“…Following standard preprocessing and HFB computation, we tested the onset response (50–350 ms, uncontaminated by either gaps or blinks) to each electrode optimal object stimuli, compared with the inter-block gray blank baseline periods (Figure 2). In agreement with previous reports (Noy et al, 2015a), responsivity of a considerable effect size was found almost entirely within the anatomically defined visual cortex, showing only minimal responses in more anterior cortical regions.10.7554/eLife.17243.006Figure 2.High-frequency broadband (HFB, 70–150 Hz) visual responses to object images.HFB responses from all participants, sampled from 50 to 350 ms following the transition from one object image to another, compared with the HFB activity sampled during inter-block blanks are presented. Each circle marks the location of one electrode on a common cortical template.…”
We hardly notice our eye blinks, yet an externally generated retinal interruption of a similar duration is perceptually salient. We examined the neural correlates of this perceptual distinction using intracranially measured ECoG signals from the human visual cortex in 14 patients. In early visual areas (V1 and V2), the disappearance of the stimulus due to either invisible blinks or salient blank video frames ('gaps') led to a similar drop in activity level, followed by a positive overshoot beyond baseline, triggered by stimulus reappearance. Ascending the visual hierarchy, the reappearance-related overshoot gradually subsided for blinks but not for gaps. By contrast, the disappearance-related drop did not follow the perceptual distinction – it was actually slightly more pronounced for blinks than for gaps. These findings suggest that blinks' limited visibility compared with gaps is correlated with suppression of blink-related visual activity transients, rather than with "filling-in" of the occluded content during blinks.DOI:
http://dx.doi.org/10.7554/eLife.17243.001
“…Following standard preprocessing and HFB computation, we tested the onset response (50–350 ms, uncontaminated by either gaps or blinks) to each electrode optimal object stimuli, compared with the inter-block gray blank baseline periods (Figure 2). In agreement with previous reports (Noy et al, 2015a), responsivity of a considerable effect size was found almost entirely within the anatomically defined visual cortex, showing only minimal responses in more anterior cortical regions.10.7554/eLife.17243.006Figure 2.High-frequency broadband (HFB, 70–150 Hz) visual responses to object images.HFB responses from all participants, sampled from 50 to 350 ms following the transition from one object image to another, compared with the HFB activity sampled during inter-block blanks are presented. Each circle marks the location of one electrode on a common cortical template.…”
We hardly notice our eye blinks, yet an externally generated retinal interruption of a similar duration is perceptually salient. We examined the neural correlates of this perceptual distinction using intracranially measured ECoG signals from the human visual cortex in 14 patients. In early visual areas (V1 and V2), the disappearance of the stimulus due to either invisible blinks or salient blank video frames ('gaps') led to a similar drop in activity level, followed by a positive overshoot beyond baseline, triggered by stimulus reappearance. Ascending the visual hierarchy, the reappearance-related overshoot gradually subsided for blinks but not for gaps. By contrast, the disappearance-related drop did not follow the perceptual distinction – it was actually slightly more pronounced for blinks than for gaps. These findings suggest that blinks' limited visibility compared with gaps is correlated with suppression of blink-related visual activity transients, rather than with "filling-in" of the occluded content during blinks.DOI:
http://dx.doi.org/10.7554/eLife.17243.001
“…Empirically, both local and global ignitions are revealed under various conditions (e.g., Dehaene and Changeux, 2005;Fisch et al, 2009;Noy et al, 2015). A plausible model for their generation is readily suggested by noting the dense lateral intra-and inter-areal connections that characterize cortical networks (e.g., Amir et al, 1993;Douglas and Martin, 1991; see review by Felleman and Van Essen, 1991).…”
Section: Mechanisms Underlying the Ignition Thresholdmentioning
confidence: 97%
“…Specifically, it has been previously proposed that, when ignition occurs in a network of cortical neurons, the corresponding content becomes subjectively available for conscious report. Alternative models emphasize a global neuronal workspace (GNW) that broadcasts a neural representation to many cortical sites (Dehaene and Changeux, 2011;Dehaene et al, 2003), or a more local framework where the subjective content depends mainly on ignition in content-selective representations (e.g., Noy et al, 2015). The neuronal ignition threshold would, therefore, be the physiological correlate of the threshold for content-specific perceptual awareness, as defined psychophysically.…”
Section: Consequences Of the Proposed Hypothesismentioning
Recent human neurophysiological recordings have uncovered two fundamental modes of cerebral cortex activity with distinct dynamics: an active mode characterized by a rapid and sustained activity ("ignition") and a spontaneous (resting-state) mode, manifesting ultra-slow fluctuations of low amplitude. We propose that both dynamics reflect two faces of the same recurrent loop mechanism: an integration device that accumulates ongoing stochastic activity and, either spontaneously or in a task-driven manner, crosses a dynamic threshold and ignites, leading to content-specific awareness. The hypothesis can explain a rich set of behavioral and neuronal phenomena, such as perceptual threshold, the high non-linearity of visual responses, the subliminal nature of spontaneous activity fluctuations, and the slow activity buildup anticipating spontaneous behavior (e.g., readiness potential). Further elaborations of this unified scheme, such as a cascade of integrators with different ignition thresholds or multi-stable states, can account for additional complexities in the repertoire of human cortical dynamics.
“…If indeed, high neural activation in visual areas (which exceed an ignition threshold; e.g., Noy et al, ) is the most critical neural property that distinguishes conscious from unconscious perception, and if higher neural activation is a critical factor that enhances the precision of a neural representation, this provides further (neural) support for the empirical association between consciousness and precision.…”
Section: Tipping the Balance For Overflowmentioning
The question of whether conscious experience is restricted by cognitive access and exhausted by report, or whether it overflows it—comprising more information than can be reported—is hotly debated. Recently, we provided evidence in favor of Overflow, showing that observers discriminated the color‐diversity (CD) of letters in an array, while their working‐memory and attention were dedicated to encoding and reporting a set of cued letters. An alternative interpretation is that CD‐discriminations do not entail conscious experience of the underlying colors. Here we argue, based on conceptual considerations and consistency with neuroscience and phenomenology, in favor of the Overflow interpretation.
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