Relative contribution of pitch and brightness to the auditory kappa effect

Pitch height is known to interfere with temporal judgment. This is the case in the auditory kappa effect in which the relative degree of pitch distance separating two tones extends the perceived duration of the inter-onset interval (IOI). However, pitch variations which result from manipulations of the fundamental frequency of tones are associated with variations of the spectral centroid, which is related to the perceived brightness. The present study aimed at determining the relative contribution of pitch and brightness to the auditory kappa effect. Forty-eight participants performed an AXB paradigm (tone X was shifted to be closer to either tone A or B) in three conditions: the three tones varied in both pitch and brightness (PB condition), pitch varied but brightness was fixed (P condition) or brightness varied but pitch was fixed (B condition). Pitch and brightness were modified by manipulating the fundamental frequency (F0) and the spectral centroid of the tones, respectively. In each condition, the percentage of trials in which the first IOI was perceived as shorter increased as X was closer (in pitch and/or brightness) to A. Furthermore, the magnitude of the effect was larger in PB than in P condition, while it did not differ between PB and B conditions, suggesting that brightness would contribute more than pitch height to the auditory kappa effect. This study provides the first evidence that auditory brightness interferes with duration judgment and highlights the importance to consider jointly the role of pitch height and brightness in future studies on auditory temporal processing.