Spatial grouping resolves ambiguity to drive temporal recalibration.

Cross-modal temporal recalibration describes a shift in the point of subjective simultaneity (PSS) between 2 events following repeated exposure to asynchronous cross-modal inputs-the adaptors. Previous research suggested that audiovisual recalibration is insensitive to the spatial relationship between the adaptors. Here we show that audiovisual recalibration can be driven by cross-modal spatial grouping. Twelve participants adapted to alternating trains of lights and tones. Spatial position was manipulated, with alternating sequences of a light then a tone, or a tone then a light, presented on either side of fixation (e.g., left tone-left light-right tone-right light, etc.). As the events were evenly spaced in time, in the absence of spatial-based grouping it would be unclear if tones were leading or lagging lights. However, any grouping of spatially colocalized cross-modal events would result in an unambiguous sense of temporal order. We found that adapting to these stimuli caused the PSS between subsequent lights and tones to shift toward the temporal relationship implied by spatial-based grouping. These data therefore show that temporal recalibration is facilitated by spatial grouping. (PsycINFO Database Record (c) 2011 APA, all rights reserved)

Sensory Mechanisms of Perceptual Uniformity

BACKGROUND AND AIMS: Visual experience appears rich in detail despite the poor performance of the vast majority of the visual field, as a result of the integration of coarse peripheral signals with the information of the comparatively tiny fovea. We examined the mechanisms of this integration by employing the uniformity illusion, in which a pattern with different properties in fovea and periphery uniformly takes the appearance of the fovea. We developed an adaptation paradigm to investigate whether the direction of an after-effect in the visual periphery followed the local, physical stimulation or the perception that arose under the Uniformity Illusion. We employed two different perceptual dimensions (orientation and spatial density) to investigate the extent to which the uniformity illusion is associated with changes in sensory encoding. RESULTS AND CONCLUSIONS: Experiments performed on two visual domains indicate that the uniformity illusion is not associated with a change in the sensory encoding on a local basis. Specifically, in our orientation experiments, the (V1-based) tilt after-effect only ever followed the local, physically presented orientation rather than the global orientation perceived under the illusion of uniformity. This was not due to insufficient exposure to the global pattern to produce an after-effect as presentation of physical uniformity for the same durations as participant reports of the illusion did produce an after-effect to the global orientation. Results on spatial-density based experiments showed an intermediate level of adaptation between (physical) low and high density, which could be consistent with an adaptation exerted by the illusory pattern. Thus, we could not rule out that the Uniformity Illusion might directly modify more abstract dimensions (such as numerosity, akin to our formalization of spatial density). However, the time invariance of the effect makes alternative explanations more likely and therefore, suggests that the uniformity illusion arises from high-level perceptual processes

Serial Dependence in Visual Variance

The recent history of perceptual experience has been shown to influence subsequent perception. Classically, this dependence on perceptual history has been examined in sensory adaptation paradigms, wherein prolonged exposure to a particular stimulus (e.g. a vertically oriented grating) produces changes in perception of subsequently presented stimuli (e.g. the tilt aftereffect). More recently, several studies have investigated the influence of shorter perceptual exposure with effects, referred to as serial dependence, being described for a variety of low and high-level perceptual dimensions. In this study, we examined serial dependence in the processing of dispersion statistics, namely variance - a key descriptor of the environment and indicative of the precision and reliability of ensemble representations. We found two opposite serial dependencies operating at different timescales, and likely originating at different processing levels: A positive, Bayesian-like bias was driven by the most recent exposures, dependent on feature-specific decision-making and appearing only when high confidence was placed in that decision; and a longer-lasting negative bias - akin to an adaptation after-effect - becoming manifest as the positive bias declined. Both effects were independent of spatial presentation location and the similarity of other close traits, such as mean direction of the visual variance stimulus. These findings suggest that visual variance processing occurs in high-level areas, but is also subject to a combination of multi-level mechanisms balancing perceptual stability and sensitivity, as with many different perceptual dimensions.</p

Sensorimotor temporal recalibration within and across limbs

Deciding precisely when we have acted is challenging, as actions involve a train of neural events spread across both space and time. Repeated delays between actions and consequent events can result in a shift, such that immediate feedback can seem to precede the causative act. Here we examined which neurocognitive representations are affected during such sensorimotor temporal recalibration, by testing if the effect generalizes across limbs and whether it might reflect altered decision criteria for temporal judgments. Hand or foot adaptation phases were interspersed with simultaneity judgments about actions involving the same or opposite limb. Shifts in the distribution of participants' simultaneity responses were quantified using a detection-theoretic model, where a shift of both boundaries together gives a stronger indication that the effect is not simply a result of decision bias. By demonstrating that temporal recalibration occurs in the foot as well as the hand, we confirmed that it is a robust motor phenomenon: Both low and high boundaries shifted reliably in the same-limb conditions. However, in cross-limb conditions only the high boundary shifted reliably. These two patterns are interpreted to reflect a genuine change in how the time of action is represented, and a timing criterion shift, respectively. (PsycINFO Database Record (c) 2013 APA, all rights reserved)

Intentional binding as Bayesian cue combination: testing predictions with trait individual differences

We investigated differences in intentional binding in high and low hypnotizable groups to explore two questions relating to (a) trait differences in the availability of motor intentions to metacognitive processes and (b) a proposed cue combination model of binding. An experience of involuntariness is central to hypnotic responding and may arise from strategically being unaware of one’s intentions. Trait differences in the ability to respond to hypnotic suggestion may reflect differing levels of access to motor intentions. Intentional binding refers to the subjective compression of the time between an action and its outcome, indicated by a forward shift in the judged time of an action toward its outcome (action binding) and the backward shift of an outcome toward a causal action (outcome binding). Intentional binding is sensitive to intentional action without requiring explicit reflection upon agency. One way of explaining the sensitivity of intentional binding is to see it as a simple case of multisensory cue combination in which awareness of intentions increases knowledge of the timing of actions. Here we present results consistent with such a mechanism. In a contingent presentation of action and outcome events, low hypnotizable had more precise timing judgments of actions and also showed weaker action binding than highs. These results support the theory that trait hypnotizability is related to access to information related to motor intentions, and that intentional binding reflects the Bayesian combination of cross-modal cues

High resolution analysis of proteome dynamics during <i>bacillus subtilis</i> sporulation

Bacillus subtilis vegetative cells switch to sporulation upon nutrient limitation. To investigate the proteome dynamics during sporulation, high-resolution time-lapse proteomics was performed in a cell population that was induced to sporulate synchronously. Here, we are the first to comprehensively investigate the changeover of sporulation regulatory proteins, coat proteins, and other proteins involved in sporulation and spore biogenesis. Protein co-expression analysis revealed four co-expressed modules (termed blue, brown, green, and yellow). Modules brown and green are upregulated during sporulation and contain proteins associated with sporulation. Module blue is negatively correlated with modules brown and green, containing ribosomal and metabolic proteins. Finally, module yellow shows co-expression with the three other modules. Notably, several proteins not belonging to any of the known transcription regulons were identified as co-expressed with modules brown and green, and might also play roles during sporulation. Finally, levels of some coat proteins, for example morphogenetic coat proteins, decreased late in sporulation