Optimization of ovine bone decalcification for increased cellular detail: a parametric study

There are many published methods of decalcifying bone for paraffin histology; however, the current literature lacks details regarding the processing of ovine tissue. Ovine bone tissue presents challenges, as samples are often denser and larger than other comparative animal models, thus increasing decalcification times. Trifluoroacetic Acid (TFAA) has previously been used to decalcify ovine bone samples for histological analysis. Unfortunately, TFAA is a strong acid and often results in loss of cellular detail, especially in the connected soft tissue. This is generally manifested as over staining with eosin, and a decrease in cellular features which impacts overall histological interpretation. It is well known that leaving tissue in acid for long periods degrades cellular detail; therefore, minimizing decalcification time is critical to accurately determine cellular morphology. Six decalcification solutions (8% TFAA, 20% TFAA, 8% formic acid, 20% formic acid, Formical-4, and XLCal, and three temperatures (room temperature, 30°C, 37°C), were examined to determine their effects on cellular detail in ovine vertebrae and humeral heads. These data clearly indicate that 20% formic acid at 30°C yielded better decalcification rates (2.6 d ± 0.9 d) and cellular detail (none to mild changes) for the vertebrae samples, and 20% formic acid at RT yielded the best cellular detail (none to minimal loss) for humerus samples with a moderate amount of time (6.5 d ± 1.7). These results should establish the optimal demineralization procedures for ovine bone used in scientific studies resulting in improved cellular detail while minimizing decalcification times.

Visual Factors in the Avoidance of Front-To-Rear-End Highway Collisions

Two visual factors in the avoidance of front-to-rear-end collisions are (a) judging time to collision so as to control braking optimally on a moment-to-moment basis, and/or (b) judging one's heading relative to the lead car so as to steer appropriately. It is known that time to contact equals θ/(dθ/dt) and it is also known that the eye is sensitive to θ and, separately, (dθ/dt) (θ is the angular size and (dθ/dt) is the rate of increase of angular size). But whether the eye is sensitive to the ratio (θ/(dθ/dt) and, if so, whether drivers use this information are further questions. We report here that the human visual system does contain neurons sensitive to the ratio θ/(dθ/dt) rather independently of θ and (dθ/dt). It is important that the driver looks directly at the lead vehicle: sensitivity to (dθ/dt) falls off steeply in peripheral view. But, over a wide range, sensitivity to (dθ/dt) is independent of contrast. In addition to the classical disparity-driven system for binocular depth perception, there is a separate binocular system for motion in depth. Precise judgements (0.2 deg) of heading are supported by this stereomotion system, but on the other hand about 20% of the population have stereomotion “blind spots” (i.e. field defects). Monocularly-available informations can also support precise judgements of heading, and field defects seem to be rare. Field studies on flight simulators and telemetry-tracked jet aircraft showed that laboratory measures of sensitivity to (dθ/dt) and to the rate of expansion of the optical flow field predicted intersubject differences in performance on flying tasks that were closely related to the rear-end collision situation.

Immune regulation of canine tumour and macrophage PD-L1 expression

Expression of programmed cell death receptor ligand 1 (PD-L1) on tumor cells has been associated with immune escape in human and murine cancers, but little is known regarding the immune regulation of PD-L1 expression by tumor cells and tumor-infiltrating macrophages in dogs. Therefore, 14 canine tumor cell lines, as well as primary cultures of canine monocytes and macrophages, were evaluated for constitutive PD-L1 expression and for responsiveness to immune stimuli. We found that PD-L1 was expressed constitutively on all canine tumor cell lines evaluated, although the levels of basal expression were very variable. Significant upregulation of PD-L1 expression by all tumor cell lines was observed following IFN-γ exposure and by exposure to a TLR3 ligand. Canine monocytes and monocyte-derived macrophages did not express PD-L1 constitutively, but did significantly upregulate expression following treatment with IFN-γ. These findings suggest that most canine tumors express PD-L1 constitutively and that both innate and adaptive immune stimuli can further upregulate PD-L1 expression. Therefore the upregulation of PD-L1 expression by tumor cells and by tumor-infiltrating macrophages in response to cytokines such as IFN-γ may represent an important mechanism of tumor-mediated T-cell suppression in dogs as well as in humans.

Oral and anal sex are key to sustaining gonorrhoea at endemic levels in MSM populations: a mathematical model

OBJECTIVES

Despite early treatment of urethral infection, gonorrhoea is endemic in urban populations of men who have sex with men (MSM) in Australia. By contrast, gonorrhoea is not common in urban heterosexual populations. Sexual activities among MSM usually involve anal or oral sex, and as these behaviours are becoming increasingly common among heterosexuals, there is a need to investigate their roles in transmission of gonorrhoea.

METHODS

We developed individual-based models of transmission of gonorrhoea in MSM and heterosexuals that incorporate anatomical site-specific transmission of gonorrhoea. We estimated the probabilities of transmission for anal sex and oral sex by calibrating an MSM model against prevalence of gonorrhoea and sexual activity data. These probabilities were then applied to a heterosexual model in order to examine whether gonorrhoea can persist in a heterosexual population through the addition of anal sex and oral sex.

RESULTS

In the MSM model, gonorrhoea can persist despite prompt treatment of urethral infections. The probability of gonorrhoea persisting is reduced if use of condom for oral sex is increased to more than 15% of acts. Assuming that treatment of symptomatic infections is prompt, gonorrhoea is unlikely to persist in a heterosexual population even with the addition of anal and oral sex.

CONCLUSIONS

Our models suggest that oral sex has an important role in sustaining gonorrhoea in a population of MSM by providing a pool of untreated asymptomatic infection. The importance of anal sex or oral sex in sustaining gonorrhoea in a heterosexual population remains uncertain due to the lack of information linking different types of sex acts and transmissibility.

