Experimental studies with depressed patients

Hedlund and Rude (1995) tested 20 currently depressed, 15 formerly depressed and 18 never depressed individuals with scrambled sentences that permitted a positive or negative solution each (e.g., winner born I am loser a).

Participants were instructed to write down "one meaningful and correct sentence"

per stimulus. Depressed individuals formed significantly more negative sentences than formerly depressed individuals and controls, thus displaying a bias for negative interpretations of ambiguous sentences. However, results could be attributable to

experimenter demand effects, selection or response bias rather than an interpretive bias in depression.

Sheppard and Teasdale (1996) presented incomplete sentences (e.g., If I could always be right then others would _____ me) to depressed patients to differentiate between increased construct accessibility and changes at a more generic level of representation (related to schematic mental models). Construct accessibility hypothesis predicts that depression is associated with more negative completions (e.g., "dislike") while the schematic mental model hypothesis predicts more positive completions (e.g., "like"). This is because schematic models reflect inter-relationships between constructs. In a depressed state, schematic models are activated that imply closer dependence of personal worth or acceptance on success and approval than the models activated in the non-depressed state. Results indicated that depressed patients gave significantly more positive completions to sentence stems than controls. Their interpretations were dysfunctional rather than negatively biased. The authors argued "mood-congruous interpretation bias arises at the level of affect-related schematic models rather than from changes in the accessibility of cognitive constructs" (p. 1050). This study did not use ambiguous stimuli. It seems to tap a different level than interpretation research does, i.e., underlying schemata or underlying fundamental beliefs. Depressed patients responded with dysfunctional, perfectionist sentence completions. In addition, experimenter demand effects and response bias could be alternative explanations for the observed results.

Lawson and MacLeod (1999) studied students scoring low and high on the Beck Depression Inventory (BDI; Beck, Rush, Shaw, & Emery, 1979). In the test stimulus set, 80 ambiguous sentences were paired with two target words, one related to a negative interpretation and one to a neutral interpretation of the ambiguous sentence. For half of the ambiguous sentences, the negative interpretation was related to loss or failure, forming the depression-linked sentence domain (e.g., Carol cried throughout the service), and half to threat or danger (e.g., The two men discussed how to blow up the dingy). Participants were presented with these ambiguous sentences and asked to read them out aloud. Sentences were followed by a negative or neutral target word that had to be named as quickly as possible. Results indicated that "individuals with high BDI scores showed a relative attenuation in the magnitude of the priming effects they displayed on target words related to the more negative interpretations of these ambiguous primes" (p. 472).

There are a number of problems with this study. The mean of the "high BDI group"

was only 9.7. According to the general guidelines from the Center for Cognitive Therapy (CCT) of the University of Pennsylvania Medical School, scores from 0 to 9 are within normal range (asymptomatic), scores from 10 to18 indicate mild to moderate depression, 19 to 29 moderate to severe depression, and 30 to 63 extremely severe depression. Therefore, the "high BDI group" is by no means

"depressed." The authors also found a negative interpretive bias for the low BDI

group. With a mean BDI score as low as 2.5, one also has to wonder how

"representative" this control group actually was. Therefore, this study is insufficient to make any argument about interpretations imposed on ambiguous sentences by depressed patients. Finally, as in all experimental paradigms investigating interpretive processes, the statements were not self-referent.

Mogg et al. (2006) conducted a study with 24 clinically depressed patients currently meeting DSM-IV diagnosis of unipolar depression and a healthy control group matched for gender, age, and years of education. This research was conducted at about the same time as my own studies. It was known to me only after its publication in 2006 and the conclusion of my own research. Mogg et al. applied two of the cognitive tasks mentioned above to investigate an interpretive bias in clinically depressed individuals: the homophone task and the same text comprehension paradigm that I used in my two studies. Self-description and memory bias were also assessed. The material of the homophone task was similar to that used by Mathews, Richards, et al. (1989) for their investigation of GAD patients. The stimuli included 14 homophones (each with a negative and a non-negative meaning, e.g. die/dye) and 14 neutral filler words presented in a tape-recorded list. Participants were asked to listen to each word and write it down.

Depressed patients chose the negative spelling of the homophone in 80.9% of the trials while control subjects chose the negative spelling significantly less frequent in only 63.3% of trials. The authors concluded that depressed patients showed a negative interpretive bias in this cognitive task. In the comprehension task, on the other hand, no such bias was found. 80 experimental sentence sets adopted from materials used by MacLeod and Cohen (1993) and Lawson and MacLeod (1999), as well as additional stimuli created by Mogg et al. (2006) were applied. The structure of the sentence sets was identical to my own material (see the methods section).

Each sentence set included an ambiguous sentence that had one negative meaning and one depression-unrelated meaning. The negative meanings reflected depression-relevant themes of loss, failure, inadequacy, and rejection, e.g., "Carol felt emotional throughout the service". For each ambiguous sentence, there were two disambiguating continuation sentences, one depression-relevant and one neutral/ depression-unrelated continuation (e.g., "Funerals always made her cry"

was the depression-relevant continuation of the ambiguous sentence above while

"Weddings always made her cry" was the neutral continuation. Just as in MacLeod and Cohen (1993) as well as my own studies, three cue conditions were attached to each scenario: a depression-relevant, depression-unrelated and a string of question marks for the uncued condition. Results of Mogg et al. (2006) indicated that participants showed a bias to interpret ambiguous sentences in a neutral or depression-unrelated manner, irrespective of group. Hence Mogg et al. (2006) found a "positive" interpretive bias for ambiguous scenarios in depressed and healthy individuals. The authors discussed this finding and suggested that the non-self-referential manner of the stimulus material may be the most likely explanation

for their inability to detect a negative interpretive bias in clinically depressed individuals. They argue that evidence of cognitive biases in depression were mostly found for explicitly self-referenced information or for information presented in an unconstrained processing context that may allow spontaneous self-referencing. The authors further suggest that this may be an important difference between interpretive biases in anxiety and depression, with self-referencing playing a less important role in interpretive biases in the former.

In summary, there is only weak evidence for a negative interpretive bias in depression stemming from a scrambled sentence paradigm. Results could be due to experimenter demand effects, selection or response bias. One study investigated underlying beliefs or schemata rather than interpretation, and a third study was conducted with students whose mean BDI score did not even reach the mildly depressed range. Finally, Mogg et al. (2006) demonstrated non-convergent evidence for a negative interpretive bias in clinically depressed individuals using two different cognitive tasks. The negative bias in the homophone task may be due to a reporting bias rather than an interpretive bias. However, it is also possible that a negative interpretive bias is only present in self-referential material. The Mogg et al. (2006) study was not yet available to me during the developmental process of my thesis. Overall, considerably more research is necessary to answer the question about the nature of interpretive processes in depression.