Perception of Nigerian Dùndún Talking Drum Performances as Speech-Like vs. Music-Like: The Role of Familiarity and Acoustic Cues

It seems trivial to identify sound sequences as music or speech, particularly when the sequences come from different sound sources, such as an orchestra and a human voice. Can we also easily distinguish these categories when the sequence comes from the same sound source? On the basis of which acoustic features? We investigated these questions by examining listeners’ classification of sound sequences performed by an instrument intertwining both speech and music: the dùndún talking drum. The dùndún is commonly used in south-west Nigeria as a musical instrument but is also perfectly fit for linguistic usage in what has been described as speech surrogates in Africa. One hundred seven participants from diverse geographical locations (15 different mother tongues represented) took part in an online experiment. Fifty-one participants reported being familiar with the dùndún talking drum, 55% of those being speakers of Yorùbá. During the experiment, participants listened to 30 dùndún samples of about 7s long, performed either as music or Yorùbá speech surrogate (n = 15 each) by a professional musician, and were asked to classify each sample as music or speech-like. The classification task revealed the ability of the listeners to identify the samples as intended by the performer, particularly when they were familiar with the dùndún, though even unfamiliar participants performed above chance. A logistic regression predicting participants’ classification of the samples from several acoustic features confirmed the perceptual relevance of intensity, pitch, timbre, and timing measures and their interaction with listener familiarity. In all, this study provides empirical evidence supporting the discriminating role of acoustic features and the modulatory role of familiarity in teasing apart speech and music.

Listening to birdsong reveals basic features of rate perception and aesthetic judgements

The timing of acoustic events is central to human speech and music. Tempo tends to be slower in aesthetic contexts: rates in poetic speech and music are slower than non-poetic, running speech. We tested whether a general aesthetic preference for slower rates can account for this, using birdsong as a stimulus: it structurally resembles human sequences but is unbiased by their production or processing constraints. When listeners selected the birdsong playback tempo that was most pleasing, they showed no bias towards any range of note rates. However, upon hearing a novel stimulus, listeners rapidly formed a robust, implicit memory of its temporal properties, and developed a stimulus-specific preference for the memorized tempo. Interestingly, tempo perception in birdsong stimuli was strongly determined by individual, internal preferences for rates of 1-2 Hz. This suggests that processing complex sound sequences relies on a default time window, while aesthetic appreciation appears flexible, experience-based and not determined by absolute event rates.

The molecular receptive range of an olfactory receptor in vivo (Drosophila melanogaster Or22a)

Understanding how odors are coded within an olfactory system requires knowledge about its input. This is constituted by the molecular receptive ranges (MRR) of olfactory sensory neurons that converge in the glomeruli of the olfactory bulb (vertebrates) or the antennal lobe (AL, insects). Aiming at a comprehensive characterization of MRRs in Drosophila melanogaster we measured odor-evoked calcium responses in olfactory sensory neurons that express the olfactory receptor Or22a. We used an automated stimulus application system to screen [Ca(2+)] responses to 104 odors both in the antenna (sensory transduction) and in the AL (neuronal transmission). At 10(-2) (vol/vol) dilution, 39 odors elicited at least a half-maximal response. For these odorants we established dose-response relationships over their entire dynamic range. We tested 15 additional chemicals that are structurally related to the most efficient odors. Ethyl hexanoate and methyl hexanoate were the best stimuli, eliciting consistent responses at dilutions as low as 10(-9). Two substances led to calcium decrease, suggesting that Or22a might be constitutively active, and that these substances might act as inverse agonists, reminiscent of G-protein coupled receptors. There was no difference between the antennal and the AL MRR. Furthermore we show that Or22a has a broad yet selective MRR, and must be functionally described both as a specialist and a generalist. Both these descriptions are ecologically relevant. Given that adult Drosophila use approximately 43 ORs, a complete description of all MRRs appears now in reach.