Sine-wave Targets Research Articles

Effects of target-amplitude and background-contrast uncertainty predicted by a normalized template-matching observer.

When detecting targets under natural conditions, the visual system almost always faces multiple, simultaneous, dimensions of extrinsic uncertainty. This study focused on the simultaneous uncertainty about target amplitude and background contrast. These dimensions have a large effect on detection and vary greatly in natural scenes. We measured the human performance for detecting a sine-wave target in white noise and natural-scene backgrounds for two levels of prior probability of the target being present. We derived and tested the ideal observer for white-noise backgrounds, a special case of a template-matching observer that dynamically moves its criterion with the background contrast (the DTM observer) and two simpler models with a fixed criterion: the template-matching (TM) observer and the normalized template-matching (NTM) observer that normalizes template response by background contrast. Simulations show that, when the target prior is low, the performance of the NTM observer is near optimal and the TM observer is near chance, suggesting that manipulating the target prior is valuable for distinguishing among models. Surprisingly, we found that the NTM and DTM observers better explain human performance than the TM observer for both target priors in both background types. We argue that the visual system most likely exploits contrast normalization, rather than dynamic criterion adjustment, to deal with simultaneous background contrast and target amplitude uncertainty. Finally, our findings show that the data collected under high levels of uncertainty have a rich structure capable of discriminating between models, providing an alternative approach for studying high dimensions of uncertainty.

Performance, complexity and dynamics of force maintenance and modulation in young and older adults.

The present study addresses how task constraints and aging influence isometric force control. We used two tasks requiring either force maintenance (straight line target force) or force modulation (sine-wave target force) around different force levels and at different modulation frequencies. Force levels were defined relative the individual maximum voluntary contraction. A group of young adults (mean age ± SD = 25 ± 3.6 years) and a group of elderly (mean age = 77 ± 6.4 years) took part in the study. Age- and task-related effects were assessed through differences in: (i) force control accuracy, (ii) time-structure of force fluctuations, and (iii) the contribution of deterministic (predictable) and stochastic (noise-like) dynamic components to the expressed behavior. Performance-wise, the elderly showed a pervasive lower accuracy and higher variability than the young participants. The analysis of fluctuations showed that the elderly produced force signals that were less complex than those of the young adults during the maintenance task, but the reverse was observed in the modulation task. Behavioral complexity results suggest a reduced adaptability to task-constraints with advanced age. Regarding the dynamics, we found comparable generating mechanisms in both age groups for both tasks and in all conditions, namely a fixed-point for force maintenance and a limit-cycle for force modulation. However, aging increased the stochasticity (noise-driven fluctuations) of force fluctuations in the cyclic force modulation, which could be related to the increased complexity found in elderly for this same task. To our knowledge this is the first time that these different perspectives to motor control are used simultaneously to characterize force control capacities. Our findings show their complementarity in revealing distinct aspects of sensorimotor adaptation to task constraints and age-related declines. Although further research is still needed to identify the physiological underpinnings, the used task and methodology are shown to have both fundamental and clinical applications.

Aging and the complexity of center of pressure in static and dynamic postural tasks

The experiment was set-up to investigate the hypothesis that there is an age-related bi-directional change in complexity of the center of pressure (COP) depending on postural task demands. Healthy young (19–28 year) and old (65–74 year) adults were instructed to match, in two 25s trials for each condition, the COP with constant and sine-wave targets at 2 levels (5 and 40%) of the maximal COP distance (MCD). The root mean square error of COP increased with aging in both MCD levels and tasks. Multi-scale entropy (MSE) and detrended fluctuation analysis showed that the complexity of COP in the old adults was lower compared to the young in the constant target, whereas it was higher in the sine-wave target. The task dependent age-related bi-directional change of COP complexity is counter to the hypothesis of a universal loss of complexity with aging but shows that there is loss of adaptive change in complexity driven by the COP dynamics.

Time gain influences adaptive visual-motor isometric force control

This study examined the influence of time gain on the visual-motor control of isometric force. Time gain denotes the spatial length on the computer screen representing the unit of elapsed time of the force output, through which the time properties of the visually perceived force output can be compressed or extended. Five time gains and three force target waveforms (sinewave, brown noise, and straight line) with different time-dependent properties were tested in the experiment. The results revealed that time gain influenced task performance nonlinearly in a way that was dependent on the predictability of the target waveforms. In the sinewave target condition, there was a U-shaped modulation of time gain on the mean and variability of force error, and an inverted U-shaped modulation on the time-dependent structure of force variability. The time gain modulation effect was weaker in the brown noise target condition and absent in the constant force target condition. The results extend the effect of visual information gain regulation from force gain to time gain. The interaction between the time gain and target waveform supports the general proposition that the control of motor output is influenced by the interaction of different categories of constraints where the influence of visual information is dependent on the temporal properties and predictability of the force output and the task requirement.

