Red-green and achromatic temporal filters: a ratio model predicts contrast-dependent speed perception

We simultaneously measured detection and identification performance by using isoluminant red-green (RG) and achromatic flickering stimuli and fitted these data with a modified line-element model that does not make high-threshold assumptions. The modeling shows that detection and identification data are adequately described by postulating only two underlying temporal filters each for RG and achromatic vision, even when more than two threshold classifications are evident. We use a spatial frequency of 1.5 cycles per degree (c/deg) and compare the derived temporal impulse response functions with those obtained previously with the use of 0.25 c/deg stimuli under otherwise identical conditions [J. Opt. Soc. Am. A 13, 1969 (1996)]. We find that at 1.5 c/deg the luminance impulse response functions peak later and integrate out to longer times compared with those measured at 0.25 c/deg. For RG stimuli, although their relative overall sensitivities change, the impulse response functions are similar across spatial frequency, indicating a constancy of chromatic temporal properties across spatial scales. In a second experiment, we measured RG and achromatic flicker discrimination over a wide range of suprathreshold contrasts. These data suggest a common nonlinear contrast response function operating after initial temporal filtering. Using a ratio model of speed perception in which both RG and achromatic filters are combined at a common motion site, we can predict (1) the perceived slowing of RG stimuli compared with the perceived drift of achromatic drifting stimuli, (2) the contrast dependency of speed perception for RG and achromatic drifting stimuli, and (3) how this dependency changes with base speed. Thus we conclude that there is no need to postulate separate mechanisms for fast and slow motion [Nature (London) 367, 268 (1994)], since a unified ratio model can explain both RG and achromatic contrast-speed dependency.     

Tuning bandwidths for near-threshold stimuli in area MT

It is not known whether psychophysical performance depends primarily on small numbers of neurons optimally tuned to specific visual stimuli, or on larger populations of neurons that vary widely in their properties. Tuning bandwidths of single cells can provide important insight into this issue, yet most bandwidth measurements have been made using suprathreshold visual stimuli, whereas psychophysical measurements are frequently obtained near threshold. We therefore examined the directional tuning of cells in the middle temporal area (MT, or V5) using perithreshold, stochastic motion stimuli that we have employed extensively in combined psychophysical and physiological studies. The strength of the motion signal (coherence) in these displays can be varied independently of its direction. For each MT neuron, we characterized the directional bandwidth by fitting Gaussian functions to directional tuning data obtained at each of several motion coherences. Directional bandwidth increased modestly as the coherence of the stimulus was reduced. We then assessed the ability of MT neurons to discriminate opposed directions of motion along six equally spaced axes of motion spanning 180 degrees. A signal detection analysis yielded neurometric functions for each axis of motion, from which neural thresholds could be extracted. Neural thresholds remained surprisingly low as the axis of motion diverged from the neuron's preferred-null axis, forming a plateau of high to medium sensitivity that extended approximately 45 degrees on either side of the preferred-null axis. We conclude that directional tuning remains broad in MT when motion signals are reduced to near-threshold values. Thus directional information is widely distributed in MT, even near the limits of psychophysical performance. These observations support models in which relatively large numbers of signals are pooled to inform psychophysical decisions.     

Structural invariance of cognitive abilities across the adult life span: A cross-sectional study.

This study examined the hypothesis that psychometric tests retain equivalent factor structures across samples widely differing in age. We estimated a best-fitting measurement model for 17 psychometric tests covering the 5 primary abilities of Inductive Reasoning, Spatial Orientation, Verbal Ability, Numerical Ability, and Perceptual Speed, using a sample of 1,621 participants (ages 22 to 95) from the 5th wave of the Seattle Longitudinal Study. We disaggregated the participants into 9 subsets (M ages?=?29, 39, 46, 53, 60, 67, 74, 81, and 90) and tesed the fit of the accepted model for each subset. We confirmed configural invariance for all subsets, but could not establish either complete or incomplete metric invariance for any set. These results confirm the stability of factor patterns across age but indicate serious limitations for valid cross-age comparisons of individual markers of psychometric abilities in age-comparative studies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

基于系统特征数据辨识的控制器设计

介绍了一种基于系统特征数据的控制器设计算法.该算法仅根据被控对象的输入、输出采样数据,按照卷积定理计算出被控对象的单位脉冲响应作为系统的特征数据;在控制量约束条件下,根据特征数据以最速响应为控制目标规划出输出参考数据和最速控制律;然后根据控制目标和最速控制律的要求计算出理想控制器的特征数据;最后,根据控制器的特征数据辨识出线性控制器参数.仿真结果表明,控制结果具有最速参考控制的特征.     

