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Concentric field
Concentric field A receptive field divided into an inner circular region and an outer ring-shaped region. Light falling in each of the two regions has opposite effects on the response of the cell.
RELATED TERMS--------------------------------------
Cell
Fundamental structural unit of all life. The cell consists primarily of an outer plasma membrane, which separates it from the environment; the genetic material (DNA), which encodes heritable information for the maintainance of life; and the cytoplasm, a heterogeneous assemblage of ions, molecules, and fluid.
SIMILAR TERMS--------------------------------------
Concatemer
Multiple copies of a DNA sequence arranged end to end in tandem. Concatenate means to link together in a chain or in a series.
Concatenate
To link together in a chain or in a series. For example, the lymph nodes that appeared enlarged were concatenated, in a row like the links of a chain.
Concentraid
Concentraid is a prescription or over-the-counter drug which is (or once was) approved in the United States and possibly in other countries. Active ingredient(s): desmopressin acetate.
Concepcion doctors
All doctors near Concepcion, Chile. Doctors who can assist a patient in Concepcion.
Conception
When a sperm and egg join to form a single cell, usually in the Fallopiantubes. After joining, the fertilized egg travels into the uterus, where itimplants in the lining on its way to growing into an embryo and then a fetus.
Conceptivity
The proclivity for the physiology and behavior of a male and female to conceive, maintain pregnancy, and progress through parturition, lactation, and the childcare of parenthood
Concerta
Concerta is a prescription or over-the-counter drug which is (or once was) approved in the United States and possibly in other countries. Active ingredient(s): methylphenidate hydrochloride.
Concord doctors
All doctors near Concord, the United States of America. Doctors who can assist a patient in Concord.
Concord Hospital
Concord Hospital is a hospital in Concord, New Hampshire (USA).
Concord Repatriation General Hospital
The Concord Repatriation General Hospital is a hospital in Concord, New South Wales, Australia.
Concordance
1. The presence of any given condition such as HIV in both members of a couple. 2. In genetics, the presence of a phenotype such as asthma in both members of a twin pair. 3. In clinical care, agreement between physician and patient.
Concordant
1. Showing concordance, complete agreement. A couple may be concordant for a sexually transmitted infection, with both partners having it. 2. In transplantation genetics, between closely related species. A concordant xenograft is a transplant between members of closely related species.
Concordant couple
A pair of long-term sexual partners in which both partners have a sexually transmitted infection. The CDC has guidelines for counseling concordant couples in which both the man and woman are HIV-infected.
Concrete thinking
Thinking characterized by immediate experience, rather than abstractions. It may occur as a primary, developmental defect, or it may develop secondary to organic brain disease or schizophrenia.
Concussion
Any alteration in cerebral function caused by direct or indirect (rotation) force transmitted to the head resulting in one or more of the following: a brief loss of consciousness, lightheadedness, vertigo, cognitive and memory dysfunction, tinnitus, difficulty concentrating, amnesia, headache, balance disorder, nausea or vomiting.
Concussion of the brain
A traumatic injury to the brain as a result of a violent blow, shaking, or spinning. A brain concussion can cause immediate and usually temporary impairment of brain function such as of thinking, vision, equilibrium and consciousness.
PREVIOUS AND NEXT TERMS--------------------------------------
Chromostereopsis
The optics of the eye are such that short wavelengths are refracted slightly more than long wavelengths creating a positional disparity on the retina. When viewed by two eyes a stereoscopic disparity is obtained. This is termed Chromostereopsis or Chromatic Stereopsis
Closed-Loop control
A control system in which the output is continuously modified by feedback from the environment.
Color opponency
When a cell is excited by one part of the visible spectrum and inhibited by another. First observed in ganglion cells in the retina.
Color opponent channel
Pathway that begins with the midget (parvo) ganglion cells in the retina and terminates within the parvocellular layer of the LGN. Conduction slower than that of Magnocellular Pathway.
Complex cells
Cells in the primary visual cortex (V1) that responding either to an edge, a bar or a slit stimulus of a particular orientation falling anywhere in its receptive field. The exact location of the stimulus within the receptive field is not as critical. Have receptive fields longer than those of simple cells. The cell behaves non-linearly, responding to a drifting cosine grating with a uniform increase in activity with no sinusiodal modulcation (i.e. insensitive to phase). For a historical perspective see Simple Cells.
Concentric field
Cone opsin
Light absorbing molecule in cone cells.
Contrast sensitivity function
The reciprocal of the threshold contrast required to obtain a criterion response from a cell or a human subject as a function of spatial frequency. Falls off in sensitivity as the spatial frequency of the test pattern increases.
Coplanar ratio hyphothesis
An hypothesis by Gilchrist in which the visual system does not use retinal contrasts to determine relative lightnesses but uses depth information to determine which regions are at the same depth (coplanar) and uses their contrasts to deteremine the lightness perceived. This hypothesis has come under recent attack.
Correspondence problem
In Stereopsis: the challenge of matching elements in one eye with elements in another eye. Also known as the Matching Problem. In Motion:
the challenge of matching moving elements in one frame with elements in a succeeding frame (especially true of random dot cinematograms).
Corticaltectal pathway
Pathway from the cortex to the superior colliculi.
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