Effect Of Signal Intensity Research Articles

Effect of Signal Intensity on Measurement of Ganglion Cell Complex and Retinal Nerve Fiber Layer Scans in Fourier-Domain Optical Coherence Tomography.

We determined the effect of Fourier-domain optical coherence tomography (OCT) signal strength index (SSI) and cropping on retinal nerve fiber layer (RNFL) and macular ganglion cell complex (GCC) scan repeatability and measurement thickness. Eyes were enrolled in the longitudinal Advanced Imaging for Glaucoma Study. At each visit, three repeat scans from the optic nerve head and macular protocols were obtained. Each measurement was associated with an SSI value from 0 to 100. Measurements with similar SSI scores were grouped to calculate repeatability defined as pooled standard deviation. Within-visit analysis was used to determine how measured thickness changed in relation to change in SSI level. The study included 1130 eyes of 569 patients. Cropped images yielded significantly worse repeatability and they were excluded from subsequent analyses. The within-visit repeatability for RNFL and GCC measurements were significantly better with higher signal strength, and optimal cutoffs were SSI ≥ 37 and ≥ 44, respectively. The coefficient of variation was <1.8% for RNFL scans with SSI ≥ 37 and < 2% for GCC with SSI ≥ 44. For scans above the cutoff SSI, higher SSI's were correlated with thicker RNFL among normal (slope = 0.056 μm/SSI unit, P < 0.001) eyes and glaucoma suspect and perimetric glaucoma (GSPPG) eyes (slope = 0.060 μm/SSI unit, P < 0.001), but not for perimetric glaucoma (PG) eyes. No significant correlation was found for GCC. Repeatability of RNFL and GCC thickness measurements may be improved by excluding images with cropped anatomic features and weak signal strength below recommended SSI cutoffs. Measurement precision and image quality of inner eye structure by advanced imaging modality are important for clinical diagnosis and tracking of glaucoma disease.

Effect of signal intensity and camera quantization on laser speckle contrast analysis

Laser speckle contrast analysis (LASCA) is limited to being a qualitative method for the measurement of blood flow and tissue perfusion as it is sensitive to the measurement configuration. The signal intensity is one of the parameters that can affect the contrast values due to the quantization of the signals by the camera and analog-to-digital converter (ADC). In this paper we deduce the theoretical relationship between signal intensity and contrast values based on the probability density function (PDF) of the speckle pattern and simplify it to a rational function. A simple method to correct this contrast error is suggested. The experimental results demonstrate that this relationship can effectively compensate the bias in contrast values induced by the quantized signal intensity and correct for bias induced by signal intensity variations across the field of view.

N100 cortical potentials accompanying disrupted auditory nerve activity in auditory neuropathy (AN): Effects of signal intensity and continuous noise

Auditory temporal processes in quiet are impaired in auditory neuropathy (AN) similar to normal hearing subjects tested in noise. N100 latencies were measured from AN subjects at several tone intensities in quiet and noise for comparison with a group of normal hearing individuals. Subjects were tested with brief 100 ms tones (1.0 kHz, 100-40 dB SPL) in quiet and in continuous noise (90 dB SPL). N100 latency and amplitude were analyzed as a function of signal intensity and audibility. N100 latency in AN in quiet was delayed and amplitude was reduced compared to the normal group; the extent of latency delay was related to psychoacoustic measures of gap detection threshold and speech recognition scores, but not to audibility. Noise in normal hearing subjects was accompanied by N100 latency delays and amplitude reductions paralleling those found in AN tested in quiet. Additional N100 latency delays and amplitude reductions occurred in AN with noise. N100 latency to tones and performance on auditory temporal tasks were related in AN subjects. Noise masking in normal hearing subjects affected N100 latency to resemble AN in quiet. N100 latency to tones may serve as an objective measure of the efficiency of auditory temporal processes.

