Can temporal resolution improve with practice?
One of the first studies on this issue reported no perceptual
learning (Rammsayer 1994). In this study, subjects were trained on
50-ms intervals for 10 min a day for 4 weeks. Subsequent studies
revealed robust learning with training (Wright et al. 1997,
Nagarajan et al. 1998, Karmarkar & Buonomano 2003). In these
studies subjects were generally trained for an hour a day
(400–800 trials) for 10 days.
The perceptual learning studies, in addition to
suggesting that the neural mechanisms underlying timing can be
fine-tuned with experience,
Generalization of training
Generalization studies reveal that interval
discrimination learning is specific to the temporal domain, and
generalization occurs in the spatial domain.
Interval learning has also been reported to
generalize across modalities. Nagarajan et al. (1998) show
that training on a somatosensory task can produce improvement on an
auditory interval discrimination task similar to the interval used
for somatosensory training. Even more surprising, training on an
auditory task appears to result in an interval-specific improvement
in a motor task requiring that the subjects tap their fingers to
mark specific intervals (Meegan et al. 2000).
The simplest interpretation of these data is
that centralized circuits exist for each interval, and with
training, either the temporal accuracy or the downstream processing
of these circuits undergoes plasticity. In this interpretation,
timing is centralized but interval based. However, it is
possible that in these tasks learning occurs as a result of
interval-specific cognitive processes other than temporal
processing per se. For example, because interval discrimination
tasks require comparing the test interval and a standard interval,
improvement could rely on better representation of the standard
interval or improved storage or retrieval from working or
short-term memory. Such alternative explanations would be
consistent with the generalization across different stimulus
markers and modalities, as well as the lack of generalization to
novel intervals. Alternatively, it could be argued that,
although many circuits are capable of temporal processing, the
relatively simple nature of these temporal tasks allows the brain
to use multimodal pathways and a single timing circuit.