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R S Allison

Publications and source records attributed to R S Allison.

At least 19 recordsLinked to original sources
PubMed2001

Effects of horizontal and vertical additive disparity noise on stereoscopic corrugation detection.

Stereoscopic corrugation detection in the presence of horizontal- and vertical- additive disparity noise was examined using a signal detection paradigm. Random-dot stereograms either represented a 3-D square-wave surface with various amounts of Gaussian-distributed additive disparity noise or had the same disparity values randomly redistributed. Stereoscopic detection of 2 arcmin peak amplitude corrugations was found to tolerate significantly greater amplitudes of vertical-disparity noise than horizontal-disparity noise--irrespective of whether the corrugations were horizontally or vertically oriented. However, this directional difference in tolerance to disparity noise was found to reverse when the corrugation and noise amplitudes were increased (so as to produce equivalent signal-to-noise ratios). These results suggest that horizontal- and vertical-disparity noise pose different problems for dot-matching and post-matching surface reconstruction as corrugation and noise amplitudes increase.

Adult↗
PubMed2000

Effects of stimulus size and eccentricity on horizontal and vertical vergence.

We measured the gain and phase of horizontal and vertical vergences of five subjects as a function of stimulus area and position. Vergence eye movements were recorded by the scleral search coil method as subjects observed dichoptic displays oscillating in antiphase either from side to side or up and down with a peak-to-peak magnitude of 0.5 degree at either 0.1 Hz or 1.0 Hz. The stimulus was a central textured disc with diameter ranging from 0.75 degree to 65 degrees, or a peripheral annulus with outer diameter 65 degrees and inner diameter ranging from 5 degrees to 45 degrees. The remaining field was black. For horizontal vergence at both stimulus frequencies, gain and the phase lag were about the same for a 0.75 degree stimulus as for a 65 degrees central stimulus. For vertical vergence, mean gain increased and mean phase lag decreased with increasing diameter of the central stimulus up to approximately 20 degrees. Thus, the stimulus integration area is much smaller for horizontal vergence than for vertical vergence. The integration area for vertical vergence is similar to that for cyclovergence, as revealed in a previous study. For both types of vergence, response gains were higher and phase lags smaller at 0.1 Hz than at 1.0 Hz. Also, gain decreased and phase lag increased with increasing occlusion of the central region of the stimulus. Vergence gain was significantly higher for a 45 degrees central disc than for a peripheral annulus with the same area. Thus, the central retina has more power to evoke horizontal or vertical vergence than the same area in the periphery. We compare the results with similar data for cyclovergence and discuss their ecological implications.

Adult↗
PubMed2000

Temporal dependencies in resolving monocular and binocular cue conflict in slant perception.

Observers viewed large dichoptic patterns undergoing smooth temporal modulations or step changes in simulated slant or inclination under various conditions of disparity-perspective cue conflict and concordance. After presentation of each test surface, subjects adjusted a comparison surface to match the perceived slant or inclination of the test surface. Addition of conflicting perspective to disparity affected slant and inclination perception more for brief than for long presentations. Perspective had more influence for smooth temporal changes than for step changes in slant or inclination and for surfaces presented in isolation rather than with a zero disparity frame. These results indicate that conflicting perspective information plays a dominant role in determining the temporal properties of perceived slant and inclination.

Cues↗
PubMed2000

Depth selectivity of vertical fusional mechanisms.

We measured the ability to fuse dichoptic images of a horizontal line alone or in the presence of a textured background with different vertical disparity. Nonius-line measurements of vertical vergence were also obtained. Diplopia thresholds and vertical vergence gains were much higher in response to an isolated vertically disparate line than to one with a zero vertical-disparity background. The effect of the background was maximum when it was coplanar with the target and decreased with increasing relative horizontal disparity. We conclude that vertical disparities are integrated over a restricted range of horizontal disparities to drive vertical vergence.

Adult↗
PubMed2000

Stereopsis with persisting and dynamic textures.

