Biomedical subjects

J M Wild

Publications and source records attributed to J M Wild.

At least 127 records · Page 7Linked to original sources

PubMed1987

A respiratory-vocal pathway in the brainstem of the pigeon.

To provide an anatomical basis for the interaction of respiration and vocalization, neuroanatomical tracing experiments were undertaken to define the link between the nucleus receiving input from the lung and the tracheosyringeal motor nucleus (nXIIts). The ventral parabrachial nucleus (PBv) receives a projection from the lateral parasolitary nucleus and from the midbrain and projects to nXIIts. The PBv is therefore well placed to gate the activity of nXIIts neurons during respiration.

Animals↗

PubMed1987

Some concepts on the use of three-dimensional isometric plots for the representation of differential sensitivity.

An increasing use is being made of three-dimensional isometric plotting to represent the topography of the visual field. The format of such plots, however, can be manipulated depending upon the parameters of the plotting routine. Problems associated with generating these plots such as resolution of the plotting grid, scaling of sensitivity and orientation of the plot are discussed with reference to both normal and abnormal fields derived by the Octopus 201 automated perimeter (stimulus size III). Recommendations for this type of perimetric representation are suggested.

Diagnosis, Computer-Assisted↗

PubMed1987

Induced intraocular light scatter and the sensitivity gradient of the normal visual field.

The influence of intraocular light scatter on the perimetric sensitivity profile of the normal eye was investigated using a series of light-scattering cells containing 0.01%, 0.02% and 0.025% concentrations of 500 nm diameter latex beads. The degree of induced intraocular light scatter was quantified by measuring contrast sensitivity using the Nicolet CS2000 system in the presence and absence of both wide- and narrow-angle glare light. Perimetric sensitivity out to an eccentricity of 30 degrees was assessed, using the Octopus 201 and the Dicon AP3000 automated perimeters, with the three light-scatter cells and in the cell-free control condition. The results for both functions were expressed as the difference between the control response and that recorded under the particular experimental condition. Perimetric attenuation increased with increase in intraocular light scatter; the extent of the attenuation varied with stimulus type, bowl luminance and eccentricity.

Adult↗

PubMed1987

Thalamic projections to the paleostriatum and neostriatum in the pigeon (Columba livia).

Thalamic projections to the paleostriatum and neostriatum in the pigeon have been studied using wheat germ agglutinin-horseradish peroxidase in anterograde and retrograde tracing experiments. Injections centred on different mediolateral regions of the dorsal thalamus produced terminal labelling in correspondingly different mediolateral regions of the striatal complex, comprising paleostriatum augmentation and lobus parolfactorius, within the ventral paleostriatum, and within the neostriatum. Injections into various loci within these regions retrogradely labelled numerous neurons within the dorsal thalamus, the location of which varied systematically with the injection placement; and within various regions of the midbrain and pons. These experiments demonstrate a major thalamic projection to the striatum analogous to that from the midline and intralaminar nuclei to the caudatoputamen in mammals, although the patchy characteristic of mammalian striatal afferent terminations was observed only within ventral regions of the pigeon paleostriatum. In addition the experiments demonstrate that striatal afferents also originate from certain nuclei of the mesencephalic midline which are possibly equivalent to the raphe nuclei.

Animals↗

PubMed1987

Serial examination of the normal visual field using Octopus automated projection perimetry. Evidence for a learning effect.

The influence of prior perimetric experience on the magnitude of both differential sensitivity and the short and long term fluctuations remains unclear, and confounds accurate interpretation of visual field data obtained by computer-assisted perimetry. The purpose of the experiment was to identify and quantify any influence of training on the automated perimetric response. The full field of the right eye of 10 clinically normal, naive subjects was examined on 8 occasions with Octopus Program 21 (target size 3) on days 1-5 inclusive, 15, 16 and 44. Sensitivity increased with serial examination in 8 subjects. By dividing the field into zones, it was demonstrated that the learning effect was greatest in the superior field and for eccentricities beyond 30 degrees.

