Stroop Interference Based on the Synaesthetic Qualities of Auditory Pitch

The equivalence of perceptual experience across the sensory modalities, most vividly observed in synaesthetes, is rarely discussed in contemporary cognitive psychology. It is suggested, however, that the concepts and paradigms of human information processing are ideally suited to test, for example, the fundamental assumption that the synaesthetic qualities of a stimulus are rapidly and automatically encoded. In a preliminary experiment subjects were asked to rate each of four auditory tones on a series of 7-point scales defined by pairs of antonyms. The results confirmed that a pure auditory tone has a range of qualities, determined by its pitch, that are shared by stimuli in other modalities. The main experiment used a paradigm based on the Stroop interference effect. Here the 50 Hz and 5500 Hz tones served as incidental stimuli and the subjects were required to respond as quickly as possible by pressing one of two keys depending on which one of four possible words appeared in the centre of the screen. Subjects were found to respond more slowly when the qualities of the tone were incongruent with the synaesthetic qualities represented by the test word. The results confirm that synaesthetic qualities of pitch are rapidly and automatically encoded and that the products of this encoding automatically interact with the mechanisms responsible for identifying word meaning and/or with the post-identification decision processes.