News and Events

Towards the neuronal correlate of visual awareness.

Publication Type:

Journal Article

Source:

Current opinion in neurobiology, Volume 6, Number 2, p.158–64 (1996)

Keywords:

Animals, Awareness, Awareness: physiology, Brain Diseases, Brain Diseases: physiopathology, Humans, Neurons, Neurons: physiology, Reference Values, Visual Cortex, Visual Cortex: physiopathology, Visual Perception, Visual Perception: physiology

Abstract:

Several encouraging developments towards identifying the neuronal correlate of visual awareness have emerged recently. Increasingly sophisticated behavioral paradigms permit the study of visual awareness in humans as well as in non-human primates. In patients with anatomically restricted lesions in striate and extrastriate cortex, highly informative deficits of visual awareness are observed. Similar deficits can be obtained in normal observers with a novel class of psychophysical displays. Taken together, these results suggest that the contents of visual awareness reflect neuronal activity in certain extrastriate, but not in striate, visual cortical areas.

Blindsight in normal observers.

Publication Type:

Journal Article

Source:

Nature, Volume 377, Number 6547, p.336–8 (1995)

URL:

http://www.nature.com/nature/journal/v377/n6547/abs/377336a0.html

Keywords:

Contrast Sensitivity, Humans, Optic Disk, Optic Disk: physiology, Psychophysics, Visual Cortex, Visual Cortex: physiology, Visual Cortex: physiopathology

Abstract:

Some patients with lesions in visual cortex lack conscious visual experience but, when tested, exhibit a significant ability, termed 'blindsight', to discriminate visual stimuli. Here we report two different visual displays that induce blindsight in normal observers. Using an objective measure, we show that conscious experience remains defective at presentation times much longer (1 s) than the onset of visual sensitivity (approximately 60 ms). To obtain this effect, we generate a contrast between visual textures and then conceal the contrast by superimposing 'complementary' textures. Complementarity can involve either opposite motion or binocular rivalry and orthogonal orientation. In both cases, observers locate the texture contrast reliably but do not, by either subjective or objective measures, consciously experience it. Taken together with present knowledge of the visual cortical site(s) at which opposite motion and rivalrous orientation interact, this observation bears upon the functional anatomy of conscious visual experience.

Attention activates winner-take-all competition among visual filters.

Publication Type:

Journal Article

Source:

Nature neuroscience, Volume 2, Number 4, p.375–81 (1999)

ISBN:

1097-6256 (Print)

URL:

http://www.nature.com/neuro/journal/v2/n4/abs/nn0499\_375.html

Keywords:

Attention, Attention: physiology, Contrast Sensitivity, Contrast Sensitivity: physiology, Discrimination (Psychology), Discrimination (Psychology): physiology, Humans, Models, Neurological, Neurons, Neurons: physiology, Pattern Recognition, Perceptual Masking, Sensory Thresholds, Space Perception, Space Perception: physiology, Visual, Visual Cortex, Visual Cortex: physiology, Visual Perception, Visual Perception: physiology, Visual: physiology

Abstract:

Shifting attention away from a visual stimulus reduces, but does not abolish, visual discrimination performance. This residual vision with 'poor' attention can be compared to normal vision with 'full' attention to reveal how attention alters visual perception. We report large differences between residual and normal visual thresholds for discriminating the orientation or spatial frequency of simple patterns, and smaller differences for discriminating contrast. A computational model, in which attention activates a winner-take-all competition among overlapping visual filters, quantitatively accounts for all observations. Our model predicts that the effects of attention on visual cortical neurons include increased contrast gain as well as sharper tuning to orientation and spatial frequency.

Attentional capacity is undifferentiated: concurrent discrimination of form, color, and motion.

