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Biomedical subjects

D Regan

Publications and source records attributed to D Regan.

At least 19 recordsLinked to original sources
PubMed1998

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.

Depth Perception↗
PubMed1998

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

UNLABELLED: 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.

Antibodies, Monoclonal↗
PubMed1997

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.

Contrast Sensitivity↗
PubMed1997

Vernier step acuity and bisection acuity for texture-defined form.

Using as the stimulus a texture pattern of short lines, we compared positional acuity thresholds for an orientation-texture-defined (OTD) boundary and a luminance-defined (LD) boundary. Texture lines had different orientations but the same luminance on either side of the OTD boundary, and different luminances but the same orientation on either side of the LD boundary. For the LD boundary, both vernier step acuity threshold and bisection acuity threshold were inversely proportional to the number of texture lines per degree (i.e., the pattern's spatial sampling frequency) over the entire 1.9-59 samples/deg frequency range investigated, though thresholds were considerably lower than the distance between adjacent lines. For the OTD boundary, both thresholds were inversely proportional to spatial sampling frequency (though thresholds were again considerably less than the distance between adjacent lines) but only for sampling frequencies below 20 samples/deg. For sampling frequencies below 20 samples/deg, the ratio between positional acuity thresholds for OTD and LD boundaries was approximately constant (3.5:1 for vernier acuity and 1.4:1 for bisection acuity). As sampling frequency was increased beyond 20 samples/deg both vernier and bisection acuity thresholds for OTD boundaries rose steeply. Both thresholds fell to a minimum near 20 samples/deg. For vernier step acuity the minimum threshold was 2.3 and 2.4 min arc (two observers), and for bisection acuity 1.7 and 1.9 min arc. We propose that these minimum thresholds approach a physiological limit of positional acuity for an OTD boundary, and that the limit is determined by a balance between the progressive improvement of positional acuity caused by increasing the frequency of spatial sampling vs the progressive reduction in visibility of the OTD boundary caused by the associated reduction in the length of texture lines. These physiological limits are far higher than the corresponding limits for sharp-edged high-contrast LD targets (2-5 and 1-5 sec arc, respectively). For an OTD boundary the effect of orientation contrast on vernier step acuity threshold approximated a square root law, while the effect of orientation contrast on bisection acuity approximated a linear law. Observers can combine positional information carried by texture contrast with positional information carried by luminance contrast. As to the combination rule, our findings are consistent with probability summation between independent channels.

Adult↗
PubMed1997

Discrimination of the direction and speed of motion in depth of a monocularly visible target from binocular information alone.

Thresholds for discriminating a monocularly visible object's direction of motion in depth and speed of motion in depth were measured using only binocular cues. Observers could discriminate the direction of motion in depth while totally ignoring speed and discriminate the speed of motion in depth while totally ignoring direction. Direction discrimination thresholds were the same for motion in depth within the vertical and horizontal meridians, even though a cue to trajectory was available for motion within the horizontal meridian that is not available for motion within the vertical meridian. Speed discrimination thresholds also were the same for motion in depth within the vertical and horizontal meridians. For the 3 observers the lowest direction discrimination thresholds were 0.14 degree, 0.18 degree, and 0.22 degree (means of horizontal and vertical thresholds).

Depth Perception↗
PubMed1997

Just-noticeable difference in the speed of cyclopean motion in depth and the speed of cyclopean motion within a frontoparallel plane.

Weber fractions for discriminating the speed and displacement of a cyclopean target moving in depth ranged, respectively, from .07-.17 and .06-.13 over 6 observers. Corresponding data for a noncyclopean target were .07-.20 and .06-.12. For motion parallel to the frontal plane, corresponding data were .09-.20 .06-.16, and .05-.13. All Weber fractions were independent of the direction of motion and of near versus far disparity. All observers based their judgments entirely on the task-relevant variable and ignored task-irrelevant variables in all cases. We conclude that speed and displacement are encoded independently and in parallel for motion in depth and for motion within a frontoparallel plane.

