Comparison of Multi-Compartment Cable Models of Human Auditory Nerve Fibers

Background: Multi-compartment cable models of auditory nerve fibers have been developed to assist in the improvement of cochlear implants. With the advancement of computational technology and the results obtained from in vivo and in vitro experiments, these models have evolved to incorporate a considerable degree of morphological and physiological details. They have also been combined with three-dimensional volume conduction models of the cochlea to simulate neural responses to electrical stimulation. However, no specific rules have been provided on choosing the appropriate cable model, and most models adopted in recent studies were chosen without a specific reason or by inheritance. Methods: Three of the most cited biophysical multi-compartment cable models of the human auditory nerve, i.e., Rattay et al. (2001b), Briaire and Frijns (2005), and Smit et al. (2010), were implemented in this study. Several properties of single fibers were compared among the three models, including threshold, conduction velocity, action potential shape, latency, refractory properties, as well as stochastic and temporal behaviors. Experimental results regarding these properties were also included as a reference for comparison. Results: For monophasic single-pulse stimulation, the ratio of anodic vs. cathodic thresholds in all models was within the experimental range despite a much larger ratio in the model by Briaire and Frijns. For biphasic pulse-train stimulation, thresholds as a function of both pulse rate and pulse duration differed between the models, but none matched the experimental observations even coarsely. Similarly, for all other properties including the conduction velocity, action potential shape, and latency, the models presented different outcomes and not all of them fell within the range observed in experiments. Conclusions: While all three models presented similar values in certain single fiber properties to those obtained in experiments, none matched all experimental observations satisfactorily. In particular, the adaptation and temporal integration behaviors were completely missing in all models. Further extensions and analyses are required to explain and simulate realistic auditory nerve fiber responses to electrical stimulation

Humans are Well Tuned to Detecting Agents Among Non-agents: Examining the Sensitivity of Human Perception to Behavioral Characteristics of Intentional Systems

For efficient social interactions, humans have developed means to predict and understand others' behavior often with reference to intentions and desires. To infer others' intentions, however, one must assume that the other is an agent with a mind and mental states. With two experiments, this study examined if the human perceptual system is sensitive to detecting human agents, based on only subtle behavioral cues. Participants observed robots, which performed pointing gestures interchangeably to the left or right with one of their two arms. Onset times of the pointing movements could have been pre-programmed, human-controlled (Experiment 1), or modeled after a human behavior (Experiment 2). The task was to determine if the observed behavior was controlled by a human or by a computer program, without any information about what parameters of behavior this judgment should be based on. Results showed that participants were able to detect human behavior above chance in both experiments. Moreover, participants were asked to discriminate a letter (F/T) presented on the left or the right side of a screen. The letter could have been either validly cued by the robot (location that the robot pointed to coincided with the location of the letter) or invalidly cued (the robot pointed to the opposite location than the letter was presented). In this cueing task, target discrimination was better for the valid versus invalid conditions in Experiment 1 where a human face was presented centrally on a screen throughout the experiment. This effect was not significant in Experiment 2 where participants were exposed only to a robotic face. In sum, present results show that the human perceptual system is sensitive to subtleties of human behavior. Attending to where others attend, however, is modulated not only by adopting the Intentional Stance but also by the way participants interpret the observed stimuli.German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) Grant awarded to AW (WY-122/1-1) and a gran twithin the LMU Excellent scheme awarded to AWScopu