Does visual flicker phase at gamma frequency modulate neural signal propagation and stimulus selection? (original) (raw)
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Gamma flicker triggers attentional selection without awareness
Proceedings of The National Academy of Sciences, 2009
Gamma band modulations in neural activity have been proposed to mediate attentional processes. To support a causal link between gamma activity and attentional selection, we attempt to evoke gamma oscillations by a 50-Hz subliminal flicker. We find that a subliminal 50-Hz flicker at a target location, before target presentation, speeds up and enhances target detection and discrimination. This effect is specific to the middle of the gamma range because it is not evident at <35-Hz flicker. It requires 300 ms to build up, dissipates within 250 ms of flicker offset, and shows a tendency to invert after 500 ms. The results are discussed in relation to a role for gamma band neural synchrony in the allocation of visual attention.
The spatial extent of lateral interactions in flicker perception
Vision Research, 2007
We investigated the influence of the relative phase of a temporally modulated annulus on the perceived flicker strength of a center stimulus having the same temporal modulation. These measurements were performed in two subjects at two temporal frequencies and with different outer diameters of the annulus. The perceived flicker strength was strongly modulated by the phase difference between center and surround stimulus. This modulation depended on the size of the annulus. In the absence of an annulus the perceived flicker strength was not modulated. The modulation initially increased with increasing annulus size and reached a plateau. The space constant of the function describing the modulation as a function of annulus size was about 0.5°and is similar to the sizes of receptive field surrounds of subcortical cells. This finding is in favor of the hypothesis that the physiological basis of the perceived flicker strength in the center stimulus is present already at a subcortical level.
Visual Flicker in the Gamma-Band Range Does Not Draw Attention
Journal of Neurophysiology, 2010
van Diepen RM, Born S, Souto D, Gauch A, Kerzel D. Visual flicker in the gamma-band range does not draw attention. , such as a flash or a startling sound, are believed to capture attention. Bauer, Cheadle, Parton, Müller, and Usher reported that attention can also be captured by a stimulus that flickers subliminally at 50 Hz, presumably by entrainment of neurons to the flicker frequency. In their reaction time (RT) task, participants had to locate a subtle change in the spatial frequency content of one of three Gabors (the target). Prior to target onset, presumably subliminal 50-Hz flicker in one of the Gabors served as a spatial cue. Bauer et al. found faster RTs when the cued location was congruent with the target location than when the cue was incongruent with the target location. In their experiments, the cue stopped to flicker at 50 Hz at target onset and was replaced by a stimulus flickering at 100 Hz (i.e., the screen refresh rate). In the present study, we show that the transition from 50 to 100 Hz results in a flash-like impression that can be localized above chance. We suggest that the illusory transition flash interfered with the localization of the subtle target, which contributed to the congruency effect. In support of this view, participants selected the flickering object more often than the non-flickering object when they failed to respond to the target. Further, no cueing effects were observed when the cue continued to flicker until the end of the trial or when the target was a salient change in polarity. In our view, the cueing effect occurs because observers confuse the illusory transition flash with the target when the two are similar. When truly subliminal flicker is used (70-Hz flicker), very small cueing effects persist in the absence of an illusory transition flash but may be accounted for by small effects on reaction time unrelated to attention.
Oscillatory mechanisms of feedforward and feedback visual processing
Trends in Neurosciences, 2015
Two recent monkey studies demonstrate that feedforward processing in the visual system is reflected by activity in the 40-90 Hz gamma band, whereas feedback is reflected by activity in the 5-18 Hz alpha and beta band. These findings can be applied to interpret human electrophysiological activity in complex visual tasks.
NeuroImage, 2013
Increases in the power of neural oscillations in the gamma (>40 Hz) band are a key signature of information processing in cortical neuronal networks. However, non-invasive detection of these very small oscillations is difficult due to the presence of potential artefacts (both muscular and ocular) in the same frequency band and requires highly optimised paradigms. Numerous studies have shown that the properties of visual gamma-band responses to simple pattern stimuli are highly tuned to the stimuli parameters used. The aim of this work was to compare gamma oscillation response properties across some of the more commonly used stimulus configurations. To do this, MEG and EEG recordings were made during the presentation of eight different stimulus types in a 2 × 2 × 2 design. For the first stimulus factor, "Type", the stimulus pattern was either an annulus grating or a square wave grating. For the second stimulus factor, "Field", stimuli were presented in either f...
Gamma-band synchronization in visual cortex predicts speed of change detection
Nature, 2006
Our capacity to process and respond behaviourally to multiple incoming stimuli is very limited. To optimize the use of this limited capacity, attentional mechanisms give priority to behaviourally relevant stimuli at the expense of irrelevant distractors. In visual areas, attended stimuli induce enhanced responses and an improved synchronization of rhythmic neuronal activity in the gamma frequency band (40-70 Hz) 1-11 . Both effects probably improve the neuronal signalling of attended stimuli within and among brain areas 1,12-16 . Attention also results in improved behavioural performance and shortened reaction times. However, it is not known how reaction times are related to either response strength or gamma-band synchronization in visual areas. Here we show that behavioural response times to a stimulus change can be predicted specifically by the degree of gamma-band synchronization among those neurons in monkey visual area V4 that are activated by the behaviourally relevant stimulus. When there are two visual stimuli and monkeys have to detect a change in one stimulus while ignoring the other, their reactions are fastest when the relevant stimulus induces strong gamma-band synchronization before and after the change in stimulus. This enhanced gamma-band synchronization is also followed by shorter neuronal response latencies on the fast trials. Conversely, the monkeys' reactions are slowest when gamma-band synchronization is high in response to the irrelevant distractor. Thus, enhanced neuronal gamma-band synchronization and shortened neuronal response latencies to an attended stimulus seem to have direct effects on visually triggered behaviour, reflecting an early neuronal correlate of efficient visuo-motor integration.