Adult↗
PubMed1997

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.

Algorithms↗
PubMed1997

Alternatives to ceramic brackets: the tensile bond strengths of two aesthetic brackets compared ex vivo with stainless steel foil-mesh bracket bases.

The mean tensile/peel bond strengths were evaluated for three types of aesthetic brackets (a ceramic-reinforced bracket and two generations of a ceramic/polycarbonate combination bracket). These were found to be significantly lower than the mean tensile/peel bond strength of a convention foil-mesh stainless steel bracket base. Failure of the ceramic-reinforced polycarbonate brackets occurred predominantly by fracture of the tie wings during testing. With the ceramic/polycarbonate combination brackets, the majority of the specimens failed due to separation of the ceramic and polycarbonate parts of the bracket.

Analysis of Variance↗
PubMed1997

Babe Ruth: with vision like that, how could he hit the ball?

Unfortunately, it is unlikely that a definitive answer will be known. We believe that it is most likely that Ruth was not amblyopic. This seems possible only if Dr. Kara had missed some amblyogenic factor such as strabismus or a significant refractive error. Our favored solution is that Ruth's unilateral vision loss was a complication of his cancer, and that Dr. Kara's examination occurred before the optic nerve damage became detectable. Of course, this is in disagreement with the ophthalmologist who examined his eyes.

Amblyopia↗
PubMed1997

Development of motion-defined figure-ground segregation in preschool and older children, using a letter-identification task.

BACKGROUND: Three-month-old infants can discriminate motion-defined (MD) form, but we do not know the age at which this ability reaches adult levels. Previous psychophysical evidence suggests that different neural mechanisms are involved in the processing of luminance-defined (LD) and MD spatial form in adults. This difference may be reflected in the development of LD versus MD form identification in children. METHODS: We measured speed threshold for identifying MD letters, letter-chart (i.e, Snellen) acuity for high-contrast LD letters and single-letter acuity for high- and low-contrast LD letters. Forty-seven children between 3 and 12 years of age and 20 adult subjects were tested. RESULTS: Development to the adult level was observed as follows: low-contrast single-letter acuity before 3 years; high-contrast single-letter acuity by 5 to 6 years; the ability to identify MD letters by 7 to 8 years; letter-chart acuity by 9 to 10 years. CONCLUSIONS: MD form identification continues to mature in preschool children. LD form identification also matures in this age group but with a different time course. MD letters are not equivalent to low-contrast letters developmentally. Our findings provide further support for the hypothesis that the spatial aspects of MD and LD form are processed separately to some extent.

Adult↗
PubMed1997

Judging the time to collision with a simulated textured object: effect of mismatching rate of expansion of object size and of texture element size.

We measured the accuracy with which subjects estimated the time to collision with a simulated textured object approaching at constant speed along the line of sight. The independent variable was the ratio R, where R = (rate of dilation of the texture elements that covered the simulated object)/ (rate of dilation of object size). When matching was perfect (i.e., R = 1.0), the mean of 12 settings was close to the nominal value of 2,000 msec for the 2 subjects. In addition, the standard error of 12 settings was only 25 and 52 msec in 2,000 msec for the 2 subjects. Discrimination threshold for time to collision was not significantly affected by R over the range investigated between R = 0 and R = 2.0. However, the accuracy of estimating time to collision was significantly affected by R. Estimated time to collision was a monotonic function of R. For example, when the mismatch was only 10% (i.e., R = 0.9) subjects judged time to collision would occur 178 msec later than the true time to collision of 2,000 msec.

Adult↗
PubMed1996

Evidence for a neural mechanism that encodes angles.

