Dimensional Representations of Dysphoria

To analyze depression as a continuous phenomenon operationalized as operating on a continuum of dysphoria rather than as a dichotomous variable, multiple regressions were performed using the difference in reaction times to positive vs. negative, neutral vs. negative, and positive vs. neutral words (the same differences as were coded for the meta-analysis) as dependent variables, and BDI, GBI, or MAACL scores as continuous independent variables, along with gender, for the 150ms SD condition.

Together BDI and gender accounted for only 1.8$\%$ of the variation in the negative vs. neutral contrast on the valence-identification task, F(2,133)=1.2, p=.303. A one unit change in BDI produced only a -1.05 ms change in the differential reaction time, t(133)=-.33, p=.74. Similarly, BDI and gender accounted for only 3.0$\%$ of the variation in the positive vs. neutral contrast, F(2,133)=2.04, p=.133, with a one unit change in BDI associated with a non-statistically significant 5.3 ms change in the rt difference, t(133)=1.71, p=.09. Together BDI and gender accounted for 4.3$\%$ of the variation in the positive vs. negative contrast, F(2,133)=2.98, p=.05. A one unit change in BDI was associated with a statistically significant 6.3ms change in the difference in reaction times, t(133)=2.38, p=.01. While changes on the order of 4-6ms may appear quite small, especially with reference to the low amount of the total variation in RT they account for, it is suggested that they may still be important given the rapid pace of neural events.

Together BDI and gender accounted for 3.3$\%$ of the variation in negative vs. neutral times on the lexical decision task, F(2,133)=2.24, p=.11. A one unit change in BDI was associated with a 2.75ms change in the reaction time difference, t(133)=1.84, p=.068. BDI and gender accounted for 2$\%$ of the variation in the difference between positive and neutral reaction times, with a one unit change in BDI uniquely associated with a 1.3ms change in the reaction time difference, t(133)=.675, p=.501. BDI and gender accounted for a .80$\%$ of the variation in the positive vs. negative contrast, with a one unit change in BDI being associated with a -1.4ms change in the reaction time difference, t(133)=-.755, p=.45. Thus, BDI was not, in general associated with large changes in reaction time differences. Potentially, this fact is due to the notorious unreliability of difference scores. Alternately, individual variation on the lexical decision task may play a larger role than may be found in such aggregate analysis. To emphasize this point, Figure 7, p. 71, depicts reaction time differences as a function of BDI for the lexical decision and valence identification tasks.

 

Figure  7.: Reaction times for lexical decision and valence identification tasks, 150ms condition, as a function of BDI score

Similar results were obtained for the other measures of mood. For example, performance on the three GBI scales (Depressed, Manic, and Biphasic) and gender together accounted for only 3.5$\%$ of the variation in the negative vs. neutral contrast on the valence identification task. No individual scale was associated with a statistically significant change in the reaction time difference. GBI and gender accounted for only 2$\%$ of the variation in the positive vs. neutral contrast. They did account for 7.8$\%$ of the variation in the positive vs. negative contrast, F(4,131)=2.79, p=.02, though this value is not statistically significant when $\alpha$ is controlled at the .016 level to account for the three tests using the GBI variables. Additionally, none of the GBI variables accounted for greater than a 2ms change in the reaction time difference on this measure. Similarly, GBI scales and gender together never accounted for more than 5$\%$ of the variation in any of the lexical decision difference scores.

The small amount of variation in lexical decision performance accounted for by measures of depression suggest that other factors are responsible for governing delays on this task. Perhaps rumination itself, independent of depression, could account for some of this variation.