Head and neck cancer in Australia between 1982 and 2005 show increasing incidence of potentially HPV-associated oropharyngeal cancers

BACKGROUND

Although tobacco- and alcohol-associated head and neck cancers are declining in the developed world, potentially human papillomavirus (HPV)-associated oropharnygeal cancers are increasing.

METHODS

We analysed oropharyngeal and oral cavity cancer rates in Australia in 1982-2005. Cancers from the oropharynx (base of tongue, tonsil and other specific oropharyngeal sites) were classified as potentially HPV associated (n=8844); cancers in other oral cavity and oropharyngeal sites not previously associated with HPV were classified as comparison (n=28,379).

RESULTS

In 2000-2005, an average of 219, 159 and 110 cancers of the tonsil, base of tongue and other oropharyngeal sites were diagnosed annually, with incidences of 1.09 (95% CI: 1.03, 1.15), 0.79 (95% CI: 0.74, 0.84) and 0.55 (95% CI: 0.50, 0.59) per 100,000, respectively. An average of 1242 comparison cancers were diagnosed annually (6.17 (95% CI: 6.03, 6.31) per 100,000). In 1982-2005, there were significant annual increases in tonsil (1.39% (95% CI: 0.88, 1.92%)) and base of tongue cancers in males (3.02% (95% CI: 2.27, 3.78%)) and base of tongue cancer in females (3.45% (95% CI: 2.21, 4.70%)). There was a significant decrease in comparison cancers in men (-1.69% (95% CI: -1.96, -1.42%)), but not in females.

CONCLUSION

Potentially HPV-associated oropharyngeal cancer in Australia is increasing; the impact of HPV vaccination on these cancers should be monitored.

Ethnically mismatched cord blood transplants in African Americans: the Saint Louis Cord Blood Bank experience

BACKGROUND

For ethnic minority patients where a suitably matched BM or peripheral blood donor is frequently unavailable, cord blood offers an opportunity for hematopoietic stem cell transplantation. Focused recruitment of ethnic minorities for cord blood donation has been proposed as the preferred strategy to improve access for minority recipients to cord blood for transplantation. The aim of this study was to evaluate cord blood characteristics for Caucasian and African American donors and the success of ethnically mismatched UC blood transplantation in African American recipients.

METHODS

Retrospective data analysis was performed comparing the characteristics of 556 cord blood units from African American and Caucasian donors. The outcomes of 18 African American ethnically mismatched transplant recipients were compared with a paired sample of 18 ethnically matched Caucasian recipients.

RESULTS

The fraction of collected units meeting acceptability criteria from African Americans was significantly lower compared with Caucasians (P = <0.0001). Additionally, African Americans had a significantly lower post-processing total nucleated cell count (TNC) compared with Caucasians (P=0.007) but there were no other significant differences in conventionally measured product characteristics. In the transplant analysis, there was no difference in overall survival at 1 year (P=0.85) or time to neutrophil engraftment (P=0.92) between the two patient populations.

DISCUSSION

At comparable levels of TNC dose and HLA matching, the use of ethnically mismatched UC blood units as a source for allogeneic unrelated transplant can result in successful transplant outcomes for African American patients.

Convergence of boundary and body information in the visual processing of aspect ratio

We used DOG ellipses and outlined ellipses that contained, respectively, only low-frequency and only high-frequency information about aspect ratio. Cross-adaptation (i.e., adapt DOG/test outline and adapt outline/test DOG) produced aspect ratio aftereffects.

CONCLUSION

Spatial information encoded in terms of the body of the stimulus and in terms of the boundary of the stimulus have substantially converged before the information-processing stage at which aspect ratio is encoded. We also report that when observers were instructed to discriminate horizontally elongated from vertically elongated test ellipses, the "just noticeably different from circular" threshold was closely constant over a 16:1 range of test ellipse areas.

Role of feedback in the accuracy of perceived direction of motion-in-depth and control of interceptive action

We quantified the accuracy of the perception of the absolute direction of motion-in-depth (MID) of a simulated approaching object using a perceptual task and compared those data with the accuracy of estimating the passing distance measured by means of a simulated catching task. For the simulated catching task, movements of the index finger and thumb of the observer's hand were tracked as participants tried to "catch" the simulated approaching object. A sensation of MID was created by providing monocular and/or binocular retinal image information. Visual stimuli were identical for perceptual and simulated catching tasks. We confirm previous reports that in the perceptual task, observers judged the object to pass wider of the head than indicated by the visual information provided. Although accuracy improved when auditory feedback was added to the perceptual (button pressing) task, consistent overestimates were still recorded. For the no-feedback simulated catching task, observers consistently overreached, i.e., the hand was further away from the midline than the simulated object at the time of hand closure. When auditory feedback was added to the simulated catching task successful catching was achieved. The relative accuracy in binocular and monocular conditions for individual observers could be partially explained by individual differences in sensitivity to unidirectional changes in angular size and changes in relative disparity. We conclude that catching an approaching ball requires that errors in the perceived direction of MID are corrected by feedback-driven learning in the motor system, and that this learning is more easily achieved for the catching action than for button pressing.