Individual differences in loudness processing and loudness scales.

Assessed parameters of the psychophysical function for loudness (a 1,000-Hz tone) for 9 undergraduates in 3 experiments: binaural loudness summation, temporal loudness summation, and judgments of loudness intervals. Findings reveal that the loudness scales that underlay the additive binaural summation closely approximated S. S. Stevens's (see record 1957-02311-001) sone scale but were nonlinearly related to the scales that underlay the subtractive interval judgments, the latter approximating W. R. Garner's (see record 1954-07051-001) lambda scale. Interindividual differences in temporal summation were unrelated to differences in scaling performance or in binaural summation. Although the exponents of magnitude-estimation functions and the exponents underlying interval judgments varied considerably from S to S, exponents computed on the basis of underlying binaural summation varied less. Results suggest that interindividual variation in the exponent of magnitude-estimation functions largely reflects differences in the ways that Ss use numbers to describe loudness and that the sensory representations of loudness are fairly uniform among people with normal hearing. The magnitude of individual variation in temporal summation seems at least as great as the magnitude of the variation in the underlying loudness scale. (78 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Model Development for Biotrickling Filter Treatment of Graywater Simulant and Waste Gas. I

A mathematical model was developed to simulate a biotrickling filter capable of simultaneous treatment of graywater simulant and waste gas contaminated with ammonia and hydrogen sulfide. The model accounts for mass transfer of gas phase contaminants into the liquid phase and subsequent transfer into a biofilm where microbial conversions of contaminants are modeled by Monod kinetics. A set of laboratory experiments was conducted to estimate parameters for each of the two components of the model. Separation of parameter estimation both decreased the total number of parameters estimated simultaneously and ensured that each component of the system was adequately represented. Process performance, as predicted by the calibrated model, was compared to results from the operation of bench-scale reactors. The model was capable of accurately predicting contaminant removal and thus was used to make a preliminary assessment on the feasibility of a proposed dual treatment biotrickling filter system. This model is a valuable tool not only to describe and predict process performance, but also to identify relevant design parameters.     

Modeling of Nitrate Adsorption and Reduction in Fe0-Packed Columns through Impulse Loading Tests

A conventional tracer study using Li+ and Cl? was conducted on four Fe0-packed column reactors for nitrate removal. Both Li+ and Cl? showed strong adsorption onto iron media and thus were not ideal tracers for the study. Tests using an impulse loading of nitrate were then innovated to investigate the transport and reduction of nitrate in the reactors. The impulse loading was superposed on a continuous constant feeding of nitrate which generated a steady effluent baseline. A multivariable model incorporating hydraulic dispersion, adsorption/desorption, and reduction of nitrate was developed and numerically solved. Both Langmuir adsorption and linear adsorption isotherms were separately applied to describe nitrate adsorption on the reactive surface. The parameters of the model were estimated by fitting the model with the response curves from the impulse loading tests. These estimated parameters were consistent with previous studies. Specifically, the modeling results suggest a significant adsorption of nitrate by the iron media, causing an evident retardation effect. The research may lead to new methods for studying the fate of contaminants in porous reactive environments.     

Timing ability and numerical competence in rats.

Counting and timing ability in Wistar rats was tested in 4 psychophysical choice experiments. After training naive rats with discrete sound sequences that confounded time and number, only time gained control of behavior; control by time was stronger and acquired more rapidly after training with separate time- and number-relevant signals. Two nonnumeric cues associated with periodic sequences, temporal ratio and sequence pattern, did not appear to provide the basis for numerical discrimination, as performance was unaffected by a sudden change from periodic signals to signals with unique temporal patterns. Even after highly accurate performance with number, time showed exclusive control of behavior for signals with conflicting time and number cues. This study provides an unequivocal demonstration that rats can count, but they do so according to H. Davis and J. Memmott's (1983) "last resort" hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal integration in duration and number discrimination.

