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At least 397 records · Page 22Linked to original sources
PubMed2000

The 5-HT(1A) receptor agonist 8-OH-DPAT reduces rats' accuracy of attentional performance and enhances impulsive responding in a five-choice serial reaction time task: role of presynaptic 5-HT(1A) receptors.

RATIONALE: Whilst several studies have investigated the role of serotonergic receptor subtypes in learning and memory, relatively few studies have examined their role in attentional processes. OBJECTIVE: The present study investigated the role of pre- and postsynaptic 5-HT1A receptors on rats' attentional performance in the five-choice serial reaction time task (5-CSRT). METHODS: Hungry rats were trained in the 5-CSRT task to detect brief (0.5 s) flashes of light presented randomly in one of five locations with a fixed intertrial interval of 5 s paced by the rat. We studied the effects of 8-OH-DPAT, a 5-HT1A receptor agonist, at various subcutaneous (SC) doses (10-100 microg/kg) on measures of rats' discriminative accuracy (the index of attentional functioning) and various behavioural indices of response control and motivation. Manipulations of basic task parameters, intracerebroventricular (ICV) injections of 5,7-dihydroxytryptamine (5,7-DHT) to deplete forebrain 5-HT and treatments with a selective 5-HT1A receptor antagonist WAY 100635 were made in order to determine the behavioural and neural specificity of the effects of 8-OH-DPAT. RESULTS: A dose of 100 microg/kg, but not lower doses, significantly reduced choice accuracy and increased errors of omission, latencies to respond correctly and to collect food reward and premature responses. All these effects were completely blocked by WAY 100635, injected SC 5 min before 8-OH-DPAT at doses from 10-100 microg/kg. WAY 100635 by itself had no effect in the task. Dimming the visual stimuli to one-third of the usual brightness did not modify the effect of 8-OH-DPAT on choice accuracy. Prolonging the stimuli from 0.5 to 1.0 s reversed 8-OH-DPAT's effect on choice accuracy but did not modify the other effects on rats' performance. An ICV injection of 150 microg 5,7-DHT, which depleted forebrain serotonin by 90%, reversed 8-OH-DPAT's effect on choice accuracy but did not modify the effects on errors of omission and latency to make correct responses. Similar effects were found by infusing 1.0 microg/0.5 microl WAY 100635 in the dorsal raphe 5 min before 8-OH-DPAT. 8-OH-DPAT increased the latency to collect the reinforcement; this effect was attenuated by ICV 5,7-DHT and completely antagonized by WAY 100635 in the dorsal raphe. Rats treated with 5,7-DHT or 8-OH-DPAT showed more premature responses and these effects were markedly reduced by the combined treatment. CONCLUSIONS: The results suggest that stimulation of presynaptic 5-HT1A receptors is involved in the ability of 8-OH-DPAT to cause attentional dysfunction and enhance impulsivity while slowing of responding and increase in errors of omission mainly depend on stimulation of post-synaptic 5-HT1A receptors.

5,7-Dihydroxytryptamine↗
PubMed2004

Accuracy of spatial localization depending on head posture in a perturbed gravitoinertial force field.

Spatial orientation is crucial when subjects have to accurately reach memorized visual targets. In previous studies modified gravitoinertial force fields were used to affect the accuracy of pointing movements in complete darkness without visual feedback of the moving limb. Target mislocalization was put forward as one hypothesis to explain this decrease in accuracy of pointing movements. The aim of this study was to test this hypothesis by determining the accuracy of spatial localization of memorized visual targets in a perturbed gravitoinertial force field. As head orientation is involved in localization tasks and carrying relevant sensory systems (visual, vestibular and neck muscle proprioceptive), we also tested the effect of head posture on the accuracy of localization. Subjects (n=10) were seated off-axis on a rotating platform (120 degrees s(-1)) in complete darkness with the head fixed (head-fixed session) or free to move (head-free session). They were required to report verbally the egocentric spatial localization of visual memorized targets. They gave the perceived target location in direction (i.e. left or right) and in amplitude (in centimeters) relative to the direction they thought to be straight ahead. Results showed that the accuracy of visual localization decreased when subjects were exposed to inertial forces. Moreover, subjects localized the memorized visual targets more to the right than their actual position, that was in the direction of the inertial forces. With further analysis, it appeared that this shift of localization was concomitant with a shift of the visual straight ahead (VSA) in the opposite direction. Thus, the modified gravitoinertial force field led to a modification in the orientation of the egocentric reference frame. Furthermore, this shift of localization increased when the head was free to move while the head was tilted in roll toward the center of rotation of the platform and turned in yaw in the same direction. It is concluded that the orientation of the egocentric reference frame was influenced by the gravitoinertial vector.