Adult↗

PubMed1987

Spatial summation and the cortical magnification of perimetric profiles.

M-scaling of the conventional spot targets of clinical perimetry at low photopic adaptation levels, such as that of the Octopus automated perimeter, does not result in the expected isosensitive profile using the current equations for humans. This disparity has been attributed to variations in the ganglion cell characteristics across the retina, most notably that of spatial summation. The hypothesis was further investigated by M-scaling the perimetric sensitivity recorded under conditions favouring reduced spatial summation, namely an increased adaptation level and a longer stimulus duration afforded by the Humphrey Field Analyzer. The M-scaled data exhibited a paracentral reduction in sensitivity relative to the theoretical isosensitive profile and an increased sensitivity beyond an eccentricity of 12 degrees. This indicates that for perimetric spot stimuli, the current human M-scaling equations under represent the fovea at the visual cortex. The implications for the design of perimetric routines are discussed.

Adult↗

PubMed1986

Stimulus investigative range in the perimetry of retinitis pigmentosa: some preliminary findings.

The manipulation of perimetric stimulus parameters over a given dynamic range has been reported to provide diagnostic information additional to that of changes in differential sensitivity. Preliminary studies (Flanagan et al., 1984a) have indicated that the perimetric response in retinitis pigmentosa behaves atypically over a range of stimulus combinations and strategies. The current study investigated the perimetric response of 17 retinitis pigmentosa patients of various genetic types over a range of stimulus parameters (target size, presentation time and background luminance) and test strategies (kinetic and threshold static) using the Octopus automated perimeter, the Goldmann and Tubinger bowl perimeters and the Dicon Autoperimeter 3000. Statokinetic dissociation was found to be present with large target sizes at 10 asb and 31.5 asb bowl luminances. Some patients demonstrated enhanced sensitivity to shorter stimulus presentations.

Adult↗

PubMed1986

The interpretation of the differential threshold in the central visual field.

Computer assisted perimetry has revolutionised the investigation of the visual field. Experience of central field assessment with the Octopus Automated Perimeter shows that sensitivity recorded with target size 3 across all age groups can frequently be greater than the published normative values. Use of the latter values can therefore provide a serious underestimation of field loss. Inter-individual variation in sensitivity is found within and between age groups. The limitations associated with the use of the measurement error to define abnormality and the additional problems of hypernormal thresholds and resolution of the blind spot are discussed. It is suggested that methods should be developed to evaluate sensitivity on an intra-individual basis.

Adolescent↗

PubMed1986

The cortical representation of gradient-adapted multiple-stimulus perimetry.

Some stimuli, if scaled in proportion to the reciprocal of inter ganglion cell receptive field separation (M-scaled) exhibit an isosensitivity profile. Perimetric profiles which are isosensitive across the extent of the normal visual field facilitate multiple stimulus perimetry and provide a convenient method for the detection of abnormality. The purpose of the investigation was to establish whether the stimulus diameters necessary to produce an isosensitive perimetric profile were scaled in proportion to M. Sensitivity profiles for a sample of 15 age-matched observers were obtained with the Friedmann VFA Mk II. The stimulus aperture diameters were then measured under 100 X magnification. The observed elliptical apertures, corrected for obliquity of viewing, plate thickness and distance from the eye were represented as diameters of circles possessing an equivalent area to that of the ellipse. The apparent diameters were then M-scaled relative to stimulus pattern h using the equations of Rovamo and Virsu (1979). An overestimation of the M-scaled diameters relative to the apparent diameters was noted which increased with eccentricity for all four cardinal meridians by a factor of up to 3.5 times. It is suggested that the over compensation indicates that the cortical representation of perimetric spot targets at low photopic adaptation levels depends not only upon retinal ganglion cell density but also upon the variation of ganglion cell characteristics with eccentricity. The implications of this finding for perimetric instrument design are discussed.

