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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.


P1 latency differences can be described in terms of a traveling alpha wave. Data are from a stroop task analyzed in Klimesch et al. (2007a). (A) A systematic and consistent travel speed was observed only for the extended alpha band and during the time window of the P1–N1 complex at around 0–200 ms post-stimulus. (B) The direction of the traveling wave can be determined by visual inspection of ERP's (Reprinted with permission).
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Figure 4: P1 latency differences can be described in terms of a traveling alpha wave. Data are from a stroop task analyzed in Klimesch et al. (2007a). (A) A systematic and consistent travel speed was observed only for the extended alpha band and during the time window of the P1–N1 complex at around 0–200 ms post-stimulus. (B) The direction of the traveling wave can be determined by visual inspection of ERP's (Reprinted with permission).

Mentions: It is well documented that the P1 exhibits topographical latency differences that are task dependent (e.g., Taylor et al., 2001). Most interestingly, recent evidence suggests that these latency differences can be interpreted as traveling alpha waves (Klimesch et al., 2007a) as the analysis of topographical alpha phase differences, observed in a stroop task, revealed. In this task subjects had to respond only to the color but to ignore the meaning of the presented words. Compared to P8, O2, and O1 (with P1 latencies of 108, 112, and 113 ms respectively), the P1 appeared considerably delayed – with a latency of 138 ms – at Pz. The analysis of traveling speed is based on the general idea that a systematic phase spread implies a certain propagation direction for each single trial. Thus, we first calculated instantaneous phase for each time point and frequency bin (between 2 and 20 Hz; width: 0.5 Hz) for each single trial and subject within a time window of ±1000 ms (with respect to stimulus onset). Then, cumulative phase was calculated for each trial. Based on these data, relative phase (i.e., phase difference) was determined for eight selected electrodes (P3, P4, P7, P8, Po3, Po4, O1, and O2) with respect to Pz as trailing site. The phase differences were transformed to latency differences in milisecond. Finally, the distance (in millimeter) between each selected electrode site and Pz (as reference site) was divided by the respective latency difference to obtain travel speed in meter per seconds (m/s; cf. Figure 4A). These data were then averaged over the eight selected electrode pairs to obtain an estimate of traveling speed for each single trial. As illustrated in Figure 4B, depending on the direction, traveling speed is characterized by positive or negative values. Positive values indicate a posterior to anterior direction whereas negative values indicate an anterior to posterior direction. If a systematic traveling direction is lacking, positive and negative values tend to cancel each other. On the other hand, in the case of a systematic traveling direction, averaging removes unsystematic noise and gives an estimate of travel speed. Travel speed was calculated for each single trial and was then averaged for each subject.


Alpha oscillations and early stages of visual encoding.

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

P1 latency differences can be described in terms of a traveling alpha wave. Data are from a stroop task analyzed in Klimesch et al. (2007a). (A) A systematic and consistent travel speed was observed only for the extended alpha band and during the time window of the P1–N1 complex at around 0–200 ms post-stimulus. (B) The direction of the traveling wave can be determined by visual inspection of ERP's (Reprinted with permission).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: P1 latency differences can be described in terms of a traveling alpha wave. Data are from a stroop task analyzed in Klimesch et al. (2007a). (A) A systematic and consistent travel speed was observed only for the extended alpha band and during the time window of the P1–N1 complex at around 0–200 ms post-stimulus. (B) The direction of the traveling wave can be determined by visual inspection of ERP's (Reprinted with permission).
Mentions: It is well documented that the P1 exhibits topographical latency differences that are task dependent (e.g., Taylor et al., 2001). Most interestingly, recent evidence suggests that these latency differences can be interpreted as traveling alpha waves (Klimesch et al., 2007a) as the analysis of topographical alpha phase differences, observed in a stroop task, revealed. In this task subjects had to respond only to the color but to ignore the meaning of the presented words. Compared to P8, O2, and O1 (with P1 latencies of 108, 112, and 113 ms respectively), the P1 appeared considerably delayed – with a latency of 138 ms – at Pz. The analysis of traveling speed is based on the general idea that a systematic phase spread implies a certain propagation direction for each single trial. Thus, we first calculated instantaneous phase for each time point and frequency bin (between 2 and 20 Hz; width: 0.5 Hz) for each single trial and subject within a time window of ±1000 ms (with respect to stimulus onset). Then, cumulative phase was calculated for each trial. Based on these data, relative phase (i.e., phase difference) was determined for eight selected electrodes (P3, P4, P7, P8, Po3, Po4, O1, and O2) with respect to Pz as trailing site. The phase differences were transformed to latency differences in milisecond. Finally, the distance (in millimeter) between each selected electrode site and Pz (as reference site) was divided by the respective latency difference to obtain travel speed in meter per seconds (m/s; cf. Figure 4A). These data were then averaged over the eight selected electrode pairs to obtain an estimate of traveling speed for each single trial. As illustrated in Figure 4B, depending on the direction, traveling speed is characterized by positive or negative values. Positive values indicate a posterior to anterior direction whereas negative values indicate an anterior to posterior direction. If a systematic traveling direction is lacking, positive and negative values tend to cancel each other. On the other hand, in the case of a systematic traveling direction, averaging removes unsystematic noise and gives an estimate of travel speed. Travel speed was calculated for each single trial and was then averaged for each subject.

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.