Tracking Musical Patterns using Joint Accent Structure

Canadian Journal of Experimental Psychology, Dec 1997 by Mari Riess Jones, Peter Q Pfordresher

Apparatus and Stimulus Generation

All melodies were created using the 5.0 version of the MIDILAB software package (Todd, Boltz, & Jones, 1989) an IBM PC compatible computer interfaced by a Roland MPU401 MI Processing unit that controlled a Yamaha TX81Z FM Tone Generator set to the "Pan Flute" voice (patch B12). The MIDILAB package allows for the construction of sound patterns, their organization into blocks of trials, and the recording of participant responses. The sound signal was transmitted to a separate experimental room and amplified using a Rane HC-6 Headphone console. Each participant listened to patterns over AKG-K270 headphones, at a comfortable listening level. Instructions were recorded and played over a cassette recorder.

Tapping responses were produced on a box that included a central "home base" pad surrounded by four optical sensors arranged in a semicircle. Participants were permitted to tap that optical sensor at the most comfortable distance from the preferred finger of their dominant hand; they had to use the same sensor throughout, however. Between taps, participants were told to rest their finger on the home base.

Procedure

Each trial consisted of a single pattern presented twice; the second pattern occurred one second after the first and was raised an octave. A trial began with a high pitched warning tone; a C-major triad then signaled the onset of each pattern within a trial.

The experimental session was divided into five blocks. The first block, a practice block, consisted of 12 trials including both melodic control patterns and joint-accented patterns. For these trials, a new set of melodies was constructed in which the melodic contour points were exaggerated in relation to experimental patterns, with the aim of insuring that listeners were primed to attend to contour as well as temporal accents. This was achieved by increasing the interval skip by one scale step (avoiding the tonic) for the existing inflection points. Melodies al and d2 were used. Temporal structure was not similarly exaggerated. Data from these trials were not analysed.

Blocks 2 and 3 consisted of 20 joint accented patterns each: concordant and discordant patterns were randomly intermingled, with the constraint that no more than two trials of one accent structure or melody type followed in succession. Across these two blocks, each of the concordant and discordant versions of the four melodies (al-d2) were presented. In block four, temporal and baseline controls were randomly intermingled within 15 trials, followed by 10 melodic control trials. Block five consisted of 10 melodic control trials followed by 15 temporal and baseline control trials. Both temporal controls and the monotone baseline melody were presented 10 times per subject, whereas each of the melodic control melodies was presented 5 times per participant.

During a trial, the participants were instructed to "hear out" accents during the first presentation of the sound pattern. An accent was defined as "any tone that stands out from the others around it." They were told to listen for between five and fifteen accents per pattern. When listening to the second presentation, participants were instructed to anticipate the occurrence of accents, and to tap selectively (on an optical sensor) only to onsets of tones they perceived as accented.