Continuous monitoring of brain dynamics with functional near infrared spectroscopy as a tool for neuroergonomic research: empirical examples and a technological development

Abstract

Functional near infrared spectroscopy (fNIRS) is a non-invasive, safe, and portable optical neuroimaging method that can be used to assess brain dynamics during skill acquisition and performance of complex work and everyday tasks. In this paper we describe neuroergonomic studies that illustrate the use of fNIRS in the examination of training-related brain dynamics and human performance assessment. We describe results of studies investigating cognitive workload in air traffic controllers, acquisition of dual verbal-spatial working memory skill, and development of expertise in piloting unmanned vehicles. These studies used conventional fNIRS devices in which the participants were tethered to the device while seated at a workstation. Consistent with the aims of mobile brain imaging (MoBI), we also describe a compact and battery-operated wireless fNIRS system that performs with similar accuracy as other established fNIRS devices. Our results indicate that both wired and wireless fNIRS systems allow for the examination of brain function in naturalistic settings, and thus are suitable for reliable human performance monitoring and training assessment.

Keywords: fNIRS; hemodynamic response; optical brain monitoring; prefrontal cortex; wireless NIRS; working memory training.

Figure 1

Air Traffic Control simulator screenshot displaying a sector with en route aircrafts (left). Control workstations with high resolution radarscope, keyboard, trackball, and direct keypad access (right).

Figure 2

(Left) Average oxygenation changes of all subjects (24 participants, and 28 trials for each participant) with increasing task difficulty. (Right) Average oxygenation changes for two different interfaces (data- and voice-based) and for 6, 12, and 18 aircraft conditions each. Error bars are standard error of the mean (s.e.m.).

Figure 3

Dual verbal-spatial working memory task.

Figure 4

Changes in Verbal span for each trainee in the adaptive training and yoked groups over 5 successive days of working memory training. Each data point represents task performance during a training block.

Figure 5

Changes in total hemoglobin in right rostral PFC for each trainee in the adaptive training and yoked groups over 5 successive days of working memory training. Each data point represents fNIRS measured brain activity during a block.

Figure 6

Changes throughout the practice levels: Self-reported ratings: perceived mental effort as measured by NASA TLX (left), Behavioral performance: average error in banking angle (middle), fNIRS measures: average total hemoglobin concentration changes (right) of all subjects throughout days. Error bars are standard error of the mean (SEM).

Figure 7

Overview of fNIR system: Computer running COBI Studio (Drexel University) collects data through hardware control box. Flexible Sensor housing 4 LED light sources, 10 photo-detectors provides 16 measurement locations.

Figure 8

General design concept (top) and implemented system components displaying 16-channel prefrontal cortex probe, pocket pc, control box, and battery (bottom). A quarter (US $0.25 piece) is also included for size comparison.

Figure 9

Timing diagram of the control circuit.

Figure 10

Block diagram of the control circuit.

Figure 11

Schematic diagram of the wireless system components. The fNIRS box (approximately the size of a cell-phone) contains, battery, wireless transmitter, and control circuitry.

Figure 12

Block diagram of the wireless fNIR controller box (left) and sensor node, circuit board implementation (right).

Figure 13

Implemented components of the wireless system.

Figure 14

Signal to noise ratio of one of the inputs for different LED currents and input gain settings (left). Comparison of wired and wireless system light intensity measurements indicated consistent response on a solid brain phantom with constant gain of 10 and LED currents ranging from 5 to 40 mA (right).

Figure 15

Effects of de- and re-oxygenation during blood test on liquid phantom as measured by the wireless fNIRS system.