William Hodos - US grants

The purpose of the proposed research is to develop a model of myopia that could be used to evaluate treatment techniques for ultimate application to humans. Our preliminary experiments have indicated that defocus of the retinal image in domestic chicks for the first three weeks of life results in an increase in the diameter of the globe of the eye that is suggestive of myopia. The specific aims of the proposed research are to replicate our preliminary findings using more precisely defined optical devices and then to use behavioral techniques to assess the degree of myopia. The myopia will be calculated from a comparison of the far point of accommodation in treated and untreated chicks. Visual acuity and intensity difference thresholds will be determined in order to assess whether the defocussing procedure has produced impairments of visual information processing either in the retina or centrally. If myopia is present in the chicks, an attempt will be made to correct the defect by interposing an optometric trial lens between the cornea and the target. Finally, an attempt will be made to evaluate the hypothesis that a cause of myopia is intensive and prolonged inspection of the spatial properties of visual stimuli close to the near point of accommodation by comparing the eyes of untreated subjects in visual acuity tests with the eyes of another group of chicks that have had equivalent experience with a test of comparable difficulty, but in which the spatial properties of the stimulus are irrelevant. The advantages of such a model are (1) very low expense, (2) very rapid development and (3) suitability for the evaluation of mechanical and surgical treatments for myopia, such as orthokeratosis, radial keratotomy, keratomileusis, hydrogel lenticular implantation, etc.

The long term objectives of the proposed research are: (a) to develop a model of the functional organization of the vertebrate visual system based on comparative data from the fields of neuroanatomy, neurophysiology and neuropsychology; (b) to apply the theories and techniques of human psychophysics and scaling, information processing and perception to the animal laboratory to make use of the powerful quantitative and analytical advantages of these methods; (c) to gain a deeper understanding of the mechanisms by which specific cells groups in the vertebrate visual system, especially those that are common to most vertebrates, process visual information; (d) to exploit certain morphological and behavioral advantages that birds offer over non-human mammalian models to investigate structure-function relationships. The ultimate goal of this research is to apply the findings to a better understanding of the human visual system with a particular view towards the amelioration of visual deficits that result from injury to its central processing mechanisms.

The long term objectives of the proposed research are: (a) to develop a model of the functional organization of the vertebrate visual system based on comparative data from the fields of neuroanatomy, neurophysiology and neuropsychology; (b) to apply the theories and techniques of human psychophysics and scaling, information processing and perception to the animal laboratory to make use of the powerful quantitative and analytical advantages of these methods; (c) to gain a deeper understanding of the mechanisms by which specific cells groups in the vertebrate visual system, especially those that are common to most vertebrates, process visual information; (d) to exploit certain morphological and behavioral advantages that birds offer over non-human mammalian models to investigate structure-function relationships. The ultimate goal of this research is to apply the findings to a better understanding of the human visual system with a particular view towards the amelioration of visual deficits that result from injury to its central processing mechanisms.

LAY ABSTRACT

Proposal ID: IBN-9818054

Principal Investigator: William Hodos

Information Processing in the Avian Visual System


The visual system is one of our most important sensory systems. A powerful methodology to determine how the visual system functions is to use the comparative approach; i.e., to study the visual system in different animals. As in all vertebrates, the avian visual system consists of two principal pathways: the thalamofugal pathway and the
tectofugal pathway. The proposed research will use sophisticated methods of visual analysis (the contrast sensitivity function) and selective lesions in the visual thalamus to determine the extent to which the thalamofugal pathway processes spatial information.
Previous studies with weaker methods have not revealed deficits in spatial vision after lesions of this pathway. The tectofugal pathway, terminates in the medial and lateral regions of the ectostriatum, a region of the telencephalon. The experiments will use stimuli that differ in their spatiotemporal properties to determine whether the medial and lateral regions of ectostriatum are functionally distinct regions.

A dictum of the comparative method is that if one wants to know how a system works, study it in a specialist. The two major visual specialists among the vertebrates are primates and birds. Because birds and primates are not closely related, their most recent common ancestor being among the early reptiles, these two groups have developed their exquisite visual systems relatively independently, but most likely by a common mechanism. Whatever information can be gained from the study of the avian visual system will add to our understanding of the general mechanisms by which visual systems
evolved among vertebrates.