Long range interactions between object-motion and self-motion in the perception of movement in depth

Self-motion through a three-dimensional array of objects creates a radial flow pattern on the retina. We superimposed a simulated object moving in depth on such a flow pattern to investigate the effect of the flow pattern on judgments of both the time to collision (TTC) with an approaching object and the trajectory of that object. Our procedure allowed us to decouple the direction and speed of simulated self motion-in-depth (MID) from the direction and speed of simulated object MID. In Experiment 1 we found that objects with the same closing speed were perceived to have a higher closing speed when self-motion and object-motion were in the same direction and a lower closing speed when they were in the opposite direction. This effect saturated rapidly as the ratio between the speeds of self-motion and object-motion was increased. In Experiment 2 we found that the perceived direction of object-MID was shifted towards the focus of expansion of the flow pattern. In Experiments 3 and 4 we found that the erroneous biases in perceived speed and direction produced by simulated self-motion were significantly reduced when binocular information about MID was added. These findings suggest that the large body of research that has studied motion perception using stationary observers has limited applicability to situations in which both the observer and the object are moving.

Binocular information about time to collision and time to passage

It is well known that, when an object's horizontal relative disparity is changing appropriately, most observers report a compelling impression that the object is approaching and will collide with the observers at some future instant. Here I derive a new equation, namely TTC approximates (ddelta/dt)/(d(2)delta/dt(2)). This equation relates TTC to retinal image variables without involving a knowledge of the approaching object's distance or speed. In this respect the new equation is the binocular equivalent of the well-known equation for tau.

Spatial frequency discrimination in cyclopean vision

It is well known that inspecting a cyclopean grating causes threshold for detecting a subsequently presented test cyclopean grating to be elevated, and that the threshold elevation is greatest at the adapting frequency. We report here that spatial frequency discrimination threshold is also elevated, but the elevation is greatest at frequencies offset from the adapting frequency, and the elevation at the adapting frequency is near-zero. We conclude that discrimination threshold is determined by the relative activity of cyclopean frequency-tuned channels, and suggest that relative activity is computed at an opponent-frequency stage. Discrimination threshold for cyclopean gratings was 2.5-4% for two observers, and remained approximately constant over the range 0.16-2.0 cycles/ degrees. Discrimination threshold for luminance-defined gratings was only slightly lower. Discrimination threshold was approximately independent of the grating's peak-to-peak disparity over a range of 45:1 for one observer and 17:1 for another. This finding as well as the low value of discrimination threshold are consistent with an opponent-process model. The dot density of every cyclopean grating used was chosen bearing in mind our finding that three or more spatial samples per grating cycle are required before sampling effects can be ignored.

Fast long-distance interactions in the early processing of motion-defined form and of combinations of motion-defined, luminance-defined, and cyclopean form

Humans can compare the orientations and locations of two motion-defined test bars several degrees apart so as to rapidly encode and place in memory their mean orientation, orientation difference, separation and mean location, while ignoring stimuli located between the two test bars. Performance is not impaired by randomly varying the location of the bars. We conclude that the two test bars are not compared by shifting gaze location or attention from one test bar to the other, nor by attending to two spatial locations. In addition, observers can discriminate the orientation difference and mean orientation of two test bars that, each of which is rendered visible by a different sub-modality (motion, disparity or luminance). Taking into account the findings reported here and previously reported findings on the early processing of luminance-defined form (Vis. Res. 40 (2000) 2291, Vis. Res. 42 (2002) 49) and cyclopean form (Proc. Roy. Soc. Lond. B 268 (2001) 213) we propose that the human visual system contains a fast long-distance comparator that compares the orientation and locations of two test bars while being insensitive to stimuli in the space between the test bars, and that this process is independent of whether the test bars are rendered visible by only one of three kinds of contrast (luminance, disparity, motion) or by combinations of the three. One role of this comparator mechanism may be to rapidly bind the spatial aspects of the retinal image across sub-modalities immediately after each saccade.

Hitting what one wants to hit and missing what one wants to miss

When an observer gazes directly at a rigid spherical object moving at constant speed along a line directed at the head, both monocular and binocular retinal image correlates of time to collision (TTC) are available provided that the object is not too small. The monocular correlate is not available for very small objects and is invalid for rotating aspherical objects, while the binocular correlate is available only when the ratio (closing speed)/(distance) is sufficiently large. Both cues are maximally effective in the central visual field so it is helpful to foveate potential collision hazards. On the other hand, in the special case of prolonged periods of driving along a straight empty road it is important to vary the direction of gaze rather than continuously gazing straight ahead so as to avoid the local adaptation to retinal image expansion that can cause errors in judging TTC when only monocular information is available. A more benign effect of self-motion is a long-distance interaction between the TTC signal generated by the approaching object and the expanding flow pattern caused by self-motion. This interaction creates a margin of safety. We also discuss eye movement strategies in executing the following two tasks: estimating the direction of self-motion; hitting a cricket ball.

Orientation characteristics of a mechanism in the human visual system sensitive to cyclopean form

Human observers viewed two superimposed cyclopean gratings in dynamic random noise. Neither grating was visible monocularly. The disparities of the two gratings were counterphase-modulated at different temporal frequencies. We recorded frequency domain brain responses at ultra-high frequency resolution (0.008 Hz) by means of nondestructive zoom-FFT. The response to the superimposed gratings was quite different to the sum of responses to the two individual gratings. We used this strong nonlinearity to investigate the orientation tuning of the cyclopean mechanism that responded to the gratings. One grating had a fixed orientation while the other was rotated. Half-sensitivity full bandwidth was greater than 90 degrees. This is considerably greater than the corresponding bandwidth (30 degrees) for luminance-defined (LD) gratings [Vis. Res. 27 (1987) 2181]. Furthermore, the cyclopean nonlinearity was different from the corresponding nonlinearity for LD gratings. Brain responses to a single cyclopean grating showed an inverse oblique effect over a 1.2-1.9 degrees range of bar widths, but not for smaller or larger bar widths.