We measured the percept of changing depth from changing disparity in stereograms composed of random-dot textures that were either persistent or dynamically changed on every frame (a dynamic random-dot stereogram). Disparity was changed between frames to depict a surface undergoing smooth temporal changes in simulated slant. Matched depth was greater with dynamic random-dot stereograms than with persistent random-dot stereograms. These results confirm and extend earlier observations at depth threshold. We posit an explanation based on cue conflict between stereopsis and monocular depth cues.

Contrast Sensitivity↗
PubMed1999

Effect of field size, head motion, and rotational velocity on roll vection and illusory self-tilt in a tumbling room.

The effect of field size, velocity, and visual fixation upon the perception of self-body rotation and tilt was examined in a rotating furnished room. Subjects sat in a stationary chair in the furnished room which could be rotated about the body roll axis. For full-field conditions, complete 360 degrees body rotation (tumbling) was the most common sensation (felt by 80% of subjects). Constant tilt or partial tumbling (less than 360 degrees rotation) occurred more frequently with a small field of view (20 deg). The number of subjects who experienced complete tumbling increased with increases in field of view and room velocity (for velocities between 15 and 30 degrees s-1). The speed of perceived self-rotation relative to room rotation also increased with increasing field of view.

Adolescent↗
PubMed1998

Temporal aspects of slant and inclination perception.

Linear transformations (shear or scale transformations) of either horizontal or vertical disparity give rise to the percept of slant or inclination. It has been proposed that the percept of slant induced by vertical size disparity, known as Ogle's induced-size effect, and the analogous induced-shear effect, compensate for scale and shear distortions arising from aniseikonia, eccentric viewing, and cyclodisparity. We hypothesised that these linear transformations of vertical disparity are processed more slowly than equivalent transformations of horizontal disparity (horizontal shear and size disparity). We studied the temporal properties of the stereoscopic slant and inclination percepts that arose when subjects viewed stereograms with various combinations of horizontal and vertical size or shear disparities. We found no evidence to support our hypothesis. There were no clear differences in the build-up of percepts of slant or inclination induced by step changes in horizontal size or shear disparity and those induced by step changes in vertical size or shear disparity. Perceived slant and inclination decreased in a similar manner with increasing temporal frequency for modulations of transformations of both horizontal and vertical disparity. Considerable individual differences were found and several subjects experienced slant reversal, particularly with oscillating stimuli. An interesting finding was that perceived slant induced by modulations of dilation disparity was in the direction of the vertical component. This suggests the vertical size disparity mechanism has a higher temporal bandwidth than the horizontal size disparity mechanism. However, conflicting perspective information may play a dominant role in determining the temporal properties of perceived slant and inclination.

Form Perception↗
PubMed1998

Translational control elements in the major human transforming growth factor-beta 1 mRNA.

Polysome analysis indicates that the major 2.4 kb transforming growth factor-beta 1 (TGF-beta 1) transcript is poorly translated, both in cultured cells, and in vivo in mouse liver. In contrast, the TGF-beta 2 transcripts are efficiently translated. The contribution of the 5'- and 3'-untranslated regions (UTRs) to the translational inhibition of the full-length TGF-beta 1 transcript was studied by deletion analysis. Despite their high G + C content, both UTRs stimulated translation in vitro. However, polysome analysis of synthetic TGF-beta 1 mRNAs transfected into MCF-7 cells suggests that the cell contains a limited pool of trans-acting factors that interact with the 5'UTR to make it inhibitory in vivo. Further deletion analysis in vitro revealed multiple stimulatory and inhibitory regions in the 5'UTR. This has important implications for the translatability of the naturally occurring shorter TGF-beta 1 transcripts and provides a framework for higher resolution mapping studies. Overall, the poor translational efficiency of the major TGF-beta 1 mRNA in vivo appears to be due to a combination of poor initiation sequence context, and inhibitory interactions of limiting transacting factors with cis-inhibitory elements embedded in an otherwise stimulatory 5'UTR.

3' Untranslated Regions↗
PubMed1997

Recharacterization of the start sites for the major human transforming growth factor-beta 1 mRNA.