Adolescent↗
PubMed2006

Accuracy and underlying mechanisms of shifting movements in cellists.

Accuracy of shifting movements between two notes was examined in nine cellists (intermediate-professional skill levels). Three pairs of notes separated by different distances were tested under the same movement rate. Finger position on the string was measured by a circuit. Angular velocities of the left upper arm and forearm were measured by two angular velocity sensors; thus elbow angular velocity during shifts was estimated. Results showed that with increased elbow velocity and shifting distance endpoint variability stayed constant. The force of gravity assisted elbow extension during shifts toward higher pitched notes compared to flexion towards lower pitched notes, but faster movement velocity did not result in increased landing variability. Performance for note E on the A string was found to be less variable than other notes, suggesting that physical cue from the cello body geometry was used as a landmark for finger position. Cutaneous feedback from the thumb when hitting the body-neck junction enabled faster elbow extension velocity compared to shifts towards other notes. Cellists who showed higher performance accuracy also showed higher perceptual ability and performance proficiency. These results suggest that long-term over-training of fast and accurate movements enables musicians to maintain accuracy and variability across different movement distances and velocities. Higher perceptual ability and performance proficiency are correlated with increased accuracy but not lower variability, indicating although perceptual ability and performance proficiency are important for pitch accuracy, movement variability is still constrained by the capacity of the motor system, which is highly fine-tuned and different than non-musicians.

Analysis of Variance↗
PubMed2003

Enhancing accuracy of magnetic resonance image fusion by defining a volume of interest.

We compared the registration accuracy for corresponding anatomical landmarks in two MR images after fusing the complete volume (CV) and a defined volume of interest (VOI) of both MRI data sets. We carried out contrast-enhanced T1-weighted gradient-echo and T2-weighted fast spin-echo MRI (matrix 256 x 256) in 39 cases. The CV and a defined VOI data set were each fused using prototype software. We measured and analysed the distance between 25 anatomical landmarks in predefined areas identified at levels L(1)-L(5) corresponding to defined axial sections. Fusion technique, landmark areas and level of fusion were further processed using a feed-forward neural network to calculate the difference which can be expected based on the measurements. We identified 975 landmarks for both T1- and T2-weighted images and found a significant difference in registration accuracy ( P<0.01) for all landmarks between CV (1.6+/-1.2 mm) and VOI (0.7+/-1.0 mm). From cranial (L(1)) to caudal (L(5)), mean deviations were: L(1) CV 1.5 mm, VOI 0.5 mm; L(2) CV 1.8 mm, VOI 0.4 mm; L(3) CV 1.7 mm, VOI 0.4 mm; L(4) CV 1.6 mm, VOI 0.6 mm; and L(5) CV 1.6 mm, VOI 1.6 mm. Neural network analysis predicted a higher accuracy for VOI (0.05-0.15 mm) than for CV fusion (0.9-1.6 mm). Deviations due to magnetic susceptibility changes between air and tissue seen on gradient-echo images can decrease fusion accuracy. Our VOI fusion technique improves image fusion accuracy to <0.5 mm by excluding areas with marked susceptibility changes.

Algorithms↗
PubMed2002

Accuracy of CT-guided biopsies in 359 patients with musculoskeletal lesions.

The study was undertaken to assess the diagnostic accuracy and clinical usefulness of computed tomography (CT)-guided biopsies and fine needle aspirates of musculoskeletal lesions. The analysis compared the accuracy according to anatomical location, size, type of lesion, and histology. On the basis of the information obtained by reviewing the report of the CT biopsy and comparing it with the final diagnosis for 359 cases, the overall accuracy was determined to be 71%. The accuracy for 101 fine needle aspirations was 63% and for 258 CT-guided core biopsies was 74%. It is of note that the biopsies of 81 pelvic lesions had higher rates of diagnostic accuracy (81%) than those of 278 non-pelvic sites (68%), and especially 94 lesions of the spine (61%). The lowest success rates occurred in 26 patients with infectious diseases (50%). We conclude that these procedures remain the logical and safe choice for diagnostic studies of patients with lesions of the musculoskeletal system.

