Gregory J. Gerling

Touch interactive displays, such as phones and tablets, have become a normal part of life over the past ten years. To replicate touching another’s hand or tissues in medical exams, the next generation of displays need to relay a sense of compliance, or ‘softness.’ While a number of groups are working to mimic compliant interactions to the finger pad—by employing tilting plates, concentric rings, particle jamming and fabric stretch—these displays do not yet feel natural. To contribute to a gap in the understanding of the biomechanical cues at the finger pad, we have developed a method for 3-D visual observation of the skin’s surface when deformed by transparent compliances. We are studying how the finger pad must deform in space and time to adequately encode the percept of compliance. In particular, time-dependent cues, or information in the rate of change of skin deformation over a spatial field, may be vital to information transfer and mechanical efficiency.

Despite past progress, the principles that govern the neural output for touch receptors have not been fully defined. We take an approach of combining computational models with experimental methods. Our work in collaboration of Dr. Ellen A. Lumpkin of Columbia University has sought to define rules in the end organ architecture of the Merkel cells and neurites that are innervated by slowly adapting type I afferents. We have built end organ models to show that the grouping of Merkel cells to heminodes strongly influence the sensitivity function of an afferent. Such computational single-unit models are built for neural afferents, comprising finite elements to capture skin mechanics, differential equations to represent sensory transduction, and integrate-and-fire models to mimic neural dynamics.

Because the end organs of touch receptors are so intertwined with the skin substrate in which they are embedded, we have performed systematic measurements of the skin stiffness and thickness so vital to constraining our models. These measurements have indicated that there is a systematic thickening of the skin with phases of the mouse hair cycle, as well as other changes to the skin’s time dependent relaxation. These skin changes in conjunction with changes in the end organ could impact homeostatic mechanisms.

Distinct patterns in neuronal firing are observed between classes of cutaneous afferents. Such differences may be attributed to end organ morphology, distinct ion-channel complements, and skin microstructure, among other factors. As well, even within the class of just slowly adapting type I afferents, neuronal sensitivity is quite variable between units. Do changes in the skin’s mechanics contribute to such variance? Our studies employing finite element analysis suggest that skin can reliably convey indentation magnitude, rate and spatial geometry to the locations of tactile receptors amidst the natural changes in skin mechanics. Indeed, there can be large variance in firing in neural responses amidst skin changes. However, it can be significantly reduced if mechanosensitive afferents are tuned to respond to a stimuli's surface pressure and stress interior to the skin near the locations of the sensory end organs.

The use of medical simulators has become increasingly widespread as the use of animals and patients for the training of novices has come under scrutiny and as medical errors (44,000-98,000 unnecessary deaths per year) are becoming better understood by the Institute of Medicine. We have worked with clinicians and medical and nursing educators to create human-machine interfaces to train health care practitioners. Specifically, we designed, built, and evaluated a physical-computerized simulators to train clinical palpation skills in breast and prostate screening. The goal is to ensure that clinicians’ skills are systematically trained, time-effective and highly accurate. We built the simulators after collecting measurements of prostate tissue stiffness obtained in the clinic as well as psychophysical evaluation of the tactile detection and discrimination thresholds of those who perform these exams. This work was done in collaboration with Dr. Marcus Martin and Prof. Reba Moyer Childress.

I teach courses on human-machine interaction and user experience design. My capstone teams have worked on UX problems for clients in many industries. In general, we design graphical, virtual, and physical user interfaces to display information and afford work processes customized to the mental models, cognitive and perceptual capabilities, and tasks and work domains of end users. An important topic is function allocation in automated systems, as well as interacting with large sets of data.

Knee arthrofibrosis, a condition where scar tissue limits motion of the knee, is encountered after 4 - 35% of ligament surgeries. We designed, built and evaluated a means of quantifying the forces and angles required to overcome arthrofibrosis during knee manipulation. To quantify relevant cues, the device was built to be mobile and attach to a common knee brace. Fixtures were designed to afford normal physician postures and manual control of torque. The device utilizes load cells, rotary potentiometers, 3D printed parts and integrated circuits. Graphical user interfaces on a mobile phone allow in-the-loop evaluation and a database was used for subsequent, offline analysis. The device is being tested in the clinic with our collaborator Dr. Seth Yarboro.