Spectral and temporal cues for perception of material and action categories in impacted sound sources

In two experiments, similarity ratings and categorization performance with recorded impact sounds
representing three material categories (wood, metal, glass) being manipulated by three different categories
of action (drop, strike, rattle) were examined. Previous research focusing on single impact
sounds suggests that temporal cues related to damping are essential for material discrimination, but
spectral cues are potentially more efficient for discriminating materials manipulated by different
actions that include multiple impacts (e.g., dropping, rattling). Perceived similarity between material
categories across different actions was correlated with the distribution of long-term spectral
energy (spectral centroid). Similarity between action categories was described by the temporal distribution
of envelope energy (temporal centroid) or by the density of impacts. Moreover, perceptual
similarity correlated with the pattern of confusion in categorization judgments. Listeners tended to
confuse materials with similar spectral centroids, and actions with similar temporal centroids and
onset densities. To confirm the influence of these different features, spectral cues were removed by
applying the envelopes of the original sounds to a broadband noise carrier. Without spectral cues,
listeners retained sensitivity to action categories but not to material categories. Conversely, listeners
recognized material but not action categories after envelope scrambling that preserved long-term
spectral content.