5.3 Results
5.3.1 Tremor Profile
Figure 5.3: Examples of Archimedes spiral drawings.
(6.%) demonstrated moderate tremor, 1 (6.7%) showed severe tremor, and 2 participants (13.3%) demonstrated marked tremor.
Figure 5.3 illustrates some examples of the Archimedes spiral test. Table 5.2 summarizes the subjective tremor assessment.
Table 5.2: Subjective tremor results for each participant.
In addition to subjective measures, we also measured tremor objectively, through the device’s accelerometer. Particularly, we measured the postural - a type of action - tremor, by asking participants to hold the mobile device at the arm’s length for 30 seconds with each hand and remain still (Selker et al., 2011). From the captured data we analyzed four main values: the acceleration standard deviations, which correspond to hand oscillations (Bergstrom-Lehtovirta et al., 2011); and the peak amplitude in the power spectrum in the 3 to 7 Hz, 7 to 12 Hz and 1 to 12 Hz range. We report the peak amplitude in different frequency ranges since physiological and pathologic tremors (such as Parkinson’s disease) are usually distinguishable. Nevertheless, we also report the peak amplitude in all frequencies spectrum, which for our participants is always located between 1 and 12 Hz.
Table 5.3: Dominant hand oscillation (inm/s2) for each axis and participant.
Results for hand oscillation showed a mean magnitude of 0.186 m/s2 (sd=0.074), 0.15 m/s2 (sd=0.63), 0.3 m/s2 (sd=0.13), and 0.137 m/s2 (sd=0.044) for X, Y, Z, and XYZ axis, respectively. Table 5.3 illustrates the oscillation for the dominant hand for each axis and participant.
Regarding the non-dominant hand, due to a logging bug we were only able to save 9 of the 15 participants’ accelerometer data. Mean oscillation was 0.174m/s2 (sd=0.07), 0.115 m/s2 (sd=0.024), 0.3m/s2 (sd=0.149), and 0.101m/s2 (sd=0.03), for X, Y, Z, XYZ axis, respectively. Table 5.4 illustrates the oscillation for the non-dominant hand for each axis and participant.
Table 5.4: Non-dominant hand oscillation (in m/s2) for each axis and participant.
Regarding the frequency analysis, results showed a mean peak magnitude of 0.362 m/s2 (sd=0.429), 0.17 m/s2 (sd=0.17), 0.489 m/s2 (sd=0.445) for the 3 to 7 Hz, 7 to 12 Hz
and 1 to 12 Hz, respectively. It is worth noticing that the results for each of the frequency ranges show high standard deviations, suggesting that tremor severity varies widely among participants. Concerning the non-dominant hand, results showed a mean peak magnitude of 0.17m/s2 (sd=0.162), 0.105m/s2 (sd=0.175), 0.287m/s2 (sd=0.189) for the 3 to 7 Hz, 7 to 12 Hz and 1 to 12 Hz, respectively. Again, as in the dominant hand results, tremor magnitudes for each of the frequency ranges show high standard deviations, suggesting that tremor severity is highly user dependent. As we can see, from all tremor profile results, our participants formed a heterogeneous user group; some with no visible tremor while others experienced marked tremor.
Therefore, we investigated the relationship between age and each of the tremor measures.
Preliminary analysis was performed to assess normality, linearity and homoscedasticity.
Pearson product-moment correlation was performed on variables that did not violate any of its assumptions previous described (Oscillation X and Oscillation XYZ), while Spear- man correlation was used for the remaining (self-report, UPDRS Rest, UPDRS Kinect, Task-specific, Oscillation Y, Oscillation, Z, Magnitude 3-7 Hz, Magnitude 7-12 Hz, and Magnitude 1-12 Hz). Table 5.5 illustrates the correlation coefficients and significance lev- els. Although we present this analysis, our goal in this user study was not to see in detail how these measures were correlated, nor could we do it due to the small number of participants. Instead, we are just reporting theses values so the reader can gain some understanding of our data.
Results show that all subjective measures present a small correlation with age. On the other hand, objective measures show a higher correlation level. Particularly, there was a strong, positive correlation betweenage and hand oscillation on the X axis [Spearman rho=0.561, n=15, p<0.05] (with 31.47% of shared variance), with high oscillation levels on older people. Also, there was a medium correlation betweenage and hand oscillation on the Z and XYZ axis, and peak magnitude on the 3 to 7 Hz range.
Table 5.5: Correlation coefficients and significance levels between age and tremor measures.
Moreover, we investigated the relationship between perceived tremor (both from par- ticipants and experimenter) and objectively measured tremor. Therefore, a correlation analysis was performed between subjective and objective measures, using Spearman cor- rection coefficient. Table 5.5 shows all coefficients and significance levels between the variables.
Self-reported measuresshowed to be strongly and positively correlated with thepeak accel- eration magnitude in the 1 to 12 Hz range [Spearman rho=0.558, n=15,p<0.05] (31.14%
of shared variance). On the other hand, there were no strong correlation between Rest Tremor and any of the objectively measured variables. Regarding the Kinect tremor there was a strong, positive correlation with the peak acceleration magnitude in the 7-12 Hz range [Spearman rho=0.59, n=15,p<0.05], which is often associated with physiologi- cal tremor (Elble and Koller, 1990). Finally,task-specific tremor measures were strongly and positively correlated with several objective measures: oscillation XYZ [Spearman rho=0.527, n=15,p=0.043] (27.77% of shared variance),peak magnitude in the 3 to 7 Hz range [Spearman rho=0.584, n=15,p=0.022] (34.12% of shared variance),peak magnitude in the 7 to 12 Hz range [Spearman rho=0.618, n=15, p=0.014] (38.19% of shared vari- ance), andpeak magnitude in the 1 to 12 Hz range [Spearman rho=0.706, n=15,p=0.003]
(49.84% of shared variance).
The strong relationship between some subjective and objective measures, suggest that results for one given test can be predicted by other. For instance, task-specific tremor could be predicted by observing the peak acceleration magnitude between 1 and 12 Hz.
Table 5.6: Correlation coefficients and significance levels between subjective and objective tremor measures.