Primary visual cortex (V1) forms the initial cortical representation of objects and events in our visual environment, and it distributes information about that representation to higher cortical areas within the visual hierarchy. Decades of work have established tight linkages between neural activity occurring in V1 and features comprising the retinal image, but it remains debatable how that activity relates to perceptual decisions. An actively debated question is the extent to which V1 responses determine, on a trial-by-trial basis, perceptual choices made by observers. By inspecting the population activity of V1 from human observers engaged in a difficult visual discrimination task, we tested one essential prediction of the deterministic view: choice-related activity, if it exists in V1, and stimulus-related activity should occur in the same neural ensemble of neurons at the same time. Our findings do not support this prediction: while cortical activity signifying the variability in choice behavior was indeed found in V1, that activity was dissociated from activity representing stimulus differences relevant to the task, being advanced in time and carried by a different neural ensemble. The spatiotemporal dynamics of population responses suggest that short-term priors, perhaps formed in higher cortical areas involved in perceptual inference, act to modulate V1 activity prior to stimulus onset without modifying subsequent activity that actually represents stimulus features within V1.
choice probability; decision-making; fMRI; visual perception; perceptual decision; V1
Endocannabinoid mediated retrograde synaptic signaling is a key regulator of GABA release at synapses formed on the perisomatic region of pyramidal cells by basket cells that co-express the cannabinoid type 1 receptor (CB1R) and cholecystokinin (CCK). However, CB1R and CCK positive GABAergic terminals are present on pyramidal cell dendrites as well, but the principles of endocannabinoid control of GABA release in dendrites are not understood. We performed paired recordings from CCK positive perisomatically (basket cells) or dendritically projecting (Schaffer-collateral associated cells) interneurons and postsynaptic CA1 pyramidal cells to determine the properties of endocannabinoid signaling at GABAergic synapses along the somato-dendritic axis. Although several key elements of the currently known molecular machinery for endocannabinoid synthesis are thought be primarily localized in dendrites, our results revealed that the depolarization-induced suppression of inhibition (DSI), the endocannabinoid-mediated tonic inhibition of GABA release, and the metabotropic glutamate receptor activation induced, CB1R mediated depression of GABA release were all significantly less effective at dendritic compared to perisomatic synapses. In addition, low concentration of exogenous CB1 receptor agonist inhibited GABA release to a lesser extent at dendritic compared to perisomatic synapses, indicating that presynaptic differences are partly responsible for the differential control of GABA release by endocannabinoids in dendrites.
Taken together, these data demonstrate a novel domain-specific regulation of GABA release by endocannabinoid signaling in the hippocampus.
endocannabinoid; interneuron; GABA; inhibition
We investigated the impact on prostate-specific antigen (PSA) and prostate volume (PV) of statin medication for 1 year in patients with benign prostatic hyperplasia (BPH).
Materials and Methods
We retrospectively investigated 791 patients in whom BPH was diagnosed. For analysis, the patients were divided into four groups according to their medications: group A, α-blocker; group B, α-blocker+statin; group C, α-blocker+dutasteride; group D, α-blockers+statin+dutasteride. To investigate changes in serum PSA, PV, and total cholesterol, we analyzed the data at the time of initial treatment and after 1 year of medication.
After 1 year, group A showed a 1.3% increase in PSA and a 1.0% increase in PV. Group B showed a 4.3% decrease in PSA and a 1.8% decrease in PV. The difference in PV reduction between groups A and B was statistically significant (p<0.001). Group C showed a 49.1% reduction in PSA and a 22.9% reduction in PV. Group D showed a 51.6% reduction in PSA and a 24.5% reduction in PV. The difference in PV reduction between groups C and D was not statistically significant (p=0.762). By use of a multivariate logistic regression model, we found that the probability of PV reduction after 1 year was more than 14.8 times in statin users than in statin nonusers (95% confidence interval, 5.8% to 37.6%; p<0.001).
Statin administration reduced PSA and PV in BPH patients. This finding may imply the improvement of lower urinary tract symptoms and prevention of cardiovascular disease and chemoprevention of prostate cancer with statin treatment.