Adolescent↗
PubMed2003

The migration of femoral components after total hip replacement surgery: accuracy and precision of software-aided measurements.

OBJECTIVE: To assess the accuracy and precision of a software-aided system to measure migration of femoral components after total hip replacement (THR) on digitised radiographs. DESIGN AND PATIENTS: Subsidence and varus-valgus tilt of THR stems within the femur were measured on digitised anteroposterior pelvic radiographs. The measuring software (UMA, GEMED, Germany) relies on bony landmarks and comparability parameters of two consecutive radiographs. Its accuracy and precision were calculated by comparing it with the gold standard in migration measurements, radiostereometric analysis (RSA). Radiographs and corresponding RSA measurements were performed in 60 patients (38-69 years) following cementless THR surgery. RESULTS AND CONCLUSIONS: The UMA software measured the subsidence of the stems with an accuracy of +/-2.5 mm and varus-valgus tilt with an accuracy of +/-1.8 degrees (95% confidence interval). A good interobserver and intraobserver reliability was calculated with Cronbach's alpha ranging from 0.86 to 0.97. Measuring the subsidence of THR stems within the femur is an important parameter in the diagnosis of implant loosening. Software systems such as UMA improve the accuracy of migration measurements and are easy to use on routinely performed radiographs of operated hip joints.

Adult↗
PubMed2002

Contrast-enhanced three-dimensional MR angiography of neck vessels: does dephasing effect alter diagnostic accuracy?

The aim of this study was to evaluate diagnostic accuracy of contrast-enhanced MRA (CEMRA) compared with digital subtraction angiography (DSA) in studying neck vessels of 48 patients. In three groups of patients, we used three MRA protocols differing for voxel size to assess if intravoxel dephasing effects could modify accuracy of CEMRA. Accuracy and correlation with DSA results were calculated in all patients and separately in the three groups. A qualitative analysis of the likeness between morphology of the stenosis in CEMRA and DSA images was also assessed. In all patients accuracy and agreement with DSA were 96% and k=0.85 in subclavian arteries, 96% and k=0.84 in vertebral artery, 97% and k=0.88 in common carotid arteries, and 94% and k=0.86 in internal carotid arteries. In the three groups accuracy and agreement with DSA did not show any significant difference. Qualitative analysis of CEMRA and DSA images revealed a better agreement in depicting the morphology of stenosis using a smaller voxel size. The CEMRA represents a powerful tool for the non-invasive evaluation of neck vessels. Overestimation trend of CEMRA is confirmed and the reduction of voxel size, decreasing the dephasing intravoxel effect, allows to have a better overlapping of stenosis morphology on CEMRA compared with DSA, but it does not yield diagnostic gain in the stenosis grading.

Aged↗
PubMed2006

Preoperative staging of rectal cancer: accuracy of 3-Tesla magnetic resonance imaging.

The purpose of this study was to evaluate the accuracy of 3-Tesla magnetic resonance imaging (MRI) for the preoperative staging of rectal cancer. Thirty-five patients with a primary rectal cancer who underwent preoperative 3-T MRI using a phased-array coil and had a surgical resection were enrolled in the study group. Preoperatively, three experienced radiologists independently assessed the T and N staging. A confidence level scoring system was used to determine if there was any perirectal invasion, and receiver operating characteristic (ROC) curves were generated. The interobserver agreement was estimated using kappa statistics. The overall accuracy rate of T staging for rectal cancer was 92%. The diagnostic accuracy was 97% for T1, 89% for T2 and 91% for T3, respectively. The predictive accuracy for perirectal invasion by the three observers was high (Az>0.92). The interobserver agreement for T staging was moderate to substantial. The overall sensitivity, specificity, and accuracy for the detection of mesorectal nodal metastases were 80%, 98%, and 95%, respectively. In conclusion, preoperative 3-T MRI using a phase-array coil accurately indicates the depth of tumor invasion for rectal cancer with a low variability.

Adenocarcinoma↗
PubMed2006

Accuracy and complications in computed tomography fluoroscopy-guided needle biopsies of lung masses.

