Interference and independence in the perception of pitch and brightness

Perception of pitch (defined by fundamental frequency, F0) and brightness (mainly affected by spectral centroid, Fc) has been suggested to be interdependent. However, the encoding mechanism of such interdependence is unclear. One hypothesis suggests that, while F0 and Fc are encoded separately, the direction of change in one feature tends to be confused with that of the other. Another hypothesis argues that F0 and Fc are encoded in a single, or at least overlapping, perceptual dimension. We conducted two experiments to disentangle these two hypotheses. First, participants were asked to make an up-down judgment in pitch or brightness as F0 and Fc varied congruently or incongruently. We found that congruent changes in F0 and Fc led to better discrimination, whereas incongruent changes led to worse discrimination, consistent with both hypotheses. Second, participants were asked to judge if there was a change, regardless of feature or direction, when only one feature varied, both varied congruently, or both varied incongruently. We found that variations in both features simultaneously were easier to detect than variations in only one feature, but there was no significant difference between the congruent and incongruent variations, arguing against the second hypothesis. [Work supported by NIH grant R01 DC005216.]