Biomedical subjects

G Brelstaff

Publications and source records attributed to G Brelstaff.

5 recordsLinked to original sources

PubMed2001

Surface color from boundaries: a new 'watercolor' illusion.

A colored line flanking a darker border will appear to assimilate its color onto the enclosed white area over distances of up to 45 deg (the Watercolor Effect). This coloration is uniform and complete within 100 ms. We found that thin (6 arcmin), winding inducing lines with different contrasts to the ground are generally more effective than thick, straight, and equiluminant lines. Blue and red lines induce the strongest effects, but watercolor spreading may also be seen with green and yellow. On a white background, color spreading is stronger than on chromatic, gray or black backgrounds. Little or no color is perceived when a narrow white zone (gap) is inserted in between the two inducing lines. However, chains of colored dots instead of continuous lines suffice to produce spreading. Edge-induced color is also observed when the two colored lines are presented dichoptically, suggesting a cortical origin. The Watercolor Effect described here may serve to enhance figure-ground segregation by imparting surface color onto the enclosed area, and to promote grouping between distant stimulus elements. As a grouping factor, watercolor coloration wins over proximity. Assimilative color spreading may arise in two steps: First, weakening of the contour by lateral inhibition between differentially activated edge cells (local diffusion); and second, unbarriered flow of color onto the enclosed area (global diffusion).

Color Perception↗

PubMed2001

Last but not least.

New variations of the spiral illusion are demonstrated. They include spiral illusions of the Café Wall illusion and the Zöllner illusion, as well as other new orientation illusions. Thus the spiral illusion is not limited to the Fraser illusion. We discuss the role that detectors of spirals in a higher visual area might play in the spiral illusion.

Humans↗

PubMed1998

Color and luminance information in natural scenes.

The spatial filtering applied by the human visual system appears to be low pass for chromatic stimuli and band pass for luminance stimuli. Here we explore whether this observed difference in contrast sensitivity reflects a real difference in the components of chrominance and luminance in natural scenes. For this purpose a digital set of 29 hyperspectral images of natural scenes was acquired and its spatial frequency content analyzed in terms of chrominance and luminance defined according to existing models of the human cone responses and visual signal processing. The statistical 1/f amplitude spatial-frequency distribution is confirmed for a variety of chromatic conditions across the visible spectrum. Our analysis suggests that natural scenes are relatively rich in high-spatial-frequency chrominance information that does not appear to be transmitted by the human visual system. This result is unlikely to have arisen from errors in the original measurements. Several reasons may combine to explain a failure to transmit high-spatial-frequency chrominance: (a) its minor importance for primate visual tasks, (b) its removal by filtering applied to compensate for chromatic aberration of the eye's optics, and (c) a biological bottleneck blocking its transmission. In addition, we graphically compare the ratios of luminance to chrominance measured by our hyperspectral camera and those measured psychophysically over an equivalent spatial-frequency range.

Color Perception↗

PubMed1995

Is the richness of our visual world an illusion? Transsaccadic memory for complex scenes.

Our construction of a stable visual world, despite the presence of saccades, is discussed. A computer-graphics method was used to explore transsaccadic memory for complex images. Images of real-life scenes were presented under four conditions: they stayed still or moved in an unpredictable direction (forcing an eye movement), while simultaneously changing or staying the same. Changes were the appearance, disappearance, or rotation of an object in the scene. Subjects detected the changes easily when the image did not move but when it moved their performance fell to chance. A grey-out period was introduced to mimic that which occurs during a saccade. This also reduced performance but not to chance levels. These results reveal the poverty of transsaccadic memory for real-life complex scenes. They are discussed with respect to Dennett's view that much less information is available in vision than our subjective impression leads us to believe. Our stable visual world may be constructed out of a brief retinal image and a very sketchy, higher-level representation along with a pop-out mechanism to redirect attention. The richness of our visual world is, to this extent, an illusion.

Eidetic Imagery↗

PubMedDate not supplied

Internet patient records: new techniques.

BACKGROUND: The ease by which the Internet is able to distribute information to geographically-distant users on a wide variety of computers makes it an obvious candidate for a technological solution for electronic patient record systems. Indeed, second-generation Internet technologies such as the ones described in this article--XML (eXtensible Markup Language), XSL (eXtensible Style Language), DOM (Document Object Model), CSS (Cascading Style Sheet), JavaScript, and JavaBeans--may significantly reduce the complexity of the development of distributed healthcare systems. OBJECTIVE: The demonstration of an experimental Electronic Patient Record (EPR) system built from those technologies that can support viewing of medical imaging exams and graphically-rich clinical reporting tools, while conforming to the newly emerging XML standard for digital documents. In particular, we aim to promote rapid prototyping of new reports by clinical specialists. METHODS: We have built a prototype EPR client, InfoDOM, that runs in both the popular web browsers. In this second version it receives each EPR as an XML record served via the secure SSL (Secure Socket Layer) protocol. JavaBean software components manipulate the XML to store it and then to transform it into a variety of useful clinical views. First a web page summary for the patient is produced. From that web page other JavaBeans can be launched. In particular, we have developed a medical imaging exam Viewer and a clinical Reporter bean parameterized appropriately for the particular patient and exam in question. Both present particular views of the XML data. The Viewer reads image sequences from a patient-specified network URL on a PACS (Picture Archiving and Communications System) server and presents them in a user-controllable animated sequence, while the Reporter provides a configurable anatomical map of the site of the pathology, from which individual "reportlets" can be launched. The specification of these reportlets is achieved using standard HTML forms and thus may conceivably be authored by clinical specialists. A generic JavaScript library has been written that allows the seamless incorporation of such contributions into the InfoDOM client. In conjunction with another JavaBean, that library renders graphically-enhanced reporting tools that read and write content to and from the XML data-structure, ready for resubmission to the EPR server. RESULTS: We demonstrate the InfoDOM experimental EPR system that is currently being adapted for test-bed use in three hospitals in Cagliari, Italy. For this we are working with specialists in neurology, radiology, and epilepsy. CONCLUSIONS: Early indications are that the rapid prototyping of reports afforded by our EPR system can assist communication between clinical specialists and our system developers. We are now experimenting with new technologies that may provide services to the kind of XML EPR client described here.

Internet↗