Adult↗

PubMed1986

Perimetric profiles and cortical representation.

The nature of the interaction between spatial summation and M-scaling was investigated by means of the Octopus automated perimeter. It was found that M-scaling of spatial stimulus parameters, alone, did not result in the expected isosensitivity profile. A clinically flat profile was, however, obtained within the central 30 degrees along the horizontal meridian using a large uniform size target (size 3; projected diameter 0.431 degrees). The eccentricities at which presentation of the standard Goldmann targets would result in an isosensitivity profile across the full extent of the visual field were calculated to further illustrate the over-compensation inherent in the current M-scaling equations.

Adult↗

PubMed1986

Binocular depth perception in the pigeon.

By means of a discrete-trial simultaneous discrimination procedure, pigeons were trained to respond differentially to visual arrays that were identical except that one of them contained a circle displaced in depth when viewed stereoscopically. Performance was severely disrupted when one eye was occluded. The monocular deficit was peculiar to the depth task, inasmuch as no such decrement was seen on a pattern discrimination. The results imply that presence of the displaced circle was discriminated on the basis of a binocular cue. It was also found that pigeons could discriminate the direction of the displacement. Discrimination of depth was independent of the global form and still occurred when elements of the array were randomly displaced in depth. Performance was not disrupted when the absolute convergence angle of the depth stimulus was changed. The cue that consistently accounted for the behavior seen was the detection of the relative angles of convergence--that is, the retinal disparity of the two planes in depth. Thus, despite the lateral position of the eyes of the pigeon, a small binocular field mediates the binocular discrimination of near objects in depth.

Animals↗

PubMed1985

The avian somatosensory system. I. Primary spinal afferent input to the spinal cord and brainstem in the pigeon (Columba livia).

The process of transganglionic transport was used to determine the pattern of primary afferent projections to the spinal cord and brainstem in the pigeon by (1) applying horseradish peroxidase (HRP) to various peripheral nerves in the leg or wing, (2) by injecting HRP-lectin into feather follicles of the wing or tail, and (3) by injecting HRP-lectin into various muscles of the leg or wing. In the spinal cord major peripheral nerves were represented heavily throughout the dorsal horn laminae but sparsely in more ventral laminae. The representations of these different nerves tended to be located in different mediolateral regions of the dorsal horn. Cutaneous nerves and feather follicles were represented predominantly in laminae I and II, and different sets of follicles were represented in different mediolateral regions of these laminae. Afferent labelling from muscles of the leg and wing was located in the lateral portion of the dorsal horn, predominantly in laminae I, II, and IV. In the caudal medulla the representation of the leg within the gracile nucleus was medial to and separate from that of the wing within the cuneate nucleus (Cu). The wing representation, however, extended laterally throughout the external cuneate nucleus (CuE) and lateral regions of the descending trigeminal tract. There was less evidence of separation of the limb representations at more rostral medullary levels where they both occupied predominantly CuE. Afferent labelling from cutaneous nerves and feather follicles was distributed lightly throughout Cu and CuE, and from muscles of both limbs primarily throughout CuE. There was also a small but specific projection from the limbs to the nucleus of the solitary tract, and from the wing to the principal sensory trigeminal nucleus. These results are discussed within a comparative context with a view to highlighting the similarities and differences in the pattern of primary afferent central projections in different vertebrates.

Afferent Pathways↗

PubMed1985

Manipulation of sensitivity in visual field investigation.

Sophistication of computer software and flexibility of stimulus and background luminance parameters in static perimeter design offer the opportunity for increased information in the assessment of the visual field. Relationships between dynamic ranges and resulting sensitivity gradients in a group of 10 normal 21 year old subjects using the Octopus automated perimeter, the Dicon Autoperimeter 2000 and the Friedmann VFA II are assessed. Inadequacies in the use of normative data to assess the visual field are noted. Implications for the use of dynamic range/sensitivity gradient relationships in visual field assessment without reliance on normative data are discussed.

