Hearing objects move: apparent motion in complex sounds

How can we perceive objects as moving based on auditory information? This information is often not continuous, such as when objects are temporarily masked by other, louder objects. To perceive these auditory objects as moving along a continuous path, rather than as one object disappearing and another one reappearing, we need to establish correspondence between the correct object instances, resulting in an auditory apparent motion percept of only one object moving across space. However, correctly linking the object instances that belong to the same object is challenging, as auditory input is often ambiguous, such as when several objects follow overlapping trajectories. Previous studies with visual objects have shown that correspondence is influenced by spatiotemporal factors and object features, such as the color, size or shape. Recent studies have shown that correspondence in the auditory modality also depends on spatiotemporal and even feature information, i.e., the frequency of simple sinewave tones. This study aimed to determine whether this finding generalizes to more complex sounds that are meaningful to us and which may involve higher levels of processing. To test this idea, we created an ambiguous apparent motion display biased with sounds from two different musical instruments, a piano and a guitar. Additionally, we manipulated spatiotemporal information. Our results demonstrate that the auditory feature bias, which was previously observed with sinewaves, extends to complex sounds. Furthermore, spatiotemporal factors had a weaker influence on correspondence for complex than for simple sounds. This suggests that auditory correspondence might involve different types of correspondence mechanisms.