Influence of loudness on sound categorization and recognition

Results based on a pairwise comparison task have shown how the perceptual timbre of the same sounds is affected when sounds were presented either with a non-normalized loudness - sounds were assigned to a specific SPL corresponding to their level in an everyday life context - or with a normalized loudness - sounds were equalised (Susini et al. , 2015). The number of dimensions of the MDS Euclidean spaces obtained in both cases was different: two dimensions, one of which correlated with the level difference between sounds, for the non-normalized condition, and three dimensions for the normalized condition. It looks like participants were unable to attend selectively to several timbre dimensions when loudness is varying across the sounds. Similarly, several categorization studies based on sorting tasks have shown that the groupings of sounds are mostly related to the SPL of the sounds. In the present study, results of two sorting tasks re- spectively with sounds presented either with a non-normalized loudness or with a normalized loudness were compared. Groupings of non-normalized sounds were based solely on the difference in sound pressure level, although sounds were mixed with one another in a more diverse way when they were normalized in loudness. One possible explanation is that dimensions are processed with different priorities, and loudness with a ”stronger” priority. A legitimate question there- fore arises: Is loudness part of a sound recognition process? Thus the influence of loudness on sound recognition was investigated in an explicit memory experiment based on a conscious recollection - test phase - of previously encoded information - study phase. Results revealed a significant study-to-test loudness change effect: loudness change between the study and the test phases affects recognition. The effect was strong in different experimental conditions suggesting that loudness seems to be an important hint for everyday sounds recognition.