The start sites for the major human TGF-beta 1 transcripts have been reexamined. A comparison of ribonuclease and S1 nuclease protection analyses on native TGF-beta 1 mRNA and in vitro transcribed human TGF-beta 1 transcripts of defined sizes places the most 5' start site for the native TGF-beta 1 message approx. 50 nucleotides upstream from the previously published start site at base +1. Furthermore, the same techniques indicate that the apparent downstream start site at base +271 is an artefact due to the presence of an A + T-rich island in the middle of an otherwise highly G + C-rich sequence. This is not apparent if S1 nuclease protection is used alone, which emphasizes the importance of using the two techniques in combination for this type of analysis. Thus the major 2.5 kb TGF-beta 1 band seen on Northern blots comprises only mRNA transcribed from the more upstream of the two previously characterized promoters. This has important implications both for the transcriptional and translational regulation of this growth factor.

Base Composition↗
PubMed1997

The dynamics of vertical vergence.

We measured the gain and phase of vertical vergence in response to disjunctive vertical oscillations of dichoptic textured displays. The texture elements were m-scaled to equate visibility over the area of the display and were aperiodic and varied in shape so as to avoid spurious binocular matches. The display subtended 65 degrees and oscillated through peak-to-peak amplitudes from 18 arc min to 4 degrees at frequencies from 0.05 to 2 Hz - larger ranges than used in previous investigations. The gain of vergence was near 1 when the stimulus oscillated at 18 arc min at a frequency of 0.1 Hz or less. As the amplitude of stimulus oscillation increased from 18 arc min to 4 degrees, vergence gain decreased at all frequencies, which is evidence of a nonlinearity. Gain declined with increasing stimulus frequency but was still about 0.5 at 2 Hz for an amplitude of 18 arc min. Phase lag increased from less than 10 degrees at a stimulus frequency of 0.05 Hz to between 100 degrees and 145 degrees at 2 Hz. Overall, the dynamics of vertical vergence resemble the dynamics of horizontal vergence and cyclovergence.

Adult↗
PubMed1997

The temporalis muscle flap in intraoral reconstruction.

BACKGROUND: Reconstruction following excision of intraoral tumours presents a challenge to the head and neck surgeon. The purpose of hte present study was to review the authors' initial experience with the temporalis muscle flap. METHODS: A retrospective review fo the use of 21 temporalis muscle flaps in intraoral reconstruction at Christchurch Hospital was performed. The muscle was used to reconstruct defects of the oral tongue, tongue base, buccal mucosa, maxilla, soft palate, retromolar trigone and tonsillar region. Epithelial cover was provided by either split-skin grafting or ingrowth from adjacent mucosa. RESULTS: One flap necrosed and one patient developed a wound haematoma requiring drainage. One patient developed a transient frontal weakness. The long-term functional results were excellent, except for one patient with slight tongue tethering. In one patient bilateral flaps were used to reconstruct a bilateral maxillectomy defect. CONCLUSION: The temporalis muscle flap is a useful option for reconstruction of moderate defects in the posterior oral cavity and oropharynx.

Female↗
PubMed1996

Combined head and eye tracking system for dynamic testing of the vestibular system.

We present a combined head-eye tracking system suitable for use with free head movement during natural activities. This system provides an integrated head and eye position measurement while allowing for a large range of head movement (approx 1.8 m of head translation is tolerated). Six degrees of freedom of head motion and two degrees of freedom of eye motion are measured by the system. The system was designed to be useful for the evaluation of the vestibulo-ocular reflex (VOR). The VOR generates compensatory eye movements in order to stabilize gaze during linear or rotational motion of the head. Current clinical and basic research evaluation of the VOR has used a restricted range of head motion, mainly low-frequency, yaw rotation. An integrated eye-head tracking system such as the one presented here allows the VOR response to linear and angular head motion to be studied in a more physiologically relevant manner. Two examples of the utility of the integrated head and eye tracking system in evaluating the vestibular response to linear and angular motion are presented.

