Search PubMed⌕ Search

Biomedical subjects

W H Ehrenstein

Publications and source records attributed to W H Ehrenstein.

41 records · Page 3Linked to original sources
PubMed1985

Foveal interocular time thresholds and latency differences in multiple sclerosis.

Nineteen patients with suspected multiple sclerosis (MS) and 28 control subjects were foveally stimulated by a small cross formed by rectangular red-light-emitting diodes. By means of crossed polarizers one eye was exposed only to the horizontal bar of the cross, the other to the vertical. Stimulus onset asynchrony ranged from 0 to +/- 300 ms (the horizontal bar preceding or following the vertical). The task was to indicate whether the horizontal or vertical bar had appeared first. Compared with normal subjects, MS patients exhibited much higher time thresholds (ranging from -150 to +130 ms) and had considerable interocular latency differences (up to 29 ms), indicating unilateral or asymmetrical impairment of the visual pathways. The psychophysical latency differences of the patients were compared to monocular latencies and interocular latency differences of the visually evoked cortical potential (VEP) obtained by foveal stimulation. Under the stimulus conditions chosen in this study, the diagnostic value of the psychophysical measurements was equal to or, for McAlpine's classes I and II of definite and probable MS patients, better than that based on VEP recordings.

Adult↗
PubMed1983

Time thresholds for increments and decrements in luminance.

Time thresholds, i.e., the minimal durations necessary to just detect a change in brightness, were measured for light increments and decrements of a 1 degree test spot centered on a background of 20 degrees. Background luminance varied from -1 to 3 log td and retinal eccentricity from 0 degree to 50 degrees. Step size ranged from 0.04 to 1.5 log units and was the same in absolute units for both directions. Two types of stimuli were used: Type A, in which increments and decrements emerge from the same uniform background, and Type B, in which increments are the same as in Type A but decrements consist of a brief interruption of the test spot. Type A stimulation resulted in similar time thresholds for increments and decrements or, under some conditions, slightly shorter decrement thresholds. Type B stimulation resulted in similar thresholds for foveal vision. However, with increasing step size, decreasing background luminance, and increasing eccentricity, the time threshold for the decrement progressively exceeded that for the increment (up to 80 msec). This difference is attributed to different rise and fall times of the photoreceptor response as well as to Troxler's effect.

Adult↗
PubMed1982

Trail Making Test and visual search.

The performance in the Trail Making Test (Form A) was correlated with a variety of verbal and nonverbal tests in 5 groups of patients: Broca's aphasics (N = 18), Wernicke's aphasics (N = 19) and nonaphasic patients with right hemisphere (N = 20), left hemisphere (N = 17) or diffuse (N = 18) lesions. Correlations with the Trail Making Test were found for two tests, both requiring visual search. The "Objects Finding Test" in which the target varies from item to item showed high correlations for all groups of patients. The "Hidden Patterns Test", in which the target is kept constant, correlated only on the groups of nonaphasic patients. It is concluded (1) that visual search, as tested here, is not restricted to lateralized cortical functions, and (2) that the performance in the Trail Making Test depends largely upon processes involved in visual search of varying targets.

Adult↗
PubMed1977

Geometry in visual space-some method-dependent (arti)facts.

The measure of scalar curvature K varies with the method used to determine it. Overconstancy is found only with simultaneous comparison, nearly perfect constancy results from successive judgement, while absolute judgement produces underconstancy.

Female↗