Could something be perceived if there is no sensory system which is dedicated to it? For everyone except parapsychologists, the obvious answer is no – but this raises questions about the ability to perceive short temporal intervals, for which there appears to be no dedicated sensory system.
In their newly in-press TICS article, Ivry and Schlerf review the state of the art in cognitive modeling of time perception – perhaps the most basic form of perception which has no sensory system dedicated to it.
Ivry and Schlerf review the attractive qualities of time perception modules, such as the pacemaker-accumulator model and so-called “spectral models” (e.g., neural oscillators with different periodicities, or the use variability in neuronal conduction delays to perceive duration). Ivry & Schlerf report that their motivation for modular models is based on the fact that time perception “transcends” the modality of a stimulus. (However, as they mention later, there are many cases where auditory and visual duration estimates significantly differ.)
Ivry & Schlerf support the idea that the cerebellum is this dedicated time perception module (the “cerebellar timing hypothesis”) with evidence that patients suffering cerebellar damage are impaired on a variety of tasks involving timing, but similar evidence has accumulated for the roles of right prefrontal regions and the basal ganglia. Ivry & Schlerf resolve this by advocating a distributed network for time perception, in which some components are dedicated (the “pacemaker” – the cerebellum, in their view) and others are domain general (basal ganglia and prefrontal cortex, which they refer to as “working memory to store temporal information”, but might just as easily correspond to the “gate” and “accumulator”, respectively).
Ivry & Schlerf contrast this proposal with those advocating “intrinsic” mechanisms for time perception, which propose that more general-purpose mechanisms (such as self-sustaining activity in the PFC and posterior parietal cortex) may be recruited for time perception in the absence of a dedicated neural system.
Ivry & Schlerf then review a variety of evidence showing modality-specificity in time perception, which would seem to support the intrinsic timing variety of models. However, they argue that intrinsic time perception should not be so broadly disrupted by focused brain damage, and that crossmodal transfer of time perception training should not occur. Regarding the latter, there is apparently remarkable specificity in training of duration discrimination.