Effect of Signal Intensity from the Accumulated Microbubbles in the Liver for Differentiation of Idiopathic Portal Hypertension from Liver Cirrhosis

To examine the possibility of using contrast material-enhanced ultrasonography (US) to differentiate idiopathic portal hypertension (IPH) from cirrhosis. This was an institutional review board-approved prospective study with written informed consent. The study consisted of 23 patients (mean age, 60 years +/- 11; range, 37-85 years) with biopsy-proved cirrhosis, 10 patients (mean age, 65 years +/- 8; range, 51-78 years) with IPH, and 27 control subjects (mean age, 46 years +/- 17; range, 26-82 years) without any focal hepatic lesions or portal vein thrombosis. The patients underwent contrast-enhanced US for the observation of the right liver lobe. The time of the onset of contrast enhancement in the right hepatic artery and right portal vein was examined at vascular phase under continuous low-power emission, and signal intensity differences (in decibels) by using instantaneous high-power emission in the liver parenchyma were analyzed at late phase (15 minutes). Interobserver variability was quantified as coefficients of variation. Onset time of contrast enhancement in the right portal vein was significantly longer for both IPH (22 sec +/- 3.9, P = .0035) and cirrhosis (19.3 sec +/- 4.7, P = .04) patients than for control subjects (17 sec +/- 3.3), with no significant difference in the onset time in the right hepatic artery. Images obtained in both IPH patients (21.2 dB +/- 1.4) and control subjects (22.1 dB +/- 2.2) had significantly higher signal intensity differences than those obtained in cirrhosis patients (13.8 dB +/- 2.8, P < .0001), with no significant difference between images of IPH patients and control subjects. Signal intensity differences of more than 18 dB had 100% sensitivity and specificity for the diagnosis in IPH patients and control subjects. Interobserver variability for signal intensity differences was 8.7%. Contrast-enhanced US may offer the possibility for a simple, easy, and noninvasive diagnosis of IPH.

Effect of signal intensity on perceived speed

The effect of signal intensity (proportion of dots moving in the same direction compared to noise dots that move in random directions) on perceived speed was investigated. It was found that increasing signal level decreased the perceived speed of the stimulus. This finding indicates that global-motion pooling processes play a role in the extraction of speed information. It is suggested that the amount of relative motion in the stimulus influences perceived speed, with perceived speed increasing with increasing relative motion. The results are discussed in relation to the notion that speed and direction are processed, at least in part, differently.

Selective effects of partial striatal 6‐OHDA lesions on information processing in the rat

The present study was aimed at characterizing the cognitive deficits caused by the degeneration of nigrostriatal dopamine (DA) pathways by using the additive factor logic [Sternberg, S. (1969) Acta Psychol., 30, 276-315], a powerful reaction time (RT) method developed in humans and recently introduced in the rat [Courtiere, A., Hardouin, J., Hasbroucq, T., Possamai, C.-A. & Vidal, F. (2000) Behav. Process., 50, 113-121]. Long-Evans rats were trained to respond to left or right (lateral) visual cues in a choice RT task. Two task factors, signal intensity and force requirement, were manipulated. Partial bilateral 6-OHDA lesions of DA nerve terminals in the striatum were then performed and their effects tested for up to 7 weeks following surgery. Reaction time was lengthened from the 2nd to the 4th week postlesion. This alteration was independent of force requirement, thereby suggesting that the related motor processes were not influenced by the DA depletion. During the 2nd week postlesion, the RT increase was accompanied by a disappearance of the effect of signal intensity, showing that the lesion altered stimulus-related processes. From the 3rd week the signal intensity effect was re-established although RT was still increased, indicating that the stimulus-related processes had recovered while other central processes were still impaired. From the 5th week after surgery, the lesioned animals had completely recovered from the RT deficits induced by the lesion. These results point at the involvement of striatal DA in sensory and central information processes.

