Biomedical subjects

Adam Seeger

Publications and source records attributed to Adam Seeger.

4 recordsLinked to original sources

PubMed2005

Factors contributing to the integration of textural qualities: evidence from virtual surfaces.

Two experiments involving indirect touch were carried out to explore the relationships among perceptual dimensions of haptically examined surfaces. Subjects in both experiments used a stylus to evaluate the properties of virtual surfaces created by a force-feedback device; four surface properties (resistance to normal force, coefficient of friction, texture scale, and vibration amplitude) were manipulated in various combinations. In Experiment 1, the extent to which there was a one-to-one relationship between specific stimulus properties and perceptual qualities ("perceptual separability") was evaluated. A substantial failure of separability was demonstrated, with friction tending to be more separable from the other properties than they were from one another. The pattern of results suggests that the amount of measured separability depends crucially on the way stimulus properties are defined (e.g., force versus displacement). In Experiment 2, surfaces with known perceptual properties were used to study the metric(s) of the relevant perceptual space. By specifying the perceptual, rather than the stimulus, coordinates of the surfaces, it was possible to bypass issues of perceptual separability. For surfaces of equal friction, a Euclidean metric captured the results (r(2) = 0.75) more effectively than a city-block metric did; neither metric did well when differences in friction were involved. The fact that-unlike stickiness-hardness, roughness, and perceived vibration intensity are all increasing functions of surface-normal forces may facilitate their integration into a Euclidean space, in both direct and indirect touch.

Adolescent↗

PubMed2004

Haptic perception of virtual surfaces: scaling subjective qualities and interstimulus differences.

We examined, in two experiments, the perceptual scaling of the properties of haptically examined virtual surfaces, and the way in which these properties subjectively combine. Participants used a consistent movement pattern to explore, with a stylus, virtual surfaces generated by a force-feedback device. In experiment 1, four surface properties (bump size, friction, resistance to normal force, and vibration amplitude) were varied individually, in separate blocks of trials. Free magnitude estimates of the subjective dimensions corresponding to these properties showed that all four dimensions conformed closely to the power law, except at very low stimulus values. Exponents for bump size (0.80) and stiffness (1.01) were consistent with values established in earlier work with direct touch of real surfaces. Surprisingly, the exponent for stickiness, not previously measured, was much higher than those for other dimensions (1.49). In experiment 2, dimensional combinations were analyzed by asking subjects to give magnitude estimates of the subjective difference between pairs of surfaces differing in one or two properties. Magnitude estimates of a given one-dimensional difference were generally larger when the subject was pressing down firmly on the surfaces, than when only gentle downward pressure was required; this result suggests that forces generated when a surface is haptically examined are interpreted as invariant indicators of the magnitudes of the surface properties themselves. Estimates of one-dimensional differences were also used to make predictions of two-dimensional differences, under assumptions of dimensional integrality and separability. The results fell between these two sets of predictions, indicating only modest integration of surface properties examined with indirect touch.

Computer Simulation↗

PubMedDate not supplied

Software acceleration techniques for the simulation of scanning electron microscope images.

A scanning electron microscope (SEM) simulator was developed based on the models used in the MONSEL software. This simulator extends earlier work by introducing an object-oriented framework and adding optimization methods based on precomputation of electron trajectories. Several optimizations enable speedup by factors of 5-100 on a single processor over unoptimized simulations without introducing additional approximations. The speedup for a particular surface depends on the self-similarity of the surface at the scale of the electron penetration depth. We further accelerate by parallelizing the calculations for a total speedup of about 100-2000 on 30 processors. The goal of this work was to create a system capable of simulating a quantitatively accurate SEM image of a relatively unconstrained surface. Results of this work include simulation software, optimization algorithms, performance measurements with various optimizations, and examples of simulated images.

Algorithms↗

PubMedDate not supplied

Scanning electron microscope charging effect model for chromium/quartz photolithography masks.

We propose a new method for fitting a model of specimen charging to scanning electron microscope (SEM) images. Charging effects cause errors when one attempts to infer the size or shape of a specimen from an image. The goal of our method is to enable image analysis algorithms for measurement, segmentation, and three-dimensional (3-D) reconstruction that would otherwise fail on images containing charging effects. Our model is applied to images of chromium/quartz photolithography masks and may also work in the more general case of isolated metal islands on a flat insulating substrate. Unlike methods based on Monte Carlo simulation, our simulation method does not handle more general topographies or specimens composed entirely of an insulator; it is a crude approximation to the physical charging process described in more detail in Cazaux (1986) and Melchinger and Hofmann (1985), but can be fit with quantitative accuracy to real SEM images. We only consider changes in intensity and do not model charging-induced distortion of image coordinates. Our approach has the advantage over existing methods of enabling fast prediction of charging effects so it may be more practical for image analysis applications.

Journal Article↗