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Biomedical subjects

W Hodos

Publications and source records attributed to W Hodos.

15 recordsLinked to original sources
PubMed1992

Visual performance of pigeons following hippocampal lesions.

The effect of hippocampal lesions on performance in two psychophysical measures of spatial vision (acuity and size-difference threshold) was examined in 7 pigeons. No difference between the preoperative and postoperative thresholds of the experimental birds was found. The visual performance of pigeons in the psychophysical tasks failed to reveal a role of the hippocampal formation in vision. The results argue strongly that the behavioral deficits found in pigeons with hippocampal lesions when tested in a variety of memory-related spatial tasks is not based on a defect in spatial vision but impaired spatial cognition.

Animals↗
PubMed1992

Age-dependent intensity-difference thresholds in pigeons.

Recent studies have reported age-related deficits in visual acuity and changes in retinal morphology in pigeons. The experiment reported here was designed to determine the effects of age on intensity difference thresholds in pigeons. Six subjects, age 2-17 yr, were trained to discriminate between two stimuli that differed in luminance. When this training was complete, the subjects were presented with a series of stimulus comparisons ranging from 0.08 to 0.43 log unit. Threshold was calculated by determining the luminance difference that corresponded to 75% correct. These data were pooled with 56 intensity-difference thresholds that had been collected from pigeons of various ages over a 20 yr period using the same procedure. A regression analysis that was performed on the pooled data set gave the result b = 0.0038, d.f. = 61 P < 0.05, r2 = 0.066 which indicates that age accounted for approx. 7% of the variance in intensity-difference threshold. This finding, although statistically significant, indicates that as pigeons age their ability to perform this type of non-spatial discrimination task is not greatly impaired. This finding suggests that deficits associated with a spatial visual task in pigeons, such as visual acuity, are task specific and are not due to a global performance deficit.

Aging↗
PubMed1991

Electroretinographic changes in aged pigeons.

Photopic electroretinograms, either to full-field light flashes (FERGs) or to contrast-reversal of square-wave gratings (PERGs) have been recorded in pigeons aged 2 years old (n = 5) and 10 years old (n = 5). Mydriatic pupil diameter, ophthalmoscopic appearance of the retinal fundus and optic media, and refractive state were comparable in the two groups. V/log I functions of individual FERG components (a-wave, b-wave and oscillatory potentials) displayed significantly lower slopes in the old birds than in the young, which suggests a reduction in retinal gain. PERG amplitude also was significantly lower in the older birds over a wide range of spatial frequencies (0.2-8.8 c/deg). Estimated visual acuity based on the extrapolated high-frequency cut off was 18 c/deg in the younger birds and 7.8 c/deg in the older birds. These results are in agreement with psychophysical data and retinal age-related losses in visual acuity, photoreceptors and retinal ganglion cells. Since these findings are comparable to those reported for humans, the results suggest that pigeons may serve as a useful model for human visual aging.

Aging↗
PubMed1991

Age-dependent changes in visual acuity and retinal morphology in pigeons.

The visual acuities of 17 pigeons that ranged in age from 2 to 17 years were tested with high-contrast, square-wave gratings. A systematic decline in visual acuity was observed that was well described by a logarithmic function. Pupillary diameter also declined with age, which decreased retinal illumination, but increased depth of focus. A small amount of presbyopia also was observed. Both the decrease in retinal illumination and the presbyopia accounted for only a trivial proportion of the acuity loss. No relationship between corneal or lenticular density and age was observed. Ophthalmoscopic examination of the optic media revealed no abnormalities associated with age. Microscopic examination of the area dorsalis of the retina (the high-density region specialized for frontal vision) revealed age-related losses of up to 33% of photoreceptors and 23% of cells in the ganglion-cell layer. A study of the photoreceptor layer within area dorsalis indicated that single-cone densities were unaffected by aging whereas the double-cone densities, which are the predominant photoreceptor type in the area dorsalis, were reduced in number by about one third. Calculation of the Nyquist limit both for photoreceptors and ganglion cells suggested that the decreased retinal density together with the decreased retinal illumination and presbyopia could not account for all of the observed acuity loss.

Aging↗
PubMed1991

The Scala naturae revisited: evolutionary scales and anagenesis in comparative psychology.

