Task-irrelevant auditory metre shapes visuomotor sequential learning

Abstract

The ability to learn and reproduce sequences is fundamental to every-day life, and deficits in sequential learning are associated with developmental disorders such as specific language impairment. Individual differences in sequential learning are usually investigated using the serial reaction time task (SRTT), wherein a participant responds to a series of regularly timed, seemingly random visual cues that in fact follow a repeating deterministic structure. Although manipulating inter-cue interval timing has been shown to adversely affect sequential learning, the role of metre (the patterning of salience across time) remains unexplored within the regularly timed, visual SRTT. The current experiment consists of an SRTT adapted to include task-irrelevant auditory rhythms conferring a sense of metre. We predicted that (1) participants' (n = 41) reaction times would reflect the auditory metric structure; (2) that disrupting the correspondence between the learned visual sequence and auditory metre would impede performance; and (3) that individual differences in sensitivity to rhythm would predict the magnitude of these effects. Altering the relationship via a phase shift between the trained visual sequence and auditory metre slowed reaction times. Sensitivity to rhythm was predictive of reaction times over all. In an exploratory analysis, we, moreover, found that approximately half of participants made systematically different responses to visual cues on the basis of the cues' position within the auditory metre. We demonstrate the influence of auditory temporal structures on visuomotor sequential learning in a widely used task where metre and timing are rarely considered. The current results indicate sensitivity to metre as a possible latent factor underpinning individual differences in SRTT performance.

Fig. 1

The Serial Reaction Time Task (Nissen & Bullemer, 1987) entails a participant making repeated motor responses to a series of visual cues, which may appear to be random, but are in fact deterministic or probabilistic in structure. Over many trials, the participant’s reaction times increase in speed, until the trained series changes to a new sequence of cues, at which point reaction times slow again. This slowing in response to a new sequence is interpreted as an indirect measure of sequential learning

Fig. 2

Metre is a central component of rhythm that functions as a structure or grid underlying events in time. Events within a metre that are perceived or enacted more strongly are said to be accented. Shown here are a few common examples of metre. a Depicts an English nursery rhyme, which is structured according to a binary pattern of accented (or stressed) and unaccented syllables, resulting in a grouping of two. In (b), boxers practice combinations of hits according to a fast–fast–slow metrical pattern, amounting to a grouping of four counts in total. Finally, c consists of a simple waltz dance step pattern, where an accented (or strong) beat is followed by two unaccented beats, invoking a metric grouping of three

Fig. 3

This figure depicts a graphical representation of possible pairings between a given visual sequence and the two auditory metre conditions, 3/4 and 4/4. In (a), an entire example sequence is shown in the upper row alongside the 3/4 m (middle row) and 4/4 m (bottom row). The same 12-element sequence can be paired with either metre. In the small lower panels, the main components of the serial reaction time task are presented. In (b), the learned metre is 3/4, and the same visual cues always coincide with the same position in the auditory metre. c shows that during the Phase-Shifted Metre Test block, the visual sequence and auditory metre each remain unchanged, but no longer correspond to one another as they did during learning. In (d) depicting the New Metre Test block, the visual sequence is again held constant, but the auditory metre condition changes, in this case, to a 4/4 pattern. Darker shaded boxes indicate accented auditory stimuli, and the rows labelled “Subdivision” depict the faster paced background rhythm to reinforce the sense of metre

Fig. 4

Overview of the the Serial Reaction Time Task showing mean-centred mean reaction times (calculated within participant). Blocks 1–8 and 10 are Learning blocks; Block 9 is the Phase-Shifted Metre Test; and Block 11 is the New Metre Test. Group means are shown by lines, with shaded region representing 95% confidence intervals of the mean. Upper panel (a): Full task. Lower panel (b): Grouped by Metre condition

Fig. 5

Mean reaction times (ms) as a function of Rhythm Score. Group mean is shown by a line, with shaded regions representing 95% confidence intervals of the mean

Fig. 6

Mean-centred mean reaction times (calculated within participant) by Accent during Learning. The data are summarised by Metre across rows, and Block across columns (note that Blocks were modelled separately and are grouped by two here for simplicity). Group means are shown by lines, with the error bars and shaded regions representing 95% confidence intervals of the mean

Fig. 7

Overview of the the Metre Test Blocks showing mean-centred mean reaction times (calculated within participant). Blocks 8 and 10 are Learning blocks; Block 9 is the Phase-Shifted Metre Test; and Block 11 is the New Metre Test. The data are binned into quarter-blocks (n = 30)

Fig. 8

Mean-centred mean reaction times (calculated within participant) during Early Learning (Blocks 1 and 2), Late Learning (Blocks 8 and 10), and the New Visual Sequence Test, wherein the learned Visual Sequence was changed, but the learned Auditory Metre was the same as during Learning. Responses are summarised by Metre Condition

Fig. 9

Mean percent correct (calculated within participant, task-wise) in the Explicit Recognition Task as a function of Rhythm Score. Lighter shaded dots indicate participants whose data were excluded from the serial reaction time task due to high ($>10\%$) rates of correctly anticipated ($<50$ ms) reaction times. Shaded regions represent 95% confidence intervals of the mean

Fig. 10

Histograms for the subtraction of Accented reaction times from Unaccented reaction times (ms), by Metre, during learning. Whereas the slight tendency for the 3/4 m towards slower Accented reaction times can be seen in the upper panel, the lower panel shows a possible bi-modal distribution of responses for the 4/4 condition

Fig. 11

Histogram for the p values associated with individual permutation tests (n$=10,000$), by participant, of mean Accent relative difference during learning. Tests shuffled responses within Key and Block. The dashed line represents an alpha level of 0.05 (false discovery rate corrected)

Fig. 12

Coefficient of Variation (CV) of responses during learning, calculated for each participant by dividing the standard deviation by mean reaction time, calculated by Accent condition, within each Block, by Participant. Group means are shown by the heavier line, with the thinner lines representing 95% confidence intervals of the mean