William Hodos

Progressive ratio as a measure of reward strength.

Four rats were trained to press a lever on a ratio schedule of reinforcement in which the number of lever presses required on each consecutive run increased by a fixed increment. Both concentration and volume of the reward were varied. Relationships were obtained between reward and deprivation variables and the size of the final completed ratio run.

Head Orientation in Pigeons: Postural, Locomotor and Visual Determinants

We have determined the pigeons head orientation for two postures and two locomotor activities that do not involve a specific visual stimulus. Using a high-speed cine camera, we filmed four pigeons (Columba livia) while (1) flying, (2) walking, (3) perching and (4) standing on a flat surface. Under these conditions, the head orientation is relatively constant, allowing us to estimate the normal horizon of the visual field and thus the horizontal meridian of the retina. Measurements of the lateral semicircular canal showed that the canal is tilted slightly up with respect to the horizon in the head orientation determined by the film analysis. In contrast to their relatively stable head posture during locomotion, the pigeons consistently altered their head orientation when presented with seed targets, apparently to fixate each seed with a small portion of the visual field around the bill tip.

A Stereotaxic Atlas of the Brain of the Pigeon (Columbia livia)

FOREWORD The problems of evolution rank among mankinds most enduring interests, and it is therefore not surprising that virtually every branch of biology and medicine has ramified in the direction of comparative studies. Although in neurology this search traditionally has been an intensive one, a lack of adequately refined techniques has long held comparative neurology confined largely within the limits of normal anatomical description. The technological scene has changed rapidly over the last few decades, and the contemporary neurologist finds an instrumentarium of unprecedented refinement available: microelectrode recording techniques, sensitive quantitative chemical methods, greatly improved techniques for both normal descriptive and experimental anatomical studies, histochemical and embryological techniques hardly dreamed of by earlier generations of neurobiologists. In the monumental writings of Edinger, the Herricks, Cajal, Ariens Kappers, Huber, Crosby and their colleagues he will find a rich store of anatomical information on the vertebrate brain, but it will not take him long to identify the great problems of interphyletic homology, both in structure and function, that have remained unresolved. Almost certainly, new insights in these problems are in store for all who venture a fresh approach by the aid of modern methods. Brain research over the years has drawn huge profits not only from a progressive refinement of physiological, chemical, and histological techniques. It owes an important part of its success to the development of accurate stereotaxic methods, spatial guides without which only few deep-lying brain structures could have been explored adequately. The appearance of this stereotaxic atlas of the pigeon brain by Drs. Karten and Hodos is therefore a source of promise and expectation. The authors, as the user will find, have succeeded in achieving standards of accuracy that match those of the best atlases used in research on the mammalian brain. Their thorough search of the available literature has extended the value of this work well beyond its primary purpose of being a practical guide in experimental research. It has also become a most useful source of general orientation in the organization of the avian brain. But no matter what its present virtues, one cannot wish this work a better fate than that of future revisions in which the currently widely accepted but unavoidably neutral labels that identify so many structures, especially in the forebrain, can be replaced or augmented by ever more meaningful indications of structure and function. ACKNOWLEDGMENTS The authors wish to gratefully acknowledge the assistance, …

Brightness and pattern discrimination deficits in the pigeon after lesions of nucleus rotundus

SummaryPigeons were trained to peck one of two discs on which were projected visual stimuli. One brightness and three pattern discrimination problems were presented. Correct responses were rewarded with grain. After the discriminations were learned, bilateral electrolytic lesions were placed stereotaxically in 13 birds, and sham operations were performed in three birds. Those birds with lesions in nucleus rotundus demonstrated severe deficits in performance of the visual discriminations. Following prolonged post-operative retraining, a gradual return to pre-operative levels of performance was observed. The post-operative relearning proceeded at a much slower rate than the pre-operative learning. Control birds with lesions in dorsal thalamus, telencephalon and mesencephalon, or sham operations, all showed considerable post-operative savings. On the basis of the anatomical, electrophysiological and behavioral data available at present, nucleus rotundus appears to be a thalamic relay of visual information from optic tectum to telencephalon in the bird.

Lower-field myopia in birds: An adaptation that keeps the ground in focus

In the lower visual field of pigeons, a myopia (near-sightedness) has been reported that progressively increases with the angle below the horizon. Previous data suggested that this lower-field myopia may be an adaptation that permits pigeons to keep the ground in focus while they forage, and simultaneously, to monitor the horizon and sky for predators. We report here a lower-field myopia in other species of birds that have a wide range of heights. A geometric model of this adaptation predicts that the amount of myopia should be systematically related to the distance from the pupil to the ground. The eyes of quail, chickens and cranes of various heights (7.0-104.1 cm) were refracted at 60 deg below the horizon. Their myopia was close to the predicted value at each height.