Fast long-range interactions in the early processing of luminance-defined form

Within a duration of 20 ms humans can compare the orientations of two test lines so as to encode and place in memory their mean orientation and orientation difference while ignoring noise lines in the space between the test lines. Furthermore, performance is not impaired by randomly varying the location of each test line from trial-to-trial. We conclude that the two test lines are not compared by shifting eye fixation or attention from one to the other, nor by attending to two spatial locations. This evidence is consistent with the proposal that the human visual system contains second-stage long-distance comparators, any one of which responds to simultaneous stimulation of two conventional first-stage spatial filters located some distance apart and is insensitive to stimuli that fall between these two first-stage filters. We suggest that our observers performed discriminations by attending to the outputs of the proposed second-stage long-distance comparators rather than by attending to two spatial locations. In addition to their mean orientation and orientation difference, humans can simultaneously encode and place in memory the separation and mean location of the two test lines while ignoring stimuli in the space between the lines. We suggest that, following each of the eye's exploratory saccades, the proposed second-stage long-distance comparators, in effect, take a snapshot of an object's retinal image that ignores the object's surface texture while encoding the shape of its boundary.

Simulated hair cell transduction of quasi-frequency-modulated and amplitude-modulated tones

This paper describes a method for calculating the effect of simulated hair cell transduction on (i) a quasi-frequency-modulated (quasi-FM) tone and on (ii) an amplitude-modulated (AM) tone. The main finding is that the effect of the transduction on AM and quasi-FM (which have the same power spectra but whose phase spectra differ), is to produce different power spectra.

Accuracy of estimating time to collision using only monocular information in unilaterally enucleated observers and monocularly viewing normal controls

Since individuals who have lost an eye in early life rely on monocular information, one asked if they would better estimate the time to collision (TTC) with an approaching object based on the monocular cue [(&theta;/(d&theta;/dt), i.e. tau] than a control group using only monocular information. Estimates of TTC were measured with a simulated approaching textured object using a staircase procedure. Seven adult observers who were unilaterally enucleated at an early age were compared with 18 normally sighted control observers who viewed the stimuli monocularly. Consistent with previous findings, the majority of the controls (13/18) underestimated TTC. Three enucleated observers had larger estimation errors than the 95% confidence interval of the mean of the control group. One enucleated observer was unable to give reliable results. These results suggest that unilaterally enucleated observers cannot estimate TTC more accurately (and may even be worse) than normal controls when estimates are based on monocular information alone. Further, the majority (83%) of enucleated observers were influenced by perceived distance information derived from the object's initial size when estimating TTC with an approaching object. The use of this other optical variable could account for their reduction in performance. It was suggested that in every day life enucleated individuals make use of as many optical variables as possible to partially compensate for the lack of binocularity.

Risky driving behavior: a consequence of motion adaptation for visually guided motor action

The authors examined the effect of adaptation to expansion on overtaking maneuvers in a driving simulator. Following driving on a straight empty road for 5 min, drivers initiated overtaking substantially later (220-510 ms) than comparable maneuvers made following viewing a static scene or following 5 min of curve driving. Following adaptation to contraction (produced by driving backward), observers initiated overtaking significantly sooner. The removal of the road texture significantly reduced the size of the adaptation effect. The authors propose that these changes in overtaking behavior are due to misestimation of the time headway produced by local adaptation of looming detectors that signal motion-in-depth for objects near the focus of expansion. This adaptation effect may increase the risk of rear-end collisions during highway driving.

Long-distance interactions in Cyclopean vision

We report on evidence for selective long-distance interactions in Cyclopean binocular vision. When presented with a pair of Cyclopean test bars observers could discriminate trial-to-trial uncorrelated variations in the mean orientation, orientation difference, separation and mean location of the test bars while ignoring random variations in the orientation, width and location of a third bar placed between the two test bars. We propose that the human visual system contains Cyclopean long-distance comparators (i) that compare the outputs of two narrow receptive fields some distance apart while being insensitive to stimuli located between those receptive fields, and (ii) the outputs of which carry orthogonally labelled indicators of orientation difference, mean orientation, separation and mean location. In the evolutionary context, one role for the proposed mechanisms might be to encode information about the silhouettes of animals whose camouflage is broken by the binocular vision of predators.

Risky driving behavior: a consequence of motion adaptation for visually guided motor action

The authors examined the effect of adaptation to expansion on overtaking maneuvers in a driving simulator. Following driving on a straight empty road for 5 min, drivers initiated overtaking substantially later (220-510 ms) than comparable maneuvers made following viewing a static scene or following 5 min of curve driving. Following adaptation to contraction (produced by driving backward), observers initiated overtaking significantly sooner. The removal of the road texture significantly reduced the size of the adaptation effect. The authors propose that these changes in overtaking behavior are due to misestimation of the time headway produced by local adaptation of looming detectors that signal motion-in-depth for objects near the focus of expansion. This adaptation effect may increase the risk of rear-end collisions during highway driving.

Coincidence detectors: visual processing of a pair of lines and implications for shape discrimination

The psychophysical data reported here bear on how the boundaries of an object's retinal image are processed in early vision. We propose that the visual system contains a mechanism sensitive to four relationships between two local stimuli some distance apart and that the output of this hypothetical mechanism encodes and labels orthogonally the four relationships. We measured the just-noticeable difference in the orientation difference between two test lines as well as the just-noticeable differences in their mean orientation, mean location, and separation. A pair of noise lines was located between the two test lines. By arranging that trial-to-trial variations in the orientation difference, mean orientation, mean location and separation of the test lines had zero correlation with each other and with trial-to-trial variations in the corresponding variables for the two noise lines we could demonstrate that psychophysical responses were based on the task-relevant variable and that, for each of the four task-relevant variables, all task-irrelevant variables were ignored. The finding that responses to the test lines were unaffected by the noise lines implies that discriminations were not influenced by first-stage spatial filters with strictly local receptive fields that responded to both test lines. Because these findings held for a presentation duration of 20 ms we can exclude the possibility that observers compared the two test lines by shifting either fixation or attention. We propose that, rather than by attending to two different locations, the test lines were selected by attending to the output of the long-distance comparator whose 'separation' label signaled the largest magnitude. The above proposals can account for several previously reported phenomena. More generally, an array of the proposed long-distance comparators constitutes a system that may be capable of specifying the shape, size, location and implicit orientation of an object's retinal image.

