Heartbeat perception has become the most widely studied example of visceral perception. In the present study scalp potentials contingent to the visceral event "heartbeat" were investigated. Scalp potentials, averaged time-locked to the EKG-R-wave, were studied at Fz, Cz, and Pz under four conditions: resting (baseline), heartbeat discrimination task, signal detection task, and heartbeat discrimination task after physical exercise. 22 subjects were assigned to the two groups "good" and "poor" perceivers, according to their performance in an initial heartbeat perception test. Event related potentials (ERPs) of "good" perceivers were more stable across conditions than those of "poor" perceivers. Peak latency within the range of 200 to 300 ms differed significantly between conditions. A principal component analysis performed on the ERP averages extracted five components. Subsequent ANOVAs across factor scores yielded significant main effects for the "groups" factor, experimental conditions and electrode sites. The strongest effects occurred over the frontal region in the latency range of 250-400 ms (following the EKG-R-wave). These were found to be not due to artifactual EKG influences.

We describe a Lmsec software timer for measuring response latencies and controlling delays on the IBM PCIXT/ATwithout additional hardware requirements. To demonstrate the machine language routines, a short BASIC example program is included. In a simple experimental design, two different stimulus words are presented on screen and keypress response latencies are measured. Precise timing of stimulus presentation is accomplished by direct manipulation of the video controller. The principles of programming interrupt-controlled timing routines are addressed to be easily adapted to other problems or different programming languages.Designs in experimental behavior research often require exact time-interval measurement and control. Subjects' response latencies or delays of external events often have to be assessed; interstimulus intervals, intertrial intervals, and duration of stimulus presentation need to be timed in order to control the experimental process. Other applications combine two or more of these components (e.g., response latency windows). Dlhopolsky (1983) proposed two Z-80 machine language millisecond timers that are software designed but based on hardware clock cycles of the TRS-80. Femano and Pfaff (1983) developed an interval handler for the 6502 microprocessor using external circuitry. Although such solutions achieve very high resolutions (less than 50 Jtsec), they depend on specific hardware requirements.Currently the standard in microcomputers, in terms of laboratory and analysis applications, tends to be established by the IBM personal computer family. A wide variety of hardware add-ons is available from numerous suppliers. However, adequate add-ons for the laboratory standard of minicomputers (DEC's PDP-II) are unavailable. Particularly, external clocks usually are unable to interrupt the processor, which causes various programming difficulties.On the other hand, the prerequisites for programming interval timing routines are already built-in features of the ffiM PC/XT/AT computer family. In order to demonstrate this, the first part of the present paper describes a simple BASIC program, which makes use of an assembly routine that performs all the difficult steps of timing control. The second part explains the technical details and programming techniques needed to tailor the assembly language routines to the reader's own requirements.The authors' mailing address is: Institut fur Psychologie, Klinische Psychologie, Universitat Munchen, Geschwister-Scholl-Platz 1, D-8000 Munchen 22, Federal Republic of Germany. REACTION-TIME MEASUREMENTThe BASIC program shown in Listing I demonstrates an experimental session in which reaction time to two different verbal stimuli is measured. Such a procedure has to fulfill two critical requirements. Delay and reaction times have to be measured precisely, and the stimulus must be presented at a predetermined point in time. These two requirements are met by an assembly language programmed timer, which is able to measure time intervals with a resolution of I msec, and a ps...

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The present experiment investigated the trial-by-trial habituation in the event-related potential (ERP) and the skin conductance response (SCR) to repeated stimuli and dishabituation to rare stimuli. In a balanced design, two groups of subjects passively observed either large black discs as repeated stimuli and small as rare, or vice versa. No consistent effects of stimulus size were obtained between the groups. Late positivity was composed of a double peak at Cz, containing contributions from P3a and P300; the latter only was observed at Pz. The SCR and P3a and P300 at Cz demonstrated habituation, but not the N100 or P200, nor the P300 at Pz. Rare stimuli elicited an enhancement, albeit nonsignificant, in SCR amplitude only. No dishabituation of any of the responses by these stimuli was observed. The SCR correlated significantly with late positivity at Cz and Pz. Discussion focuses on SCR and late positivity as OR components.