The data were well fitted in all cases by power functions of contrast minus threshold, with exponents of the order of 0.5 implying similar mechanisms in both fovea and periphery. The data also demonstrate that, at high physical contrast, the visual system is generally driven toward an operating state in which two stimuli of equal physical contrast have equal perceived contrast even if the thresholds are quite different. As a consequence, peripheral perceived contrasts produced by high physical contrasts show almost no change with eccentricity, whereas thresholds increase by at least an order of magnitude. This implies that mechanisms mediating threshold detection and suprathreshold perception may be different.

Acoustic Stimulation↗
PubMed1984

A study of stimulus range effects in free modulus magnitude estimation of contrast.

The exponents of perceived contrast functions determined for sine wave gratings varied from 1.1, when perceived contrasts were estimated over a 0.6 log unit range of stimulus contrast, to 0.56 when perceived contrasts were estimated over a 1.9 log unit range of stimulus contrast. Intermediate stimulus contrast ranges produced intermediate exponents. This contrast range effect appears to account for the different exponents reported in previous magnitude estimation studies and for the fact that some studies show an exponent increasing with increasing spatial frequency while others do not.

Form Perception↗
PubMed1984

Large-sample norms for contrast sensitivity.

A portable microprocessor-controlled instrument automatically measured the static and dynamic contrast sensitivity functions (CSF's) of 265 observers for a normal population at the Dayton Air Fair and Air Force Museum. Repeat measures for six observers taken 6 months later show small, nonsystematic differences from original measurements. Median values of contrast sensitivity as well as regions encompassing 75 of 90% of our sample are shown.

Adult↗
PubMed1983

Evoked potential contrast sensitivity in the parafovea: spatial organization.

Visual evoked potential contrast sensitivity functions (VEP/CSFs) were determined for counterphase flickered sine-wave gratings in circular fields up to 8 degrees in diameter centered on the fovea. VEP sources responding to 16 c/deg gratings appeared to be concentrated in the central 2 degrees of the visual field while sources responding to lower spatial frequencies appeared to be distributed over progressively wider areas of the visual field as spatial frequency decreased. It was also found that independently determined VEP/CSFs for non-overlapping annular regions of the visual field centered on the fovea summed to equal the VEP/CSF obtained when both regions were stimulated simultaneously.

Evoked Potentials, Visual↗
PubMed1983

Comparison of three methods for rapid determination of threshold contrast sensitivity.

Threshold contrast sensitivity functions for 13 subjects were determined on 5 consecutive days using three psychophysical methods. Each method was implemented on a microprocessor controlled display system and considered as a possible candidate for a rapid visual screening test. The methods used were Bekesy tracking, method of adjustment, and method of increasing contrast. The method of increasing contrast proved superior to the other methods in repeatability, speed, and the preservation of individual differences in contrast sensitivity over the testing period.

Form Perception↗
PubMed1980

Suprathreshold processing of complex visual stimuli: evidence for linearity in contrast perception.

Magnitude estimation experiments show that perceived contrast for both sine and square waves is a linear function of stimulus contrast. The suprathreshold sine:square ratio required for equal perceived contrast derived from these data was verified by contrast matching experiments. These findings imply a high degree of linearity in suprathreshold visual processing of contrast.

Form Perception↗