Threshold Procedure Research Articles

Good vibrations: Human interval timing in the vibrotactile modality

This article reports a detailed examination of timing in the vibrotactile modality and comparison with that of visual and auditory modalities. Three experiments investigated human timing in the vibrotactile modality. In Experiment 1, a staircase threshold procedure with a standard duration of 1,000 ms revealed a difference threshold of 160.35 ms for vibrotactile stimuli, which was significantly higher than that for auditory stimuli (103.25 ms) but not significantly lower than that obtained for visual stimuli (196.76 ms). In Experiment 2, verbal estimation revealed a significant slope difference between vibrotactile and auditory timing, but not between vibrotactile and visual timing. That is, both vibrations and lights were judged as shorter than sounds, and this comparative difference was greater at longer durations than at shorter ones. In Experiment 3, performance on a temporal generalization task showed characteristics consistent with the predications of scalar expectancy theory (SET: Gibbon, 1977) with both mean accuracy and scalar variance exhibited. The results were modelled using the modified Church and Gibbon model (MCG; derived by Wearden, 1992, from Church & Gibbon 1982). The model was found to give an excellent fit to the data, and the parameter values obtained were compared with those for visual and auditory temporal generalization. The pattern of results suggest that timing in the vibrotactile modality conforms to SET and that the internal clock speed for vibrotactile stimuli is significantly slower than that for auditory stimuli, which is logically consistent with the significant differences in difference threshold that were obtained.

Visual fields after refractive surgery

Abstract Purpose Laser correction of ametropias is achieved by changing the radius of curvature of a central portion of the cornea. Although current refractive laser technology allows relative uniform correction across an optical zone larger than the scotopic pupil it must be kept in mind that centration of the ablation pattern pertains only to objects on the line of sight. Off‐axis objects are imaged not only through the corrected portion of the cornea but additionally through a meniscus of paracentral cornea involving the transition zone as well as untreated cornea. It was the purpose of this study to investigate the role of this optical effect in the peripheral visual fields in patients undergoing photorefractive keratectomy. Methods Twenty one eyes of thirteen patients were evaluated before and 3 months following PRK for the correction of myopia (average: ‐3.4D, SD:2.4D) at an optical zone of 6.5mm with the Allegretto 400 Excimer laser. Evaluation of the optical fields was made using the MEDMOND M700 visual fields analyzer using a full threshold procedure. Measurements were performed under cycloplegia while in all cases the subjects were corrected for the distance of the stimulus (+3 D) Results The detection threshold exhibited a decrease ranging from 0.5 to 9 dB (mean:1.5 dB, SD:2.5) for the periphery of the optical field (30 to 40 degrees). This change was statistically significant (p=0.00628). No statistically significant difference was observed for the central visual field (0‐22 degrees). Conclusion The loss of peripheral visual fields following refractive surgery may be attributed to the deteriorated retinal image quality in the peripheral visual field. A mathematical model of this reduction is proposed

Randomized phase effects in amplitude modulated/quasi‐frequency modulated discrimination.

This study investigated the bandwidth of phase sensitivity (i.e., discrimination of waveform envelopes). Subjects discriminated amplitude modulated (AM) tones, and quasi‐frequency modulated (QFM) tones in a 2IFC. An adaptive threshold procedure was used to estimate modulation depth m needed to make the discrimination as a function of carrier and modulation frequency. Nonmonotonic threshold functions were often observed at higher modulation frequencies. The effect is discussed in terms of two potential cues: (1) waveform envelope, (2) cubic distortion products. In order to degrade the information obtained from the distortion products, the phase for the carrier frequency was randomly sampled with a range of, Δθ=π/3. The randomized phase diminishes the nonmonotonicities of the threshold functions. Final results show that bandwidths of maximum sensitivity are not proportional to carrier frequencies. There are also noticeable individual differences in both the effects of the distortion products and the maximum bandwidths of sensitivity. [Work supported by NSF BCS‐07464003.]