Coherence masking protection for speech in children and adults

In three experiments, we tested the hypothesis that children are more obliged than adults to fuse components of speech signals and asked whether the principle of harmonicity could explain the effect or whether it is, instead, due to children’s implementing speech-based mechanisms. Coherence masking protection (CMP) was used, which involves labeling a phonetically relevant formant (the target) presented in noise, either alone or in combination with a stable spectral band (the cosignal) that provides no additional information about phonetic identity and is well outside the critical band of the target. Adults and children (8 and 5 years old) heard stimuli that were either synthetic speech or hybrids consisting of sine wave targets and synthetic cosignals. The target and cosignal either shared a common harmonic structure or did not. An adaptive procedure located listeners’ thresholds for accurate labeling. Lower thresholds when the cosignal is present indicate CMP. Younger children demonstrated CMP effects that were both larger in magnitude and less susceptible to disruptions in harmonicity than those observed for adults. The conclusion was that children are obliged to integrate spectral components of speech signals, a perceptual strategy based on their recognition of when all components come from the same generator.

The relationship between object spatial profile and accommodation microfluctuations in emmetropes and myopes

The accommodation microfluctuations are thought to be used by the accommodation controller to obtain information about the direction and magnitude of the required response by monitoring changes in the contrast gradient of this image. The contrast gradient can be altered by presenting different spatial frequency (SF) targets to the eye. Twelve myopes (MYOs) and 12 emmetropes (EMMs) viewed sine and square wave targets of SF 0.5, 1, 2, 4, 8, 16 cpd in a Badal optical system. Accommodation responses were recorded continuously using the Shin-Nippon SRW-5000 autorefractor. There is no change in magnitude of the accommodation microfluctuations as the SF of square waves is altered. While viewing sine wave targets, the microfluctuations are smallest for mid (2, 4 cpd) SFs and increase for low (0.5 cpd) and high (16 cpd) SFs. MYOs show a significantly larger increase in the microfluctuations for the 16 cpd target compared to the EMMs. MYOs have significantly larger microfluctuations than the EMMs throughout. The microfluctuations seem to be monitoring the contrast gradient of the cortical image, which is likely to be used by the accommodation control system during error detection. The results indicate that MYO subjects may have a shallower contrast gradient and the potential reasons and implications of this are discussed.

Visual search: The role of peripheral information measured using gaze-contingent displays

Two of the factors limiting progress in understanding the mechanisms of visual search are the difficulty of controlling and manipulating the retinal stimulus when the eyes are free to move and the lack of an ideal observer theory for fixation selection during search. Recently, we developed a method to precisely control retinal stimulation with gaze-contingent displays (J. S. Perry & W. S. Geisler, 2002), and we derived a theory of optimal eye movements in visual search (J. Najemnik & W. S. Geisler, 2005). Here, we report a parametric study of visual search for sine-wave targets added to spatial noise backgrounds that have spectral characteristics similar to natural images (the amplitude spectrum of the noise falls inversely with spatial frequency). Search time, search accuracy, and eye fixations were measured as a function of target spatial frequency, 1/f noise contrast, and the resolution falloff of the display from the point of fixation. The results are systematic and similar for the two observers. We find that many aspects of search performance and eye movement pattern are similar to those of an ideal searcher that has the same falloff in resolution with retinal eccentricity as the human visual system.