We measured the discrimination threshold (delta theta)Th for angle theta, where theta was either the angle of a Vee composed of two straight lines contained within the frontoparallel or the angle intersection of two straight lines contained within the frontoparallel plane. The two-line pattern was rotated bodily through a random angle between trials with the aim of eliminating the absolute orientation of one or the other line as a reliable cue to the task. We report evidence that this aim was achieved. Our main conclusion is that the ability to discriminate a change in angle theta cannot entirely be explained in terms of the ability to discriminate changes in the orientations of the individual lines that comprise the Vee. We propose that the human visual pathway contains a neural mechanism that encodes the difference in the orientations of two simultaneously-presented straight lines. Discrimination threshold for angle (delta theta)Th is roughly twice orientation discrimination threshold for an isolated line. When subjects cannot use the orientation of one or another line as a cue to the task, the plot of (delta theta)Th vs theta is approximately flat between the delta = 20 and 160 deg.

Cues↗
PubMed1996

Magnetic and electrical brain responses to chromatic contrast in human.

Differences between magnetic responses to red-green chromatic gratings and yellow-black luminance gratings were: (1) response waveforms differed considerably; (2) at some recording sites the chromatic grating response was considerably greater than the sum of responses to the red and green components of the chromatic grating; (3) the latencies of the successive peaks in the response to the onset of chromatic contrast were greater than the latencies of the corresponding peaks in the response to luminance contrast onset; (4) chromatic grating responses were lowpass with respect to spatial frequency while luminance grating responses were bandpass; (5) chromatic grating responses attenuated more steeply with increasing frequency above 2 c/deg than did luminance grating responses. Items (3)-(5) above are consistent with well-known psychophysical findings that contrast sensitivity is lowpass for chromatic gratings and chromatic responses are more sluggish than luminance responses. In subsidiary experiments we found that magnetic responses to red-green and blue-yellow equiluminant gratings had similar waveforms in all six subjects tested, but the topographical distributions were different in three subjects. The results of comparing magnetic and electrical responses to the onset and offset of contrast can be understood in terms of the considerable intersubject variability in the relation between neuroanatomy and cortical function that has been demonstrated by other techniques.

Adult↗
PubMed1996

Cyclopean motion perception produced by oscillations of size, disparity and location.

UNLABELLED: For cyclopean and monocularly-visible targets we measured psychophysical thresholds for perceptions produced by the following three stimuli: oscillations of disparity (DO), oscillations of size (SO) and oscillatory motion within the frontoparallel plane (FPO). RESULTS: thresholds for motion in depth perception produced by DO were similar for cyclopean and non-cyclopean targets over the entire 0.25-8 Hz frequency range investigated. Thresholds for perceiving motion in depth produced by SO were considerably (up to 2.5 times) higher for cyclopean targets than for monocularly-visible targets, as were thresholds for perceiving size oscillations. For both cyclopean and monocularly-visible target the perception of motion in depth could be canceled by pitting DO vs SO. Thresholds for perceiving FPO were similar to DO thresholds for the monocularly-visible target, but for the cyclopean targets FPO thresholds rose more steeply than DO thresholds for oscillation frequencies above 1 Hz. CONCLUSIONS: (1) for our subjects, the effective binocular stimulus for motion in depth perception is a rate of change of disparity; an interocular velocity difference is significant only to the extent that it produces a rate of change of disparity. (2) The sensations of motion in depth produced by DO and SO are qualitatively identical. (3) Neural signals produced by DO and SO converge onto a single neural mechanism that signals motion in depth.

Adaptation, Ocular↗
PubMed1996

Cyclopean discrimination thresholds for the direction and speed of motion in depth.

