Search PubMed⌕ Search

Biomedical subjects

W Spileers

Publications and source records attributed to W Spileers.

42 records · Page 3Linked to original sources
PubMed1987

Responses of cat striate neurons to moving light and dark bars: changes with eccentricity.

Responses of area-17 neurons to light and dark bars moving over a wide range of speeds were measured over a range of receptive-field locations in anesthetized and paralyzed cats. For both light bars and dark bars, velocity sensitivity shifted to higher speeds with increasing eccentricity, whereas response strength and direction selectivity hardly changed. The good correlation between response strength and velocity sensitivity for light and dark bars suggests that ON and OFF inputs converge upon most area-17 cells. The correlation between direction selectivities for light and dark bars was not better than that between velocity sensitivities for light and dark bars. Only cells with strong direction selectivity were equally direction selective for light bars and dark bars. Comparison with previous studies done with high-contrast stimuli shows that the shift in sensitivity to higher speeds with increasing eccentricity is contrast dependent.

Animals↗
PubMedDate not supplied

Visually evoked potentials evoked by moving unidimensional noise stimuli: effects of contrast, spatial frequency, active electrode location, reference electrode location, and stimulus type.

We determined the relative importance of electrode derivation, stimulus type, spatial frequency and contrast in determining the relative size of the late negative and early positive responses of motion elicited VEPs. Seven subjects aged 22-48 years with normal vision were tested binocularly. Motion onset and motion reversal were employed as modes of stimulus presentation. For both, pseudo-random one-dimensional noise patterns whose peak power was at 5.2, 2.6, 1.3, 0.325 and 0.1625 cycles per degree (cpd) were stimuli. Contrasts were 70% and 5%. Active electrodes were placed at Oz, 5 cm to the left of Oz, 5 cm to the right of Oz and a frontal midline position (Fpz) and referenced to linked mastoids. Transient motion reversal elicited a prominent positive response present in all subjects and at low contrasts. Motion onset VEPs have a complex waveform which may be either predominantly positive or negative. The most important variables in determining whether a prominent positivity or negativity is present in the motion onset VEP are the contrast and the spatial frequencies. Data such as these are first efforts in developing recommendations for the motion VEP.

Acoustic Stimulation↗
PubMedDate not supplied

Cortical visual impairment following perinatal hypoxia: clinicoradiologic correlation using magnetic resonance imaging.

PURPOSE: To evaluate the value of magnetic resonance imaging (MRI) in the visual prognosis of cortical visual impairment following perinatal hypoxia. METHODS: MRI findings of 19 babies with the diagnosis of a perinatal hypoxic-ischemic insult and cortical visual impairment (CVI) were reviewed. Two groups of patients based on gestational age were compared. Babies with a gestational age > or = 34 weeks were included in group 1(n = 8). Infants < 34 weeks' gestation were included in group 2(n = 11). All 19 children underwent MRI. RESULTS: Normal MRI always correlated with better visual outcome, regardless of the gestational age at which the insult occurred. Among infants born at or later than 34 weeks' gestation, a favorable visual recovery occurred in two with normal MRI findings. The presence of infarcts or periventricular leukomalacia indicated that full visual recovery would not occur. Among infants born before 34 weeks' gestation, the MRI findings were normal in two who had a favorable visual outcome. A normal visual cortex and the absence of periventricular leukomalacia were helpful in prognosticating the visual outcome. A general delay in the myelination-particularly in the myelination of the optic radiation-was a common finding and until now has not been described in children with CVI routinely. CONCLUSION: MRI's ability to follow the process of myelination may be of predictive value. MRI, therefore, should be obtained in a child with CVI following perinatal hypoxia.

Asphyxia Neonatorum↗