Strategies for enhancing automatic fixation detection in head-mounted eye tracking.

Moving through a dynamic world, humans need to intermittently stabilize gaze targets on their retina to process visual information. Overt attention being thus split into discrete intervals, the automatic detection of such fixation events is paramount to downstream analysis in many eye-tracking studies. Standard algorithms tackle this challenge in the limiting case of little to no head motion.

Quantitative videomicroscopy reveals latent control of cell-pair rotations in vivo.

Collective cell rotations are widely used during animal organogenesis. Theoretical and in vitro studies have conceptualized rotating cells as identical rigid-point objects that stochastically break symmetry to move monotonously and perpetually within an inert environment. However, it is unclear whether this notion can be extrapolated to a natural context, where rotations are ephemeral and heterogeneous cellular cohorts interact with an active epithelium.

Gaze-angle dependency of pupil-size measurements in head-mounted eye tracking.

Pupillometry - the study of temporal changes in pupil diameter as a function of external light stimuli or cognitive processing - requires the accurate and gaze-angle independent measurement of pupil dilation. Expected response amplitudes often are only a few percent relative to a pre-stimulus baseline, thus demanding for sub-millimeter accuracy. Video-based approaches to pupil-size measurement aim at inferring pupil dilation from eye images alone.

In Vivo Force Application Reveals a Fast Tissue Softening and External Friction Increase during Early Embryogenesis.

During development, cell-generated forces induce tissue-scale deformations to shape the organism [1,2]. The pattern and extent of these deformations depend not solely on the temporal and spatial profile of the generated force fields but also on the mechanical properties of the tissues that the forces act on. It is thus conceivable that, much like the cell-generated forces, the mechanical properties of tissues are modulated during development in order to drive morphogenesis toward specific developmental endpoints.

Adherens Junction Length during Tissue Contraction Is Controlled by the Mechanosensitive Activity of Actomyosin and Junctional Recycling.

During epithelial contraction, cells generate forces to constrict their surface and, concurrently, fine-tune the length of their adherens junctions to ensure force transmission. While many studies have focused on understanding force generation, little is known on how junctional length is controlled. Here, we show that, during amnioserosa contraction in Drosophila dorsal closure, adherens junctions reduce their length in coordination with the shrinkage of apical cell area, maintaining a nearly constant junctional straightness.

Actin cortex architecture regulates cell surface tension.

Animal cell shape is largely determined by the cortex, a thin actin network underlying the plasma membrane in which myosin-driven stresses generate contractile tension. Tension gradients result in local contractions and drive cell deformations. Previous cortical tension regulation studies have focused on myosin motors.

Patterned Contractile Forces Promote Epidermal Spreading and Regulate Segment Positioning during Drosophila Head Involution.

Epithelial spreading is a fundamental mode of tissue rearrangement occurring during animal development and wound closure. It has been associated either with the collective migration of cells [1, 2] or with actomyosin-generated forces acting at the leading edge (LE) and pulling the epithelial tissue [3, 4]. During the process of Drosophila head involution (HI), the epidermis spreads anteriorly to envelope the head tissues and fully cover the embryo [5].

Spontaneous oscillations of elastic contractile materials with turnover.

Single and collective cellular oscillations driven by the actomyosin cytoskeleton have been observed in numerous biological systems. Here, we propose that these oscillations can be accounted for by a generic oscillator model of a material turning over and contracting against an elastic element. As an example, we show that during dorsal closure of the Drosophila embryo, experimentally observed changes in actomyosin concentration and oscillatory cell shape changes can, indeed, be captured by the dynamic equations studied here.

Monitoring actin cortex thickness in live cells.

Animal cell shape is controlled primarily by the actomyosin cortex, a thin cytoskeletal network that lies directly beneath the plasma membrane. The cortex regulates cell morphology by controlling cellular mechanical properties, which are determined by network structure and geometry. In particular, cortex thickness is expected to influence cell mechanics.

Spontaneous voltage oscillations and response dynamics of a Hodgkin-Huxley type model of sensory hair cells.

We employ a Hodgkin-Huxley type model of basolateral ionic currents in bullfrog saccular hair cells to study the genesis of spontaneous voltage oscillations and their role in shaping the response of the hair cell to external mechanical stimuli. Consistent with recent experimental reports, we find that the spontaneous dynamics of the model can be categorized using conductance parameters of calcium activated potassium, inward rectifier potassium, and mechano-electrical transduction ionic currents. The model is demonstrated to exhibit a broad spectrum of autonomous rhythmic activity, including periodic and quasiperiodic oscillations with two independent frequencies as well as various regular and chaotic bursting patterns.

Coupling a sensory hair-cell bundle to cyber clones enhances nonlinear amplification.

The vertebrate ear benefits from nonlinear mechanical amplification to operate over a vast range of sound intensities. The amplificatory process is thought to emerge from active force production by sensory hair cells. The mechano-sensory hair bundle that protrudes from the apical surface of each hair cell can oscillate spontaneously and function as a frequency-selective, nonlinear amplifier.

Local exponents of nonlinear compression in periodically driven noisy oscillators.

Nonlinear compression of periodic signals is a key feature of the active amplifier in inner ear organs of all vertebrates. Different exponents alpha(0) in [-0.88,-0.

WITHDRAWN: Coupled hair bundles could endow the cochlear amplifier with sharp frequency tuning and nonlinear compression.

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.

WITHDRAWN: Coupled hair bundles could endow the cochlear amplifier with sharp frequency tuning and nonlinear compression.

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.

Enhancement of sensitivity gain and frequency tuning by coupling of active hair bundles.

The vertebrate inner ear possesses an active process that provides nonlinear amplification of mechanical stimuli. A candidate for this process is active hair bundle mechanics observed, for instance, for hair cells of the bullfrog's sacculus. Hair bundles in various inner ear organs are coupled by overlying membranes.