Inter- and intra-individual variation in earprints
Meijerman, L.Citation
Meijerman, L. (2006, February 15). Inter- and intra-individual variation in earprints. Barge's Anthropologica, Leiden. Retrieved from https://hdl.handle.net/1887/4292
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PRELIM INARY COM PARISON OF EARPRINTS THAT W ERE M ADE
BEFORE AND AFTER CLEANING THE EAR
L.M eijerman,C.van der Lugt,G.van Antwerpen,R.J.van M unster and G.J.R.M aat
Inter- and intra-individual variation in earprints
Abstract
7.1 Introduction
An earprint is a two-dimensional reproduction of the parts of the external ear that touch a surface, like the print of a rubber stamp. Oils and waxes that are naturally present on the ear serve as the ‘ink’ on the stamp. The amount of these secretions present on the ear may vary depending on outside temperature, and whether the ear was recently cleaned or not. More or less secretions available for printing may possibly influence dimensions and/or intensity of the imprinted area. In turn, this may affect the area in which characteristics can be found, or the visibility of such details.
W e expect the amount of secretions available for printing to be relatively high at the end of a day with high outside temperatures. W e further assume the amount of secretions to be relatively low after a wash with water and soap. W e therefore set out to compare print-mass, which is a characterisation of the earprint based on intensity and size of the imprinted area, of prints that were made under such different circumstances.
7.2 Materials and methods
At the end of a hot summers afternoon, eight subjects each listened three times at a solid vertical surface that was first covered with an acetate sheet. The first and second listening efforts were performed without foregoing preparation of the ear; in between the second and third listening efforts, the ear was thoroughly cleaned using water and soap.
Inter- and intra-individual variation in earprints
M = - x,y(I(x,y)-B)
where M denotes print-mass, I(x,y) the intensity of a pixel in the imprinted area, and B either the intensity median or the intensity of a (white) background pixel. Values for print-mass of the three prints per subject were compared applying a Paired Samples T-Test.
7.3 Results and discussion
For two subjects, relative print-mass among the three prints differed whether mass was calculated relative to the intensity median or relative to white. For the six remaining subjects, relative proportions of print-mass did not vary depending on applied methods, but for the two above-mentioned subjects, prints mass calculated relative to the intensity median was comparatively low for one of their three prints. We therefore needed to choose between the two methods in order to reach a conclusion regarding the effect on earprints of a reduction in the amount of secretions present on the ear.
Calculating print-mass relative to the intensity median was included in the current as well as a previous analysis of print-mass (Meijerman et al., 2004a), as the intensity of the entire imprinted area may vary among prints depending on brushing technique: Alberink and Ruifrok (2004) found a significant operator effect on mean grey-values of prints. Calculating print-mass relative to the intensity median would reduce such an effect. Intensity and size of extra-auricular areas, however, affect the prints intensity median and therefore the mass of the imprinted area relative to this median. The prints that were analysed for this study were all dusted by a single operator, reducing the chance of variation between prints due to a difference in brushing technique. Because examination of the prints revealed that for one subject the deviating print contained a comparatively intense imprint of the cheek, while for the other subject it contained a comparatively intense imprint of area superior to the ear (see Fig. 7.1 for prints of this subject), it was presumed that ‘print-mass relative to white’ produced a more reliable characterisation of the print (i.e., imprinted ear surface). Conclusions regarding possible differences in print-mass caused by variation in the amount of secretions that were present on the ear were therefore based on the analysis of print-mass relative to white.
listening effort before cleaning the ear (print 1), of the second listening effort before cleaning the ear (print 2) and of the listening effort after having cleaned the ear (print 3). For four out of the eight print donors, the value for print-mass of the last print – the print that was produced by a washed ear – was not the lowest among their three values for print-mass. Table 7.1 provides p-values for paired samples correlations and paired differences between each of the three print types.
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Fig. 7.1 Example of three prints by one ear: The third (right) print contains a comparatively intense representation of the area superior to the ear.
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___________________________________________________________________________ Table. 7.1 P-values for paired samples correlations and paired differences between print-mass (relative to white) of three print types: of the first listening effort before cleaning the ear (print 1), of the second listening effort before cleaning the ear (print 2) and of the listening effort after having cleaned the ear (print 3). (p-values < 0.05 are considered significant).
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Paired Samples Paired samples correlations Paired differences
Print 1 – Print 2 0.043 0.918
Print 1 – Print 3 0.007 0.192
Inter- and intra-individual variation in earprints ___________________________________________________________________________ 0,00E+00 2,00E+07 4,00E+07 6,00E+07 8,00E+07 1,00E+08 1,20E+08 1,40E+08 1,60E+08 1,80E+08 1 2 3 prints p ri n t m a ss r el a ti v e to w h it e
subject 1 subject 2 subject 3 subject 4 subject 5 subject 6 subject 7 subject 8
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Fig. 7.2 Print-mass (relative to white) for three print types: of the first listening effort before cleaning the ear (print 1), of the second listening effort before cleaning the ear (print 2) and of the listening effort after having cleaned the ear (print 3).
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The Paired Samples T-Test revealed no significant difference in print-mass of the third print compared with that of either the first or the second print of the same ear. As the number of examined prints was relatively low, a further study including more subjects will be carried out by Van der Lugt et al. (work in progress).
7.4 Conclusion
Acknowledgments
Francesca De Conti and Sarah Sholl are thanked for suggestions to improve the English text.
x Cleaning the ear before listening at a surface does not appear to significantly affect
print-mass of the resulting earprint.
x The stability of features that are valuable for the individualization of earprints needs to be