Radioimmunotherapy with iodine (131)I tositumomab for relapsed or refractory B-cell non-Hodgkin lymphoma: updated results and long-term follow-up of the University of Michigan experience

CD20-targeted radioimmunotherapy is a promising new treatment for B-cell non-Hodgkin lymphoma (NHL). We now provide updated and long-term data on 59 chemotherapy-relapsed/refractory patients treated with iodine (131)I tositumomab in a phase I/II single-center study. Fifty-three patients received individualized therapeutic doses, delivering a specified total-body radiation dose (TBD) based on the clearance rate of a preceding dosimetric dose. Six patients received dosimetric doses only. Dose-escalations of TBD were conducted separately in patients who had or had not undergone a prior autologous stem cell transplant (ASCT) until a nonmyeloablative maximally tolerated TBD was established (non-ASCT = 75 cGy, post-ASCT = 45 cGy). Fourteen additional non-ASCT patients were treated with 75 cGy. Unlabeled antibody was given prior to labeled dosimetric and therapeutic doses to improve biodistribution. Forty-two (71%) of 59 patients responded; 20 (34%) had complete responses (CR). Thirty-five (83%) of 42 with low-grade or transformed NHL responded versus 7 (41%) of 17 with de novo intermediate-grade NHL (P =.005). For all 42 responders, the median progression-free survival was 12 months, 20.3 for those with CR. Seven patients remain in CR 3 to 5.7 years. Sixteen patients were re-treated after progression; 9 responded and 5 had a CR. Reversible hematologic toxicity was dose limiting. Only 10 patients (17%) had human anti-mouse antibodies detected. Long-term, 5 patients developed elevated thyroid-stimulating hormone levels, 5 were diagnosed with myelodysplasia and 3 with solid tumors. A single, well-tolerated treatment with iodine (131)I tositumomab can, therefore, produce frequent and durable responses in NHL, especially low-grade or transformed NHL. (Blood. 2000;96:1259-1266)

Simulated self-motion alters perceived time to collision

Many authors have assumed that motor actions required for collision avoidance and for collision achievement (for example, in driving a car or hitting a ball) are guided by monitoring the time to collision (TTC), and that this is done on the basis of moment-to-moment values of the optical variable tau [1] [2] [3]. This assumption has also motivated the search for single neurons that fire when tau is a certain value [4] [5] [6] [7] [8]. Almost all of the laboratory studies and all the animal experiments were restricted to the case of stationary observer and moving object. On the face of it, this would seem reasonable. Even though humans and other animals routinely perform visually guided actions that require the TTC of an approaching object to be estimated while the observer is moving, tau provides an accurate estimate of TTC regardless of whether the approach is produced by self-motion, object-motion or a combination of both. One might therefore expect that judgements of TTC would be independent of self-motion. We report here, however, that simulated selfmotion using a peripheral flow field substantially altered estimates of TTC for an approaching object, even though the peripheral flow field did not affect the value of tau for the approaching object. This finding points to long range interactions between collision-sensitive visual neurons and neural mechanisms for processing self-motion.

Estimating the time to collision with a rotating nonspherical object

We measured the precision (i.e. Weber fraction) and the accuracy with which the time to collision (TTC) with a simulated approaching object is estimated. We simulated a rigid spherical object and a rigid nonspherical object (an oblate spheroid whose longer axis was vertical). We used the following viewing conditions: that the available information about TTC was only monocular (M), only binocular (B) and monocular plus binocular (M and B). In addition to the approaching SPHERE condition, we used the following three simulation conditions for the oblate spheroid: (2) a slow rotation through 90 degrees (SIDE-END); (3) a slow rotation through 90 degrees (END-SIDE); (4) several complete rapid rotations (RROT). Weber fractions for discriminating TTC were similar for all 12 combinations of viewing and simulation conditions. When only monocular information was available, perceived TTC was longer in the M/SIDE-END condition than in the M/SPHERE condition, and shorter in the M/END-SIDE condition than in the M/SPHERE condition. As well, observers were strongly influenced by task-irrelevent variables in the M/SIDE-END condition so that they could not properly perform the task. The addition of binocular information considerably improved the accuracy of estimating TTC in simulation conditions SPHERE, END-SIDE and RROT, and allowed reliably accurate estimations to be made in the SIDE-END simulation condition. We suggest that, when binocular information is combined with monocular information about TTC, the two kinds of information are weighted roughly equally when the approaching object is a rigid sphere, but the binocular information is weighted more heavily when the approaching object is nonspherical and rotating.

Do monocular time-to-collision estimates necessarily involve perceived distance?