Investigated temporal integration in duration and number discrimination among 6 male albino rats through the use of a psychophysical choice procedure. A response on 1 lever ("short" response) following a 1-sec white-noise signal (WNS) was followed by food reinforcement, and a response on the other level ("long" response) following a 2-sec WNS was also followed by food reinforcement. Either response following a signal of 1 of 5 intermediate durations was unreinforced. This led to a psychophysical function in which the probability of a long response was related to signal duration in an ogival manner. On 2 test days, a WNS with 5, 6, 7, 8, or 10 segments of either 0.5-sec on and 0.5-sec off or 1-sec on and 1-sec off was presented, and a choice response following these signals was unreinforced. The probability of a long response was the same function of a segmented signal and a continuous signal if each segment was considered equivalent to 200 msec. A quantitative fit of scalar estimation theory suggested that the latencies to initiate temporal integration and to terminate the process are both about 200 msec and that the same internal accumulation process can be used for counting and timing. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Trends in odor intensity for human and electronic noses: relative roles of odorant vapor pressure vs. molecularly specific odorant binding

Response data were collected for a carbon black-polymer composite electronic nose array during exposure to homologous series of alkanes and alcohols. The mean response intensity of the electronic nose detectors and the response intensity of the most strongly driven set of electronic nose detectors were essentially constant for members of a chemically homologous odorant series when the concentration of each odorant in the gas phase was maintained at a constant fraction of the odorant's vapor pressure. A similar trend is observed in human odor detection threshold values for these same homologous series of odorants. Because the thermodynamic activity of an odorant at equilibrium in a sorbent phase is equal to the partial pressure of the odorant in the gas phase divided by the vapor pressure of the odorant and because the activity coefficients are similar within these homologous series of odorants for sorption of the vapors into specific polymer films, the data imply that the trends in detector response can be understood based on the thermodynamic tendency to establish a relatively constant concentration of sorbed odorant into each of the polymeric films of the electronic nose at a constant fraction of the odorant's vapor pressure. Similarly, the data are consistent with the hypothesis that the odor detection thresholds observed in human psychophysical experiments for the odorants studied herein are driven predominantly by the similarity in odorant concentrations sorbed into the olfactory epithelium at a constant fraction of the odorant's vapor pressure.     

Comparison of psychophysical and electrophysiological testing in early glaucoma

PURPOSE: To compare the sensitivity and specificity of a wide range of psychophysical and electrophysiological tests in the detection of early glaucomatous damage. METHODS: Forty-three normals and 43 patients with early glaucoma, some still without field defects, were tested with differential light threshold perimetry, short-wavelength automated perimetry, high-pass resolution perimetry, motion detection, flicker contrast sensitivity, flickering and isoluminantly matched letter tests, and pattern and flash electroretinography, including photopic, scotopic, oscillatory potentials, and 30 Hz flicker. Receiver operating characteristic analysis was applied to continuous variables derived from each of the tests. RESULTS: Most parameters reflected glaucomatous loss to some degree, even though only single variables were analyzed separately in the receiver operating characteristic analysis. The pattern electroretinogram and some of the letter acuity tests had the best sensitivity and specificity, followed by short-wavelength automated perimetry and high-pass resolution-perimetry. Motion detection, flicker contrast, and flash electroretinogram parameters scored poorly. Six patients with normal results on the Humphrey field test had abnormal results on many of the other tests. CONCLUSIONS: Applying different psychophysical and electrophysiological tests may add to our ability to detect early glaucomatous damage.     

Extraction of perceptually salient contours by striate cortical networks

We present a cortical-based model for computing the perceptual salience of contours embedded in noisy images. It has been suggested that horizontal intra-cortical connections in primary visual cortex may modulate contrast detection thresholds and pre-attentive "pop-out". In our model, horizontal connections mediate context-dependent facilitatory and inhibitory interactions among oriented cells. Strongly facilitated cells undergo temporal synchronization; and perceptual salience is determined by the level of synchronized activity. The model accounts for a range of reported psychophysical and physiological effects of contour salience. In particular, the model proposes that intrinsic properties of synchronization account for the increased salience of smooth, closed contours. Application of the model to real images is demonstrated.     

Self-stimulation in the rat: Quantitative characteristics of the reward pathway.