Chemoprevention; Dutasteride; Prostate; Prostate-specific antigen; Statins
We live in a cluttered, dynamic visual environment that poses a challenge for the visual system: for objects, including those that move about, to be perceived, information specifying those objects must be integrated over space and over time. Does a single, omnibus mechanism perform this grouping operation, or does grouping depend on separate processes specialized for different feature aspects of the object? To address this question, we tested a large group of healthy young adults on their abilities to perceive static fragmented figures embedded in noise and to perceive dynamic point-light biological motion figures embedded in dynamic noise. There were indeed substantial individual differences in performance on both tasks, but none of the statistical tests we applied to this data set uncovered a significant correlation between those performance measures. These results suggest that the two tasks, despite their superficial similarity, require different segmentation and grouping processes that are largely unrelated to one another. Whether those processes are embodied in distinct neural mechanisms remains an open question.
perceptual grouping; biological motion; fragmented figures; individual differences
This study was to determine the prevalence of herniated intervertebral disc (HIVD) among Korean 19-year-old male in a large national sample and to compare the prevalence across geographic regions based on the data of conscription.
Materials and Methods
We analyzed the conscription data of 615508 cases who were 19-year-old male, given an examination for conscription at nationwide Korean Military Manpower Administration from January 2008 to December 2009. Prevalence was determined by dividing the number of cases by the number of persons enrolled for 2 years. The analyses included of a cross-tabulations and nonparametric chi-square to compare the prevalence according to geographic region, disc severity, and conscription year.
The prevalence of HIVD among 19-year-old male was 0.47%. Seoul had the highest prevalence of HIVD (total HIVD was 0.60%, and severe HIVD was 0.44%). The prevalence of HIVD was lower in Jeollabuk-do and Jeollanam-do (total HIVD was 0.25-0.27%, and severe HIVD was 0.16-0.17%). Annual prevalence of HIVD was slightly decreased in 2009, but geographic distribution annually was not different.
In Korean 19-year-old male, the national prevalence of adolescent HIVD was 0.60%, but different geographic distribution was observed. It is quite possible that secondary contributing factor(s) interfere with the different geographic prevalence of HIVD.
Herniated intervertebral disc; adolescent; prevalence; conscription
To investigate the effect of gastrocnemius muscle fatigue on postural control ability in elderly people.
Twenty-four healthy elderly people participated in this study. The postural control ability of single leg standing was evaluated with Health Improvement & Management System (HIMS) posturography before and after fatiguing exercises. After evaluating initial postural control ability, the maximal voluntary contraction (MVC) of ankle plantarflexion was assessed using a surface electromyogram from the medial belly of the gastrocnemius muscle. After a 5-minute resting period, subjects began submaximal isometric ankle plantarflexion (40% MVC) until 40% of MVC was dropped below 95% for 5 seconds, or subject couldn't continue working out due to muscle fatigue. And postural control ability was assessed after fatiguing exercise. The mean deviation of center of pressure (COP), length of COP movement, occupied area of COP were measured, and analyzed by paired t-test.
Mediolateral deviation, length of COP movement, and area of COP occupied were increased after fatiguing exercise of the gastrocnemius muscle. Anteroposterior deviation and length of COP movement were also increased, but had low statistical significance.
These findings suggest that the gastrocnemius muscle fatigue affects mediolateral stability and accuracy during single leg standing in elderly people. Therefore muscle endurance training is necessary to prevent falls in elderly people.
Balance; Posture; Elderly; Fatigue; Ankle
While the diversity of neocortical and hippocampal GABAergic interneurons is recognized in terms of their anatomical, molecular, and functional properties, principal cells are usually assumed to constitute homogenous populations. However, even within a single layer, subpopulations of principal cells can often be differentiated by their distinct long-range projection targets. Such subpopulations of principal cells can have different local connection properties and excitatory inputs, forming subnetworks that may serve as separate information-processing channels. Interestingly, as reviewed here, recent evidence has revealed specific instances where interneuron cell types selectively innervated distinct subpopulations of principal cells, targeting only those with particular long-distance projection targets. This organization represents a novel form of interneuron specialization, providing interneurons with the potential to selectively regulate specific information-processing streams.
Endothelial progenitor cells (EPCs) play a critical role in restoration of ischemic diseases. However, the actual status of EPC development and the mechanisms of EPC dysfunctions in patients with various ischemic diseases remain unknown.