Affective and somatic aspects of spontaneous and precipitated nicotine withdrawal in C57BL/6J and BALB/cByJ mice

The aversive aspects of nicotine withdrawal are powerful motivational forces contributing to the tobacco smoking habit. We evaluated measures of affective and somatic aspects of nicotine withdrawal in C57BL/6J and BALB/cByJ mice. Nicotine withdrawal was induced by termination of chronic nicotine delivery through osmotic minipumps or precipitated with the nicotinic acetylcholine receptor (nAChR) antagonists mecamylamine or dihydro-β-erythroidine (DHβE). A rate-independent discrete-trial intracranial self-stimulation threshold procedure was used to assess brain reward function. Anxiety-like behavior and sensorimotor gating were assessed in the light–dark box and prepulse inhibition (PPI) tests, respectively. Acoustic startle response and somatic signs of withdrawal were also evaluated. Spontaneous nicotine withdrawal after 14-day exposure to 10–40 mg/kg/day nicotine induced no alterations in anxiety-like behavior, startle reactivity, PPI, or somatic signs in either strain, and no changes in thresholds in C57BL/6J mice. Extended 28-day exposure to 40 mg/kg/day nicotine induced threshold elevations, increased somatic signs, and anxiety-like behavior 24 h post-nicotine in C57BL/6J mice; thresholds returned to baseline levels by day 4 in nicotine-exposed mice. Mecamylamine or DHβE administration induced threshold elevations in nicotine-exposed C57BL/6J mice compared with saline-exposed mice. In conclusion, administration of relatively high nicotine doses over prolonged periods of time induces both the affective and somatic aspects of spontaneous nicotine withdrawal in the mouse, while exposure to nicotine for shorter periods of time is sufficient for nAChR antagonist-precipitated nicotine withdrawal. The current study is one of the first to demonstrate reward deficits associated with both spontaneous and nAChR antagonist-precipitated nicotine withdrawal in C57BL/6J mice.

Alcohol Does Not Affect Dark Adaptation or Luminance Increment Thresholds

It has been proposed that alcohol might induce within the retina a state akin to dark adaptation. However, the evidence to support this proposal is quite indirect. Another possibility is that alcohol might affect retinal gain control rather than sensitivity. To investigate these proposals psychophysically, we measured dark adaptation functions and increment thresholds with the increment threshold procedure in individuals with moderate blood alcohol concentrations (BACs). Individuals were tested under both alcohol and no-alcohol conditions (BAC approximately .08%). In Experiment 1, thresholds for the detection of a parafoveal target were measured over a 25-minute period following a 3-minute bleach in six males. In Experiment 2, the cone dark adaptation function of four males was examined in more detail for a foveal target following bleaching at three different levels. In Experiment 3, we measured the thresholds of nine men for a small target superimposed on a background field that varied over 4 log units in luminance. We found no effects of alcohol on either the rod or the cone portion of the dark adaptation curve or on increment thresholds. Together, these data indicate that moderate alcohol ingestion does not affect the recovery of visual sensitivity in the dark nor does it affect gain control at the retinal level.

Equalization of the Antenna Pattern in Shape Reconstruction of Metallic Objects

We address the problem of reconstructing the shape of perfectly electric conducting cylinders for a two-dimensional scalar geometry when the physical optics (PO) model is exploited. We are interested in analyzing how the radiation pattern of the source providing the incident field affects the shape reconstruction problem. We find that, owing to the regularization necessary to deal with the ill-posedness of the problem, the more "weakly" illuminated objects are more "weakly" reconstructed. As a consequence, these objects can be mistaken for spurious artifacts appearing in the reconstruction and thus can be discarded when a threshold procedure is employed to curtail spurious artifacts. In order to overcome such a problem, we present a simple equalization strategy based on the knowledge of the incident field to compensate for the differences in amplitude of reconstructed image. Furthermore, we give a criterion which restricts the region over which we apply the procedure which enables us to perform the equalization in a stable way. The effectiveness of the equalization procedure is shown by reconstructions obtained with synthetic data and considering the unknown cylinders embedded in both a homogeneous and a half-space background medium, under single- and multi-view/multi-frequency measurement configuration

Data reduction for multiple functional data with class information

The term ‘functional data’ (or ‘curve’) refers to an analog or digital signal measured during each operational cycle of a manufacturing process. Functional data contain rich information concerning the process condition and product quality for quality improvement. We propose a vertical group-wise threshold (VGWT) procedure for the reduction of multiple high-dimensional functional data containing class information. The proposed method selects important wavelet coefficients for the whole set of multiple curves by a comparison between every vertical energy metric and a threshold (VGWT). The VGWT increases the class separability with a reasonably small loss in data-reduction efficiency. A real-life example is presented to illustrate the proposed method, and a Monte Carlo simulation is performed to study the impact of different levels of class variation and noise.

