News and Events

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>

Spatial and temporal attention revealed by microsaccades

Publication Type:

Journal Article

Source:

Vision research, Volume 85, p.45-57 (2013)

URL:

http://www.sciencedirect.com/science/article/pii/S0042698912003641?v=s5

Abstract:

<p>We compared the spatial and temporal allocation of attention as revealed by microsaccades. Observers viewed several concurrent &ldquo;rapid serial visual presentation&rdquo; (RSVP) streams in the periphery while maintaining fixation. They continually attended to, and discriminated targets in one particular, cued stream. Over and above this continuous allocation, spatial attention transients (&ldquo;attention shifts&rdquo;) were prompted by changes in the cued stream location and temporal attention transients (&ldquo;attentional blinks&rdquo;) by successful target discriminations. Note that the RSVP paradigm avoided the preparatory suppression of microsaccades in anticipation of stimulus or task events, which had been prominent in earlier studies. Both stream changes and target discriminations evoked residual modulations of microsaccade rate and direction, which were consistent with the presumed attentional dynamics in each case (i.e., attention shift and attentional blink, respectively). Interestingly, even microsaccades associated with neither stream change nor target discrimination reflected the continuous allocation of attention, inasmuch as their direction was aligned with the meridian of the target stream. We conclude that attentional allocation shapes microsaccadic activity continuously, not merely during dynamic episodes such as attentional shifts or blinks.</p>

Disparate time-courses of adaptation and facilitation in multi-stable perception

Publication Type:

Journal Article

Source:

Learning and Perception, Volume 5, Issue s2, p.101-118 (2013)

URL:

http://www.akademiai.com/content/9601q7447638l761/

Abstract:

<p>Far from being &ldquo;memoryless&rdquo;, the phenomenal appearance of an ambiguous display depends in complex ways on the recent history of similar perceptions. Given several possible appearances, the continued dominance of one appearance mitigates against its renewed dominance at a later time. This &ldquo;negative priming&quot; effect is likely caused by neural adaptation. At the same time, continued dominance of one appearance mitigates it in favor of its renewed dominance when stimulation resumes after an interruption. This &ldquo;positive priming&rdquo; effect may reflect some kind of neural facilitation. We have used a multi-stable, kinetic depth display to disentangle these positive and negative priming effects. We report that negative priming builds up and decays in seconds, whereas positive priming builds up in seconds and decays in minutes. Moreover, unambiguous displays induce negative, but not positive, priming. This difference, together with their disparate time-courses of recovery, render the two effects cleanly dissociable.</p>

Structure-from-motion: dissociating perception, neural persistence and sensory memory of illusory depth and illusory rotation

Publication Type:

Journal Article

Source:

Attention, perception & psychophysics, Volume 75, Issue 2, p.322-40 (2013)

URL:

http://www.springerlink.com/index/10.3758/s13414-012-0390-0

Keywords:

3D perception, Depth and shape from motion, Motion in depth, Multi-stable displays, Rivalry/bistable perception

Abstract:

<p>In the structure-from-motion paradigm, physical motion on a screen produces the vivid illusion of an object rotating in depth. Here we show how to dissociate illusory depth and illusory rotation in a structure-from-motion stimulus using a rotationally-asymmetric shape and reversals of physical motion. Reversals of physical motion create a conflict between the original illusory states and the new physical motion: either illusory depth remains constant and illusory rotation reverses, or illusory rotation stays the same and illusory depth reverses. When physical motion reverses after the interruption in presentation, we find that illusory rotation tends to remain constant for long blank durations (Tblank&ge;0.5 s), but illusory depth is stabilized if interruptions are short (Tblank&le;0.1 s). The stability of illusory depth over brief interruptions is consistent with the effect of neural persistence. When this is curtailed using a mask, stability of ambiguous vision (either for illusory depth or illusory rotation) is disrupted. We also examined the selectivity of the neural persistence of illusory depth. We found that it relies on a static representation of an interpolated illusory object, as changes to low level display properties had little detrimental effect. We discuss our findings with respect to other types of history dependence in multi-stable displays (sensory stabilization memory, neural fatigue, etc.). Our results suggest that when brief interruptions are used during the presentation of multi-stable displays, switches in perception are likely to rely on same neural mechanisms as spontaneous switches rather than switches due to the initial percept choice at the stimulus onset.</p>

The role of attention in ambiguous reversals of structure-from-motion

Publication Type:

Journal Article

Source:

PLoS ONE, Volume 7, Issue 5 (2012)

URL:

http://dx.plos.org/10.1371/journal.pone.0037734

Abstract:

<p>Multiple dots moving independently back and forth on a flat screen induce a compelling illusion of a sphere rotating in depth (structure-from-motion). If all dots simultaneously reverse their direction of motion, two perceptual outcomes are possible: either the illusory rotation reverses as well (and the illusory depth of each dot is maintained), or the illusory rotation is maintained (but the illusory depth of each dot reverses). We investigated the role of attention in these ambiguous reversals. Greater availability of attention – as manipulated with a concurrent task or inferred from eye movement statistics – shifted the balance in favor of reversing illusory rotation (rather than depth). On the other hand, volitional control over illusory reversals was limited and did not depend on tracking individual dots during the direction reversal. Finally, display properties strongly influenced ambiguous reversals. Any asymmetries between ‘front’ and ‘back’ surfaces – created either on purpose by coloring or accidentally by random dot placement – also shifted the balance in favor of reversing illusory rotation (rather than depth). We conclude that the outcome of ambiguous reversals depends on attention, specifically on attention to the illusory sphere and its surface irregularities, but not on attentive tracking of individual surface dots.</p>

Believable change: bistable reversals are governed by physical plausibility

Publication Type:

Journal Article

Source:

Journal of Vision, Volume 12, Issue 1 (2012)

URL:

http://www.journalofvision.org/content/12/1/17.full

Abstract:

<p>Planar motion flows can induce the illusory appearance of a volume rotating in depth (“depth-from-motion”; Sperling and Dosher, 1994). This appearance changes spontaneously from time to time, reversing simultaneously its depth and its direction of rotation. We investigated asymmetric illusory volumes, which reverse more frequently at some angles of view than at others. In three experiments, we studied spontaneous joint reversals of depth and motion, as well as induced reversals of either motion or depth alone. We find that depth reversals occur exclusively when the illusory volume is depth symmetric (so that the shape of the volume remains unchanged). In contrast, motion reversals occur at all view angles, but their frequency varies with the motion speed. The probability of joint reversals is well approximated by the product of the individual reversal probabilities, suggestive of two independent random processes. We hypothesize that reversals of illusory volumes are conditioned by prior experience of physical transformations in the visual world.</p>

Feature-based attention spreads preferentially in an object-specific manner

Publication Type:

Journal Article

Source:

Vision Research, Volume 54 (2012)

URL:

http://www.sciencedirect.com/science/article/pii/S0042698911004111

Keywords:

Attention, Motion, Psychophysics

Abstract:

<p>We studied the spreading of feature-based attention from attended to ignored motion fields (linear, circular, and combinations). When observers attended one of two superimposed motion fields on one side of the visual midline, sub-threshold priming by an ignored motion field was altered significantly on the opposite side of the midline. This attentional spreading was observed only when attended and ignored motion fields conformed to a complex global flow, not when they shared the same linear motion. These findings corroborate an earlier study (Festman and Braun, 2010), which obtained similar results with a complementary methodology. We conclude that feature-based attention is more complex than hitherto appreciated in that it spreads preferentially in an object-specific manner.</p>

Robust working memory in an asynchronously spiking neural network realized in neuromorphic VLSI

Publication Type:

Journal Article

Source:

Frontiers in Neuroscience, Volume 5 (2011)

ISBN:

1662-453X

URL:

http://www.frontiersin.org/Journal/Abstract.aspx?s=755&name=neuromorphic_engineering&ART_DOI=10.3389/fnins.2011.00149

Abstract:

<p>BACKGROUND: We demonstrate bistable attractor dynamics in a spiking neural network implemented with neuromorphic VLSI hardware. The on-chip network consists of three interacting populations (two excitatory, one inhibitory) of integrate-and-fire (LIF) neurons. One excitatory population is distinguished by strong synaptic self-excitation, which sustains meta-stable states of ?high? and ?low?-firing activity. Depending on the overall excitability, transitions to the ?high? state may be evoked by external stimulation, or may occur spontaneously due to random activity fluctuations. In the former case, the ?high? state retains a ?working memory? of a stimulus until well after its release. In the latter case, ?high? states remain stable for seconds, three orders of magnitude longer than the largest time-scale implemented in the circuitry. Evoked and spontaneous transitions form a continuum and may exhibit a wide range of latencies, depending on the strength of external stimulation and of recurrent synaptic excitation. In addition, we investigated ?corrupted? ?high? states comprising neurons of both excitatory populations. Within a ?basin of attraction?, the network dynamics ?corrects? such states and re-establishes the prototypical ?high? state. We conclude that, with effective theoretical guidance, full-fledged attractor dynamics can be realized with comparatively small populations of neuromorphic hardware neurons.</p>

Pages