To investigate the detailed function of EPCs in experimental murine models, we have established an EPC colony forming assay (EPC-CFA) in murine EPCs. The abilities of murine EPCs in differentiation, adhesive capacity, proliferative potency, and transplantation in vitro and in vivo were then examined.
Peripheral blood mononuclear cells (PB-MNCs), bone marrow mononuclear cells (BM-MNCs) or bone marrow c-Kit+/Sca-1+ lineage negative (BM-KSL) cells differentiated into two types of EPC colony forming units (EPC-CFUs), large sized EPC (large-EPC)-CFUs and small sized EPC (small-EPC)-CFUs. Gene expression analysis demonstrated that both EPC-CFU-derived cells expressed eNOS, Flk-1 and VE-cadherin, markers of endothelial cells (ECs), although the small-EPCs derived from small-EPC-CFU were higher in number and showed more immature features (higher population of KSL cells). Functionally, the large-EPCs derived from large-EPC-CFU had higher adhesive capacity but lower proliferative potency than small-EPCs, showing improved tubular forming capacity and incorporation potency into primary EC-derived tube formation. Importantly, hindlimb ischemia increased the frequencies of large-EPC-CFUs differentiated from PB-MNCs and bone marrow. Actually, transplantation of large-EPCs into ischemic hindlimb enhanced neovascularization in hindlimb ischemia model, although small-EPCs or murine ECs did not, suggesting that large-EPC-CFUs might play an important role in restoration of ischemic diseases.
We demonstrated, using a murine ischemia model, that the EPC-CFA could be a useful way to investigate the differentiation levels of murine EPCs, further providing a crucial clue that large-EPC-CFU status may be more functional or effective EPCs to promote neovascularization.
Hemodialysis (HD) patients have multiple causes of immune dysfunction and poor immune response to influenza vaccination. We investigated the antibody response rate to a pandemic H1N1/2009 influenza vaccination and clinical parameters influencing the induction of antibody responses in HD patients.
A total of 114 HD patients were vaccinated with a monovalent adjuvanted H1N1 inactivated influenza vaccine. Titers of neutralizing antibodies were evaluated by hemagglutination inhibition (HI) assay at pre- and 4 weeks after vaccination. Seroconversion was defined as either a pre-vaccination HI titer < 1:10 and a post vaccination HI titer > 1:40 or a pre-vaccination HI titer ≥ 1:10 and a minimum four-fold rise in post-vaccination HI antibody titer. Seventeen out of 114 HD patients (14.9%) tested positive for antibodies against influenza A/H1N1/2009 before vaccination. The remaining 97 baseline sero-negative patients were included in the analysis.
Only 30 (30.9%) HD patients had seroconversion 4 weeks after vaccination. The elderly patients, those over 65 years of age, showed significantly lower seroconversion rate compared to younger HD patients (20.5% vs. 39.6%, p = 0.042). Furthermore, patients with hemoglobin values less than 10 g/dL had a significantly lower seroconversion rate compared to those with higher hemoglobin values (20.0 vs. 38.6%, p = 0.049). By multivariate logistic regression analysis, only age ≥65 years (OR = 0.336, 95% confidence interval (CI) 0.116-0.971, p = 0.044) and hemoglobin levels <10 g/dL (OR = 0.315, 95% CI 0.106-0.932, p = 0.037) were independently associated with seroconversion after vaccination.
Our data show that HD patients, especially who are elderly with low hemoglobin levels, are at increased risk for lower seroconversion rate after influenza A/H1N1 vaccination. Further studies are needed to improve the efficacy of vaccination in these high risk patients.
Hemodialysis; Pandemic H1N1/2009 influenza; Vaccine; Seroconversion
To present the accuracy and safety of cervical pedicle screw insertion using the technique with direct exposure of the pedicle by laminoforaminotomy.
We retrospectively reviewed 12 consecutive patients. A total of 104 subaxial cervical pedicle screws in 12 patients had been inserted. We also assessed the clinical and radiological outcomes and analyzed the direction and grade of pedicle perforation (grade 0: no perforation, 1: <25%, 2: 20% to 50%, 3: >50% of screw diameter) on the postoperative vascular-enhanced computed tomography scans. Grade 2 and 3 were considered as incorrect position.
The correct position was found in 95 screws (91.3%); grade 0-75 screws, grade 1-20 screws and the incorrect position in 9 screws (8.7%); grade 2-6 screws, grade 3-3 screws. There was no neurovascular complication related with cervical pedicle screw insertion.