Recent suggestions that evolutionary scales have a place in theorization about the evolution of behavior have been based on the concept of anagenesis, formerly associated with notions of biological progress. An associated concept is that of grades, often used as units of anagenetic advance. Advocates of anagenetic analysis in comparative psychology cite the writings of biologists Bernard Rensch, Julian Huxley, George Gaylord Simpson, and Stephen Jay Gould to support the usefulness of anagenesis but treat the positions of each of these theorists as if they were the same. In fact, they differ considerably in their definition of anagenesis and in its application to specific issues in evolution. The anagenetic approach is criticized as axiological and frequently anthropocentric. Although the formation of grades can be useful, a sequence of grades must not be assumed to represent historical stages in the evolution of specific structures or behaviors.

Adaptation, Physiological↗
PubMed1991

Intraocular pressure and eye enlargement in chicks.

In chicks, the application of optical devices that blur vision results in eye enlargement and ametropia. The research presented here investigated changes in intraocular pressure (IOP), specifically intravitreal pressure, that occur with eye enlargement induced by this means. Plastic goggles (domes) were glued over one eye in 25 domestic chicks. Plastic rings were glued around one eye in 25 control chicks to control for the mechanical effects of the treatment but which left their vision undisturbed. Following two weeks of treatment, domes and rings were removed and IOP was measured. Mean IOP of the domed eyes was 1.14 mm Hg lower than that of control eyes, a difference that was not statistically significant. The eyes of an additional group of 20 chicks that experienced similar treatments were refracted; these refractions revealed that the dome-treated eyes had a mean refractive state that was 7.98 D myopic relative to the ring controls, which was statistically significant. The results indicate that IOP does not change significantly in chicks with experimental eye enlargement induced by retinal-image degradation.

Animals↗
PubMed1990

Avian models of experimental myopia: environmental factors in the regulation of eye growth.

During normal development a precise match between the length of the path of light within the eye and the refractive state of the eye's optical elements is required for the retinal image to remain sharply in focus. Recent studies have shown that this match between eye growth and refractive state is partially under the control of environmental factors. Investigations in several species of ground-foraging birds have shown the existence of an optical mechanism that maintains the retinal image of the ground in focus on the upper retina without a change in accommodation, when the bird is standing erect. Moreover, as a young bird grows, the refractive state changes to maintain a sharp focus of the retinal image of the ground. These findings suggest that the quality of the retinal image may be an important regulator of the matching of refractive state to growth of the ocular globe. We have found in young, rapidly growing birds that the application of optical devices that degrade the quality of the retinal image interferes with the normal regulation of eye growth and results in excessive growth and severe myopia. Additional environmental variables that affect eye growth include nutritional deficiencies of calcium and vitamin D and elevated ocular temperature.

Animal Nutritional Physiological Phenomena↗
PubMed1977

Intensity difference thresholds after lesions of the visual Wulst in pigeons.

Visual intensity difference thresholds were studied before and after telencephalic lesions in pigeons. Subjects with visual Wulst lesions showed initial postoperative threshold elevations that represented losses of 19%-49% of their preoperative sensory capacity. This initial loss was correlated with the extent of damage to three components of the visual Wulst: nucleus intercalatus hyperstriati accessorii, hyperstriatum intercalatus suprema, and hyperstriatum accessorium. The damage to hyperstriatum dorsale, another component of the visual Wulst, made no contribution to the initial deficit. The sensory capacity of all but one pigeon improved as a result of postoperative retraining.

Animals↗
PubMed1976

Behavioral correlates of 'tectal compression' in goldfish. I. Intensity and pattern discrimination.

Goldfish were trained to perform visual intensity and pattern discriminations. Three groups of fish had bilateral ablation of the caudal optic tectum, a fourth consisted of unoperated controls and a fifth group consisted of sham-operated controls. The fish were tested after various postoperative intervals ranging from 19 to 147 days. The lesions produced modest deficits in intensity discrimination irrespective of postoperative interval. The fish that began training on the pattern discrimination after 14-18 postoperative days showed no improvement in performance. Fish that began training after 39 postoperative days showed improvements in performance after about 65 postoperative days. The group that began training 158-160 postoperative days showed steady and persistent improvements in discrimination performance. The results suggest that improvements in pattern vision after partial tectal ablation follow the same time course as compression of the retinotectal map after partial ablation of the tectum.

