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C Martinoya

Publications and source records attributed to C Martinoya.

16 recordsLinked to original sources
PubMed1991

[Method for measuring sensitivity to periodic spectral energy modulations in human].

The distribution of spectral energy of a visual stimulus can be subject to Fourier analysis. In this perspective, we have built a device which produces periodic variations in energy (square waves) over the visible spectrum (400-700 nm), and where the amplitude, phase and frequency of the stimuli can be independently controlled. From the non-modulated spectrum, supplying a white spot, for a given frequency and phase, there is a minimal amplitude modulation (contrast threshold) for which the spot becomes chromatic. As an illustrative example we present here a curve of optimal sensitivity values (inverse of contrast) as a function of frequency (from 0.5 to 3.6 cycles/300 nm) for a normal subject.

Color Perception↗
PubMed1990

Color mixing in the pigeon. A psychophysical determination in the longwave spectral range.

Pigeons were trained to discriminate between spectral lights and additive mixtures in the 580-640 nm range. Two behavioral procedures were used: (I) a simultaneous instrumental discrimination and (II) successive "autoshaping" discrimination. Pigeons were able to make color mixture matches within this spectral range with satisfactory precision. Matchings determined by the animal correspond well to those predicted on the basis of the spectral sensitivities of two (or even three) pigment-droplet combinations present in the pigeon retina.

Animals↗
PubMed1988

Depth resolution in the pigeon.

Pigeons possess a binocular visual field and a retinal region of higher cellular density pointing to the center of this overlap. These features and the precision of pecking behavior suggest that in this lateral-eyed bird cues other than monocular ones might participate in depth judgements. Pigeons were trained with an operant procedure to discriminate between luminous points differing in depth which appeared to the observer as floating in the dark. The accuracy of depth judgements was found to be a function of the ratio between the interstimulus distance and the mean eyes-to-stimulus distance. In a first test (experiment I) no external binocular disparity cues were available, the animal only seeing one luminous point at a time (near or far). In a second test (experiment II) where binocular disparity cues were available, the animal having this time to discriminate a pair of points placed at equal depth from a pair placed at unequal depths, only one pair being visible at a time, depth resolution did not improve. This suggests that, at least within the range of distances explored, the pigeon has no stereoscopic vision. Notwithstanding this, binocular cues do play a role, since when tests were done comparing binocular with monocular viewing (experiment III), monocular depth resolution was significantly worse.

Animals↗
PubMed1984

Pigeon's eyes converge during feeding: evidence for frontal binocular fixation in a lateral-eyed bird.

Pigeons' head-in-space and eye-in-head positions were simultaneously recorded (EOG) in video during feeding. A linear correlation was found between the experimentally measured eye convergence (sum of both EOGs ) and grain parallax (calculated from interocular and eye-to-grain distances). This graded convergence of the eyes on approaching a target is considered evidence of frontal binocular fixation. Since such convergence prevails when the animal is forced to rely on frontal monocular or on lateral vision, a central mechanism controlling frontal fixation in the pigeon must be presupposed .

Animals↗
PubMed1984

Comparing frontal and lateral viewing in the pigeon. III. Different patterns of eye movements for binocular and monocular fixation.

The presence in the pigeon's retina of two areas of higher cellular density which we have shown mediate different visual functions, suggests the existence of two modes of fixation: a lateral monocular and a frontal binocular one. The participation of eye movements in these modes of fixation remained unexplored. We analyzed oculomotor behaviour in awake head-restrained pigeons by means of EOG and video film. Orienting saccades attaining up to 17 degrees from the resting positions could be elicited by presenting stimuli in different parts of the visual field. Two typical ocular patterns were consistently observed to the sudden presentation of large and novel stimuli: coordinated vergence of both eyes (even with one eye occluded) to stimulation within the frontal binocular field, and uncoordinated ipsilateral saccades to stimuli moving in one lateral field. Results point towards two different and reciprocally exclusive mechanisms of oculomotor control in the pigeon. The relevance of a trident mode of vision correlated to retinal organization and living praxis of some lateral-eyed vertebrates is discussed.

Animals↗
PubMed1983

Comparing frontal and lateral viewing in the pigeon. II. Velocity thresholds for movement discrimination.