This technique (technique with direct exposure of the pedicle by laminoforaminotomy) could be considered relatively safe and easy method to insert cervical pedicle screw.
Cervical pedicle screw; Laminoforaminotomy; Pedicle perforation
The prevalence of intervertebral disc herniation (IDH) of the thoracic spine is rare compared to the cervical or lumbar spine. In particular, IDH of the upper thoracic spine is extremely rare. We report the case of T1-2 IDH and its treatment, with a literature review. A 37-year-old male patient visited our hospital due to radiating pain at the left upper extremity and weakness of grip power. In cervical spine magnetic resonance images, T1-2 disc space showed herniated disc material and compressed T1 root was identified. Laminoforaminotomy was performed with a posterior approach. The radiating pain and weakness of grip power improved immediately after the surgery. Of patients who show radiating pain or numbness at the medial aspect of forearm, or weakness of intrinsic muscle of hand, can be suspected to have T1 radiculopathy. A detailed physical examination and a radiologic evaluation including this area should be required for the T1 radiculopathy.
Thoracic Vertebrae; Intervertebral Disc; Radiculopathy; Laminotomy
The incidence of horseshoe kidney is about 1 in 400 cases. The presence of Wilms' tumor with a horseshoe kidney is unusual, and the occurrence of Wilms' tumor in a horseshoe kidney is estimated at 0.4 to 0.9% of all Wilms' tumors. We report the case of a 5-year-old boy who presented with a stage IV Wilms' tumor in a horseshoe kidney. The patient was treated with preoperative chemotherapy followed by surgical resection and adjuvant chemotherapy. This case illustrates the role of preoperative chemotherapy for preserving renal function and aims to highlight the multimodality treatment of Wilms' tumor.
Adjuvant chemotherapy; Neoadjuvant therapy; Wilms tumor
Animal tumor models are important for the evaluation of novel therapeutic modalities. Since the initial report of an orthotopic bladder tumor model, several modifications have been proposed to improve the tumor take rate. Here we compared the HCl-pretreated and electrocauterization-pretreated orthotopic murine bladder tumor models.
Materials and Methods
MBT-2 murine bladder cancer cells were transurethrally implanted in the bladder of syngeneic C3H/He mice. The mice were divided into three groups according to pretreatment methods (electrocautery, HCl, and control group) and were subjected to pretreatment before instillation of MBT-2 tumor cells into the bladder. Mice were sacrificed on day 21, and bladders were harvested, weighed, and examined histopathologically.
The tumor take rate of the control, electrocautery, and HCl groups was 0%, 54%, and 100%, respectively. The tumor take rate of the HCl group was significantly higher than that of the control group (p<0.01) and the electrocautery group (p=0.01). Pathologic reports revealed that all established bladder tumors were high-grade papillary urothelial carcinomas.
The HCl pretreatment model was a preferable murine bladder tumor model for evaluating further therapeutic interventions.
Animal models; Intravesical administration; Urinary bladder neoplasms
Mu opioid receptors (μORs) are selectively expressed on interneurons in area CA1 of the hippocampus. Fast-spiking, parvalbumin expressing, basket cells express μORs, but circumstantial evidence suggests that another major, unidentified, GABAergic cell class must also be modulated by μORs. Here we report that the abundant, dendritically targeting, neurogliaform family of cells (Ivy and neurogliaform cells) is a previously unrecognized target of direct modulation by μORs. Ivy and neurogliaform cells are not only numerous, but also have unique properties, including promiscuous gap junctions formed with various interneuronal subtypes, volume transmission, and the ability to produce a postsynaptic GABAB response after a single presynaptic spike. Using a mouse line expressing green fluorescent protein under the neuropeptide Y promoter, we find that across all layers of CA1, activation of μORs hyperpolarizes Ivy and neurogliaform cells. Further, paired recordings between synaptically coupled Ivy and pyramidal cells show that Ivy cell terminals are dramatically inhibited by μOR-activation. Effects in Ivy and neurogliaform cells are seen at similar concentrations of agonist as those producing inhibition in fast-spiking PV basket cells. We also report that Ivy cells display the recently described phenomenon of persistent firing, a state of continued firing in the absence of continued input, and that induction of persistent firing is inhibited by μOR-activation. Together these findings identify a major, previously unrecognized, target of μOR-modulation. Given the prominence of this cell type in and beyond CA1, as well as its unique role in microcircuitry, opioid modulation of neurogliaform cells has wide implications.
