Speech acoustics can be modulated by cognitive interference in a vowel-modified Stroop task

How are speech acoustics influenced by cognitive processes? In the current study, we used a novel variant of the Stroop test to measure whether the interference between color naming and reading could modulate vowel formant frequencies. Seventeen healthy participants named the color of words in three categories: (1) congruent words (e.g., “red” written in red), (2) color-incongruent words (e.g., “green” written in red), and (3) vowel-incongruent words with phonetic properties that partially matched their color (e.g., “rid” written in red). We hypothesized that the cognitive effort needed to inhibit reading—saying “red,” not “rid”—could affect vowel acoustics. For example, the correct spoken response (“red”) could more acoustically resemble the inhibited word “rid;” alternatively, the vowel could be influenced in the opposite direction, resembling “rad,” which would serve to accentuate the acoustic contrast between the spoken and inhibited words. As expected, participants were slower to produce words on color-incongruent trials than on congruent trials. Interestingly, vowel-incongruent trials were not significantly slower than congruent trials, but preliminary acoustic analyses of the first formant (F1) showed that some subjects systematically modulated their productions in the presence of incongruent vowels. This finding lends insight into how the brain integrates multiple pieces of information to produce speech.