Biomaterial Database

Refractive state, contrast sensitivity, and resolution in the freshwater turtle, Pseudemys scripta elegans, determined by tectal visual-evoked potentials. 1991

D P Northmore, and A M Granda

Department of Psychology, University of Delaware, Newark 19716.

Visual-evoked potentials (VEPs) were recorded from the surface of the optic tectum of the freshwater turtle, Pseudemys scripta elegans, in response to phase reversal of square-wave gratings of different spatial frequency and contrast. The refractive state of a group of 12 turtles in air was assessed from VEPs by placing trial lenses in front of the eye. The group mean refraction did not differ significantly from emmetropia, as compared to 4.8 diopters of hyperopia when refracted retinoscopically. The difference was explained by the retinoscopic reflex originating from the interface between vitreous humor and retina. Peak VEP amplitude was approximately linear with log grating contrast; extrapolation to zero VEP amplitude yielded contrast thresholds as low as 1%. High spatial-frequency cutoffs ranged from 4.4-9.9 cycle/deg in different animals, the highest values corresponding to the intercone spacing in the area centralis and to behavioral measures of acuity in a related species.

UI	MeSH Term	Description	Entries
D008027	Light	That portion of the electromagnetic spectrum in the visible, ultraviolet, and infrared range.	Light, Visible,Photoradiation,Radiation, Visible,Visible Radiation,Photoradiations,Radiations, Visible,Visible Light,Visible Radiations
D012029	Refraction, Ocular	Refraction of LIGHT effected by the media of the EYE.	Ocular Refraction,Ocular Refractions,Refractions, Ocular
D005074	Evoked Potentials, Visual	The electric response evoked in the cerebral cortex by visual stimulation or stimulation of the visual pathways.	Visual Evoked Response,Evoked Potential, Visual,Evoked Response, Visual,Evoked Responses, Visual,Potential, Visual Evoked,Potentials, Visual Evoked,Response, Visual Evoked,Responses, Visual Evoked,Visual Evoked Potential,Visual Evoked Potentials,Visual Evoked Responses
D000221	Adaptation, Ocular	The adjustment of the eye to variations in the intensity of light. Light adaptation is the adjustment of the eye when the light threshold is increased; DARK ADAPTATION when the light is greatly reduced. (From Cline et al., Dictionary of Visual Science, 4th ed)	Light Adaptation,Adaptation, Light,Adaptations, Light,Adaptations, Ocular,Light Adaptations,Ocular Adaptation,Ocular Adaptations
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D013477	Superior Colliculi	The anterior pair of the quadrigeminal bodies which coordinate the general behavioral orienting responses to visual stimuli, such as whole-body turning, and reaching.	Colliculus, Superior,Optic Lobe, Human,Optic Lobe, Mammalian,Optic Tectum,Anterior Colliculus,Superior Colliculus,Tectum, Optic,Colliculi, Superior,Colliculus, Anterior,Human Optic Lobe,Human Optic Lobes,Mammalian Optic Lobe,Mammalian Optic Lobes,Optic Lobes, Human,Optic Lobes, Mammalian,Optic Tectums,Tectums, Optic
D014426	Turtles	Any reptile including tortoises, fresh water, and marine species of the order Testudines with a body encased in a bony or cartilaginous shell consisting of a top (carapace) and a bottom (plastron) derived from the ribs.	Sea Turtles,Terrapins,Tortoises,Sea Turtle,Terrapin,Tortoise,Turtle,Turtle, Sea,Turtles, Sea
D014792	Visual Acuity	Clarity or sharpness of OCULAR VISION or the ability of the eye to see fine details. Visual acuity depends on the functions of RETINA, neuronal transmission, and the interpretative ability of the brain. Normal visual acuity is expressed as 20/20 indicating that one can see at 20 feet what should normally be seen at that distance. Visual acuity can also be influenced by brightness, color, and contrast.	Acuities, Visual,Acuity, Visual,Visual Acuities
D015350	Contrast Sensitivity	The ability to detect sharp boundaries (stimuli) and to detect slight changes in luminance at regions without distinct contours. Psychophysical measurements of this visual function are used to evaluate VISUAL ACUITY and to detect eye disease.	Visual Contrast Sensitivity,Sensitivity, Contrast,Sensitivity, Visual Contrast