Friday, October 31, 2008

Understanding the IQ brain clock: Excellent overview article

[double click on image to enlarge]

Damn I love the journal Trends in Cognitive Science. It routinely publishes concise articles that circumscribe the state of the knowledge in important areas of human cognition/intelligence. I just finished reading yet another outstanding article ("Dedicated and intrinsic models of time perception") by Ivry and Schlerf (2008) (click to review)

Throughout the past year I've posted material regarding different neural models that have been advanced to explain the IQ brain clock (temporal processing). I've never felt I've done a good job in pulling all of this together. These authors do an exceptional job in describing the four primary hypothesized models that have been advanced to explain the neural mechanisms underlying the human brain clock. More importantly they do so which the aid of great visual-graphics (see the one above). I liked the article so much that I've added it to the "key research articles" section of this blog and have also added Dr. Ivry to the "mental timing scholars" link section.
  • Abstract: Two general frameworks have been articulated to describe how the passage of time is perceived. One emphasizes that the judgment of the duration of a stimulus depends on the operation of dedicated neural mechanisms specialized for representing the temporal relationships between events. Alternatively, the representation of duration could be ubiquitous, arising from the intrinsic dynamics of nondedicated neural mechanisms. In such models, duration might be encoded directly through the amount of activation of sensory processes or as spatial patterns of activity in a network of neurons. Although intrinsic models are neurally plausible, we highlight several issues that must be addressed before we dispense with models of duration perception that are based on dedicated processes.
A few tidbits extracted (directly) from the article, some that reinforce information posted at the IQ Brain Clock over the past few years---and some that is new. italics added by blogmaster:
  • we focus on a fundamental question that has defined much of the recent discussion: is our perception of the passage of time the consequence of dedicated, clock-like neural mechanisms? Or is duration coded in an accessible manner as an intrinsic and ubiquitous property of neural activity?
  • The facile manner with which we compare time across different modalities suggests some sort of internal clock.
  • Dedicated models of time perception are, at their core, modular. As vision scientists speak of dedicated mechanisms for color or motion perception, modular models of time perception entail some sort of specialized mechanism that represents the temporal relationship between events. The pacemaker-counter model is one example of a modular system .
  • Intrinsic models offer a radically different perspective on the perception of time. These models assume that there is no specialized brain system for representing temporal information, asserting that time is inherent in neural dynamics.
  • the cerebellar timing hypothesis is based on the assumption that the cerebellum has a unique representational capability and is accessed whenever a particular task requires precise timing.
  • Similar arguments have been developed for other neural regions that might serve as dedicated timing systems [25]. These include the basal ganglia [26,27], supplementary motor area [28,29] and prefrontal cortex, especially in the right hemisphere [30,31]. For the most part, converging evidence has been offered in support of all of these candidate regions.
  • considerable debate continues on the question of whether temporal-processing deficits are uniquely associated with damage to a particular neural structure.
  • Other dedicated models avoid localization issues by postulating that the representation of time results from activity across a network of regions
  • The role of nontemporal factors on perceived duration Performance on time-perception tasks entails several component processes, many of which are not specific to time. These include attention, working memory and long-term or reference memor

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