Measurements

3.2.5a. Psychophysiological measures, data reduction and scoring of parameters EMG activity from the corrugator supercilii, zygomatic major, and forearm extensor, skin temperature, skin conductance, ECG, and respiration were measured on-line with Contact Precision Instruments, throughout the duration of the whole experimental session, at a sample rate of 800 Hz. A separate digital channel recorded the different game events of interest, each of which was represented by an unique value between 0 and 255. On the basis of these values, the onset of events of interest could be

accurately determined and data could be reduced as a function of these event

indicators. For all measures, data blocks of 8 seconds, 1 second before and 7 seconds after the onset of the appearance of the character were extracted from the data files for further processing. All measures except skin conductance (see below) were reduced over blocks of 5 seconds length, starting at the onset of the appearance of the

character. Routines specifically developed for off-line processing and data reduction were created with LabView 4.

EMG. The muscle sites were cleaned with alcohol and rubbed in with electrode paste to reduce the skin resistance to below 10 kOhm. Four mm Ag-Ag/Cl Med Associates electrodes were placed on the corrugator supercilii, zygomatic major and forearm extensor in accordance with the guidelines provided by Cacioppo, Tassinary, and Fridlund (1990). Raw EMG data was sampled, with a band-pass filter of 3 - 300 Hz.

Each of the EMG signals was rectified and smoothed off-line using a digital

Butterworth low-pass filter with a cut-off frequency of 4 Hz., after which the signal was down-sampled to 20 Hz. and averaged within the 5 second time window.

Skin conductance. Eight mm Ag-Ag/Cl Med Associates electrodes were placed on the tips of the index and third finger. The electrodes were filled with a special NaCl paste

(0.9% of isotone NaCl in unibase) which resembles the consistency of human perspiration. A constant voltage of 0.6 Volts was applied across the two electrodes.

The skin conductance signal was low-pass filtered (cut-off of 0.7 Hz) and down-sampled to 20 Hz. before parameter extraction in order to eliminate high frequency spikes introduced by a problem with the automatic back-off system and the A-D converter. An automated routine enabled the scoring of the number of skin conductance responses within the time block as well as the amplitudes of the responses detected. The focus was on the amplitude of the first response for further analysis, as this response was expected to contain the most relevant information concerning possible schematic appraisal. Such scoring is also conform to research on conditioning where for multiple occurring anticipatory responses, the first anticipatory response has been found to be the most reliable index of classical conditioning (see Hugdahl, 1995). When the number of second responses is sufficiently high, the data of the amplitudes of the second responses will be provided. A skin conductance response was scored when the increase in skin conductance level exceeded 0.05 microSiemens, and when this increase started during the period of 1 second to 6 seconds after the onset of the appearance of the character (event-related skin

conductance responses typically occur within 1 to 3 seconds after stimulus onset, see also Dawson, Schell, & Filion, 1990). The amplitudes were scored as the difference between the onset and the maximum deflection. The amplitude was set to missing when no response was detected, in order to keep the measures of amplitude and frequency as independent as possible.

ECG. Pre-gelled, disposable ECG electrodes were placed on the chest according to the Einthoven's triangle. The inter-beat interval (IBI) derived from the R-R interval was calculated off-line. IBIs of shorter than 400 and longer than 1500 milliseconds were considered as artefacts and eliminated from further analysis. For each 5-second block, the mean IBI was calculated.

Skin temperature. A CPI skin temperature probe was placed on the little finger of the non-dominant hand. Cotton wool was wrapped around the finger, to reduce influences of the ambient temperature upon the skin temperature measures. For each window of 5 seconds, the slope of finger temperature changes was calculated off-line, using a

curve fitting-function, where the first derivative served as an index for the slope of skin temperature change.

3.2.5b. Reaction time measures

For each event of interest, the latency between the onset of the sound and the button press as well as the correctness of the response were recorded and saved in a data file containing also information on the nature of the event.

3.2.5c. Subjective feeling

Once per event type (conducive - schematised, conducive-discrepant, obstructive - schematised, obstructive - discrepant), 4 seconds after the reaction to the character and before the feedback concerning the loss or gain of points, the participants were asked to provide a report of their current emotional state, by pronouncing aloud "En ce moment, je me sens..." ("At this moment, I feel..."), and then completing the sentence by choosing one or more emotion words and giving an intensity for each one. The player was provided with a list of 8 emotion words, including “irrité”,

“déçu”, “content”, “stressé”, “surpris”, “soulagé”, “impuissant”, and “alarmé”

(irritated, disappointed, contented, stressed, surprised, relieved, helpless, and alarmed) and a 10-point scale of which three points were accompanied with labels (1 with

“very little”, 5 with “moderately”, and 10 with “extremely”). These emotion labels were chosen on the basis of their expected likelihood to be elicited through the manipulations of Goal Conduciveness (i.e. contentment, irritation, disappointment) and the expected feeling states which could be experienced when playing a computer game (i.e. stress, surprise, helplessness, etc.). This list was placed above the computer screen in an easy to read, large font. Players could also use their own words in the case that none of the words on the list corresponded to their felt emotion. The player provided the intensity of the felt emotion by speaking an integer from 1 to 10. Players rehearsed the words on the list before the experiment to facilitate their easy recall during the experiment, thus minimising their need to refer to the list while playing.

The resulting speech segments were recorded but used in another part of the experiment, which falls beyond the scope of the current report.