from PhysioNet, the research resource for complex physiologic signals


Noise Enhancement of Sensorimotor Function

These data were collected for, and first described in:

Priplata AA, Niemi JB, Harry JD, Lipsitz LA, Collins JJ. Vibrating insoles and balance control in elderly people. Lancet 362: 1123-1124 (2003).

Please cite the above publication when referencing this material, and also include the standard citation for PhysioNet:

Goldberger AL, Amaral LAN, Glass L, Hausdorff JM, Ivanov PCh, Mark RG, Mietus JE, Moody GB, Peng C-K, Stanley HE. PhysioBank, PhysioToolkit, and PhysioNet: Components of a New Research Resource for Complex Physiologic Signals. Circulation 101(23):e215-e220 [Circulation Electronic Pages; http://circ.ahajournals.org/cgi/content/full/101/23/e215]; 2000 (June 13).

This database contains postural sway measurements for 15 healthy young (mean age 23, standard deviation 2), and 12 healthy elderly (mean age 73, standard deviation 3) volunteers. Each subject's postural sway was recorded during a test of 10 minutes for the young subjects, or 5 minutes for the elderly subjects, in all cases with a 2-minute seated break midway through the test. Each test was divided into 30-second trials, and each file of the database contains data for one of these 30-second trials.

In each shoe, subjects wore a gel-based insole, which included vibrating elements (tactors) beneath the forefoot and heel. The vibrations were generated using a digitized uniform white noise signal, low-pass filtered with 100 Hz cutoff. Before beginning the test, each subject adjusted the amplitude of the vibrations produced by the tactors to a level that could be felt only slightly. The stimulation level was then reduced by 10% so that the vibrations were subsensory.

The data from the young and elderly subjects are contained within the yng and eh (elderly healthy) directories respectively. Within these, separate directories for each subject contain the data for that subject. For each subject, subsensory vibration was applied during half of the 30-second trials (those recorded in the database files within the STIM subdirectories of the subject directories), and no stimulus was applied during the remaining (control) trials (those in the NULL subdirectories). The sequence of noise and control trials was randomized in a pairwise fashion, so that subjects were not aware of the presence or absence of the stimulus in any given trial.

An example should make this arrangement clear. Within the eh directory are subdirectories for each of the 12 healthy elderly volunteers, designated as MT1502, MT1503, etc. Within the directory for the first of these, MT1502, are subdirectories NULL and STIM, containing control and noise trial data for subject MT1502. Within each of these are the data files, with names that indicate their positions within the sequence of trials for that subject. For example, the data for the first trial, fMT150201.txt, are found in the NULL subdirectory, so this indicates that subject MT1502's first trial was a control trial.

The data files are two-column text files, and the data are measurements of the displacement of a reflective marker placed on the subject's shoulder to characterize whole body postural sway. A Vicon motion analysis system was used to record the mediolateral (side-to-side) and anteroposterior (front-to-back) displacement (normalized by the height of the marker) in columns 1 and 2 respectively, at a rate of 60 samples per second, throughout each 30 second trial.

The data may be downloaded as individual files, from the eh and yng directories, or as a gzip-compressed tar archive of the entire data set (nesfdb.tar.gz, 6.5 Mb). For information about unpacking .tar.gz archives, see the FAQ.