Teoría de la Carga Cognitiva (TCC)

As described in section 2.2.5.1.2, it is assumed tasks vary in their demands on cognitive resources, and that performance reflects the resources invested in the task. Based on this premise, Tyler, Hertel, McCallum and Ellis (1979) explored the effect of different

encoding processes on performance. They concluded increased effort at encoding leads to higher recall. Studies have compared the performance of depressed and nondepressed Ss on tasks which vary effort during encoding, and also during retrieval.

2.3.5.1 Clinical Samples

Structuring material during encoding or retrieval is an effortful strategy likely to improve recall. Studies have found control Ss are more likely than depressed Ss to recall words in clustered form even when they are presented in unclustered form (Backman & Forsell, 1994; Koh, Kayton & Berry, 1973, Experiment 1; Russell & Beekhuis, 1976; Calev & Erwin, 1985; Weingartner, Cohen, Murphy, Martello & Gerdt, 1981, Experiment 3), with two exceptions (Calev et al., 1986; Silberman, Weingartner, Targum & Byrnes, 1985). Watts and Cooper (1989) assessed recall of a prose passage and included an internal comparison of story-units that differed in how central they were to the gist. Depressed Ss failed to show the usual superior recall of the central aspects, suggesting a failure to use structure to organise the stories.

Other studies have considered the relationship between depression and performance on tasks where the degree of organisation or structure has been manipulated by the experimenter, and these have produced conflicting results. Two studies used approximation to text as a means of manipulating task structure (Levy & Maxwell, 1968; Manschreck et al., 1991). Ss are presented with a series of word-lists that at one extreme form a normal sentence, and at the other consist of random words. An example of intermediate approximation to text would be, "They saw the play Saturday and sat down beside him." Both studies compared depressed, schizophrenic and control Ss on free recall. Levy and Maxwell (1968) found all three groups had equivalent recall of less structured material, but depressed and schizophrenic Ss showed less benefit from increasing approximation to text. However, since the word-lists were presented to all Ss in order of increasing level o f contextual constraint, this finding may be explained by fatigue effects. In contrast, Manschreck et al. (1991) found no significant differences between depressed and control subjects on any measure, in fact the depressed group performed marginally better, and this could not be explained in terms of group differences in age, sex or education.

controls in their recall of a word-list when there was no structure to the list, or when the structure was not immediately apparent, but achieved similar levels of recall when the word-list was highly structured. Tancer, Brown, Evans, Ekstrom, Haggerty et al. (1990) compared depressed patients with a group of psychiatric patients of mixed diagnosis and found the depressed Ss to be significantly impaired in their recall of a list of random words, but no different when the list consisted of categorised words clustered together. However, since Ss always received the clustered list first this finding, like that of Levy and Maxwell (1968), may be due to the effects of fatigue.

Watts, Dalgleish, Bourke and Healy (1990) studied both approximation to text and clustering by semantic categories, and found while depressed Ss showed an overall decrement in performance, this did not interact with structure. Exploratory post-hoc analyses suggested the groups differed more on medium than low levels of structure. Watts et al. (1990) suggested materials of medium structure might be more sensitive to memory deficits in depression than very unstructured materials because the latter do not repay efforts to restructure them. Support for this hypothesis was found by Channon et al. (1993a). Depressed and nondepressed Ss were compared on their retrieval of high, medium and low structured material, using word-lists consisting of uncategorised words and categorised words presented in randomised and clustered order. The depressed Ss were found to be impaired only on the medium level o f structure (randomised categories list). Backman and Forsell (1994) compared performance on word-lists equivalent to the low and medium structured lists described by Channon et al. (1993a). They found depressed Ss were equally impaired on both lists, showing no benefit from the structure available in the medium list, while the controls showed significant improvement on the medium relative to the low structured condition. The authors do not report whether the group difference was significantly greater in the medium structure condition, so it is not clear whether this was actually more sensitive to depression. Finally, Brown et al. (1994) compared depressed and normal control Ss on three word-lists of similar structure to those of Channon et al. (1993a) and found depressed Ss to be impaired overall compared with controls. However, both groups showed the same pattern of performance, with recall highest on the medium structured list and lowest on the list of random words.

