Gamma flicker triggers attentional selection without awareness

Abstract

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.visual attention ͉ neural synchrony ͉ gamma ͉ psychophysics ͉ subliminal T he nature of the neural mechanisms underlying visual attention-the ability of humans and animals to select a limited number of stimuli from the multitude simultaneously present in the visual field for prioritized processing-remains a fundamental problem in visual neuroscience (1). A complete theory of visual attention must explain how the relative salience of selected stimuli is enhanced in neural terms, even though they are often not singled out by increased firing rates (2, 3). One recently proposed solution is the ''Attention-Gamma'' hypothesis, according to which synchronized gamma band (40-70 Hz) modulations in neural activity mediate attentional processes (4-10). This hypothesis is supported by a correlation, across trials, between the speed of behavioral responses in a visual detection task and the power in the gamma frequency range of V4 neurons (10-12). In these studies, Fries, Womelsdorf, and colleagues demonstrated that top-down visual attention is associated with internal gamma band synchrony in task-specific neural populations, which could be generated by top-down attentional modulations (13, 14). Thus, it is possible that selected neural representations are given a gamma band oscillatory tag by a top-down attention mechanism (15). If this is the case, it may be possible to trigger the effects of selective attention (enhanced selection and perception) by externally evoking gamma band oscillations of the relevant neural representation, thus mimicking the attentional tag.To test this hypothesis, we examined whether external stimulus flicker at a specific location, which is expected to evoke phaselocked neural activity at the same frequency, results in attentional orientation to that location in the absence of conscious detection of the flicker; if the flicker were detectable, it could lead to an orienting of attention toward its location as a result of exogenous or endogenous processes that are not specific to the temporal modulation. To test whether subliminally evoked neural synchronization has an attentional effect, we built on recent studies demonstrating that visual flicker in the midgamma band range (40-70 Hz) entrains periodic neural responses at the same frequency in the visual cortex [refs. 16 and 17; ...

Masked singleton effects

“…The reason is that reactive modification of processing following a misguiding visual prime would be much harder with invisible than with visible stimuli (see Ansorge, Heumann, & Scharlau, 2002;Cheesman & Merikle, 1985). Ivanoff and Klein (2003) observed that after initial capture by invisible stimuli, attention could not be deallocated from the position of the capturing stimulus within 300 msec (see also Bauer, Cheadle, Parton, Müller, & Usher, 2009). Likewise, Ansorge et al (2002) found that the pace of learning to deallocate attention from an irrelevant singleton was proportional to the singleton's visibility.…”

Temporal tagging of attended objects

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“…Selective attention is the triage process of extracting the most relevant sensory information and suppressing the remainder. In a recent issue of PNAS, through an ingenious psychophysical experiment, Bauer et al (1) provide insight into the mechanisms underlying this cognitive function.…”

Good vibrations switch attention: An affective function for network oscillations in evolutionary simulations

“…From the different frequency bands, gamma oscillations have most consistently been associated with attention (Bauer, Cheadle, Parton, Müller, & Usher, 2009;Womelsdorf & Fries, 2007). The relevance of these oscillations, if any (Pareti & DePalma, 2004), remains a matter of debate.…”