The relationship between cortical activation and perception investigated with invisible stimuli

When a uniformly illuminated surface is placed eccentrically on a dynamic textured background, after a few seconds, it is perceived to disappear and be replaced by the background texture. Such texture filling-in is thought to occur in retinotopic visual cortex, but it has proven difficult to distinguish the contributions of invisible target and visible background to signals measured in these areas. Here, we used magnetoencephalography to measure time-dependent brain responses in human observers experiencing texture completion. We measured responses specifically associated with the filled-in target, by isolating neural population signals entrained at the frequency of flicker of the target. When perceptual completion occurred, and the target became invisible, there was significant reduction in the magnetoencephalography power at the target frequency over contralateral posterior sensors. However, even a subjectively invisible target nevertheless evoked frequency-specific signals compared with a notarget baseline. These data represent evidence for a persistent targetspecific representation even for stimuli rendered invisible because of perceptual filling-in. magnetoencephalography ͉ perception ͉ perceptual completion ͉ visual cortex

Section: Discussionsupporting

confidence: 89%

Section: Discussionmentioning

confidence: 95%

Neural correlates of perceptual filling-in of an artificial scotoma in humans

Weil

Kilner

Haynes

et al. 2007

“…However, a second, equally important conclusion can be drawn from the results described: the presence of different, directionally selective neuronal populations in human V5, as is the case with its monkey homologue (14). It is known from previous studies that nonperceived monocular information is not lost beyond the point of convergence of the two eyes in V1, but is still present in the higher visual areas of the brain (2,6,7,24). If human V5 also contains directionally selective units, the two monocular inputs in the Opposite condition should activate two different neuronal populations in this area (i.e., twice as many neurons as activated by the Same condition).…”

Section: Psychophysicsmentioning

confidence: 64%

Motion processing, directional selectivity, and conscious visual perception in the human brain

Moutoussis

Zeki²

2008

Several human and monkey studies have demonstrated a close relationship between motion perception and activation of area V5, leading to the general view that activity in this area correlates with the subjective experience of motion. In the present study, we investigate whether the responses of this area are still governed by the motion percept when the latter is in conflict with the reality of the physical visual stimulation. We simultaneously presented two different, specially designed random-dot kinematograms, one to each eye. These stimuli either both had a single direction of motion and worked in synergy, or had opposite motion directions and thus cancelled each other out perceptually. In this way, we were able to pit the visual stimulus (one vs. two stimulating directions) against the reported perception (directional motion vs. motion noise) of human volunteers during fMRI experiments. We found that a strong motion stimulus that is weakly perceived is more effective in activating V5 (as well as V3) than a weaker motion stimulus, which is nevertheless robustly perceived. Thus, contrary to the prevailing view of perception being the correlate of activity in higher visual areas, we show here that activity is instead dominated by the properties of the physical stimulus, raising the question of whether there is a subpopulation of cells in V5 whose activity is critical for generating the motion percept. In addition, our results provide the first robust evidence for the presence of directionally selective neuronal populations in human prestriate cortex.consciousness ͉ fMRI ͉ area V5

“…In recent years, a diversity of putative objective correlates of consciousness have been described. Candidates include sustained activity in primary visual area V1 (1-3), amplification of perceptual processing (4,5), correlation across distant regions (6,7), joint parietal, frontal, and cingulate activation (4,8,9), cortico-cortical or thalamo-cortical ␥-band oscillations (10,11), and P300 waveform (12). Although these diverse measurements are often viewed as incompatible findings about the nature of conscious states, an increasingly attractive alternative is that they constitute different reflections of a single underlying phenomenon: the settling of brain activity into a temporary metastable state of global activity.…”

mentioning

confidence: 99%

A neuronal network model linking subjective reports and objective physiological data during conscious perception

Dehaene

Sergent

Changeux

2003

736

657

The subjective experience of perceiving visual stimuli is accompanied by objective neuronal activity patterns such as sustained activity in primary visual area (V1), amplification of perceptual processing, correlation across distant regions, joint parietal, frontal, and cingulate activation, ␥-band oscillations, and P300 waveform. We describe a neuronal network model that aims at explaining how those physiological parameters may cohere with conscious reports. The model proposes that the step of conscious perception, referred to as access awareness, is related to the entry of processed visual stimuli into a global brain state that links distant areas including the prefrontal cortex through reciprocal connections, and thus makes perceptual information reportable by multiple means. We use the model to simulate a classical psychological paradigm: the attentional blink. In addition to reproducing the main objective and subjective features of this paradigm, the model predicts an unique property of nonlinear transition from nonconscious processing to subjective perception. This all-or-none dynamics of conscious perception was verified behaviorally in human subjects.