The aim of this study was to determine the diagnostic accuracy and frequency of complications of lung biopsy procedures with or without CTF guidance of needle insertion. Records and images of 99 consecutive percutaneous coaxial cutting needle lung biopsy procedures performed on 85 patients were reviewed retrospectively. Fifty-seven and 42 procedures had been done with and without CTF guidance, respectively. Histological results were compared to diagnosis after surgery or after a follow-up period of 12 months. Diagnostic accuracy and the occurrence of pneumothorax and/or bleeding related to the procedures were registered. The level of accuracy of the diagnosis was comparable. The diagnostic accuracy was 96% (50/52) and 95% (34/36) sensitivity 95% (35/37) and 93% (26/28), specificity 100% (15/15) and 100% (8/8) with CTF and conventional CT techniques, respectively. There were fewer post procedure pneumothoraces using the CTF than conventional technique [26% (15/57) vs. 38% (16/42)], but the difference was not statistically significant (P = 0.274). The insertion of a chest tube was required in only one (2%) procedure using the CTF technique, while this was needed in four (10%) using the conventional technique. Small or large hemorrhages occurred in 23% of the procedures, with no apparent difference between the two groups. In conclusion, CTF-guided biopsy of lung lesions provides high diagnostic accuracy, comparable to that of conventional CT-guided procedures, with a low rate of complications, even for small tumors.

Adolescent↗
PubMed2002

Accuracy of a peristaltic finger-type infusion pump during hyperbaric oxygen therapy.

PURPOSE: To evaluate the accuracy of a peristaltic finger-type pump during hyperbaric oxygen therapy (HBO). METHODS: Using two examples of one type of infusion pump, we evaluated its accuracy at 2 ATA (atmospheres absolute) by measuring the actual volumes pumped at given time points (flow rate) and comparing these data with the corresponding data obtained at 1 ATA. RESULTS: There was no significant difference in flow rates between 2 and 1 ATA. In terms of accuracy, the present pump was superior to the syringe pump tested in our previous study. Under our conditions, the ambient pressure might have acted equally on the inlet and outlet sides of the infusion line, which may explain the lack of effect of 2 ATA on flow rates. This is not the case with a syringe pump, and the difference in flow-generating mechanisms may help explain the different results obtained in our two studies. CONCLUSION: The present type of pump could be used during HBO (at 2 ATA) with the same accuracy as at 1 ATA. Whether the ambient pressure can affect pump input and output (peristaltic-pump infusion line) or only pump output (syringe type) may determine whether accuracy suffers under HBO conditions.

Journal Article↗
PubMed2003

Image fusion of MR images and real-time ultrasonography: evaluation of fusion accuracy combining two commercial instruments, a neuronavigation system and a ultrasound system.

OBJECTIVE: The aim of our study was to evaluate MRI/Ultrasonography fusion accuracy depending on three ultrasonographic parameters. METHOD: An ultrasonography and MRI compatible model was created, consisting of a plastic box, which contained 3 objects. MRI scans were performed with 128 sagittal slices. The objects were segmented and 3D reconstructions were created. A special ultrasound adapter with 3 reflective markers was fixed to the ultrasound probe. Thus, the probe could be tracked by the navigation system (Vector Vision(2), BrainLab, Heimstetten, Germany) and the segmented shape of the 3D-objects obtained from the MR images were overlaid onto the ultrasound display (Elegra, Siemens, Erlangen, Germany). The dependency of fusion accuracy on different depth of ultrasound display, different distances between probe and objects and different angles between the axis of the ultrasound probe and the centre of the spheres was evaluated. 435 single measurements were performed. FINDINGS: Overall fusion accuracy was 1.08 mm+/-0.61 mm (mean +/- standard deviation) for spheres and 1.6 mm+/-1.1 mm for arrow heads. If the ultrasound probe was directed more tangentially to the surface of the spheres the fusion became increasingly inaccurate (P<0.05). Fusion accuracy decreased the more distant the US probe was held to the object (P<0.05). Different depth of ultrasound display had no significant effect on fusion accuracy. CONCLUSIONS: Highly accurate fusion of MR images and real-time ultrasonography could be achieved. However, careful interpretation of the fused data is necessary, when different angles and distances of the US probe to the object are concerned.

Brain↗
PubMed2000

Mechanical accuracy of a new stereotactic guide.

