Biomedical subjects
Publications and source records attributed to K A Macko.
Normative data are reported for the visual acuity, luminance-difference threshold and size-difference threshold of pigeons (Columba livia). The mean visual acuity was 12.66 c/deg or 2.53 min (N = 54), the mean log luminance-difference threshold was 0.11 (N = 105) and the mean size-difference threshold was 0.94 mm (N = 20).
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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.
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.
The [2-14C]deoxyglucose method was used to identify the cerebral areas related to vision in the rhesus monkey (Macaca mulatta). This was achieved by comparing glucose utilization in a visually stimulated with that in a visually deafferented hemisphere. The cortical areas related to vision included the entire expanse of striate, prestriate, and inferior temporal cortex as far forward as the temporal pole, the posterior part of the inferior parietal lobule, and the prearcuate and inferior prefrontal cortex. Subcortically, in addition to the dorsal lateral geniculate nucleus and superficial layers of the superior colliculus, and structures related to vision included large parts of the pulvinar, caudate, putamen, claustrum, and amygdala. These results, which are consonant with a model of visual function that postulates an occipito-temporo-prefrontal pathway for object vision and an occipito-parieto-prefrontal pathway for spatial vision, reveal the full extent of those pathways and identify their points of contact with limbic, striatal, and diencephalic structures.
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.