The doctoral dissertation combines metrology, physiology and psychology with an aim to estimate contributions to the measurement uncertainty in psychophysiological measurement.
In the physiological part the dissertation deals with measurements in psychophysiology. In the part of the metrology of physiological variables (skin conductance, heart rate, blood pressure, skin temperature, respiration rate ...) the dissertation deals with sensors and transducers of psychophysiological instrumentation, measurements of variables, metrological evaluation of sensors and measuring instrumentation in terms of determining the influential quantities and estimation of measurement uncertainty. The psychological part of the dissertation deals within the field of sensory metrology or psychophysics, i.e. quantities that commonly, unlike conventional physical quantities such as electrical conductance, pressure or temperature, do not yet have generally accepted references, standards, scales and units. These are different psychological variables, e.g. feelings of different sensory modalities, emotions and other psychological constructs. The psychological part of the dissertation also includes the definition and measurements of anxiety as a condition. We consider the anxiety to be a contribution to the combined measurement uncertainty.
Skin conductance, skin temperature and blood pressure are physiological functions regulated by the autonomic nervous system. Their operation depends on the person's psycho-physiological state. The essential characteristic of the autonomic nervous system is that in principle it cannot be controlled consciously by the person itself, so it acts independently of the person's will. The psychophysiological state of the person is highly variable, so the physiological variables vary greatly at different times and when in different psychological states.
Anxiety is reflected as an increased activity of the autonomous (sympathetic) nervous system, leading to muscular tension, respiratory response and changes in heart rate and skin activity. The person experiences it as an unpleasant feeling of tension, which is usually difficult to define and non-specific. Strongly expressed anxiety can affect the result of the measurement or even the measurement itself. To what extent anxiety affects the results, it depends primarily on the individual and his/her current psychophysiological state. These influences are not negligible and with appropriate identification and evaluation can be considered when interpreting the measurement results of any psychophysiological variable and further diagnosis.
Further on, dissertation describes two preliminary experiments (Chapters 3.4 and 3.5), based on which we have developed guidelines for the preparation of the protocol of psychophysiological measurement. In the first experiment we observed the effects of successive measurements of blood pressure using a home blood pressure monitor on the psychophysiology of the observed person. We performed five consecutive blood pressure measurements (i.e. disturbances), and observed changes in psychophysiology (i.e. blood pressure, skin conductance and other physiological variables). We confirmed that the highest blood pressure value is measured at the first disturbance, i.e. the first measurement by home blood pressure monitor, while the real value is closest to the third consecutive measurement. The mean difference between them was +2.1 mmHg for the systolic and +2.8 mmHg for the diastolic pressure. On average, the amplitude is decreasing until the third measurement, and then begins to rise or fluctuate again. It then depends on the number of previous disturbances. Therefore, any possible correction of the final variable should be carried out irrespective of the time elapsed since the start of the measurement, but according to the number of occurrence of the disturbances prior. The relaxation time of psychophysiological variables depends on the level of amplitude of the initial change. If the change was high, the physiological variable will more rapidly decrease to the baseline level as if would when low.
In the second experiment, we focused on various forms of measuring methods for measuring psychophysiological variables. We ranged the selected measuring instruments into three categories of measurement methods; non-intrusive measuring methods have been defined as measuring methods in which the measured person is unaware that he/she is being measured / observed. Less-intrusive measuring methods represent methods that are disturbing at the beginning of the measurement and the measured person is aware of, but gets habituated over time and then forgets them. Intrusive measurement methods were defined as methods in which the measured person is very aware of being measured / observed. An experiment was performed to determine the influence of the intrusiveness of the used measurement methods in relation to the changes in the psychophysiology of the measured person and his/her perception of the measurement situation.
The results showed that during the measurement process, the measured persons are most agitated by the attachment of measurement instruments and the speech of experimenter. These events trigger the highest reactions of skin conductance response, while the level of skin conductance is increased during questioning. Intrusiveness of the measuring instrument also depends on the number of other instruments used or simultaneously attached to the measured person.
From these experiments we can deduct that when measuring physiological variables, it is necessary to use as few measuring instruments as possible, preferably only one which is minimally intrusive, the measurement experimenter must not speak much, preferably at all or it is not even present in the room, and all the questionnaires should be administered after the measurement of physiological variables. Regarding the personality types, we found that less acceptable and more introvert people are more measurement anxious, and therefore the consideration of the above limitations on these persons is more influential.
On the basis of the above findings, a final measurement protocol was prepared which included only three blood pressure measurements (disturbances), measurement of the influence of disturbance on the skin conductance. Psychological questionnaires for measuring personal characteristics and self-assessment scale were placed at the end of physiological measurements. Similar to the first two experiments the results of this experiment indicated that the most burdensome events in the process of measurement were the speaking of the experimenter and the beginning of solving psychological tests. People who were more agitated during the measurement were also more agitated by an individual event within the measurement process, especially for less confident individuals who responded more strongly to certain disturbances within the measurement process. Data analysis also showed that the measured persons were more measurement anxious when the measurement was carried out by a male person. On average, the results of this experiment indicate lower response rates for all measured persons. This can be attributed to the random selection of people as such or to the actually less burdensome protocol of measurement.
On the basis of all performed measurements we also evaluated the measurement uncertainties of classical psychophysiological measurements and prepared a proposal to reduce the measurement uncertainty of psychophysical measurements, which is at the same time the basis for the preparation of a nonintrusive measurement protocol of psychophysiological measurements.
We conclude that non-invasive blood pressure measurement with home blood pressure monitor represents an intrusive disturbance that increases the activity of skin conductance by less than 1 μS and affects the blood pressure value. On average, the systolic and diastolic blood pressure values increased by less than 15 mmHg at the first disorder, with a measurement uncertainty of under 10 mmHg. A strong increase of physiological changes was characteristic of less confident and more introvert people. A detailed consideration of these findings on a larger number of measured persons presents future challenges in the field of metrology of psychophysiological measurements.