Academic journal article Journal of Social and Psychological Sciences

Review: The Neuroanatomical Substrates of Cognitive Control

Academic journal article Journal of Social and Psychological Sciences

Review: The Neuroanatomical Substrates of Cognitive Control

Article excerpt

Top-down and Bottom-up mechanisms involved in selective attention

Although not identical, a somewhat similar distinction to automatic and controlled mechanisms can be made between bottom-up and top-down processing, which also attempts to investigate the extent to which one can exert control over action-selection processes. Action can be said to be top-down driven when selection occurs in a voluntary and goal-directed manner (i.e. driven by knowledge, expectation and goals). In contrast, when specific properties of the environment determine the selection, irrespective of one's beliefs selection is said to occur in a stimulus-driven, involuntary, bottom-up manner (Schoelles & Gray, 2003). Whether or not a task starts from the bottom or top level of the cognitive system, it is thought that bottom-up and top-down processing are mixed. Some studies have addressed the ways in which this mixing occurs. For instance, Posner and Snyder (1975) found that the deliberate attentional focus in a perceptual task facilitates its processing. Similarly, contextual factors can also play an important role in perceptual recognition (i.e. an object which fits its context is better perceived).

Conscious will and voluntary action

It is well established that voluntary movement is preceded by increased neural activity. This activity begins at around two seconds prior to movement onset (see Cunnington et al, 1993; Toro et al, 1993; Ball et al, 1999; Cunnington et al, 2003). The first study of movement preparation in the human brain was conducted by Korhuber and Deecke (1965) who termed this phenomenon as Bereitschaftspotential (Readiness Potential). This study served as a catalyst for subsequent studies on conscious experience, consciousness and willed action. Perhaps one of the most useful insights into understanding conscious will came from a well known study by Benjamin Libet (1985). Libet's main aim was to establish a link between people's subjective feelings of volition and unconscious readiness potential. In this study, subjects were instructed to flex their wrist at any time they chose, but to simultaneously record the time at which they decided to do so. Specifically, timing was recorded by noticing the position of a dot on a clock face. In this way, one of the key aims of this experiment was to record voluntary, internally generated action.

Libet averaged several RPs occurring in the supplementary motor area and found that they occurred at around 550ms before action occurred. Moreover, subjects' conscious intentions to move was recorded 200ms before they actually moved. The difference between preparing to flex the wrist and the conscious intention to act was of 350ms (see Cunnington et al, 1993). Libet demonstrated, therefore, that readiness potentials (RPs) precede voluntary actions, and that people's conscious intention to perform an act occurs after preparations to execute that act have been put in motion.

These results provided a strong case for establishing the timing of conscious intention as 200ms before movement. When discussing the philosophical implications of these findings Libet pointed out that they do not impinge upon our free will since that the timing of conscious intent gives us time to consciously permit our actions. This study gives further insights into importance and usefulness of studying the timing and perception of peoples' action. So far the models proposed about how cognitive control is achieved received criticisms from some researchers (see Botvinick et al, 2001) who argued that these models tend to focus too much on the influence exerted by control itself as opposed to understanding how the intervention of control processes per se are initiated. This issue is discussed in more depth in the subsequent sections of this paper.

Luria's (1966) description the functions of prefrontal regions of the brain (being these regulation, verification and programming of activity) closely correspond to currently held assumptions of neuronal mechanisms involved in higher cognitive processes. …

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