Publication Type:

Journal Article

Source:

Perception & psychophysics, Volume 61, Number 7, p.1241–55 (1999)

URL:

http://www.springerlink.com/content/x66212t263077734/

Keywords:

Attention, Attention: physiology, Color Perception, Color Perception: physiology, Discrimination Learning, Discrimination Learning: physiology, Female, Form Perception, Form Perception: physiology, Humans, LeeKochBraun1999, Models, Motion Perception, Motion Perception: physiology, Theoretical, Time Factors

Abstract:

We report a series of experiments on the concurrent discrimination of form, color, and motion attributes. All tasks involved joint discrimination of attributes, and positions and were highly demanding of attention. We quantified interference between concurrent discriminations by establishing the attention-operating characteristic. Interference was indistinguishable for similar and dissimilar task combinations (form-form, color-color, motion-motion, and color-form, color-motion, motion-color, and motion-form, respectively). These results suggest strongly that different visual discriminations draw on the same attentional capacity–in other words, that the capacity of visual attention is undifferentiated.

Spatial vision thresholds in the near absence of attention.

Publication Type:

Journal Article

Source:

Vision research, Volume 37, Number 17, p.2409–18 (1997)

URL:

http://www.sciencedirect.com/science/article/pii/S0042698997000552

Keywords:

Attention, Attention: physiology, Contrast Sensitivity, Contrast Sensitivity: physiology, Humans, Photic Stimulation, Photic Stimulation: methods, Psychophysics, Sensory Thresholds, Space Perception, Space Perception: physiology

Abstract:

It is well known that attention increases the discriminability of some types of spatial information. To ascertain more specifically which types of spatial information benefit from attention, we have measured spatial vision thresholds both in the presence and in the near absence of attention. To obtain near absence of attention, we induce subjects to focus attention elsewhere in the display by means of a suitably demanding concurrent visual task. We measure contrast and orientation thresholds for sine-wave gratings, as well uni- and bidirectional offset thresholds for vernier targets. The results suggest that attention selectively lowers some thresholds but not others: orientation thresholds are far more affected than contrast thresholds, and bidirectional vernier thresholds are far more affected than unidirectional thresholds.

A short-term memory of multi-stable perception.

Publication Type:

Journal Article

Source:

Journal of vision, Volume 8, Number 13, p.7.1–14 (2008)

ISBN:

1534-7362

URL:

http://www.journalofvision.org/content/8/13/7.long

Keywords:

Adult, Female, Humans, Male, Memory, Models, PastukhovBraun2008, Psychological, Short-Term, Short-Term: physiology, Time Factors, Visual Perception, Visual Perception: physiology

Abstract:

It is well known that pauses in the presentation of an ambiguous display may stabilize its perceptual appearance. Here we show that this stabilization depends on an extended history spanning several dominance periods, not merely on the most recent period. Specifically, appearance after a pause often reflects less recent (but longer) dominance periods rather than more recent (but shorter) periods. Our results imply the existence of a short-tem memory for perceptual appearance that builds up over seconds, decays over minutes, and is robust to perceptual reversals. Although this memory is most evident in paused displays, it influences perceptual reversals also when display presentation continues: while the memory of one appearance prevails over that of the other, successive dominance durations are positively correlated. This highly unusual successive dependence suggests that multi-stable perception is not the memory-less 'renewal process' as which it has long been regarded. Instead, a short-term memory of appearance must be added to the multiple processes that jointly produce reversals of perceptual appearance.

Cumulative history quantifies the role of neural adaptation in multistable perception

Publication Type:

Journal Article

Source:

Journal of Vision, Volume 11, Number 10 (2011)

URL:

http://www.journalofvision.org/content/11/10/12.abstract

Abstract:

Neural adaptation plays an important role in multistable perception, but its effects are difficult to discern in sequences of perceptual reversals. Investigating the multistable appearance of kinetic depth and binocular rivalry displays, we introduce cumulative history as a novel statistical measure of adaptive state. We show that cumulative history\{$\backslash$textemdash\}an integral of past perceptual states, weighted toward the most recent states\{$\backslash$textemdash\}significantly and consistently correlates with future dominance durations: the larger the cumulative history measure, the shorter are future dominance times, revealing a robust effect of neural adaptation. The characteristic time scale of cumulative history, which may be computed by Monte Carlo methods, correlates with average dominance durations, as expected for a measure of neural adaptation. When the cumulative histories of two competing percepts are balanced, perceptual reversals take longer and their outcome becomes random, demonstrating that perceptual reversals are fluctuation-driven in the absence of adaptational bias. Our findings quantify the role of neural adaptation in multistable perception, which accounts for approximately 10% of the variability of reversal timing.

