The Absolute Threshold of Vision in Cat and Man With Observations on Its Relation to the Optic Cortex

Absolute threshold of vision in the rat after removal of striate cortex.

“…The lesioned Ss of both experiments reach a chance level of performance at a higher light intensity than do control Ss. In this respect the results are in close agreement with the report of Bridgman and Smith (1942) and it could be concluded that the threshold to light has been directly affected. However, there are several reasons for not accepting this conclusion.…”

“…If there was at least one log step difference in threshold between lesioned and control rats, it would seem reasonable to assume a departure from the baseline level at a higher intensity for the Ss without striate cortex. These considerations, as well as the reports of Gunter (Weizkrantz, 1961) and Kliiver (1942), do not support the contention of Bridgman and Smith (1942) that the striate cortex is directly involved in determining the absolute threshold to light. Possibly a closer analysis of Bridgman and Smith's data would, like the present experiments, indicate that the loss is attributable to some other factor.…”

“…The aim of the present study was also to determine the effects of striate cortex removal on the absolute threshold to light. It is similar in design to that of Bridgman and Smith (1942) except that rats were used. In addition, to investigate the effects of visual neocortex removal on retention of the light-dark discrimination habit utilized, pre-as well as postoperative training was given in one experiment.…”

On the Reported Inhibition of Monoamine Oxidase by an Agent with Sedative Properties

“…Bridgman and Smith (6), however, have shown that with brightness discriminations at or near threshold levels in the cat, the striate cortex is involved and thus is essential for critical performance at these levels. Hence, if the chiasmal and callosal sections are complete in the animals reported here, the present results indicate that a simple, suprathreshold brightness discrimination is transferred by undetermined subcallosal commissures.…”

Photochemistry of Vision

“…Several behavioural experiments have shown that the absolute threshold of the cat is between 5 and 10 times lower than that of man (BRIDGEMAN and SMITH, 1942;GUNTER, 1951), and WEALE believes that this difference can be accounted for by the tapetum. The optical power of the cat's eye is also greater than man 's, and according to V AKKUR and BISHOP (1963) the retinal image of a given object, when the pupil is maximally dilated, will be 5.2 times brighter in cat than man.…”