We measured just-noticeable differences in the direction and speed of motion in depth of cyclopean and monocularly visible targets. Our stimulus set comprised different combinations of (d phi/dt)/(d delta/ dt), d delta/dt, d phi/dt and delta delta, where d phi/dt was the angular frontal plane speed of the binocularly-fused target, d delta/dt was its rate of change of disparity and delta delta was its disparity displacement. Our three subjects based their direction discriminations entirely on the task-relevant variable (d phi/dt)/(d delta/dt), and based their speed discriminations entirely on the task-relevant variable d delta/dt. They ignored all task-irrelevant variables in both tasks. Performance on both tasks was the same for motion within the horizontal and vertical meridians. Direction discrimination threshold rose significantly as the reference direction grew more oblique with respect to a line passing midway between the eyes and perpendicular to the frontal plane. Performance on the direction discrimination task was significantly better for the noncyclopean than for the cyclopean target, but the difference was not great. For the cyclopean target, the lowest value of the direction discrimination threshold was 0.70 deg (mean of three observers and two meridians). The Weber fraction for discriminating speed was not significantly different for the cyclopean and monocularly visible targets, and did not depend on the direction of motion in depth. The lowest values (mean of three observers and two meridians) were 0.12 (cyclopean) and 0.10 (noncyclopean). Findings did not scale for viewing distance. We propose that the human visual pathway contains: (a) a cyclopean mechanism sensitive to variations in the ratio (d phi/dt)/(d delta/dt) that is comparatively insensitive to both d phi/dt and d delta/dt; and (b) a speed-sensitive cyclopean mechanism that responds to variations in the value of d delta/dt, but is comparatively insensitive to d phi/dt. We also propose that a single speed-sensitive mechanism determines speed discrimination thresholds for both cyclopean and monocularly visible targets.

Adult↗
PubMed1996

Two-dimensional aspect ratio discrimination for shape defined by orientation texture.

A pattern of 12,860 short (0.15 x 0.05 deg) texture lines contained an orientation texture-defined (OTD) rectangle of aspect ratio a/b (a was the rectangle's height and b was its width). All the lines within the rectangle had the same orientation and all the lines outside the rectangle had the same orientation. These two orientations were theta deg symmetrically clockwise and anticlockwise of the vertical. The rectangle's visibility was created entirely by the orientation difference 2 theta. Aspect ratio discrimination threshold for the texture-defined rectangle was a U-shaped function of theta that was approximately symmetrical about theta = 45 deg. The lowest values of aspect ratio discrimination threshold were 2.8% (SE = 0.1%), 2.7% (SE = 0.1%) and 5.1% (SE = 0.3%) for three observers. A luminance-defined (LD) rectangle with the same spatial sampling as the OTD rectangle was created by removing all texture lines outside the rectangle. Aspect ratio discrimination threshold for the LD rectangle was 1.1% (SE = 0.1%), 1.7% (SE = 0.1%) and 2.2% (SE = 0.1%)) for the same three observers. Although these discrimination thresholds were not greatly lower than discrimination thresholds for the OTD rectangle, they were significantly lower at the P < 0.001 level. Discrimination thresholds for the OTD rectangle are comparable with the lowest aspect ratio discrimination thresholds for motion-defined (MD) rectangles (2 and 3% for two observers), and for disparity-defined (DD) rectangles (3.1, 3.4, 4.0 and 7.4% for four observers), even though the MD and DD rectangles were much smaller than the 185 deg2 OTD rectangle used in the present study.

Adult↗
PubMed1996

Accuracy of reproducing angles: is a right angle special?

The ability to set the angle of a 'V' to a designated value in the following three conditions was compared: (1) verbal designation of V angle; (2) initial 30 s visual demonstration of the designated V angle; (3) verbal designation of V angle plus feedback after every setting. The designated angles were 90 degrees and 45 degrees plus three arbitrary angles (65 degrees, 125 degrees, and 145 degrees). Each run comprised thirty consecutive settings. To ensure that our observers based their settings entirely on V angle it was arranged that line orientation did not provide a reliable cue to V angle. In condition (1), accuracy of setting V angle was significantly worse when the designated angle was other than 90 degrees or 45 degrees. This was not the case in condition (2), indicating that observers maintained a memory of the initial demonstration throughout a run of thirty settings. Setting error was not significant in condition (3) for any of the five angles. However, even in condition (3), setting-to-setting variability was significantly lower for the 90 degrees angle than for the other angles.

Adult↗