Biomedical subjects

T Vetter

Publications and source records attributed to T Vetter.

At least 19 recordsLinked to original sources

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↗

PubMed2001

Breathing pattern and perception at different levels of volume assist and pressure support in volunteers.

OBJECTIVE: Volume assist (VA) amplifies the breathing effort whereas pressure support ventilation (PSV) provides a fixed, effort-independent ventilatory support. According to the concept of VA, its level should compensate for the pathologically increased (additional) elastance (Eadd). However, it is unclear whether breathing subjects prefer an exact compensation of Eadd and whether they are able to adjust the support level by themselves. DESIGN: Prospective, interventional study. SETTING: Laboratory. SUBJECTS: Twelve healthy volunteers, nine females, three males, aged 21-33 yrs. INTERVENTIONS: Increased Eadd was generated by banding of the thorax and abdomen. Volunteers breathed via a mouthpiece with VA or PSV using a positive end-expiratory pressure of 5 cm H2O (0.5 kPa). The study was subdivided into two parts. In part I, volunteers were instructed to adjust the level of VA and PSV themselves starting from three different, randomly applied levels in each mode (2, 8, 14 cm H2O or cm H2O/L; 0.2, 0.8, 1.4 kPa[/L]). In part II, 20 levels of VA and PSV (1-20 cm H2O or cm H2O/L, 0.1-2 kPa[/L]) were randomly selected by an investigator and estimated by the volunteers using a visual analog scale. Additionally, the breathing pattern was characterized. MEASUREMENTS AND MAIN RESULTS: Eadd (7.1 +/- 1.5 cm H2O/L [0.7 +/- 0.2 kPa/L], mean +/- sd) corresponded almost exactly to the "self-adjusted" VA level of part I (7.0 +/- 3.3 cm H2O/L [0.7 +/- 0.3 kPa/L]) and to the adequate level of part II (8-9 cm H2O/L [0.8-0.9 kPa/L]). The accordant PSV levels were 5.7 +/- 2.6 cm H2O (0.6 +/- 0.3 kPa) and 6-7 cm H2O (0.6-0.7 kPa). The breathing pattern was less influenced by changes of the support level with VA compared with PSV, which may explain in part the greater comfort of VA. CONCLUSIONS: We confirmed the theoretical assumption that VA should be adapted to Eadd. Furthermore, we demonstrated that conscious subjects are able to adjust the level of VA and PSV themselves.

Adult↗

PubMed2000

An integrated head-holder/coil for intraoperative MRI in open neurosurgery.

With the invention of "open" magnetic resonance imaging (MRI) systems, access to the patient is possible during the imaging procedure. An important application of these systems is intraoperative MRI to control the extent of resection during tumor surgery. Up to now flexible surface coils wrapped around, or placed at each side of the head, were used for imaging. These flexible coils have several disadvantages such as unreliability, interindividual problems, difficult handling, poor hygienic properties, and often unsatisfactory or inhomogeneous image quality. To solve most of these problems, an MR-compatible head-holder in combination with an integrated surface coil for use in a 0.2 T C-shaped magnet was developed. Forty-eight patients with known cranial tumors underwent MRI intraoperatively. In 32 patients (67%), residual tumor was found, and additional surgical resection was performed. The integrated head-holder/coil is a safe and practical tool for intraoperative MRI, providing efficient and reliable resection control during neurosurgical procedures.

Brain↗

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↗

PubMed2000

The face typicality-recognizability relationship: encoding or retrieval locus?

Using a crossover recognition memory testing paradigm, we tested whether the effects on face recognition of the memorability component of face typicality (Vokey & Read, 1992, 1995) are due primarily to the encoding process occurring during study or to the retrieval process occurring at test. At study, faces were either veridical in form or at moderate (Experiment 1) or extreme (Experiment 2) levels of caricature. The variable of degree of facial caricature at study was crossed with the degree of caricature at test. The primary contribution of increased memorability to increased hit rate was through increased distinctiveness at study. Increased distinctiveness at test contributed to substantial reductions in the false alarm rate, too. Signal detection analyses confirmed that the mirror effects obtained were primarily stimulus/memory-based, rather than decision-based. Contrary to the conclusion of Vokey and Read (1992), we found that increments in face memorability produced increments in face recognition that were due at least as much to enhanced encoding of studied faces as they were to increased rejection of distractor faces.

Adult↗

PubMed1999

Use of continuous retropleural bupivacaine in postoperative pain management for pediatric thoracotomy.