Quantitative characteristics of the neural pathway that carries the reinforcing signal in electrical self-stimulation of the male Sprague-Dawley rat's brain were established by finding which combinations of stimulation parameters give the same performance in a runway. The reward for each run was a train of evenly spaced monophasic cathodal pulses from a monopolar electrode. With train duration and pulse frequency held constant, the required current was a hyperbolic function of pulse duration, with chronaxie c?=?1.5 msec. With pulse duration held constant, the required strength of the train (the charge delivered per second) was a hyperbolic function of train duration, with chronaxie C?=?500 msec. To a first approximation, the values of c and C were independent of the choice either of train duration and pulse frequency or of pulse duration, respectively. Hence, the current intensity required by any choice of train duration, pulse frequency, and pulse duration depended on only 2 basic parameters, c and C, and 1 quantity, Qi, the required impulse charge. These may reflect, respectively, current integration by directly excited neurons; temporal integration of neural activity by synaptic processes in a neural network; and the peak of the impulse response of the network, assuming that the network has linear dynamics and that the reward depends on the peak of the output of the network. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral measures of auditory streaming in ferrets (Mustela putorius).

An important aspect of the analysis of auditory “scenes” relates to the perceptual organization of sound sequences into auditory “streams.” In this study, we adapted two auditory perception tasks, used in recent human psychophysical studies, to obtain behavioral measures of auditory streaming in ferrets (Mustela putorius). One task involved the detection of shifts in the frequency of tones within an alternating tone sequence. The other task involved the detection of a stream of regularly repeating target tones embedded within a randomly varying multitone background. In both tasks, performance was measured as a function of various stimulus parameters, which previous psychophysical studies in humans have shown to influence auditory streaming. Ferret performance in the two tasks was found to vary as a function of these parameters in a way that is qualitatively consistent with the human data. These results suggest that auditory streaming occurs in ferrets, and that the two tasks described here may provide a valuable tool in future behavioral and neurophysiological studies of the phenomenon. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Force variability in isometric responses.

In the present study we examined the contribution of different impulse parameters to peak force variability in an isometric task. Five experiments are reported that each held constant a different impulse parameter while allowing the other impulse parameters to vary. The results indicate that change in force level is the parameter that has the greatest effect on peak force variability, although time to peak force and preload also systematically influence response variability. A formula that accommodates the relation between impulse parameters and force variability is proposed. The data suggest that even in isometric tasks, it is the force-time properties of the impulse, rather than discrete parameters such as peak force, that determine the outcome variability. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Receptor noise as a determinant of colour thresholds

Inferences about mechanisms at one particular stage of a visual pathway may be made from psychophysical thresholds only if the noise at the stage in question dominates that in the others. Spectral sensitivities, measured under bright conditions, for di-, tri-, and tetrachromatic eyes from a range of animals can be modelled by assuming that thresholds are set by colour opponency mechanisms whose performance is limited by photoreceptor noise, the achromatic signal being disregarded. Noise in the opponency channels themselves is therefore not statistically independent, and it is not possible to infer anything more about the channels from psychophysical thresholds. As well as giving insight into mechanisms of vision, the model predicts the performance of colour vision in animals where physiological and anatomical data on the eye are available, but there are no direct measurements of perceptual thresholds. The model, therefore, is widely applicable to comparative studies of eye design and visual ecology.     

Load-Displacement of Masonry Panels with Unbonded and Intermittently Bonded FRP. I: Analytical Model

An experimental study was carried out to develop and test innovative fiber-reinforced polymer (FRP) rehabilitation techniques that meet the stringent requirements of restoration of historical buildings and are cost-effective alternatives applicable to existing masonry structures. In these techniques, FRP reinforcement was either unbonded or intermittently bonded to the masonry wall. In order to analyze performance, extend the range of the investigated parameters, and define limitations, a simplified analytical model was developed to predict the postcracking lateral load-displacement response under biaxial bending. The response of the retrofitted walls cannot be modeled by conventional approaches. The proposed model is based on balancing internal and external work and rigid body mechanics. It is assumed that all postcracking deformations take place at cracks between wall subpanels. Postcracking displacements are calculated from rotation rather than curvature. The adequacy of the model was verified by comparisons with the experimental results and a good agreement was found. The model could be used as the basis for a design method.