Action planning is usually studied in the laboratory with speeded reaction time (RT) tasks in which participants respond to stimuli by making pre-specified movements as quickly as possible. Research employing the speeded RT paradigm has revealed that action planning involves the anticipation of action effects: RTs are typically faster when movements are compatible with ensuing action effects than when movements and their effects are incompatible. Such compatibility effects have been observed for discrete actions and for action sequences with music-like auditory effects. In contrast to action planning, action execution is usually not susceptible to compatibility effects in speeded RT tasks, probably because ballistic movements are fully pre-planned. In the current study, we test whether the findings from speeded RT tasks generalize to a task that requires short auditory sequences to be produced at a specific tempo, rather than as fast as possible. This new task is more closely related to typical requirements in music.
In our experiment, skilled musicians responded to each of four color-patch stimuli by producing a unique sequence of three taps on three vertically-aligned keys. The color-patch stimulus in each trial flashed three times with a 600 ms inter-onset interval (IOI), and participants made their tapping responses as regularly as possible at this tempo after a further three 600 ms IOI flashes of a neutrally colored stimulus. Each tap triggered a tone. Response-effect (key-to-tone) mapping was either compatible—taps on the top, middle, and bottom keys triggered high, medium, and low pitched tones, respectively, or incompatible—key-to-tone mapping was scrambled or reversed. The results indicate that produced intervals were closer to their (600 ms) target for the compatible response-effect mapping than for either of the two incompatible mappings (for which produced intervals did not differ reliably). This effect of compatibility on timing accuracy was present to a similar degree across the three taps. The presence of a compatibility effect on the first tap provides evidence for action effect anticipation (imagined sound) because the first tone in each trial was presented only after the first tap had been made. However, although pre-planning (tap 1) and execution (taps 2 and 3) were both affected by compatibility, these effects were uncorrelated. Our findings suggest that brief evenly-timed music-like sequences are pre-planned using a feedforward mechanism that brings sounds to mind shortly before they are produced, but this pre-planning perhaps does not shield movement execution from disruption by incompatible feedback.