MR imaging in chronic hepatitis and cirrhosis

The role of magnetic resonance imaging (MRI) in the evaluation of diffuse parenchymal abnormalities of the liver has been expanded by recent technical advances of MR systems as well as the evolution of intravenous contrast media. Currently, MR is undoubtedly the most useful imaging modality for detecting the presence of chronic liver disease. Tailored sequences allow acurate depiction of specific disorders, including steatohepatitis and iron-overload states. Morphologic changes and signal intensity effects not only facilitate the diagnosis of chronic liver disease with MRI but they also help to distinguish between different etiologies, and they assist in staging the histologic severity of certain chronic conditions. Moreover, the faster MRI scanning techniques presently available permit the dynamic assessment of contrast enhancement, which permits improved characterization of focal hepatic lesions, including regenerative nodules, dysplastic nodules, and hepatocellular carcinoma (HCC). Although overlap in MRI findings still may exist among different types of chronic liver disease and among focal liver lesions, familiarity with certain specific imaging features may be diagnostic in the proper clinical setting. Finally, comprehensive MRI examination, including MR angiography and MR cholangiography, is the most sensitive and cost-effective technique for detecting extrahepatic disease, diagnosing vascular disorders, and evaluating the patient before or after liver transplantation. This article focuses on the current role of MR imaging in patients with chronic liver disease. The subjects covered include the detection and characterization of chronic hepatitis and cirrhosis, specific findings seen in steatohepatitis and certain metabolic diseases, the evaluation of extrahepatic vascular complications of cirrhosis, and patient assessment before and after liver transplantation. The characterization of hepatic masses is also included briefly. This subject is covered in greater depth elsewhere in this issue.

Detection of visual signals by rats: effects of signal intensity, event rate, and task type

Animal models of human cognitive processes are being developed for investigating the neurobiological mechanisms of these processes and for identifying potential therapies for intoxication and neurodegenerative diseases. One promising method involves assessment of sustained attention in rats by use of a discrete-trial signal detection task. Several psychophysical and procedural factors have been identified in the literature that affect sustained attention in normal human subjects. Three key parameters that affect the level of performance, and whether that performance level deteriorates over time, include the quality of the signal, the event rate, and the type of task employed (simultaneous or successive discrimination). These three parameters were manipulated in this study to assess the degree of similarity in the behavior patterns engendered in rats by this signal detection task, in relation to the behavior observed in humans performing a variety of sustained attention tasks. Signal quality was manipulated by varying the increment in the intensity of a lamp (duration=300 ms), and event rate was varied among values of 4, 7, and 10 trials/min. The ‘standard’ detection task was used as a simultaneous discrimination and a successive discrimination task was designed in which a dim light flash was defined as a non-signal event and any of three brighter flashes were signal events. Accuracy of signal detection was quantified by the proportion of correct detections of the signal [P(hit)] and the proportion of false alarms [P(fa), i.e., incorrect responses on non-signal trials]. P(hit) fell with decreasing signal intensity, increasing event rate, and was lower in the discrimination task compared to the detection task. P(fa) increased with increasing event rate, but only in the detection task. A decrement in P(hit) across trial blocks was observed in the discrimination task primarily, and was most evident with a high event rate and dim signals. These data confirm that these tasks assess process(es) in rats that are very similar to those considered as sustained attention in humans.

Total Lifetime Distribution Analysis for Fluorescence Fingerprinting and Characterization

A new technique, total lifetime distribution analysis (TLDA), is described for rapid, sensitive, and accurate lifetime characterization of complex samples. Multiharmonic Fourier transform technology in a commercial, frequency-domain fluorescence lifetime instrument allows rapid acquisition of TLDA data. High sensitivity derives from the use of the entire fluorescence emission from the sample in the lifetime measurement. The maximum entropy method (MEM) provides a consistent basis for modeling of the lifetime data for accurate recovery of the total lifetime distribution of the sample. Because MEM is self-modeling, it is not subject to the same sources of bias that influence nonlinear least-squares fits of lifetime data to a priori models. These features make TLDA an effective tool for sample characterization and fingerprinting that is based on the responsiveness of fluorescence lifetime to the chemical composition and dynamic processes that contribute to the uniqueness of the sample. TLDA results are presented for coal liquids and a humic substance. The effect of signal intensity on lifetime recovery is investigated, and comparison is made between MEM and conventional nonlinear least-squares for data analysis.

