Showing papers on "Latency (engineering) published in 1981"

Pattern Evoked Cortical Potentials and Automated Perimetry in Chronic Glaucoma

Abstract: Chronic glaucoma causes visual field defects and in some cases an increase in the latency of pattern evoked visual potentials (P E P). To assess the contribution of field defects to the latency increase in PEP we have reexamined 16 glaucoma patients out of a group of 27 whose PEP had been recorded two years before (Huber and Wagner 1978). PEP measurements and visual fields measured by automated static perimetry (Octopus) where compared. A significant increase in PEP latency could only be demonstrated in the presence of a relative central scotoma. The depth of the relative scotoma is related to the increase in latency. Peripheral field defects do not affect the PEP latency as a small central island of vision with normal sensitivity is sufficient to produce a normal PEP. A large visual field with reduced central sensitivity can however result in a large latency increase. Over a period of two years the shape of the individual PEP is constant. The latency increase in glaucoma thus represents a differential diagnosis of increased PEP latency in the context of neurological diseases. PEPs are not an adequate method for the detection of early glaucoma as the sensitivity of the visual field’s center can be unaffected for a long time in this disease.

A reassessment of sensory evoked potential parameters in multiple sclerosis: a discriminant analysis approach.

Abstract: The sensitivity of the different parameters (absolute latency, interwave latency, latency asymmetry, amplitude) of both cervical and cerebral responses evoked by stimulation of the median nerve at the wrist was assessed in patients with multiple sclerosis by discriminant analysis. The peak latency of N13 or N20 SEP components or both was found to be more sensitive than their amplitude, provided that a preliminary covariation with the height of the subjects was performed. The measurement of latency asymmetry between the two sides increased the test's sensitivity, while amplitude asymmetry turned out to be of little diagnostic value. A linear discriminant function with four variates (that is mean amplitude, mean latency, latency asymmetry and height of the subject) was computed to summarise the information provided by the different parameters to give a rapid and exact method for the assessment of SEP abnormalities in multiple sclerosis patients.

[Characteristics of the unitary end-plate potential of the frog (author's transl)].

Abstract: When the transmitter release is reduced in physiological solutions with low calcium and high magnesium content (70% of transmission failure), most of the end-plate potentials are evoked by the release of one quantum. Observing a short sequence of the unitary potentials (10-30), one can see that they distribute into a few patterns of similar amplitude, latency and time to peak. The amplitude and latency frequency distributions show successions of peaks frequently set at regular intervals. The average number of peaks is 11 for the amplitude distribution and 14.5 for the latency distributions. Lowering the temperature (20-10 degrees C) lengthens the interval between the latency peaks (Q10 = 2). These observations suggest the existence of a limited number of releasing sites set at regular intervals (10-20 micrometers) along the branches of the nerve terminal. This hypothesis is discussed with regard to the well-known interpretation of the amplitude sub-units of the unitary response and the sub-miniature potentials. The time-distribution of the unitary-evoked potentials of identical latency is frequently periodic (about 60 s at 4 HZ of frequency stimulation). Slightly different frequencies can be observed at different latency values. Through our interpretation of the sub-units, these facts mean that the few active zones follow a periodic process which can explain the periodic oscillation already shown for the total activity of the neuromuscular junction.

Effects of pretraining and highly redundant irrelevant dimensions on acquisition and response latency in identification of concepts

Abstract: 64 subjects were required to learn a concept identification task. One half of the subjects learned a task in which one of the irrelevant dimensions was highly (p = .75) redundant with the relevant dimension and one-half of the subjects learned a task in which all irrelevant dimensions were normally (p = .5) redundant. One half of each of these groups received additional pretraining. The major findings were that mean response latencies were longer and acquisition was slower for groups trained with a highly redundant irrelevant dimension than for groups trained with normally redundant irrelevant dimensions. These results were interpreted as supporting an hypothesis that sampling sets remain large for groups trained with a highly redundant irrelevant dimension and are the basis for slower acquisition.