Motivated by the debate between indirect and direct theories of perception, a large number of researchers have attempted to determine whether judgments of time to collision are based on the ratio of perceived distance to perceived speed or on the ratio theta/(d theta/dt), i.e. tau. Despite the considerable research effort devoted to this question there seems to be no clear resolution. We used a staircase tracking procedure to estimate errors in estimating time to collision for a simulated approaching object. To investigate the role of perceived distance in the judgment of time to collision, we asked observers to alternate between two viewing distances (100 and 500 cm). For the 500 cm viewing distance, we magnified the visual display by a factor of five so that the retinal images [and the values of theta/(d theta/dt) through time] were identical for the two viewing distances. All visual cues to distance were available. There were no significant differences between estimates of time to collision made at the two viewing distances. We conclude that our observers ignored perceived distance when estimating time to collision and based their responses on theta/(d theta/dt). We concur with recent proposals that, in the future, time-to-collision research should move away from the either/or analysis of different information sources that has dominated previous studies towards investigations of how different information sources are integrated.

Similarities and differences between the effects of heparin and glypican-1 on the bioactivity of acidic fibroblast growth factor and the keratinocyte growth factor

The keratinocyte growth factor (KGF or FGF-7) is unique among its family members both in its target cell specificity and its inhibition by the addition of heparin and the native heparan-sulfate proteoglycan (HSPG), glypican-1 in cells expressing endogenous HSPGs. FGF-1, which binds the FGF-7 receptor with a similar affinity as FGF-7, is stimulated by both molecules. In the present study, we investigated the modulation of FGF-7 activities by heparin and glypican-1 in HS-free background utilizing either HS-deficient cells expressing the FGF-7 receptor (designated BaF/KGFR cells) or soluble extracellular domain of the receptor. At physiological concentrations of FGF-7, heparin was required for high affinity receptor binding and for signaling in BaF/KGFR cells. In contrast, binding of FGF-7 to the soluble form of the receptor did not require heparin. However, high concentrations of heparin inhibited the binding of FGF-7 to both the cell surface and the soluble receptor, similar to the reported effect of heparin in cells expressing endogenous HSPGs. The difference in heparin dependence for high affinity interaction between the cell surface and soluble receptor may be due to other molecule(s) present on cell surfaces. Glypican-1 differed from heparin in that it stimulated FGF-1 but not FGF-7 activities in BaF/KGFR cells. Glypican-1 abrogated the stimulatory effect of heparin, and heparin reversed the inhibitory effect of glypican-1, indicating that this HSPG inhibits FGF-7 activities by acting, most likely, as a competitive inhibitor of stimulatory HSPG species for FGF-7. The regulatory effect of glypican-1 is mediated at the level of interaction with the growth factor as glypican-1 did not bind the KGFR. The effect of heparin and glypican-1 on FGF-1 and FGF-7 oligomerization was studied employing high and physiological concentrations of growth factors. We did not find a correlation between the effects of these glycosaminoglycans on FGFs biological activity and oligomerization. Altogether, our findings argue against the heparin-linked dimer presentation model as key in FGFR activation, and support the notion that HSPGs primarily affect high affinity interaction of FGFs with their receptors.

Randomized, double-blind, placebo-controlled trial to evaluate the hematopoietic growth factor PIXY321 after moderate-dose fluorouracil, doxorubicin, and cyclophosphamide in stage II and III breast cancer

PURPOSE

To measure the effect of PIXY321 (granulocyte-macrophage colony-stimulating factor/interleukin-3 S. cerevisiae fusion protein) on the incidence, duration, and complications of neutropenia and thrombocytopenia after moderate-dose fluorouracil 600 mg/m(2), doxorubicin 60 mg/m(2), and cyclophosphamide 750 mg/m(2) (FAC) chemotherapy in patients with stage II and III breast cancer.

PATIENTS AND METHODS

In this multicenter, randomized, double-blind placebo-controlled trial, 71 women were to receive four 21-day cycles of treatment with moderate-dose FAC chemotherapy by short intravenous infusion on day 1, followed by either placebo or PIXY321 (375 microg/m(2) subcutaneously twice a day) on days 3 to 15. All patients were to receive prophylactic oral ciprofloxacin when the absolute neutrophil count was less than 1,000/microL.

RESULTS

PIXY321 significantly reduced the incidence and duration of grade 3 and grade 4 neutropenia in cycles 1 and 2 and the duration of grade 3 neutropenia in cycles 1 through 4. In cycles 3 and 4, grade 3 thrombocytopenia was significantly more common with PIXY321 (P <.05). Two patients, both in the PIXY321 group, required platelet transfusions. Fever and hospitalization for intravenous antibiotics were significantly more common in the PIXY321 group during cycle 1 only. More patients in the PIXY321 group achieved hematologic recovery by day 22 in cycles 1 through 3, and time to recovery was significantly shorter with PIXY321 in all cycles. FAC dose intensity was roughly 2% higher in the PIXY321 group (P = NS). Nonhematologic events of any intensity occurring with significantly greater overall frequency in the PIXY321 group included injection-site reactions, fever, chills, abdominal pain, and arthralgia. No patient died on study or within 30 days of her last dose of study drug.

CONCLUSION

PIXY321 decreased the incidence and duration of FAC-induced grade 3 and 4 neutropenia in cycles 1 and 2 and significantly shortened the time to hematologic recovery in all cycles. However, it produced more systemic toxicity as well as thrombocytopenia in cycles 3 and 4.

Adapting to expansion increases perceived time-to-collision

We used a tracking method to measure errors in estimating absolute time-to-collision caused by adapting to an expanding target. After adaptation, the estimated time-to-collision was longer than in the baseline condition. This was the case whether estimates were based on binocular information alone or monocular information alone. Estimates of time-to-collision were lengthened by 8-16% when based on binocular information alone, and by 18-25% when based on monocular information alone. These findings are consistent with a previous proposal that changing-size and changing-disparity information converge before the stage at which motion-in-depth signals are generated.

