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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.


Instantaneous phase alignment (IPA) as analyzed by Gruber et al. (2005) for the data of a memory retrieval task. (A) Example of the ERP with the P1-component. (B) The frequency characteristic of the ERP is reflected by a measure termed evoked power. It represents the filtered ERP. (C) Significant phase locking can be observed in a broad frequency range. (D) Significant IPA can be observed particularly for the time window of the P1 and N1. The white line represents the ERP. For the P1, phase alignment is around the positive peak, for the N1 it is most pronounced for the positive going slope beyond the negative peak. Note that the IPA is significant only for the broad alpha frequency range. (E) Time–frequency representation of absolute phase. Note the vertical red and blue bands (around 100–200 ms post-stimulus) representing the positive and negative peak of aligned frequencies. These bands correspond to the positive and negative peaks of the ERP, i.e., to the P1 and N1 respectively (Reprinted with permission).
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Figure 3: Instantaneous phase alignment (IPA) as analyzed by Gruber et al. (2005) for the data of a memory retrieval task. (A) Example of the ERP with the P1-component. (B) The frequency characteristic of the ERP is reflected by a measure termed evoked power. It represents the filtered ERP. (C) Significant phase locking can be observed in a broad frequency range. (D) Significant IPA can be observed particularly for the time window of the P1 and N1. The white line represents the ERP. For the P1, phase alignment is around the positive peak, for the N1 it is most pronounced for the positive going slope beyond the negative peak. Note that the IPA is significant only for the broad alpha frequency range. (E) Time–frequency representation of absolute phase. Note the vertical red and blue bands (around 100–200 ms post-stimulus) representing the positive and negative peak of aligned frequencies. These bands correspond to the positive and negative peaks of the ERP, i.e., to the P1 and N1 respectively (Reprinted with permission).

Mentions: For the calculation of phase alignment between frequencies Gruber et al. (2005) developed a method, which was termed “instantaneous phase alignment” (IPA). The calculation – which was done for data of a memory retrieval task – is based on the following analyzing steps. First, those frequencies were determined showing a significant phase locking (as calculated by the phase locking index, PLI). The average PLI for a 120-ms pre-stimulus period (ranging from −840 to −720 ms pre-stimulus) for each frequency bin was computed. From these data confidence intervals were calculated. Only those frequencies and time periods post-stimulus were used for further analyses, in which the PLI exceeded the upper confidence limit (cf. Figure 3C). Second, based on these data, the phase angle was calculated for each frequency and time point (cf. Figure 3E). Note that at around 100 ms a vertical red band reflecting a positive peak followed by a blue band (reflecting a negative peak at about 150 ms) can be observed. By using circular statistics, frequencies with significant phase alignment were determined. The results are depicted in Figure 3D and demonstrate significant phase alignments at certain frequencies and latencies.


Alpha oscillations and early stages of visual encoding.

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

Instantaneous phase alignment (IPA) as analyzed by Gruber et al. (2005) for the data of a memory retrieval task. (A) Example of the ERP with the P1-component. (B) The frequency characteristic of the ERP is reflected by a measure termed evoked power. It represents the filtered ERP. (C) Significant phase locking can be observed in a broad frequency range. (D) Significant IPA can be observed particularly for the time window of the P1 and N1. The white line represents the ERP. For the P1, phase alignment is around the positive peak, for the N1 it is most pronounced for the positive going slope beyond the negative peak. Note that the IPA is significant only for the broad alpha frequency range. (E) Time–frequency representation of absolute phase. Note the vertical red and blue bands (around 100–200 ms post-stimulus) representing the positive and negative peak of aligned frequencies. These bands correspond to the positive and negative peaks of the ERP, i.e., to the P1 and N1 respectively (Reprinted with permission).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: Instantaneous phase alignment (IPA) as analyzed by Gruber et al. (2005) for the data of a memory retrieval task. (A) Example of the ERP with the P1-component. (B) The frequency characteristic of the ERP is reflected by a measure termed evoked power. It represents the filtered ERP. (C) Significant phase locking can be observed in a broad frequency range. (D) Significant IPA can be observed particularly for the time window of the P1 and N1. The white line represents the ERP. For the P1, phase alignment is around the positive peak, for the N1 it is most pronounced for the positive going slope beyond the negative peak. Note that the IPA is significant only for the broad alpha frequency range. (E) Time–frequency representation of absolute phase. Note the vertical red and blue bands (around 100–200 ms post-stimulus) representing the positive and negative peak of aligned frequencies. These bands correspond to the positive and negative peaks of the ERP, i.e., to the P1 and N1 respectively (Reprinted with permission).
Mentions: For the calculation of phase alignment between frequencies Gruber et al. (2005) developed a method, which was termed “instantaneous phase alignment” (IPA). The calculation – which was done for data of a memory retrieval task – is based on the following analyzing steps. First, those frequencies were determined showing a significant phase locking (as calculated by the phase locking index, PLI). The average PLI for a 120-ms pre-stimulus period (ranging from −840 to −720 ms pre-stimulus) for each frequency bin was computed. From these data confidence intervals were calculated. Only those frequencies and time periods post-stimulus were used for further analyses, in which the PLI exceeded the upper confidence limit (cf. Figure 3C). Second, based on these data, the phase angle was calculated for each frequency and time point (cf. Figure 3E). Note that at around 100 ms a vertical red band reflecting a positive peak followed by a blue band (reflecting a negative peak at about 150 ms) can be observed. By using circular statistics, frequencies with significant phase alignment were determined. The results are depicted in Figure 3D and demonstrate significant phase alignments at certain frequencies and latencies.

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.