Adaptation to Rhythmic Auditory Stimuli

Reference: Tecchio, F., C. Salustri, M.H. Thaut, P. Pasqualetti, P.M. Rossini. Experimental Brain Research (2000) 135:222-230. Conscious and preconscious adaptation to rhythmic auditory stimuli: a magnetoencephalographic study of human brain responses.

Review: the aim of this study was to identify the degree to which subjects could consciously distinguish and adapt to variations in the rhythmic occurrence of brief tones. The inter stimulus intervals (ISI) varied from 2%-20% from a central value. Subjects consciously detected the 20% ISI changes whereas they never consciously detected the 2% ISI changes, yet they always correctly adjusted their tapping to them. Subjects were required to tap their fingers in synchrony with a rhythmic metronome sequence spontaneously adjusting their tapping to perturbations of the rhythm frequency even when these perturbations are so small as to be undetectable consciously (Thaut et al. 1998 mentioned in Tecchio et al. 2000).
For this study they used MEG to investigate the response of the human auditory cortex to incoming rhythmic stimuli. The aims were to basically measure the response of the auditory cortex to auditory stimuli that were randomly administered in a series with small differences in variations of ISI. This was to identify whether brain responses involved in the sensory stimulus are linked to conscious or preconscious motor synchronization to the dispatched rhythm. (basically tapping to a tone that varied from the steady repetition by 2-20%).
Results: All subjects counted the ISI changes correctly when their variation was 20% of the central frequency. In no case were they able to identify the 2% ISI changes. Yet they were able to quickly adjust (within 1-2 motor responses ) to the new ISI, both at the 20% and 2% variation. Results confirm from other studies which suggest conscious and preconscious tuning to rhythm changes.
The findings suggest that rhythmic discrimination is at least in part taking place at the auditory cortical level and that the auditory cortex may contribute directly to synchronize the motor output ( Tecchio et al.). Also suggested is that the local sensory memory is characterized by a sensitivity of at least 2% in the 2hz rhythmicity (60bpm).
Their findings prove that the auditory cortex identifies changes even when they are not consciously recognized.

Reflection: I found this study and discussion to be fascinating in terms of how quickly and accurately (within a small number of ms) humans can adjust and match pulses which vary from a central rhythm. There was not any discussion that I am aware of that looked for differences between trained musicians’ and novices’/untrained musicians’ responses. It is also fascinating that humans are this accurate at auditory perception. I am referring to the fact that subjects had no visual cues. When a band speeds up or slows down in live performance or live recording, there are usually visual and auditory cues to pick up on. An important distinction is implied between the terms unconscious/subconscious and preconscious: it seems to me that the authors use the term preconscious since there is a physical awareness of changes in the pulses, but not cognitive – high brain - awareness. Also, I am going out on a limb by stating that stimulus-response research at this level was outside the realm of Freudian ideas (I am trying to be funny here).