ISSN:
1432-1106
Keywords:
Subcortical vision
;
Selective attention
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary The present experiments were designed to study the control of visual thresholds in relation to selective attention and goal directed saccadic eye movements in human subjects. The results demonstrate that visual thresholds increase by about 0.5–1 log unit when targets are repeatedly presented in the periphery of the visual field while the subjects are fixating. The diameter of the adapted area and the amplitude of the threshold elevation increase with retinal eccentricity but do not depend on other stimulus parameters such as target size or target luminosity. Irrespective of target size the diameter of the adapted field is in the range of 5 ° close to the fovea and reaches up to 20 ° in the visual field periphery. This elevation of detection thresholds can be reset either by adapting a mirror symmetric area in the contralateral visual field or by directing a saccadic eye movement towards a target which is presented in an area mirror symmetric to the adapted field. When saccades are performed in the absence of the target stimulus or when they are directed towards targets outside the mirror symmetric area no resetting occurs. Adaptation is further prevented when the subject is allowed to saccade towards the adapting target. Measurements in patients with cortical hemianopia indicate, that these phenomena are mediated by subcortical visual centers since they can be influenced by stimulation in the blind hemifield. Participation of subcortical centers, especially of the tectum, is further suggested by the numerous correlations between the present psychophysical observations and the available neurophysiological data on subcortical visual pathways. It is concluded that it is one of the functions of the retino-tectal system to determine detection thresholds in a retinotopically organized way and to guide visual attention towards particular areas within the visual field. The observations in hemianopic patients suggest that these operations are accomplished in parallel to cortical analysis and remain functional after striatal lesions. They are, however, inaccessible to conscious experience.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00237040