Sex differences in tracking performance in patients with Parkinson's disease

Carey JR, Deskin KA, Josephson KT, Wichmann RL. Sex differences in tracking performance in patients with Parkinson's disease. Arch Phys Med Rehabil 2002;83:972-7. Objective: To examine whether Parkinson's disease affects men and women differently, relative to age-matched controls, in manual tracking. Design: Cross-sectional exploratory study. Setting: Ambulatory activity center. Participants: Ten men and 10 women with Parkinson's disease; 10 men and 10 women age-matched controls. Interventions: Patients tracked a sinewave target on a computer monitor in stimulus-response compatible (finger extension/flexion in vertical) or incompatible (horizontal) conditions. Main Outcome Measure: Accuracy Index (AI) score on finger movement tracking tests. Results: With data collapsed across sexes, AI scores were significantly higher for control subjects compared with subjects with Parkinson's disease in compatible (P<.001) and incompatible (P<.001) positions. With data partitioned out across sexes, control men tracked significantly higher than men with Parkinson's disease in compatible (P=.004) and incompatible (P<.001) positions, but control women did not track significantly different from women with Parkinson's disease in either position. Control men tracked significantly higher than control women in compatible (P=.003) and incompatible (P=.001) positions, but men with Parkinson's disease did not track significantly different from women with Parkinson's disease in either position. Conclusion: Parkinson's disease affects men and women disproportionately in manual tracking. Comparisons between subjects with Parkinson's disease and controls in spatial skill should include sex as a factor. More research is needed to confirm these findings. © 2002 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

Increased use of target cues during visuo‐motor tracking in Parkinson's disease

The effect of temporarily suppressing the visual display of either the target or actual movement trajectory upon the accuracy of visuo-motor tracking was studied in patients with Parkinson's disease (PD) and healthy subjects. Subjects made wrist movements to superimpose a movement cursor upon a target cursor on a VDU screen. The tracking of slow ramp and sinewave target waveforms was investigated. Trials involving the three conditions of visual suppression, namely, target suppressed (TS), movement suppressed (MS) and non-suppressed (NS) were ordered randomly. In TS and MS trials, respectively, the target or movement cursor disappeared from the subject's view for a 4 s period whilst in NS trials both the target and movement cursors were continuously present. Prior to experimental trials, subjects initially practised a series of NS movements. Tracking errors were analysed by ANOVA for group, suppression condition and waveform effects. The tracking performance of the PD patients, during each form of suppression condition, was worse than that of healthy subjects. Both TS and MS elicited significant reductions in accuracy across groups and waveforms. TS induced a more pronounced impairment of tracking accuracy in the PD group than in the control group suggesting that parkinsonians exhibit an abnormally increased reliance upon visual information of the required trajectory during the present visuo-motor tracking tasks. By contrast, there was no between-group effect of MS in these tasks, suggesting that PD patients show a comparable dependence upon visual feedback of their own movements to that shown by controls.

Finger-movement tracking scores in healthy subjects.

The purpose of this study was to examine the effects of age, sex, and hand preference on precise control of voluntary movement at the index finger metacarpophalangeal joint in able-bodied volunteers. An electrogoniometer was attached to this joint and connected to a computer. The computer screen displayed a sine wave target that each subject attempted to track with careful extension and flexion finger movements. Accuracy index scores were calculated for the extension phases, flexion phases, and the total sine wave. Each subject performed three tracking trials and the average for each of the above scores was computed. The results showed that younger subjects tracked significantly more accurately than older subjects and men tracked significantly more accurately than women. Also, the subjects tracking with the nonpreferred hand (15 right, 105 left) tracked significantly more accurately than those subjects tracking with the preferred hand (112 right, 8 left) in the flexion phases of the test. The data from these able-bodied subjects provide a base for comparison of patients' data, which may be helpful in the early recognition and monitoring of problems with precision in movement control.

Modulation transfer function measurement technique for small-pixel detectors

A modulation transfer function (MTF) measurement technique suitable for large-format, small-pixel detector characterization has been investigated. A volume interference grating is used as a test image instead of the bar or sine wave target images normally used. This technique permits a high-contrast, large-area, sinusoidal intensity distribution to illuminate the device being tested, avoiding the need to deconvolve raw data with imaging system characteristics. A high-confidence MTF result at spatial frequencies near 200 cycles/mm is obtained. We present results at several visible light wavelengths with a 6.8-microm-pixel CCD. Pixel response functions are derived from the MTF results.

