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Caltech Authors (147.820 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 339

  1. Persistent Single-Neuron Activity during Working Memory in the Human Medial Temporal Lobe

    Kornblith, Simon; Quian Quiroga, Rodrigo; Koch, Christof; Fried, Itzhak; Mormann, Florian
    Working memory is an essential component of human cognition. Persistent activity related to working memory has been reported in many brain areas, including the inferior temporal and prefrontal cortex [1; 2; 3; 4; 5; 6; 7 ; 8]. The medial temporal lobe (MTL) contains “concept cells” that respond invariantly to specific individuals or places whether presented as images, text, or speech [9 ; 10]. It is unknown, however, whether the MTL also participates in working memory processes. We thus sought to determine whether human MTL neurons respond to images held in working memory. We recorded from patients with chronically intractable...

  2. Scene-selective coding by single neurons in the human parahippocampal cortex

    Mormann, Florian; Kornblith, Simon; Cerf, Moran; Ison, Matias J.; Kraskov, Alexander; Tran, Michelle; Knieling, Simeon; Quiroga, Rodrigo Quian; Koch, Christof; Fried, Itzhak
    Imaging, electrophysiological, and lesion studies have shown a relationship between the parahippocampal cortex (PHC) and the processing of spatial scenes. Our present knowledge of PHC, however, is restricted to the macroscopic properties and dynamics of bulk tissue; the behavior and selectivity of single parahippocampal neurons remains largely unknown. In this study, we analyzed responses from 630 parahippocampal neurons in 24 neurosurgical patients during visual stimulus presentation. We found a spatially clustered subpopulation of scene-selective units with an associated event-related field potential. These units form a population code that is more distributed for scenes than for other stimulus categories, and less...

  3. Relationship between selective visual attention and visual consciousness

    Tsuchiya, Naotsugu; Koch, Christof
    The relationship between attention and consciousness is a close one, leading many scholars to conflate the two. However, recent research has slowly corroded a belief that selective attention and consciousness are so tightly entangled that they cannot be individually examined.

  4. Using semantic content as cues for better scanpath prediction

    Cerf, Moran; Frady, E. Paxon; Koch, Christof
    Under natural viewing conditions, human observers use shifts in gaze to allocate processing resources to subsets of the visual input. There are many computational models that try to predict these shifts in eye movement and attention. Although the important role of high level stimulus properties (e.g., semantic information) stands undisputed, most models are based solely on low-level image properties. We here demonstrate that a combined model of high-level object detection and low-level saliency significantly outperforms a low-level saliency model in predicting locations humans fixate on. The data is based on eye-movement recordings of humans observing photographs of natural scenes, which contained one...

  5. Effects of Chronic Sleep Restriction during Early Adolescence on the Adult Pattern of Connectivity of Mouse Secondary Motor Cortex

    Billeh, Yazan N.; Rodriguez, Alexander V.; Bellesi, Michele; Bernard, Amy; de Vivo, Luisa; Funk, Chadd M.; Harris, Julie; Honjoh, Sakiko; Mihalas, Stefan; Ng, Lydia; Koch, Christof; Cirelli, Chiara; Tononi, Giulio
    Cortical circuits mature in stages, from early synaptogenesis and synaptic pruning to late synaptic refinement, resulting in the adult anatomical connection matrix. Because the mature matrix is largely fixed, genetic or environmental factors interfering with its establishment can have irreversible effects. Sleep disruption is rarely considered among those factors, and previous studies have focused on very young animals and the acute effects of sleep deprivation on neuronal morphology and cortical plasticity. Adolescence is a sensitive time for brain remodeling, yet whether chronic sleep restriction (CSR) during adolescence has long-term effects on brain connectivity remains unclear. We used viral-mediated axonal labeling...

  6. Low-level awareness accompanies “unconscious” high-level processing during continuous flash suppression

    Gelbard-Sagiv, Hagar; Faivre, Nathan; Mudrik, Liad; Koch, Christof
    The scope and limits of unconscious processing are a matter of ongoing debate. Lately, continuous flash suppression (CFS), a technique for suppressing visual stimuli, has been widely used to demonstrate surprisingly high-level processing of invisible stimuli. Yet, recent studies showed that CFS might actually allow low-level features of the stimulus to escape suppression and be consciously perceived. The influence of such low-level awareness on high-level processing might easily go unnoticed, as studies usually only probe the visibility of the feature of interest, and not that of lower-level features. For instance, face identity is held to be processed unconsciously since subjects...

