Abstract:

Unitization refers to the manipulation that can integrate two or more items into a single entirety. Previous studies found that unitization facilitated associative memory, however, the effect of unitization on item memory was controversial. Some researchers argued that unitization promoted associative recognition at the cost of item recognition (the view of “benefits and cost”), others held that unitization could promote associative recognition without impairing item recognition (the view of “benefits-only”). These two views seemed to be arguing the impact of unitization on item memory, but in fact, they were discussing the relationship between associative encoding and item encoding during unitization.

The present study intended to explore the relationship between associative encoding and item encoding in the process of unitization through two experiments, by examining the effects of words unitization and characters unitization on associative memory and item memory as well as the differences of neural mechanisms between the two unitization strategies. In experiment 1 (Figure 1), we used associative recognition paradigm to explore the unitization effects on associative memory. In the study phase, participants were asked to judge whether the character pairs could form to a multiple-component character (characters unitization) or a compound word (words unitization) or couldn’t (non-unitization). In the test phase, participants were asked to judge whether the character pairs were same or rearranged. In experiment 2, item recognition paradigm was used. Procedure of the study phase was the same as Experiment 1. In the test phase, characters instead of character pairs learned or not learned in the study phase were displayed on the screen. Participants were asked to judge whether the characters were old or new. In addition, EEG signals were recorded during the task to explore the neural mechanism during memory encoding.

The behavioral results showed that: i) the encoding process of characters unitization was more difficult and had longer response time compared to words unitization; ii) the performances of associative recognition was significantly higher for the words and characters unitization conditions than the non-unitization condition (characters (M ± SD): 0.75 ± 0.15, non-characters: 0.26 ± 0.18, t = 14.50, p < 0.001; words: 0.67 ± 0.15, non-words: 0.40 ± 0.20, t = 8.51, p < 0.001), and their performances of item recognition was not decreased; iii) the performances of associative recognition (characters: 0.75 ± 0.15, words: 0.67 ± 0.15, t = 2.94, p = 0.006) and item recognition (characters: 0.50 ± 0.14, words: 0.41 ± 0.13, t = 5.23, p < 0.001) was significantly higher for the characters unitization condition than words unitization condition. The EEG results showed that: iv) the LNC during words unitization encoding was mainly distributed in the frontal area and occurred earlier than characters unitization encoding, while the LNC during characters unitization encoding was mainly located in the occipital area and occurs later than words unitization encoding (Figure 2); v) the desynchronization of neural oscillation within α/β band was stronger for characters unitization condition compared to words unitization condition (Figure 3), and the desynchronization of neural oscillation within α/β band during encoding was significantly correlated with the hit of item recognition during retrieval (Figure 4).

These results indicate from the perspectives of memory encoding and retrieval that the manipulation of unitization does not damage the processing of items while strengthening the processing of associative information, supporting the view of “benefits-only”. This research has deepened our understanding that the brain processes multiple-component Chinese characters and compound words, and also provided a reference for the arrangement of Chinese learning materials from the perspective of empirical evidence.

Key words: item encoding, associative encoding, multiple-component characters, compound words, item memory, associative memory