Biomedical subjects

V Blanz

Publications and source records attributed to V Blanz.

6 recordsLinked to original sources

PubMed2005

A new mathematical process for the calculation of average forms of teeth.

STATEMENT OF PROBLEM: Qualitative visual inspections and linear metric measurements have been predominant methods for describing the morphology of teeth. No quantitative formulation exists for the description of dental features. PURPOSE: The aim of this study was to determine and validate a mathematical process for calculation of the average form of first maxillary molars, including the general occlusal features. MATERIAL AND METHODS: Stone replicas of 174 caries-free first maxillary molar crowns from young patients ranging from 6 to 9 years of age were measured 3-dimensionally with a laser scanning system at a resolution of approximately 100,000 points. Then, the average tooth was computed, which captured the common features of the molar's surface quantitatively. This new method adapts algorithms both from computer science and neuroscience to detect and associate the same features and same surface points (correspondences) between 1 reference tooth and all other teeth. In this study, the method was tested for 7 different reference teeth. The algorithm does not involve any prior knowledge about teeth and their features. RESULTS: Irrespective of the reference tooth used, the procedure yielded average teeth that showed nearly no differences (less than +/-30 microm). CONCLUSION: This approach provides a valid quantitative process for calculating 3-dimensional (3D) averages of occlusal surfaces of teeth even in the event of a high number of digitized surface points. Additionally, because this process detects and assigns point-wise feature correspondences between all library teeth, it may also serve as a basis for a more substantiated principal component analysis evaluating the main natural shape deviations from the 3D average.

Algorithms↗

PubMed2005

New procedure for fully automatic occlusal surface reconstruction by means of a biogeneric tooth model.

The goal of this study is to present a completely new procedure for automatic occlusal surface reconstruction and to test it in several inlay situations. The starting point is the mathematical analysis of a large number of occlusal surfaces from a tooth library. Learning algorithms used in pattern recognition and image processing were adapted for the special needs of dental morphology. A biogeneric tooth model resulted which can mathematically describe a certain type of tooth only with a few parameters. This model was tested on 40 simulated inlay situations and as an example on two clinical inlay situations. The results show that fully automatic reconstruction was possible except for four cases. In a majority of the cases, no further interactive improvements would have been necessary. Because of the general, theoretically well-founded approach, fully automatic reconstruction of the occlusal surface can also be extended in the future to full crowns or reduced crown substructures (copings).

Adolescent↗

PubMed2001

Prototype-referenced shape encoding revealed by high-level aftereffects.

We used high-level configural aftereffects induced by adaptation to realistic faces to investigate visual representations underlying complex pattern perception. We found that exposure to an individual face for a few seconds generated a significant and precise bias in the subsequent perception of face identity. In the context of a computationally derived 'face space,' adaptation specifically shifted perception along a trajectory passing through the adapting and average faces, selectively facilitating recognition of a test face lying on this trajectory and impairing recognition of other faces. The results suggest that the encoding of faces and other complex patterns draws upon contrastive neural mechanisms that reference the central tendency of the stimulus category.

Adaptation, Physiological↗

PubMed2000

On the other side of the mean: the perception of dissimilarity in human faces.

We created a 'face space' using a laser-scan representation of faces. In this space, a caricature can be made by moving a face away from the average face, along the line connecting the particular face to the average face. Here, we move the face along this line in the other direction, proceeding through the mean and 'out the other side'. This results in a face that is 'opposite', in a computational sense, to the original face. We morphed several faces into their anti-faces and sampled the morph trajectory in five discrete steps. We then collected similarity ratings from human participants for all possible pairs of morphed faces to determine how the distances in the 'physical face space' related to the distances in the 'psychological face space'. The data indicate that there is a perceptual discontinuity of face identity as the face crosses over to the 'other side of the mean'. We consider these results in the context of face-space models of human face processing.

Adult↗

PubMed1999

Three-dimensional shape and two-dimensional surface reflectance contributions to face recognition: an application of three-dimensional morphing.

We measured the three-dimensional shape and two-dimensional surface reflectance contributions to human recognition of faces across viewpoint. We first divided laser scans of human heads into their two- and three-dimensional components. Next, we created shape-normalized faces by morphing the two-dimensional surface reflectance maps of each face onto the average three-dimensional head shape and reflectance-normalized faces by morphing the average two-dimensional surface reflectance map onto each three-dimensional head shape. Observers learned frontal images of the original, shape-normalized, or reflectance-normalized faces, and were asked to recognize the faces from viewpoint changes of 0, 30 and 60 degrees. Both the three-dimensional shape and two-dimensional surface reflectance information contributed substantially to human recognition performance, thus constraining theories of face representation to include both types of information.

Discrimination Learning↗

PubMed1999

What object attributes determine canonical views?

We investigated preferred or canonical views for familiar and three-dimensional nonsense objects using computer-graphics psychophysics. We assessed the canonical views for objects by allowing participants to actively rotate realistically shaded three-dimensional models in real-time. Objects were viewed on a Silicon Graphics workstation and manipulated in virtual space with a three-degree-of-freedom input device. In the first experiment, participants adjusted each object to the viewpoint from which they would take a photograph if they planned to use the object to illustrate a brochure. In the second experiment, participants mentally imaged each object on the basis of the name and then adjusted the object to the viewpoint from which they imagined it. In both experiments, there was a large degree of consistency across participants in terms of the preferred view for a given object. Our results provide new insights on the geometrical, experiential, and functional attributes that determine canonical views under ecological conditions.

Adolescent↗