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Open Access Publications from the University of California

Scholarly Works (10 results)

  • Article
  • Peer Reviewed
UC Riverside Previously Published Works (2020)
Infants visual experiences are important for learning, and may depend on how information is structured in the visual field. This study examined how objects are distributed in 12-month-old infants field of view in a mobile play setting. Infants wore a mobile eye tracker that recorded their field of view and eye movements while they freely played with toys and a caregiver. We measured how centered and spread object locations were in infants field of view, and investigated how infant posture, object looking, and object distance affected the centering and spread. We found that far toys were less centered in infants field of view while infants were prone compared to when sitting or upright. Overall, toys became more centered in view and less spread in location when infants were looking at toys regardless of posture and toy distance. In sum, this study showed that infants visual experiences are shaped by the physical relation between infants bodies and the locations of objects in the world. However, infants are able to compensate for postural and environmental constraints by actively moving their head and eyes when choosing to look at an object.
    Cover page: Head and body structure infants visual experiences during mobile, naturalistic play.Creative Commons 'BY' version 4.0 license
    • Article
    • Peer Reviewed
    UC Riverside Previously Published Works (2022)
    Previous studies have demonstrated that people trade off between expending motor effort and memorization effort when completing a copying task that requires looking in different directions to gather information. When information is easy to gather with minimal movement, people choose to look more frequently and rely on less on memorization, however, they reduce motor effort and rely on memory more when looking requires larger (and more effortful) shifts of gaze. This paper investigated the eye-head-body movements that guided looking as well as participants’ trade-off between using motor effort and memory in a copying task. We add to prior work by characterizing the coordination between eyes, head, and body required to look at targets at different angles. In the task, participants copied models onto a board while wearing a mobile eye tracker that measured eye rotations and motion sensors that measured head rotations. We manipulated the angle of the model relative to the participant and the memorization difficulty of the models. Results showed that eye movements contributed more to small gaze shifts but the head and body contributed more as the angle of the target increased (requiring larger amplitude shifts of gaze). Participants chose to look frequently when models were adjacent to the workspace, but chose to rely more on memory for models that required greater shifts of gaze. Memorization difficulty affected the trade-off such that participants used more memory when the models were easy to remember. We discuss how participants’ decisions to look versus remember may depend on the contribution of eyes, head, and body to shift gaze by varying amplitudes.
      Creative Commons 'BY' version 4.0 license
      • Thesis
      • Peer Reviewed
      UC Riverside Electronic Theses and Dissertations (2023)

      The aim of the dissertation is to investigate how people trade off between expending motor effort and memorization effort when visually exploring in different directions to gather information. Specifically, Chapter 2 studied how the motor effort of eye-head-body movements and memorization difficulty affected the motor-memory trade-off in a copying task. Chapter 3 studied how people adjusted the motor-memory trade-off after repeated practice with the task. Lastly, Chapter 4 studied whether inducing people to test a different strategy led to discovery and later adoption of a more efficient strategy. Each chapter examined both the copying strategies (i.e. the trade-off between using more motor effort versus more memory) and the eye-head-body coordination underlying the task. Results showed that participants expended more motor effort when the eye-head-body movements to make gaze shifts were less effortful and when the information was difficult to remember (Chapter2); participants used more memory after repeated practice with the task (Chapter 3); exposing participants to test a different strategy led them to adopt a memory-based strategy (Chapter 4). Overall, participants coordinated their eyes, head, and body differently according to the task conditions such as angle and external restriction. They also changed the eye-head-body coordination to decrease total motor cost over the course of doing the task. The findings suggested that people are adaptive in trading off between motor effort and use of memory.