Pigeons have been described as poor movement detectors when tested in the frontal binocular field. Retinal organization and behaviour suggest that motion sensitivity may be better in the lateral field. Pigeons were trained to discriminate the direction of moving square gratings (0.3 cyc/deg) appearing briefly (250 msec) contingent upon pecking a key (behavioural fixation). Stimuli were presented at isoacuity distance (40 cm) 25 degrees below the beak for frontal and 80 degrees back from the beak for lateral viewing. The animal had to discriminate the direction of movement for decreasing angular velocities. Results show that lateral motion sensitivity in the pigeon is 3 times better than frontal motion sensitivity. The fovea centralis, looking laterally, seems to be adapted for motion detection and may play a special role in the recognition of moving predators.

Animals↗
PubMed1982

Comparing frontal and lateral viewing in the pigeon. I. Tachistoscopic visual acuity as a function of distance.

Pigeon's visual acuity has mainly been tested in free viewing conditions so that the direction of gaze could not be controlled. In order to be able to compare the resolving power of the two retinal areas of higher cellular density--the area dorsalis in the red field with frontal binocular projection and the fovea centralis with lateral monocular projection--a method of behavioural fixation was used. This method consists in a forced pecking schedule and a tachistocopic presentation of the stimulus. The pigeon has to discriminate the orientation (vertical, positive; horizontal, negative) of square gratings of increasing spatial frequency. Tests were done with the stimuli appearing 25 degrees below the beak for frontal and 80 degrees back from the beak for lateral viewing, at distances of 10, 20, 40 and 80 cm for each direction. Results show that while frontal acuity decreases with distance, lateral acuity increases with distance. These psychophysical data confirm previous dioptric measurements done on frozen eyes, showing that the pigeon is myopic in the frontal field and hyperopic in the lateral field. Pigeons seem to be well adapted for visually guided frontal tasks at near distances (feeding, landing) and for visually guided lateral tasks at far distances (warning).

Animals↗
PubMed1981

Reactivity to light and development of classical cardiac conditioning in the kitten.

Kittens studied from 7 days onwards revealed that the earliest age at which cardiac conditioning can be established is 30 days, after some 30 light-electric shock associations. Older kittens showed both cardiac as well as motor conditioning. Animals younger than 21 days old had no well-defined cardiac responses to the clearly nociceptive unconditioned stimulus so that no cardiac conditioning was established; neither did they show signs of motor conditioning. This failure could be due to immaturity of the cardiac-emotional reactivity to nociceptive stimulation and immaturity of the neural structures involved in associative learning. Lack of reactivity to the light used as conditioned stimulus must be excluded because it already produced eye blink by 2 days of age. Moreover, a light-dark preference test done during the 1st postnatal week showed that kittens are able to discriminate light from dark by 8 days of age.

Age Factors↗
PubMed1966

The permeability of the gastric mucosa of dog.

1. Tritiated water, [(14)C]urea, [(14)C]thiourea, [(14)C]sucrose and [(59)Fe]-haemoglobin were used to study the permeability of a semi-isolated piece of the great curvature of the canine stomach.2. The osmotic pressure of the solutions placed in contact with the secretory surface of the epithelium was changed by means of dextrose or urea. The mucosa behaved as a semi-permeable membrane, meaning that water flowed under gradients of osmotic pressure. Regardless of the solute used, about 45 x 10(-6) ml. of water flowed/cm(2)/min under a gradient of one atmosphere.3. The permeability constants of the probing molecules were determined under zero net volume flow obtained by placing isosmotic dextrose or isosmotic urea in the chamber. The constants decreased as the molecular volume of the probing molecules increased.4. The transport of all the non-electrolytes across the epithelium decreased significantly when the chamber contained isosmotic dextrose. Basically, this effect seems to be a result of the reduction of the area available for diffusion caused by the high molecular volume of dextrose.5. The increased hindrance to diffusion of the probing molecules caused by the added solutes is considered as good evidence that the probing molecules diffuse by way of pores filled with water.6. The equation derived by Renkin (1954) fits the results obtained if we assume that the equivalent membrane has pores of at least two different radii. The calculated radii vary somewhat with the solute placed in the chamber, though about 88% of the area available for diffusion consists of pores with radii smaller than 2.5 A.7. The equivalent pore radius, calculated from Kedem & Katchalsky's (1961) formula for pores of one single radius, contradicts some experimental findings. Once again, the results obtained would be reproduced more accurately by an equivalent membrane pierced by parallel pores of at least two different diameters.8. A procedure is suggested for calculating the proportion of pores of different radii. It seems likely that the pore radii vary in a continuous distribution from the large pores which allow the diffusion of haemoglobin, to pores hardly permitting the passage of water. The wide pores would form a small fraction of the total area available for the diffusion of water.

Animals↗