Startle reflex onset latency was determined by visual inspection of the respective traces from 40 to 100 ms for OOc and from 50 to 120 ms for SCM following IS.
Percentages of trials with startle signs were calculated separately for each subject and type of trial and were then compared among trial types using Friedman [chi square] test.
Wilcoxon signed rank test was also used to compare the effect of presence or absence of startle signs on latencies and iEMG of ECR responses in all trial types employing 240[degrees]/s velocity.
In order to acquire a sufficient number of trials per condition at 240[degrees]/s containing startle signs, trials of different velocities occasionally had to be repeated according to protocol, thereby amounting to 65 to 85 trials per subject.
There were no startle signs in OOc or SCM at all in trials at 6[degrees]/s and only few in trials at 60[degrees]/s (0-1/subject).
As startle signs were absent in trials at 6[degrees]/s and scarce in 60[degrees]/s and in some 240[degrees]/s conditions (i.e., 240PrepStartReact, 240StartControl, and 240StartKnown), subsequent statistical comparisons were only performed between conditions 240StartReact and 240ContraStartReact.
In OOc, startle latency was significantly shorter in condition 240ContraStartReact [72 (50, 74) ms] than in 240StartReact [79 (77, 112) ms] (Z = -2.1, P < 0.05; Cohen's d = 0.2) but not in SCM [240ContraStartReact: 78 (69, 87) ms; 240StartReact: 80 (75, 85) ms; Z = -0.9, P = 0.3; Cohen's d = 0.5].
Effects of Startle on Reaction Time (StartReact Effect).
Startle magnitude was inversely related to the affective valence ratings of the pictures, r = -.54, p < .01, but did not correlate with the arousal ratings.
Magnitude and latency of the startle reflex, affective valence ratings, and viewing time were related to the Valence factor, whereas arousal ratings, SCR, heart rate, and viewing time were related to the Arousal factor.
The main aim of this research was to test the two-factor model of the emotional response, by including two indices--magnitude and latency of the startle blink reflex--that have not been used in this type of analyses, and by studying how well these indices fit into this model.
Our data show an affective valence modulation of the startle response, in accordance with past research (e.g., Bradley et al., 1990; Vrana et al., 1988).
The magnitude and latency components of the startle reflex fit into a two-dimensional model of emotion and are related to the affective valence dimension, thus supporting results obtained in previous research works (Lang, 1994, 1995; Lang et al., 1992, 1997, 1998).
Emotion, novelty, and the startle reflex: Habituation in humans.
Differentiating orienting, startle, and defense responses: The role of affect and its implications for psychopathology.