BACKGROUND/PURPOSE: The aim of this study was to evaluate the use of a continuous bupivacaine infusion into the retropleural space as an adjunct for postoperative pain management in pediatric thoracotomy. METHODS: A retrospective chart review was performed on 13 pediatric patients undergoing thoracotomy over a 3-year period (April 1995 through July 1997). In seven patients, insertion of a retropleural catheter was accomplished before closure of the thoracotomy by placing an epidural catheter posterior to the parietal pleura. This potential space was entered two intercostal levels below the incision and advanced superiorly four intercostal spaces. Bupivacaine (0.125% or 0.25%) was infused at 0.5 mL/kg/h. Postoperative intravenous narcotic requirement was compared between the study population (n = 7) and the control population (n = 6). Statistical analysis was conducted using the "separate" Student's t test. RESULTS: Thirteen pediatric patients (age range, 7 to 18 years) were evaluated for total morphine use after thoracotomy. Seven patients had anterior spinal release and fusion, whereas five had mediastinal operations, and one patient had a lobectomy. The two groups were comparable in age, weight, and type of operation. Infusion through the retropleural catheter continued for an average of 3.8 days (range, 3 to 6 days). The total mean postoperative morphine requirement was 2.32 mg/kg (0.544 mg/kg/day) in the control population and 0.88 mg/kg (0.204 mg/kg/day) for the patients with a retropleural catheter (P<.001). CONCLUSION: A continuous infusion of bupivacaine through a unique retropleural technique decreases the postoperative need for morphine in postoperative pediatric thoracotomy patients.

Adolescent↗

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↗

PubMed1998

Facial aging, attractiveness, and distinctiveness.

A standard facial caricature algorithm has been applied to a three-dimensional (3-D) representation of human heads, those of Caucasian male and female young adults. Observers viewed unfamiliar faces at four levels of caricature--anticaricature, veridical, moderate caricature, and extreme caricature--and made ratings of attractiveness and distinctiveness (experiment 1) or learned to identify them (experiment 2). There were linear increases in perceived distinctiveness and linear decreases in perceived attractiveness as the degree of facial caricature (Euclidean distance from the average face in 3-D-grounded face space) increased. Observers learned to identify faces presented at either level of positive caricature more efficiently than they did with either uncaricatured or anticaricatured faces. Using the same faces, 3-D representation, and caricature levels, O'Toole, Vetter, Volz, and Salter (1997, Perception 26 719-732) had shown a linear increase in judgments of face age as a function of degree of caricature. Here it is concluded that older-appearing faces are less attractive, but more distinctive and memorable than younger-appearing faces, those closer to the average face.

Adult↗

PubMed1997

Top-down learning of low-level vision tasks.

Perceptual tasks such as edge detection, image segmentation, lightness computation and estimation of three-dimensional structure are considered to be low-level or mid-level vision problems and are traditionally approached in a bottom-up, generic and hard-wired way. An alternative to this would be to take a top-down, object-class-specific and example-based approach. In this paper, we present a simple computational model implementing the latter approach. The results generated by our model when tested on edge-detection and view-prediction tasks for three-dimensional objects are consistent with human perceptual expectations. The model's performance is highly tolerant to the problems of sensor noise and incomplete input image information. Results obtained with conventional bottom-up strategies show much less immunity to these problems. We interpret the encouraging performance of our computational model as evidence in support of the hypothesis that the human visual system may learn to perform supposedly low-level perceptual tasks in a top-down fashion.

Algorithms↗

PubMed1997

Hamartoma of the triceps surae muscle.

A 9-year-old, otherwise healthy girl presented with a 5-year history of pain in her right calf with retarded growth and development of an equinus contracture of her right leg. Magnetic resonance imaging showed an irregular mass with heterogeneous enhancement after contrast in her right triceps surae muscles, especially the soleus. Histological studies of this triceps surae muscle tissue revealed a haphazard distribution of adipose and connective tissue, striated and smooth muscle cells, vessels and lymphoid follicles, as well as nerve bundles which, together, were considered components of a hamartoma.

Child↗

PubMed1997

Sex classification is better with three-dimensional head structure than with image intensity information.

The sex of a face is perhaps its most salient features. A principal components analysis (PCA) was applied separately to the three-dimensional (3-D) structure and graylevel image (GLI) data from laser-scanned human heads. Individual components from both analyses captured information related to the sex of the face. Notably, single projection coefficients characterized complex differences between the 3-D structure of male and female heads and between male and female GLI maps. In a series of simulations, the quality of the information available in the 3-D head versus GLI data for predicting the sex of the face has been compared. The results indicated that the 3-D head data supported more accurate sex classification than the GLI data, across a range of PCA-compressed (dimensionality-reduced) representations of the heads. This kind of dual face representation can give insight into the nature of the information available to humans for categorizing and remembering faces.

Adult↗

PubMed1997

Three-dimensional caricatures of human heads: distinctiveness and the perception of facial age.