Cerebral hemispheric smooth pursuit disorders

The pursuit system utilizes input from cerebral cortical pathways specialized for analyzing visual motion. Impaired smooth pursuit in humans with cerebral lesions usually signifies damage to posterior parietal hemispheric regions. The authors have recently studied horizontal smooth pursuit in 23 patients with discrete unilateral cerebral hemispheric lesions. Ten patients had pursuit asymmetry with lower gain when tracking toward the side of cerebral hemispheric damage. None had lower gain when tracking away. Two patients with lower ipsilateral gain had frontal lobe lesions. Areas of anatomical overlap of lesions associated with asymmetric pursuit in eight patients provide evidence for a pursuit pathway that originates in Brodmann's areas 19 and 39 (angular gyrus), and that these cortical areas are the human homologues of areas MT and MST in the simian cerebral cortex. A normal phase relationship between smooth eye motion and target motion in these patients indicated that prediction in the smooth pursuit system is resistant to cerebral hemispheric damage.The initiation of smooth pursuit in response to step-ramp targets was studied in 18 patients with focal cerebral hemispheric lesions. Seven patients had retinotopic pursuit defects, consisting of low smooth eye movement gain in both horizontal directions in the hemi field contralateral to the cerebral lesions. Only four of those seven patients had complete hemianopia and three had normal visual fields, indicating that ‘blindness’ for motion detection and/or motion generation can occur independently of damage to the geniculostriate pathway. Four patients with complete hemianopia occasionally made smooth eye accelerations to targets stepped into the blind hemifield, in the correct direction, but with low velocity. They did not adjust saccade amplitude to the direction or size of the target step.These measurements of steady state responses to sine wave targets and to step ramp targets enabled the authors to identify four classes of cerebral hemispheric smooth pursuit defects: (1) Ipsilateral low gain pursuit. Contralateral pursuit gain may be normal, low or high. (2) Bidirectional low gain smooth pursuit. (3) Retinotopic impairment of pursuit in both directions in the contralateral visual field. (4) Craniotopic paralysis of pursuit contralateral to the midline after acute non-dominant hemispheric lesions.

Visual responses of Purkinje cells in the cerebellar flocculus during smooth-pursuit eye movements in monkeys. II. Complex spikes

1. We report the complex-spike responses of two groups of Purkinje cells (P-cells). The cell were classified according to their simple-spike firing during smooth eye movements evoked by visual and vestibular stimuli with the use of established criteria (Lisberger and Fuchs 1978; Stone and Lisberger 1990). During pursuit with the head fixed, ipsi gaze-velocity P-cells (GVP-cells) showed increased simple-spike firing when gaze moved toward the side of the recording, whereas down GVP-cells showed increased simple-spike firing when gaze moved downward. 2. During pursuit of sinusoidal target motion, the complex-spike firing rate was modulated out-of-phase with the simple-spike firing rate. Ipsi GVP-cells showed increased complex-spike firing during pursuit away from the side of the recording, and down GVP-cells showed increased complex-spike firing during upward pursuit. The strength of the complex-spike response increased as a function of the frequency of sinusoidal target motion. 3. GVP-cells showed directionally selective complex-spike responses during the initiation of pursuit to ramp target motion. Ipsi GVP-cells had increased complex-spike firing 100 ms after the onset of contralaterally directed target motion and decreased complex-spike activity after the onset of ipsilaterally directed target motion. Down GVP-cells had increased complex-spike firing 100 ms after the onset of upward target motion and decreased firing after the onset of downward target motion. As during sinusoidal target motion, each cell's simple- and complex-spike responses had the opposite directional preferences. 4. When the monkeys fixated a stationary target during a transient vestibular stimulus, the retinal slip caused by the 14-ms latency of the vestibuloocular reflex (VOR) affected the complex-spike firing rate. For ipsi GVP-cells, ipsilateral head motion caused transient contralateral image motion and an increase in complex-spike firing. The same vestibular stimulus in darkness caused an almost identical eye movement but had no effect on complex-spike firing. We conclude that complex spikes in ipsi GVP-cells are driven by contralaterally directed image motion. 5. To determine the events surrounding complex-spike firing during pursuit, we triggered averages of eye and target velocity on the occurrence of complex spikes during pursuit of sine-wave target motion. The averages revealed a transient pulse of retinal image motion that peaked approximately 100 ms before the complex spike. We conclude that complex spikes during steady-state pursuit are driven by the retinal slip associated with imperfect pursuit.(ABSTRACT TRUNCATED AT 400 WORDS)

脳性麻ひ者のトラッキング動作の研究 筋収縮と動作知覚について

Two tracking experiments were carried out to investigate the motor control system in adults with cerebral palsy. The first experiment analysed the frequency response characteristics and the surface electromyogram from biceps brachii and triceps brachii, when the cerebral palsy subjects made isometric contractions during the pursuit tracking task with sine wave targets. Patterns of reciprocal innervation of the antagonists explained the frequency response characteristics of tracking behavior of the cerebral palsy subjects. The second experiment analysed perceived response velocity during the compensatory tracking task by means of magnitude estimation method. Fitting power function to the relation between the input frequency and the perceived response velocity, coefficients of determination for the cerebral palsy subjects were found to be lower than those for the normal subjects. It suggests that the cerebral palsy subjects can discriminate their response velocity less exactly than the normal subjects in manual tracking system.

