Differentiating between Affine and Perspective-Based Models for the Geometry of Visual Space Based on Judgments of the Interior Angles of Squares

This paper attempts to differentiate between two models of visual space. One model suggests that visual space is a simple affine transformation of physical space. The other proposes that it is a transformation of physical space via the laws of perspective. The present paper reports two experiments in which participants are asked to judge the size of the interior angles of squares at five different distances from the participant. The perspective-based model predicts that the angles within each square on the side nearest to the participant should seem smaller than those on the far side. The simple affine model under our conditions predicts that the perceived size of the angles of each square should remain 90°. Results of both experiments were most consistent with the perspective-based model. The angles of each square on the near side were estimated to be significantly smaller than the angles on the far side for all five squares in both experiments. In addition, the sum of the estimated size of the four angles of each square declined with increasing distance from the participant to the square and was less than 360° for all but the nearest square.

Koffka, Köhler, and the "crisis" in psychology

This paper examines the claims of the Gestalt psychologists that there was a crisis in experimental psychology ca. 1900, which arose because the prevailing sensory atomism excluded meaning from among psychological phenomena. The Gestaltists claim that a primary motivation of their movement was to show, against the speculative psychologists and philosophers and Verstehen historians, that natural scientific psychology can handle meaning. Purportedly, they revealed this motivation in their initial German-language presentations but in English emphasized their scientific accomplishments for an American audience. The paper finds that: there was a recognized crisis in the new experimental psychology ca. 1900 pertaining especially to sensory atomism; that the Gestaltists responded to the crisis with new experimental findings and theoretical concepts (Gestalten) that challenged atomism; in both languages, they raised problems of meaning and discussed the contest with speculative psychology and philosophy only after presenting their scientific case; that they introduced phenomenological observations on meaning and perceptual organization into their psychology but did not develop a theory of meaning or solve philosophical problems; that they argued "philosophically," that is, using abstract, conceptual arguments; and that this aspect of their cognitive style was not received well by some prominent members of their American audience.

Representation and constraints: the inverse problem and the structure of visual space

Visual space can be distinguished from physical space. The first is found in visual experience, while the second is defined independently of perception. Theorists have wondered about the relation between the two. Some investigators have concluded that visual space is non-Euclidean, and that it does not have a single metric structure. Here it is argued (1) that visual space exhibits contraction in all three dimensions with increasing distance from the observer, (2) that experienced features of this contraction (including the apparent convergence of lines in visual experience that are produced from physically parallel stimuli in ordinary viewing conditions) are not the same as would be the experience of a perspective projection onto a frontoparallel plane, and (3) that such contraction is consistent with size constancy. These properties of visual space are different from those that would be predicted if spatial perception resulted from the successful solution of the inverse problem. They are consistent with the notion that optical constraints have been internalized. More generally, they are also consistent with the notion that visual spatial structures bear a resemblance relation to physical spatial structures. This notion supports a type of representational relation that is distinct from mere causal correspondence. The reticence of some philosophers and psychologists to discuss the structure of phenomenal space is diagnosed in terms of the simple materialism and the functionalism of the 1970s and 1980s.

V gamma 2 TCR repertoire overlap in different anatomical compartments of healthy, unrelated rhesus macaques

Gammadelta T cells show preferential homing that is characterized by biased TCR repertoire at different anatomical locations. The processes that regulate this compartmentalization are largely unknown. A model that allows repeated multiple sample procurement under different conditions and enables with relatively straightforward extrapolation to a human situation will facilitate our understanding. The peripheral blood Vgamma2 T cell population is the best-characterized human gammadelta T cell subset. To determine its diversity at multiple immunocompartments matching blood, colon, and vagina samples from rhesus macaques were investigated. Four joining segments used in Vgamma2-Jgamma transcripts were identified, including one segment with no human counterpart. Like in humans, the rhesus peripheral blood Vgamma2 TCR repertoire was limited and contained common sequences that were shared by genetically heterogeneous animals. Furthermore, this subset comprised several phylogenetically conserved Vgamma2 complementarity-determining region 3 (CDR3) motifs between rhesus and humans. Common sequences were also found within the colon and vagina of the same animal, and within the peripheral blood and intestine of different unrelated animals. These results validate rhesus macaques as a useful model for gammadelta TCR repertoire and homing studies. Moreover, they provide evidence that the concept of limited but overlapping Vgamma TCR repertoire between unrelated individuals can be extended including the mucosa of the digestive and reproductive tract.

