Detecting surface changes in a familiar tune: exploring pitch, tempo and timbre.

Humans recognize a melody independently of whether it is played on a piano or a violin, faster or slower, or at higher or lower frequencies. Much of the way in which we engage with music relies in our ability to normalize across these surface changes. Despite the uniqueness of our music faculty, there is the possibility that key aspects in music processing emerge from general sensitivities already present in other species. Here we explore whether other animals react to surface changes in a tune. We familiarized the animals (Long-Evans rats) with the "Happy Birthday" tune on a piano. We then presented novel test items that included changes in pitch (higher and lower octave transpositions), tempo (double and half the speed) and timbre (violin and piccolo). While the rats responded differently to the familiar and the novel version of the tune when it was played on novel instruments, they did not respond differently to the original song and its novel versions that included octave transpositions and changes in tempo.

Beat perception in polyrhythms: Time is structured in binary units.

In everyday life, we group and subdivide time to understand the sensory environment surrounding us. Organizing time in units, such as diurnal rhythms, phrases, and beat patterns, is fundamental to behavior, speech, and music. When listening to music, our perceptual system extracts and nests rhythmic regularities to create a hierarchical metrical structure that enables us to predict the timing of the next events. Foot tapping and head bobbing to musical rhythms are observable evidence of this process. In the special case of polyrhythms, at least two metrical structures compete to become the reference for these temporal regularities, rendering several possible beats with which we can synchronize our movements. While there is general agreement that tempo, pitch, and loudness influence beat perception in polyrhythms, we focused on the yet neglected influence of beat subdivisions, i.e., the least common denominator of a polyrhythm ratio. In three online experiments, 300 participants listened to a range of polyrhythms and tapped their index fingers in time with the perceived beat. The polyrhythms consisted of two simultaneously presented isochronous pulse trains with different ratios (2:3, 2:5, 3:4, 3:5, 4:5, 5:6) and different tempi. For ratios 2:3 and 3:4, we additionally manipulated the pitch of the pulse trains. Results showed a highly robust influence of subdivision grouping on beat perception. This was manifested as a propensity towards beats that are subdivided into two or four equally spaced units, as opposed to beats with three or more complex groupings of subdivisions. Additionally, lower pitched pulse trains were more often perceived as the beat. Our findings suggest that subdivisions, not beats, are the basic unit of beat perception, and that the principle underlying the binary grouping of subdivisions reflects a propensity towards simplicity. This preference for simple grouping is widely applicable to human perception and cognition of time.

Non-human animals detect the rhythmic structure of a familiar tune.

The musical motives of a song emerge from the temporal arrangement of discrete tones. These tones normally have few durational values, and are organized in structured groups to create metrical patterns. In the present study we show that the ability to detect the rhythmic structure of a song, while ignoring surface changes, is also present in other species. We familiarized rats (Rattus norvegicus) with an excerpt of the Happy Birthday song. During test, we presented the animals with (i) the same excerpt of the familiarization, (ii) a constant-pitch version of the excerpt that reduced melodic intervals to only one tone (i.e., isotonic) but preserved rhythmic structure, and (iii) a rhythmically scrambled version of the excerpt that preserved the melodic intervals. The animals discriminated the rhythmically scrambled version from the versions that preserved the original rhythm. This demonstrates that rats were sensitive to at least some parts of the rhythmic structure of the tune. Together with previous findings, the present set of results suggests that the emergence of rhythmic musical universals might be based on principles shared with other species.

Discrimination of temporal regularity in rats (Rattus norvegicus) and humans (Homo sapiens).

The perception of temporal regularities is essential to synchronize to music and dance. Here, we explore the detection of isochrony in two mammal species. We trained rats (Rattus norvegicus) and humans (Homo sapiens) to discriminate sound sequences with regular intervals from sound sequences with irregular intervals using a go/no-go paradigm. We used four different tempi in the training sessions and two new tempi in the tests. We found that both rats and humans responded more to the novel regular test sequences than to the novel irregular test sequences. Differently from previous studies with birds, rats seem to have focused on the relative duration of the sounds, which means that they paid attention to global features defining the regularity of the sequences. In sum, this study suggests that detecting temporal regularities in sequences of sounds may have ancient evolutionary roots and could rely on timing mechanisms present in distantly related mammals. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Ternary meter from spatial sounds: Differences in neural entrainment between musicians and non-musicians.

The present study explores the relationship between the rhythmic structure of music and the spatial dimension of sound. We study how the brain interacts with spatially-separated sounds to build up a metrical structure. Participants listened to sequences of isochronous sounds that came from different positions on the azimuth plane: 0° (control condition), ±30°, ±60° or ±90° (spatial conditions). Ternary meter was signaled by the alternation of one sound on one side and two sounds on the symmetrical side. In Experiment 1, musicians and non-musicians paid attention to the spatial sounds. In Experiment 2, participants paid attention to a visual distractor. We recorded their electroencephalograms and performed frequency-tagging analyses. In both experiments, the isochronous beat elicited steady-state evoked-potentials at the frequency of the beat (2.4 Hz). While in Experiment 1 the alternation produced clear responses at the frequency of the ternary meter (0.8 Hz), in Experiment 2 these responses were only significant in the Spatial 90° condition, and mainly in musicians. This suggests that top-down attentional mechanisms are in play for meter induction. Besides, musicians showed stronger responses to beat and meter than non-musicians, suggesting that formal musical training enhances the neural entrainment to spatially-defined rhythms.

Look at the Beat, Feel the Meter: Top-Down Effects of Meter Induction on Auditory and Visual Modalities.

Recent research has demonstrated top-down effects on meter induction in the auditory modality. However, little is known about these effects in the visual domain, especially without the involvement of motor acts such as tapping. In the present study, we aim to assess whether the projection of meter on auditory beats is also present in the visual domain. We asked 16 musicians to internally project binary (i.e., a strong-weak pattern) and ternary (i.e., a strong-weak-weak pattern) meter onto separate, but analog, visual and auditory isochronous stimuli. Participants were presented with sequences of tones or blinking circular shapes (i.e., flashes) at 2.4 Hz while their electrophysiological responses were recorded. A frequency analysis of the elicited steady-state evoked potentials allowed us to compare the frequencies of the beat (2.4 Hz), its first harmonic (4.8 Hz), the binary subharmonic (1.2 Hz), and the ternary subharmonic (0.8 Hz) within and across modalities. Taking the amplitude spectra into account, we observed an enhancement of the amplitude at 0.8 Hz in the ternary condition for both modalities, suggesting meter induction across modalities. There was an interaction between modality and voltage at 2.4 and 4.8 Hz. Looking at the power spectra, we also observed significant differences from zero in the auditory, but not in the visual, binary condition at 1.2 Hz. These findings suggest that meter processing is modulated by top-down mechanisms that interact with our perception of rhythmic events and that such modulation can also be found in the visual domain. The reported cross-modal effects of meter may shed light on the origins of our timing mechanisms, partially developed in primates and allowing humans to synchronize across modalities accurately.