Spatial contrast sensitivity of birds

Contrast sensitivity (CS) is the ability of the observer to discriminate between adjacent stimuli on the basis of their differences in relative luminosity (contrast) rather than their absolute luminances. In previous studies, using a narrow range of species, birds have been reported to have low contrast detection thresholds relative to mammals and fishes. This was an unexpected finding because birds had been traditionally reported to have excellent visual acuity and color vision. This study reports CS in six species of birds that represent a range of visual adaptations to varying environments. The species studied were American kestrels (Falco sparverius), barn owls (Tyto alba), Japanese quail (Coturnix coturnix japonica), white Carneaux pigeons (Columba livia), starlings (Sturnus vulgaris), and red-bellied woodpeckers (Melanerpes carolinus). Contrast sensitivity functions (CSFs) were obtained from these birds using the pattern electroretinogram and compared with CSFs from the literature when possible. All of these species exhibited low CS relative to humans and most mammals, which suggests that low CS is a general characteristic of birds. Their low maximum CS may represent a trade-off of contrast detection for some other ecologically vital capacity such as UV detection or other aspects of their unique color vision.

Reduction in choroidal blood flow occurs in chicks wearing goggles that induce eye growth toward myopia

Goggles that degrade the retinal image produce axial enlargement of the ocular globe and large myopic refractive errors. Many authors have assumed that visual image degradation itself leads to myopia. Hodos and co-authors have shown, however, that goggled eyes in chicks are considerably warmer than normal. Such temperature changes may either underlie or be a consequence of alterations in choroidal blood flow (CBF). Since alterations in CBF could affect eye growth, we explored the effect of monocular goggling on CBF in chicks. Plastic goggles were glued over one eye in four-day old chicks and the goggles were left in place for 12 or 14 days. Fourteen days after the goggling, CBF was measured using laser Doppler velocimetry. Three groups of chicks were studied: 1) chicks with goggles for 14 days; 2) chicks with goggles for 12 days followed by no goggles for the two days; 3) age matched non-goggled chicks. A -scan ultrasonography confirmed that the visual deprivation produced vitreous chamber elongation in the goggled eye and that the degree of elongation for the goggled eye was the same for the two goggled groups. The results were: 1) blood flow in non-goggled chicks was similar in both eyes; 2) blood flow was significantly reduced in the goggled eye in chicks wearing goggles for 14 days- 37% of control; and 3) blood flow was still significantly reduced in the goggled eye in chicks whose goggles were removed two days before measurement- 51% of control. These results show that CBF is reduced by goggles that result in myopic eye growth.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Reversal learning in pigeons: Effects of selective lesions of the Wulst

The effects of bilateral lesions of individual laminae of the Wulst on reversal-learning performance in pigeons were evaluated. After surgery, the birds were trained to perform a simultaneous color discrimination. Once successful discrimination was achieved, the positive and negative stimuli were reversed, and the birds were again trained to criterion. Twenty such reversals were carried out. A multiple regression analysis indicated that those components of the Wulst that were critical for increasing the numbers of errors on each reversal were the laminae that receive the thalamofugal visual projections, that is, the nucleus intercalatus of the hyperstriatum accessorium and the hyperstriatum dorsale. Lesions in the other laminae of the Wulst (the hyperstriatum accessorium and the hyperstriatum intercalatus superior) had no effect on errors. There was no evidence of an increase in either perseverative errors or position habits in the birds with lesions, which suggested that the reversal deficits were not likely to be due to perseveration, attentional impairment, or inappropriate processing of spatial information. The deficit may have been produced by excessive interference between learning in a given session and learning in previous sessions.

Visual Intensity and Pattern Discrimination Deficits after Lesions of the Optic Lobe in Pigeons; pp. 165–179

Pigeons were trained to discriminate stimuli that differed in luminance or geometric pattern. Following discrimination training, bilateral stereotaxic lesions were made in the optic tectum and in the associated nuclei isthmi, located within the depth of optic lobe. In some cases the nuclei isthmi were destroyed with only minimal injury to the tectal strata. After recovery from surgery, the discrimination performance of the birds was again tested. Cases with massive destruction of the optic tectum and either direct or indirect damage to the nuclei isthmi showed extremely severe postoperative deficits in visual discrimination performance. Some cases were unable to reliably discriminate gross stimulus differences even after extensive postoperative retraining. Others eventually were able to perform the simpler discrimination tasks, but failed to recover their preoperative performance capabilities on the more difficult discrimination tasks. Cases with injury confined principally to the nuclei isthmi had less impairment of performance than the ones with injury to the tectum and the isthmic nuclei. In general, the results of this study suggested that lesions of the optic tectum in pigeons produced more severe and intractable deficits of visual discrimination performance than did lesions of structures more rostral in the tectofugal pathway (i.e. nucleus rotundus or ectostriatum). The data further suggest a separate role of the nuclei isthmi in the processing of visual information. The implications of the results for the understanding of the evolution of the vertebrate visual system are discussed.