Abstract:

Many previous studies have explored the relationship between retrieval interference and explicit memory by comparing memory performance in the divided-attention condition with that in the full-attention condition. However, relatively few studies have discussed the effect of target detection on explicit memory during retrieval in dual-task situations by comparing a target detection condition, in which participants carry out a recognition task and press the spacebar simultaneously when a target appears, with a distractor rejection condition, in which participants perform the same recognition task and do not respond when they see a distractor. Because the detection of a target requires more attention than the rejection of a distractor, an interesting question remains as to whether target detection and distractor rejection have different influences on recognition memory.

Sixty undergraduate students (30 students in experiment 1 and 30 students in experiment 2) participated in this study. A study-test (encoding/recognition) paradigm was adopted, and the participants were required to perform a shallow/deep encoding task with two-character Chinese words as stimuli. They were then asked to conduct a target detection task and an old/new recognition task simultaneously in the retrieval phase. For the target detection task, in experiment 1, the participants were instructed to press the spacebar (overt detection); in experiment 2, the participants were instructed to perform a counting operation (covert detection) when they detected the target (a “+”) rather than the distractor (a “-”). The participants were told that the recognition task and the target detection task were equally important. They were asked to perform both tasks as quickly and as accurately as possible. The reaction time (RT) and accuracy data in the retrieval phase were recorded and analyzed by analysis of variance.

The results showed that in experiment 1 (the keypress response task) and experiment 2(the counting response task), regardless of the kind of processing was required (i.e., shallow or deep processing), the reaction times for the old words were significantly shorter in the target condition than in the distractor condition, and the accuracy scores for recognizing the old words were significantly higher in the target condition than in the distractor condition, indicating that explicit memory retrieval was regulated by the participants' available attention resources. However, for the new words, we found the exactly opposite phenomenon: the reaction times were significantly longer in the target condition than in the distractor condition, and the accuracy scores were also significantly lower in the target condition than in the distractor condition. More importantly, we calculated the sensitivity index (d′) and decision criterion (C) established by signal detection theory. The participants' sensitivity indexes showed no significant variations between the target condition and the distractor condition, but the mean values of the decision criteria decreased in the target condition when compared to those in the distractor condition.

The results revealed that detecting a target in the explicit memory retrieval phase did not boost the retrieval of words but decrease participants' decision criteria. Participants responded in a more liberal way in the target condition than in the distractor condition, and the effects of target detection on explicit memory retrieval may not be affected by the depth of processing and different reaction modes. Thus, explicit memory retrieval was also modulated by the available attention resources and, therefore, was not wholly automatic.

Key words: attentional boost effect, target detection, memory retrieval, dual task