Adult↗

PubMed1985

Telencephalic connections of the trigeminal system in the pigeon (Columba livia): a trigeminal sensorimotor circuit.

A combination of autoradiography and horseradish peroxidase histochemistry was used to identify telencephalic structures linking the sensory and motor components of the trigeminal system in the pigeon. A direct telencephalic projection from the principal trigeminal sensory nucleus upon the nucleus basalis via the quintofrontal tract was confirmed. Nucleus basalis projects upon a belt of neurons within the overlying neostriatum. This region (neostriatum frontale, pars trigeminale: NFT) gives rise to the fronto-archistriate tract which terminates both in the archistriatum intermedium and in the overlying neostriatum caudale, medial to the ventricle (neostriatum caudale, pars trigeminale: NCT). NCT projects, in turn, upon a region of archistriatum intermedium containing cell bodies of the occipito-mesencephalic tract. This pathway provides a link between the telencephalon and premotor areas within the lateral (parvicellular) reticular formation of the lower brainstem. The trigeminal sensorimotor circuit defined in these experiments has been implicated by neurobehavioral studies in the control of pecking, grasping, and feeding in the pigeon.

Animals↗

PubMed1985

Invariance of retinal output during visual learning.

Visually conditioned heart-rate change in the pigeon has been developed as a vertebrate model system for the cellular analysis of associative learning. This development included identifying the visual pathways that transmit the conditioned stimulus information. That, in turn, established a foundation for neurophysiological analyses during conditioning to determine whether these pathways behave merely as input lines or undergo training-induced modification. We began this analysis at the visual periphery, the retina. By recording the activity of single optic tract fibers over the acquisition of the conditioned response it was demonstrated that neither the maintained nor CS-evoked activity of retinal ganglion cells are modified during non-associative or associative paradigms. Thus, the data (a) describe the temporal properties of the CS-evoked retinal response, (b) exclude various possibilities that might have modified this response during learning, and (c) establish a firm foundation for cellular neurophysiological analysis of central visual structures involved in transmitting the CS information.

Animals↗

PubMed1985

Some statistical concepts in the analysis of vision and visual acuity.

As conventionally recorded, visual acuity data constitute an ordinal scale of measurement. An investigation of four different clinical samples shows that visual acuity is not normally distributed amongst these populations. Furthermore, acuity is often measured on charts which, by the inherent restriction of the stimulus size, have the effect of truncating the upper limit of the scale producing, in statistical terms, an incomplete distribution. The distribution of acuity for each sample is found to be adequately described in terms of the equation: F(x) = Ax alpha (T - x) beta, where F(x) is the cumulative distribution of the statistical population, T is the truncation level (known), x is the Snellen decimal acuity (known) and A, alpha and beta are parameters. Alternative analytical procedures based upon this model, which overcome these limitations, are discussed.

Humans↗

PubMed1985

The employment and education of the partially sighted in the period immediately after leaving special school.

Initial results are reported of a major study undertaken to determine factors which could be used to predict employment success of partially-sighted school leavers. The sample involved 355 individuals from 13 schools for the partially sighted taken from three successive final academic years and followed up 1 year after leaving school. Questionnaire techniques were used, the response rate being 85.6%. Analysis revealed that 55.6% sought or experienced employment and 44.4% undertook further education. Eighty-seven per cent of those seeking employment obtained jobs alongside the normally sighted. Only 12 leavers remained totally unemployed. Forty-seven per cent were still in their initial employment.

Adolescent↗

PubMed1984

The qualitative comparative analysis of the visual field using computer assisted, semi-automated and manual instrumentation: I. Scoring system.

Previous methods for the qualitative evaluation of visual field instruments are subject to certain limitations. A system is proposed to overcome these deficiencies. It has been developed from experiences of a clinical study involving 5 different visual field instruments. The method uses 4 levels of analysis and permits separate appraisals of diagnostic potential and detailed inter-instrument comparative evaluation.

Computers↗