Sub-population genetic algorithm with mining gene structures for multiobjective flowshop scheduling problems

According to previous research of Chang et al. [Chang, P. C., Chen, S. H., & Lin, K. L. (2005b). Two phase sub-population genetic algorithm for parallel machine scheduling problem. Expert Systems with Applications, 29(3), 705-712], the sub-population genetic algorithm (SPGA) is effective in solving multiobjective scheduling problems. Based on the pioneer efforts, this research proposes a mining gene structure technique integrated with the SPGA. The mining problem of elite chromosomes is formulated as a linear assignment problem and a greedy heuristic using threshold to eliminate redundant information. As a result, artificial chromosomes are created according to this gene mining procedure and these artificial chromosomes will be reintroduced into the evolution process to improve the efficiency and solution quality of the procedure. In addition, to further increase the quality of the artificial chromosome, a dynamic threshold procedure is developed and the flowshop scheduling problems are applied as a benchmark problem for testing the developed algorithm. Extensive tests in the flow-shop scheduling problem show that the proposed approach can improve the performance of SPGA significantly.

Urban vegetation mapping using sub‐pixel analysis and expert system rules: A critical approach

Since the traditional hard classifier can label each pixel only with one class, urban vegetation (e.g. trees) can only be recorded as either present or absent. The sub‐pixel analysis that can provide the relative abundance of surface materials within a pixel may be a potential solution to effectively identifying urban vegetation distribution. This study examines the effectiveness of a sub‐pixel classifier with the use of expert system rules to estimate varying distributions of different vegetation types in urban areas. The Spearman's rank order correlation between the vegetation output and reference data for wild grass, man‐made grass, riparian vegetation, tree, and agriculture were 0.791, 0.869, 0.628, 0.743, and 0.840 respectively. Results from this study demonstrated that the expert system rule using NDVI threshold procedure is reliable and the sub‐pixel processor picked the signatures relatively well. This study reports a checklist of the sources of limitation in the application of sub‐pixel approaches.

Nociceptive threshold and analgesic response to morphine in aged and young adult rats as determined by thermal radiation and intracerebral electrical stimulation

The present experiment compared the nociceptive threshold and analgesic response to morphine in young (4–5 months) and aged (24 months) rats using peripheral thermal stimulation and intracerebral electrical stimulation. Responses to thermal stimuli were assessed using both the classical tail-flick procedure in which latency of response is the dependent variable and a new method in which threshold in calories of heat is the dependent variable. In the intracerebral nociceptive threshold procedure, electrical stimuli were delivered via an electrode implanted in the mesencephalic reticular formation (MRF), a pain pathway, and the animals were trained to terminate the stimulation by turning a cylindrical manipulandum embedded in one wall of the experimental chamber. For the classical tail-flick method, the aged rats required a greater intensity of stimulation to produce a basal response latency that was between 2.5 and 3.5 s. Using the new psychophysical method for determining the tail-flick threshold, the aged rats' basal thresholds were significantly higher than that of the young rats. However, the basal thresholds obtained by direct stimulation of the MRF failed to show a significant age effect, suggesting that the registration of pain is not different between young and aged rats. These age-related differences in baseline tail-flick response may be due to changes in the spinal reflex associated with aging. Although, there was no difference in the analgesic effects of morphine between young and aged rats using the latency of the tail-flick response, evidence for decreased analgesic response was seen using the tail-flick threshold measure and the intracerebral stimulation threshold method.

Reply: On the Methodology of the Conconi Test

The aim of our study was to investigate the relationship between “anaerobic thresholds” obtained from incremental exercise testing and the maximal lactate steady-state (MLSS) in elite cyclists. Because the vast majority of cyclists use heart rate as an index of exercise intensity, we were particularly interested to find out the threshold procedure yielding the most precise prediction of heart rate corresponding with the MLSS. Dr. Grazzi and his co-workers criticize the test protocol we have used to eventually conclude that the “Conconi threshold” (deflection of the heart rate/power curve) is an inadequate method to predict MLSS exercise intensity. We acknowledge the criticism that we did not use the test procedures as originally described by Grazzi and his co-workers [[5]]. Thus, we cannot exclude that this procedure still might yield a good prediction of MLSS. However, it must at the same time be emphasized that experimental evidence is entirely missing which proves that the test protocol by Grazzi et al. allows to adequately predict MLSS heart rate or power output. In fact, the reliability and validity of the Conconi threshold principle has been a matter of debate at several earlier occasions [[2], [3], [7], [8]].