Electrooculography↗
PubMed1995

Peritonsillar infection in Christchurch 1990-2: microbiology and management.

AIM: To review the management and microbiology of peritonsillar infection in Christchurch. METHOD: The hospital records of patients admitted acutely to Christchurch Hospital with peritonsillar infection between January 1990 and December 1992, were reviewed. RESULTS: 109 patients were admitted with peritonsillar infection, of which 74 (68%) were found to have a peritonsillar abscess. Of these 74, needle aspiration was performed in 22, incision and drainage in 15, both aspiration and drainage in 31, and acute tonsillectomy in 6. Interval tonsillectomy was performed in 35 patients. Sixteen pathogenic bacterial groups or species were cultured from 39 aspirates. Of the total number of bacteria isolates, obligate anaerobes were cultured in 48%, and group A beta-haemolytic streptococci in 29%, while aerobic beta-lactamase producing bacteria were cultured in only 6%. CONCLUSION: Central to the management of peritonsillar abscess is drainage. This was commonly achieved by needle aspiration and/or incision. As beta-lactamase producing organisms are infrequent, penicillin remains the antibiotic of choice. Metronidazole may be required in a non responding patient, particularly if resistant anaerobes are cultured.

Adult↗
PubMed1995

Transforming growth factor-beta1 circulates in normal human plasma and is unchanged in advanced metastatic breast cancer.

A method has been developed to determine true plasma transforming growth factor beta (TGF-beta) levels by using the platelet alpha granule-specific marker, platelet factor 4, to correct for the TGF-beta contributed by platelets degranulated ex vivo. TGF-beta levels were measured on acid-ethanol extracts of human plasma using isoform-specific sandwich enzyme-linked immunosorbent assays. Normal human subjects had 4.1 +/- 2.0 ng/ml TGF-beta1 (range, 2.0-12.0; n = 42), <0.2 ng/ml TGF-beta2, and <0.1 ng/ml TGF-beta3 in their plasma. There were no significant changes with age or with hormonal status, but any given individual showed fluctuations of up to 3-fold in measured plasma TGF-beta levels due to unknown factors. Of 28 patients with advanced metastatic breast cancer, 2 had greatly elevated TGF-beta1 levels, while the rest were in the normal range. The presence of physiologically significant levels of TGF-beta1 in the plasmas of normal human subjects may indicate previously unsuspected endocrine roles for this peptide, while TGF-beta2 and TGF-beta3 appear to act only in a local autocrine/paracrine fashion.

Adult↗
PubMed1993

Microtympanometry, microscopy and tympanometry in evaluating middle ear effusion prior to myringotomy.

OBJECTIVE: To determine the accuracy of a hand-held microtympanometer (Microtymp, Welch Allyn) used by a general practitioner when compared with findings at myringotomy. METHOD: Independent preoperative assessment of children's ears using microtympanometry by a general practitioner, microscopy and pneumatic otoscopy by a specialist otologist and impedance bridge tympanometry by a specialist audiologist were performed and compared with findings at myringotomy. SUBJECTS: Fifty children (100 ears) on the waiting list for bilateral myringotomies and ventilation tube insertion for recurrent acute otitis media or otitis media with effusion. RESULTS: Microscopy with pneumatic otoscopy had a 90.9% sensitivity and a 92.9% specificity in detecting middle ear effusions. Impedance bridge tympanometry had a 94.4% sensitivity and a 71.8% specificity if type B and C2 were combined to predict middle ear effusion. Microtympanometry had 100% sensitivity and 75% specificity if type B and C tympanograms were combined; if type B tympanograms alone were used, a sensitivity of 83.4% and specificity of 75% in predicting middle ear effusions was obtained. CONCLUSION: The Microtypm is a useful instrument in general practice for assessment of middle ear effusions as no ears with fluid were missed in this study if type B and C tympanograms were considered abnormal. The Microtymp would also be useful as a screening instrument by suitably trained personnel.

Acoustic Impedance Tests↗