This study investigated whether the P300 elicited by novel stimuli was affected by the requirement of target detection. A sequence of stimuli consisting of a 1000Hz tone (p =.7), a 2000Hz tone (p=.15) and a novel noise sound (p=.15) were presented to six subjects under two conditions. In the active condition the subjects were required to respond to each rare tone (2000Hz) whereas in the passive condition the subjects were only instructed to hear the sequence of stimuli.
The rare tone elicited P300 only in the active condition. The novel stimuli evoked a prominent P300 in both conditions. The amplitude and scalp distribution of P300 elicited by the novel stimuli did not differ between the two conditions. The findings suggest that the detection task has little effect on the P300 that is elicited by the novel stimulus.

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A photoelectric plethysmograph was newly devised using a commercial photo-reflector (Hamamatsu Photonics P2826 type) that is a photoelectric device with a light-emitting diode (LED) and a phototransistor (Ptr) combined together. Having fit the photoelectric plethysmograph in the least volume (4 x 4 x 2 mm), we were able to make it inexpensive and compact in the size which permitted us to attach to every place of bodily skin surface under consideration. Compared to a conventional tungsten lamp, the LED has an electric characteristic of a narrow spectral distribution in the infrared range, the characteristic of which makes it possible to take photometric measurements of skin tissue independently of the interference of visible light. Further, the LED has a large share of the spectral distribution with the Ptr output. The fact that the LED produces cool light means that we can avoid the problem of a local vasomotor reflex as an artifact due to heat generation caused by the light source put on some skin surface. Another advantage the Ptr has is in that it is relatively free from both ambient air temperature and prior light history effect. These considerations proved the photo-reflector plethysmograph to be superior to the bulky miniature tungsten lamp-photoconductive cell combination generally employed in photoplethysmo-graphy : Thus, the photo-reflector plethysmograph is a useful psychophysiological device to meet the transducer criteria necessary for quantitative photoplethysmography.

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An automated personal computer-controlled analyzing system was developed to detect eye blinks by means of video tape recording. First, cornea images were taken by video camera and were digitized into black and white. Displacement of the black part triggered by upper eyelid movement was input into the computer at intervals of 1/60 second, so this system did not require a large amount of storage capacity or processing time. After noise was removed from the data, eyeblinks were detected on the basis of wave amplitude, duration, and acceleration. Most blinks were detected in the same way as in observing the eye, since the criteria of the identification could be set with the parameters. Moreover, this measurement closely resembled that of the EOG method, which suggests the validity of this measure. This automated system enabled us to measure the time of blink onset, blink waveforms, and blink duration with considerable ease.

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