Research Article: Stimulus-dependent modulation of perceptual and motor learning in a serial reaction time task

Date Published: May 21, 2012

Publisher: University of Finance and Management in Warsaw

Author(s): Waldemar Kirsch, Joachim Hoffmann.


In two experiments, we investigated the impact of spatial attributes on the
representation acquired during a serial reaction time task. Two sequences were
used, in which structural regularities occurred either in the horizontal or in
the vertical locations of successive stimuli. After training with the dominant
hand, participants were required to respond with the non-dominant hand to either
the original sequence or to a mirror-ordered version of the original sequence
that required finger movements homologous to those used during training. We
observed that a difference in reaction times between the two transfer conditions
was smaller in the vertical sequence than in the horizontal sequence. This
pattern of results was independent of whether three fingers (Experiment 1) were
used or only one finger (Experiment 2) was used for responding. This result
suggests that perceptual and motor learning mechanisms may be weighted
differently depending on the context in which the stimulus is presented.

Partial Text

In serial reaction time (SRT) tasks, participants respond to sequences of stimuli
with sequences of corresponding responses. Reaction times (RTs) typically decrease
more quickly in response to structured sequences than to random sequences (Nissen & Bullemer, 1987), which suggests
that participants acquire knowledge about the sequence structure. Another method
often used to measure the learning of the sequence structure is to replace the
structured sequence with a random sequence after participants have practiced a task.
The magnitude of the decrease in performance in the random sequence may then reflect
the magnitude of learning.

Participants performed an SRT task, in which they responded to circular locations
arranged in a 3 × 3 matrix by pressing assigned keys on a numerical keypad with
their index, middle, and ring fingers. After an initial practice block, a fixed
first-order conditional sequence of nine elements was repeatedly presented. The
critical manipulation was related to the redundancies in the stimulus sequence. One
group of participants practiced a sequence that could be parsed into three
subsequences, each with three elements presented in the same succession of locations
in the horizontal dimension (i.e., the horizontal sequence). That is, the order of
right, left, and middle circle positions was repeated three times in the
nine-element sequence. The second group of participants practiced another sequence,
which was identical to the horizontal sequence in the statistical and the relational
structures. However, it contained vertical regularities (i.e., the vertical
sequence). After practicing with the dominant hand, participants had to perform the
SRT task with their non-dominant hands. In one condition, participants responded to
the original sequence of stimuli (and of response keys) with an unpracticed pattern
of finger movements (parallel condition). In another condition, the stimulus
sequence was modified to reverse the left and right targets around the vertical
midline leading to the response sequence, which involved finger movements homologous
to those used during training (mirror condition). Accordingly, participants had to
rely on a sequence of homologous finger movements by responding to a changed
stimulus sequence. As a consequence of more effective perceptual learning, we
expected better intermanual transfer of the horizontal sequence, compared with the
vertical, in the parallel condition. In the mirror condition, in contrast, the
vertical sequence might be better transferred to the untrained hand than the
horizontal sequence due to greater sequential motor knowledge.

In Experiment 2, we aimed to replicate and extend the results of Experiment 1. To
evaluate the extent to which the use of multiple fingers and of a respective
key-finger assignment may account for the pattern of results observed in Experiment
1, in Experiment 2 the participants were asked to respond with only their index
fingers. All other manipulations remained the same as in the first experiment. If
the difference between the parallel and mirror transfer costs were reduced for the
vertical sequence, compared with the horizontal sequence, then this interaction
would not be attributable to such specific factors as the number of effectors and
the key-finger assignment.

We investigated the influence of visual stimulus characteristics on the nature of
representations acquired during a perceptual-motor task in two experiments. The
primary question of interest was whether the amount of motor and perceptual
knowledge depends on spatial regularities in the horizontal dimension versus the
vertical dimension. In one condition, the horizontal positions of stimuli were more
predictable than the vertical positions (horizontal sequence). In another condition,
the vertical stimulus dimension was more redundant (vertical sequence). We predicted
a better intermanual transfer of the horizontal than of the vertical sequence in the
parallel condition and predicted a reversed pattern in the mirror condition. We
observed a difference in the intermanual transfer costs between the parallel and the
mirror condition that depended on whether horizontal or vertical regularities were
present in the stimulus sequence. This difference in transfer costs was smaller for
the vertical sequence than for the horizontal sequence. However, we did not find
significant differences between the two sequence conditions when the two transfer
conditions were considered separately, although mean values indicated a trend in the
expected direction. Thus, although the data allow only restricted conclusions, the
results suggest that perceptual learning mechanisms may be more sensitive to the
horizontal dimension of the sequence structure than to the vertical dimension and/or
that motor learning may be more responsive to the vertical structure of a




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