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Alpha oscillations and early stages of visual encoding.

Klimesch W, Fellinger R, Freunberger R - Front Psychol (2011)

Bottom Line: The physiological function of alpha is interpreted in terms of inhibition.We assume that alpha enables access to stored information by inhibiting task-irrelevant neuronal structures and by timing cortical activity in task relevant neuronal structures.We discuss a variety findings showing that evoked alpha and phase locking reflect successful encoding of global stimulus features in an early post-stimulus interval of about 0-150 ms.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiological Psychology, University of Salzburg Salzburg, Austria.

ABSTRACT
For a long time alpha oscillations have been functionally linked to the processing of visual information. Here we propose an new theory about the functional meaning of alpha. The central idea is that synchronized alpha reflects a basic processing mode that controls access to information stored in a complex long-term memory system, which we term knowledge system in order to emphasize that it comprises not only declarative memories but any kind of knowledge comprising also procedural information. Based on this theoretical background, we assume that during early stages of perception, alpha "directs the flow of information" to those neural structures which represent information that is relevant for encoding. The physiological function of alpha is interpreted in terms of inhibition. We assume that alpha enables access to stored information by inhibiting task-irrelevant neuronal structures and by timing cortical activity in task relevant neuronal structures. We discuss a variety findings showing that evoked alpha and phase locking reflect successful encoding of global stimulus features in an early post-stimulus interval of about 0-150 ms.

No MeSH data available.


Findings from an object recognition task show that the onset of ERD is not related to the onset of stimulation. Data are from Freunberger et al. (2008b). (A) Example of stimuli (upper panel). (B) A large ERD (indicated by an arrow) develops during the time window, in which an object is recognized. The upper panel shows time–frequency power plots for object- and control-items. The lower panel shows absolute power values for the lower and upper alpha band (Reprinted with permission).
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Figure 2: Findings from an object recognition task show that the onset of ERD is not related to the onset of stimulation. Data are from Freunberger et al. (2008b). (A) Example of stimuli (upper panel). (B) A large ERD (indicated by an arrow) develops during the time window, in which an object is recognized. The upper panel shows time–frequency power plots for object- and control-items. The lower panel shows absolute power values for the lower and upper alpha band (Reprinted with permission).

Mentions: If the onset of ERD signals the onset of retrieval, it should be possible to show that sensory encoding precedes ERD. In an attempt to dissociate these two processes, we designed a task in which stimuli were presented with progressively decreasing levels of distortion. In this study by Freunberger et al. (2008b), a pool of 150 pictures of familiar objects was used. In addition, 50 pictures were used as control items that were obtained by smearing real objects. Objects and control items were presented randomly. A trial consists of a series of four pictures that were presented in four different levels of distortion (for an illustration see Figure 2A) starting with maximal distortion (= level 4) down to minimal distortion (level 1). Pretesting ensured that objects could be reliably recognized within level 2. The task was designed to put a subject in a “top-down control mode” characterized by the expectancy to recognize an object (with comparably high probability of 66%) at a certain level of degradation (i.e., at level 2, as determined by pretesting).


Alpha oscillations and early stages of visual encoding.

Klimesch W, Fellinger R, Freunberger R - Front Psychol (2011)

Findings from an object recognition task show that the onset of ERD is not related to the onset of stimulation. Data are from Freunberger et al. (2008b). (A) Example of stimuli (upper panel). (B) A large ERD (indicated by an arrow) develops during the time window, in which an object is recognized. The upper panel shows time–frequency power plots for object- and control-items. The lower panel shows absolute power values for the lower and upper alpha band (Reprinted with permission).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3108577&req=5

Figure 2: Findings from an object recognition task show that the onset of ERD is not related to the onset of stimulation. Data are from Freunberger et al. (2008b). (A) Example of stimuli (upper panel). (B) A large ERD (indicated by an arrow) develops during the time window, in which an object is recognized. The upper panel shows time–frequency power plots for object- and control-items. The lower panel shows absolute power values for the lower and upper alpha band (Reprinted with permission).
Mentions: If the onset of ERD signals the onset of retrieval, it should be possible to show that sensory encoding precedes ERD. In an attempt to dissociate these two processes, we designed a task in which stimuli were presented with progressively decreasing levels of distortion. In this study by Freunberger et al. (2008b), a pool of 150 pictures of familiar objects was used. In addition, 50 pictures were used as control items that were obtained by smearing real objects. Objects and control items were presented randomly. A trial consists of a series of four pictures that were presented in four different levels of distortion (for an illustration see Figure 2A) starting with maximal distortion (= level 4) down to minimal distortion (level 1). Pretesting ensured that objects could be reliably recognized within level 2. The task was designed to put a subject in a “top-down control mode” characterized by the expectancy to recognize an object (with comparably high probability of 66%) at a certain level of degradation (i.e., at level 2, as determined by pretesting).

Bottom Line: The physiological function of alpha is interpreted in terms of inhibition.We assume that alpha enables access to stored information by inhibiting task-irrelevant neuronal structures and by timing cortical activity in task relevant neuronal structures.We discuss a variety findings showing that evoked alpha and phase locking reflect successful encoding of global stimulus features in an early post-stimulus interval of about 0-150 ms.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiological Psychology, University of Salzburg Salzburg, Austria.

ABSTRACT
For a long time alpha oscillations have been functionally linked to the processing of visual information. Here we propose an new theory about the functional meaning of alpha. The central idea is that synchronized alpha reflects a basic processing mode that controls access to information stored in a complex long-term memory system, which we term knowledge system in order to emphasize that it comprises not only declarative memories but any kind of knowledge comprising also procedural information. Based on this theoretical background, we assume that during early stages of perception, alpha "directs the flow of information" to those neural structures which represent information that is relevant for encoding. The physiological function of alpha is interpreted in terms of inhibition. We assume that alpha enables access to stored information by inhibiting task-irrelevant neuronal structures and by timing cortical activity in task relevant neuronal structures. We discuss a variety findings showing that evoked alpha and phase locking reflect successful encoding of global stimulus features in an early post-stimulus interval of about 0-150 ms.

No MeSH data available.