We performed L1 posterior vertebral columnar resection and posterior correction for Andersson's lesion and thoracolumbar kyphosis in an ankylosing spondylitis patient during motor evoked potential (MEP) monitoring. We checked MEP intra-operatively, whenever a dangerous procedure for neural elements was performed, and no abnormal findings were seen during surgery. After the operation, we examined neurologic function in the recovery room; the patient showed a progressive neurologic deficit and no response to MEP. After emergency neural exploration and decompression surgery, the neurologic deficit was recovered. We questioned whether to acknowledge the results of this case as a false negative. We think the possible reason for this result may be delayed development of paralysis. So, we recommend that MEP monitoring should be performed not only after important operative steps but also after all steps, including skin suturing, for final confirmation.
Spine operation; Deformity correction; Motor evoked potential; Delayed paraplegia
Inhibiting the bioactivities of circulating endothelial progenitor cells (EPCs) results in significant inhibition of neovessel formation during tumor angiogenesis. To investigate the potential effect of phloroglucinol as an EPC inhibitor, we performed several in vitro functional assays using CD34+ cells isolated from human umbilical cord blood (HUCB). Although a high treatment dose of phloroglucinol did not show any cell toxicity, it specifically induced the cell death of EPCs under serum free conditions through apoptosis. In the EPC colony-forming assay (EPC-CFA), we observed a significant decreased in the small EPC-CFUs for the phloroglucinol group, implying that phloroglucinol inhibited the early stage of EPC commitment. In addition, in the in vitro expansion assay using CD34+ cells, treatment with phloroglucinol was shown to inhibit endothelial lineage commitment, as demonstrated by the decrease in endothelial surface markers of EPCs including CD34+, CD34+/CD133+, CD34+/CD31+ and CD34+/CXCR4+. This is the first report to demonstrate that phloroglucinol can inhibit the functional bioactivities of EPCs, indicating that phloroglucinol may be used as an EPC inhibitor in the development of biosafe anti-tumor drugs that target tumor angiogenesis.
Endothelial progenitor cell; Tumor angiogenesis; Phloroglucinol; Colony forming assay
We studied the action potential of Primo-vessels in rats to determine the electrophysiological characteristics of these structures. We introduced a mathematical analysis method, a normalized Fourier transform that displays the sine and cosine components separately, to compare the action potentials of Primo-vessels with those for the smooth muscle. We found that Primo-vessels generated two types of action potential pulses that differed from those of smooth muscle: (1) Type I pulse had rapid depolarizing and repolarizing phases, and (2) Type II pulse had a rapid depolarizing phase and a gradually slowing repolarizing phase.
A patterned film (electrode) with lozenge-shaped Si tiles could be successfully fabricated by masking with an expanded metal foil during film deposition. Its electrochemical properties and structural stability during the charge-discharge process were examined and compared with those of a continuous (conventional) film electrode. The patterned electrode exhibited a remarkably improved cycleability (75% capacity retention after 120 cycles) and an enhanced structural stability compared to the continuous electrode. The good electrochemical performance of the patterned electrode was attributed to the space between Si tiles that acted as a buffer against the volume change of the Si electrode.
patterned electrode; silicon film; stress; anode
The aim of this study was to determine whether anterior column support is required in Smith-Petersen osteotomy procedure with correction angles of more than 10°, while examining the subsequent healing patterns in relation to the disrupted area.
An analysis was done on 26 segments of 19 patients who showed a correction angle of more than 10° in the anterior opening after SPO. There were 17 male and two female patients with a mean age of 40 years (24–56 years). The mean follow-up period was 6.5 years (2–9.1 years). The patients were classified according to the site of the anterior opening, as the disc level, the lower end-plate of the upper body (upper body), or the upper end-plate of the lower body (lower body). The healing patterns of anterior opening and the radiological correction angles were evaluated relative to the opening site.
In all cases, bony fusion was confirmed at a mean period of 5.6 months (3–6.7 months) after surgery and the anterior opening gap was healed in 18 segments (69.2%). For patients that developed an opening in the upper body, all of the gaps were healed. The gaps in the lower body opening group were healed in 85.7% of the cases, and for the opening at the disc level, the gaps were healed only in 12.5% of the cases. The least amount of correction was obtained when anterior opening occurred in disc level.
