Showing papers on "Adaptation (eye) published in 1970"

Electrical activity of vertebrate photoreceptors.

Abstract: It has been known since the time of Schultze (1866) that in the vertebrate retina there are two types of photoreceptors, rods and cones, and that they serve different visual functions; rods for scotopic vision, and cones for photopic. The terminology originates from the shape of the outer segments in which the photosensitive pigment molecules are contained. The cone outer segments are conic and taper towards the tips, while the rod outer segments are typically cylindrical. Fig. 1 is a schematic diagram from Brown, Gibbons & Wald (1963) of the ultrastructure of the rod and cone outer segments of the mudpuppy, Necturus, as studied by electron microscopy. Both appear to be made up of a pile of transverse paired membranes. In cones these arise by infolding of the plasma membrane, and in rods they have probably arisen in a similar way, but each pair of membranes is sealed around the edge so as to form a closed double-membrane disc (Sjostrand, 1961). Because of the universal lamellation within the rod and cone outer segments, it looks as if there were no appreciable intracellular space, but yet Toyoda, Nosaki & Tomita (1969), and Toyoda et al. (1970) were successful in intracellular recording from the outer segments of single rods of the nocturnal gecko and frog.

Suprathreshold spectral properties of single optic tract fibres in cat, under mesopic adaptation: cone-rod interaction.

Abstract: 1. Responses of 122 on-centre or off-centre ganglion cells in cat to suprathreshold monochromatic stimulation have been analysed under mesopic adaptation with white light, recording from their single fibres in the optic tract at a level posterior to the chiasma. Fields described are monocularly driven, located in the right half-fields of either eye, and are all within 30° of the area centralis. 2. Retinal receptors are of two types, viz. 556 nm cones and 502 nm rods. At high mesopic adaptation (1 log cd/m2) all units receive mixed cone—rod input. Under low mesopic adaptation (0 log cd/m2) the great majority receive mixed input; a few receive pure rod input. These results are in agreement with the threshold data (Andrews & Hammond, 1970). 3. Peaks of spectral response curves of units, to suprathreshold monochromatic stimuli of different wave-length but equal quantum flux, fall primarily between 550 and 560 nm for high mesopic adaptation, and between 500 and 520 nm for low mesopic adaptation. Peak position depends on the degree of rod or cone contamination, in units treated under high or low mesopic levels respectively. 4. Units with cone—rod input to the field centre receive similar but antagonistic cone—rod input to the surround. In units with pure rod input to the field centre, only rods input to the surround. 5. Cone and rod components of on-centre discharges are identifiable in terms of colour sensitivity and latency. The cone component is primarily a short-latency, high-frequency, excitatory transient; the rod component is a longer latency, lower frequency, maintained phase of excitation. 6. Less direct evidence indicates that cone and rod input to the field surround give rise to inhibitory components of comparable latency, magnitude and time course. 7. The identified cone and rod components of responses are used in further experiments to show that cone and rod input have different spatial organization both in the receptive field centre and in the surround. 8. The boundary between the field centre and surround for rods has a diameter on average about twice as large as that for cones. This organization is such that the field centre for rods substantially overlies the cone surround. 9. Changes in receptive field organization occur within the mesopic range, associated with the changeover from cone to rod vision. 10. It is suggested that the difference between cone and rod input in the mesopic range may form the basis of the cat's ability behaviourally to discriminate between colours.

