News and Events

Stochastic Accumulation by Cortical Columns May Explain the Scalar Property of Multistable Perception

Publication Type:

Journal Article

Source:

Physical Review LettersPhysical Review Letters, Volume 113, Issue 9, p.098103 (2014)

URL:

http://link.aps.org/doi/10.1103/PhysRevLett.113.098103

Abstract:

The timing of certain mental events is thought to reflect random walks performed by underlying neural dynamics. One class of such events—stochastic reversals of multistable perceptions—exhibits a unique scalar property: even though timing densities vary widely, higher moments stay in particular proportions to the mean. We show that stochastic accumulation of activity in a finite number of idealized cortical columns—realizing a generalized Ehrenfest urn model—may explain these observations. Modeling stochastic reversals as the first-passage time of a threshold number of active columns, we obtain higher moments of the first-passage time density. We derive analytical expressions for noninteracting columns and generalize the results to interacting columns in simulations. The scalar property of multistable perception is reproduced by a dynamic regime with a fixed, low threshold, in which the activation of a few additional columns suffices for a reversal.

The Slow Science Manifesto

We are scientists. We don’t blog. We don’t twitter. We take our time.

Don’t get us wrong—we do say yes to the accelerated science of the early 21st century. We say yes to the constant flow of peer-review journal publications and their impact; we say yes to science blogs and media & PR necessities; we say yes to increasing specialization and diversification in all disciplines. We also say yes to research feeding back into health care and future prosperity. All of us are in this game, too.

However, we maintain that this cannot be all. Science needs time to think. Science needs time to read, and time to fail. Science does not always know what it might be at right now. Science develops unsteadi­ly, with jerky moves and un­predict­able leaps forward—at the same time, however, it creeps about on a very slow time scale, for which there must be room and to which justice must be done.

Slow science was pretty much the only science conceivable for hundreds of years; today, we argue, it deserves revival and needs protection. Society should give scientists the time they need, but more importantly, scientists must take their time.

We do need time to think. We do need time to digest. We do need time to mis­understand each other, especially when fostering lost dialogue between humanities and natural sciences. We cannot continuously tell you what our science means; what it will be good for; because we simply don’t know yet. Science needs time.

—Bear with us, while we think.

http://slow-science.org/

 

Perceptual adaptation to structure-from-motion depends on the size of adaptor and probe objects, but not on the similarity of their shapes

Publication Type:

Journal Article

Source:

Attention, perception & psychophysics, Volume 76, Issue 2, p.473-88 (2014)

URL:

http://link.springer.com/article/10.3758%2Fs13414-013-0567-1

Abstract:

<p>Perceptual adaptation destabilizes the phenomenal appearance of multistable visual displays. Prolonged dominance of a perceptual state fatigues the associated neural population, lowering the likelihood of renewed perception of the same appearance (Nawrot &amp; Blake in Perception &amp; Psychophysics, 49, 230–44, 1991). Here, we used a selective adaptation paradigm to investigate perceptual adaptation for the illusory rotation of ambiguous structure-from-motion (SFM) displays. Specifically, we generated SFM objects with different three-dimensional shapes and presented them in random order, separating successive objects by brief blank periods, which included a mask. To assess the specificity of perceptual adaptation to the shape of SFM objects, we established the probability that a perceived direction of rotation persisted between successive objects of similar or dissimilar shape. We found that the strength of negative aftereffects depended on the volume, but not the shape, of adaptor and probe objects. More voluminous objects were both more effective as adaptor objects and more sensitive as probe objects. Surprisingly, we found these volume effects to be completely independent, since any relationship between two shapes (such as overlap between volumes, similarity of shape, or similarity of velocity profiles) failed to modulate the negative aftereffect. This pattern of results was the opposite of that observed for sensory memory of SFM objects, which reflects similarity between objects, but not volume of individual objects (Pastukhov et al. inAttention, Perception &amp; Psychophysics, 75, 1215–1229, 2013). The disparate specificities of perceptual adaptation and sensory memory for identical SFM objects suggest that the two aftereffects engage distinct neural representations, consistent with recent brain imaging results (Schwiedrzik et al. in Cerebral Cortex, 2012).</p>

