From perception to action: phase-locked gamma oscillations correlate with reaction times in a speeded response task

<p>Abstract</p> <p>Background</p> <p>Phase-locked gamma oscillations have so far mainly been described in relation to perceptual processes such as sensation, attention or memory matching. Due to its very short latency (≈90 ms) such oscillations are a plausible candidate for very rapid integration of sensory and motor processes.</p> <p>Results</p> <p>We measured EEG in 13 healthy participants in a speeded reaction task. Participants had to press a button as fast as possible whenever a visual stimulus was presented. The stimulus was always identical and did not have to be discriminated from other possible stimuli. In trials in which the participants showed a fast response, a slow negative potential over central electrodes starting approximately 800 ms before the response and highly phase-locked gamma oscillations over central and posterior electrodes between 90 and 140 ms after the stimulus were observed. In trials in which the participants showed a slow response, no slow negative potential was observed and phase-locked gamma oscillations were significantly reduced. Furthermore, for slow response trials the phase-locked gamma oscillations were significantly delayed with respect to fast response trials.</p> <p>Conclusion</p> <p>These results indicate the relevance of phase-locked gamma oscillations for very fast (not necessarily detailed) integration processes.</p

Time Pressure Modulates Electrophysiological Correlates of Early Visual Processing

BACKGROUND: Reactions to sensory events sometimes require quick responses whereas at other times they require a high degree of accuracy-usually resulting in slower responses. It is important to understand whether visual processing under different response speed requirements employs different neural mechanisms. METHODOLOGY/PRINCIPAL FINDINGS: We asked participants to classify visual patterns with different levels of detail as real-world or non-sense objects. In one condition, participants were to respond immediately, whereas in the other they responded after a delay of 1 second. As expected, participants performed more accurately in delayed response trials. This effect was pronounced for stimuli with a high level of detail. These behavioral effects were accompanied by modulations of stimulus related EEG gamma oscillations which are an electrophysiological correlate of early visual processing. In trials requiring speeded responses, early stimulus-locked oscillations discriminated real-world and non-sense objects irrespective of the level of detail. For stimuli with a higher level of detail, oscillatory power in a later time window discriminated real-world and non-sense objects irrespective of response speed requirements. CONCLUSIONS/SIGNIFICANCE: Thus, it seems plausible to assume that different response speed requirements trigger different dynamics of processing

Impairments of Gestalt perception in the intact hemifield of hemianopic patients are reflected in gamma-band EEG activity

Gamma-band responses (GBRs) are associated with Gestalt perception processes. In the present EEG study, we investigated the effects of perceptual grouping on the visual GBR in the perimetrically intact visual field of patients with homonymous hemianopia and compared them to healthy participants. All observers were presented either random arrays of Gabor elements or arrays with an embedded circular arrangement. For the hemianopic patients, the circle was presented in their intact hemifield only. For controls, the hemifield for the circle presentation was counterbalanced across subjects. The participants were instructed to detect the circle by pressing a corresponding button. A wavelet transform based on Morlet wavelets was employed for the calculation of oscillatory GBRs. The early evoked GBR exhibited a larger amplitude and shorter latency for the healthy group compared to hemianopic patients and was associated with behavioral measures. The late total GBR between 200 and 400 ms after stimulus onset was significantly increased for Gestalt-like patterns in healthy participants. This effect was not manifested in patients. The present findings indicate deficits in the early and late visual processing of Gestalt patterns even in the intact hemifield of hemianopic patients compared to healthy participants

AM patterns for fast and slow motor responses and reaction time histogram

<p><b>Copyright information:</b></p><p>Taken from "From perception to action: phase-locked gamma oscillations correlate with reaction times in a speeded response task"</p><p>http://www.biomedcentral.com/1471-2202/8/27</p><p>BMC Neuroscience 2007;8():27-27.</p><p>Published online 17 Apr 2007</p><p>PMCID:PMC1868743.</p><p></p> Top: Reaction time histogram of all trials from all participants. Time axis is like below. Middle: Time frequency representation of AM for fast response trials. Bottom: Time frequency representation of AM in slow response trials. Data from the posterior ROI have been averaged to obtain the time frequency representations. Stimulus onset is at 0 ms. Note that the response time histogram peaks considerably earlier than the gamma activity

Evoked gamma band responses for fast and slow motor responses (right) and topographic maps of the evoked gamma responses in the time range 60 to 130 ms (left) averaged across all participants

<p><b>Copyright information:</b></p><p>Taken from "From perception to action: phase-locked gamma oscillations correlate with reaction times in a speeded response task"</p><p>http://www.biomedcentral.com/1471-2202/8/27</p><p>BMC Neuroscience 2007;8():27-27.</p><p>Published online 17 Apr 2007</p><p>PMCID:PMC1868743.</p><p></p> The vertical black lines indicate stimulus onset, dotted lines indicate mean response times of fast response trials (red) and slow response trials (blue). Note the marked increase of the response for fast response trials

Time frequency representations of eGBR (top) and phase-locking (bottom) for fast responses (left) and slow responses (right) of a single representative participant

<p><b>Copyright information:</b></p><p>Taken from "From perception to action: phase-locked gamma oscillations correlate with reaction times in a speeded response task"</p><p>http://www.biomedcentral.com/1471-2202/8/27</p><p>BMC Neuroscience 2007;8():27-27.</p><p>Published online 17 Apr 2007</p><p>PMCID:PMC1868743.</p><p></p> Both measures show a considerable enhancement for fast responses

Strength of the eGBR in trials with weak and strong negative potential preceding the stimulus

<p><b>Copyright information:</b></p><p>Taken from "From perception to action: phase-locked gamma oscillations correlate with reaction times in a speeded response task"</p><p>http://www.biomedcentral.com/1471-2202/8/27</p><p>BMC Neuroscience 2007;8():27-27.</p><p>Published online 17 Apr 2007</p><p>PMCID:PMC1868743.</p><p></p> Subaverages with weak negative potential are marked in grey, subaverages with strong negative potential are marked in white. Error bars indicate standard error of mean. Note the large error bars, that result from the fact that less than half of the participants responded with an enhanced evoked gamma peak in strong negativity trials, while this effect was even reversed in some participants

Averaged event related potentials for fast and slow responses (left) and topographic maps of the average activity in the time window -0

<p><b>Copyright information:</b></p><p>Taken from "From perception to action: phase-locked gamma oscillations correlate with reaction times in a speeded response task"</p><p>http://www.biomedcentral.com/1471-2202/8/27</p><p>BMC Neuroscience 2007;8():27-27.</p><p>Published online 17 Apr 2007</p><p>PMCID:PMC1868743.</p><p></p>5 to 0 s. The stimulus was presented at 0 s. Dotted lines indicate mean response times of fast response trials (red) and slow response trials (blue). Note that the negative potential starting approximately 700 ms before stimulus onset for fast response trials is virtually absent for slow response trials