A standard facial-caricaturing algorithm was applied to a three-dimensional representation of human heads. This algorithm sometimes produced heads that appeared 'caricatured'. More commonly, however, exaggerating the distinctive three-dimensional information in a face seemed to produce an increase in the apparent age of the face--both at a local level, by exaggerating small facial creases into wrinkles, and at a more global level via changes that seemed to make the underlying structure of the skull more evident. Concomitantly, de-emphasis of the distinctive three-dimensional information in a face made it appear relatively younger than the veridical and caricatured faces. More formally, face-age judgments made by human observers were ordered according to the level of caricature, with anticaricatures judged younger than veridical faces, and veridical faces judged younger than caricatured faces. These results are discussed in terms of the importance of the nature of the features made more distinct by a caricaturing algorithm and the nature of human representation(s) of faces.

Age Factors↗

PubMed1994

The importance of symmetry and virtual views in three-dimensional object recognition.

BACKGROUND: Human observers can recognize three-dimensional objects seen in novel orientations, even when they have previously seen only a relatively small number of different views of the object. How our visual system does this is a key problem in vision research. Recent theories and experiments suggest that the human visual system might store a relatively small number of sample two-dimensional views of a three-dimensional object, and recognize novel views by a process of interpolation between the stored sample views. These sample views may be collected during a training phase as the visual system familiarizes itself with the object. RESULTS: Here, we investigate whether constraints on the shapes of objects commonly encountered in the real world can reduce the number of training views required for recognition of three-dimensional objects. We are particularly concerned with the constraint of object symmetry. We show that if an object is bilaterally symmetrical, then additional 'virtual views' can automatically be generated from one sample view by symmetry transformations. These virtual views should make it more easy to recognize novel views of a symmetric than an asymmetric object, when a single sample view has been seen. Recognition should be particularly facilitated when the novel views are close to the virtual view. We present psychophysical results that bear out these predictions. CONCLUSIONS: Our results show that the human visual system can indeed exploit symmetry to facilitate object recognition, and support the model for object recognition in which a small number of two-dimensional views are remembered and combined to recognize novel views of the same object. These results raise questions about how symmetry is recognized, and symmetry transformations implemented, in real, biological neural networks.

Depth Perception↗

PubMed1994

Symmetric 3D objects are an easy case for 2D object recognition.

According to the 1.5-views theorem (Poggio, Technical Report #9005-03, IRST, Povo, 1990; Ullman and Basri, IEEE Trans. PAMI 13, 992-1006, 1991) recognition of a specific 3D object (defined in terms of pointwise features) from a novel 2D view can be achieved from at least two 2D model views (for each object, for orthographic projection). This note considers how recognition can be achieved from a single 2D model view by exploiting prior knowledge of an object's symmetry. It is proved that, for any bilaterally symmetric 3D object, one non-accidental 2D model view is sufficient for recognition since it can be used to generate additional 'virtual' views. It is also proved that, for bilaterally symmetric objects, the correspondence of four points between two views determines the correspondence of all other points. Symmetries of higher order allow the recovery of Euclidean structure from a single 2D view.

Algorithms↗

PubMed1992

Cable properties of arborized Retzius cells of the leech in culture as probed by a voltage-sensitive dye.

Retzius cells of Hirudo medicinalis were cultivated on extracellular matrix protein so that extended arborizations were formed. The propagation of voltage transients along 1-microns-thick neurites was observed at a resolution of 8 microns at 10 kHz by use of a voltage-sensitive dye. Delay and width of the fluorescence transients caused by hyperpolarization of the soma are described by passive spread of voltage in a homogeneous cable (time constant, 10 ms; space constant, 320 microns). The local sensitivity of the dye was determined from a comparison of the amplitudes of fluorescence and of fitted voltage. The fluorescence transients caused by depolarization were scaled using the sensitivity profile. Action potentials were found to pervade the neurites without significant change of amplitude but with enhanced pulse width.

Action Potentials↗

PubMed1991

Guided outgrowth of leech neurons in culture.

Sensory neurons of Hirudo medicinalis were cultivated on patterns of extracellular matrix (ECM) protein which were prepared by UV irradiation using copper grid masks. The relation of the patterns and of the outgrowth of neurites was observed by scanning electronmicroscopy after gold decoration. The neurites were guided by narrow (10 microM) lanes of ECM protein. Branching of neurites was induced by branched lanes. Bent neurites were pulled off bent lanes at some distance behind the growth cone such that their length was reduced. Regularly spaced sites of adhesion became visible which remained connected to the neurites by extended filaments.

Animals↗

PubMed1991

A neuron-silicon junction: a Retzius cell of the leech on an insulated-gate field-effect transistor.

An identified neuron of the leech, a Retzius cell, has been attached to the open gate of a p-channel field-effect transistor. Action potentials, spontaneous or stimulated, modulate directly the source-drain current in silicon. The electronic signals match the shape of the action potential. The average voltage on the gate was up to 25 percent of the intracellular voltage change. Occasionally weak signals that resemble the first derivative of the action potential were observed. The junctions can be described by a model that includes capacitive coupling of the plasma membrane and the gate oxide and that accounts for variable resistance of the seal.

Action Potentials↗

PubMed1989

[Not Available].

Explore the source record for details and available documents.

France↗