  7. Graph-Based Visual Saliency

    Harel, Jonathan; Koch, Christof; Perona, Pietro
    A new bottom-up visual saliency model, Graph-Based Visual Saliency (GBVS), is proposed. It consists of two steps: first forming activation maps on certain feature channels, and then normalizing them in a way which highlights conspicuity and admits combination with other maps. The model is simple, and biologically plausible insofar as it is naturally parallelized. This model powerfully predicts human fixations on 749 variations of 108 natural images, achieving 98% of the ROC area of a human-based control, whereas the classical algorithms of Itti & Koch ([2], [3], [4]) achieve only 84%.

  8. Journal of Near-Death Studies

    Manwani, Amit; Koch, Christof
    Here we derive measures quantifying the information loss of a synaptic signal due to the presence of neuronal noise sources, as it electrotonically propagates along a weakly-active dendrite. We model the dendrite as an infinite linear cable, with noise sources distributed along its length. The noise sources we consider are thermal noise, channel noise arising from the stochastic nature of voltage-dependent ionic channels (K^+ and Na^+) and synaptic noise due to spontaneous background activity. We assess the efficacy of information transfer using a signal detection paradigm where the objective is to detect the presence/absence of a presynaptic spike from the post-synaptic membrane...

  9. An Integrated Vision Sensor for the Computation of Optical Flow Singular Points

    Higgins, Charles M.; Koch, Christof
    A robust, integrative algorithm is presented for computing the position of the focus of expansion or axis of rotation (the singular point) in optical flow fields such as those generated by self-motion. Measurements are shown of a fully parallel CMOS analog VLSI motion sensor array which computes the direction of local motion (sign of optical flow) at each pixel and can directly implement this algorithm. The flow field singular point is computed in real time with a power consumption of less than 2 mW. Computation of the singular point for more general flow fields requires measures of field expansion and rotation, which...

  10. Attentional Modulation of Human Pattern Discrimination Psychophysics Reproduced by a Quantitative Model

    Itti, Laurent; Braun, Jochen; Lee, Dale K.; Koch, Christof
    We previously proposed a quantitative model of early visual processing in primates, based on non-linearly interacting visual filters and statistically efficient decision. We now use this model to interpret the observed modulation of a range of human psychophysical thresholds with and without focal visual attention. Our model - calibrated by an automatic fitting procedure - simultaneously reproduces thresholds for four classical pattern discrimination tasks, performed while attention was engaged by another concurrent task. Our model then predicts that the seemingly complex improvements of certain thresholds, which we observed when attention was fully available for the discrimination tasks, can best be explained by...

  11. A Model of Early Visual Processing

    Itti, Laurent; Braun, Jochen; Lee, Dale K.; Koch, Christof
    We propose a model for early visual processing in primates. The model consists of a population of linear spatial filters which interact through non-linear excitatory and inhibitory pooling. Statistical estimation theory is then used to derive human psychophysical thresholds from the responses of the entire population of units. The model is able to reproduce human thresholds for contrast and orientation discrimination tasks, and to predict contrast thresholds in the presence of masks of varying orientation and spatial frequency.

  12. An Analog VLSI Model of the Fly Elementary Motion Detector

    Harrison, Reid R.; Koch, Christof
    Flies are capable of rapidly detecting and integrating visual motion information in behaviorly-relevant ways. The first stage of visual motion processing in flies is a retinotopic array of functional units known as elementary motion detectors (EMDs). Several decades ago, Reichardt and colleagues developed a correlation-based model of motion detection that described the behavior of these neural circuits. We have implemented a variant of this model in a 2.0µm analog CMOS VLSI process. The result is a low-power, continuous-time analog circuit with integrated photoreceptors that responds to motion in real time. The responses of the circuit to drifting sinusoidal gratings qualitatively resemble the...

  13. An Adaptive WTA using Floating Gate Technology

    Kruger, W. Fritz; Hasler, Paul; Minch, Bradley A.; Koch, Christof
    We have designed, fabricated, and tested an adaptive Winner-Take-All (WTA) circuit based upon the classic WTA of Lazzaro, et al [1]. We have added a time dimension (adaptation) to this circuit to make the input derivative an important factor in winner selection. To accomplish this, we have modified the classic WTA circuit by adding floating gate transistors which slowly null their inputs over time. We present a simplified analysis and experimental data of this adaptive WTA fabricated in a standard CMOS 2µm process.

