Experimental evidence of the second signaling system of man

After the first principles of the conditional reflexes had been elucidated by Pavlov and his followers, Pavlov named the neurophysiologic entity common to both animals and men thefirst signaling system. He recognized that man has another signaling system,viz., language, and he proposed that it be named thesecond signaling system. Few experimental studies relating to the second signaling system have been done. Only occasional studies of the effects of spoken language on animals and men, or the effects of spoken language upon EEG and other motor activities of men have been reported. In this paper, the author reports experimental investigation of the second signaling system through the classical conditional salivary method in man, and the development of its methodology.     

Category labels versus feature labels: Category labels polarize inferential predictions

What makes category labels different from feature labels in predictive inference? This study suggests that category labels tend to make inductive reasoning polarized and homogeneous. In two experiments, participants were shown two schematic pictures of insects side by side and predicted the value of a hidden feature of one insect on the basis of the other insect. Arbitrary verbal labels were shown above the two pictures, and the meanings of the labels were manipulated in the instructions. In one condition, the labels represented the category membership of the insects, and in the other conditions, the same labels represented attributes of the insects. When the labels represented category membership, participants’ responses became substantially polarized and homogeneous, indicating that the mere reference to category membership can modify reasoning processes.     

Distinguishing the neural correlates of episodic memory encoding and semantic memory retrieval

Episodic memory and semantic memory interact very closely. In particular, episodic memory encoding (EE) tends to elicit semantic memory retrieval (SR), and vice versa. Thus, similar activations for EE and SR in functional neuroimaging studies may reflect shared memory processes, or they may reflect the fact that EE and SR are usually confounded. To address this issue, we used a factorial functional magnetic resonance imaging approach to disentangle the neural correlates of EE and SR. Within the left temporal lobe, the hippocampus was associated with successful EE, whereas a posterior lateral region was associated with successful SR. Within the left inferior prefrontal cortex, a posterior region was involved in SR, a mid region was involved in both SR and EE, and an anterior region was involved in EE, but only when SR was also high. Thus, the neural correlates of EE and SR are dissociable but interact in specific brain regions.