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Biomedical subjects

K H Ruddock

Publications and source records attributed to K H Ruddock.

15 recordsLinked to original sources
PubMed1990

Terbium simulates the action of calcium on electrophysiological activity in the isolated fish retina.

It has been suggested that terbium (Tb) could be substituted for calcium (Ca) in biological tissue and, because of its useful spectroscopic properties, provide an assessment of calcium distribution in the tissue. In order to assess their physiological effects, we have examined the action of free terbium ions on the membrane potential and light-evoked responses of horizontal cells, and on the massed light evoked response (ERG) of the neural retina. Measurements were performed by intracellular and extracellular recording from the isolated fish retina, superfused with Ringers of various ionic compositions, and certain technical difficulties which occurred in the use of terbium are discussed. We show that Tb ions mimic Ca ions in suppression of the ERG and in hyperpolarization of the horizontal cell membrane potential. The effects of Tb persist after its removal from the superfusate for a longer period than do those of calcium, which indicates that terbium binds more firmly at its site(s) activity. Tb and Ca both suppress the light-evoked S-potentials from the horizontal cells, although some differences were observed in the waveform of the S-potentials during the onset of suppression. We conclude that the physiological effects of Tb on the retina are essentially similar to those of Ca, and that Tb could, therefore, prove a useful marker of Ca distribution in neural tissue.

Animals↗
PubMed1990

Effects of stimulus complexity on simple spatial discriminations.

We have extended previous measurements on the detection of a target, differentiated in orientation or magnification from a number of identical reference elements. In these new experiments, we have used more than one class of reference element from which the target must be discriminated. For example, in the case of orientation discrimination, the reference elements are of two classes, which differ from each other in orientation, but are otherwise identical. Representatives of the two classes are present in equal numbers, and the target to be detected is presented at an orientation angle different from that of either class of reference element. Data for discrimination of target magnification or orientation are given for simple geometric elements, namely lines, squares and triangles. In nearly all cases, the characteristic time required for 50% probability of target detection, T1/2, is greater with two classes of reference elements than with a single class. In nearly all cases, T1/2 values for the mixed reference elements increase with the number of reference elements, N, corresponding to discrimination by serial processing. This remains the case even when detection is parallel (T1/2 independent of N) for either class of reference element used separately. We discuss the properties of the spatial discrimination mechanisms which give rise to these responses.

Depth Perception↗
PubMed1990

Spatial, colour and contrast response characteristics of mechanisms which mediate discrimination of pattern orientation and magnification.

We have measured response times for the detection of a single target presented against a set of reference elements which are characterised by combinations of four different stimulus parameters; colour, contrast polarity, magnification and orientation. The aim of the experiments was to determine the response characteristics of visual mechanisms which mediate target detection through the discrimination of orientation and magnification. In the first experiments, we determined sensitivity to differences in colour and contrast polarity, and show that the mechanisms responsible for the discrimination of orientation and of magnification are both selective in their responses to colour and to contrast polarity. There are, nonetheless, residual interactions between patterns of different contrast polarities and between those of different colour, and in the latter case, weak interactions persist under equiluminance conditions. In a second set of experiments, we examined the interactions between orientation and magnification. We conclude that the responses of visual mechanisms which mediate target detection through discrimination of orientation are markedly dependent on stimulus magnification whereas those which mediate detection through discrimination of magnification are, in contrast, relatively insensitive to stimulus orientation.

Adult↗
PubMed1979

Effects of picrotoxin and strychnine on fish retinal S-potentials: evidence for inhibitory control of depolarizing responses.

Simultaneous recording of the light evoked electrical signals from different classes of slow(S)-potential unit in the isolated fish retina established that picrotoxin, an antagonist of GABA, selectively suppresses the depolarizing component of C-type S-potentials. In contrast, equivalent concentrations of strychnine have no effect on S-potentials, but suppress a component of transient amacrine cell responses. On the basis of these and other experimental data [3,4] we propose a network diagram for the C-type S-potential units in the cyprinid fish retina. This network includes a GABA-ergic feed-back loop and is essentially similar to that proposed by Fuortes and Simon [5].

Animals↗
PubMed1979

A colour-dependent abnormality in human visual detection of stimulus motion and spatial structure.

We have studied the wavelength dependence of visual responses in a single human subject, M.W., who has an unusual visual defect. It is shown that for red stimuli, both spatial resolution for grating patterns and detection of target movement are grossly abnormal. On the basis of these and other [8] experimental data, we argue that M.W.'s response pattern implies interdependent central visual processing of colour, movement and spatial structure. We examine this conclusion in relation to recent anatomical and electrophysiological findings.

