Introduction

In this first attempt to study supervisory functioning at the encoding and the retrieval stages of memory in a dual task paradigm, a categorized list recall task is chosen as the primary task for the following reasons: First, the recall of categorized lists is one of the paradigms/tasks which has been suggested to involve higher order systems (Moscovitch, 1992ab) and is also the one that has been studied with a dual task design. However, the studies on it have produced contradictory results specifically in relation to the retrieval processes. The findings in regard to the encoding processes of the task are much clearer. Second, the categorized list recall task used in the present study is equipped with an additional feature in order for it to involve a particular type of supervisory processes, that is the verification processes.

As discussed in Chapter 1, the dual task studies which have investigated the processing requirements of the two stages of the categorized list recall task give consistent results as regards the secondary task effect on the encoding processes involved in the task but give inconsistent ones concerning the effect on retrieval. The literature concerning the kind of processes that operate in performing a categorized list recall task have also been discussed in Chapter 2. There it was argued that, in the task of recall of items from different categories presented randomly in a list, the categorical nature of the list material led subjects to use supervisory processes both at encoding and retrieval but in different ways. During encoding, the supervisory systems are assumed to be involved in the organization of the list items into two or more exclusive conceptual categories (memory organization). During retrieval, supervisory systems would be involved in search operations to generate category labels

which are then used to cue the category items. Therefore, it was concluded that a secondary task would interfere with both of the processing stages (encoding and retrieval). However, while some authors have found no effect of a secondary task at retrieval, some others have found that the secondary task interfered with both the encoding and the retrieval processes although the secondary task effect was larger at encoding (see Chapter 1 for the detail of the studies). These contradictory results undermine the assumption concerning the involvement of supervisory systems in the recall of categorized lists. Thus, the present study aimed to reexamine the processing requirements of the two stages of the categorized list recall task.

As was discussed in Section 1.9.2 in Chapter 1, there are some problems in applying dual task methodology and the choice of a secondary task is important in designing dual task experiments. It has been suggested that a secondary task should not be a very demanding task (Moscovitch, 1994a) nor should it be a task that can be performed automatically (Fisk et al, 1986). A card sorting task was selected as the secondary task for the present study. The card sorting task employed by the present study was used before in dual task experiments. As reported in Section 1.9.3 in Chapter 1, Baddeley et al's (1984) study showed that the card sorting task did not interfere with free recall of unrelated words, so it is not a very demanding task. On the other hand the Baddeley et al study also showed that the sorting task had an effect on recall of categorized lists. The categorized list recall task to be used in the present study has got different features than that used by Baddeley et al; these features will be described in the next section.

provides a replication of the first one but there are a number of, mostly, technical differences between the two experimental designs. In addition, the second experiment employs a four choice response task as secondary task. It is assumed that the card sorting task and the four choice response task are essentially similar to each other for they both require manual responses to four random stimuli. Craik et al (1996) employed a four choice response task quite similar to the one used in Experiment 2. As discussed in Section 1.9.3 in Chapter 1, the Craik et al study showed that the four choice response task interferes with free recall of unrelated common nouns.

3.2 Experiment 1

The design of Experiment 1 resembles that of the Baddeley et al (1984) experiment which also employed categorized list recall task. There is a 15 seconds interval between the offset of the presentation of each list and the onset of the list-recall. During this interval subjects were prevented from rehearsing the input material by carrying out a number-repetition task. The aim of using this interval was to diminish the influence of the recall of primary memory representations on the recall-performance of the subjects. It has been pointed out that the use of a distractor task like repetition of numbers appears to be an effective means of preventing rehearsal (Baddeley et al, 1984; Eysenck, 1994). One major different feature of the present experiment was the way in which the category items were distributed across the 14 lists. For each category employed there was not only a group of elements in one list but there was also a single element in each of the four lists presented before it. This distribution of category items is called the ( 1 1 1 1 4/6)-pattern, the four Is correspond to the four single elements in the previous four lists and the 4/6 corresponds to the group of

elements (4 or 6) in the following list (see Figure 3.1).

Figure 3.1 The structure of the word lists

No list 1 list 2 list 3 list 4 list 5

6 6 insects 10 4 relatives

11 1 soft-drinks 6 soft-drinks 12 1 reading materials 4 reading materials

13 1 fish 1 fish 6 fish

14 1 kind of cloths 1 kind of cloths 4 kind of cloths

15 1 type of Music 1 type of Music 1 type of Music 6 type of Music 16 1 military titles 1 military titles 1 military titles 4 military titles

n 1 kitchen utensils 1 kitchen utensils 1 kitchen utensils 1 kitchen utensils 6 kitchen utensils