OBJECTIVE: A new stereotactic guide using a navigational computer is developed for stereotactic procedures. In order to compare the mechanical accuracy of the guide to frame based systems, an error analysis study was designed. METHODS: A biopsy procedure was simulated using a phantom model. Targets with known co-ordinates in a three-dimensional Cartesian co-ordinate system were positioned inside the skull model. A biopsy needle was inserted along computer set trajectories from three different entry points. The position of the biopsy needle in the co-ordinate system was measured. Distance from needle tip to target was calculated and defined as the error of the system for each trial. The results were statistically analyzed for precision and biasedness. RESULTS: A total of 242 accuracy measurements (182 on two MRI scans, 60 on one CT scan) were carried out. Mean incision length along the trajectories was 59 mm. Mean error using MRI scans was 3.8 mm and for the CT scan 2.9 mm. The error of the stereotactic computer was found to be 1.0 mm with both MR and CT imaging. The main cause of error for the MRI based trials was distortion of the magnetic field. CONCLUSION: The results indicate a stereotactic system with high degree of accuracy. This is confirmed by a clinical study of 39 biopsies where all tumours were reached. MRI affected the mechanical accuracy significantly due to distortion of the magnetic field. The accuracy is comparable to other studies performed on both stereotactic computers and frame based systems.

Biopsy, Needle↗
PubMed2006

Accuracy of audio computer-assisted self-interviewing (ACASI) and self-administered questionnaires for the assessment of sexual behavior.

This study examined the accuracy of two retrospective methods and assessment intervals for recall of sexual behavior and assessed predictors of recall accuracy. Using a 2 [mode: audio-computer assisted self-interview (ACASI) vs. self-administered questionnaire (SAQ)] by 2 (frequency: monthly vs. quarterly) design, young women (N =102) were randomly assigned to one of four conditions. Participants completed baseline measures, monitored their behavior with a daily diary, and returned monthly (or quarterly) for assessments. A mixed pattern of accuracy between the four assessment methods was identified. Monthly assessments yielded more accurate recall for protected and unprotected vaginal sex but quarterly assessments yielded more accurate recall for unprotected oral sex. Mode differences were not strong, and hypothesized predictors of accuracy tended not to be associated with recall accuracy. Choice of assessment mode and frequency should be based upon the research question(s), population, resources, and context in which data collection will occur.

Adolescent↗
PubMed2006

Effects of coancestry on accuracy of individual assignments to population of origin: examples using Great Lakes lake trout (Salvelinus namaycush).

Methods for assigning individuals to population of origin are widely used in ecological genetics, resources management, and forensics. Characteristics of genetic data obtained from putative source populations that enhance accuracy of assignment are well established. How non-independence within and among unknown individuals to be classified [i.e., gene correlations within individual (inbreeding) and gene correlations among individuals within group (coancestry)] affect assignment accuracy is poorly understood. We used empirical data for six microsatellite loci and offspring from full-sib crosses of hatchery strains of lake trout (Salvelinus namaycush; Salmonidae) representing known levels of coancestry (mean theta = 0.006 and 0.06) within families to investigate how gene correlations can affect assignment. Additional simulations were conducted to further investigating the influence of allelic diversity (2, 6 or 10 alleles per locus) and inbreeding (F = 0.00, 0.05, and 0.15) on assignment accuracy for cases of low and high inter-population variance in allele frequency (mean F (st) = 0.01 and 0.1, respectively). Inbreeding had no effect on accuracy of assignments. In contrast, variance in assignment accuracy across replicated simulations, and for each empirical case study increased with increasing coancestry, reflecting non-independence of probabilities of correct assignment among members of kin groups. Empirical estimates of assignment error rates should be interpreted with caution if appreciable levels of coancestry are suspected. Additional emphasis should be placed on sampling designs (spatially and temporally) that define or minimize the potential for sampling related individuals.

Animal Population Groups↗
PubMed1988

Surfactant proteins in the diagnosis of fetal lung maturity. I. Predictive accuracy of the 35 kD protein, the lecithin/sphingomyelin ratio, and phosphatidylglycerol.

The concentration of the major surfactant protein with a molecular weight of 35 kD was determined in 469 amniotic fluid specimens from 284 pregnancies by the two-site simultaneous immunoassay with monoclonal antibodies. The predictive accuracy of the 35 kD protein was compared with that of the lecithin/sphingomyelin ratio and phosphatidylglycerol (the lung profile). Immature levels of 35 kD protein (less than 0.6 micrograms/ml) predicted 59% of all cases of respiratory distress syndrome (RDS) with an accuracy of 91%, and mature levels of 35 kD protein (greater than 3.0 micrograms/ml) predicted 68% of all infants who did not have RDS with an accuracy of 100%. The overall accuracy of the 35 kD protein in predicting the risk of developing respiratory distress syndrome was similar to that of the lung profile. In addition, testing with 35 kD protein improved the predictive value of an indeterminate lung profile (lecithin/sphingomyelin ratio of 1:1.9 and no phosphatidylglycerol) from 52% to 74%. The present results show that the lecithin/sphingomyelin ratio, phosphatidylglycerol, and 35 kD apoprotein have additive effects in improving the accuracy of the diagnosis of lung maturity.

