The validity of finger pulse line length for the detection of concealed information

Building on the orienting theory of the Concealed Information Test, Elaad and Ben-Shakhar [Elaad, E., & Ben-Shakhar, G. (2006). Finger pulse waveform length in the detection of concealed information. Int. J. Psychophysiol., 61, 226–234.] proposed a new measure for the detection of concealed information: finger pulse line length (FPLL). This measure is recorded with a plethysmograph and combines pulse rate and pulse amplitude. Because the validity of finger pulse amplitude is still not established, one could question the benefits of FPLL to well validated measures such as heart rate. In the present study we compared the validity of FPLL, finger pulse rate and finger pulse amplitude in the detection of concealed information. Male community volunteers (n = 77) who had acquired crime knowledge through a mock crime procedure, were instructed to deny knowledge in a Concealed Information Test. Skin conductance, finger pulse line length, finger pulse rate and amplitude, heart rate and respiration were recorded. FPLL validity was significantly higher than that of finger pulse amplitude and heart rate. These data, together with its ease of measurement, support the use of FPLL.