This paper expands and revises some of the details of the architectural and processing aspects of the process model. It also reports the results of five four-choice experiments that used Types 1, 2, and 3 ensembles. For this summary only the first two experiments are included.
Because S-R compatibility is determined by the interaction, and not by the independent effects of stimulus and response attributes, we used two sets of stimuli: letters, and left/right hand icons with index and middle fingers extended; there were also two sets of responses: verbal letter names, and key presses. Each stimulus set was combined with each of the two response sets, one of which it overlapped with, and the other with which it did not overlap. This resulted in four ensembles: two with DO (hand icons/key presses, and letters/letters names), and two without DO (hand incons/letter names, and letters/keypresses). Any performance differences between these ensembles, therefore, cannot be attributed to either the stimulus or the response set, since both are represented in both ensembles: the ensembles with DO and the one without DO. Such difference must, therefore, be the result of the presence/absence of DO. This is the underlying logic of the experimental design of these experiments.
The two sets of stimuli were visually presented. In the case of the hand icon, the stimulus to be responded to was indicated by placing an asterisk in one of the extended fingers. In the case of the letter stimuli these were presented on the screen. For the ensemble with DO (i.e. letters/letter names & hand icons/keypresses), one mapping was congruent, the other incongruent. For the ensemble without DO, the mapping was random.
The ensemble with DO had a mapping effect of 203 ms. The ensemble without DO a had a mapping effect of 15ms. (which was barely significant). These results join others that conform to the predictions of the model. Given the logic of the design, the non-DO ensemble is an appropriate neutral condition for comparison, and according to the model should fall between the congruent and incongruent RT – which it does.
In terms of stimuli and responses, Experiment 2, with one exception, is identical to Experiment 1: instead of indicating the finger with an asterisk, the finger is indicated with a letter. That is, regardless of condition, the stimulus always consisted of a hand icon with a letter in a fingertip. Like in Experiment 1, there were two response sets: key-presses, and letter names. Depending on which stimulus dimension was relevant (finger or letter), the responses were to be made either according to the identity of the finger, making finger the relevant stimulus, (and to ignore the letter), or according to the letter on the finger tip, making letter the relevant stimulus (and ignore the finger). Each stimulus set was mapped onto each response set, thus yielding four SR ensembles of which two were Type 2, and two were Type3.
Mapping A associated a finger stimulus, that had been identified by a letter, to a key – the letter was to be ignored,. Mapping C associated a letter that had appeared in one of the finger tips, to a letter name – the finger was to be ignored. In mappings A and C the relevant stimuli overlapped with the responses, thus producing SR Ensembles Type 2, with DO. SR assignments were congruent or incongruent.
Mapping B associated a finger stimulus to a letter name – the letter was to be ignored. Mapping D associated a letter stimulus that had appeared in a finger, to a finger – the finger was to be ignored. With mapping B and D, the relevant stimuli did not overlap with the responses, but the irrelevant stimuli did, thus producing SR Ensembles Type 3. Two different SR assignments were used for mappings B and D.
In terms of relevant stimulus dimension, Experiments 1 and 2 are identical. In terms of irrelevant dimensions they differ in that there were no irrelevant stimuli in Experiment 1.
The mean mapping effect (congruent minus incongruent RT) for overlapping ensembles (mapping A and C), is identical to what it was in Experiment 1: 203 ms. The mean “mapping effect” (RT for mapping 1 minus RT for mapping 2) for non-overlapping ensembles (B and D), is zero. In Experiment 1 it was 15 ms. and barely significant. Both mapping effects thus confirm the predictions of the model, and replicate the data of our own and other experiments. In addition, because of the choice of stimulus and response sets, these results clearly reflect the interaction between the stimulus and response sets and not the effects of these sets by themselves – which was the object of this experiment.
One of the model’s predictions is: Given an ensemble with overlap between the irrelevant dimensions and the response, the RT for SR consistent trials will be faster than for SR inconsistent trials – where “SR consistent” trials is the case where the irrelevant stimulus and the response have an attribute in common, and “SR inconsistent” trials is where no such common attribute exists. For example, in this experiment “consistent” is when hand icon is the irrelevant stimulus, and key presses is the response to letters. The RT for SR consistent trials is 50 ms. faster than for inconsistent trials, confirming the model’s prediction.