According to the model, the effects of irrelevant dimensions in Type 3 and Type 4 ensembles are mediated by two separate stages: the response production stage for Type 3, and the stimulus identification stage for Type 4. The model postulates that these stages are additive (cf. Sternberg, 1969). If these overlap properties are now combined in a Type 7 ensemble, performance with Type 7 should be predictable from the individual performances with Type 3 and Type 4 ensembles.
The stimuli consisted of the colors blue, green, and grey, presented in the upper, lower, left, or right half of a rectangle. There were four words: BLUE, GREEN, NOVEL, ELBOW, and a five-letter string. Left/Right key presses were the responses. The relevant stimulus was color; position, word, and letter string were all irrelevant.
FOUR KINDS OF TRIALS:
Neutral (Type 1 ensemble): the colors were presented in the upper or lower half of the rectangle, the irrelevant words were NOVEL or ELBOW.
Simple SR overlap (Type 3 ensemble): colors were presented in the left or right half of the rectangle; words were NOVEL or ELBOW. This combination produced two SR consistent and two SR inconsistent trials.
Simple SS overlap (Type 4 ensemble): Colors presented in the upper or lower half of the rectangle, words were BLUE or GREEN. This produced two SS consistent and two SS inconsistent trials.
Composite SS/SR overlap (Type 7 ensemble):Colors were presented in the left or right half of the rectangle, the words were BLUE or GREEN. This combination produced two SS/SR consistent trials, and two SS/SR inconsistent trials. There were also two SS/SR “Hybrid Trials” in which the word conflicted with the color, but the side matched the response.
The nature of the irrelevant stimulus was indicated by a prime which preceded the actual stimulus by either 0 or 200ms.
For the irrelevant word, the word was presented in the rectangle before the color was. For irrelevant positions, that half of the rectangle in which the color would eventually appear was filled with grey, which was subsequently replaced by a color. Both irrelevant dimensions, word and position, were present in all trials and were displayed in the manner just described.
Simple SS overlap, & Simple SR overlap:
pure blocks (each for SS and SR) = 1/3 consistent, 1/3 inconsistent, and 1/3 neutral.
mixed blocks (SS mixed with SR) = 1/6 SS consistent, 1/6 SS inconsistent, 1/6 SR consistent, 1/6 SR inconsistent, 1/3 neutral.
Composite SS/SR overlap:
SS/SR overlap: 1/6 SS/SR consistent, 1/6 SS/SR inconsistent,
1/3 SS/SR hybrid trials – with half being SS consistent and the other half being SS inconsistent, 1/3 neutral.
In simple pure and mixed blocks, there was practically no consistency effect for SS overlap at lag zero; however, at lag 200 it was 48 ms. In contrast, the consistency effect for SR overlap was 40 ms. at lag zero, and 32 ms. at lag 200.
In composite SS/SR blocks, the consistency effect for SR overlap at zero lag was 36 ms. and practically non-existent for SS overlap. However, at lag 200 ms. SS overlap had a consistency effect of 53 ms. and SR overlap was 17 ms.
The results make it very clear that the processing of irrelevant stimulus dimensions differs greatly depending on whether they overlap with the relevant stimulus (Type 4), or with the response (Type 3). These differences also interact with lag, (the nature of this interaction is well accounted for by the computational form of the DO model).