A further experimental analysis of the behavioral deficit that follows injury to the primate frontal cortex

The results of these experiments show that when the situation is made ambiguous in one manner—i.e., by increasing the number of alternatives of choice—the frontal injury has no effect and the lesions do modify behavior when the ambiguity of the situations is increased by making the relationships between stimuli and response variable unreliable.

Abstract

The results of seven experiments that use monkeys are reported. Behavior is examined in modifications of the Yerkes or Wisconsin General Testing Apparatus and in operant conditioning situations. The focus of the studies is the effect on behavior of removal of the frontal eugranular isocortex; unoperated controls and controls with the inferotemporal cortex removed serve as background to the studies. The first two experiments test whether the effects of frontal lesions are restricted to the visual or the somatic sensory mode. The results show that they are not. The next two experiments test whether the effects of the lesion are similar to changes in behavior produced by starvation. Again the results show that there is no similarity. However, the experiment that follows reveals an intersting finding: Monkeys with frontal lesions do not react as do the controls when the test apparatus runs out (deliberately) of rewards. The final pair of experiments explore further the conditions over which this altered behavior can be demonstrated. The results of these experiments show that when the situation is made ambiguous in one manner—i.e., by increasing the number of alternatives of choice—the frontal injury has no effect. On the other hand, the lesions do modify behavior when the ambiguity of the situation is increased by making the relationships between stimuli (cueing or reinforcing) and response variable, i.e., unreliable.