Harvard Psychological Studies, Volume 1 eBook

This eBook from the Gutenberg Project consists of approximately 757 pages of information about Harvard Psychological Studies, Volume 1.

The occipital centers which mediate sensations of color are of course most closely associated with those other centers (probably the parietal) which receive sensations from the eye-muscles and which, therefore, mediate sensations which furnish space and position to the sensations of mere color.  Now it is these occipital centers, mediators of light-sensations merely, which the experiments have shown most specially to be anaesthetic.  The discharge of such centers means particularly the passage of excitations on to the parietal localization-centers.  There are doubtless other outlets, but these are the chief group.  The movements, for instance, which activity of these cells produces, are first of all eye-movements, which have to be directly produced (according to our present psychophysical conceptions) by discharges from the centers of eye-muscle sensation.  The principal direction of discharge, then, from the color-centers is toward the localization-centers.

Now the experiment with falsely and correctly localized after-images proves that before the anaesthesia all localization is with reference to the point of departure, while afterwards it is with reference to the final fixation-point.  The transition is abrupt.  During the anaesthesia, then, the mechanism of localization is suffering a readjustment.  It is proved that during this interval of readjustment in the centers of eye-muscle sensation the way is closed to oncoming discharges from the color-centers; but it is certain that any such discharge, during this complicated process of readjustment, would take the localization-centres by surprise, as it were, and might conceivably result in untoward eye-movements highly prejudicial to the safety of the individual as a whole.  The much more probable event is the following: 

Although Schwarz suggests that the moment between seeing the false and seeing the correct after-image is the moment that consciousness is taken up with ‘innervation-feelings’ of the eye-movement, this is impossible, since the innervation-feelings (using the word in the only permissible sense of remembered muscle-sensations) must precede the movement, whereas even the first-seen, falsely localized streak is not generated till the movement commences.  But we do have to suppose that during the visual anaesthesia, muscle-sensations of present movement are streaming to consciousness, to form the basis of the new post-motum localization.  And these would have to go to those very centers mentioned above, the localization-centers or eye-muscle sensation centers.  One may well suppose that these incoming currents so raise the tension of these centers that for the moment no discharge can take place thither from other parts of the brain, among which are the centers for color-sensations.  The word ‘tension’ is of course a figure, but it expresses the familiar idea that centers which are in process of receiving peripheral stimulations, radiate that energy to other parts of the brain

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Harvard Psychological Studies, Volume 1 from Project Gutenberg. Public domain.
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