  14. Control of Selective Visual Attention: Modeling the "Where" Pathway

    Niebur, Ernst; Koch, Christof
    Intermediate and higher vision processes require selection of a subset of the available sensory information before further processing. Usually, this selection is implemented in the form of a spatially circumscribed region of the visual field, the so-called "focus of attention" which scans the visual scene dependent on the input and on the attentional state of the subject. We here present a model for the control of the focus of attention in primates, based on a saliency map. This mechanism is not only expected to model the functionality of biological vision but also to be essential for the understanding of complex scenes in machine...

  15. Parallel analog VLSI architectures for computation of heading direction and time-to-contact

    Indiveri, Giacomo; Kramer, Jörg; Koch, Christof
    We describe two parallel analog VLSI architectures that integrate optical flow data obtained from arrays of elementary velocity sensors to estimate heading direction and time-to-contact. For heading direction computation, we performed simulations to evaluate the most important qualitative properties of the optical flow field and determine the best functional operators for the implementation of the architecture. For time-to-contact we exploited the divergence theorem to integrate data from all velocity sensors present in the architecture and average out possible errors.

  16. Visual Motion Computation in Analog VLSI Using Pulses

    Sarpeshkar, Rahul; Bair, Wyeth; Koch, Christof
    The real time computation of motion from real images using a single chip with integrated sensors is a hard problem. We present two analog VLSI schemes that use pulse domain neuromorphic circuits to compute motion. Pulses of variable width, rather than graded potentials, represent a natural medium for evaluating temporal relationships. Both algorithms measure speed by timing a moving edge in the image. Our first model is inspired by Reichardt's algorithm in the fiy and yields a non-monotonic response vs. velocity curve. We present data from a chip that implements this model. Our second algorithm yields a monotonic response vs. velocity curve and is currently being translated into silicon.

  17. Computing Motion Using Resistive Networks

    Koch, Christof; Luo, Jin; Mead, Carver; Hutchinson, James
    To us, and to other biological organisms, vision seems effortless. We open our eyes and we "see" the world in all its color, brightness, and movement. Yet, we have great difficulties when trying to endow our machines with similar abilities. In this paper we shall describe recent developments in the theory of early vision which lead from the formulation of the motion problem as an ill-posed one to its solution by minimizing certain "cost" functions. These cost or energy functions can be mapped onto simple analog and digital resistive networks. Thus, we shall see how the optical flow can be computed by injecting currents into resistive networks and...

  18. Neurodata Without Borders: Creating a Common Data Format for Neurophysiology

    Teeters, Jeffery L.; Godfrey, Keith; Young, Rob; Dang, Chinh; Friedsam, Claudia; Wark, Barry; Asari, Hiroki; Peron, Simon; Li, Nuo; Peyrache, Adrien; Denisov, Gennady; Siegle, Joshua H.; Olsen, Shawn R.; Martin, Christopher; Chun, Miyoung; Tripathy, Shreejoy; Blanche, Timothy J.; Harris, Kenneth; Buzsáki, György; Koch, Christof; Meister, Markus; Svoboda, Karel; Sommer, Friedrich T.
    The Neurodata Without Borders (NWB) initiative promotes data standardization in neuroscience to increase research reproducibility and opportunities. In the first NWB pilot project, neurophysiologists and software developers produced a common data format for recordings and metadata of cellular electrophysiology and optical imaging experiments. The format specification, application programming interfaces, and sample datasets have been released.

  19. Optical Flow and Surface Interpolation in Resistive Networks: Algorithms and Analog VLSI Chips

    Koch, Christof; Luo, Jin; Hutchinson, James; Mead, Carver
    To us, and to other biological organisms, vision seems effortless. We open our eyes and we "see" the world in all its color, brightness, and movement. Flies, frogs, cats, and humans can all equally well perceive a rapidly changing environment and act on it. Yet, we have great difficulties when trying to endow our machines with similar abilities. In this article, we describe recent developments in the theory of early vision that led from the formulation of the motion problem as an ill-posed one to its solution by minimizing certain "cost" functions. These cost or energy functions can be mapped onto...

  20. The Secrets of Salient Object Segmentation

    Li, Yin; Hou, Xiaodi; Koch, Christof; Rehg, James M.; Yuille, Alan L.
    In this paper we provide an extensive evaluation of fixation prediction and salient object segmentation algorithms as well as statistics of major datasets. Our analysis identifies serious design flaws of existing salient object benchmarks, called the dataset design bias, by over emphasising the stereotypical concepts of saliency. The dataset design bias does not only create the discomforting disconnection between fixations and salient object segmentation, but also misleads the algorithm designing. Based on our analysis, we propose a new high quality dataset that offers both fixation and salient object segmentation ground-truth. With fixations and salient object being presented simultaneously, we are...

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