• psychoacoustics
• perception
• motor control

In 1995 Milner and Goodale postulated two separate visual systems in the human brain.
Evidences from studies of both humans and other primates have shown that there is a
distinction between “vision for perception” and “vision for action”, which is reflected in
the organization of the visual pathways in the cerebral cortex of primates. In recent
years, psychoacoustical experiments (Repp 2000, 2005, Hafke 2008) seemed to confirm the
existence of a similar dissociation between action and perception in human audition: motor
control of phonation and finger tapping are found to be sensible to subliminal variations of
the auditory feedback. After showing the existence of two processing streams in audition
too, now the real importance of “hearing for action” to carry out more elaborate action
control tasks and the crosstalk with “hearing for perception” have to be checked.
For that reason an original experiment is carried out to analyze the motor control
reaction to the introduction/removal of (trans-)subliminal delay amounts to the auditory
feedback. The effect of delayed auditory feedback (DAF) were previously investigated by
several researchers connected with music research, speech and hearing disorders. Only
great and perceivable delays were used: the idea that a subliminal amount of delay could
provoke any effect was implicitly rejected or simply not taken into account because of
weak and unperceived task repercussions. In order to find the sub jective delay perception
threshold, an auxiliary experiment was performed. Both experiments are conducted at the
Pozna ́n Institute of Acoustics. Although eight pianists are involved and stimuli materials
are simple melody repetitions, the goal of the study is only secondarily connected with
music research. During the experiment several MIDI files containing the trials are recorded
and successively imported into MATLAB environment. A statistical analysis is carried
out through various techniques and tests (e.g. ANOVA, χ2 test, Levene’s or Bartlett’s
test).
The thesis is divided into four chapters. The first one begins introducing the Milner
and Goodale theory of vision and the cognitional implications of importing that theory
into audition. A description of the previous works supporting the dissociation between
“hearing for action” and “hearing for perception” concludes the chapter.
At the beginning of the second chapter an introduction to the DAF technique is pro-
vided and experiments involving DAF are reported. An accurate description of the ex-
periments follows. In particular, participants, stimulus materials, apparatus and design of
the experiments are described.
The third chapter is divided into two sections. In the first section a report of the
sub jective delay perception threshold related to the auxiliary experiment is provided. An
asymmetry between positive and negative delay perception threshold was founded for all pianists: the phenomenon is completely justified and explained. The second section
concerns the main experiment analysis and it is the core of the thesis. Firstly the initial
synchronization to the metronome is analyzed. Although the basic experiment concepts
are completely different, the same results of Repp are here obtained: the action motor
control has access to subliminal temporal information revealing its partial independence
from perception when a synchronization task has to be performed. After the metronome
is turned off, a natural deviation from the exact tempo is founded and its features are
examined. Finally, the response of the motor control to the introduction or removal of
delay is analyzed. Obviously, the results are more controversial: some pianists reveal to
be sensible to subliminal delay, attempting to compensate it slowing or accelerating their
playing tempo. The same feature, although at greater extent, is clearly visible when trans-
subliminal delay are involved. As counterpart the other sub jects show different behaviours
reacting exclusively at trans-subliminal delays.
A discussion and a resume of the results, theirs implications and ideas for new exper-
iments conclude the paper.