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Biomedical subjects

W Hodos

Publications and source records attributed to W Hodos.

At least 55 records · Page 3Linked to original sources
PubMed1984

A weighted index of bilateral brain lesions.

Attempts to correlate the amount of bilateral brain injury with behavioral changes can be complicated if the lesions are bilaterally unsymmetrical in volume. Further complications are introduced if unilateral lesions are ineffective in producing behavioral changes. An index, W%, is proposed which is based on the product of the volumes of the damage on the right and left sides. The index ranges from 0 to 100 such that conditions of no injury or unilateral injury produce an index of zero. In contrast, relatively large values of the index are generated by symmetrical lesions. Grossly unsymmetrical lesions, in which one side is nearly intact, produce very low index values. For lesions that are bilaterally equivalent in volume, the percentage of tissue destroyed on either side is equal to 10 square root of W%. Some properties of the proposed index are discussed.

Animals↗
PubMed1984

Near-field acuity after visual system lesions in pigeons. I. Thalamus.

Visual acuity determinations were made for 14 pigeons trained to discriminate high-contrast, square-wave gratings of successively higher spatial frequencies from blank stimuli of equal average luminances. The stimuli were presented according to the method of constant stimuli. Video-taped motion pictures of the key-pecking response provided a measure of the cornea-to-stimulus distance. The preoperative results indicated that the mean minimal-separable visual angle was 2.3 min (range 1.6-3.6) under conditions of photopic adaptation with the stimulus luminance at 70 cd/m2. When performance was stable, bilateral electrolytic lesions were placed in: nucleus rotundus (RT), nucleus opticus principalis thalami (the OPT complex); and RT plus the OPT complex. Lesions confined to the OPT complex did not impair resolution threshold while lesions confined to the nucleus rotundus produced permanent threshold elevations. When the destruction of OPT and RT was combined, the deficit was more severe. The results indicated that the integrity of the tectofugal pathway of the pigeon is required for normal performance of spatial frequency discrimination near threshold. These observations suggest that nuclei containing neurons with wide receptive fields are capable of processing visual information with fine spatial detail.

Adaptation, Physiological↗
PubMed1984

Near-field acuity changes after visual system lesions in pigeons. II. Telencephalon.

Pigeons were trained to perform in a psychophysical task that measured their minimum-separable visual acuity. After their performance stabilized, lesions were made in telencephalic components of the visual system. In one group, lesions were made in the ectostriatum, which is the telencephalic target of the tectofugal visual pathway. These cases showed severe to moderate losses of acuity. The magnitude of the loss was correlated with the extent of ectostriatal damage. In another group, lesions were made in the visual Wulst, a portion of which receives the ascending fibers of the thalamofugal visual pathway. Within this group, only lesions that were large and included all components of the visual Wulst were effective in decreasing visual acuity to a moderate degree. A partial correlation analysis indicated that the components of the visual Wulst that were responsible for the acuity changes were the accessory hyperstriatum and the hyperstriatum ventrale. However, lesions that were generally confined to these regions alone were ineffective. Also ineffective were lesions of the granular components of the visual Wulst, which receive the ascending thalamofugal fibers. The results raise questions about the presumed roles of the tectofugal pathway as a background-vision mechanism and the thalamofugal pathway as a fine-detail vision mechanism.

Animals↗
PubMed1984

Retinal-image degradation produces ocular enlargement in chicks.

Two groups of 3-day-old broiler chicks were fitted over the right eye with plastic goggles that degraded the retinal image by producing spherical aberration, reduction of contrast, and blurring of edges. In one group of chicks, the goggles were hemispheric and affected the entire visual field. In the second group, the goggles only affected the frontal visual field. In both groups, the left eye was used as a control. A third group of chicks served as an untreated control group. After 3 weeks, the chicks were killed, the eyes removed, hemisected, and measured in the axial and equatorial planes. Because the avian eye is flattened in the equatorial plane, both sets of measurements are necessary in order to represent changes in its size and shape. The axial length of a laterally located avian eye is related to distance vision. The equatorial length is related to vision in the frontal field, which is used for near vision. For each group of chicks, the difference between the right eye and the left eye was compared. The treated eyes of the full- goggle group were significantly larger than their untreated eyes in both the axial and equatorial dimensions. The treated eyes of the frontal- goggle group differed only in the equatorial dimension. These results suggest that the increased equatorial length found after retinal-image degradation may serve as an animal model of myopia.

Animals↗
PubMed1982

Interactions between components of the avian visual system.

Pigeons were trained to perform in a psychophysical procedure for determining luminance difference thresholds. After the psychometric data had stabilized, lesions were made in specific cell populations of the tectofugal visual pathway. In one group of pigeons, the lesions were confined to nucleus rotundus (Rt). In a second group, the lesions included not only Rt, but also the pars ventralis of the lateral geniculate nucleus (GLv). In the third group, the lesions included Rt, GLv and nucleus subpretectalis (SP). The postoperative performance of the birds in the Rt group showed elevations in threshold that represented substantial losses in sensory capacity. In contrast, the birds with lesions of Rt + GLv showed little or no change in their postoperative thresholds. Finally, the birds in the Rt + GLv + SP group were as impaired postoperatively as the birds with lesions of Rt alone. The results are interpreted in the context of the interaction between components of parallel routes within the tectofugal pathway and parallel pathways within the visual system.

Animals↗
PubMed1982

Properties of the receptive fields of frog retinal ganglion cells as revealed by their response to moving stimuli.

Quantitative mapping of the excitatory receptive fields of frog retinal ganglion cells revealed that the precise spatial position and locus of maximal activity within the excitatory receptive field were dependent upon the exact sequence with which the moving stimulus scanned the region of visual space in which the excitatory receptive field was embedded. A first-order asymmetry dependent upon the direction from which the moving stimulus entered the excitatory receptive field was noted. A second-order asymmetry, orthogonal to the first and sensitive to the direction in which a moving stimulus systematically traversed successive columns with in the excitatory receptive field was also described. These findings indicate that complicated interactions, both excitatory and inhibitory, occur between component parts of the receptive field in the frog retina.

Animals↗
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↗