ChemInform Abstract: STRUCTURE ELUCIDATION USING SIGNAL INTENSITY EFFECTS IN CARBON‐13 NUCLEAR MAGNETIC RESONANCE

Chemischer InformationsdienstVolume 15, Issue 25 Physical Organic Chemistry ChemInform Abstract: STRUCTURE ELUCIDATION USING SIGNAL INTENSITY EFFECTS IN CARBON-13 NUCLEAR MAGNETIC RESONANCE M. J. SHAPIRO, M. J. SHAPIROSearch for more papers by this authorM. X. KOLPAK, M. X. KOLPAKSearch for more papers by this authorT. L. LEMKE, T. L. LEMKESearch for more papers by this author M. J. SHAPIRO, M. J. SHAPIROSearch for more papers by this authorM. X. KOLPAK, M. X. KOLPAKSearch for more papers by this authorT. L. LEMKE, T. L. LEMKESearch for more papers by this author First published: June 19, 1984 https://doi.org/10.1002/chin.198425048Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume15, Issue25June 19, 1984 RelatedInformation

Structure elucidation using signal intensity effects in carbon-13 nuclear magnetic resonance

Structure elucidation using signal intensity effects in carbon-13 nuclear magnetic resonance

The effects of signal intensity upon conditioned suppression: Effects upon responding during signals and intersignal intervals

Two rat experiments were run to study the effects of a wide range of signal (CS) intensities on the suppression of licking. In Experiment 1, a light CS was varied over five levels, including zero intensity. Conditioned suppression was found to vary directly with CS intensity, but basal lick rates were not different among groups. In Experiment 2, an attempt was made to disturb the basal rate of licking, while a tone CS was varied over four levels, including zero intensity. Here the suppression of the CS rates was found to be directly related and basal rates inversely related to CS intensity. The results as a whole were consistent with the Perkins-Logan hypothesis regarding the effects of CS intensity upon conditioning, but not with the Rescorla-Wagner model of classical conditioning.

The Cardiac Component of the Orienting Response: Effects of Signal Intensity, Clinical Interpretation, and Procedural Limitations

The effects of stimulus intensity on the cardiac component of the orienting response were explored in male and female subjects. The acoustic stimuli were 10 recorded repetitions of an identical consonant vowel cluster spoken by an adult male. Heart rate data were obtained for both subject groups at three sensation levels across the baseline heart rate and at 10 stimulus presentation trials. A significant main effect was noted for trials. Significant linear and quadratic trend components were observed, reflecting habituation of the orienting response as a function of trials, and indicating the nonmonotonicity of heart rate change over trials. A lower mean heart rate was observed for Condition Two (20 dB SL) than for either of the other conditions, 10 dB and 30 dB SL respectively. Analysis of group variability and individual subjects' heart rate data suggested limitations in generalizing from group to individual data, as well as a need for further investigation if proper interpretation of single subject heart rate data are to be useful in the clinical situation.

The Relationship between Reaction Time and Intensity in Discrete Auditory Tasks

The effect of signal intensity upon reaction time (RT) was studied in three auditory RT tasks in which the signal was a tone of high or low frequency. Experiment I showed the well-known negative gradient with intensity of simple RT when the subject was instructed to ignore the frequency and give the same response to both tones. But when the subject had to discriminate the frequency in a choice RT task, the RT/intensity relationship appeared to be U-shaped. Experiment II showed that when the subject was required to make a response to one signal but withhold it for the other, a task which requires discrimination of the frequency of the tone but removes the necessity to choose between overt responses, no increase in RT at high intensities was obtained. The results indicate that it is the response choice stage rather than the stimulus encoding stage which is retarded at higher energy levels. Experiment I also demonstrated that visual and auditory leading signals have similar facilitating effects without affecting the RT/intensity relationships.

Auditory reaction time as a function of stimulus intensity, frequency, and rise time

The effects of signal intensity, frequency, and rise time on auditory reaction time (RT) were investigated in this study. Equal-loudness data were first obtained for 100-, 1,000-, and 10,000-Hz tones at intensity levels of 20, 40, 60, and 80 phons. These tones were presented subsequently as RT signals with variable rise times. The main effects indicated that (1) RT increased systematically with signal rise time, (2) RT was inversely related to signal intensity, and (3) equally loud stimuli did not produce equivalent RTs at different signal frequencies. In view of our failure to obtain equal-RT functions across signal frequencies, it was proposed that the detection of a stimulus and the judgment of its loudness require different perceptual processes.

