description of the stimuli indicates that the manipulated temporal information refers to
slower changes resulting, for example, from the permutation of two notes. As previously
emphasized, left-hemisphere damage affected the processing of fast but not slow temporal
information explaining therefore why left cerebral lesions do not systematically interfere
with time-related judgement involved in musical sequences (which usually concerned
longer temporal information superior to 200 ms^33 ).
To try to clarify the role of the LTL in fast temporal coding in music, we examined the
consequences of unilateral temporal lobe dysfunction in processing rapid sequential informa-
tion. In this chapter, we present evidence supporting the hypothesis that LTL structures are
predominantly involved in auditory temporal processes within the 10–100 ms time frame.
For this purpose, inter-onset interval (IOI) was manipulated in a psychophysical task of
anisochrony discrimination by using simple auditory sequences, as well as in a detection
task involving rhythmic changes in real tunes.
Perception of inter-onset increment in simple auditory sequences:
anisochrony discrimination
As frequently suggested, an important component of the rhythmic subjective structure is
its underlying isochrony (i.e. a regular beat), which corresponds to musical metre (or
tempo). In its simplest form, the metre can be expressed as a series of regular sounds. In
the present study, we designed an experiment based on anisochrony perception which
refers to the ability to differentiate a regular from an irregular sequence of sounds. The goal
of this experiment was to test the effect of tempo on anisochrony (or irregularity) dis-
crimination in patients with unilateral temporal lobe dysfunction, using an adaptive pro-
cedure. The rate of presentation or tempo (defined by the IOI separating the sounds in the
sequence) was systematically manipulated to compare anisochrony discrimination using
different tempos.
The anisochrony paradigm is very adequate for looking at temporal processing. As indi-
cated by the results of experiments carried out in normal subjects,^34 anisochrony discrim-
ination remains unaffected by duration or number of tones but it is influenced by tempo
or presentation rate. By using sequences presented at various tempos ranging from 80 ms
(fast) to 1000 ms (slow) IOI, it allows to compare perception of fast to slow sequential
information without changing the task demands. Results obtained in normal listeners also
showed that the discrimination thresholds for the anisochronous sequences were propor-
tional to the size of the IOI for tempos between 300 and 1400 ms, whereas sensitivity deteri-
orated for IOIs of 80 ms as compared to slower tempos. This finding corroborates the
assumption of different processes for temporal stimuli inferior or equal to 200–300 ms
compared to longer ones.35–37
Furthermore, the paradigm that we designed uses an adaptive procedure which offers
the opportunity to determine precise and fine individual thresholds which represent sensi-
tive measures of perceptual abilities. In particular, the use of such a method in neuropsy-
chology improves the chance of documenting subtle perceptual difficulties in
brain-injured patients that could not be detected by classical paradigms involving fixed
levels of stimulation common to all subjects.
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