It has been suggested (Repressed Ss may impose organisation during encoding, but may not take advantage of this at retrieval. Russell and Beekhuis (1976) found depressed,

schizophrenic and normal control Ss did not differ in their initial categorisation of a list of nouns, but the recall and clustering of both patient groups was inferior to that of the controls at retrieval. Weingartner et al. (1981, Experiment 2) reported depressed patients imposed more organisation than controls when instructed to sort random words into categories, but then recalled fewer, although they were equivalent to controls in their recall of a list of related words.

Weingartner and his colleagues also found evidence of depressive deficits in recalling semantically processed material Weingartner et al. (1981, Experiment 1) reported when Ss were instructed to produce either a semantically related or an acoustically related response to each of a series of stimulus words, depressed Ss were impaired relative to controls in their recall of semantically but not acoustically processed words. Roy-Byme, Weingartner, Bierer, Thompson and Post (1986, Procedure 1) found depressed Ss to be impaired relative to nondepressed Ss in their ability to recall noun-pairs after making comparative judgements about them. Silberman, Weingartner, Laraia, Byrnes and Post (1983) instructed Ss to rate the emotional impact of a list of words counterbalanced with respect to high versus low emotionality and concreteness. While there was no group difference in word-ratings, depressed Ss were impaired in their retrieval of the material on both recognition and free recall tasks. Group differences were greater for free recall of high concrete-emotional words, and for recognition of low concrete-emotional words. Thus, the depressed Ss benefitted from salient stimulus qualities less than normals in free recall, and more than normals in recognition. The authors concluded low impact material (low concrete emotional) was not stored with strong enough traces to be retrieved, even in the recognition condition, while high impact (high concrete-emotional) was processed deeply enough for recognition, but not free recall.

This review indicates a proliferation of studies, resulting in complex and often contradictory findings. There is evidenceRepressed Ss differ from nondepressed Ss in performance on this type of task, with most studies finding significant group differences. The exact nature of these differences is less clear-cut. The hypothesis that depressed Ss make less use of encoding and retrieval strategies such as structuring, organisation and clustering of material is supported, although whether these deficits occur at encoding, retrieval or both remains to be fully investigated. The relationship between depressive deficits and degree of structuring has proved difficult to identify, with authors arguing

materials with high (Levy & Maxwell, 1968), medium (Channon et al., 1993a; Watts et al., 1990) and low (Weingartner et al., 1981, Experiment 3) structure are most sensitive to depressive deficits. It is possible that for each study, the material with the highest pay­ off in terms of improved recall resulting from effort expended in encoding or retrieval strategies will be most sensitive to depressive deficits. This needs further investigation.

2.3.5.2 Nonclinical Samples

Few studies have investigated the use of encoding and retrieval strategies in nonclinical samples. The findings have been mixed, with two studies (Hasher & Zacks, 1979, Experiment 4; Potts, Camp & Coyne, 1989) finding evidence of group differences, and two studies (Hertel & Rude, 1991a, Experiment 3; Kwiatkowski & Parkinson, 1994) finding no group differences. Hasher and Zacks (1979, Experiment 4) compared dysphoric and nondysphoric students, selected on the basis of the BDI, on their ability to recall a list of words. Ss were presented with a recognition test consisting of the studied words, semantic and acoustic associates of the studied words, and unrelated words. Dysphoric Ss chose fewer incorrect semantic associates than the controls, suggesting less semantic processing of the studied words. Potts et al. (1989) compared dysphoric and control students on their recall of target words from simple and elaborated sentences. They found control Ss recalled more elaborate sentences than simple, while dysphoric Ss recalled equal numbers of both, but there was no overall difference in level of recall. Hertel and Rude (1991a, Experiment 3) presented dysphoric and nondysphoric students with a series of incomplete sentences, and asked them to judge whether a word presented simultaneously would fit sensibly into the sentence. Half were judged to be easy and half difficult. It was predicted dysphoric Ss should be differentially impaired in their recall of the more difficult items, but in fact no group differences were found on any of the task measures. Kwiatkowski and Parkinson (1994) found no differences between dysphoric and control students in their recall of target words from simple and elaborated sentences.