Solution of Hallen's integral equation using multiwavelets

An effective method based upon Alpert multiwavelets is proposed for the solution of Hallen's integral equation. The properties of Alpert multiwavelets are first given. These wavelets are utilized to reduce the solution of Hallen's integral equation to the solution of sparse algebraic equations. In order to save memory requirement and computation time, a threshold procedure is applied to obtain algebraic equations. Through numerical examples, performance of the present method is investigated concerning the convergence and the sparseness of resulted matrix equation.

The wane of childhood amnesia for autobiographical and public event memories

We modified Bruce, Dolan, and Phillips-Grant's (2000) threshold procedure for determining the wane of childhood amnesia. In two experiments, undergraduates labelled childhood events (e.g., your first permanent tooth came in) as know or recollect memories and estimated their age at the event's occurrence. In both studies the estimated transition from mostly know memories to mostly recollect memories was roughly 4.7 years. This transition estimate was replicated in a sample of adults (ages 24-65 years) with both Bruce et al.'s event-generation task and the Experiment 1a questionnaire. By contrast, in two experiments a transition estimate of roughly 6 years was found for undergraduates' memories of public events (e.g., the Challenger explosion). The wane of childhood amnesia appears to occur around 4.7 years.

Shape reconstruction of perfectly conducting objects by multiview experimental data

This paper deals with the experimental validation of an algorithm, based on the Kirchhoff approximation, for the shape reconstruction of conducting objects from scattered field data. Measured data are collected in a controlled environment under a reflection mode with a finite observation domain and multiview/multistatic/multifrequency configuration. The results show the effectiveness of the approach which takes into account the view diversity by a simple strategy and a threshold procedure.

Estimating a “consumer rejection threshold” for cork taint in white wine

Cork taint in wine produced by 2,4,6-trichloroanisole (TCA) is characterised by generally unacceptable musty or earthy odours. Estimates of TCA threshold in wine have been reported in the low parts per trillion (ppt) range, although it is not clear at what levels TCA begins to render a wine unacceptable. We conducted two studies to address this question by using a method that combined a paired preference test with a method of constant stimuli threshold procedure. The aim was to determine the point at which wine consumers would begin to reject a wine containing TCA, which we termed the consumer rejection threshold (CRT). Regular white wine consumers (Ss) received pairs of samples of white wine––one spiked with TCA in eight ascending concentrations––and were asked to indicate which of the samples was preferred. Detection thresholds (DT) for TCA in wine were also determined using triangle tests. The CRT and DT were 3.1 and 2.1 ppt, respectively. CRT and DT were significantly positively correlated with one another, and negatively correlated with TCA knowledge. A replication provided a similar CRT value, and suggested that a percentage of consumers are either highly insensitive to TCA or do not find it objectionable. These results suggest that the use of this method may provide a rational basis on which to assess the real impact of TCA in white wine.

Efficient Numerical Techniques for Solving Pocklington's Integral Equation Using Multiwavelets

A procedure is presented for solving the electric field integral equation for a thin wire. The method is based upon Alpert multiwavelets functions approximation. The properties of Alpert multiwavelets are first given. These wavelets are utilized to reduce the solution of Pocklington's integral equation to the solution of sparse algebraic equations. In order to save memory requirement and computation time, a threshold procedure is applied to obtain sparse algebraic equations. Through numerical examples, performance of the present method is investigated concerning the convergence and the sparseness of the resulted matrix equation.