Animals↗
PubMed1976

Behavioral correlates of 'tectal compression' in goldfish. II. Visual acuity.

Visual acuity was measured in three normal goldfish and two goldfish in which the caudal optic tectum had been ablated bilaterally. Compression of the retinotectal map was assumed to have occurred in the two operated fish, which were tested more than 200 days after surgery. The results indicated that the visual acuity of the normal fish ranged from 0.94 to 0.95 degrees of visual angle. The visual acuity of the fish with presumed compression of their retinotectal maps ranged from 1.91 to 2.07 degrees. The results suggest that compression of the retinotectal map occurs at the expense of the spatial-resolution ability of the visual system.

Animals↗
PubMed1976

Near-field visual acuity of pigeons: effects of head location and stimulus luminance.

Two pigeons were trained to discriminate a grating stimulus from a blank stimulus of equivalent luminance in a three-key chamber. The stimuli and blanks were presented behind a transparent center key. The procedure was a conditional discrimination in which pecks on the left key were reinforced if the blank had been present behind the center key and pecks on the right key were reinforced if the grating had been present behind the center key. The spatial frequency of the stimuli was varied in each session from four to 29.5 lines per millimeter in accordance with a variation of the method of constant stimuli. The number of lines per millimeter that the subjects could discriminate at threshold was determined from psychometric functions. Data were collected at five values of stimulus luminance ranging from--0.07 to 3.29 log cd/m2. The distance from the stimulus to the anterior nodal point of the eye, which was determined from measurements taken from high-speed motion-picture photographs of three additional pigeons and published intraocular measurements, was 62.0 mm. This distance and the grating detection thresholds were used to calculate the visual acuity of the birds at each level of luminance. Acuity improved with increasing luminance to a peak value of 0.52, which corresponds to a visual angle of 1.92 min, at a luminance of 2.33 log cd/m2. Further increase in luminance produced a small decline in acuity.

Accommodation, Ocular↗
PubMed1976

Detection of the velocity of movement of visual stimuli by pigeons?

Nine pigeons were trained to discriminate a moving stimulus from a stationary stimulus. In one experiment, the stimulus was a rotating disc with radial stripes. In a second experiment, the stimulus was a vertically moving film strip with horizontal bars. Several psychophysical procedures were used to determine the minimal detectable velocity of movement. The detection thresholds for most of the pigeons fell in the range of 4.4 to 6.5 millimeters per second, corresponding to a retinal velocity of 4.1 to 6.01 degrees per second. A signal detection analysis of the psychophysical data indicated systematic changes in response bias that were related to the ordinal position of the stimulus velocity in the sequence.

Animals↗
PubMed1975

Intensity and pattern discrimination after lesions of the pretectal complex, accessory optic nucleus and ventral geniculate in pigeons.

Pigeons were trained to discriminate between pairs of visual stimuli that differed in intensity or pattern. After completion of training, bilateral, stereotaxic lesions were made in various cell groups in the mesencephalon and diencephalon that receive terminals of the optic tract. The target regions were nucleus ectomamillaris (accessory optic nucleus), nucleus lentiformis mesencephali and area pretectalis (prectal complex) and the nucleus geniculatus lateralis, pars ventralis (ventral geniculate). In some cases, combined lesions of nucleus lentiformis mesencephali and area pretectalis were made. Lesions of nucleus ectomamillaris, nucleus lentiformis mesencephali, area pretectalis, or ventral geniculate did not produce major impairments of discrimination performance nor did combined lesions of nucleus lentiformis mesencephali and area pretectalis. A number of cases of intended destruction of the ventral geniculate also had extensive damage of the overlying nucleus rotundus. In several of these cases of combined destruction of nucleus rotundus and ventral geniculate, the previously reported discrimination deficits following nucleus rotundus lesions did not appear. In those cases in which the nucleus rotundus deficit was observed, the lesions were found to include the nucleus subpretectalis, which, like nucleus rotundus, receives tectofugal fibers via the brachium of the superior colliculus. The data of the ventral geniculate + rotundus cases and ventral geniculate + rotundus + subpretectalis cases suggest that sensory deficits following a lesion in a particular cell group may not necessarily indicate that the sensory information is processed in that cell group, but rather that the lesion had deprived other cell groups of the appropriate input necessary for their proper functioning.

Animals↗