Evidence for a mechanism sensitive to the speed of cyclopean form

We measured Weber fractions for discriminating the speed of cyclopean gratings and Weber fractions for discriminating the speed of luminance gratings. Of our 14 observers, five were unable to see the cyclopean grating sufficiently well to discriminate its speed. One observer experienced great difficulty in discriminating the speed of cyclopean gratings, even though her threshold for detecting cyclopean gratings was low, and even though she discriminated the speed of luminance gratings on the basis of the task-relevent variable. But several observers based their speed discriminations on trial-to-trial variations of the task-relevent variable while ignoring associated trial-to-trial variations in all task-irrelevant variables (specifically: displacement; temporal frequency; spatial frequency; and presentation duration). We conclude that the visual systems of these observers contain a specialized neural mechanism for the speed of cyclopean gratings that supports acute discriminations of speed (Weber fractions were as low as 0.05-0.07).

Motion in depth: adequate and inadequate simulation

We measured errors in estimating the absolute time to collision with a simulated approaching textured object. The texture elements were circular bright dots. When we matched the rate of angular expansion of the simulated object, the rate of expansion of the texture dots, and the rate of increase of dot separation, so as to accurately simulate an approaching object, errors were small underestimations that were independent of dot size (mean of 3.2%). When dot angular size was held constant during the simulated approach, errors were the same as when the simulation was accurate, provided that dot size was less than 2.2-4.4 min of arc. As dot size was progressively increased, errors changed to overestimations. For the largest dot size used (10.5 min of arc at time t = 0), time to collision was overestimated by up to 21%. A sufficiently large overestimation would mean that measures taken to avoid collision would be too late. We suggest that the relevance to everyday life of data on the perception of motion in depth and self-motion collected using constant-sized dot displays might be questionable if dot size exceeds 2.2-4.4 min of arc.

Orientation-tuned spatial filters for texture-defined form

Detection threshold for an orientation-texture-defined (OTD) test grating was elevated after adapting to an OTD grating of high orientation contrast. Threshold elevation was greatest for a test grating parallel to the adapting grating, and fell to zero for a test grating perpendicular to the adapting grating. We conclude that the human visual system contains an orientation-tuned neural mechanism sensitive to OTD form, and propose a model for this mechanism. We further propose that orientation discrimination for OTD bars and gratings is determined by the relative activity of these filters for OTD form.

Spatial frequency discrimination and detection characteristics for gratings defined by orientation texture

We describe evidence consistent with the proposal that the visual system contains a parallel array of size-tuned mechanisms sensitive to orientation texture-defined (OTD) form, and propose that the relative activity of these mechanisms determines spatial frequency discrimination threshold for OTD gratings. Using a pattern of short lines we measured spatial frequency discrimination thresholds for OTD gratings and luminance-defined (LD) gratings. For OTD gratings, the orientation of texture lines varied sinusoidally across the bars of the gratings, but line luminance was constant. For LD gratings, line orientation was constant, but line luminance varied sinusoidally across the bars of the grating. When the number of texture lines (i.e. spatial samples) per grating cycle was below about six, spatial sampling strongly affected both the spatial frequency discrimination and grating detection thresholds for OTD and LD gratings. However, when the number of spatial samples per grating cycle exceeded about six, plots of both discrimination threshold and detection threshold were different for OTD and LD gratings. For an OTD grating of any given spatial frequency, spatial frequency discrimination threshold fell as the number of samples per grating cycle was increased while holding texture line length constant: the lower limit was reached at six to ten samples per cycle. When we progressively increased the viewing distance (keeping the cycles per degree (cpd) constant), spatial frequency discrimination threshold reached a lower limit and increased thereafter. We propose that this minimum threshold represents a balance between opposing effects of the number of samples per grating cycle and the length of texture lines, and approaches the absolute physiological lower limit for OTD gratings. Spatial frequency discrimination was possible up to at least 7 cpd. Grating acuity for an OTD grating was considerably lower than the physiological limit for LD gratings, presumably because detectors of OTD form include a spatial integration stage following the processing of individual lines. For an LD grating, discrimination threshold fell as the number of samples per grating cycle was increased and asymptoted at six to ten samples per cycle. Spatial frequency discrimination thresholds for OTD and LD gratings were similar at low spatial frequencies (up to 3-4 cpd), but increased more steeply for OTD gratings at high spatial frequencies. For both OTD and LD gratings, discrimination threshold fell steeply as the number of grating cycles was increased from 0.5 to ca. 2.5 cycles, and thereafter decreased more slowly or not at all suggesting that, for both OTD and LD gratings, spatial frequency discrimination can be regarded as a special case of line interval or bar width discrimination. As orientation contrast was progressively increased, discrimination threshold for an OTD grating fell steeply up to about four to five times grating detection threshold, then saturated. This parallels the effect of luminance contrast on discrimination threshold for an LD grating.

Iodine-131 anti-B1 antibody for B-cell lymphoma: an update on the Michigan Phase I experience

Iodine-131 anti-B1 antibody radioimmunotherapy for B-cell lymphoma was previously reported to have substantial antitumor activity in B-cell non-Hodgkin's lymphoma (NHL) after failures of standard and salvage chemotherapy. In this article, the University of Michigan Phase I clinical experience is updated, with follow-up of up to 6 yr since initial treatment reported.

METHODS

Thirty-four patients with CD20-expressing NHL were first studied with one or more dosimetric doses of approximately 5 mCi of 1311 anti-B1 antibody (after varying predoses of unlabeled anti-B1 antibody). They were then treated with a patient-specific radioimmunotherapeutic dose designed to deliver a specified radiation dose to the whole body of between 25 and 85 cGy. Patients were observed for toxicity and tumor response.

