Differences of Emotional Words in Implicit and Explicit Memory Tests: An ERP Study

Abstract

The previous studies have shown that for negative and positive stimuli, the deep physiological mechanisms are different in the processing of unconscious encoding and retrieval. Nonetheless, the responses to the emotional words in the retrieval phase have shown contradictions in the conscious explicit memory tests. Due to the differences of the encoding tasks and experimental paradigms, however, we cannot attribute the performance differences to stimulus type differences. Therefore, the same task was conducted in the encoding phase to investigate how different emotional stimuli impact the performance in implicit and explicit memory tests. Furthermore, many researchers have proved that the encoding of the emotional words is implicit, and the implicit memory and explicit memory is dissociated, we also want to explore whether the processing of emotional words will influence the implicit or explicit retrieval. An ERP study was conducted to explore the differences between positive words and negative words in implicit and explicit memory tests, adopting the study-test paradigm. 16 right-handed participants were employed in the study. There were three phases in each block: (1) The study phase required the participants to decide whether a word was a noun or an adjective with different key-pressing response. After the study phase, the participants were asked to substract 3 from a 3-digit number shown on the screen.(2) The lexical decision was conducted after the study phase in which participants need to decide the item was a word or a pseudo-word by pressing the keys as soon as possible (3) The recognition test asked the participants to judge whether they had saw the presented word in the study phase and make a key-pressing response. Each stimulus lasted 800 ms, ISI 1100 ± 100 ms. The results showed that negative words were associated with a more positive ERP than positive words in the lexical decision. There was an ERP dissociation of retrieval formats between the implicit and the explicit memory tests during 450~900 ms, that is, there was a significant difference between negative words and positive words in the implicit memory whereas there was no difference between them in the explicit memory. So we can come to the conclusion that the implicit retrieval was sensitive to emotional stimuli while the explicit retrieval was not. The strong attention-grabbing of negative words was shown in the implicit retrieval phase.