Summary
Contents
Subject index
The recent findings from cognitive science – one of the fastest growing disciplines worldwide – presented in the volume will serve as a useful resource for scientists/psychologists working in the area. The book highlights the current trends in major sub-disciplines in cognitive science and contains high quality succinct papers covering current challenges, with cross-linking of different interfacing disciplines like psychology, neuroscience, computer science, linguistics, and philosophy.
Localization and Dynamics of Cerebral Activations Involved in Time Estimation: Studies Combining PET, fMRI, and EEG Data
Localization and Dynamics of Cerebral Activations Involved in Time Estimation: Studies Combining PET, fMRI, and EEG Data
Introduction
Time is crucial for our everyday activities. Humans, as other animals, process temporal information over different timescales (for example, Buhusi and Meck, 2005; Mauk and Buonomano, 2004). This chapter concerns the scale of tens to hundreds of milliseconds, which is fundamental for speech and motor coordination, and the scale of seconds to minutes, which is generally seen as the conscious perception of time. Without the ability to discriminate differences in duration and appreciate time, other cognitive functions, visual and auditory awareness, would be severely impaired. In the range of seconds, we estimate the duration of traffic lights in order to cross the roads when cars have stopped. Or when we drive a car we are able to anticipate the right moment to start again. In the millisecond range timing is crucial for speech, music and motor control. For example, we have to discriminate the duration of linguistic sounds and accurately pause between sentences and speaking turns, to achieve optimal communication.
Yet, the neural mechanisms involved in the processing of these duration-ranges remain largely unknown, in contrast with the mechanisms involved in other timescales, such as those controlling the circadian sleep-wake activity. Whereas time is clearly a source of information, which shapes one's behaviour, nobody has yet evidenced any sense or sense organ by which time can be directly perceived. The stimulus “time “is not a stimulus per se, but could correspond to an internally generated activity in the nervous system (thus increased neural activity with time could code for elapsed duration). The register of this internal activity the internal clock dedicated to interval timing (hundreds of ms to several seconds) has long been thought to be centralized, using the same brain circuitry for motor and perceptive timing, as well as for estimating the duration of an auditory or visual stimulus. However, from a behavioural point of view, a distributed (rather than unified) view of psychological time has recently been proposed (for example, Grondin, 2001), suggesting that more than one central timekeeping system may contribute to time perception. In addition, thanks to brain imaging studies, neuroscientists have recently shown that multiple brain areas are involved in the judgement or production of brief intervals. But, two questions remain a matter of debate: How do neurons in those regions measure time? Is the observed pattern of activation specific to time processing? This chapter will give a bird's eye view of EEG electrophysiological), fMRI (Functional Magnetic Resonance Imagery) and PET (Positron Emission Topography) studies, which have contributed to answer these questions.
Eeg Studies: How Does the Brain Code for Target Times?
In the 1960s, electrophysiologists described a slow negative wave, called the Contingent Negative Variation (CNV) that develops between two stimuli: S1 corresponding to a warning stimulus and S2 to an imperative stimulus (for example, Walter et al., 1964). One of the processes reflected by this wave was thought to be the estimation of time between S1 and S2 (Figure 13.1). The CNV is generally observed between two stimuli, but this wave also occurs during a continuous stimulus where onset and offset correspond to warning and imperative stimulus, respectively. EEG studies have shown that: (a) this slow wave develops over wide areas of the scalp, mainly over frontal and central areas; (b) it reflects the preparation and/or anticipation of a response; (C) it is associated with several cognitive processes including expectancy and attention.
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