In our study of subjects presenting with anterior opening angles from 10° to 32°, we obtained successful fusion without the need for additional anterior interbody fusion. Improved gap healing and increased correction angles were obtained when the opening was present in the upper or lower body endplates compared to those at the disc space level.
Ankylosing spondylitis; Kyphotic deformity; Smith-Petersen osteotomy
Parvalbumin-expressing, fast-spiking basket cells play key roles in the generation of synchronous, rhythmic population activities in the hippocampus. Here we show that GABAA receptor-mediated synaptic inputs from murine parvalbumin-expressing basket cells are selectively modulated by the membrane voltage- and intracellular chloride-dependent chloride channel ClC–2. These data demonstrate a novel cell type-specific regulation of intracellular chloride homeostasis in the perisomatic region of hippocampal pyramidal neurons.
interneuron; GABAA receptor; excitability; microcircuit; intracellular chloride
Can human observers distinguish physical removal of a visible stimulus from phenomenal suppression of that stimulus during binocular rivalry? As so often happens, simple questions produce complex answers, and that is the case in the study reported here. Using continuous flash suppression to produce binocular rivalry, we were able to identify stimulus conditions where most – but not all – people utterly fail to distinguish physical from phenomenal stimulus removal, although we can be certain that those two equivalent perceptual states are accompanied by distinct neural events. More interestingly, we find subtle variants of the task where distinguishing the two states is trivially easy, even for people who utterly fail under the original conditions. We found that stimulus features are differentially vulnerable to suppression. Observers are able to be aware of existence/removal of some stimulus attributes (flicker) but not others (orientation), implying that interocular suppression breaks down the unitary awareness of integrated features belonging to a visual object. These findings raise questions about the unitary nature of awareness and, also, place qualifications on the utility of binocular rivalry as a tool for studying the neural concomitants of conscious visual awareness.
awareness; interocular suppression; continuous flash suppression; temporal modulation; orientation; feature-selectivity
The Gestalt psychologists were fascinated with dynamics evident in visual perception, and they theorized that these dynamics were attributable to ever-changing electrical potentials within topographically organized brain fields. Dynamic field theory, as it was called, was subsequently discredited on grounds that the brain does not comprise a unitary electrical field but, instead, a richly interconnected network of discrete computing elements. Still, this modern conceptualization of brain function faces the challenge of explaining the fact that perception is dynamic in space and in time. To pursue the question of visual perception and cortical dynamics, we have focused on spatio-temporal transitions in dominance during binocular rivalry. We have developed techniques for initiating and measuring these transitions psychophysically and for measuring their neural concomitants using functional magnetic resonance imaging (fMRI). Our findings disclose the existence of waves of cortical activity that travel across the retinotopic maps that define primary and secondary visual areas within occipital cortex, in correspondence with the subjective perception of spreading waves of dominance during binocular rivalry. This paper reviews the results from those studies.
binocular vision; binocular rivalry; visual cortex; fMRI (functional magnetic resonance imaging); dynamic of neuronal process
The role of collinear facilitation was investigated to test predictions of a model for traveling waves of dominance during binocular rivalry (H. Wilson, R. Blake, & S. Lee, 2001). In Experiment 1, we characterized traveling wave dynamics using a recently developed technique called periodic perturbation (M.-S. Kang, D. Heeger, & R. Blake, 2009). Results reveal that the propagation speed of waves for a collinear stimulus increased regardless of whether that stimulus was suppressed (replicating earlier work) or dominant; this latter finding is contrary to the model’s prediction. In Experiment 2, we measured perceptual dominance durations within a localized region in the center of two rival stimuli that varied in degree of collinearity. Results reveal that increased collinearity did not change average dominance durations regardless of the rivalry phase of the stimulus, again contrary to the model’s prediction. Incorporating pattern-dependent modulation of adaptation rate into the model accounted for results from both experiments. Using model simulations, we show how interactions between collinear facilitation and pattern-dependent adaptation may influence the dynamics of binocular rivalry. We also discuss alternative interpretations of our findings, including the possible role of surround suppression.
binocular rivalry; computational modeling; collinear facilitation; perceptual organization; perceptual dynamics