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Biomedical subjects

K H Ruddock

Publications and source records attributed to K H Ruddock.

12 recordsLinked to original sources
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↗