Mesopic increment threshold spectral sensitivity of single optic tract fibres in the cat: cone—rod interaction

Abstract: 1. Mesopic increment threshold spectral sensitivities of sixty-six on-centre and twenty-five off-centre ganglion cells in the cat were determined by recording from single fibres of the left optic tract at a level posterior to the optic chiasma.2. All units were monocularly driven; receptive fields were located almost exclusively in the right visual half-fields within 30 degrees of the area centralis, but with slight overlap across each retinal mid line to the left half-fields. The extent of field spread to the right temporal hemi-retina was significantly larger than that to the left nasal hemi-retina. Field centre diameters ranged from less than 0.25 degrees for central units to 2 degrees for more peripheral units.3. At high mesopic adaptation of 1 log cd/m(2) all responsive units (forty-four fibres) received mixed cone-rod input. Threshold curves could always be fitted by the absorption spectra of visual pigment 556 together with varying contributions from visual pigment 507, each derived from the Dartnall nomogram.4. Of forty-seven fibres analysed under low mesopic background (0 log cd/m(2)) 92% received similar cone-rod input, being fitted predominantly by visual pigment 507 with slight cone contamination. The remaining 8% received pure rod input and could be matched by visual pigment 507 alone.5. In conclusion, the cat retina presumably contains a single class of cones with absorption maxima at 556 nm, and a single class of rods. Discrepancy between the presumed rod absorption maximum (502 nm) and the low-mesopic sensitivity maxima of tract fibres (507 nm) is considered in terms of tapetal reflectivity, and absorption by ocular media. Both mechanisms input to the great majority of retinal ganglion cells. At high mesopic levels the cone mechanism predominates. At low mesopic levels the rod mechanism predominates. A small proportion of ganglion cells within the central 30 degrees of the retina receive input only from rods, and in these the rod mechanism saturates completely below 1 log cd/m(2).

Prismatic adaptation under scotopic and photopic conditions.

Abstract: Prismatic adaptation under scotopic and photopic conditions in subjects, using transfer experiments

Nonequivalence of backgrounds during photopic dark adaptation.

Abstract: Using the equivalent-background transformation, Crawford has demonstrated the equivalence of adaptive states (dark and light adaptation) in scotopic vision. The critical feature of this transformation is that the threshold sensitivity of the eye at a particular time in the dark can be specified in terms of the steady-state, light-adapted condition necessary to produce the same threshold for all target diameters. This indicates that a single variable may control the spatial integration of light. Equivalence was investigated in the present study for long-term photopic dark adaptation using two target diameters (0.13° and 0.33°) and four chromatic combinations of red and green test and adapting stimuli (red on red, red on green, green on green, and green on red). Except under special conditions employing color-defective observers for which there was more complete isolation of cone mechanisms, equivalence between adaptive states was generally found not to exist. It is concluded that more than one process is needed to control the spatial integration of light in the photopic system, and these are hypothesized to be the wavelength-dependent excitatory and inhibitory processes of the visual receptive field.

Adaptation to displaced vision: Amount of optical displacement and practice

Abstract: The influence of two variables, length of exposure and amount of optical distortion, on adaptation to displaced vision was examined The extent of adaptation was positively related to number of trials in a task involving spatial localization of a target displaced by a wedge prism A substantial adaptation (38%) was produced after only two trials The adaptation was also positively related to degree of optical displacement, except at the highest level used The findings are discussed in terms of availability of information about the discrepancy between vision and task

Dark Adaptation in Strabismic Amblyopia: The Use of Acuity Targets

Abstract: Acuity-dark adaptation curves for 11 different sized Landolt Cs were performed on the normal and amblyopic eye of 5 strabismic amblyopes. The results of these studies are presented and possible mechanisms which might account for defects in acuity-dark adaptation are discussed.

Integration of responses between different types of cones and between rods and cones.

Abstract: : Separation and identification of function of rods and cones in a mixed receptor population was achieved. Threshold level mixtures of two monchromatic stimuli with varying degrees of spectral separation showed the degree of integration of response between different receptor types. A small degree of integration of response was observed between rods and long wavelength cones. As the two monochromatic stimuli became more spectrally separated the degree of integration between different cone types decreased gradually. This was accounted for in terms of a trichromatic-opponent theory of color vision. A much larger degree of integration between different cone types was observed in the parafovea than had been observed in the fovea by previous investigators. A possible difference in the way the three cone mechanisms interact in the fovea and parafovea was suggested. (Author)