A Motion-Tracking Ultrasonic Sensor Array for Behavioral Monitoring

The application of Kalman filtering to track subjects' movements during a behavioral experiment is discussed. Specifically, an overhead array of wireless, ultrasound sensors automatically tracks the position of a parent, child, and stranger over a 4.45 m × 4.23 m observation area. This WiPsy (Wireless sensors for Psychology research) system provides accurate, real-time quantitative metrics for psychological evaluation in lieu of traditional qualitative manual coding. Moreover, tracking subjects using ultrasound sensors is less error-prone than existing methods that track based on human coding of video. In particular, the Kalman filter, which forms the core of this tracking system, can locate targets with a mean square error of about 1.3 m². Overall, WiPsy strives to streamline data acquisition, processing, and analysis by providing previously unavailable assessment parameters.

I. Introduction

Human behavior has important significance across many levels of functioning including the organism level, the psychological level, and the relational level. At the organism level, behavior serves to promote survival through accessing basic needs. At the psychological level, behavior may satisfy a need or motivation aimed at satisfying emotional needs. At the relational level, behavior guides an individual through a social world. Thus, the quantification of human behavior has ramifications for better understanding people across many levels of analysis. This behavioral analysis is primarily limited to human subjective ratings and laboratory assessments. Endless possibilities exist by quantifying behavior and exporting it to contexts beyond the lab. This research bridges this gap by developing a sensor network that allows for online data processing. The previously expensive and time consuming process of human coding is replaced with more accurate, quantitative measurements.