Sensory memory of illusory depth in structure-from-motion

Publication Type:

Journal Article

Source:

Attention, perception & psychophysics, Volume 76, Issue 1, p.123-32 (2014)

Keywords:

multi-stability, sensory memory, structure-from-motion

Abstract:

<p>When multistable displays (stimuli consistent with two or more equally plausible perceptual interpretations) are presented intermittently, their perceptions are stabilized by sensory memory. Independent memory traces are generated not only for different types of multistable displays (Maier, Wilke, Logothetis, &amp; Leopold, Current Biology 13:1076–1085, 2003), but also for different ambiguous features of binocular rivalry (Pearson &amp; Clifford, Journal of Vision 4:196–202, 2004). In the present study, we examined whether a similar independence of sensory memories is observed in structure-from-motion (SFM), a multistable display with two ambiguous properties. In SFM, a 2-D planar motion creates a vivid impression of a rotating 3-D volume. Both the illusory rotation and illusory depth (i.e., how close parts of an object appear to the observer) of an SFM object are ambiguous. We dissociated the sensory memories of these two ambiguous properties by using an intermittent presentation in combination with a forced-ambiguous-switch paradigm (Pastukhov, Vonau, &amp; Braun, PLoS ONE 7:e37734, 2012). We demonstrated that the illusory depth of SFM generates a sensory memory trace that is independent from that of illusory rotation. Despite this independence, the specificities levels of the sensory memories were identical for illusory depth and illusory rotation. The history effect was weakened by a change in the volumetric property of a shape (whether it was a hollow band or a filled drum volume), but not by changes in color or size. We discuss how these new results constrain models of sensory memory and SFM processing.</p>

Alexander Pastukhov receives "Best Article Award 2013"

Alexander Pastukhov receives "Best Article Award 2013"

The award is presented by the Psychonomic Society for the best contribution of the year in the prestigious scientific journal “Attention, Perception & Psychophysics” (August 2013).

Alexander Pastukhov

Alexander Pastukhov, Postdoc in the lab of Jochen Braun (Bernstein Group Magdeburg, Otto-von-Guericke-University Magdeburg), receives the award for his work on neural representation of three-dimensional visual objects. He was nominated for two different publications by two independent editors. At the moment, Alexander Pastukhov habilitates at the Center for Behavioral Brain Sciences, Magdeburg.

The award will be ceremonially conferred at the annual meeting of the Psychonomic Society in Toronto, Canada, in November 2013.

The nominated contributions are:

Pastukhov, A., & Braun, J. (2013). Structure-from-motion: dissociating perception, neural persistence, and sensory memory of illusory depth and illusory rotation. Attention, perception & psychophysics, 75 (2), p.322-40.

Pastukhov, A., Fullekrug, J., & Braun, J. (2013). Sensory memory of structure-from-motion is shape specific.Attention, perception & psychophysicsб 75(6), p. 1215-1229.

 

Jochen Braun participates in Marie Curie Network “INDIREA”

Jochen Braun participates in Marie Curie Network “INDIREA”

The Marie Curie Initial Training Network (ITN) “Individualized Diagnostics and Rehabilitation of Attention, INDIREA” focuses on improving the diagnosis and rehabilitation of neuropsychological disorders of attention (August 2013).

Jochen Braun an Marie Curie Network “INDIREA” beteiligt_140813

Jochen Braun
Image: Otto-von-Guericke-Universität Magdeburg

The ITN – coordinated by Glyn Humphreys, Oxford – will run over a period of 3.5 years and is supported by the EU with a total funding volume of over 3.7 M €. It will finance research projects and training opportunities of 13 PhD students.  Additionally, regular meetings and exchanges between partners will take place.

The network involves neuropsychologists, neuroscientists, and industry partners in Oxford, Munich, Copenhagen, Magdeburg, Barcelona, Dublin, and elsewhere. German contributing scientists are Jochen Braun (coordinator of the Bernstein Group Magdeburg) and Hermann Müller (LMU Munich).  The common goal is to deepen our understanding of the neurobiological basis of attention, by linking computational models, brain imaging information, and behavioral performance, and by applying the results to clinical procedures for diagnosis and rehabilitation.

