Auditory Kappa Effects Can Be Explained by Perceptual Grouping Based on Feature Similarity

Pitch, timing, and space in auditory perception interact, causing changes in one dimension to distort judgments of others (Boltz, 1998; Henry et al., 2009; Jones et al., 2006). The auditory kappa effect exemplifies this, as larger pitch changes between sequential tones create an illusion of longer time intervals (Cohen et al., 1954). Traditionally studied with three-tone sequences (‘A-X-B’), this effect shows that varying the middle tone’s pitch relative to the first and third tones skews time interval perception. The prevailing auditory motion hypothesis (Henry & McAuley, 2009) proposes that a “pitch velocity” is inferred from a consistent pitch trajectory. We tested this against the auditory grouping hypothesis, which proposes that feature similarity affects perceived timing. Experiment 1 tested the kappa effect under varying pitch separations, revealing slower pitch velocities produced larger effects, contradicting the motion hypothesis. Experiment 2 examined inconsistent pitch trajectories to challenge the stability of pitch velocity referents, and still found kappa effects, further supporting the auditory grouping hypothesis. Experiment 3 investigated the kappa effect in auditory space, confirming that sounds presented closer in space are judged as occurring closer in time. These findings suggest that the kappa effect results from the grouping of auditory events by feature similarity, opposing the auditory motion hypothesis.