Perceptual reversals need no prompting by attention.

Publication Type:

Journal Article

Source:

Journal of vision, Volume 7, Number 10, p.5.1–17 (2007)

ISBN:

1534-7362

URL:

http://www.journalofvision.org/content/7/10/5.long

Keywords:

Adult, Attention, Attention: physiology, Contrast Sensitivity, Contrast Sensitivity: physiology, Depth Perception, Depth Perception: physiology, Female, Humans, Male, Models, Motion Perception, Motion Perception: physiology, Pastukhov2007, Photic Stimulation, Photic Stimulation: methods, Psychological, Psychophysics, Rotation, Time Factors, Visual Perception, Visual Perception: physiology

Abstract:

Many ambiguous patterns elicit spontaneous alternations of phenomenal appearance. Attention is known to influence these phenomenal reversals, as do several other factors. We asked whether a shift of attention individually prompts each reversal of phenomenal appearance. By combining intermittent presentation with a proven method of attention control, we monitored phenomenal alternations in the complete absence of attention shifts. We found that reversals become less frequent but continue even when observers neither report on nor shift attention to an ambiguous pattern. The statistical variability of reversals remains unaffected. We conclude that reversals of phenomenal appearance are not prompted externally by attention shifts, but internally by an intrinsic instability of the neural representation of ambiguous patterns.

Rare but precious: Microsaccades are highly informative about attentional allocation.

Publication Type:

Journal Article

Source:

Vision research, Volume 50, p.1173–1184 (2010)

URL:

http://www.sciencedirect.com/science/article/pii/S004269891000163X

Abstract:

To clarify the relation between attention and microsaccades, we monitored microsaccades while observers performed tasks with different attentional demand. In four high-demand conditions, observers shifted attention covertly to a peripheral location, or focused attention at fixation. Three corresponding low-demand conditions on physically identical displays provided a basis for comparison. Our results revealed two distinct effects of attentional load: higher loads were associated consistently with lower microsaccade rates, but also with increased directional selectivity (up to 98% congruent). In short, when microsaccades were most rare, the direction of microsaccades proved most informative about the location of the attention focus. The detailed time-courses of the two effects differed, however, suggesting that they may reflect independent processes.

Visual attention is a single, integrated resource.

Publication Type:

Journal Article

Source:

Vision research, Volume 49, Number 10, p.1166–73 (2009)

ISBN:

0042-6989

URL:

http://www.sciencedirect.com/science/article/pii/S0042698908002162

Keywords:

Attention, Attention: physiology, Color Perception, Color Perception: physiology, Discrimination (Psychology), Discrimination (Psychology): physiology, Female, Field Dependence-Independence, Humans, Male, PastukhovEtal2009, Pattern Recognition, Photic Stimulation, Photic Stimulation: methods, Psychophysics, Visual, Visual: physiology

Abstract:

Recent evidence for separate forms of attention for different visual attributes seems to conflict with Duncan's "integrated competition" theory of visual attention. To resolve this conflict, we established attention-operating characteristics for four pairs of visual discriminations. While one task was common to every pair, the other tasks were different and concerned different visual attributes. In all pairs, the common task exhibited the same performance-resource function, whether the other tasks involved entirely similar, partially similar, or entirely dissimilar visual attributes. These results confirm that visual attention conforms exactly to the predictions of a single, integrated resource.

Pages