Clozapine treatment attenuated somatic and affective signs of nicotine and amphetamine withdrawal in subsets of rats exhibiting hyposensitivity to the initial effects of clozapine

Background Based on the phenomenologic similarity between symptoms of drug withdrawal and the negative symptoms of schizophrenia (e.g., anhedonia), we hypothesized that treatment with clozapine may be effective against nicotine and amphetamine withdrawal. Methods A rate-independent discrete-trial threshold procedure was used to assess brain stimulation reward in rats prepared with electrodes in the lateral hypothalamus. Somatic signs of nicotine withdrawal were also assessed. Results Clozapine administration (.75 or 1.5 mg/kg) during nicotine or amphetamine withdrawal did not affect the threshold elevations associated with drug withdrawal. The .75 mg/kg clozapine dose reversed the increased number of somatic signs of nicotine withdrawal. Ten days of clozapine treatment (3 mg/kg/b.i.d.) before exposure to nicotine prevented the threshold elevations in a subset of rats and the increases in somatic signs in all subjects. Fourteen-day pretreatment with clozapine (6 mg/kg/day) decreased the duration of amphetamine withdrawal. Conclusions Correlational analyses indicated that the ability of clozapine to prevent the affective aspects of drug withdrawal depended on low sensitivity to acute clozapine under baseline conditions. The results are consistent with the clinical situation where clozapine is partially effective against the negative symptoms of schizophrenia and more effective in some individuals than others. These results indicate that lack of sensitivity to the initial negative effects of clozapine may predict its a subsequent therapeutic response. Finally, the data suggest that there may be commonalities in the neurosubstrates mediating affective aspects of drug withdrawal and the negative symptoms of schizophrenia.

Can continuous streamflow data support flood frequency analysis? An alternative to the partial duration series approach

Common procedures for flood frequency modeling are based on analysis of series of annual maxima (AMS) of the instantaneous discharge. A practical alternative to AMS series is usually considered when the record length is short. In this case, analysis of partial duration series (PDS) on continuous streamflow records allows one to increase the available information by using more than one flood peak per year. In this paper, the analysis of continuous streamflow data is reconsidered from the beginning: a filtered peaks over threshold (FPOT) procedure is proposed as an alternative to the PDS approach, and objective criteria are devised for choosing a reasonable threshold and for determining the average annual number of events λ. The revised procedure demonstrates that there is no need for specific limitations on the magnitude of λ to preserve the basic hypotheses of the marked point process build in the PDS procedure. The proposed FPOT method is applied to 33 time series of daily runoff from rivers of northwestern Italy. Significant advantages over the classical PDS method are demonstrated, both in terms of physical interpretability of the parameters and efficiency of the estimates.

Short-wavelength sensitivity deficits in patients with migraine.

To examine short-wavelength sensitivity in patients with migraine using short-wavelength automated perimetry (SWAP) and Stiles 2-color increment threshold procedures. Twenty-five subjects with migraine with (n = 11) and without (n = 14) aura and 20 age-matched headache-free subjects underwent testing. All subjects underwent standard automated perimetry (SAP) and SWAP (using a Humphrey field analyzer; 24-2 presentation pattern). In 2 migraine patients (one with and another without aura), the 2-color increment threshold procedure was used to determine whether sensitivity losses were specific to short-wavelength sensitivity pathways or a generalized loss to multiple pathways. No statistically significant differences between migraine patients and controls were found for mean deviation (MD) or pattern-standard deviation (PSD) for SAP. However, for SWAP, MD and PSD were worse for the migraine group (P =.04). Twelve migraine patients had more than 4 locations with sensitivity worse than the 5% probability level (reference value). Increment threshold determinations in the 2 selected migraine patients indicated a selectively greater loss for short-wavelength sensitivity mechanisms. Approximately 50% of subjects with migraine (with or without aura) demonstrate SWAP sensitivity losses, at times between migraine events. These findings, in conjunction with previous results for SAP and flicker perimetry, suggest that migraine patients should be excluded from normative databases of visual function, and warrant further investigations of the relationship between migraine and glaucoma.

Measuring threshold shifts for brain stimulation reward using the method of limits.

Thresholds determined from the frequency of pulses and the current for rewarding brain stimulation were obtained from rats with lateral hypothalamic electrodes. The threshold, defined as the frequency or current corresponding to one-half the maximum response rate, was interpolated from reward summation functions. Daily trials of both ascending and descending sequences of frequency and current yielded no significant difference between order of presentation. While there was more variability in the maximum response rates across the sessions, neither frequency- nor current-based threshold evaluations yielded significant rate effects. Our findings suggest that the threshold procedure is generally not influenced by the sequence of delivery of stimulus values and, thus, may be regarded as a reliable measure of the reinforcing properties of brain-stimulation reward.