Cross-modal Tasks are a type of choice reaction time task that use structural overlap between stimulus dimensions of different sensory modalities. As a result, there is dimensional overlap between the irrelevant stimulus and the relevant stimulus, but no dimensional overlap with the responses. In the dimensional overlap taxonomy, these are considered to be Type 4 tasks. Other Type 4 tasks include the Flanker task and the Stroop-like task.
Robert Melara and Lawrence Marks (1990; Marks, 1987; Melara, 1989) are two of the first to study stimulus-stimulus consistency effects using cross-modal tasks. In a typical cross-modal task, subjects are told to press a left key or a right key depending on the brightness of a stimulus light. In conjunction with the stimulus light, subjects hear a tone of either a high or a low pitch, or a loud or a soft volume. The stimulus dimensions of brightness, pitch, and volume are not perceptually similar, and no specific level of brightness has an associative link with any particular pitch or loudness of sound. However, all of these dimensions can be rank-ordered from “low” to “high” along a continuum. As a result, the relationship between the elements of the relevant stimulus set (high and low brightness) and the relationship between the elements of the irrelevant stimulus set (high or low pitch or volume) allows them to be paired. Thus, although the tone is irrelevant to the task, it can be either consistent (e.g. a bright light paired with a loud sound) or inconsistent (e.g. a bright light paired with a soft sound) with the light. Responses are faster and more accurate for consistent stimuli than inconsistent stimuli.
This type of task validates the generality of the dimensional overlap theory. If the stimulus-stimulus consistency effect only appeared in Flanker tasks, a theory could be proposed that the effect was caused directly by a perceptual mechanism. If the stimulus-stimulus consistency effect only appeared in Stroop-like tasks, a theory could be put forth that was based on individual learned associations (such as the learned association between a color and its color word). The fact that the effect appears in cross-modal tasks, however, demonstrates that it is truly the dimensional overlap–in the most abstract sense–between the two stimulus dimensions that is key to the appearance of the consistency effect.