Color Perception↗
PubMed1979

The response characteristics of an inhibitory binocular interaction in human vision.

1. The contrast threshold level for visual detection of a linear grating consisting of parallel light and dark bars is increased by adaptation to a high contrast grating of spatial characteristics similar to those of the test grating (e.g. Blakemore & Campbell, 1969). This so-called contrast threshold elevation effect is significantly reduced if two adaptation gratings, with appropriate different spatial characteristics, are presented one to either eye (Ruddock & Wigley, 1976). We have studied the contrast threshold elevation effect obtained with a test and an adaptation grating presented to one eye and a second adaptation grating, referred to as the conditioning grating, presented to the other. 2. Preliminary data are presented for three subjects with normal stereoscopic vision. In each case, the contrast threshold elevation effect for a pair of spatially identical test and adaptation gratings is significantly reduced by a conditioning grating of spatial frequency in the range 1-5 c/deg. 3. Reduction in the contrast elevation effect is observed whether the conditioning and adaptation gratings are of the same or of different wave-lengths and the effect of the conditioning grating increases to a steady-state level over a period of some 30 sec following onset of its presentation. 4. Measurements were made with a 5 deg diameter circular test grating presented at retinal locations up to 8 deg in the horizontal and vertical meridians from a foveal fixation point. It was found that in the horizontal meridian, the amplitude of the suppression effect associated with the conditioning grating falls as the displacement angle of the test field from the fixation point increases. For displacements in the vertical meridian, however, the amplitude of the suppression effect is virtually independent of the retinal location of the test field. 5. Under experimental conditions which yield suppression of the contrast threshold elevation effect for subjects with normal stereoscopic vision, no suppression was found for three subjects who possessed neither global nor fine stereoscopic vision. Results for a subject who possessed fine, but not global stereoscopy, did, however, show the suppression effect.

Adaptation, Ocular↗
PubMed1978

Properties of length-selective and non-length-selective adaptation mechanisms in human vision.

The contrast threshold elevation effect has been measured for one dimensional (grating) and for two dimensional (spot) stimulus patterns. It has been shown previously (Burton and Ruddock, 1978) that such stimuli elicit, respectively, non-length-selective and length-selective adaptation effects. It is established that, unlike the frequency shift effect, the contrast threshold elevation effect is sensitive to the width of the light but not to that of the dark elements of the stimulus patterns. Adaptation to spot patterns elicits a significant threshold elevation for detection of both spot and grating test stimuli, but only under monoptic viewing conditions. The experimental findings are summarized in a block-diagram and it is shown that adaptation to grating patterns is successfully described by the spatial frequency response data given by Maudarbocus and Ruddock (1973).

Adaptation, Physiological↗
PubMed1978

Central representation of colour vision deduced from studies on a subject with a central colour vision defect.

M.W.'s grossly defective responses to red light stimuli are caused by an abnormality of central vision which is highly specific in its action. The abnormal activity does not affect stereoscopic function and only partially modifies the parametric characteristics of the contrast threshold elevation effect. These experimental observations lend support to the concept of parallel processing of different attributes of the visual stimulus, possibly by different cortical areas. We suggest that understanding of central visual processes could be facilitated by further studies on subjects with malfunction of the visual cortex.

Adult↗
PubMed1975

The effects of maintained light stimulation on S-potentials recorded from the retina of a teleost fish.

1. S-potential responses to transient and maintained light stimuli have been recorded from units in the mixed rod-cone retina of a teleost fish species Eugerres plumieri. 2. Four spectral classes of S-potential were observed, three cone- and one rod-type. The cone-type responses were subdivided into two L-type (referred to as L1 and L2), and a C-type response. Two classes of transient depolarization response were also recorded from those retinal levels associated with the S-potential responses and these are attributed, tentatively, to rod and cone bipolar activity. 3. L2-type S-potentials do not yield constant hyperpolarization during maintained light stimulation, the time course of the response potential, V, being given approximately by (see article) where Vt is the response potential at time t sec following the onset of stimulation, Vo being the initial response potential. In contrast, both hyperpolarizing and depolarizing components of the C-type response were maintained under conditions of steady illumination. 4. Under maintained light stimulation at saturation illumination level, the rod S-potentials escape from hyperpolarization in a manner similar to that previously observed for the skate (Dowling & Ripps, 1971). 5. L2-type responses to transient test stimuli of illumination level I, superimposed on a steady background field of illumination level I', are in some respects consistent with Alpern, Rushton & Torii's (1970) empirical formula (see article) with K, I one-half and ID constants. However, for the present data, the value of I one-half is dependent on I'. 6. The significance of Ricco's law for S-potential responses is discussed in relation to these findings.

Action Potentials↗