auditory sequences and musical patterns have been used to investigate the cerebral struc-
tures underlying musical temporal processes. Studies reported in the literature will be
reviewed first. Then, experimental findings that we obtained in two different studies will be
reported to clarify the role of the left (LTL) as opposed to the right temporal lobe (RTL)
structures in processing subtle temporal variations within a range of 10–100 ms.
Temporal processing in simple auditory sequences
Several studies have explored time-related processing by using simple auditory sequences.
In this domain, several paradigms classically used in experimental psychology have been
adapted to neuropsychology. In a seminal paper, Efron^1 investigated the ability of brain-
damaged patients to judge the temporal order of two-tones of different frequencies sep-
arated by a silent interval. The results showed that aphasic patients with left-hemisphere
lesions required longer intervals (between 140 and 400 ms) to discriminate temporal order
than nonaphasic patients with right-hemisphere lesion or normal subjects (75 ms interval).
It was therefore suggested that the left hemisphere structures generally thought to be
involved in language processing may also contribute to the temporal analysis of fast aud-
itory sequential information. Subsequently, Tallal and Newcombe^2 provided convergent
evidence by demonstrating that selective damage to the left but not to the right hemisphere
disrupted the ability to process two-tones separated by a short interval (300 ms or less
between the tones). Importantly, neither left- nor right-hemisphere damaged subjects were
affected when longer intervals were used. This finding has been reproduced with similar
paradigms and generalized to other tasks involving gap detection or perception of sim-
ulaneity and succession.3–7One case report of an amusic patient (HV) seems to contradict
previous results since a deficit in temporal order processing of rapid patterns was observed
in presence of a right-hemisphere lesion.^8 However, the authors noted that the cortical lesion
of this patient was associated with an underlying bilateral white matter lesion which may
have caused bilateral cortical deafferentation. Such a cerebral dysfunction, that presumably
involved the left hemisphere, might have been responsible for the disruption of rapid
temporal processing explaining therefore the apparent contradiction between the results.
However, inconsistent results were reported in studies investigating the perception of
duration. Indeed, results of different studies have shown that impairments in this percep-
tual ability have been observed in patients with unilateral lesions implicating the right or
the left hemisphere,^9 in a case of auditory agnosia following a bilateral cerebral dysfunc-
tion^10 as well as in patients with RTL lesions.^11 These findings suggest that the perception
of continuous signals, as opposed to discrete events, depends on different processing
involving distinct neural substrate.
Except for the perception of duration, the results previously reviewed suggest that left-
hemisphere structures are predominantly involved in the processing of rapid sequential
information. Recent electrophysiological results indicate that this function can be linked to
auditory cortices of the LTL. By recording intracerebral evoked potentials to syllables in
the right and the left human auditory cortices, Liégeois-Chauvel and her collaborators^12
demonstrated a specialization of the left auditory cortex for speech perception that
depends on rapid temporal coding (within a few tens of milliseconds). If the left temporal
cortex is dominant for fine grained time-related processing of language, it seems
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