        Cover page: Movements or Memorization: A Trade-Off in a Copying Task
        • Article
        • Peer Reviewed
        UC Riverside Previously Published Works (2021)
        How can researchers best measure infants motor experiences in the home? Body position-whether infants are held, supine, prone, sitting, or upright-is an important developmental experience. However, the standard way of measuring infant body position, video recording by an experimenter in the home, can only capture short instances, may bias measurements, and conflicts with physical distancing guidelines resulting from the COVID-19 pandemic. Here, we introduce and validate an alternative method that uses machine learning algorithms to classify infants body position from a set of wearable inertial sensors. A laboratory study of 15 infants demonstrated that the method was sufficiently accurate to measure individual differences in the time that infants spent in each body position. Two case studies showed the feasibility of applying this method to testing infants in the home using a contactless equipment drop-off procedure.
          Cover page: A Contactless Method for Measuring Full-Day, Naturalistic Motor Behavior Using Wearable Inertial Sensors.
          • Article
          • Peer Reviewed
          UC Irvine Previously Published Works (2018)
          The micro-fabricated thin film electrode array (TFEA) has been a promising design for cochlear implants (CIs) because of its cost-effectiveness and fabrication precision. The latest polymer-based cochlear TFEAs have faced difficulties for cochlear insertion due to the lack of structural stiffness. To stiffen the TFEA, dissolvable stiffening materials, TFEAs with different structures, and TFEAs with commercial CIs as carriers have been invested. In this work, the concept of enhancing a Parylene TFEA with Kapton tape as a simpler carrier for cochlear insertion has been proved to be feasible. The bending stiffness of the Kapton-aided TFEA was characterized with an analytical model, a finite element model, and a cantilever bending experiment, respectively. While the Kapton tape increased the bending stiffness of the Parylene TFEA by 10³ times, the 6-μm-thick TFEA with a similar Young's modulus, as a polyimide, in turn significantly increased the bending stiffness of the 170-μm-thick Kapton carrier by 60%. This result indicated that even the TFEA is ultra-flexible and that its bending stiffness should not be neglected in the design or selection of its carrier.
            Cover page: Study of the Carrier-Aided Thin Film Electrode Array Design for Cochlear Insertion.Creative Commons 'BY' version 4.0 license
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2017)
            First-principles based cluster expansion models are the dominant approach in ab initio thermodynamics of crystalline mixtures enabling the prediction of phase diagrams and novel ground states. However, despite recent advances, the construction of accurate models still requires a careful and time-consuming manual parameter tuning process for ground-state preservation, since this property is not guaranteed by default. In this paper, we present a systematic and mathematically sound method to obtain cluster expansion models that are guaranteed to preserve the ground states of their reference data. The method builds on the recently introduced compressive sensing paradigm for cluster expansion and employs quadratic programming to impose constraints on the model parameters. The robustness of our methodology is illustrated for two lithium transition metal oxides with relevance for Li-ion battery cathodes, i.e., Li2x Fe2(1-x)O2 and Li2x Ti2(1-x)O2, for which the construction of cluster expansion models with compressive sensing alone has proven to be challenging. We demonstrate that our method not only guarantees ground-state preservation on the set of reference structures used for the model construction, but also show that out-of-sample ground-state preservation up to relatively large supercell size is achievable through a rapidly converging iterative refinement. This method provides a general tool for building robust, compressed and constrained physical models with predictive power.
              Cover page: Construction of ground-state preserving sparse lattice models for predictive materials simulations
              • Article
              • Peer Reviewed
              UC Irvine Previously Published Works (2019)
              OBJECTIVE: To improve the existing manually assembled cochlear implant electrode arrays, a thin-film electrode array (TFEA) was microfabricated having a maximum electrode density of 15 sites along an 8-mm length, with each site having a 75 μm × 1.8 μm (diameter × height) disk electrode. METHODS: The microfabrication method adopted photoresist transferring, lift-off, two-step oxygen plasma etching, and fuming nitric acid release to reduce lift-off complexity, protect the metal layer, and increase the release efficiency. RESULTS: Systematic in vitro characterization showed that the TFEAs bending stiffness was 6.40 × 10-10 N·m2 near the base and 1.26 × 10-10 N·m2 near the apex. The TFEA electrode produced an average impedance of 16 kΩ and a maximum current limit of 800 μA, measured with 1-kHz sinusoidal current using monopolar stimulation in saline. A TFEA prototype was implanted in a cat cochlea to obtain in vivo measurements of electrically evoked auditory brainstem and inferior colliculus responses to monopolar stimulation with 41-μs/phase biphasic pulses. Both physiological responses produced a threshold of ∼300 μA and a dynamic range of 5-8 dB above the threshold. Compared with existing arrays, the present TFEA had 104 times less bending stiffness, 97% less electrode area, and comparable physiological thresholds. CONCLUSION: Using a simplified structure and stable fabrication method, the present TEFA produced physical and physiological performance comparable to existing commercial devices. SIGNIFICANCE: The present TFEA represents a step closer toward an automated process replacing the labor-intensive and expensive manual assembly of the cochlear implant electrode arrays.
                Cover page: Design, Fabrication, and Evaluation of a Parylene Thin-Film Electrode Array for Cochlear Implants.
                • Article
                • Peer Reviewed
                ICTS Publications (2018)