Amniotic Fluid↗
PubMed1983

Manipulation of P3 latency: speed vs. accuracy instructions.

Twelve young female subjects were presented with a series of horizontal line-pairs of same or different length in a two-alternative, forced-choice RT task, with 60 of each type pair in each block of trials. In one block (Easy) lines differed by 30%, in another block (Difficult) lines differed by 7%. Subjects were first given 60 practice trials with the Easy discrimination and with the instruction that speed and accuracy should be emphasized equally. For the next block of trials, accuracy was emphasized with a monetary bonus for accurate performance. Finally, in the last block of trials, speed was emphasized with a monetary bonus for speedy performance. Additionally, a penalty was incurred for RTs that exceeded a criterion level based on each individual subject's performance. The order of Easy and Difficult discrimination blocks was maintained within a subject but balanced across subjects. From the latency-adjusted P3s recorded from Pz, we obtained P3 latencies, amplitudes and single-trial P3 latency/RT correlations. RT to correct and incorrect trials and error data were also collected. P3 was considerably larger during the Speed than Accuracy conditions. The single-trial P3 latency/RT correlation was higher in Speed than in Accuracy runs. RT was 235 msec faster and P3 was 40 msec earlier during the Speed than during the Accuracy runs. On the other hand, discrimination difficulty delayed P3 and RT about equally, 28 and 43 msec respectively. This pattern suggests that speed instructions and discrimination difficulty affect stimulus processing time and response production time differently.

Adult↗
PubMed1990

Timing and accuracy of visually directed movements in children: control of direction and amplitude components.

The reaction times (RTs), movement times (MTs), and final accuracy of hand movements directed towards visual goals were measured in 6-, 8-, and 10-year-old children, using tasks in which direction and amplitude components of movement were distinctly required. The tasks were performed with and without visual feedback of the limb. RTs decreased with age, and were shorter in directional than in amplitude task, in all ages. MTs were the longest at age 8 in both tasks, equally short at ages 6 and 10 in the directional task, the shortest at age 10, and intermediate at age 6, when amplitude had to be regulated. In the amplitude task, the target distance generally affected MTs under both visual conditions, but to a lower degree at age 10 than in the two younger groups. Movement accuracy, which was in all cases higher with visual feedback, showed different developmental trends among the two spatial components: directional accuracy was not different among the three groups of age, whereas amplitude accuracy showed a nonmonotonic development in the nonvisual condition, with an increase between age 6 and age 10, and the lowest level at age 8. In the visual condition, amplitude accuracy did not change with age. The specification of direction seems therefore to predominantly load the preparatory stage of the response. Amplitude specification seems to be more dependent on on-going regulations and to undergo a longer and more complex development, with a critical period around age 8 when a greater propensity for a feedback-based control appears on the two components. With increasing age, amplitude tends to be specific to a greater extent by a feedforward process.

Attention↗
PubMed1996

Sub-pixel accuracy: psychophysical validation of an algorithm for fine positioning and movement of dots on visual displays.

Many visual experiments call for visual displays in which dots are plotted with very fine positional accuracy. Spatial hyperacuities and motion displacement thresholds can be as low as 5 sec arc. On computer graphics displays small angular displacements of a pixel can be obtained only with long viewing distances which impose a small field of view. To overcome this problem, we describe a method for positioning the centroid of a quadrel (a 2 x 2 block of pixels) with very high accuracy, equivalent to 0.4% of a pixel width. This enables dot displays to be plotted with high positional accuracy at short viewing distances with larger fields of view. We show psychophysically that hyperacuities can be measured with sub-pixel accuracy in quadrel displays. Motion displacement thresholds of 16 sec arc were measured in multiple-dot and single-dot displays even though the pixel spacing was 1.2 min arc. Quadrel displays may be especially useful in studies of optic flow and structure-from-motion which demand a fairly large field of view along with fine positional accuracy.

Algorithms↗