Dynamic characteristics of compensatory tracking behavior in adults with cerebral palsy

Dynamic characteristics of motor control system of adults with cerebral palsy was examined by a compensatory tracking task with step wave, sine wave and random wave targets. The velocity of responses to step wave targets by the cerebral palsy subjects was lower than that by the normal subjects. In terms of the closed-loop transfer functions in responses to sine wave targets compared with those to random wave targets, it was revealed that the normal subjects could switch their feedback tracking behavior to precognitive control behavior in order to reduce their tracking phase lag which was greater with random wave targets than with sine wave targets, while the cerebral palsy subjects could not do so. These results suggest that the cerebral palsy subjects have difficulty in generating precognitive control behavior to match sine wave targets.

Spatial/temporal interactions: Backward and forward metacontrast masking with sine-wave gratings

A metacontrast masking paradigm is presented in which the detectability of a sine-wave target is measured in the presence of a spatially-flanking sine-wave mask. The onset of the mask either precedes (forward masking) or follows (backward masking) the onset of the target. Target detectability is measured as a function of stimulus onset asynchrony (SOA) for stimuli varying in spatial frequency and contrast. For low spatial-frequency targets, target detectability varies as a U-shaped function of SOA both in forward and backward masking. For high spatial frequency targets, U-shaped masking is observed only in backward masking. The magnitude of the masking effect at each SOA of maximal masking (SOA max) depends on the spatial-frequency similarity of target and mask. SOA max does not vary with contrast, but does vary with spatial frequency. These data are considered within the context of a model positing inhibitory interactions between the responses of fast- and slow-responding spatial-frequency selective channels, where the latency to channel response increases with spatial frequency.

C0-contraction and stretch reflexes in spasticity during treatment with baclofen.

Surface electromyograms were recorded from the quadriceps and hamstring muscles of 11 spastic patients during cyclical flexion and extension movements of the knee. A potentiometer strapped to the knee recorded the angle of the joint, the output signal being displayed on an oscilloscope. The patient used this signal to track a sine wave target for 20 cycles. The observer then moved the patient's limb through a further 20 cycles tracking the same target. Recordings were repeated at intervals for four hours after an oral dose of baclofen. Analysis of the recordings showed that the response of a spastic muscle to lengthening is not the same during passive movement as during voluntary movement. In mild spasticity stretch reflexes appear to be suppressed by voluntary effort whereas in severe spasticity they are enhanced. Baclofen suppressed the response to passive stretch by over 30% at plasma concentrations of over 250 ng/ml and by 50% at concentrations of over 400 ng/ml, but this effect was largely extinguised during voluntary movement.

Visibility of low-spatial-frequency sine-wave targets: Dependence on number of cycles.

The number of cycles in a low-frequency sinusoidal display is a crucial variable in determining the visibility of the display. In particular, the threshold contrast is essentially independent of spatial frequency for these displays. We have extended the above experiments, using more cycles and a variety of targets and observer tasks. The results confirm previous findings; they also show that the type of target or task has little influence. For low-frequency sinusoids that contain up to about 3 cycles, the threshold contrast is determined by the number of cycles. For high-number-of-cycles targets with spatial frequencies above 6-10 cycles per degree, visibility is predominantly dependent on the spatial frequency. The results suggest that the low-frequency decrease in reported MTF's is due to the decrease of the number of cycles used in determining them.

Plane of Best Focus for a Sine-Wave Target in the Presence of Spherical Aberration

Plane of Best Focus for a Sine-Wave Target in the Presence of Spherical Aberration

Recording Electronic Lens Bench

The measurement of lens characteristics by the method of contrast rendition of a sine wave target has been studied extensively in recent years. This method has not, however, been widely used because of the time required to measure a lens at many field angles and focal positions as well as the time required to reduce the data to suitable form. These limitations are caused by poor signal-to-noise ratio from the photoreceptor when operating at reduced lens aperture or with wavelength limiting filters. A system is described which uses sweep frequency sine wave targets with rectification and filtering of the electrical signal to reduce the required band width thereby overcoming these difficulties. Rapid scanning with oscilloscope presentation is used for preliminary adjustment of lens parameters. An X-Y recorder combines curves for a number of lens adjustments on preprinted paper for permanent records at a rate of ten seconds per curve.