 

Sensory memory of structure-from-motion is shape-specific

Publication Type:

Journal Article

Source:

Attention, Perception, & Psychophysics, Volume 75, Issue 6, p.1215-1229 (2013)

URL:

http://link.springer.com/article/10.3758/s13414-013-0471-8/fulltext.html

Keywords:

structure-from-motion; sensory memory

Abstract:

<p>Perceptual priming can stabilize the phenomenal appearance of multi-stable visual displays (Leopold, Wilke, Maier, &amp; Logothetis, 2002). Prior exposure to such displays induces a sensory memory of their appearance, which persists over long intervals and intervening stimulation and which facilitates renewed perception of the same appearance. Here, we investigated perceptual priming for the apparent rotation in depth of ambiguous structure-from-motion (SFM) displays. Specifically, we generated SFM objects with different three-dimensional shapes and presented them in random order and with intervening blank periods. To assess perceptual priming, we established the probability that a perceived direction of rotation persisted between successive objects. In general, persistence was largest between identical objects, intermediate between similar objects, and negligible between dissimilar objects. These results demonstrate unequivocally that sensory memory for apparent rotation is specific to three-dimensional shape, contrary to previous reports (e.g., Maier, Wilke, Logothetis, &amp; Leopold, 2003). As persistence did not depend on presentation order for any pair of objects, it provides a commutative measure for the similarity of object shapes. However, it is not clear exactly which features or aspects of object shape determine similarity. At least, we did not find simple, low-level features (such as volume overlap, heterogeneity, or rotational symmetry) that could have accounted for all observations. Accordingly, it seems that sensory memory of SFM (which underlies priming of ambiguous rotation) engages higher-level representations of object surface and shape.</p>

Multi-stable perception balances stability and sensitivity

Publication Type:

Journal Article

Source:

Frontiers in Computational Neuroscience, Volume 7, Issue 17 (2013)

URL:

http://www.frontiersin.org/Computational_Neuroscience/10.3389/fncom.2013.00017/full

Keywords:

ambiguous displays, binocular rivalry, cumulative history, multi-stability, structure-from-motion

Abstract:

<p>We report that multi-stable perception operates in a consistent, dynamical regime, balancing the conicting goals of stability and sensitivity. When a multi-stable visual display is viewed continuously, its phenomenal appearance reverses spontaneously at irregular intervals. We characterized the perceptual dynamics of individual observers in terms of four statistical measures: the distribution of dominance times (mean and variance) and the novel, subtle dependence on prior history (correlation and time-constant). The dynamics of multi-stable perception is known to re ect several stabilizing and destabilizing factors. Phenomenologically, its main aspects are captured by a simplistic computational model with competition, adaptation, and noise. We identi ed small parameter volumes (~3% of the possible volume) in which the model reproduced both dominance distribution and history-dependence of each observer. For 21 of 24 data sets, the identi ed volumes clustered tightly (~15% of the possible volume), revealing a consistent `operating regime&#39; of multi-stable perception. The `operating regime&#39; turned out to be marginally stable or, equivalently, near the brink of an oscillatory instability. The chance probability of the observed clustering was &lt;0.02. To understand the functional signi cance of this empirical `operating regime&#39;, we compared it to the theoretical `sweet spot&#39; of the model. We computed this `sweet spot&#39; as the intersection of the parameter volumes in which the model produced stable perceptual outcomes and in which it was sensitive to input modulations. Remarkably, the empirical `operating regime&#39; proved to be largely coextensive with the theoretical `sweet spot&#39;. This demonstrated that perceptual dynamics was not merely consistent but also functionally optimized (in that it balances stability with sensitivity). Our results imply that multi-stable perception is not a laboratory curiosity, but re ects a functional optimization of perceptual dynamics for visual inference. We surmise that a marginally stable dynamics arbitrates the exploitation-exploration dilemma of a system that acquires prior experience through reinforcement learning.</p>

Pages