Effects of signal intensity and noise on the pitch mixture of dichotic chords.

The relative salience of the two pitch components (the pitch mixture) of a two-tone dichotic chord (one tone to each ear via earphones) has been shown to be invariant with respect to the interaural intensity difference (ΔI) over a wide range of ΔI [Efron and Yund, J. Acoust. Soc. Am. 59, 889–898 (1976)]. This range of invariance of the pitch mixture was systematically studied as a function of absolute signal level and signal-to-noise ratio. Results indicate that a decrease in the signal-to-noise ratio and a decrease in the sound-pressure level both served to decrease the range of interaural intensity differences over which the invariance occurs. However, while a decrease in both parameters decreased the range of intensity independence, there was a strong interaction between these parameters: The addition of noise eliminated the effect of sound-pressure levels. These findings are discussed in the context of the model described in the companion paper [Yund and Efron, J. Acoust. Soc. Am. 62, XXX–XXX(1977)].

Effects of signal intensity and reinforcer intensity on detection of electrical brain stimulation

The effects of intensity of signal and intensity of reinforcer on “yes/no” discrimination behavior were studied using electrical brain stimulation of one site for the signal and of another, contralateral site for the reinforcer. Accuracy declined as signal intensity declined, whereas accuracy was greatest with middle values of reinforcers. There was no statistical interaction between intensity of signal and intensity of reinforcer, indicating that processing of the aftereffects of the signals was not differentially influenced by intensity of reinforcers. Analysis of the detection behavior suggests that reinforcer level influenced decision criteria rather than sensitivity to the signal.

Selective attention and the auditory vertex potential. II. Effects of signal intensity and masking noise

A randomized sequence of tone bursts was delivered to subjects at short inter-stimulus intervals (mean ISI of 333 msec), with the tones originating from one of three spatially and frequency-specific channels. The subject's task was to count the tones in one of the three channels at a time, ignoring the other two, and press a button after each tenth tone. In different conditions, tones were given at high (60 dB SL) and low (20 dB SL) intensities and with or without a background white noise to mask the tones. The N 1 component of the auditory vertex potential was found to be larger in response to attended-channel tones than in relation to unattended tones. This selective enhancement of N 1 was minimal for loud tones presented without noise and increased markedly for the lower tone intensity and in noise-added conditions. The selectivity of attention as measured physiologically in this multichannel listening task was thus greater when tones were faint and/or difficult to detect.

Detection of Tones in the Absence of External Masking Noise. I. Effects of Signal Intensity and Signal Frequency

Twelve highly trained listeners detected tonal signals in the absence of external masking noise. The signals were 150 msec long and ranged from 125 to 4000 Hz. Fitted psychometric functions were steeper at high than at low frequencies requiring between 3- and 8-dB increase in signal level to raise performance from 60% to 95% correct. The signal levels that yield 76% correct detection in a two-alternative, forced-choice psychophysical procedure were in good agreement with the International Standards Organization's recommended values of audiometric zero. The results are consistent with a limitation imposed on auditory sensitivity by a “system noise” which is composed of the noise in the ear canal at low frequencies, and a low-level (−11 dB SPL) component of unspecified origin at medium and high frequencies. No qualitative differences were observed between detection without external masking noise and previous data on the detection of tones masked by noise.

Effects of signal intensity on increase of reaction time on an auditory monitoring task.

5 Ss were required to respond as rapidly as possible to auditory signals of threshold, 34, 48, and 88 db intensity, mixed within the same 2-hr. session. Reaction time increased over time for all signal intensities, but the increase was larger for the threshold signal. There were two kinds of increase, one independent of signal intensity transferring the entire distribution toward longer reaction times. The other kind of increase was dependent on signal intensity and increased the number of long reaction times for the threshold signal.