Biomedical subjects

R S Noss

Publications and source records attributed to R S Noss.

4 recordsLinked to original sources

PubMed1998

Very late pain-related activity identified with topographically mapped frequency domain analysis of evoked potentials.

OBJECTIVE: To identify low-frequency activity in the pain-evoked potential at very late latencies, consistent with C-fiber transmission velocities. METHODS: Brief (1 ms) painful (intracutaneous) and two levels of non-painful (mild and strong) electrical pulses were applied to the index and middle fingers of the left hand. Evoked potentials (EPs) were recorded from 30 electrodes covering the entire scalp. Data from the 3 stimulus conditions (approximately 60 trials per condition per subject) were compared using the frequency domain technique of complex demodulation applied to single trial data. Subjects were 14 normal right-handed male human volunteers, aged 19-36 years. RESULTS: Using descriptive probability mapping, pain versus strong non-pain differences were found in grand average data as well as in 8 of 14 subjects, consisting of greater low-frequency power at latencies from 700 to 1100 ms at electrodes near the contralateral central sulcus and at the vertex. CONCLUSIONS: There are topographically focal, pain versus non-pain differences in the 700-1100 ms latency range that can be seen using frequency-domain analytic techniques. These differences were not seen with traditional time domain analyses. They may be due to a C-fiber-related mechanism or to very late activity triggered by faster fibers.

Adult↗

PubMed1996

Apparent motion confounds early vernier visual evoked potentials.

Human scalp potentials evoked by vernier stimuli have been recorded for offsets less than the diameter of a foveal cone, but always for abruptly moving stimuli. Those evoked potentials were related to the magnitude of vernier offset. Here we report results for stimuli containing no apparent motion confound, using multichannel recordings and multivariate analysis methods which stress the concept of a sampling of the scalp field. We found evidence of cortical activity dependent on the direction of vernier offset, at much shorter latencies (ca. 75 ms) than previously reported, but no evidence of early cortical activity related to the magnitude of offset. Repeating the experiments and analysis using a stimulus containing apparent motion, we found evidence of cortical activity dependent on the magnitude of offset at both 75 and 200 ms, but none related to direction of offset. These findings suggest that previous studies which contained the apparent motion confound might not have obtained visual evoked potentials entirely due to vernier offset.

Electroencephalography↗

PubMed1996

Steady-state analysis of somatosensory evoked potentials.

We report the development of a new method for frequency domain analysis of steady-state somatosensory evoked potentials (SEPs) to amplitude-modulated electrical stimulation, which can be recorded in significantly less time than traditional SEPs. Resampling techniques were used to compare the steady-state SEP to traditional SEP recordings, which are based on signal averaging in the time domain of cortical responses to repetitive transient stimulation and take 1-2 min or more to obtain a satisfactory signal/noise ratio. Median nerves of 3 subjects were stimulated continuously with electrical alternating current at several modulation frequencies from 7 to 41 Hz. Amplitude modulation was used to concentrate the power in higher frequencies, away from the modulation frequency, to reduce the amount of stimulus artifact recorded. Data were tested for signal detectability in the frequency domain using the T(circ)2 statistic. A reliable steady-state response can be recorded from scalp electrodes overlying somatosensory cortex in only a few seconds. In contrast, no signal was statistically discriminable from noise in the transient SEP from as much as 20 s of data. This dramatic time savings accompanying steady-state somatosensory stimulation may prove useful for monitoring in the operating room or intensive care unit.

Adult↗

PubMed1994

Line intensity affects perceived shape.

A method for measuring the variation of one stimulus parameter with respect to another is applied to show how line intensity affects the perceived tilt of lines, internal angle of chevrons, and curvature of circular arcs. Perceived curvature increased with increasing line intensity, but analogous effects were found only for obtuse chevrons, not for acute ones, suggesting a limit to the range of orientations which contribute to the processing of curvature. The absence of a clear trend for tilted lines and acute angles highlights the specificity of the curvature findings. Explanations based on a computer model and other psychophysical and single-unit studies are examined.

Computer Simulation↗