Gammadelta T cell receptor repertoire in blood and colonic mucosa of rhesus macaques

Although their precise roles are not well defined, gammadelta T lymphocytes are recognized as regular components of immune responses. These cells express a limited T cell receptor repertoire and they can be stimulated by soluble ligands without conventional processing and presentation by major histocompatibility antigens. Progress in this area has been limited by the substantial differences between murine and human gammadelta T cells and the lack of knowledge about these cells in nonhuman primates. We used molecular analysis of T cell receptor diversity to characterize gammadelta T cell populations from peripheral blood and colon of rhesus macaques (Macaca mulatta). The gammadelta T cell receptor diversity was limited and distinct for these tissue compartments, particularly in the TCRGV2 family. Furthermore, the TCRDV1 + subset of peripheral blood gammadelta T cells showed signs of progressive oligoclonalization as a function of age. Similar observations have been reported for human tissue samples and our results validate rhesus macaques as an appropriate animal model for studying primate gammadelta T cell populations.

MR imaging surface display of the cerebral cortex in children

The purpose of this study was to introduce the use of three-dimensional (3D) surface MR imaging display for clinical use. Surface display was created using images acquired with T1 magnetization prepared rapid acquisition gradient echo (MPRAGE) in 24 cases of migrational defects, cortical dysplasia and prenatal asphyxia. Schizencephaly and cortical dysplasia were pathologically confirmed. The precise configurations of cortical abnormalities, and their relation to the adjacent gyri and sulci were demonstrated. The topography of schizencephalic clefts was clearly defined. The appearance of ulegyria was characteristic and it was sometimes possible to differentiate polymicrogyria from pachygyria.

Simulation of stochastic micropopulation models--III. COGNET: an artificial neural network for visual recognition

COGNET, based on a neural network first described by Fukushima, demonstrates the relationship between connectionist and other micropopulation models. Its success and physiological orientation led to an implementation using the SUMMERS simulation shell. After self-supervised learning, COGNET uses forward and backward propagation of signals to recognize partial and noisy patterns, and to reconstruct the originals. Stochastic features include variable thresholds for neuronal firing and occasional cell death. The successful implementation of COGNET demonstrates the generality of the concepts embodied in SUMMERS, which in turn promotes the reusability of software and facilitates the extension of computational models in biomedical research. COGNET itself forms a framework for building other physiologically oriented neural network models.

Aminopyrine N-demethylation: a prognostic test of liver function in patients with alcoholic liver disease

To determine whether results of the aminopyrine breath test, an indirect measurement of functional hepatic microsomal mass, can be correlated with mortality and changes in clinical status and liver function, 51 hospitalized patients who had alcoholic hepatitis were studied prospectively for 3 wk. The aminopyrine breath test was performed weekly, and the results were compared with clinical features of liver disease and SGOT, SGPT, bilirubin, albumin, and prothrombin time. Only an aminopyrine breath test of > 1% of administered dose of 14C as 14CO2 correlated with 3-week survival (P = 0.0075). Only an increase of more than 100% in the aminopyrine breath test was associated with clinical improvement (P = 0.0036). For the 21 patients who had histologic confirmation of alcoholic liver disease, the aminopyrine breath test also correlated best with the degree of histologic severity. In this group of patients with alcoholic hepatitis the aminopyrine breath test predicted short-term survival, clinical improvement, and histologic severity more reliably than conventional liver function tests.

Perceived shape at a slant as a function of processing time and processing load

Shape and slant judgments of rotated or frontoparallel ellipses were elicited from three groups of 10 subjects. A masking stimulus was introduced to control processing time. Backward masking trials were presented with interstimulus intervals of 0,25 and 50 msec. Reduction of processing time altered shape judgments in the direction of projective shape and slant judgments in the direction of frontoparallelness. This finding is consistent with the shape-slant invariance hypothesis. In order to study the effects of processing load, one group of subjects was given prior knowledge of the kind of judgment to be made on each trial, one group had no prior knowledge, and a third group made both judgments on each trial. The effects of the processing load manipulation were interpreted in terms of the role of attention in perceptual encoding. Consistent with previous findings, allocation of attention did not affect perceptual encoding.

Perceived shape at a slant as a function of processing time and processing load

Shape and slant judgments of rotated or frontoparallel ellipses were elicited from three groups of 10 subjects. A masking stimulus was introduced to control processing time. Backward masking trials were presented with interstimulus intervals of 0,25 and 50 msec. Reduction of processing time altered shape judgments in the direction of projective shape and slant judgments in the direction of frontoparallelness. This finding is consistent with the shape-slant invariance hypothesis. In order to study the effects of processing load, one group of subjects was given prior knowledge of the kind of judgment to be made on each trial, one group had no prior knowledge, and a third group made both judgments on each trial. The effects of the processing load manipulation were interpreted in terms of the role of attention in perceptual encoding. Consistent with previous findings, allocation of attention did not affect perceptual encoding.