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Cortical and Subcortical Processing of Color |
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Figure 19. An experimental session was consisted of 45 trials with a mean intertrial interval of 15 sec (10-20 sec). In the first five trials, only startle stimulus was presented as control trials. In the following trials, startle stimulus was presented with or without prepulse. The lead interval of prepulse and the startle stimulus was 100 ms.
3.4. Results
3.4.1. Measurements of the Response Amplitude
The EOG recordings of corneal blink elicited by the air-puff was composed of two positive deflections with a latency at 80 ms and 150 ms, respectively, followed by a large negative deflection at 300 ms (Fig. 20). The early positive deflection was sharp and small in amplitude as compaired to the second positive deflection. The early component is consisted of high frequency activities, presumably EMG activities of the orbicularis occuli muscles. A peak-to-peak amplitude of the second positive and the large negative components was measured for the amplitude of the startle response.
Figure 21 shows a typical example of blink responses in one session (Group R-B). A total of 45 trials were displayed in a line. Although slight decrement in the blink amplitude was noted during the habituation trials, relatively consistent amplitudes were recorded throughout the session. In most trials without preceding prepulse (marked by filled circles), a clear blink response was elicited by the air puff. On the contrary, remarkable decrease in the amplitude was observed in the prepulse trials (marked by open circles) as compared to the non-prepulse trials.
3.4.2. Typical Example of PPI of the Blink Response
Figure 22 shows superimposed traces of 5 trials each, excluding the first 5 trials. A filled circle indicates the onset of the air puff and an open circle indicates the onset of the prepulse. The left column shows recordings in the early half and the right column shows ones in the late half of the session. The second five traces marked 7-24 show the recordings without prepulse from 7th to 24th trials. In these five trials, a slight decrease in the blink amplitude was noted as compared to the control trials. A remarkable decrease in the amplitude was found in the following prepulse trials. A similar decrease of the blink amplitude in the prepulse trials was observed in the late half of the session. As compaired to the five trials
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Hitoshi Sasaki |
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without prepusle (29-44th trials), the blink amplitude was small in prepulse trials either in 2632th, 33-38th, or 39-45th trials.
Figure 20. A typical waveform of corneal blink response elicited by air-puff to the corneal surface. Five recordings were superimposed from 100 ms before and 900 ms after the onset of air-puff. The thick bar indicates duration of the air-puff for 50 ms. A waveform of the blink response consisted of two positive deflections (a and b) and a large negative one (c). A peak-to-peak amplitude (b-c) was measured as the startle amplitude.
Figure 21. A sequence of blink responses consisting of 45 trials in an experimental session of Group R- B. Each trial was sampled for a 1-sec epoch. Open circles indicate trials with the prepulse, and filled circles indicate trials without prepulse. Vertical line indicates end of the habituation period. Red and blue prepulses are not distinguished here. Amplitudes of the blink responses decreased in the prepulse trials as compared to those in no prepulse trials.
3.4.3. Responses to Chromatic and Achromatic Prepulses
Effect of prepulses on the startle amplitudes was examined using % inhibition as an inhibition index, calculated by the following equation:
%inhibition = (mean amplitude in prepulse trials)/(mean amlitude in non-prepulse trials)
x100