                The micro-fabricated thin film electrode array (TFEA) has been a promising design for cochlear implants (CIs) because of its cost-effectiveness and fabrication precision. The latest polymer-based cochlear TFEAs have faced difficulties for cochlear insertion due to the lack of structural stiffness. To stiffen the TFEA, dissolvable stiffening materials, TFEAs with different structures, and TFEAs with commercial CIs as carriers have been invested. In this work, the concept of enhancing a Parylene TFEA with Kapton tape as a simpler carrier for cochlear insertion has been proved to be feasible. The bending stiffness of the Kapton-aided TFEA was characterized with an analytical model, a finite element model, and a cantilever bending experiment, respectively. While the Kapton tape increased the bending stiffness of the Parylene TFEA by 10³ times, the 6-μm-thick TFEA with a similar Young's modulus, as a polyimide, in turn significantly increased the bending stiffness of the 170-μm-thick Kapton carrier by 60%. This result indicated that even the TFEA is ultra-flexible and that its bending stiffness should not be neglected in the design or selection of its carrier.

                  Cover page: Study of the Carrier-Aided Thin Film Electrode Array Design for Cochlear Insertion.Creative Commons 'BY' version 4.0 license
                  • Article
                  • Peer Reviewed
                  UC Irvine Previously Published Works (2019)

                  Objective

                  To improve the existing manually assembled cochlear implant electrode arrays, a thin-film electrode array (TFEA) was microfabricated having a maximum electrode density of 15 sites along an 8-mm length, with each site having a 75 μm × 1.8 μm (diameter × height) disk electrode.

                  Methods

                  The microfabrication method adopted photoresist transferring, lift-off, two-step oxygen plasma etching, and fuming nitric acid release to reduce lift-off complexity, protect the metal layer, and increase the release efficiency.

                  Results

                  Systematic in vitro characterization showed that the TFEA's bending stiffness was 6.40 × 10-10 N·m2 near the base and 1.26 × 10-10 N·m2 near the apex. The TFEA electrode produced an average impedance of 16 kΩ and a maximum current limit of 800 μA, measured with 1-kHz sinusoidal current using monopolar stimulation in saline. A TFEA prototype was implanted in a cat cochlea to obtain in vivo measurements of electrically evoked auditory brainstem and inferior colliculus responses to monopolar stimulation with 41-μs/phase biphasic pulses. Both physiological responses produced a threshold of ∼300 μA and a dynamic range of 5-8 dB above the threshold. Compared with existing arrays, the present TFEA had 104 times less bending stiffness, 97% less electrode area, and comparable physiological thresholds.

                  Conclusion

                  Using a simplified structure and stable fabrication method, the present TEFA produced physical and physiological performance comparable to existing commercial devices.

                  Significance

                  The present TFEA represents a step closer toward an automated process replacing the labor-intensive and expensive manual assembly of the cochlear implant electrode arrays.
                    Cover page: Design, Fabrication, and Evaluation of a Parylene Thin-Film Electrode Array for Cochlear Implants.
                    • Article
                    • Peer Reviewed
                    UC Berkeley Previously Published Works (2016)
                    Lattice models, also known as generalized Ising models or cluster expansions, are widely used in many areas of science and are routinely applied to the study of alloy thermodynamics, solid-solid phase transitions, magnetic and thermal properties of solids, fluid mechanics, and others. However, the problem of finding and proving the global ground state of a lattice model, which is essential for all of the aforementioned applications, has remained unresolved for relatively complex practical systems, with only a limited number of results for highly simplified systems known. In this paper, we present a practical and general algorithm that provides a provable periodically constrained ground state of a complex lattice model up to a given unit cell size and in many cases is able to prove global optimality over all other choices of unit cell. We transform the infinite-discrete-optimization problem into a pair of combinatorial optimization (MAX-SAT) and nonsmooth convex optimization (MAX-MIN) problems, which provide upper and lower bounds on the ground state energy, respectively. By systematically converging these bounds to each other, we may find and prove the exact ground state of realistic Hamiltonians whose exact solutions are difficult, if not impossible, to obtain via traditional methods. Considering that currently such practical Hamiltonians are solved using simulated annealing and genetic algorithms that are often unable to find the true global energy minimum and inherently cannot prove the optimality of their result, our paper opens the door to resolving longstanding uncertainties in lattice models of physical phenomena. An implementation of the algorithm is available at https://github.com/dkitch/maxsat-ising.
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