RESULTS

Seventeen (50%) patients had low-grade NHL, 9 (26%) had low-grade transformed NHL and 8 (24%) had de novo intermediate-grade NHL. At study entry, 17 (50%) had an elevated lactate dehydrogenase level, 12 (35%) had high tumor burden and 18 (53%) had not responded to their last chemotherapy. The median number of prior NHL therapies was 4.1. Twenty-eight of 34 patients completed treatment, with 22 of 28 (79%) achieving a response and 14 of 28 (50%) achieving a complete response (CR). The median duration of response was 357 days. The median duration of response for CRs was 471 days, with 4 CRs having a duration of > 1000 days (maximum = > 1460 days). Bone marrow toxicity was dose-limiting and dependent on the total-body dose (TBD) of radiation. Thrombocytopenia appeared to be more marked in patients with prior bone marrow transplantation. The TBD of 75 cGy was established as the maximum tolerated dose in patients who had not had prior bone marrow transplantation. Duration of CR was significantly longer (p < 0.04) in patients who received a TBD of 65-75 cGy (1109 days) than it was in those who received a lower TBD of 25-60 cGy (385 days). Four of 34 (12%) patients developed detectable human antimouse antibody levels. The median survival from study entry for all patients was 1508 days (range = 63 to >2226 days). Sixteen of 17 patients who achieved a response of > or = 6 mo duration remain alive.

CONCLUSION

This update of the Phase I results after 1311 anti-B1 antibody treatment for NHL indicates that CRs can be durable and that survival can be of long duration. This form of therapy for NHL should have increasing application in clinical practice after confirmation of these results in larger multicenter studies.

Accuracy of estimating time to collision using binocular and monocular information

We measured both the just-noticeable difference in time to collision (TTC) with an approaching object, and the absolute accuracy in estimating TTC in the following cases: only binocular information available; only monocular information available; both binocular and monocular information available as in the everyday situation. Observers could discriminate trial-to-trial variations in TTC on the basis of binocular information alone: the just-noticeable difference in TTC (5.1-9.8%) was the same for a small (0.03 deg) target and for a large (0.7 deg) target. In line with previous reports, when only monocular information was available, the just-noticeable difference in TTC was 5.8-12% for the large target. However, observers could not reliably discriminate trial-to-trial variations in TTC with the small target when only monocular information was available. When both binocular and monocular information was available, the just-noticeable difference in TTC for the large target was not significantly different from when only binocular or only monocular information was available. Observers could make reliable estimates of absolute TTC using binocular information only. Errors ranged from 2.5 to 10% for the large target, and 2.6 to 3.0% for the small target, all being overestimates. Errors for the small target were the same or lower than errors for the large target. Observers could make reliable estimates of TTC with the large target using monocular information only. Errors ranged from 2.0 to 12%, all being underestimates. Since monocular information did not provide a basis for reliable estimates of absolute TTC with the small target we conclude that, in everyday conditions, accurate estimates of TTC with small targets are based on binocular information when the object is small and is no more than a few metres away. Errors in estimating absolute TTC were lower in the case where both binocular and monocular information were available (as in the everyday situation) than when only binocular information or only monocular information was available. Errors ranged from 1.3 to 2.7%. An error of 1.3% approaches the accuracy required to explain the +/- 2.0-2.5 msec accuracy with which top sports players can estimate the instant of impact between bat and ball.

Reversible dissociation of sensitivity to dynamic stimuli in Parkinson's disease: is magnocellular function essential to reading motion-defined letters?

A group of 20 control subjects carried out the following visual tests: Snellen acuity; contrast detection threshold for a temporally unmodulated grating and for a temporally modulated grating; speed threshold for recognising motion-defined dotted letters. Normal limits were defined as 2.5 standard deviations from the respective control means. A patient with Parkinson's disease carried out the tests 12 hr after medication was withheld at a time when symptoms were evident ("off" stage), and after administration of medication when it had taken full effect ("on" stage). Confirming previous reports, contrast detection threshold for the temporally modulated grating was much higher during the "off" stage than during the "on" stage, but contrast detection threshold for the temporally unmodulated grating showed little difference. Speed threshold for recognising motion-defined letters did not, however, fall during the "on" stage. We suggest that magnocellular function is not essential for the recognition of motion-defined form.

Visual factors in hitting and catching

To hit or catch an approaching ball, it is necessary to move a bat or hand to the right place at the right time. The performance of top sports players is remarkable: positional errors of less than 5 cm and temporal errors of less than 2 or 3 ms are reliably maintained. There are three schools of thought about how this is achieved. One holds that predictive visual information about where the ball will be at some future instance (when) is used to achieve the hit or catch. The second holds that the bat or hand is moved to the correct position by exploiting some relation between visual information and the required movement. The third focuses on the use of prior knowledge to supplement inadequate visual information. For a rigid spherical ball travelling at constant speed along or close to the line of sight, the retinal images contain both binocular and monocular correlates of the ball's instantaneous direction of motion in depth. Also, the retinal images contain both binocular and monocular information about time of arrival. Humans can unconfound and use this visual information, but they are unable to estimate the absolute distance of the ball or its approach speed other than crudely. In cricket, this visual inadequacy allows a slow bowler to cause the batsman to misjudge where the ball will hit the ground. Such a bowler uses a three-pronged strategy: first, to deliver the ball in such a way as to prevent the batsman from obtaining the necessary visual information until it is too late to react; secondly, to force the batsman to rely entirely on inadequate retinal image information; thirdly, to allow the batsman to learn a particular relationship between the early part of the ball's flight and the point where the ball hits the ground, and then to change the relationship with such skill that the batsman does not detect the change.